7.2 Organisation of an Ecosystem

What are the producers of biomass for life on Earth?

Photosynthetic organisms

Levels of Organisation:

• Feeding relationships within a community can be represented by _______ _________.

• All ______ ________ begin with a ____________ which _____________ molecules.

• This is usually a green plant or alga which makes ___________ by ______________.

• A range of experimental methods using __________ and ___________ are used by ecologists to determine the _____________ and ______________ of species in an _____________.

• food chains

• food chains

• producers

• synthesises

• glucose

• photosynthesis

• transects

• quadrats

• distribution

• abundance

• ecosystem

• The growth of daisy plants on a lawn is affected by biotic factors and by abiotic factors.

• The figure shows a plan of a garden.

• A student estimates the number of daisy plants growing on the lawn:

  • The student places a quadrat at 10 different positions on the lawn.

  • The quadrat measures 50 cm × 50 cm.

  • The student counts the number of daisy plants in each quadrat.

• The mean number of daisy plants in each quadrat is 6.

Calculate the number of daisy plants on the lawn. [6 marks]

Give your answer to 3 significant figures.

• 50 cm = 0.5 m

• 0.5 × 0.5 = 0.25 m² — area of quadrat

• (½ × 16 × 10) - (3 × 6) = 62 m² — area of the lawn

• 62 ÷ 0.25 = 248 — quadrats in the lawn

• 6 × 248 = 1488

  • to 3sf = 1490

What is the order of a food chain?

producers → primary consumers → secondary consumers → tertiary consumers

• Primary consumers are _____________.

• Secondary consumers are _____________.

• Tertiary consumers are ______________.

• herbivores

• carnivores

• carnivores

• Consumers that kill and eat other animals are ___________, and those eaten are ______.

• In a ________ ______________ the numbers of predators and prey _____ and _____ in ________.

• predators

• prey

• stable community

• rise

• fall

• cycles

What is the definition of a predator?

Consumers that kill and eat other animals.

What is the definition of prey?

Animals that are eaten by predators.

Required Practical 9 — Field Investigation — Activity 1 (Investigating the Population Size of a Plant Species Using Random Sampling)

Describe a method to investigate the population size of a plant species using random sampling.

• Use two tape measures to set up a 10 m × 10 m survey area

• Use a random number generator to get 10 sets of coordinates

• Lay the quadrat (0.25 m²) on the ground at first coordinate

• Count and record the number of plants inside the quadrat

• Repeat for every set of coordinates — 10 sets total

• Estimate the population of this plant species:

  • estimated population size = (total area ÷ area sampled) × number of plant species counted

Required Practical 9 — Field Investigation — Activity 2 (Investigating the Effect of Light Intensity on Plant Distribution Using a Transect Line)

Describe a method to investigate the effect of light intensity on plant distribution using a transect line.

• Place a 30 m tape measure in a line from the base of a tree → open area of ground

• Place a quadrat (0.25 m²) against the transect line — one corner should touch 0 m mark on tape measure

• Count and record the number of plants inside the quadrat

• Use a light meter — measure light intensity at this position

• Repeat for different distances along the transect line

State the independent, dependent, and control variables for:

Required Practical 9 — Field Investigation — Activity 1 (Investigating the Population Size of a Plant Species Using Random Sampling)

• Independent — area being sampled

• Dependent — number of plant species counted in each quadrat

• Control:

  • size of quadrat used

  • how the plant species is counted

State the independent, dependent, and control variables for:

Required Practical 9 — Field Investigation — Activity 2 (Investigating the Effect of Light Intensity on Plant Distribution Using a Transect Line)

• Independent — distance along transect line (light intensity)

• Dependent — number of plants counted at each distance along the transect line

• Control:

  • size of quadrat used

  • how the plant species is counted

What are quadrats used to do?

Measure the abundance of an organism.

What is sampling along a transect line used to do?

Measure the distribution of organisms.

• The growth of daisy plants on a lawn is affected by biotic factors and by abiotic factors.

• The figure shows a plan of a garden.

• A student estimates the number of daisy plants growing on the lawn.

• The student places a quadrat at 10 different positions on the lawn.

• The quadrat measures 50 cm × 50 cm.

• The student counts the number of daisy plants in each quadrat.

How should the student decide where to place the quadrat? [2 marks]

Give the reason for your answer.

• Grid and coordinates

• To achieve randomness

• The growth of daisy plants on a lawn is affected by biotic factors and by abiotic factors.

• The figure shows a plan of a garden.

• A student estimates the number of daisy plants growing on the lawn.

• The student places a quadrat at 10 different positions on the lawn.

• The quadrat measures 50 cm × 50 cm.

• The student counts the number of daisy plants in each quadrat.

• The mean number of daisy plants in each quadrat is 6.

• Using the mean from this investigation to calculate the number of daisy plants on the lawn may not be accurate.

Give two reasons why. [2 marks]

• Sample size too small

• Sample may not be representative of the lawn

• A student estimated the percentage cover of buttercup plants in a field.

• The student used a quadrat.

• The quadrat was divided into 25 equal squares.

• Figure 1 shows the quadrat.

• This is the method used:

  • Place the quadrat on the ground.

  • Record how many squares in the quadrat contain buttercup plants.

  • Place the quadrat in a new position in the field.

  • Record how many squares in the quadrat contain buttercup plants.

  • Repeat steps 3 and 4 another three times.

What method should the student have used for placing the quadrat? [1 mark]

Place the quadrat using random coordinates.

• A student estimated the percentage cover of buttercup plants in a field.

• The student used a quadrat.

• The student calculated the percentage cover of buttercup plants for each quadrat.

• The table below shows the student’s results.

Quadrat number	Number of squares containing buttercup plants	Percentage cover of buttercup plants
1	10	40
2	13	52
3	22	88
4	20	80
5	10	40

• The table above shows that quadrat 1 and quadrat 5 each had 40% cover of buttercup plants.

• Figure 2 shows the results for quadrat 1 and quadrat 5.

• The student’s method of estimating the percentage cover of buttercup plants is not accurate.

How does Figure 2 show this? [1 mark]

The area of buttercup plants in quadrat 5 is much larger.

• A student estimated the percentage cover of buttercup plants in a field.

• The student used a quadrat.

• The quadrat was divided into 25 equal squares.

• Figure 1 shows the quadrat.

• This is the method used:

  • Place the quadrat on the ground.

  • Record how many squares in the quadrat contain buttercup plants.

  • Place the quadrat in a new position in the field.

  • Record how many squares in the quadrat contain buttercup plants.

  • Repeat steps 3 and 4 another three times.

• The student calculated the percentage cover of buttercup plants for each quadrat.

• The student wanted to get a more valid estimate of the percentage cover of buttercup plants in the field.

Suggest two improvements to the method to make the results more valid. [2 marks]

• Place more quadrats

• Divide quadrats into smaller squares

• A student estimated the percentage cover of buttercup plants in a field.

Give three environmental factors that would affect the growth of buttercup plants in a field. [3 marks]

• Light

• Water

• Mineral ions

• Some students investigated the size of a population of dandelion plants in a field.

• The diagram shows the field.

• The table below shows the students’ results.

Quadrat number	Number of dandelion plants
1	6
2	9
3	5
4	8
5	0
6	10
7	2
8	1
9	8
10	11

• Quadrats 5, 7 and 8 were each placed less than 10 metres from the woodland.

• The students made the hypothesis:

  • ‘Light intensity affects the number of dandelion plants that grow in an area.’

Plan an investigation to test this hypothesis. [6 marks]

• Place a 30 m tape measure in a line from the base of a tree in woodland (low light intensity) to an open area in the field (high light intensity)

• Place a quadrat (0.25 m²) at regular intervals along transect line — one corner should touch a specific mark on tape measure

• Count and record the number of plants inside the quadrat at each position

• Use a light meter to measure light intensity each position

• Repeat the entire transect line 3 times in different areas

• Compare data from different light intensity

• All materials in the living world are ____________ to provide the building blocks for future __________.

• The carbon cycle returns carbon from ____________ to the ___________ as ________ _________ to be used by plants in _____________.

• The water cycle provides _______ _______ for plants and animals on land before draining into the ______.

  • Water is continuously ___________ and ______________.

• recycled

• organisms

• organisms

• atmosphere

• carbon dioxide

• photosynthesis

• fresh water

• seas

• evaporated

• precipitated

What does the carbon cycle do?

Returns carbon from organisms → atmosphere as CO₂ — used by plants in photosynthesis

What does the water cycle do?

Provides fresh water for plants and animals on land → drains into seas

Describe the carbon cycle.

• CO₂ removed from air — photosynthesis by green plants and algae

  • Use carbon to make:

    • carbohydrates

    • proteins

    • fats

  • They are eaten → carbon moves up food chain

• CO₂ returned to air — plants, algae, and animals respire

  • Decomposers respire while returning mineral ions to soil

• CO₂ returned to air → wood and fossil fuels are burned (combustion) — they contain carbon from photosynthesis

Describe the water cycle.

• Water evaporates from seas and lakes → water vapour — caused by sun’s energy

  • Transpiration in plants → water vapour

• Water vapour rises and condenses → forms clouds

• Water is returned to land by precipitation → runs into lakes — provides water for plants and animals

• Runs into seas — cycle repeats

What are decomposers?

Organisms (bacteria or fungi) that release enzymes — catalyses the breakdown of dead plant and animal material → simpler organic matter

• Organic substances decay into simpler substances.

• The leaves fall off many trees in autumn.

• The dead leaves contain carbon compounds and nitrogen compounds.

Describe how carbon and nitrogen in compounds in the leaves are recycled and used by living trees. [6 marks]

You should include a description of:

• how the leaves are broken down

• how substances are taken in and used by the trees

• Microorganisms cause decay — they use enzymes to breakdown the dead plant material (leaves) into small molecules

• Carbon dioxide is released into the air after being produced by microorganisms respiring

• Carbon dioxide is taken in by stomata and used in photosynthesis → makes glucose and starch

• Microorganisms release nitrate ions in the soil — it is taken in by roots (by active transport) and used to make amino acids

Decay occurs in a compost heap.

Figure 7 shows a compost heap.

Describe:

• how microorganisms in the layers of soil help to recycle chemicals in the dead plants

• how the chemicals are used again by living plants

[6 marks]

• Microorganisms use enzymes to breakdown the dead plant material (large molecules) → small molecules

• Microorganisms release mineral ions in the soil

• Carbon dioxide is released into the air after being produced by microorganisms respiring

• Carbon dioxide is taken in by stomata (by diffusion) and used in photosynthesis → makes glucose and starch

• Mineral ions taken in by roots (by active transport) and nitrate ions are used to make amino acids

What does anaerobic decay produce?

Methane gas

What can biogas generators be used to do?

Produce methane gas as a fuel

• Gardeners and farmers try to provide ____________ conditions for rapid _______ of _______ ____________ ________.

• The compost produced is used as a __________ ___________ for growing garden plants or ________.

• optimum

• decay

• waste biological material

• natural fertiliser

• crops

What factors affect the rate of decay of biological material? (3)

• Temperature

• Water

• Availability of oxygen

Describe how temperature affects the rate of decay of biological material.

• Chemical reactions work faster in warmer conditions

• If it is too hot enzymes may denature → stops decomposition

Describe how water affects the rate of decay of biological material.

• Microorganisms grow faster in conditions with water — needed for respiration

• Water also makes food easier to digest

Describe how availability of oxygen affects the rate of decay of biological material.

Most decomposers respire aerobically — oxygen needed for aerobic respiration

Required Practical 10 — Decay

Describe a method to investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change.

• Add 5 cm³ of lipase solution to a boiling tube

• Add the following to a different boiling tube and place a thermometer in:

  • 5 drops of cresol red solution

  • 5 cm³ of milk

  • 7 cm³ of sodium carbonate solution

  • Solution should be purple

• Place both boiling tubes into a water bath — wait until they both reach the same temperature as the water bath

• Use a pipette to transfer 1 cm³ of heated lipase → milk

  • Start stopwatch and stir the milk boiling tube — until solution is yellow

• Record time taken for colour to change to yellow

• Repeat for different temperatures of water bath

State the independent, dependent, and control variables for:

Required Practical 10 — Decay

• Independent — temperature of water bath

• Dependent — time taken for milk solution to turn yellow

• Control:

  • volumes of solutions used

  • age of milk

  • starting pH of milk

Name two types of microorganism that cause decay. [2 marks]

• Bacteria

• Fungi

• This question is about the decay of milk.

• Cows’ milk is pH 6.6.

• As milk decays, lipids in the milk are broken down.

• One of the products of the breakdown of lipids causes the pH of milk to decrease.

Name the product that causes the pH to decrease. [1 mark]

Fatty acids

• This question is about the decay of milk.

• A student investigated the effect of temperature on the time taken for different types of box milk to decay.

• This is the method used:

  • Put cows’ milk in six test tubes.

  • Keep each test tube at a different temperature.

  • Measure the pH of the milk in each tube every day for 12 days.

  • Record the number of days taken to reach pH 5.

  • Repeat steps 1 to 4 with goats’ milk and with almond milk.

Give one way the pH can be measured. [1 mark]

pH probe

• Give two control variables the student should have used in this investigation.This question is about the decay of milk.

• A student investigated the effect of temperature on the time taken for different types of box milk to decay.

• This is the method used:

  • Put cows’ milk in six test tubes.

  • Keep each test tube at a different temperature.

  • Measure the pH of the milk in each tube every day for 12 days.

  • Record the number of days taken to reach pH 5.

  • Repeat steps 1 to 4 with goats’ milk and with almond milk.

Give two control variables the student should have used in this investigation. [2 marks]

• Age of milk

• Volume of milk

• This question is about the decay of milk.

• A student investigated the effect of temperature on the time taken for different types of box milk to decay.

• The student improved the investigation to produce valid results.

• Figure 1 shows the results.

Which type of milk stays fresh the longest at 10 °C? [1 mark]

Almond milk

• This question is about the decay of milk.

• A student investigated the effect of temperature on the time taken for different types of box milk to decay.

• The student improved the investigation to produce valid results.

• Figure 1 shows the results.

Describe the effect of temperature on the time taken for goats’ milk to reach pH 5. [2 marks]

Use data from Figure 1 in your answer.

• As temperature increases up to 15 °C the time taken to reach pH 5 decreases

• Above 15 °C the time taken to reach pH 5 stays the same

• This question is about the decay of milk.

• A student investigated the effect of temperature on the time taken for different types of box milk to decay.

• The student improved the investigation to produce valid results.

• Figure 1 shows the results.

• The time taken for cows’ milk to reach pH 5 at 10 °C is less than the time taken for cows’ milk to reach pH 5 at 5 °C.

Suggest one reason why. [1 mark]

There is more kinetic energy

• This question is about the decay of milk.

• A student investigated the effect of temperature on the time taken for different types of box milk to decay.

• The student improved the investigation to produce valid results.

• Figure 1 shows the results.

Suggest two reasons why the different types of milk took different lengths of time to reach pH 5.

• Different starting pH

• Different concentration of fat

• This question is about the decay of milk.

• A student investigated the effect of temperature on the time taken for different types of box milk to decay.

• The student improved the investigation to produce valid results.

• Figure 1 shows the results.

• The student said:

  • ‘The temperature milk is stored at affects how likely the milk is to cause food poisoning.’

How can the investigation be developed to find out if the student is correct? [1 mark]

Determine the types of bacteria present in the milk

• A student investigated the effect of temperature on the decay of milk.

• Figure 3 shows the apparatus the student used.

• This is the method used:

  • Set up the apparatus as shown in Figure 3 with the milk at 20 °C.

  • Record the pH over 5 days using the computer.

  • Repeat with another batch of fresh milk at 25 °C.

How could the student keep the milk at a constant temperature for 5 days? [1 mark]

Put beaker in a water bath

What can environmental changes do?

Affect the distribution of species in an ecosystem

What can environmental changes that can affect the distribution of species in an ecosystem be? (3)

• Seasonal

• Geographic

• Caused by human interaction

What are some examples of environmental changes that can affect the distribution of species in an ecosystem? (3)

• Temperature

• Availability of water

• Composition of atmospheric gases