Download NATIONAL 5 BIOLOGY Life on Earth

NATIONAL 5 BIOLOGY
Life on Earth
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Biodiversity and the distribution of life
The study of living things in their environment is called ecology. Living things
are found living almost everywhere – land, water, air and even inside us! The
place where an organism lives is called its habitat. Examples of habitats
include ponds, forests, rivers, deserts and the sea etc.
All the plants and animals that live in a habitat is called the community.
Together a habitat and its community, make up an ecosystem.
The total variety of all living things on Earth is described as biodiversity_.
Summary
Word
Meaning
Habitat
the place where an organism lives.
Population
a group of organisms which belong to the same species
Ecosystem
habitat and community
Community
all the plants and animals which live in the same habitat
Biodiversity
all of the different plants on animals living on Earth
Niche
the role an organism plays within a community
Remember, an ecosystem consists of all the organisms living in a particular
environment and the non-living components with which the organisms interact.
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What are biomes?
A biome is an environment containing plant (flora) and animal (fauna) species
that live in a specific geographic region. Biomes can be on land or sea. The
nature of a biome is determined primarily by its distinctive climate, including a
region's annual average temperature and amount of rainfall.
Below is a list of some of the major types of biome:

Forest

Desert

Grassland

Tundra

Alpine
Unfortunately human activities have drastically altered biomes.
What is a Niche?
Every organism has its own niche. A niche is the role that an organism plays
within a community. This includes the use it makes of the resources in it’s
ecosystem, including light, temperature and nutrient availability and of course
how it interacts with the other organisms in the community. These interactions
might include competition, parasitism and predation.
Biotic and abiotic factors
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Biotic and Abiotic Factors
Both biotic and abiotic factors can affect the biodiversity in an ecosystem.
Biotic factors are related directly to living organisms whereas abiotic factors
are without life. The table below gives some examples of each.
TYPE OF FACTOR
ABIOTIC (non-living)
BIOTIC (living)
temperature
humidity/moisture
light intensity
pH of soil / water
salinity
food
predation
disease
competition
grazing
Competition could be for food, shelter, space or mates.
Measuring abiotic factors
Abiotic factors are often related to climate and they affect the distribution of
organisms in an ecosystem. An organism is only able to survive in a certain
habitat and play its part in an ecosystem if a combination of these factors
suited to its needs are present there.
There is a range of modern instruments that can be used to measure abiotic
factors. Most have some sort of probe that can be in contact with the
environment and a scale which is easy to read in order to get a result.
Abiotic factor
Measurement instrument
pH meter
Light meter
Thermometer
moisture meter
oxygen meter
soil pH
light intensity
temperature
moisture level
oxygen concentration
soil pH
meter
digital
thermometer
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light and
moisture meter
Sampling Organisms in an Ecosystem
It would be impossible to count all of the plants and animals that live in an
ecosystem. For this reason a sample of the ecosystem is taken. In order to be
representative, an appropriate number of samples need to be taken. This also
helps to improve the reliability of the results.
Sampling Techniques
These techniques are used to:
 find out which plants and animals live in an ecosystem
 find out how common or rare plants and animals are in a given ecosystem
 investigate the reasons why the plant or animal lives there
1.
Quadrats
Quadrats can be used to sample low growing
plants or very slow moving animals. A quadrat is used
to mark off an exact area of the ground so that the
organisms in that area can be identified and counted.
In order to improve the reliability of
the results:
o quadrats should be placed randomly
o multiple samples should be taken
Example
Counting daises in field
10 metres
1
2
3
10 metres
4
5
5
Results
Number of daisy plants (per m2)
6
3
12
8
6
7
Quadrat
1
2
3
4
5
Average
So in this field there is estimated to be a total of 700 daises:
Population of daises
=
Average number
of daises per m2
7
X
Total number of
m2
100 (10X10)
Sampling Using a Pitfall Trap
Pitfall traps can be used to sample small invertebrates living on the soil surface
or in leaf litter ( dead leaves). These small invertebrates fall into the trap and
are unable to climb out again. The diagram below shows a simple pitfall trap
that can be made from an empty yoghurt carton.
Stones
Cover
Pitfall trap
Alcohol
To improve the reliability of the results, the traps should be placed randomly.
They should be checked regularly since birds might eat trapped invertebrates.
Also some of the invertebrates might eat other invertebrates that have fallen
into the trap.
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Possible limitations and sources of error
Using either a quadrat or a pitfall trap have their limitations and errors can
sometimes be made as summarised in the table below.
Technique
Quadrat
sampling
Pitfall trap
sampling
Limitations
Usually only suitable for
low-growing, rooted
plants.
Number of samples
possible limits
reliability.
Usually only suitable for
small surface-crawling
invertebrates.
Number of traps set
limits reliability.
Possible errors
Quadrats may not be
placed randomly.
Ways to minimise errors
Place quadrats randomly.
Too few quadrats
used.
Use many quadrats.
Traps may not be
placed randomly.
Place traps randomly
Too few traps used.
Birds may eat trapped
invertebrates.
Some invertebrates
may eat others.
Set up many traps.
Check traps regularly or
disguise the opening with a lid
supported on stones.
Check traps regularly or put
a preserving liquid e.g. alcohol
in the trap.
Human Influences on the Environment
Human activities can also have an impact on biodiversity. These include:
Pollution:
When fossil fuels such as coal and gas are
burned, carbon dioxide gas is released
into the air which damages many plants and animals.
Habitat destruction:
When forests are cleared, many animals lose their
habitat and/or food source. Many plants and
animals species are lost forever.
Overexploitation:
Some animals have been hunted and killed to such an
extent that they are now in danger of becoming
extinct.
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Energy in Ecosystems
Producers and Consumers
The source of energy for all living things is the sun. Only green plants can use
the light energy from the sun and change it into chemical energy (in glucose)
during the process of photosynthesis
The energy in the plants can then be passed on to animals when they eat the
plants as shown in the diagram below.
LETTUCE
CATERPILLAR
SMALL BIRD
FOX
This type of diagram is called a food chain, and the arrows represent the
direction of the flow of energy
In the above food chain:
1.
The green plant is the producer. (only green plants can be producers).
2.
The rabbit and the fox are both consumers.
Around 90% of the energy is lost between one level and the next. The main
ways in which energy can be lost from a food chain is:

movement

heat

undigested material (e.g. skin and hair)
This means that only 10% of the energy from one level is available to the next
level for growth as shown below.
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Food Webs
Rarely do single food chains occur in nature. We usually find many food chains
which are connected as shown below. This is called a food web. Below is an
example of a food web.
A FOOD WEB
fox
hawk
weasel
slug
Predator and Prey
sparrow
rabbit
caterpillar
General
lettuce
lettuce
An example of a food chain from the above food web is:
Lettuce
_________
_________
Many options
fox/ hawk
Ecological terms
Word
Meaning
Species
organisms which can breed and produce fertile young
Population
a group of organisms which belong to the same species
Producer
an organism which can make its own food
Consumer
an organism which can’t make its own food
Herbivore
an animal which only eats plants
Carnivore
an animal which only eats other animals
Omnivore
an animal which eats both plants and animals
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Disrupting a food chain/web
Human activities such as hunting, fishing using chemicals that cause pollution
can all disrupt a food chain or a food web. The diagram below shows part of a
woodland food web.
If all the mice were killed by a disease, what effect would this have on the
populations of greenflies and stoats?
Greenflies: Decrease
Reason:
Stoats:
Decrease
Reason:
Increase
Reason:
Since the mice feed on ladybirds, there would be more
ladybirds left to eat the greenfly.
Less mice for stoats to eat, so some of the stoats
would starve and die.
OR
Less food for weasels so they decrease. Then, there
would be less food for foxes so they decrease, and
so less stoats would be eaten by the foxes.
OR
Stay the same
Reason:
Combination of both the reasons given for increase
and decrease.
*Marks come with reason, not
Direction*
weasel
stoat
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Pyramids of number, biomass and energy
1.
Pyramid of numbers
Consider the following food chain:
leaves
caterpillar
blue tit
hawk
In terms of numbers, the producers (in this example, the leaves), are always
found to be the most numerous. This is then followed by the herbivores and so
on along a food chain, with the final consumer which will be a carnivore being
the least numerous. There are a couple of exceptions which do not produce
true pyramid shape.
Irregular Pyramids
A
When the producer is a tree
B
So the number of organisms
doesn’t always decrease from the
bottom to the top of the pyramid.
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When a parasite
is part of the food chain.
Predator and prey numbers
The number of prey animals is always greater than the number of predator as
illustrated by a pyramid of numbers. The graph below shows the relationship
that exists between predator and prey over a given length of time.
1 Rabbit
2 Fox
Number
2.
Pyramid of biomass
Time (months)
The biomass of a population is the total mass of living matter in
that population. This can be represented in a diagram called a
pyramid of biomass like the example below.
The width of each bar in this pyramid is a quantitative measure, showing how
much biomass there is at each level. In a food chain, the biomass always
decreases from the producer to the final consumer. This is a more reliable way
to compare the organisms found at different levels in a food chain since it is
based on productivity. As the pyramid on the previous page shows, this is
measured as grams of dry mass per m2 per unit of time (e.g. month / year). It
can then be changed into its energy equivalent in joules (J) or kilojoules (kJ),
and be used to draw up a pyramid of energy.
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3.
Pyramid of energy
Like a pyramid of biomass, a pyramid of energy always produces a true
pyramid like the example given below. The energy at each level of the
food chain is measured in units called Joules (J)
Nitrogen in ecosystems
Proteins (and therefore a mino acids ) contain the element nitrogen. Both
plants and animals need nitrogen to make their own poteins. Despite 80% of
the air being nitrogen, plants and animals cannot make use of this nitrogen gas
directly. Animals need to eat food that provides them with protein (and
therefore nitrogen) in order to be able make their own proteins. (The piece of
cheese or chicken that you ate two weeks ago is now your hair, nails or
muscles!!!!)
Plants don’t eat so they need to get their nitrogen from the soil so that they
too can make their own proteins. Plants manufacture proteins using nitrogen
from compounds present in the soil called nitrates.
The nitrates are absorbed from the soil through the plant’s roots. Plants do not
grow well in soil that is low in nitrates. This is because the nitrates provide the
plants with the elememts that they need to make proteins and proteins are
needed for growth. In nature, nitrogen is recycled via the nitrogen cycle which
is shown on the next page.
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The Nitrogen Cycle
nitrogen
6
5
4
Dead plant and
animal protein
nitrates
3
1
2
ammonium
nitrites
Important processes in the nitrogen cycle
The nitrogen cycle is dependent on the activities of several different types of
bacteria, each playing a key role in the nitrogen cycle.
Decomposition:
(1)
the conversion of dead plant or animal protein (and animal
waste e.g. faces and urea) to ammonium by
bacteria and fungi (the “decomposers”)
the conversion of ammonia to ammonium, then
nitrites to nitrates by nitrifying bacteria.
the conversion of nitrates to nitrogen
gas by denitrifying bacteria.
converts nitrogen gas to nitrates.
Nitrification:
(2 and 3)
Denitrification:
(4)
Lightning:
(5)
Nitorgen fixation:
(6)
free-living soil bacteria absorb nitrogen gas and “fix”
it into nitrate. Other bacteria live inside swellings on
the roots (called root nodules of some
plants) and do the same thing.
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More about Nitrogen Fixation
A special group of plants called legume plants (e.g. peas, beans and cloves ),
are able to absorb nitrogen gas and “fix” it into nitrate. This process is called
nitrogen fixation and it is carried out by nitrogen-fixing bacteria. These
bacteria either live freely in the soil or in swellings on a leguminous plant’s roots
called root nodules as shown in the diagram below.
nodules
Competition in Ecosystems
Whenever two or more members of a community need the same resource, and
that resource is in limited supply, competition occurs between them. For
example green plants may compete with each other for light, water and soil
nutrients (e.g. nitrate); animals may compete with each other for water,
food or territory.
Competition can affect an organism’s chance of survival. There are two
different types of competition:
1.
Interspecific competition.
This type of competition takes place between plants or animals
that belong to a different species. An example of this is the
competition that exists between grey and red squirrels.
Although they are both squirrels they are different species of
squirrel.
2.
Intraspecific_ competition.
This type of competition takes place between plants or animals that belong
to the same species. An example of this is the competition that exists
between two or more robins.
Since members of the same species will compete for exactly the same
resources in an ecosystem, intraspecific competition is much more intense
than interspecific competition. (Members of a different species might
compete for the same food, but compete for different mates or territory).
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Summary
 Interspecific competition is when individuals of a different species
require similar resources in an ecosystem.
 Intraspecific competition is when individuals of the same species
require the same resources in an ecosystem.
What is a species?
Remember if two organisms breed to produce fertile offspring, this means
that they belong to the same species. If they produce infertile offspring, this
means that they do not belong to the same species. For example, a horse and
donkey can still breed, but the offspring that are produced (called mules) can’t
breed as they are sterile
+
horse
=
donkey
The horse and donkey are fertile, but the mule will be infertile.
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mule
Adaptation, natural selection and the evolution of species
Mutations
A mutation is said to occur when an organism’s genetic material has been
altered. They can affect single genes or whole chromosomes. These changes
occur spontaneously (they just happen) and randomly, but mutations are rare.
If a change in an organism’s genotype produces a change in their phenotype,
the organism is called a mutant.
Mutations can be neutral and have little or no effect on an organism. Mutations
can be harmful_ and this gives the organism a disadvantage and so this will
decrease its chance of survival. Mutations might be useful as they might give
the organism an advantage and so this will increase its chance of survival.
Without mutations, organisms would never change – in other words evolution
would not occur. This is because mutations are the only source of new alleles
in a population. Mutations therefore increase variation within members of the
same species. Variation within a population makes it possible for a population to
evolve over time in response to changing environmental conditions.
Mutagenic agents
The rate of mutations can be increased by environmental factors such as
radiation (e.g. X-rays), UV light (from the Sun), and some chemicals e.g.
mustard gas. These are all examples of mutagenic agents.
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Natural Selection
Species produce more offspring than the environment can support due to the
limited resources available. A struggle for survival then takes place as they
compete for these limited resources.
Differences exist between members of a population – this is called variation.
Those organisms which are best suited or adapted to their environment will
survive and reproduce. This means that favourable alleles will be passed on to
their offspring. These favourable alleles might give these organism an
advantage over others of the same species and so increase their chance of
survival. This process is called natural selection or “survival of the fittest”.
The diagram below shows how natural selection might have occurred in giraffes.
1.
Variation exists between members of the
same population. In this example some giraffes have
a longer neck than others.
2.
If there is a shortage of food on the ground (the
selection pressure here), the giraffes will have
to eat the leaves of trees. The giraffes with the
longer necks will be able to reach the leaves at the top
of the tree whilst those with shorter necks won’t.
3.
Due to natural selection (or survival of the fittest),
only those giraffes with the long necks
survive and so they would be able to pass on
the gene that caused this characteristic to the next
generation.
So, natural selection results in the survival of those organisms whose variation
makes them best suited to their environment (which constantly changes).
Some individuals survive, but others don’t – this is why it is called “survival of
the fittest”.
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Natural selection or survival of the fittest occurs when there are selection
pressures. Selection pressures are factors that act on members of a population
and results in the death of some members of the population and the survival
of others. Selection pressures include:

predation

disease

temperature

food availability
Another example of natural selection can be seen in moths. In polluted areas,
tree trunks are covered in soot particles and turn black. In non-polluted areas
the tree trunks remain a silvery-grey colour.
There are two different varieties of the same species of this moth:
1.
2.
light moth
dark moth (the mutant)
Tree trunk in nonpolluted environment
Tree trunk in polluted
environment
The population of light moths would increase in a non-polluted environment,
whilst the population of dark moths in this environment would decrease. This is
because the light moths are well camouflaged and are therefore not as easily
seen by predators. So in this environment, the light moths enjoy a selective
advantage and so more of them survive.
In a polluted environment, the population of dark moths would increase, whilst
the population of light moths in this environment would decrease.
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Speciation
Speciation is the term used to describe the formation of two or more new
species from one original species. This process takes millions of years. The
diagram below shows how all these different species had the same common
ancestor i.e. they all came from one original species .
Another example of speciation is demonstrated by the ostrich, rhea and kiwi.
They have the same common ancestor, but have evolved to become three
different species, but they are quite similar.
ostrich
rhea
kiwi
Speciation occurs after part of a population (sub-population) becomes isolated
(separated from the remainder of the population). An isolating mechanism
might be sea, mountains, ravines etc. They act as barriers to gene exchange as
they prevent sub-populations from interbreeding.
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Mutations then occur in each of the isolated sub-populations. Natural
selection then selects for different mutations in each group. This is due to
different selection pressures. As long as the sub-populations are prevented
from interbreeding, each sub population eventually becomes a different
species, but this takes millions of years. This is because the mutations that
have occurred over this time make them so genetically different that they
would no longer be able to interbreed and produce fertile offspring.
Speciation has occurred.
Speciation in action - Darwin’s Finches
The Galapagos islands are isolated in the Pacific ocean 600 kilometres from the
coast of South America. It is thought that a species of finch-like bird (the
founder species) left the mainland and arrived on these islands hundreds of
thousands of years ago. The birds spread out over these islands and a lack of
competition allowed their populations to increase. Groups became isolated from
each other and this prevented them from interbreeding. Different mutations
occurred within the populations on the different islands and selection pressures
varied between the islands because of habitat differences. Over the years,
they became so genetically different that they no longer belonged to the same
species - so speciation had taken place. Today there are about 13 different
species of finch that inhabit these islands, but they all have a common ancestor
(the “founder species”). The diagram below shows some of these new species of
finch.
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These finch species have many different features, but the most striking
difference is the shape and size of their beak. Having a different shaped
beak meant that they could eat different things - so their beak allowed them
to inhabit a different island and this helped them to survive as it reduced
competition for food.
Human Impact of the Environment
The Human Population
Year on year, the human population is increasing. In 2011, it was estimated to
be 7,021,836,029. Today it is even higher. Tomorrow it will be higher still.
In order to provide enough food to meet the needs of our ever increasing
population, methods to increase food yield are needed. The main way in which
humans guarantee food is via farming, and farmers are always looking for new
ways to increase food production.
Unfortunately, some of the methods that farmers have used to increase food
yield (known as intensive farming) have had a negative effect on biodiversity.
Intensive Farming
Intensive farming usually involves growing a specific crop species e.g. only
growing wheat or only growing barley etc. in huge fields. The main drawback is
that harmful chemicals (fertilisers and pesticides) are used in order to
increase plant growth (and therefore yield).
Fertilisers
Fertilisers are used to add nutrients to the soil, and this helps to improve
plant growth, and therefore helps to increase yield.
Unfortunately fertilisers can cause problems. The main problem is that
fertilisers can be leached into fresh water (e.g. ponds, streams, rivers and
lochs) when it rains heavily. The fertilisers greatly increase the growth of
plants called algae which live in the fresh water, and leads to something called
an algal bloom forming. These algal blooms cause the levels of oxygen in the
water to decrease and many of the animals that live there die as a result.
Algal blooms can therefore affect the biodiversity of a freshwater ecosystem.
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Pesticides
These chemicals are used to deter a variety of different pests that affect
plant growth. They too therefore help to increase yield and so increases the
amount of crops that can be harvested.
Unfortunately, like fertilisers, pesticides can also cause problems. The main
problem with pesticides that are sprayed onto crop plants is that, over time,
they can accumulate in the bodies of organisms. They are passed on from one
organisms to the next via a food chain, and as they are passed along food chains,
toxicity increases and can reach levels that are lethal to many animals especially the ones at the top of a food chain. This is called biomagnification an
example of which is shown in the diagram below.
Increasing
toxicity
DDT is an example of a pesticide that was used to kill the mosquitos that were
responsible for causing malaria. Although it undoubtedly saved many lives it
killed other insects and it accumulated in the food chain. Every molecule of
DDT that was ever used is still somewhere in the world’s ecosystems!!!!
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Biological controls
Instead of using pesticides to kill the pests that affect plant growth, natural
predators of these pests could be used - this is what is meant by biological
control. This works well in enclosed spaces like greenhouses but is more
difficult in open fields.
Ladybirds are used as biological controls as they are the natural predators of
aphids which are pests.
GM crops (Genetically Modified)
Another alternative to using fertilisers and pesticides is to grow crop plants
that have been genetically modified (changed). Plants can be genetically
modified by genetically engineering them. This of course now means that their
genetic information has been changed usually by the addition of a useful gene
from another organism. Common GM foods include tomatoes, rice cabbage and
potato.
These crop plants are genetically modified to:
 increase yield.
 reduce the need to use fertilisers and pesticides.
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Indicator species
An indicator species is a species that by their presence or absence gives us
information about:
 the quality of it’s environment
 levels of pollution in it’s environment.
Animal indicator species
All the water invertebrates shown below are examples of indicator species.
They all give information about the levels of pollution in a river
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So, if the water is very clean (is not polluted), then we would expect group 1
to be present in the river, however, group 3 would be absent as they are only
found in a river that is heavily polluted.
Plant indicator species
Lichen are simple plants. Different species of lichen can tolerate different
levels of a gas called sulphur dioxide (SO2) which is produced when fossil
fuels (e.g. coal, oil and gas) are burned. The presence or absence of such
species indicate the levels of pollution by this gas.
Crusty lichen
can tolerate high
levels of sulphur
dioxide
Leafy lichen
can tolerate
moderate levels
of sulphur dioxide
Hairy lichen
cannot tolerate
sulphur dioxide at
all
So, only crusty lichen would be present in an environment that is highly
polluted with sulphur dioxide. The other two species of lichen (leafy and hairy)
would be absent
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