Download World of Plants Notes

Introducing Plants
The Sun is the source of all energy on Earth. Green plants are the link between man and
the Sun. Without green plants most life on Earth would not exist.
Give examples of advantages of there being a wide variety of plants
There is an enormous range of plants on Earth. This variety has many advantages:
 There is a large range of characteristics for breeding from
 There is a greater choice for use as raw materials
 They provide different sources of food for many animals
 They provide a variety of habitats for many animals
 They maintain the gas balance of the atmosphere
Green plants take in carbon dioxide and produce oxygen
 They make homes, gardens and all ecosystems more beautiful
Describe 3 specialised uses of plants
There are countless ways in which man uses plants.
Here are three:
Food
Raw materials
Medicines
Explain possible consequences to man and other animals of a reduction in the variety of
species
If any species of plant is allowed to die out, the possible consequences are very serious
both for man
and the other living things that share our planet. Here are a few possible consequences:
Many plants represent potential resources (food or raw materials) which may
become essential in the future.
Lots of plants may contain valuable products that have not yet been discovered
 Every plant provides food or shelter for a variety of other organisms, some of
which may only be able to live on that particular species.
 Biologists can transfer useful genetic characteristics from one species to another.
The loss of any species will reduce the gene pool (number of genes in the world).

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Describe a production or refining process, e.g. malting barley, rape seed, raspberries,
timber
Timber production
There are a number of steps involved in the production of timber
 Seeds are sown in nurseries
 After 2-4 years small trees are planted out in rows.
 After 15 years a third of the trees are removed to thin them out. This involves
removing the smaller and poorer trees.
 Thinning continues at 5 year intervals and each thinning is more valuable than the
one before.
 At 40-50 years the forest is finally harvested and the replanting programme is
started over again.
Describe two potential uses of plants or plant products e.g. new medicines, new food
sources
Scientists are always looking to find new uses of plants and plant products.
New Sources of Food
Earth is thought to have 75 000 species o edible plant. At present only about 20
species are used to produce most of the world’s food.
New Sources of Medicines
It is possible that, for example, in the rainforest there may be plants that could be
used to cure disease. However deforestation means that some species may lost forever.
Growing Plants
All living things must reproduce to ensure that they do not become extinct.
In order to reproduce, flowering plants produce seeds.
Describe the functions of the three main parts of the seed of a dicotyledon, i.e. seed
coat, embryo, food store
Structure of a seed
A seed is made up of
an embryo - small undeveloped plant
a food store - food supply until the plant can make its own
a seed coat/testa - tough protective coat
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Describe the effect of temperature and the availability of water and oxygen on
germination
Germination is the development of a plant embryo into an independent plant with green
leaves. During germination the food store present is used to give the young plant energy
for growth. Seeds need certain conditions in order to germinate.
To germinate seeds need: Water, Oxygen, Warmth
Describe the changes in percentage germination that occurs over a range of
temperatures
Almost no seed will germinate at temperatures below 5C.
High temperatures (above 45C) also prevent germination.
Between 5C and 45C, percentage germination increases with increases temperature
until a temperature where germination is at its best. This is called its optimum
temperature.
Germination does not take place at high temperatures as enzymes are denatured.
Describe the functions of the parts of flowers, i.e. sepal, petal, stamen, anther, stigma,
ovary, nectary
Structure
Sepal
Petal
Stamen
Function
Protects the unopened flower bud
Brightly coloured to attract insects
Male part of the flower, contains anther and
filament
Produces male gametes (pollen)
Top of the female part which collects the pollen
Produces female sex cells (ovules)
Produce sugary nectar which attracts insects
Anther
Stigma
Ovary
Nectary
Describe the methods of pollination
Pollination is the transfer of pollen from the anther to the stigma.
self-pollination
Pollen is transferred from the anther of one flower to the stigma of the same flower
or another flower on the same plant
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cross-pollination
Pollen is transferred from the anther of one flower to the stigma of a flower on a
different plant
There are 2 methods of pollination:
 Insect
 Wind
Insect pollination
Pollen is brushed onto the insect’s body when it sucks
nectar from a flower. Pollen is carried by the insect.
When the insect goes to another flower the pollen
grains stick to the stigma.
Wind pollination
Pollen is blown by the wind from the anther hanging
outside of the flower. Pollen is carried by the wind.
Pollen sticks to stigmas hanging outside of the flower.
Explain the structure of wind- and insect-pollinated flowers in relation to sexual
reproduction
You can tell whether a plant is insect- or wind- pollinated by looking at the flowers it
produces
Insect pollinated flowers
Wind pollinated flowers
Large brightly coloured petals
Scent
Nectar
Large, rough pollen grains
Anthers and stigmas inside flower
very small petals
no scent
no nectar
small, smooth pollen grains
anthers and stigmas outside flower
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Describe the growth of the pollen tube and fusion of gametes
When a pollen grain lands on the stigma, it grows a tube down
through the style into the ovary. This allows the male nucleus
to fuse with the nucleus of the female gamete. Fusion of the
2 nuclei is called fertilisation. Fertilisation produces a zygote.
Describe fertilisation and fruit formation
After fertilisation ovules become seeds each contains an embryo, a seed coat and a
food store. The ovary becomes a fruit this is often fleshy and succulent (e.g. plums
etc) but can also be very tough and dry (e.g. nuts)
Describe one example of each of the following different dispersal mechanisms: wind,
animal – internal, animal -external
The seeds and fruits must be carried away (dispersed) from the parent plant so that
there is less competition for:
 Light
 Water
 Nutrients
There are 3 main methods of seed dispersal:
 Wind
 Animal internal
 Animal external
The structure of the seeds and fruits is suited to its method of dispersal.
Wind
Fruits are light and have extensions e.g. parachutes or wings so that they
will have greater air resistance and catch the wind.
The poppy seeds are like pepper pots that are shaken by the wind.
Animal internal
Fruits are usually brightly coloured and juicy to encourage the animal to
eat them. The seeds are indigestible which allows them to pass out of the
animal far away from the parent.
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Animal external
The fruits have hooks that are used to
attach them to the animal’s coat and be
dropped off later.
Describe ways of propagating flowering plants artificially by cuttings and grafting
Man can produce new plants by artificial methods that would not take place naturally.
The most common methods are:
 Cuttings
 Graftings
Cuttings
A piece of stem with some leaves is taken from the
parent plant. It is then placed in a suitable compost to
allow it to form roots.
Grafting
A bud or shoot of a valuable plant is taken and
joined to the developed root stock of a hardy plant.
Explain the advantages to man of artificial propagation in flowering plants
Artificial methods of propagating plants have many advantages to man:
 Large numbers of plants can be generated quickly
 The plants are all identical so desirable qualities can be maintained
 Seedless plants can only be grown by artificial propagation e.g. banana and seedless
grapes
 Rare plants can be saved from extinction
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Describe asexual reproduction by runners and tubers
Some plants can reproduce asexually (without flowers or fertilisation). Asexual
reproduction involves only one parent. Many plants have special structures that allow
them to reproduce sexually.
Runners
Side shoots grow out from the parent plant.
Buds form along the runner. These obtain
food and water from the parent until they
grow their own roots. Eventually they
become detached from the parent. e.g
strawberry, spider plant
runner
Tubers
Underground food store that stores enough food over winter to start the
growth of a new plant. Each new plant can then make its own food and form
several tubers for the next winter. A shoot grows from an eye. Shoot
forms leaves. food made by leaves is sent down to make new tubers. plant
withers but tubers stay in soil until next year e.g. potato, dahlias, crocus.
Describe what is meant by the term “clone”
A clone is a group of cells or organisms that have all been produced asexually from the
same single parent. This means that they are all genetically identical to one another.
Describe the advantages of both sexual and asexual reproduction in plants
Method of
reproduction
sexual
asexual
Advantage
2 parents mean that each plant shows variation from the rest so
species would survive a disaster in the environment e.g. disease
plants well distributed meaning less competition
seeds stay dormant until conditions for growth are good
Plants are all identical so good features will always be passed on
Young plant can outgrow competitors as it receives food and water
from its parent
Only one parent is needed
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Making Food
Explain the need for transport systems in a plant
Plants need transport systems as all parts of the plant need water (taken in through
the roots) and food (made in the green parts of the plant). Plants therefore need
transport systems to move these substances around.
Describe the pathways of movement of water and food in xylem and phloem
Xylem vessels carry water which is absorbed from the soil by the roots and is carried
up to all parts of the plant.
Phloem vessels carried dissolved food (sugars) from the leaves down to all parts of the
plant that cannot make their own food e.g. roots, flower
Describe the structure of phloem and xylem and identify other functions of the
transport system
Xylem and phloem are the two main transport systems. The two sets of tubes are found
together in bundles. The bundles are called vascular bundles. The position of the
vascular bundles in stems and roots is not the same.
Xylem
Xylem vessels are dead
The end walls of the cells have disintegrated to form hollow tubes
The side walls have become impregnated with rings of lignin, which
strengthens the tubes
Phloem
Phloem cells are alive and consist of 2 types of living cells:
sieve and companion cells. The end walls of the sieve cells
have pores. Each tube cell has a companion cell. Companion
cells provide the energy for the sieve cells. Food is
transported through the pores from cell to cell in the form of
dissolved sugar
Other functions of the transport system
Xylem transport minerals
The tough lignified xylem tubes support the plant
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State that plants take in carbon dioxide from the air through stomata which can open
and close
Plants take in carbon dioxide from the air through tiny pores on
the surface of the leaves. These pores are called stomata.
State that water vapour is lost through stomata
Stomata open during the day and close at night
Describe the external features and internal structure (epidermis, mesophylls, veins) of
a leaf in relation to its function in gas exchange
The leaf is the organ that plants use to make food by photosynthesis.
Structure
Epidermis
Palisade mesophyll
cells
Spongy mesophyll
cells
Air spaces
Veins
Stomata
Guard cells
Function and other features
Protection. Also transparent to let light through
Site of most photosynthesis (cells contain many chloroplasts)
Cells are tightly packed to absorb maximum light
Photosynthesis (cells contain some chloroplasts)
Have air spaces between them
Diffusion of gases
Contain xylem and phloem which transport water and food
Allow gas exchange
Control the size of the stomata
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State that green plants make their own food which may be stored as starch
Green plants make food in the form of sugar. This sugar can be used straight away or
converted into the storage carbohydrate, starch.
When a plant is left in the dark it uses up its stored food, this is called destarching.
Describe the fate of carbon dioxide as structural and storage carbohydrates in plants
and as energy sources
The food that plants make is in the form of carbohydrates.
Plants make carbohydrates by combining carbon dioxide from the air with water
The simplest useful form of carbohydrate made is glucose. Glucose can be used as a
source of energy or converted into:
Storage carbohydrates e.g. starch or
Structural carbohydrates e.g. cellulose in the plant cell walls or lignin in xylem.
State that green plants convert light energy to chemical energy using chlorophyll
Chlorophyll captures light from the Sun and converts it into chemical energy which is
used to make glucose
Describe the process of photosynthesis in terms of raw materials and products
Photosynthesis is the process by which green plants use light energy to make food.
Carbon dioxide + water
raw materials
light energy
glucose + oxygen
products

chlorophyll
Explain what is meant by a limiting factor and describe the main limiting factors in the
process of photosynthesis
A limiting factor is a factor that slows down a process because it is in short supply.
Photosynthesis can sometimes be limited because certain factors are in short supply.
Light
Carbon dioxide
Temperature
can all act as limiting factors
We can measure the rate of photosynthesis by counting the number of bubbles coming
from an Elodea plant
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