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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 it’s 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

Grasslan

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.

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 an scale which is easy to read in order to get a result.

Abiotic factor Measurement instrument

soil pH pH meter

light intensity Light meter

temperature Thermometer

moisture level moisture meter

oxygen concentration oxygen meter

TYPE OF FACTOR

ABIOTIC (non-living) BIOTIC (living)

temperature

humidity/moisture

light intensity

pH of soil / water

salinity

food

predation

disease

competition

grazing

soil pH meter

digital thermometer

light and moisture meter

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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 randomely

o miltiple samples should be taken

Example

Counting daises in field

10 metres

10 metres

1

3

5

2

4

6

Results

Quadrat Number of daisy plants (per m2)

1 6

2 3

3 12

4 8

5 6

Average 7

So in this field there is estimated to be a total of 700 daises:

7 100 (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.

To improve the reliability of the results, the traps should be placed

randomely. 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.

Population of daises = Average number Total number of

of daises per m2 m2

X

Stones

Alcohol

Cover

Pitfall 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 Limitations Possible errors Ways to minimise errors

Quadrat

sampling

Usually only suitable for

low-growing, rooted

plants.

Number of samples

possible limits

reliability.

Quadrats may not be

placed randomely.

Too few quadrats

used.

Place quadrats randomely.

Use many quadrats.

Pitfall trap

sampling

Usually only suitable for

small surface-crawling

invertebrates.

Number of traps set

limits reliability.

Traps may not be

placed randomely.

Too few traps used.

Birds may eat trapped

invertebrates.

Some invertebrates

may eat others.

Place traps randomely

Set up mny 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.

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.

LETTUCE CATERPILLAR SMALL BIRD FOX

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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.

Predator and Prey General

An example of a food chain from the above food web is:

Lettuce _________ _________ fox/ hawk

Many options

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

A FOOD WEB fox hawk

weasel sparrow

slug rabbit caterpillar

lettuce

lettuce

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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: Since the mice feed on ladybirds, there would be more

ladybirds left to eat the greenfly.

Stoats: Decrease

Reason: Less mice for stoats to eat, so some of the stoats

would starve and die.

OR

Increase Reason: 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*

stoat

weasel

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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 When a parasite

is part of the food chain.

So the number of organisms doesn’t always decrease from the bottom to the top of the pyramid.

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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.

2. Pyramid of biomass

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.

1 Rabbit

2 Fox

Time (months)

Number

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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

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: the conversion of dead plant or animal protein (and animal (1) waste e.g. faces and urea) to ammonium by

bacteria and fungi (the “decomposers”)

Nitrification: the conversion of ammonia to ammonium, then

(2 and 3) nitrites to nitrates by nitrifying bacteria.

Denitrification: the conversion of nitrates to nitrogen

(4) gas by denitrifying bacteria.

Lightning: converts nitrogen gas to nitrates.

(5)

Nitorgen fixation: free-living soil bacteria absorb nitrogen gas and “fix”

(6) it into nitrate. Other bacteria live inside swellings on

the roots (called root nodules of some

plants) and do the same thing.

nitrates

nitrites ammonium

Dead plant and

animal protein

nitrogen

2

4

3

5

1

6

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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.

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).

nodules

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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

The horse and donkey are fertile, but the mule will be infertile.

+

=

horse donkey mule

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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 randomely, 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 harmfull_ 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), UVlight (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. light moth

2. dark moth (the mutant)

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.

Tree trunk in non- polluted environment

Tree trunk in polluted environment

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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.

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.

ostrich rhea kiwi

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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.

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!!!!

Increasing

toxicity

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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.

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

Crusty lichen

Hairy lichen Leafy lichen

can tolerate high levels of sulphur

dioxide

can tolerate moderate levels

of sulphur dioxide

cannot tolerate sulphur dioxide at

all