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GCSE Biology: Year 9Feeding Relationships &

The Environment

4.7.2.1 Levels of organisation

Students should understand that photosynthetic organisms are the producers of biomass for life on Earth.

Feeding relationships within a community can be represented by food chains. All food chainsbegin with a producer which synthesises molecules. This is usually a green plant which makes glucose by photosynthesis.

A range of experimental methods using transects and quadrats are used by ecologists to determine the distribution and abundance of species in an ecosystem.

Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers and then tertiary consumers.

Consumers that eat other animals are predators, and those eaten are prey. In a stable community the numbers of predators and prey rise and fall in cycles.

Required practical 7: Investigate the population size of a common species in a habitat.

4.7.4.1 Trophic levels

Students should be able to describe the differences between the trophic levels of organisms within an ecosystem.

Trophic levels can be represented by numbers, starting at level 1 with plants and algae. Further trophic levels are numbered subsequently according to how far the organism is along the food chain.

Level 1: Plants and algae make their own food and are called producers.

Level 2: Herbivores eat plants/algae and are called primary consumers.

Level 3: Carnivores that eat herbivores are called secondary consumers.

Level 4: Carnivores that eat other carnivores are called tertiary consumers. Apex predators are carnivores with no predators.

Decomposers break down dead plant and animal matter by secreting enzymes into the environment. Small soluble food molecules then diffuse into the microorganism.

4.7.4.2 Pyramids of biomass

Pyramids of biomass can be constructed to represent the relative amount of biomass in each level of a food chain. Trophic level 1 is at the bottom of the pyramid.

4.7.4.3 Transfer of biomass

Students should be able to explain how the loss of biomass at each trophic level affects the number of organisms at each level.

Producers are mostly plants and algae which transfer about 1% of the incident energy from light for photosynthesis

Only approximately 10% of the biomass from each trophic level is transferred to the level above it.Students should be able to calculate the efficiency of biomass transfer between trophic levels.

Losses of biomass are due to:• not all the ingested material is absorbed, some is egested as faeces• some absorbed material is lost as waste, such as carbon dioxide and water in respiration and water and urea in urine.

Large amounts of glucose are used in respiration.

4.7.1.1 Communities

Throughout ‘Adaptations, interdependence and Competition’ students should be able to, when provided with appropriate information:• suggest the factors for which organisms are competing in a given habitat• suggest how organisms are adapted to the conditions in which they live.

An ecosystem is the interaction of a community of living organisms with the non-living (abiotic) parts of their environment.

To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there.

Plants in a community or habitat often compete with each other for light and space, and for water and mineral ions from the soil. Animals often compete with each other for food, mates and territory.

Within a community each species depends on other species for food, shelter, pollination, seed dispersal etc. If one species is removed it can affect the whole community. This is called interdependence.

A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant. Tropical rainforests and ancient oak woodlands are stable communities.

4.7.1.2 Abiotic factors

Students should be able to explain how a change in an abiotic factor would affect a given community given appropriate data or context.

Abiotic (non-living) factors which can affect a community are: light intensity temperature moisture levels soil pH and mineral content wind intensity and direction carbon dioxide levels for plants oxygen levels for aquatic animals.

4.7.1.3 Biotic factors

Students should be able to explain how a change in a biotic factor might affect a given community given appropriate data or context.

Biotic (living) factors which can affect a community are: availability of food new predators arriving new pathogens one species outcompeting another so the numbers are no longer sufficient to breed, such as

the introduction of grey squirrels into southern Britain outcompeted the native red squirrels.

4.7.1.4 Adaptations

Students should be able to explain how organisms are adapted to live in their natural environment, given appropriate information.

Organisms have features (adaptations) that enable them to survive in the conditions in which they normally live. These adaptations may be structural, behavioural or functional.

Some organisms live in environments that are very extreme, such as at high temperature, pressure, or salt concentration. These organisms are called extremophiles. Bacteria living in deep sea vents are extremophiles.

Food Chains

Photosynthetic organisms (p _ _ _ _ _ and a _ _ _ _) are the producers of biomass (living material) for life on Earth.

Feeding relationships within a c _ _ _ _ _ _ _ _ can be represented by food chains. All food chains begin with a producer which synthesises molecules. This is usually a green p _ _ _ _ which makes g _ _ _ _ _ _ _ by p _ _ _ _ _ _ _ _ _ _ _ _ _.

Producers are eaten by p _ _ _ _ _ _ c _ _ _ _ _ _ _ _, which in turn may be eaten by s _ _ _ _ _ _ _ _ consumers and then t _ _ _ _ _ _ _ consumers.

Trophic levels can be represented by numbers, starting at level 1 with plants and algae. Further trophic levels are numbered subsequently according to how far the organism is along the food chain.

Level 1: Plants and algae make their own food and are called producers.

Level 2: Herbivores eat plants/algae and are called primary consumers.

Level 3: Carnivores that eat herbivores are called secondary consumers.

Level 4: Carnivores that eat other carnivores are called tertiary consumers. Apex predators are carnivores with no predators.

Decomposers break down dead plant and animal matter by secreting enzymes into the environment. Small soluble food molecules then diffuse into the microorganism.

Food WebsA food web is made up of many food chains. If one species is removed it can affect the whole community. This is called interdependence.

Write out 3 food chains found in this food web (remember – food chains must start with a producer)

1)

2)

3)

Example GCSE Questions: Food Chain and Webs (6 marks)

Q1) A pupil studied the organisms in a pond. From her observations she drew this simple food web.

perch

sm all fish

w ate r flea s

w ate r boatm en

tad po les

m icroscopic plan ts

(a) Use only the information in the food web to answer the following.

(i) Write down one food chain from this food web. There should be four organisms in the food chain. 1 mark

(ii) Write down the producer in the food web. 1 mark

(b)Disease suddenly kills all the small fish. Complete the sentence to explain what is likely to happen to the number of water boatmen. 2 marks

“The number of water boatmen is likely to _________________because ___________________________

_____________________________________________________________________________________________”

Q2)

Bats are mammals that can fly. In many parts of the world bats live in caves. Many other animals live in the caves and some feed on bat droppings. Bats fly out of the caves at night to catch insects.

fleas

ha rvestm en cave spiders bats

beetles m illipedes spring tails flies m oths

bat dropp ings inthe cave

flow ering p lan tsgrow ing ou ts ide

the cave

The diagram shows part of a food web which includes the organisms living in a cave.

(a) In summer, birds enter the caves and eat large numbers of beetles. Suggest why this might cause the population of millipedes to:

(i) go up; 1 mark

(ii) go down. 1 mark

Predator-Prey Relationships

Consumers that eat other animals are predators, and those eaten are prey. In a stable community the numbers of predators and prey rise and fall in cycles.

What are the features of a predator-prey graph?

Pyramids of BiomassBiomass is the mass of living organisms. A pyramid of biomass is a diagram showing the relative amount of biomass in each level of a food chain. Tropic level 1 is at the bottom of the pyramid. Label each level of the pyramid with as much detail as you are given.

Pyramids of biomass must be drawn with (1) bars equally spaced around the midpoint (2) bars touching (3) bar for the producer at the bottom (4) length of each bar proportional to the amount of biomass available at each trophic level (if you are given this information)

Drawing Pyramids:

Example GCSE Questions: Pyramids of Biomass (7 marks)

2)

3)

Energy Transfer Along the Food Chain

Producers are mostly p _ _ _ _ _ and a _ _ _ _ which transfer about 1% of the energy from l _ _ _ _ for photosynthesis

Only approximately ________% of the biomass from each trophic level is transferred to the level above it.

Why is energy and biomass lost at each step of the food chain?

Energy lost in urine and faeces Energy (glucose) used when the organism does respiration Energy used when the organism moves Energy used by the organism to maintain body temperature Energy escapes to the environment as heat Not all of the biomass is eaten and absorbed, e.g. bones and feathers. This biomass can be lost in

faeces.

Basic rule of energy: Energy going in to an organism = Energy stored by the organism (growth) + Energy lost from organism

What percentage of the energy in the secondary consumer is passed to the tertiary consumer?

What percentage of the energy in the primary consumer is passed to the secondary consumer?

What percentage of the energy in the producer is passed to the tertiary consumer?

GCSE Example Questions: Energy Loss Along the Food Chain (10 marks)

Competition

Animals compete for: Plants compete for:

Ecosystems and Communities

An ecosystem is the interaction of a community of living organisms with the non-living (abiotic) parts of their environment.

If one species is removed it can affect the whole community. This is called interdependence.

Within a community each species depends on other species for:1)

2)

3)

4)

A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant. Tropical rainforests and ancient oak woodlands are stable

communities.

Factors Affecting DistributionWhat factors in this pond might affect how big the turtle population gets, or where the fish choose to live?

Abiotic (non-living) factors which can affect a community

Biotic (living) factors which can affect a community

Case Study: Grey Squirrels and Red SquirrelsWhy has the red squirrel population decreased?

Sampling TechniquesA range of experimental methods using transects and quadrats are used by ecologists to determine the distribution and abundance of species in an ecosystem.

Transects Random Sampling using QuadratsWhen would you use this method?Used to look for a change in distribution (spread) in a straight lineExamples:

When would you use this method?When you want to measure the abundance of organisms in an area (measure population size)Examples:

How do you do this method?• Line perpendicular (90 degrees) to area of

study• Sample along the line• Repeat the transect to see if your results

are reliable

How do you do this method?• Split sampling area up into a grid• Use table of random numbers (avoid bias)

to generate random coordinates• Use quadrat to count abundance• Scale this up to estimate how many there

would be in whole areaWhen measuring organisms it is important to avoid sampling bias. This is when you choose an area that looks full of the organism you are observing. This means your results will not be valid.

To avoid sampling bias, you should use random sampling. This is where you generate a random set of coordinates for your sampling site, using a table of random numbers or the random number button on a calculator.

Example GCSE Question: Sampling Techniques (4 marks)

Practical: Is the distribution of Pleurococcus affected by the direction a tree is facing?

Pleurococcus is a genus of green algae, thought to be the most abundant organism on the planet at ten trillion trillion! They can be found growing on moist, dark patches of trees, rocks and soil

Do Pleurococcus grow more on North, South, East or West facing parts of a tree?

• Independent variable (1):• Dependent variable (1):• Control variables (2):• Table (2): (enough space to look at North, South, East and West faces

of 3 trees)• Graph (4):

GCSE Biology required practical: Field investigationsThere are two parts to this Investigation:

1. Investigating the population size of a plant species using random sampling

2. Investigating the effect of a factor on plant distribution using a transect line.

1. Investigating the population size of a plant species using random sampling.

1. Collect two numbers, one from each bag.2. Use the numbers and the tape measures to locate the first position for your quadrat.

3. Lay the 25cm x 25 cm quadrat on the ground.

4. Replace the numbers in the bags.

5. Count and record the number of plantain inside the quadrat.

6. Collect two more numbers from the bags and use them to locate the next site.

7. Replace the numbers in the bags for other students to use.

8. Count and record the number of plantain inside the quadrat. Repeat steps 1 – 5 until you have recorded the numbers of plantain in 10 quadrats.

10. Your teacher will show you how to estimate the population of plantain using the equation:

estimated population size = area sampled total area x number of plantain counted

2. Investigating the effect of a factor on plant distribution using a transect line

1. Lay the 30m tape measure in a line from the base of a tree to an open area of ground. 2. Put the 25cm x 25cm quadrat against the transect line. One corner of the quadrat should touch the 0

m mark on the tape measure.3. Count the number of plants within the quadrat and record them in a table4. Move the quadrat 5 m up the transect line and count the number of plants again. Record in the table.

5. Continue to place the quadrat at 5 m intervals and count the number of plants in each quadrat.

Example Exam Questions: GCSE Biology required practical: Field investigations (25 marks)

Things I have learnt from the past paper questions about TRANSECTS

Things I have learnt from the past paper questions about RANDOM SAMPLING

AdaptationsOrganisms have features (adaptations) that enable them to survive in the conditions in which they normally live. These adaptations may be structural, behavioural or functional.

Structural – a physical feature that helps an organism survive in its environment

Functional – a process that happens in an organism that allows it to survive in its environment

Behavioural – actions that allow an organism to survive in its environment

Some organisms live in environments that are very extreme, such as at high temperature, pressure, or salt concentration. These organisms are called extremophiles. Bacteria living in deep sea vents are extremophiles.

Case Study: Bacteria Living in Deep Sea Vents

Key Word Revision

Community

Ecosystem

Habitat

Interdependence

Stable community

Competition

Producer

Consumer

Predator

Prey

Adaptation

Structural adaptationBehavioural adaptationFunctional adaptationExtremophile

My Revision Notes: