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biology
BY3031
PLANT RESPONSES TO THEIR EXTERNAL ENVIRONMENT
NCEA LEVEL 3
2013/1
biology
ncea level 3
Expected time to complete work
This work will take you about 20 hours to complete.
You will work towards the following standard:
Achievement Standard 91603 (Version 1) Biology 3.3
Demonstrate understanding of the responses of plants and animals to their external
environment
Level 3, External
5 credits
In this booklet you will focus on these learning outcomes:
•• describing the environment, adaptations and ecological niche
•• discussing plant responses to the biotic environment
•• discussing plant responses to the abiotic environment.
You will continue to work towards this standard in booklet BY3032: Animal responses to
their external environment.
Copyright © 2013 Board of Trustees of Te Aho o Te Kura Pounamu, Private Bag 39992, Wellington Mail Centre, Lower Hutt 5045,
New Zealand. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without
the written permission of Te Aho o Te Kura Pounamu.
© te ah o o te k u ra p ou n am u
contents
1
The environment: an overview
2
Competition and cooperation
3
Defence and cooperation
4
Orientation responses
5
Control of plant growth
6
Timing responses
7
Teacher-marked assignment
8
Answer guide
Glossary
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how to do the work
When you see:
Use the Topic webpage or the Internet.
1A Complete the activity.
Check your answers.
Contact your teacher.
You will need:
•• a pen and paper
•• access to the Internet
•• the teacher-marked assignment (BY3031A).
Resource overview
Throughout this booklet you are directed to many links to websites and videos. These provide
useful and interesting information that will help to explain the subject content. You should aim to
access these links. The assumption is that you allocate at least three hours to each lesson: one to
two hours to view and work through these websites and one hour to work through each lesson. If
you have not studied NCEA Level 2 Biology, contact your teacher to discuss this.
In this booklet, you will read about a range of responses plants exhibit towards their biotic and
abiotic environment.
This booklet is for your own use and does not need to be sent in for marking. However, you are
asked to send in your answers to the teacher-marked assignment (BY3031A) as well as your selfassessment.
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© te ah o o te k u ra p ou n a mu
the environment: an overview
learning intentions
In this lesson you will learn to:
•• describe the biotic and abiotic environment
•• explain adaptations
•• explain the ecological niche of an organism.
introduction
You have probably seen or experienced most of the following situations:
•• the leaves of deciduous trees changing colour and falling during autumn
•• insects drawn towards lights at night
•• dogs growing thicker coats as winter approaches
•• plants on the forest floor growing upwards towards the light
•• a cat raising the hairs on its back and arching its back to appear larger when approaching a
rival cat
•• plants producing flowers in summer
•• a snail retreating into its shell if threatened
•• shellfish such as pipi and clams burrowing down into the sand when disturbed
•• blue penicillin mould growing on old bread or fruit
•• your stomach feeling as if it has ‘butterflies’ inside when you are nervous or excited.
These are just a few of many examples
of plants, animals and microorganisms
responding to changes in their environments.
Every species needs to be responsive to
changes and stimuli in their surrounding
environments and make suitable responses to
these stimuli, in order to survive.
A stimulus (plural: stimuli) is a change in the
environment that causes a response in an
organism.
istockphoto.com
1
Fig 1.1: When people are excited or happy they are responding to
their environment.
Animals, being mobile, are able to respond quickly, usually by moving towards or away from a
stimulus, to find more favourable conditions. Plants are usually not mobile, so they respond to
stimuli by adjusting their growth and development. In this topic you will learn how plants and
animals respond to environmental changes and stimuli, and how these responses optimise the
plants’ and animals’ survival in their particular ecological niches.
There are a large number of biological terms associated with this topic so we suggest you make
up a glossary as you go through the work. This will help you learn and remember the many terms
and their meanings.
The glossary at the back of this booklet could provide you with a good start.
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the environment: an overview
the environment: an overview
The environment surrounding a plant or animal in its habitat (the place where it lives) is made
up of all the living organisms (the biotic environment), the non-living factors (the abiotic
environment) and the nutrient cycles and energy flows that connect all of these. Together they
form an ecosystem.
biotic environmental factors
These are the influences of living organisms on each other in a community. All the organisms of
every species in any community interact with each other and influence each other.
Some species provide shelter and protect others, while other species harm their neighbours in
the community. The living organisms that make up the biotic environment act as stimuli to which
other organisms in the environment need to respond.
Biotic factors may be:
•• intraspecific – between members of the same species, (‘intra’ means within)
or
•• interspecific – between members of different species, (‘inter’ means between).
Some examples of intraspecific biotic factors are competition for resources such as:
food, water, light, space,
nesting sites and mates
cooperation strategies within species for
defence, hunting and survival
aggressive interactions to establish
hierarchies and defend territories
Intraspecific competition can be intense, as all the individuals have the same requirements for
resources.
Interspecific competition occurs if different species have similar requirements for any resource.
Some examples of interspecific biotic factors are competition for resources such as:
food, water, light and space
mutualism, which is an association between
species for their mutual benefit
exploitation of one species by another, such as
parasitism and predator/prey interactions
abiotic environmental factors
These are physical factors that can act as stimuli to which the organisms need to respond.
Factors like these are all non-living (abiotic) influences:
soil type
intensity and direction of light
salinity and clarity of water
availability and amount of water
availability and quality of air
pressure (altitude)
the average and range of temperature
velocity and direction of wind
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the effect of gravity
the presence of chemicals and nutrients
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the environment: an overview
adaptations
In order to survive in its habitat and environment, every organism has special adaptations.
An adaptation is any inherited characteristic that enables an organism to survive and
reproduce in its habitat.
Adaptations may be structural, behavioural or physiological.
istockphoto.com
Structural adaptations (Fig 1.2) are features of body
structure. Some examples of structural adaptations
are a snail’s shell for protection; a bird’s wing for flight;
a cat’s claw to catch prey; a plant’s leaves to trap
sunlight for photosynthesis; and a plant’s flower to
attract pollinators.
Fig 1.2: A cat’s claws are a structural adaptation to
catch its prey.
istockphoto.com
Behavioural adaptations (Fig 1.3) are types of
behaviour that help an organism to survive. Some
examples of behavioural adaptations are a male bird
feeding the female bird sitting on the nest; a hedgehog
curling into a ball when threatened; a possum’s
nocturnal activities; and slaters (woodlice) hiding
under logs to escape from high temperatures on the
soil surface during the day.
Fig 1.3: Meerkats work as a team and stand guard.
This behaviour protects the family group from
predators.
istockphoto.com
Physiological adaptations (Fig 1.4) are often chemical
or physical adaptations. For example, humans keep
their body temperature the same (about 37ºC)
despite changes in the temperature of the external
environment; pale skin tans when exposed to sun over
long periods; and callouses form on hands and feet in
response to repeated contact or pressure.
Fig 1.4: A snake producing venom to defend itself is a
physiological adaptation.
1A
adaptations and behaviours
Go to the Topic webpage to learn more about adaptations and behaviours.
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the environment: an overview
ecological niche
An organism’s ‘way of life’ or ecological niche encompasses the ways in which an organism
carries out all its life processes. This includes its interactions with its biotic and abiotic
environment, such as:
•• its relationships with other organisms
•• its reproductive strategies to ensure the species survives
•• the resources and opportunities provided by the habitat
•• and the adaptations it has which enable it to take advantage of these opportunities.
The work of a Russian microbiologist and ecologist, Georgii Gause, led him to publish the
principle of competitive exclusion. This principle became known as Gause’s principle. It states
that no two species with identical ecological niches can co-exist for long in the same place.
If there is fierce competition between species, one species may be eliminated. If the competition
is only moderate the two species can co-exist in the same habitat because their ecological niches
are slightly different.
1B
ecological niches
Go to the Topic webpage to learn more about ecological niches.
tolerance
Although plants and animals are adapted to their particular environments and ecological niches,
they need to be able to adapt to slow changes in their environments or they may not survive
otherwise. An organism’s ability to survive variation in environmental conditions is called its
tolerance. Tolerance to change in environmental factors varies between individuals of the same
species. Acclimatisation is the ability of an organism to adjust its tolerance limits or optimum
range in response to slow changes in its environment.
For example, mountain climbers who want to conquer high-altitude peaks normally live at low
altitudes. They have to spend several days at middle altitudes to prepare their bodies for the
decreased amount of oxygen at high altitudes. During this period of acclimatisation, their bodies
increase the production of red blood cells (the cells that carry oxygen around the body). This is
a physiological adaptation. This is just one example that shows how organisms can adjust their
range of tolerance, provided the changes occur slowly.
Most organisms can adapt to keep within their ‘optimum range’ of tolerance. If any factor in
an environment is outside an organism’s range of tolerance, the organism cannot live in that
environment. Constant monitoring of the environment to detect the stimuli that indicate
changing environmental conditions is vital if an organism is to survive.
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© te ah o o te k u ra p ou n a mu
the environment: an overview
Look at Fig 1.5 below showing how the effect of different physical factors must be kept within a
narrow optimum range. This range is known as the level of tolerance for each species.
Lower limit
of tolerance
Optimum range
Zone of physiological stress
Zone of physiological stress
Upper
limit of
tolerance
preferred niche
too cold
too wet
too acidic
temperature
-5°C
15°C
25°C
50°C
moisture (%) of soil
5
10
3.0
4.0
20
30
40
50
pH
5.5
7.5
9
too hot
too dry
too alkaline
10
Fig 1.5: Level of tolerance of a daisy to three abiotic factors. Source of data: NZQA
As you can see from the graph, the preferred niche of the plant has a narrow temperature,
moisture and pH range. As conditions change, the plant needs to be able to detect the stimuli
indicating change and respond to the changes in order to survive (zone of physiological stress).
If the conditions become too extreme (beyond its lower or upper limit of tolerance), the plant
will not survive.
Plants and animals continually have to interact and respond to their environments in order to
survive. The term ‘fitness’ is used to describe how well suited an organism is to survive in its
habitat.
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the environment: an overview
1C
defining terms
Define the following terms.
Stimulus:
Habitat:
Biotic environment:
Abiotic environment:
Ecosystem:
Intraspecific:
Interspecific:
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© te ah o o te k u ra p ou n a mu
the environment: an overview
Adaptation:
Tolerance:
Acclimatisation:
Ecological niche:
Check your answers.
the new zealand falcon
The New Zealand falcon (Fig 1.6) is a bird of
prey. New Zealand falcons hunt for live prey,
mainly by watching from a vantage point and
making a fast direct flying attack, flying at
speeds of over 100 km/h and either striking
or grasping the prey with their sharp talons.
They kill their prey with a quick, powerful bite
to the neck. They prey on insects, mammals
and lizards, but their diet consists mainly of
birds.
rob suisted
1D
Fig 1.6: New Zealand falcon/kārearea (Falco novaeseelandiae).
The falcon has many adaptations to catch its
prey while in flight (‘on the wing’). Explain at
least two adaptations that the falcon has that
suit it to its ecological niche.
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the environment: an overview
Adaptation 1:
Adaptation 2:
Explanation:
Check your answers.
key words
key points
stimulus
habitat
adaptations
biotic environment
abiotic environment
ecological niche
•• A stimulus is a change in the environment that causes a
response in an organism.
•• A habitat is the place where an organism lives.
•• An adaptation is an inherited characteristic that enables
an organism to survive and reproduce in its habitat.
•• Adaptations may be structural, behavioural or
physiological.
•• The biotic environment is the influences of living
organisms on each other.
•• The abiotic environment is the non-living influences on
an organism.
•• The ecological niche is a description of how the organism
feeds, the opportunities provided by the habitat and the
adaptive features of the organism which enable it to take
advantage of these opportunities.
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© te ah o o te k u ra p ou n a mu
competition and cooperation
learning intentions
In this lesson you will learn to:
•• discuss competitive plant–plant responses to the biotic environment
•• discuss cooperative plant–plant responses to the biotic environment.
introduction
You may think that plants are not very exciting organisms – they grow, some flower, and some
have leaves that change colour and fall in autumn, but you may not think of them as very
responsive organisms. This is just not true! Plants are in fact extremely evolved organisms,
acutely attuned to their environment. They are able to detect very subtle changes or stimuli in
the environment and respond to these, in some cases with great rapidity. In this lesson you will
learn how plants compete but also cooperate with each other, and what strategies they have
evolved to get a competitive edge.
competition for resources
In any habitat, the plants all have basic requirements for resources such as light, water, space to
grow, minerals from the soil and carbon dioxide from the atmosphere. If any of these resources
are in short supply, the plants’ growth will be slowed. If many plants are growing close together
in the same habitat and they have similar, or the same, resource requirements, there will be
fierce competition among the plants for these resources. Whenever two niches overlap there will
be competition between the organisms concerned.
Those plants that are best suited to monopolise the resources will have a competitive advantage
and will be more successful in growing and reproducing than their neighbours. In plants the
competition is usually indirect, through the resource, rather than directly with the other plants.
Competition may be intraspecific or interspecific and may be either through interference in the
growth of other species or through exploitation of other species.
sunlight
Plants compete fiercely for sunlight, an
essential requirement for photosynthesis. In
a forest (Fig 2.1), taller plants receive more
light and may block most of the light from
reaching the forest floor. The plants on the
forest floor have adapted to survive in lower
light intensities, some growing larger leaves
to compensate for the lack of light. Plants
in a forest have adapted to different light
intensities. The plant growth forms vertical
layers, with those plants that demand a lot
of light growing in the canopy and those
Fig 2.1: A forest showing stratification.
that require less light growing in the layers
below. This vertical layering of plants is called
stratification and is shown in the image on the right.
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don laing
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competition and cooperation
The main way plants compete for sunlight is to grow towards the light, overshadowing other
competing plants nearby, and slowing their growth. They are utilising the available resources
more quickly than neighbouring plants. Other ways plants compete by better utilising the
available resources are by growing longer roots or a more extensive root system to take
advantage of the water supply, or being better able to tolerate adverse conditions. Note that
while the available resources are abiotic environmental factors, the competition between plants
for these resources is biotic, as the plants are living elements of the environment.
seeds
Other plants depend on birds or insects to
Fig 2.2: A gorse plant on a Wellington hillside.
spread their seeds so that the seedlings
are able to grow in more favourable, less
competitive conditions away from the parent plant.
don laing
When walking in the hills you may have heard
the explosive ‘popping’ sounds that gorse
seedpods (Fig 2.2) make as they break open
and scatter their seeds over a large area. This
is a strategy that the gorse plants have evolved
to ensure their seeds are spread over a wide
area and the seedlings will not compete with
the parent plant or with each other.
chemical competition
Some plants produce chemicals that are toxic to other plants, so that the growth of nearby
competing plants is inhibited. The production of toxic chemicals that inhibit growth is called
allelopathy. The toxic chemicals leach from the roots into the surrounding soil or accumulate in
the soil around the plant as the leaves drop and decay.
Desert plants also use allelopathy as a means
of ensuring no plants grow nearby so that their
roots can use the scarce water resource to their
advantage. Many other plants including wetland
species, grasses, tobacco, rice and pea plants
are known to produce root allelotoxins to reduce
competition with neighbouring plants.
2A
istockphoto.com
An example is the walnut tree (Fig 2.3), which
produces a chemical called juglone in its leaves
and roots that inhibits the growth of other plants
nearby.
Fig 2.3: A walnut tree.
allelopathy
Go to the Topic webpage to learn more about allelopathy.
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competition and cooperation
exploitation
Some species actively exploit their neighbours in order to compete for resources. In the forest
you may have noticed the long vines or lianas that grow up trees to reach the sunlight. These
lianas are making use of (exploiting) the trunks of neighbouring trees to help them reach the
sunlight they need for photosynthesis. Epiphytes such as some orchids perch high up on the
branches of tall trees so that they can reach light of a higher intensity than on the forest floor and
are protected from herbivores.
rob suisted
The beautiful native Northern rātā
(Metrosideros robusta) (Fig 2.4) can start life
as an epiphyte or seedling plant perched high
on a host tree, usually a rimu. The rātā grows
roots down to the ground, finally enclosing
and strangling its host as it grows into a big
tree. In this way the rātā exploits the host tree
to establish itself and gain access to sunlight
higher up in the forest canopy.
Fig 2.4: The Northern rātā.
rob suisted
Mistletoe (Fig 2.5) is another example of a
plant that exploits another by parasitising it.
The mistletoe is in fact semi-parasitic, as it
has green leaves that can photosynthesise but
it relies on tapping into the xylem tissues of a
host tree for water and nutrients.
Fig 2.5: A mistletoe plant.
2B
competition between plants
Go to the Topic webpage to learn more about plant competition.
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competition and cooperation
plant cooperation
Although competition between plants can be fierce, plants also cooperate with each other in
order to survive.
cooperative strategies
Some plants find it beneficial to grow close together. In this way they provide support for each
other to grow tall and reach the light. Wind-pollinated plants also use this strategy to reach the
higher wind levels so that their pollen can be blown easily to other plants of the same species.
2C
cooperative strategies
Fig 2.6: Feijoa trees need another feijoa tree for pollination.
istockphoto.com
The roots of marigold plants (Tagetes species)
(Fig 2.7) secrete a chemical that kills plant
parasitic nematodes, a kind of roundworm that
damages plants. The nematodes cause
swellings on the roots, which stunt the plants’
growth and can lead to their death. Producing
a toxic chemical is a form of allelopathy, but
unlike in the previous examples, where
allelopathic chemicals were detrimental to the
growth of other plants, the chemical produced
by marigolds is beneficial, as it kills the
nematodes which can damage the plants. This
is an example of allelopathic cooperation
between plants.
istockphoto.com
Some fruit trees such as feijoas (Feijoa
sellowiana) (Fig 2.6) cannot be self-pollinated,
so they need another tree of the same species
growing nearby for pollination. By growing
close together, both trees benefit from crosspollination and can produce flowers and fruit
with increased genetic diversity as a result.
Fig 2.7: Marigold plants.
Go to the Topic webpage to learn more about the association between marigolds and nematodes.
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Some species of plants actively benefit others growing
nearby. For example, plants of the legume family (including
peas, beans, clover, peanuts, alfalfa and soy) have rhizobium
bacteria living in nodules on their roots (Fig 2.8). The
rhizobium bacteria can convert nitrogen gas from the air
into ammonium in the soil. This process is called nitrogen
fixation because the rhizobium bacteria ‘fix’ the nitrogen
by converting it from the unavailable form found in the
atmosphere to a form which plants can use. The legume
plants receive nitrogen in a useful form for growth and the
rhizobium receives carbohydrates from the plant, produced
by photosynthesis. The relationship between legumes
and rhizobium bacteria is symbiotic or mutualistic (both
organisms benefit). Although most of the useful nitrogen
is removed when the legumes are harvested, significant
amounts can remain in the soil for the use of future crops.
te kura
competition and cooperation
Fig 2.8: Plant roots showing nodules on the
roots where rhizobium bacteria live.
plant–fungus relationships
lichens
te kura
You have probably seen lichen (Fig 2.9)
growing on trees or old fence posts. Lichen
is actually not a plant but a symbiotic
relationship between a fungus and an alga.
The fungus’s hyphae (fine threads or filaments)
provide a sheltered place for the alga as well
as providing it with water and nutrients. In
return the alga, which contains chlorophyll,
carries out photosynthesis and provides
carbohydrates for the fungus.
Fig 2.9: Lichens growing on a tree.
2D
lichens
Go to the Topic webpage to learn more about lichens.
did you know?
Some lichens are used to create colours to dye for!
New Zealand spinners who dye their own wool prize the lichen Pseudocyphellaria
coronata. Compared with brightly coloured synthetic dyes, lichen dyes, some of which are
pleasantly fragrant, yield a wide range of subtle colours depending on what mordant is
used.
Source: http://www.teara.govt.nz/en/lichens/2
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competition and cooperation
mycorrhizal fungi
Mycorrhizal fungi have a close and beneficial association with the roots of plants. Most plants
co-exist with these fungi, which help them absorb nutrients from the surrounding soil. The
fungal hyphae extend from the host plant into the surrounding soil. This increases the surface
area for absorption of water and nutrients by both the fungus and the host plant. The fungi also
secrete growth factors that stimulate the roots to grow and branch and may produce antibiotics
that may protect the plant from pathogens. In return the fungus receives carbohydrates made
by photosynthesis in the plant’s leaves. Mycorrhizal fungi are an important part of pine forest
ecosystems. The mushrooms that appear above ground around the trees are the fruiting bodies of
these fungi.
2E
mycorrhizal fungi
Go to the Topic webpage to learn more about mycorrhizal fungi.
2F
competitive strategies
1. Define allelopathy and explain why this process gives plants a competitive advantage.
Allelopathy:
Explanation:
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competition and cooperation
phil bendle
2. The perching lily, Collospermum hastatum,
(kahakaha or ‘widow maker’) (Fig 2.10)
is one of the largest epiphytes in the
New Zealand bush, growing high in the
branches of canopy trees. Perching
lilies are tall, clump-forming plants with
long, arching leaves. What competitive
advantages do epiphytes such as the
perching lily have compared to lower
growing forest plants?
Fig 2.10: Perching lilies.
Check your answers.
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competition and cooperation
2G
plant cooperation
Truffles, such as the black truffle, Tuber melanosporum, are an expensive fungal delicacy. These
mycorrhizal fungi are now cultivated in New Zealand, on the roots of oak and hazel trees. Discuss
why trees that have an association with mycorrhizal fungi tend to grow better than those which
don’t have this association.
Check your answers.
key words
key points
competition
exploitation
allelopathy
resources
cooperation
symbiotic association
mutualistic association
•• Competition may be intraspecific or interspecific and
may be either through interference in the growth of other
species or through exploitation of other species.
•• Resources for which plants compete include sunlight,
water, nutrients in the soil, carbon dioxide from the
atmosphere and space to grow.
•• Plants compete with each other for resources in order to
survive in the environment.
•• Plants have developed cooperative strategies that help
them to survive. These may be symbiotic associations
with other plants.
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defence and cooperation
learning intentions
In this lesson you will learn to:
•• discuss defensive plant–animal responses to the biotic environment.
•• discuss cooperative plant–animal responses to the biotic environment.
introduction
Plants are at the start of all food chains. They are eaten by herbivores, which are in turn eaten
by carnivores. There are many kinds of herbivores: grazers such as sheep and cattle that eat
pasture plants; browsers such as giraffes and elephants that eat leaves of shrubs and trees; fruit
and seed eaters such as humans, bats and birds; sap suckers such as aphids; and nectar feeders
such as birds and butterflies. However, plants generally prefer not to be eaten! As they cannot
move away from their predators, they have developed strategies to avoid predation by many
herbivores.
physical defences
If you have ever picked blackberries or roses from the garden you will know that some plants
have thorns or spines. These are a very effective defence against herbivores that are likely to
browse on the plant. The New Zealand native plant matagouri is an example of a plant with
thorns.
Many plants produce protective barriers such as bark or gum or thick waxy cuticles to prevent
predation by herbivores.
Others have evolved defensive growth habits.
An example is divarication, where plants
branch repeatedly and produce a tangle of
stems with the outer branches having smaller
and fewer leaves than the inner branches.
The stems of divaricating plants are often
tough and difficult to break. This adaptation
makes it difficult for browsers to reach the
inner, larger leaves. New Zealand has many
divaricating plants, such as the Coprosma
species (Fig 3.1). It is thought that the many
divaricating species in New Zealand arose as
an adaptation to browsing by moa.
wikimedia commons
3
Fig 3.1: A Coprosma plant showing divarication.
Some trees such as beech trees prevent their seeds being eaten by a process called seed
masting. Every few years all the trees of the same species release all their seed simultaneously.
This has two advantages for the trees: first, with so many seeds available as food, they won’t all
be eaten by seed-eating animals and so some will survive to germinate. Secondly, as there are
not enough seeds in the intervening years to support a large population of seed-eating animals,
there is less chance of the seeds being eaten during a mast year.
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defence and cooperation
chemical defences
Some plants prevent attack by herbivores by producing chemicals that are unpalatable, toxic or
insect-resistant. Familiar herbs and spices such as lavender, thyme, rosemary, mint, cinnamon
and cloves, for example, produce oils in their leaves (essential oils) that we enjoy in cosmetics
and food, the real purpose of which is to discourage insect predators from eating their leaves.
Substances such as morphine in opium poppies and nicotine in tobacco are other examples of
toxic chemicals produced as plant protection.
In New Zealand the toxin 1080 is commonly used against browsing possums that are destroying
native forests. This is a human-made chemical reproduction of a naturally occurring,
biodegradable toxin, sodium monofluoroacetate, found in many Australian, South American
and South African plants such as eucalyptus. Low concentrations are also found naturally in
tea (Camellia species). Plants have developed monofluoroacetate as a natural defence against
browsing mammals in those countries.
Some plants produce an unusual amino acid called canavanine, which is similar to the amino
acid arginine, which insects need as part of their diet. When insects eat these plants, they
incorporate canavanine instead of arginine into their proteins. This makes these proteins
ineffective, and eventually the insects die.
When willow trees are attacked by pathogens, they produce anti-microbial compounds called
phytoalexins, which destroy the pathogens. The willows also produce other chemicals such
as salicylic acid, which travel through the tree, triggering an anti-microbial response to the
pathogens in leaves in other parts of the tree.
Some plants go even further and release chemicals that attract predatory animals to prey on
their attackers. These plants, when eaten by caterpillars, release volatile (airborne) chemicals
that attract dragonflies that feed on the caterpillars. Others attract parasitic wasps that lay
their eggs inside the caterpillars that are eating the plants’ leaves. The eggs hatch inside the
caterpillars and eat their way out, killing the caterpillars in the process. The plants benefit from
the destruction of the caterpillars.
Some plants and animals produce life-saving chemicals.
Certain chrysanthemums, for example, produce chemicals called pyrethrins in their leaves,
which are very poisonous to insects and stop them from eating the leaves. However, the
caterpillars of certain moths and butterflies have developed an enzyme that can detoxify (break
down) the pyrethrins, and these caterpillars can eat the leaves unharmed (Fig 3.2 on next page).
Some chrysanthemum species have gone one better, and produced another chemical called
sesamin that can knock out the protective enzyme in these caterpillars. There certainly is
chemical warfare in nature!
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defence and cooperation
Pyrethrins (in powder form and as sprays) are used by gardeners for protecting plants against
insects.
Prevents most
insects from
attacking the
plant.
Detoxifying enzymes of
some larvae allow them
to eat the plant.
Chrysanthemum
Sesamin (inhibitor of
detoxifying enzymes) protects
plant from larvae again.
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Plant produces
pyrethrin (toxin).
Fig 3.2: Chrysanthemum and the production of pyrethrin.
plant communication
Unbelievable as it may seem, plants are even able to communicate with each other for their
mutual benefit. Chemicals are the way plants communicate with each other.
Leaves damaged by pathogens or insect attack produce defensive molecules, such as ethene
(ethylene), which can travel through the air to other plants to activate their plant defence genes.
These volatile chemicals or ‘signalling’ molecules serve as a warning to others of the same
species that they are under attack by herbivores. The neighbouring plants are then stimulated to
produce their own chemical responses against the herbivores.
When a willow tree (Fig 3.3) is attacked by insects, the
leaves produce a chemical called salicin in response.
This chemical travels through the tree and induces it
to produce pathogenic chemicals (phytoalexins) that
protect the tree from further attack. Some of the volatile
salicin becomes airborne and is sensed by other willow
trees nearby, warning them of the insect attack so that
they can start to produce defensive chemicals too.
© te ah o o t e k ur a p o un a m u
istockphoto.com
Acacia trees, for example, produce tannins to defend
themselves when they are grazed on by animals such as
giraffes. The tannins make the leaves unpalatable so after
a few mouthfuls the giraffe moves away to another tree.
But the acacias release the gaseous hormone ethene into
the air. The airborne scent of the ethene is picked up by
other acacia trees, which then start to produce tannins
themselves as a protection from the grazers.
Fig 3.3: Willow trees produce chemical-signalling
molecules.
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defence and cooperation
Did you know?
If you have ever taken an aspirin you will have used the willow’s own defences – aspirin
is in fact a form of salicylic acid. Many cultures have used willow bark to lower fevers
and ease pain. Studies in salicilin led to the development of aspirin, initially created from
salicylic acid.
3A
chemical defences
Go to the Topic webpage to learn more about chemical defences and plant defence.
carnivorous plants
Plants are not always the victims of animal attacks. Sometimes, it is the plant that attacks.
Plants that naturally grow in bogs lack essential minerals such as nitrogen, which is in low supply
in boggy soils. These plants have overcome this deficiency by devouring insects and digesting
their bodies to obtain the minerals they need. Some examples of carnivorous plants are the
Venus fly trap, pitcher plants and sundews.
Once the insect is inside the plant, digestive
juices are released by the plant, digesting the
prey and making its minerals available to the
plant.
3B
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Some of these plants, such as the Venus fly
trap (Fig 3.4), have sensitive hairs that sense
the presence of an insect when it lands on
them and cause it to shut rapidly, trapping
the insect. Pitcher plants are shaped in such a
way that an insect entering the plant looking
for nectar is unable to escape. Sundews have
sticky hairs that trap insects.
Fig 3.4: A Venus fly trap leaf showing its sensitive hairs.
venus fly trap in action
Go to the Topic webpage to watch videos of a Venus fly trap and a sundew catching flies.
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defence and cooperation
plant–animal cooperation
Plants not only repel animals in their environments. In many cases they cooperate successfully
with animals for their mutual existence.
Plants have evolved ingenious ways of getting pollinators to visit them and transfer pollen. Many
animals may be plant pollinators, including bees and wasps, butterflies and moths, flies, some
beetles and birds and even bats.
The most obvious ways are through colourful petals and strong scents, but other flowers use
more subtle ways to entice their pollinators to call. Some offer a reward in the form of nectar.
Nectar is a sweet, sugary solution produced in special glands called nectaries, deep inside the
flower. Some flowers such as pansies and foxgloves even have ‘honey guides’, which are markings
such as spots, stripes or dark splotches that serve as guides to the centre of the flower where the
nectaries lie.
Did you know?
Bees like white, yellow and blue flowers, and cannot see red very well.
Bee-pollinated plants often have honey guides on them. Some honey guides are invisible to
us but are visible to bees as they can see in the UV range of light.
Bees can smell, so the flowers they pollinate are scented.
Birds can see red and like bright-coloured flowers.
tūī and mistletoe flower
Go to the Topic webpage to watch a video of tūī opening mistletoe flowers.
There are other plants that resort to mimicry to
get animals to visit them and transfer pollen to
other plants of the same species. A well-known
example is that of the Australian hammer orchid
(Drakaea species) (Fig 3.5) and thynnid wasps.
The shape of the orchid flower resembles that
of the female wasp, complete with shiny head
and furry body. In addition the orchid releases a
pheromone (a hormone that is volatile and travels
through the air) to attract male wasps. When the
male wasp tries to mate with the ‘female wasp’, it
collects pollen from the orchid that is transferred
to the next orchid the wasp visits. In this way,
the orchid achieves pollination, but the wasp
achieves nothing!
© te ah o o t e k ur a p o un a m u
wikimedia commons
3C
Fig 3.5: The Australian hammer orchid resembles a female
wasp.
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defence and cooperation
Some plants ensure their seeds are spread far from the parent tree to increase their chance of
germination. They do this by having a close relationship with birds which eat the fruit containing
the seeds. These then pass through the digestive tract of the bird and are deposited some
distance from the parent tree. This mutualistic relationship ensures the birds have food from the
tree and the tree increases the chance of its seeds successfully germinating. Some seeds actually
require their tough seed coats to be scratched or given an abrasive treatment before they can
germinate. This can occur naturally, as seeds are scratched by stones in the soil, but it also
happens when the seeds pass through an animal’s digestive tract, as the digestive juices break
down the seed coat.
New Zealand’s native wood pigeon, the kererū, is a disperser of large fruits such as those of the
karaka and taraire trees in our native forests, and is essential in aiding the regeneration of native
forests.
Some plants, such as acacias, have colonies of stinging ants living among their thorns. The ants
feed on sugary nectar provided by the trees. They guard the trees and if another animal such as a
browsing giraffe tries to eat the leaves, they swarm out and attack the browser. The relationship
between the ants and the tree is a remarkable example of mutualism. The ants earn shelter and
food, while the acacia gains protection from herbivores and competitors.
3D
acacia and ants: mutualism
Go to the Topic webpage to learn more about the mutualistic relationship between acacias and
ants.
plant defences
Matagouri or wild Irishman (Discaria
toumatou) is an example of a New Zealand
native plant with thorns. These may be several
centimetres long. Matagouri’s growth form is
described as divarication (Fig 3.6). The plant
grows up to six metres high and has very small
leaves and small greenish-white flowers. It is
widespread in the eastern South Island and
Central Otago.
doc
3E
Fig 3.6: A matagouri plant.
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defence and cooperation
Define the term ‘divarication’, and discuss why thorns and divarication are thought to be an
adaptation to protect the plants against browsing by moa.
Check your answers.
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defence and cooperation
3F
plant communication
Lima beans (Phaseolus lunatus) may become infested with two-spotted spider mites
(Tetranychus urticae) which damage their leaves. The lima beans produce volatile chemicals
that can be detected by other bean plants growing nearby. When this distress signal reaches
surrounding lima beans, they, too, begin to send the signal chemicals even though they are not
under attack. In addition, the chemicals attract another species of spider mite that is carnivorous
and preys on the two-spotted mite.
Discuss how the production of volatile chemicals benefits the population of lima beans.
Check your answers.
3G
plant cooperation
The two endemic mistletoe species (Peraxilla) both have large red showy flowers, unlike most
New Zealand plant species, which have small and inconspicuous flowers. Both Peraxilla species
have specialised ‘explosive’ flowers that require birds to tweak the buds before they will open.
To open the flowers, birds grasp the top of the bud with their beaks and twist. This causes the
flower petals to spring open (in less than a quarter of a second), and the bird can then insert its
beak to drink nectar and in so doing pollinate the flower. Flower buds that are protected from all
potential pollinators do not open their petals, although the petals do eventually separate as a
unit from the base of the flower. The main birds that can twist open Peraxilla flowers are the tūī
(Prosthemadera novaeseelandiae) and bellbird (Anthornis melanura), which are both endemic
honeyeaters.
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defence and cooperation
What is the term given to the relationship between the mistletoe and the birds? Discuss how this
relationship is of benefit to both bird species and the mistletoe species.
Check your answers.
key words
key points
physical defences
chemical defences
plant communication
plant cooperation
•• Plants employ a range of physical and chemical defensive
strategies to protect themselves from predation by
herbivores.
•• Plants can communicate with each other by chemical
signalling.
•• Plants cooperate with each other and with animals for
their mutual benefit.
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orientation responses
learning intention
In this lesson you will learn to:
•• describe plant orientation responses to the abiotic environment.
introduction
Plants are acutely aware of their abiotic environment and are able to make suitable responses to
stimuli. They are able to sense sunlight – not just its presence, but also the direction of the light,
its intensity, and even the different wavelengths of light – and make appropriate responses to
it. They can detect gravity, temperature, and the presence of water or chemicals, and can sense
if they are touched. They can track the time of day and the time of year and adjust their growth
accordingly.
As almost no plants can move unaided, their responses are usually to alter their growth to move
towards more favourable environments or away from less favourable environments. For example,
if a plant is being shaded by a larger one, the smaller plant will grow taller or grow outwards to
the side, to reach more sunlight. If a seed lands on the ground its roots will grow downwards
and its stem upwards. In this lesson you will learn how plants respond to stimuli in their abiotic
environment by orientating (positioning) themselves appropriately.
tropisms
A tropism is a growth response made by plants to external stimuli in their abiotic environment.
The direction of the stimulus determines the direction of the growth response. Plants usually
respond to stimuli such as sunlight, water, temperature, gravity, chemicals, touch and wind. The
tropic response may be positive – the plant grows towards the stimulus; or negative – the plant
grows away from the stimulus.
Some tropisms you should know:
•• light (phototropism): for example, a
plant’s stem grows towards light so we
say the stem is positively phototropic. A
plant’s roots grow down into the soil, away
from light, so the roots are negatively
phototropic.
The tree’s shoots grow towards the light, so
they are positively phototropic.
•• water (hydrotropism)
•• temperature (thermotropism)
•• gravity (geotropism or gravitropism)
•• sun (heliotropism)
•• chemicals (chemotropism)
•• touch (thigmotropism)
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4
•• current (rheotropism).
Fig 4.1: The tree’s roots grow down into
the soil, away from light, so the roots are
negatively phototropic.
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orientation responses
nastic responses
A nasty or nastic response is a non-directional movement of part of a plant in response to an
external environmental stimulus. Nastic responses are made to the intensity of the stimulus
rather than to the direction. For example, plants make nastic responses to the intensity of light,
temperature and humidity, rather than to their direction. Nastic responses are turgor responses
(turgor means the rigidity of the plant tissue due to inflation of the cells with water).
You may have noticed that some flowers close at night and open in the daytime. These ‘sleep’
movements are in response to light intensity (photonasty) or temperature (thermonasty). These
are nastic responses because they are triggered by external stimuli (light, temperature) but the
response is directed internally.
The movement is the result of growth or a turgor change. Crocus or tulip flowers close at night by
the lower sides of the petals growing more rapidly and open by day by a more rapid growth of the
upper sides.
Some leaves show drooping or ‘sleep’ movements too. Several species of clover have structures
called pulvini (singular: pulvinus). The pulvinus is a swelling at the base of the petiole or leaflet
and has large parenchyma cells. Rapid turgor pressure changes in these cells cause the pulvinus
to act as a hinge and bring about movement in the leaves.
Movements that are triggered by the intensity of touch are called haptonastic. Haptonastic
movements are perhaps the most fascinating of all plant movements – they bring about a rapid
and elaborate response. Insectivorous plants snap shut in response to external pressure – like
the Venus fly trap (which you learned about in the previous lesson) when its sensitive hairs are
touched. Some of these movements are haptonastic.
The mimosa plant (Mimosa pudica) responds very rapidly to touch. It is sometimes called the
‘sensitive plant’. If the leaflets at the tip are shocked by a sharp blow or even a sudden change
in temperature or light intensity, they fold upwards in seconds. If the stimulus is sustained,
successive pairs of leaflets fold upward and eventually the whole leaf drops. The stimulus is
thought to be transmitted by a hormone that moves through the xylem; electrical changes are
associated with its passage (but it does not have a nervous system).
4A
mimosa leaves: haptonastic response
Go to the Topic webpage to watch a video of mimosa leaves showing haptonastic responses.
Note that tropisms are plant growth movements that are not usually reversible. Nastic
movements on the other hand are reversible (for example, the crocus flower closes at night and
opens again in the morning; the mimosa leaves close when touched and then open again).
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orientation responses
4B
plant responses
1. Define a tropism and a nastic response.
Tropism:
Nastic response:
2. Name each of the tropisms described below; say whether the tropism is positive or negative;
and describe the biological advantage to the plants.
a. A young stem grows upwards towards the light.
Tropism:
Biological advantage:
b. Roots grow downwards into the soil.
Tropism:
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Biological advantage:
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orientation responses
c. Roots grow towards water.
Tropism:
Biological advantage:
d. A stem grows away from the Earth’s gravitational pull.
Tropism:
Biological advantage:
e. Tendrils (modified leaves) touch a trellis and coil around it.
Tropism:
Biological advantage:
f. A climbing plant twines upwards around a supporting plant’s stem.
Tropism:
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orientation responses
Biological advantage:
g. Roots grow away from a copper pipe in the soil.
Tropism:
Biological advantage:
h. A pollen tube grows from a pollen grain towards the chemicals given off by the flower’s
ovary.
Tropism:
Biological advantage:
3. The leaves of Oxalis species droop at night. What is this plant response called, how does it
occur and what is the biological advantage of this?
Response:
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How it occurs:
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orientation responses
Biological advantage:
Check your answers.
key words
key points
tropism
nastic response
•• A tropism is a growth response made by plants to
external stimuli in their abiotic environment. The
direction of the stimulus determines the direction of the
growth response. The tropic response may be positive –
the plant grows towards the stimulus; or negative – the
plant grows away from the stimulus.
•• A nasty or nastic response is a non-directional
movement of part of a plant in response to an external
environmental stimulus. Nastic responses are made
to the intensity of the stimulus rather than to the
direction.
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control of plant growth
5
learning intention
In this lesson you will learn to:
•• discuss the plant hormones influencing plant growth.
introduction
You may have noticed that the leaves on a pot plant on a window sill turn to face the light. The
leaves are displaying positive phototropism. If a seed lands on the soil, the roots will grow down
into the soil and the stem will grow upwards. The roots are positively geotropic and the stem is
positively phototropic.
How do parts of the plant detect light or gravity or other stimuli? There are receptor cells in
the leaves, shoots and roots that can detect the presence of the light and gravity stimuli and
then respond appropriately to these stimuli. They do this by producing chemicals (hormones).
Hormones are chemicals that are produced in one area of the plant and transported to other
areas where they produce an appropriate growth response.
plant hormones
Charles Darwin and his son Francis carried out experiments on a species of Phalaris canariensis
or canary grass. They sprouted the grass seeds and noticed that the coleoptile (a sheath that
covers the first leaves as they emerge from the soil) bent towards the light coming from a
window. The bending didn’t occur at the tip but in the elongating part behind the tip. Darwin
covered the elongating part of the coleoptiles and shone light on the tips and the coleoptiles
still bent towards the light. Next he covered the tips of the coleoptiles, shone light on them and
found they did not bend.
He concluded that there was some substance in the tip of the coleoptiles that was affected by
light. This substance must be moving down the coleoptile and causing the lower part to bend
towards the light. The light-sensitive region in the tip of the coleoptiles is called the receptor and
the part below that elongates is the effector, where the response occurs.
Many other scientists followed on from these experiments, and eventually the substance
affecting growth was identified as a hormone and named ‘auxin’, from the Greek word ‘auxein’,
which means to grow. Auxin was the first substance to be identified as a plant hormone. Auxin is
in fact a group of hormones, the main one being indoleacetic acid (IAA).
5A
auxins
Go to the Topic webpage to learn about the early experiments to identify auxins.
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control of plant growth
auxin
Auxin is being made all the time by the cells in the tip of the shoot. The auxin diffuses downward
from the tip into the rest of the shoot. Auxin makes the cells just behind the tip get longer. The
more auxin there is, the faster they will grow. Without auxin they will not grow. When the light
shines on a shoot from one side, the auxin at the tip concentrates on the shady side. This makes
the cells on the shady side grow faster than those on the light side, so the shoot bends towards
the light. This is explained in the diagram below:
Auxins and phototropism
Auxin is made here.
Light
Cells on this
side grow
quickly.
Cells on this side
grow slowly.
Light
The uneven concentration
of auxin causes the shady
side to grow faster than the
light side, so the shoot bends
towards the light.
Auxin made in this tip
diffuses unevenly down the
shoot, concentrating on the
shady side.
auxin has opposite effects on stems and roots
It seems from experimental evidence that the concentration of auxin has opposing effects on
stems and roots. Roots are much more sensitive to auxin concentration than stems. Root growth
is actually inhibited by high concentrations of auxin.
Accumulation of auxin
stimulates growth on
this side of plumule.
Accumulation of auxin
is present on lower side
of elongating zones of
plumule and radicle.
© te ah o o t e k ur a p o un a m u
gravity
Accumulation of auxin
inhibits growth on this
side of radicle.
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control of plant growth
Auxin accumulates by gravity on the lower sides of stems and roots. In the root (radicle), this
high concentration inhibits growth on the lower side of the elongating cells so that the elongating
cells on the upper side grow downward.
In the stem (plumule), the high concentration of auxin on the lower side has the opposite effect,
stimulating growth of the lower cells and making the stem bend upwards.
Geotropism enables the roots to grow downwards in the soil irrespective of the seed’s orientation
under the soil surface. This will help to anchor the plant and to absorb the water and minerals
needed from the soil.
But how does the seed tell up from down? It uses gravity receptors. These are small starch grains
(called amyloplasts or ‘statoliths’) in the cells. They move to the lower side of the cells and affect
the distribution of auxin so that there is more auxin on the underside.
Positive geotropism in roots
Whichever way up a seed is
planted, its radicle always grows
downwards.
If you have an old pot plant, you could try a similar experiment by simply lying the potted plant
on its side and seeing what happens to it over a two-week period.
Potted plant lying on its side
Hormone accumulates
on lower side of stem and
stimulates cell growth –
stem turns up.
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Hormone accumulates on
lower side of root and inhibits
cell growth – root turns
downwards.
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control of plant growth
apical dominance
The tip (apex) of a plant produces the most auxin, so the plant grows upwards. The side shoots
(laterals) do not grow, as auxin inhibits their growth. However, if the tip of the shoot is cut off (a
process called ‘pinching out’ by gardeners) then the side shoots will develop and the plant will
grow bushier!
effects of plant hormones
There are five major groups of plant hormones involved in plant growth. These are:
•• auxins
•• gibberellins
•• cytokinins
•• abscisic acid
•• ethene (ethylene) gas.
The main effects of these plant hormones are summarised in the table below. Their effects are
more complex and interactive than given here. Note that you do not need to remember the
specific effects of these hormones. You do, however, need to understand that they are produced
in response to environmental stimuli and they allow plants to make appropriate growth-tropic
responses, to help them adapt and survive changing environmental conditions.
main plant hormones and their effects
Hormone
Main effects
Auxin
Promotes stem elongation.
Controls cell enlargement.
Causes apical dominance by suppressing growth of lateral buds.
Stimulates cell division in cambium (secondary vascular growth).
Stimulates root initiation.
Suppresses root elongation.
Delays onset of leaf fall.
Delays fruit ripening.
Stimulates growth of flower parts.
Gibberellin
Promotes stem elongation.
Delays dormancy and leaf fall.
Breaks dormancy in seeds and buds.
Cytokinin
Stimulates cell division.
Promotes growth of young fruit.
Balances root and shoot growth.
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control of plant growth
5B
Abscisic acid
Inhibits growth, produces winter dormancy.
Induces fruit fall.
Promotes seed dormancy.
Acts on guard cells; produced in response to water stress and
promotes closing of stomata.
(The effects of abscisic acid are generally the opposite of those of
auxins, gibberellins and cytokinins.)
Ethene (ethylene)
gas
Induces fruit to ripen.
Aids leaf fall.
plant hormones
Go to the Topic webpage to read an overview on plant hormones.
5C
plant hormones
1. When water levels in a plant are low, due to low rainfall or drought conditions, the synthesis
of abscisic acid in the plant is stimulated. One of the functions of abscisic acid is to stimulate
the closing of the pairs of guard cells surrounding stomata in the leaves. Discuss how this
response helps the plant to survive the dry conditions.
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control of plant growth
2. A seedling is placed horizontally on the soil surface. Explain the role of auxin in the geotropic
(gravitropic) response of both the shoot and the root of this seedling and discuss why this
response helps the seedling to survive and grow into a plant.
Check your answers.
key words
key points
plant hormones
receptor
effector
•• Hormones are chemicals that are produced in one area
of the plant and transported to other areas where they
produce an appropriate growth response.
•• Receptor cells in the leaves, shoots and roots detect the
presence of the light and gravity stimuli and then respond
appropriately to these stimuli by producing hormones.
•• The effector is the region of the plant where the growth
response occurs.
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timing responses
learning intentions
In this lesson you will learn to:
•• explain plant photoperiod timing responses
•• explain the plant phytochrome system.
introduction
If you have a garden or live on a farm you have probably noticed seasonal changes in plant
growth and development. Most plants flower in the heat of summer; spring is a good time to
plant seedlings; many fruit and vegetables ripen in autumn; some leaves change colour and fall
from deciduous trees in autumn; other plants go dormant in winter; and new leaves and buds
appear in spring.
If you are observant you may have noticed
that some flowers open in the daylight and
close at night while others, like the evening
primrose (Oenothera biennis) (Fig 6.1), open in
the late afternoon. Some flowers are scented
and produce nectar in the daytime, and others
open and are scented at night. Obviously,
plants are able to detect environmental stimuli
that tell them the time of day and the time of
year, so that they can adjust their growth and
flowering and fruiting times accordingly.
timing rhythms
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Fig 6.1: The evening primrose flowers open in the evening, when
light levels are lower.
Some plants such as the evening primrose above show daily (or diurnal) rhythms that may be
triggered by light or temperature. Daily rhythms are also called circadian rhythms (circadian
means ‘about a day’, from the Latin ‘circa’ meaning ‘about’ and ‘dies’ meaning ‘a day’). Flowers
that open in the sunlight and close when the sun sets are displaying a circadian rhythm. Leaves
that droop at night and are upright during the day are also displaying a circadian rhythm.
Some plants show yearly (circannual) rhythms, as they produce buds and new leaves in spring,
flower at one time of the year (often spring or summer), lose their leaves in autumn, and go
dormant at other times (usually in winter, but in summer for some plants). These plants are
following a yearly cycle of growth and development.
•• Annual plants grow, flower and set seed during one year (for example, petunias and pansies).
•• Biennial plants grow leaves and store food in their first year and flower in the second year (for
example, carrots and foxgloves).
•• Perennials grow and flower every year for a number of years. Many die down and become
dormant, usually over winter, then grow new leaves in spring (for example, dahlias and
lavender).
•• Ephemerals are desert plants that germinate, grow, flower and set seed in a few weeks, after
rainfall. They contain a chemical that inhibits the seeds from germinating until sufficient rain
has fallen. Then they carry out their life cycle quickly, before the desert dries out again.
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timing responses
If the stimulus that brings about these plant responses comes from outside the plants, it is called
‘exogenous’ (‘exo’ means ‘outside’). A stimulus may also be produced internally within the plant.
This is termed ‘endogenous’ (‘endo’ means ‘inside’).
change in leaf
colour
change
from leaf
development
to flower
development
grass tillering
leaf drop in
deciduous
trees in
autumn
plant responses
to day length
bud break of
fruit tree in
spring
tuber and bulb
formation
start of winter
dormancy
germination of
some seeds, for
example, lettuce
photoperiod and phytochrome
The control over the life cycle of plants (from seed → reproductive maturity → seed) is achieved
by the cyclic change in day length (and temperature). The further plants are from the equator,
where days are almost a constant 12 hours long, the greater the seasonal variation in day length.
In plants, phenomena such as flowering, fruit and seed production, bud and seed dormancy,
leaf fall, and germination are closely attuned to seasonal differences such as day length and
temperature. The survival of the plant depends on these.
The process that involves the most profound change is flowering, when shoot meristems (growing
points) switch from producing leaves and lateral buds to producing flowers. It is vital for plants
to coordinate their flowering times, so that pollination can take place. The flowers of the same
species need to flower in synchronisation so that pollen can be transferred from one to another,
and at the right time of year for their pollinators such as insects and birds to be present.
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timing responses
There are many environmental cues that affect flowering, such as temperature, but it is mainly
the length and sequence of the light and dark periods, rather than the total amount of light
received, that stimulates reproduction (flowering).
The term photoperiodism is used to describe the plants’ biological response to the relative
amounts of light and darkness in any 24-hour period (the photoperiod). Plants use the
photoperiod to tell the length of day and therefore which season it is. How can plants sense
the length of day and night? They use a sensory blue-green pigment, called a phytochrome.
Phytochromes are protein pigments in plants that are sensitive to red and infrared light. Two
interchangable forms exist:
•• Pr, which absorbs red light and
•• Pfr, which absorbs infrared light.
Each form changes back to the other when it absorbs light. On absorbing light in the daytime, Pr
converts to Pfr. At night, Pfr reverts back to Pr.
Pfr is the biologically active form that acts as a switch to turn on plant responses. This is shown in
the diagram below:
in daylight
Pr
Pfr
plant
response
at night
inactive form
active form
Phytochromes are important in the control of flowering.
They also act in:
•• the germination of seeds, which need a brief exposure to light before they germinate
•• stem elongation (infrared light)
•• leaf expansion (red light)
•• growth of side roots (infrared light).
The photoperiod stimulus is sensed in the leaves via the phytochrome system. A chemical
messenger is then sent to the buds to form flowers. (The messenger has been called ‘florigen’,
but has not yet been isolated and may be a mixture of hormones.)
6A
phytochromes
Go to the Topic webpage to learn more about the phytochrome system and the control of
flowering.
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timing responses
photoperiod and flowering reponses
From the early twentieth century, scientists discovered the importance of the photoperiod in
flower formation. It was shown that tobacco plants would flower only after exposure to a series
of short days. This occurred naturally in autumn, but could also be induced artificially in a
greenhouse by limiting daylight to seven hours. Plants that need a short day and long night to
flower are called short-day plants. They will only flower if the photoperiod is less than a certain
critical length.
Other plants require long days and short nights for flowering (long-day plants). In order to
flower, these plants need a photoperiod that exceeds a certain critical length.
Some other plants flower when they are mature, whatever the photoperiod is. These are dayneutral plants.
Later advances to our understanding have shown that it is actually the length of the dark
period that is the critical factor.
So short-day plants are really long-night plants. If these are grown in short days but the long
night is interrupted by a short light period, then flowering is prevented. Similarly, long-day plants
(short-night plants) will flower in short days if the long night is interrupted. Long-day plants will
flower only when red light or a long period of sunlight causes an accumulation of Pfr. Short-day
plants flower when red light or a long period of darkness causes an accumulation of Pr.
Short-day plants (SDP) typically flower in the spring or autumn when the length of day is short.
Long-day plants (LDP) typically flower during the summer months of longer photoperiod.
This is explained in the following diagram.
= flowering
Short-day
plant (SDP)
= no flowering
Long-day
plant (LDP)
24 hours
16 hours light (long day)
8 hours light (short day)
8 hours dark
16 hours dark
8 hours light
6B
8 hours light
red
8 hours light
red
infrared
long-day/short-day plants
Go to the Topic webpage to view an animation explaining long-day/short-day plants.
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timing responses
more plant responses to the abiotic environment
temperature (vernalisation)
Temperature changes can act as cues for plant responses. Some plant species require exposure
of a growth stage to cold before flowering can proceed. This need for a cold spell is called
vernalisation. Here, the stimulus is picked up by the mature stem apex or by the embryo of the
seed, not the leaves, as in photoperiodism.
Long-day plants (such as cabbage), short-day plants (chrysanthemum) and day-neutral plants
(ragwort) can all require vernalisation. The length of chilling can vary from four days to three
months, with temperatures around 4°C generally being most effective.
During vernalisation, the level of gibberellins increases. Gibberellins can be used artificially on
unvernalised plants to substitute for vernalisation.
Seeds may also be subjected to cold by placing them in a refrigerator if they are to be grown out
of season. Some species have their seeds planted in the autumn so that they germinate before
the winter cold because flowering will not occur unless the young seedlings have been exposed
to cold.
Plants from the southern areas of New Zealand may not survive when planted in more northerly
parts of the country, because they may not be exposed to sufficiently cold periods for a long
enough time.
importance in plant survival
Both photoperiodism and vernalisation work to synchronise the reproductive behaviour of plants
with their environment to ensure reproduction at the most favourable times of the year. This will
also ensure that members of the same species will flower at the same time, encouraging crosspollination and cross-fertilisation, with the advantages these bring in genetic variability.
dormancy in plants
Dormancy occurs when growth and development in plants cease and the plants’ metabolic rates
fall to a point which is only just sufficient to keep the cells alive. This is the normal winter state of
most plants in temperate regions.
Dormancy is brought about by light and temperature acting through hormones. Winter buds in
temperate trees (such as birch, beech and sycamore) form as a photoperiodic response to the
shortening days in autumn. This stimulus is perceived in the leaves and hormones are produced,
which leads to a build-up in the chemical abscisic acid. Abscisic acid inhibits growth and also
induces leaf fall.
Storage organs (for example, bulbs and tubers) are also involved when the plant goes into a
dormant state, and again, photoperiodism is involved. Short days induce tuber formation in
potatoes and long days induce onion bulb formation.
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timing responses
leaf fall (abscission)
Leaf fall can result from a number of factors. These include:
•• water shortage as a result of drought conditions or the freezing of water in the soil
•• lowering of light intensity
•• a drop in temperature
•• shortening of day length.
As a result of a build-up in abscisic acid, a layer of weakened cells collects at the base of the
petiole. The leaf eventually breaks off from the parent plant at this point. This is most obvious in
deciduous plants.
rhythm and phase
Leaves of the plant Bryophyllum (a common New Zealand weed, also called ‘mother of millions’)
show a circadian rhythm in their output of carbon dioxide gas. This rhythm can be altered by a
number of abiotic factors, including light and temperature.
Figure 6.2 shows the normal rhythm of the Bryophyllum in continuous darkness at constant
temperature, and the altered rhythm when the Bryophyllum was exposed to four hours of light
(dark line on the graph).
output
60
CO₂ exchange (relative amount)
Continuous darkness, at constant temperature
4 hours light
40
leaf in darkness
(normal rhythm)
leaf in darkness
plus 4 hours light
20
0
-20
-40
-60
-80
-100
-120
-140
intake 0
midnight
0
0
0
0
midnight
Time of day
NZQA
6C
Fig 6.2: Rhythm of CO2 production in continuous darkness and with 4 hours of light, once around midnight.
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timing responses
Figure 6.3 shows how the normal rhythm in continuous light at 15°C can be altered (dark line) by
increasing the temperature to 40°C for three hours without altering the light.
output
60
CO₂ exchange (relative amount)
40
Continuous light at 15°C
untreated leaf
(normal rhythm)
3 hours at 40°C
20
altered rhythm
plus 3 hours of
higher temperature
0
-20
-40
-60
-80
-100
-120
0
0
midnight
midnight
0
0
0
Time of day
NZQA
-140
intake
Fig 6.3: Rhythm of CO2 production in continuous light except for 3 hours of higher temperature.
Both figures show the rhythm over five days.
1. What does the term ‘circadian’ mean?
2. Explain how the exposure to four hours of light has altered the circadian rhythm (Fig 6.2).
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timing responses
3. How is the effect on the circadian rhythm of the exposure to 40°C (Fig 6.3) different to the
effect of the exposure to light (Fig 6.2)? Assume that both the differences in duration of
‘treatments’ (4 hours of light versus 3 hours of higher temperature) and timing of treatments
(3 hours leading up to midnight versus 2 hours on either side of midnight) can be ignored.
4. Explain from the data why this rhythm is endogenous.
Check your answers.
6D
photoperiod and flowering
The changing length of day and night regulates the onset of flowering in many plants.
1. Give the term that describes the regulation of activity in plants by day and night length.
2. Describe two advantages of having the time of flowering regulated by an environmental
factor.
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timing responses
3. Name one process in plants, other than flowering, controlled by the length of day and night.
4. Study the information in the diagram below, and then answer the questions that follow.
Equal
length days
and nights
Short days,
long nights
flower
Cocklebur
Corn
flower
Long days,
short nights
flower
NZQA
Spinach
flower
a. Is spinach a short-day or a long-day or a day-neutral plant?
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timing responses
b. Describe the environmental factor that initiates flowering in short-day plants.
c. Explain how cocklebur, a short-day plant, can flower when day and night lengths are
equal.
d. Poinsettia is a short-day plant with a critical day length of around 13 hours. Poinsettia
plants were put in a glasshouse under conditions of short days and long nights. Explain
what will happen to the flowering if the day period is interrupted by a few minutes of
darkness.
Check your answers.
key words
key points
circadian (diurnal)
rhythm
endogenous
exogenous
photoperiod
photoperiodism
phytochrome
short-day plant (SDP)
long-day plant (LDP)
vernalisation
dormancy
abscission
•• Stimuli may be endogenous (internal) or exogenous
(external) to a plant.
© te ah o o t e k ur a p o un a m u
•• Plant responses may follow a circadian rhythm.
•• Photoperiodism describes the plants’ biological response
to the relative amounts of light and darkness in any 24hour period (the photoperiod).
•• Plants sense the photoperiod using phytochromes.
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7
teacher-marked assignment
learning intention
In this lesson you will:
•• review your progress over this topic and practise exam-type questions.
introduction
In this lesson, have a quick look back at all the lessons you have completed in this topic. Think
about what you have learned. When you are ready, try the teacher-marked assignment BY3031A.
If you did not receive this with your booklet, contact your teacher.
When you have finished, complete the self-assessment section in the teacher-marked
assignment. Send the self-assessment and the teacher-marked assignment to your teacher.
Make sure that you have written your name and ID number on the cover sheet of the teachermarked assignment. You can also use a label if you have one at hand.
By post:
Put the self-assessment and teacher-marked assignment in the plastic envelope provided.
Make sure that the address card shows the address for Te Aho o Te Kura Pounamu (The
Correspondence School). Seal the envelope with tape before you post it.
By email:
Scan the pages including the cover sheet and email to your teacher. The standard format for Te
Kura teacher email addresses is: [email protected]
If you aren’t sure who your teacher is, call 0800 65 99 88.
Before you finish off this topic you should have agreed your next steps with your teacher. If you do
not have your next set of study materials, contact your teacher immediately. If you are not sure
what to do next, ask your teacher for advice.
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answer guide
8
1. the environment: an overview
1C
Stimulus: a change in the environment that causes a response in an organism
Habitat: the place where an organism lives
Biotic environment: the influences of living organisms on one another
Abiotic environment: the non-living influences on an organism
Ecosystem: a community of living organisms (biotic environment) together with non-living factors
(abiotic environment) and the nutrient cycles and energy flows that connect all
Intraspecific: relationships within a species
Interspecific: relationships between species
Adaptation: an inherited characteristic that enables an organism to survive and reproduce in its
habitat. Adaptations may be structural, behavioural or physiological
Tolerance: an organism’s ability to survive variation in its environmental conditions
Acclimatisation: the ability of an organism to adjust its tolerance limits or optimum range to slow
changes in its environment
Ecological niche: a description of how the organism feeds, the opportunities provided by the
habitat and the adaptive features of the organism which allow it to take advantage of these
opportunities
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answer guide
1D
Activity 1.2: Adaptations
Answers will vary but may include:
Achieved answer
Merit answer
Gives at least two adaptations. Structural
adaptations include:
Links the adaptations to the falcon’s
niche:
•• wings for flight
•• The falcon’s niche is that of a bird
of prey. Its wings allow it to fly long
distances to seek prey.
•• sharp talons to catch and hold onto
prey
•• excellent eyesight
•• strong beak to kill prey.
•• Its sharp eyesight helps it locate prey
even while flying at speed.
•• The falcon can catch prey while in
flight and uses its strong talons to hold
onto its prey and its strong beak to kill
its prey. These adaptations make the
falcon a successful hunter.
2. competition and cooperation
2F
1.
Achieved answer
Merit answer
Defines ‘allelopathy’.
As for Achieved AND explains competitive
advantage. For example:
Allelopathy is the production of toxic
chemicals in the roots and leaves of
a plant that prohibits the growth of
neighbouring plants.
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•• This is an advantage to the plant
producing the chemicals because it
stops or greatly reduces the growth
of neighbouring plants which would
compete with the plant for resources
such as sunlight, water, minerals from
the soil, space to grow, availability
of pollinators, etc. This gives the
allelopathic plant a competitive edge
in surviving in the environment, to the
detriment of its neighbours.
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answer guide
2.
2G
Achieved answer
Merit answer
Epiphytes grow high in the branches of
canopy trees so they are able to access
more sunlight than plants growing lower
in the forest.
As for Achieved AND explains competitive
advantage.
This gives them an advantage as they
can carry out more photosynthesis and
therefore grow bigger and quicker than
lower growing plants that receive less
sunlight. Being epiphytic also protects
these plants from ground-feeding
herbivores.
Achieved answer
Merit answer
Excellence answer
For example:
The fungal hyphae of the
Tuber melanosporum
extend from the host tree
into the surrounding soil.
This increases the surface
area for absorption of
water and nutrients by
the fungus or the host
tree.
As for Achieved AND
explains the advantage.
As for Merit AND gives
detailed full comparison/
answer.
© te ah o o t e k ur a p o un a m u
For example:
The fungi also secrete
growth factors that
stimulate the roots to
grow and branch and
may produce antibiotics
that may protect the tree
from pathogens. In return
the fungus receives
carbohydrates made by
photosynthesis in the
tree’s leaves.
For example:
Because of the extra root
area for absorption of
water and minerals and
protection that the Tuber
melanosporum provides,
trees infected with this
fungus grow better than
other trees that are not
infected.
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answer guide
3. defence and cooperation
3E
Achieved answer
Merit answer
Excellence answer
Definition given.
As for Achieved AND
explains advantage of
either divarication OR
thorns.
As for Merit AND gives full
account/comparison of
advantage of both thorns
and divarication.
For example:
Divarication makes it
difficult for moa to reach
the inner, larger leaves.
For example:
It is thought that the
many divaricating
species in NZ arose
as an adaptation to
browsing by moa, as the
combination of thorns
and divarication means
it is difficult for browsers
to reach the inner, larger
leaves. The shrub is
more tightly bound in a
compact shape, making
it harder to break off
a branch. The extra
toughness of the stems
protects the plant against
browsing. The high
proportion of stem to leaf
also made the plant less
attractive to moa.
For example:
Divarication is a form
of growth where plants
branch repeatedly and
produce a tangle of stems
with the outer branches
having smaller and fewer
leaves than the inner
branches. The stems of
divaricating plants are
often tough and difficult
to break.
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answer guide
3F
Achieved answer
Merit answer
Excellence answer
Describes at least one
effect of the production
of volatile chemicals.
As for Achieved AND
explains the effect.
As for Merit AND gives
full account/comparison
linking several effects.
For example:
The production of
volatile chemicals by
the lima bean has two
effects. Firstly, the
chemicals benefit the
plants growing nearby
by warning them of the
attack by the two-spotted
spider mites.
3G
For example:
These plants can then
produce chemicals of
their own to repel any
spider mite attacks.
For example:
In addition, the chemicals
attract a different species
of spider mite that does
not eat the lima beans
but preys on the twospotted spider mites. This
reduces the numbers of
two-spotted mites eating
the lima beans, thus
benefiting the plants.
Achieved answer
Merit answer
Excellence answer
States the type of interrelationship.
As for Achieved AND
explains benefit.
For example:
The relationship between
the bird species and
the mistletoe species is
mutualism (symbiosis),
as both the bird species
and the mistletoe species
benefit.
For example:
The birds benefit from
opening the mistletoe
flowers by obtaining
nectar, which is a
nutritious food source.
As for Merit AND gives
full account/comparison
of benefit for all three
species.
OR
The flowers benefit from
being opened by the
birds by being pollinated
as the birds carry pollen
from the open flower to
the next flower that they
open.
© te ah o o t e k ur a p o un a m u
For example:
Cross-pollination could
benefit the mistletoe
population by creating
genetic variation in the
mistletoe population/
gene pool and, of course,
it may increase seed
production.
Having access to this
energy-rich nectar may
enable birds to produce
more eggs, resulting in
more offspring surviving.
This in turn could
increase their population
size.
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answer guide
4. orientation responses
4B
Note: all these answers are at Achieved level.
1. A tropism is a growth response made by plants to external stimuli in their abiotic
environment. The direction of the stimulus determines the direction of the growth response.
Tropisms may be positive or negative.
A nasty or nastic response is a non-directional movement of part of a plant in response to an
external environmental stimulus. Nastic responses are made to the intensity of the stimulus
rather than to the direction.
2. a. A young stem grows upwards towards the light.
Tropism: Positive phototropism
Biological advantage: The stem and leaves reach sunlight that is needed for
photosynthesis.
b. Roots grow downwards into the soil.
Tropism: Positive geotropism (or gravitropism)
Biological advantage: The roots anchor the plant in the soil and the roots can find water
and minerals.
c. Roots grow towards water.
Tropism: Positive hydrotropism
Biological advantage: The roots can find water, which is essential for all chemical
processes in the plant.
d. A stem grows away from the Earth’s gravitational pull.
Tropism: Negative geotropism (or gravitropism)
Biological advantage: The stem does not grow into the soil where it will not be able to get
sunlight for photosynthesis.
e. Tendrils (modified leaves) touch a trellis and coil around it.
Tropism: Positive thigmotropism
Biological advantage: The plant can be supported as it grows.
f. A climbing plant twines upwards around a supporting plant’s stem.
Tropism: Positive phototropism
Biological advantage: The plant can be supported as it grows. The plant can grow upwards
to reach the sunlight, for photosynthesis. Flowers can be held up, so that pollinators can
reach them.
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answer guide
g. Roots grow away from a copper pipe in the soil.
Tropism: Negative chemotropism
Biological advantage: The roots avoid a potentially toxic substance that may harm the
plant’s growth.
h. A pollen tube grows from a pollen grain towards the chemicals given off by the flower’s
ovary.
Tropism: Positive chemotropism
Biological advantage: The pollen tube will grow towards the ovule in the ovary and the
plant will be pollinated so that seeds can form to produce new plants.
3. Response: The leaves of Oxalis species drooping at night is a photonastic response.
How it occurs: This response is brought about by changes in turgor pressure in the cells at
the base of the leaves.
Biological advantage: The drooping of leaves reduces heat and water loss during the
night and reduces the amount of moonlight on the leaves (so that the plant does not
photosynthesise at night).
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answer guide
5. control of plant growth
5C
1.
58
Achieved answer
Merit answer
Excellence answer
Describes how stomata
open and close.
As for Achieved AND
explains role of stomata.
For example:
The paired guard cells
on either side of the
stomata open and close
the stomata by changes
in their turgor (water)
pressure.
For example:
The stomata control
gases and water vapour
entering and exiting the
plant. The plant has to
balance the amount of
carbon dioxide coming
into the plant for
photosynthesis, and the
amount of water vapour
escaping through the
open stomatal pores by
transpiration.
As for Merit AND detailed
answer given including
role of water in life of
plant.
BY3031
For example:
By producing abscisic
acid the plant is
responding to the
environmental stimulus of
lack of water. The abscisic
acid promotes the
closing of the stomata,
which prevents water
vapour from leaving the
plant by transpiration,
thereby regulating water
loss and conserving the
water available to the
plant. Plants need water
for all their metabolic
processes.
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answer guide
2.
Achieved answer
Merit answer
Excellence answer
Defines geotropic
(gravitropic).
As for Achieved AND
states the effect of auxin
on shoot/root.
As for Merit AND full
answer given, explaining
the effect of auxin on
shoot AND root.
For example:
The geotropic responses
of both shoots and
roots are due to the
presence of auxin. Shoots
grow towards light and
away from the force of
gravity, so shoots are
positively phototropic
and negatively geotropic.
Roots grow towards
gravity, so they are
positively geotropic.
© te ah o o t e k ur a p o un a m u
For example:
When a developing shoot
is placed horizontally,
auxin moves to the lower
side of both the shoot
and the roots. The growth
rate of the cells on the
upper and lower parts of
both the shoot and root
differ in response to the
presence of auxin.
For example:
In the shoots auxin
causes elongation of
the cells on the lower
surface, which causes the
shoots to grow upwards.
Root elongation on the
other hand is inhibited
by high levels of auxin on
the lower side of the root.
The cells that elongate
the most are therefore
found on the upper
surface of the root, so the
root grows downwards.
These tropic responses
are essential for the
seedling’s survival as they
ensure the shoots grow
upwards towards the
light, which is needed for
photosynthesis, and the
roots grow downwards to
anchor the plant in the
soil and absorb water
and nutrients needed for
plant growth.
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answer guide
6. timing responses
Achieved answer
6C
Merit answer
1. Circadian means daily/about a day.
2. It has shifted the rhythm by 12 hours/
half a cycle.
As for Achieved AND links this shift to CO2
production. For example:
•• Because of the one-off treatment of
four hours of light around midnight, the
peak of CO2 production shifts to being
at midnight for at least the next three
days, instead of being at midday.
3. Gives one difference.
For example:
•• The direction of the phase shift in one
direction is opposite to the direction of
the phase shift in the other.
•• While the rhythm peak reduces with
time in Fig 6.3 this peak remains the
same for Fig 6.2.
•• While the period (time between two
peaks) is increasing in Fig 6.3, this
period remains the same in Fig 6.2.
4. The rhythm is endogenous because it is
maintained in the absence of external
cues/under constant environmental
conditions.
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As for Achieved AND gives evidence of
rhythm being endogenous. For example:
•• Both figures maintain a cyclic pattern
of CO2 production with highs and lows
appearing even when there is no change
to the environmental conditions/
treatment.
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answer guide
6D
1. Photoperiodism (not photoperiod)
•• ensures flowering at a time when pollinators are available
•• flowers in suitable environmental conditions for seed production or germination
•• time of flowering coordinated for plants of the same species to ensure pollination.
•• leaf fall
•• bud dormancy
•• bulb and tuber formation
•• chlorophyll synthesis
•• dormancy
•• vernalisation
•• germination
2. a. Long-day plant.
b. When the length of the night exceeds a certain period.
c.
Achieved answer
Merit answer
Correct answer given.
As for Achieved AND states number of
hours for critical day length.
For example:
Cocklebur, being a short-day plant, will
flower:
•• when the night length that triggers
flowering is more than or equal to 12
hours
For example:
Cocklebur has a critical day length (CDL)
of 12 hours or less.
•• when day and night length are equal
•• nights are getting longer.
d.
Achieved answer
Merit answer
Correct answer given.
As for Achieved AND gives explanation.
The poinsettia:
For example:
Because length of darkness, not length
of day, triggers flowering.
•• will flower
•• nothing will change
•• no effect on flowering.
© te ah o o t e k ur a p o un a m u
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glossary
abscission
Leaf fall from deciduous trees in autumn.
abiotic environment
The non-living environment; the non-living influences on an organism.
acclimatisation
The ability of an organism to adjust its tolerance limits or optimum
range to slow changes in the environment.
adaptation
An inherited characteristic that enables an organism to survive and
reproduce in its habitat. Adaptions may be structural, behavioural or
physiological.
allelopathy
The production of toxic chemicals in the roots and leaves of a plant that
prohibit the growth of other plants.
auxin
A plant hormone that affects growth and development.
biotic environment
The living environment; the influences of living organisms on one
another.
circadian
An event repeating itself about every 24 hours.
diurnal
Daily or circadian rhythm.
dormancy
A resting phase in an organism when metabolic rate falls to a low level.
ecological niche
A description of how the organism feeds, opportunities provided by the
habitat and the adaptative features of the organism that allow it to take
advantage of these opportunities.
ecosystem
A community of living organisms (biotic environment) together with
non-living factors (abiotic environment), and the nutrient cycles and
energy flows that connect all.
endogenous
A factor or stimulus that originates within an organism.
exogenous
A factor or stimulus that originates outside an organism.
habitat
The place where an organism lives.
long-day plants
Plants which flower in response to a day length longer than a critical
period.
nastic response
A non-directional movement of part of a plant in response to an external
environmental stimulus.
periodicity
Regularly changing behaviour.
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glossary
photoperiod
The relative amount of light and darkness in a 24-hour period.
photoperiodism
A changing pattern or response based on length of light available.
phytochrome
A protein pigment in plants sensitive to red and infrared light.
plant hormone
A chemical that is produced in one part of the plant and has effects in
another part.
short-day plants
Plants that flower in response to a day length shorter than a critical
period.
stimulus
A change in the environment that causes a response in an organism.
symbiotic (mutualistic) association
An association between two organisms for their mutual benefit.
tolerance
An organism’s ability to survive variation in its environmental
conditions.
tropism
A growth response made by plants to external stimuli in their abiotic
environment.
vernalisation
The exposure of a plant to a period of low temperature to promote later
growth and flowering.
© te ah o o t e k ur a p o un a m u
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acknowledgements
Every effort has been made to acknowledge and contact copyright holders. Te Aho o Te Kura Pounamu apologies for any omissions
and welcomes more accurate information.
Photos
Cover: Korukoru, Scarlet mistletoe in flower (Peraxilla [Elytranthe] colenso) on beech tree, # 11441FP13 © Rob Suisted
© naturespic.co.nz.
Sunset friends, # 17889609 © Alex Koch © istockphoto.com.
Calico kitten playing with a toy, # 13048177 © Erik Zunec © istockphoto.com.
Kalahari meerkats, # 16440743 © Peter Malsbury © istockphoto.com.
Cape cobra, # 1694906 © Nico Smit © istockphoto.com.
New Zealand falcon, #39587CE00 © Rob Suisted/www.naturespic.com, Wellington, NZ. Used by permission.
Tree tops, © Don Laing, Wellington, NZ: Te Aho o Te Kura Pounamu. Used by permission.
Gorse, Close up of gorse flower 1, © Don Laing, Wellington, NZ: Te Aho o Te Kura Pounamu. Used by permission.
Walnut, Ready to fall, # 14430606 © Barry Sutton © istockphoto.com.
Flowering Northern rātā trees in forest canopy (Metrosideros robusta), Kahurangi National Park, West Coast, NZ, # 6548FG@01
© Rob Suisted © naturespic.co.nz.
Hemiparasitic red mistletoe (Peraxilla [Elytranthe] tetrapetala), NZ native bush on silver beech tree (Nothofagus menziesii) Arthur’s
Pass National Park, NZ, # 5277FP06 © Rob Suisted © naturespic.co.nz.
Feijoa flower, # 4956437 © Alan Drummond © istockphoto.com.
Marigolds, # 16448303 © Waseef © istockphoto.com (used twice).
Plant root showing nodules; Lichen, by Veronica Armstrong, © Te Aho o Te Kura Pounamu. Used by permission
Lichens growing on a tree, © Don Laing, Wellington, NZ: Te Aho o Te Kura Pounamu. Used by permission.
Perching lilies, photo by Phil Bendle, retrieved from http://www.terrain.net.nz/friends-of-te-henui-group/new-plant-page/perchinglily.html, © 2008–2012 T.E.R:R.A.I.N. Used in any medium for education and its promotion by permission.
Coprosma rhamnoides, by Rudolph89, Wikimedia Commons, retrieved from http://commons.wikimedia.org/wiki/File:Coprosma_
rhamnoides_11.JPG, 9 November 2012. Creative Commons CC0 1.0 Universal public domain dedication.
Chryanthemum, # 19377214 © Ivan Vasilev © istockphoto.com (used twice).
Chryanthemum leaves, # 17115637 © Thomas Acop © istockphoto.com.
Green caterpillar, # 13980701 © Alasdair Thomson © istockphoto.com.
Willow at riverside, # 12454245 © Jose Ignacio Soto © istockphoto.com (used twice).
Venus fly trap, # 7122250 © Mark Goddard © istockphoto.com.
Sketch of Drakaea elastica (Hammer Orchid) from John Lindley’s A Sketch of the Vegetarian of the Swan River Colony, http://
commons.wikimedia.org/wiki/File:A_Sketch_of_the Vegetation_ofthe_Swan_River_Colony_–_Figure_3.png, accessed September
2012.
Matagouri, Discaria toumatou, close up of flowers and spikes, © Chris Rance © DOC.
Herb – Oenothera biennis, # 15609495 © Davidenko Andrey © istockphoto.com.
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acknowledgements
Graphs
Circadian rhythm of Bryophyllum in 1) darkness compared to light; 2) light compared to heat, source not given; from University
Entrance, Bursaries and Scholarships Examination: Biology: 1998, © New Zealand Qualifications Authority 1998, Wellington, NZ.
Extract only.
Table
Flowering in short-day and long-day plants; sources not given, from University Entrance, Bursaries and Scholarships Examination:
Biology: 1998, © New Zealand Qualifications Authority 1998, Wellington, NZ. Extract only.
Illustration
All illustrations and diagrams copyright © Te Aho o Te Kura Pounamu, Wellington, NZ.
BY3031A
Photos
Muehlenbeckia complexa climbing a tree; Muehlenbeckia complexa hugging the ground, © Claire Neiman, Wellington, NZ:
Te Aho o Te Kura Pounamu. Used by permission.
Wire vine (Muehlenbeckia complexa), in flower, Tiritiri Matangi Island, Wikimedia Commons, http://en.wikipedia.org/wiki/
File: Muehlenbeckia_complexia_in_flower_T2i_IMG_104_1452.jpg, accessed October 2012. Public domain.
Cross section of a fig, by Rainer Zenz, Wikimedia Commons, http://en.wikipedia.org/wiki/File:Feige-Schnitt.jpg, accessed September
2012. Public domain.
© te ah o o t e k ur a p o un a m u
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65
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