Calderglen High School National 5 Biology Life on Earth … · Life on Earth National 5 Course...

Life on Earth National 5 Course Notes

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Calderglen High School

National 5 Biology

Life on Earth Unit


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Life on Earth

Subtopic 1: Ecosystems

A species are a group of organisms that can interbreed and produce fertile

offspring.

Biodiversity is a term used to describe the different species of organisms in an

ecosystem. It also includes variation between the same species e.g. rabbits

with black coats and rabbits with grey coats.

Ecosystems with high biodiversity (a lot of different species) are healthier than

ecosystems with low biodiversity (few different species) and therefore more

likely to survive.

Producer: - a green plant that makes its own energy by photosynthesis using energy from the sun.

Consumer: - an animal that eats the plants or other animals.

We can form a food chain which shows these relationships.

e.g. grass rabbit fox . (producer) (primary consumer) (secondary consumer)

The arrows in the food chain show the direction of energy flow.

Further definitions

Herbivore: - animal that eats green plants e.g. the rabbit in the above food chain

Carnivore: - animal that eats other animals e.g. the fox in the above food chain.

Omnivore: - animal that eats green plants and other animals e.g. bear.

Food chains rarely exist in isolation e.g. in the above food chain the grass may also be eaten by deer and rabbits may also be eaten by hawks. A series of interconnecting food chains make up a food web.


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An ecosystem consists of all the organisms (the community) living in a

particular habitat and the non-living components with which the organisms

interact. e.g. a wood or a pond.

A habitat is the place an organism lives and the community is made up of all

the organisms in the ecosystem.

A niche is the role an organism plays within an ecosystem. This relates to the

resources it requires in its ecosystem, such as light and nutrient availability and

its interactions with other organisms in the community. It involves competition

and predation and conditions it can tolerate e.g. temperature. For example a

rabbit would have predators like foxes, hawks and weasels and would feed on

grass and small plants. The rabbit would also be host to many diseases and

carcasses could provide food for flies and crows.

Predation

A predator kills and eats its prey.

In cases of extreme predation the prey can be wiped out but more often

a decrease in prey is followed by a decrease in predators. The prey will

then increase again followed by the predators etc.

A food web


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The predators are actually beneficial to the prey because without them they

would exhaust the food supply.

Competition

Competition in an ecosystem occurs when resources are in short supply.

Examples of resources include water, light and nutrient availability.

Competition can be divided into interspecific (different species) and

intraspecific (same species).

Interspecific (different species)

Occurs amongst individuals of different species for one or a few of the

resources they require.

Red squirrel and grey squirrel.

Grey squirrels are stronger and more aggressive in pursuit of food so in areas

where both types are present the red squirrels have been eliminated.

Red squirrels still survive in coniferous woodland because they can survive on a

diet of pine seeds alone whereas grey squirrels cannot.

Image BBC Bitesize

http://www.scran.ac.uk/database/image.php?usi=000-000-617-728-R&cusi=000-000-617-728-C&searchdb=scran&






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Intraspecific competition (same species)

This occurs between members of the same species and is for all the resources

they require. It is therefore more intense than interspecific competition.

Images scran

Grey squirrel

Red squirrel


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Subtopic 2: Distribution of Organisms

Biotic :- living factors e.g. disease, predation, food availability, grazing and

competition.

Abiotic :- non-living factors e.g. light intensity, temperature, mositure, pH.

Both the above effect the biodiversity and distribution of organisms.

Measurement of Biotic Factors

Sampling techniques are designed to quantify the numbers of an organism in a

habitat without having to count every individual. It is important enough

samples are taken to make the results more reliable and that they are taken in

a random manor i.e. if quantifying the daises on a lawn it would not be

appropriate to sample only the areas where daisies were clumped.

Quadrats

This device can be used to estimate numbers of plants or very slow moving

animals. The quadrat could be used to estimate the daisies in a field. The

quadrat is divided into squares. it is placed in several random locations and

each square containing daisies counted. An average is taken and used to

estimate the total number of daisies in the field. N.B. quadrats must be placed

randomly.

Transect lines

This involves placing quadrats at equal distances along a line e.g. to see the

effect of increasing light intensity as the line emerges from woodland.

Pitfall Traps

These are used to estimate numbers of small invertebrates in a habitat such as

leaf litter in woodland.


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The trap must be covered to prevent predators such as birds eating the

contents and to prevent excess rainwater.

The trap must be level with the ground to allow animals to fall in.

The trap must be checked regularly to prevent carnivorous trapped

animals eating other animals.

The trap should have pinholes in the base to allow water to escape.

Sufficient traps should be set to give a more reliable result.

Measuring Abiotic factors

Temperature

This is measured in degrees Celsius (oC ) using a thermometer. There are

several types including soil thermometers that have a probe to stick into the

soil.

Which ever type you are using you must ensure

you do not hold the detecting part

allow the instrument to stabilise before taking a reading.

Take enough readings of the area to obtain a more reliable result.

Light

Measured in lux using a light meter.

The detector should face the light source

Avoid shading the detector


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Take enough samples to give a more reliable result

This is a measure of acidity or alkalinity. The range is 0-14 with pH 7 being

neutral. Acids become stronger as they move away from 7 towards 0 and

alkalis become stronger as they move away from 7 towards 14.

Soil Moisture

This has a probe to measure moisture levels in the soil.

With this meter and the pH meter it is important to

clean the probe between each use to remove any

moisture from the previous reading.

Paired-statement keys

These can be used to identify organisms.

Statement

1. Does the animal have four legs Yes – go to statement 2

No – go to statement 4

2. Does the animal have a curly tail? Yes – pig

No – go to statement 3

3. Does the animal have a hoof divided into two parts? Yes – cow

No - horse

4. Does the animal have webbed feet? Yes – duck

No - human

BBC Bitesize


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.The effect of abiotic factors on biodiversity

pH

Most aquatic environments have a pH range between 6-8. Acidification due to

pollution e.g. pollution from factories causing acid rain.

Temperature

The north sea temperature is rising due to climate change forcing cold water

species such as sardines and anchovies to move further north. At the same

time warm water species like red mullet are beginning to inhabit the north sea.

Indicator Species

An Indicator species is a species that can show the

levels of pollution of an environment by being

absent or in some cases present.

For example, the Stonefly nymph shown in the diagram is only found in water which does not have any sewage pollution.

Lichens are found on the bark of trees and indicate the levels of air pollution (particularly sulphur dioxide). Crusty lichen is found at all levels of pollution, whereas lung Lichen is only found in unpolluted air.

Stonefly Nymph

imageBBC Bitesize


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Subtopic 3: Photosynthesis

Photosynthesis

Photosynthesis is the process in green plants involving the manufacture of glucose

sugar from Carbon dioxide gas and water, producing Oxygen gas as a by-product.

Leaves contain a special pigment known as CHLOROPHYLL that allows plants to capture

the energy of light to drive the process.

The sugar can be used by the plant cells themselves during respiration, stored in the

leaves as starch or built up into cellulose, a chemical that makes up cell walls.

Summary:

Carbon dioxide + Water Glucose + Oxygen

The process of photosynthesis takes place in the chloroplast and occurs in two stages:

the light reaction and the carbon fixation stage.

Stage 1 – The light reactions

The light energy from the sun is trapped by chlorophyll in the chloroplasts and is

converted into chemical energy in the form of ATP. Water is split to produce hydrogen

and oxygen. The oxygen diffuses from the cell.

Light energy

Chlorophyll

Sunlight energy is absorbed by the

chlorophyll inside the chloroplast.

Light energy is used

to split water (H2O)

Oxygen

diffuses out of

the leaf

Energy is used to join

ADP + Pi

This forms

ATP

Hydrogen

is formed


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Stage 2 – Carbon Fixation

Hydrogen and ATP produced by the light reaction is used with carbon dioxide to

produce glucose in an enzyme controlled process.

Factors affecting Photosynthesis

We might expect an increase in the following to have an increase in the rate of

photosynthesis:

Concentration (availability) of Carbon dioxide

Light intensity

Temperature

Aquatic plants such as elodea can be used to investigate these hypotheses either by

observing the rate of production of oxygen bubbles or by using colour changes in

bicarbonate indicator solution as measures of the rate of photosynthesis:

hydrogen

Carbon dioxide

ATP

Glucose

The glucose can be used for

respiration or converted into starch

or cellulose.

Carbon

fixation

stage


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Limiting Factors Graph

The graph below shows the effect of increasing carbon dioxide concentration on the

rate of photosynthesis at different light intensities and temperatures.

The limiting factor at A, B and C on the graph above

Area of graph

being limited

Limiting factor Explanation

A Carbon dioxide

concentration.

As the concentration of carbon dioxide

increases to 1% the rate of photosynthesis

increases.

B Light intensity By comparing points B and C on the graph-

the only difference between these to

points is light intensity. Point B has a lower

light intensity therefore the rate of

photosynthesis is lower.

C temperature By comparing points C and D on the graph-

the only difference between these to

points is temperature. Point C has a lower

temperature therefore the rate of

photosynthesis is lower.

Apparatus to investigate the rate of Photosynthesis by production of Oxygen:

0.5

0.4

0.3

0.2

0.1

Rat

e of

phot

osyn

thes

is

(cm

3 C

O2 u

sed p

er m

inut

e)

0.5 1.0 1.5 2.0 2.5

Carbon dioxide concentration (%)

B

A

Light intensity 20 kilolux

Temperature 16oC


Temperature 10oC


Temperature 10oC

C

D


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Action Adjusted variable

Move the lamp closer to the plant The light intensity increases

Substitute warmer water Temperature increases

Add Sodium bicarbonate Increases the concentration of dissolved

Carbon dioxide

The rich biodiversity of the rain forests is depleted by this human activity and when deforestation occurs on hillsides this can cause landslip which causes the loss of vegetation and increases the chance of flooding.

Aquatic plant

Oxygen


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Subtopic 4: Energy in Ecosystems

In transfer of energy from 1 level of a food chain to the next. The majority of the energy is lost as heat, movement or undigested material. Only a very small quantity is used for growth and can then be passed on to the next level of the food chain.

Pyramids

A pyramid of numbers is used to represent the numbers of different organisms in a food chain. The wider the bar the greater the number of organisms.

Pyramid of numbers

Normally the bars get smaller going up the pyramid (remember energy is lost at each stage). However this is not always the case. For example suppose there is one big producer. Or small secondary consumers (e.g. oak tree, midge)

Image

BBC

BiteSize

Grass

rabbits

fox


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Pyramid of energy

This gives the energy each species produces per metre squared per year (kj/ m2/ year). This is calculated using dry mass and should always give the correct pyramid shape.

Small bird

Caterpillar

Oak tree

Bird of prey

Image BBC Bitesize


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Subtopic5: Food Production

Human Population growth curve

An increasing population requires an increased food yield. This can involve the

use of fertiliser and pesticides. Fertilisers provide chemicals such as nitrates

which increase crop yield. Plants and animals which reduce crop yields can be

reduced by pesticides.

Fertilisers

Nitrates occur naturally in the soil but are removed by growing plants.

Fertilisers can be added to the soil to increase the nitrate content.

The nitrates in the fertiliser dissolves in water ad is absorbed into the plant.

These nitrates are used by the plant to produce amino acids which can be

synthesised into plant proteins. Animals can then consume these plants or

other animals to obtain amino acids for protein production.

Image BBC Bitesize


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Problems with fertilisers

Leaching (washing out) of fertiliser into rivers and lochs adds extra unwanted

nitrates to the water. This a source of food for algae which rapidly increase in

population causing an algal bloom. Algal blooms reduce light levels, killing

aquatic plants. Both the dead plants and dead algae are a food source for

bacteria which rapidly increase in number. These bacteria use up oxygen

reducing its availability to other organisms e.g. fish, which will therefore

decrease in numbers.

Pesticides and Bioaccumulation

As pesticides are toxic and a predator will usually eat many pests the quantity

of pesticide in organisms tends to increase as they are passed along the food

Diagram BBC

Bitesize


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chain. This has led to problems with animals at the top of a food chain e.g.

birds of prey have been found to produce soft shelled eggs. DDT was a

chemical used to spray crops in the 1970’s. It was found to have such harmful

effects that it is now banned in many countries although not all.

Alternatives to pesticides and fertilisers

Biological Control

Biological control is the use of one species to control numbers of another.

Myxomatosis

Used in 1950’s to control rabbit population (95% of Britain’s rabbits killed in

1955) this virus is still present in rabbit populations today.

Ladybirds

These can be bread in large numbers to feed on aphids which are a plant pest.

Genetically Modified (GM) crops

E.g. a gene that enables plants to be unaffected by a higher pesticide levels

could be inserted to the plant by genetic engineering. The plant could then be

sprayed with higher levels of pesticide eliminating the pests while growing

normally itself.

Image BBC bitesize

Combined pH,

moisture meter


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Subtopic 6: Evolution of the Species

A mutation is a random change to genetic material.

Mutations may be disadvantageous, neutral or advantageous to

survival.

Mutations are spontaneous and are the only source of new alleles.

However, certain environmental factors increase the rate of mutations.

These include radiation and some chemicals e.g. mustard gas.

Disadvantageous

These mutations give rise to proteins that may not function normally.

e.g. haemophilia is a blood clotting disorder 33% of cases are caused by

spontaneous mutation other cases are inherited.

Neutral

These have neither an advantage or disadvantage to survival e.g. some

different DNA sequences code for the same amino acid if one is altered

other sequences can code for the same amino acid.

Advantageous

These mutations are rare but individuals who inherit them are more

likely to increase in numbers because they have an advantage over other

individuals to survival. E.g. a mutation to a protein that helps remove

cholesterol from arteries making it more effective.

New alleles (forms of a gene) produced by a mutation can result in

plants and animals becoming better adapted to their environment.

Variation within a population makes it possible for a population to

evolve over time in response to changing environmental conditions.

Some members of a species will be more suited to survive and

reproduce in the present environment or in a changed environment than

other members of its species.

Examples of adaptations

Kangaroo rat : - this desert mammal has several adaptations making it

suited to a very hot environment.

It produces large volumes of a hormone (ADH) causing

reabsorption of water from the kidneys.

Feeds at night staying in cool burrows during daytime.

Produces very dry faeces.

Has no sweat glands. Reduce water loss


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Bee Orchid: - this plant has adapted to look like a female bee. This

attracts male bees for pollination.

Natural Selection and Speciation

Natural selection is often referred to as survival of the fittest.

In normal conditions a species will produce more offspring than the

environment can support. Variation will be present among the species and

some will be better suited to the environment than others. The best adapted

individuals in a population survive and pass on their favourable genes to their

offspring. E.g. If a rabbit has a gene (that has arisen through mutation) giving it

stronger leg muscles it is more likely to escape predators because it can run

faster than rabbits without the gene.

Speciation occurs after part of a population becomes isolated by an isolation

barrier which can be geographical, ecological or behavioural. E.g. a

geographical barrier could occur to a river changing course and isolating some

of the population.

Mutations occur within each sub-population and natural selection will select

different mutations in each sub-population due to the different selection

pressures that suit their environment. The sub-populations evolve into

genetically different species.

Galapagos Finches

Image BBC Bitesize

Charles Darwin’s drawings

of the different beaks

shapes found on finches in

the Galapagos islands

Beak for seed and nut

eating

Beak for insect

eating


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Finches from the South American mainland colonised these islands. Natural

selection enabled finches with different variations to occupy separate

ecological niches. Beak shape is related to diet. This had not been possible on

the mainland as other species already occupied these niches.

Arctic Char

These are related to salmon and would have naturally migrated out to sea as

young fish. During the ice age populations of these fish were trapped in some

of Scotland’s freshwater lochs where they have evolved into a true freshwater

species.

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