6.5 - Ecosystems

Question 1

What is a producer?

Answer 1

An organism that synthesises organic molecules from simple inorganic ones such as carbon dioxide and water. Most producers are photosynthetic and form the first trophic level in a food chain.

Question 2

What is a consumer?

Answer 2

An organism that obtains energy by ‘eating’ other organisms.

Question 3

What is a primary/secondary/tertiary/quaternary consumer?

Answer 3

A primary consumer feeds on producers.
A secondary consumer feeds primary consumers.
A tertiary consumer feeds secondary consumers.
A quaternary consumer feeds on tertiary consumers.

Question 4

What is a trophic level?

Answer 4

The position of an organism in a food chain.

Question 5

Give the energy gain percentage between each trophic level.

Answer 5

1-3% from sun to producers.
5-10% from producers to primary consumers.
15-20% from consumer to consumer.

Question 6

How does energy enter an ecosystem?

Answer 6

Sunlight is converted to chemical energy in photosynthesis.

Question 7

Why is not all sunlight energy transferred to plants?

Answer 7

Wrong wavelength.
Reflected (over 90%).
Pass straight through the leaf.
Hits non-photosynthesising parts of the plant e.g. bark.

Question 8

Why is energy lost in the transfer of energy from producers to primary consumers and consumers to consumers?

Answer 8

Some of the organism is not eaten / cannot be digested.
Energy used to maintain body temperature.
Some of the energy is lost in excretion and egestion.
Some energy is used in respiration.

Question 9

What is the difference between excretion and egestion?

Answer 9

Excretion is the removal of waste products from a living organism.
Egestion is the removal of undigested waste from the body (faeces).

Question 10

Why do food chains have a maximum of 5 trophic levels?

Answer 10

Insufficient energy is available to support a large enough breeding population at trophic levels higher than five.

Question 11

What is biomass?

Answer 11

The mass of living material (without water).

Question 12

Why is a pyramid of biomass more accurate than a pyramid of numbers?

Answer 12

It shows how much of the energy transferred ends up in the next organism.
Biomass indicates how much energy an organism contains.

Question 13

Define gross productivity and describe how this is calculated in plants and animals.

Answer 13

Total energy captured or assimilated by an organism.
In plants = total sunlight energy used in photosynthesis.
In animals = Energy in food eaten – energy in faeces.

Question 14

How is net productivity calculated?

Answer 14

Net productivity (energy used for growth)= gross productivity – respiratory losses.

Question 15

How is efficiency of energy transfer calculated?

Answer 15

Energy transfer efficiency = (energy available after transfer / energy available before transfer) X 100

Question 16

How do you measure net productivity?

Answer 16

1. Calculate the amount of biomass in a sample of the organisms.
2. Sample x total population size = total amount of energy in the organisms at that trophic level.
3. The difference in energy between the trophic levels is the amount of energy transferred.

Question 17

What is an ecosystem?

Answer 17

An ecosystem = all living organisms (biotic) + all non-living conditions (abiotic).

Question 18

Detail the biotic & abiotic factors that have an impact on a rock pool, playing field and a large tree.

Answer 18

Rock pool: Biotic - seaweed (producer), limpet (consumer), competition for food will limit number of organisms present. Abiotic - pH, salinity, temperature, low tide results in extreme abiotic conditions – special adaptations needed.
Playing field: Biotic - grass, daisies, clover, dandelion (producers), caterpillars, bees, rabbits (consumers). Abiotic - rainfall & sunlight will affect growth. This in turn will affect the number of consumers the ecosystem can support.
Large tree: Biotic - Leaves are food source for caterpillars & other insects. If too many are eaten this will affect tree growth. Abiotic - drought conditions will impact growth.

Question 19

What techniques do farmers use to increase productivity in agricultural crops and why?

Answer 19

Herbicides - reduces competition from weeds.
Fungicides - Crops use more energy for growth & less for fighting infection.
Insecticides and/or introduce natural predators to eat pest species – less biomass lost from the crop.
Fertilisers – growth is not limited due to mineral deficiency.
All of the above means that crops grow faster & become larger, increasing productivity.

Question 20

What techniques do farmers use to increase productivity in livestock and why?

Answer 20

Intensive farming methods increase the efficiency of energy conversion so more biomass is produced & productivity is increased: Animals kept in warm, indoor pens & restrict movement. Less energy is wasted keeping warm & moving around. Animals given high energy feed, so more energy available for growth.

Question 21

Define a decomposer (Saprotrophs).

Answer 21

Can digest cellulose. Secrete enzymes outside of their bodies & absorb the products of digestion = saprotrophic nutrition. Absorbed substances used for respiration.

Question 22

Define a Detritivore.

Answer 22

Cannot break down cellulose. Break down dead matter into smaller pieces. Create a larger surface area for enzymes to work on.

Question 23

How is carbon taken from the atmosphere?

Answer 23

Photosynthesis.

Question 24

Explain how carbon found in dead matter is made available for plants.

Answer 24

Saprotrophs release enzymes.
Extracellular digestion.
They then absorb the products of digestion.
They respire, producing carbon dioxide.
Carbon dioxide is taken into the plant in photosynthesis.
Through the stomata.

Question 25

What are the important greenhouse gases?

Answer 25

Methane and carbon dioxide.

Question 26

What is the role of limestone in the carbon cycle?

Answer 26

Limestone is biological sedimentary rock formed from shells of dead marine organisms that collected on the seabed over millions of years ago.
When limestone is weathered the carbon is released back into the atmosphere as carbon dioxide.

Question 27

Which processes remove carbon dioxide from the air?

Answer 27

Photosynthesis by plants. Dissolving in the oceans.

Question 28

Which processes return carbon dioxide from the air?

Answer 28

Respiration by plants, animals and microbes.
Combustion ie burning wood and fossil fuels such as coal, oil and gas.
Weathering of limestone & chalk.
Thermal decomposition of limestone, for example, in the manufacture of iron, steel and cement.

Question 29

What mineral ions are released by the break down of?

Answer 29

Chlorophyll? Magnesium ions.
Phospholipids? Phosphate ions.
Proteins? Nitrate ions.
Nucleic acids? Nitrate ions.

Question 30

Which form must nitrogen be in to be taken up by plants?

Answer 30

Ammonium (NH4+) or nitrate (NO3-).

Question 31

What are the 3 stages of the nitrogen cycle?

Answer 31

1. Saprotrophic digestion = decomposers digest proteins → amino acids.
2. Ammonification = amino acids → form ammonium compounds (NH4+).
3. Nitrification = conversion of ammonium compounds (NH4+) → nitrates (NO3-).

Question 32

How is nitrogen in dead matter converted back into nitrogen gas in the atmosphere?

Answer 32

Decomposers and saprotrophic micro-organisms break down the ammonium (NH3) containing molecules into ammonium ions (NH4+) by ammonification.
The ammonium ions (NH4+) are converted to nitrite ions (NO2-), then nitrate ions (NO3-) in nitrification.
The nitrate ions (NO3-) are converted into nitrogen gas in denitrification.

Question 33

What conditions are needed for denitrification and which bacteria are involved?

Answer 33

Pseudomonas bacteria require anaerobic conditions, e.g. waterlogged soil.

Question 34

Which bacteria are involved in nitrification?

Answer 34

There are 2 stages of the oxidation carried out by nitrifying bacteria:

1. Ammonium ions (NH4+) → Nitrosomonas → Nitrite ions (NO2-).
2. Nitrite ions (NO2-) → Nitrobacter → Nitrate Ions (NO3-).

Question 35

What conditions are needed for nitrification?

Answer 35

This requires oxygen (aerobic) – occurs in soil with air pockets e.g. aerated, well drained soil.

Question 36

What are the two ways that nitrogen gas in the air can be fixed into nitrogen containing compounds?

Answer 36

Can occur industrially (Haber process) or when lightning happens. By bacteria.

Question 37

Which bacteria are involved in nitrogen fixation?

Answer 37

Free living bacteria – Azobacter - produce ammonia from nitrogen gas. Make amino acids. Release them when they die.
Mutualistic bacteria – Rhizobium - live in root nodules in peas and beans. Bacteria obtain carbohydrates from plant and plant gets amino acids from bacteria.

Question 38

Why do plants grow at a much slower rate when the soil becomes waterlogged?

Answer 38

Fewer aerobic nitrifying and nitrogen fixing bacteria in waterlogged soil.
More anaerobic denitrifying bacteria in waterlogged soil.
This means there is less nitrogen containing molecules for plants.
Therefore plants will grow slower as less proteins and DNA can be made.

Question 39

Why are nitrogen fertilisers used on crops?

Answer 39

Nitrogen is an important molecule in plant growth as it is used to make proteins and DNA.

Question 40

Why is it not good for nitrates (fertilisers) to get into water ecosystems?

Answer 40

Rapid growth of algae blocks light.
Reduced photosynthesis of submerged plants so they die.
Saprotrophic microorganisms break down dead plants.
In doing this they respire aerobically, using up the oxygen.
Less oxygen for fish to respire, so aerobic organisms die (eutrophication).

Question 41

What is a pioneer species?

Answer 41

The first species to colonise an area.

Question 42

Why are pioneer species adapted to live in inhospitable environments?

Answer 42

At start of succession there is little soil.
Bare soil temperatures fluctuate.
Little nutrients to help growth.

Question 43

How are pioneer species adapted to live in inhospitable environments?

Answer 43

Rapid reproduction.
Ability to fix nitrogen from the atmosphere.
Tolerance to extreme conditions – xerophytes.

Question 44

What is a climax community?

Answer 44

Where there is a balanced equilibrium of species where new species do not come and outcompete others.

Question 45

Describe the process of ecological succession.

Answer 45

The pioneer species first colonise an area and grow. They then die and the dead matter forms humus. Now a less hostile environment so new species are able to live in the area due to the improved conditions, and they are a better competitor so the pioneer species are outcompeted. Change in biodiversity. New species able to live in the area due to the improved conditions and they are a better competitor so the previous species are outcompeted. This step keeps repeating until a climax community is reached.

Question 46

Why is the diversity of animal species higher towards the climax community end of succession than the pioneer species end?

Answer 46

More food sources. More variety of habitats.

Question 47

Why is conservation important?

Answer 47

To prevent a climax community from forming everywhere. Increases biodiversity.

Question 48

What are the reasons for conservation?

Answer 48

Increasing biodiversity. Means new drugs and other chemicals can be developed from different species in the future. Aesthetic reasons. Ethical reasons.

Question 49

Define deflected succession and give an example.

Answer 49

When succession is prevented by human activity – the path of succession is deflected from its natural course. For example – a regularly mown grassy field will not develop woody plants as the growing points of woody plants are cut off – only grasses will survive – this then
forms the unnatural climax community.

Question 50

When succession is stopped artificially by humans what is the climax community called?

Answer 50

Plagioclimax – the community that develops is different to any of the natural stages of the ecosystem.

Question 51

What techniques could be used for measuring abundance and/or species richness? (Random sampling).

Answer 51

Point / frame quadrat. Randomly place a quadrat in an area. Record the number of individuals of each species in the quadrat. Repeat multiple times. Percentage cover can be used for frame quadrats when frequency
is hard to measure.
Mark-release-recapture techniques (for more mobile species). A known number of individuals are captured, marked and released. Appropriate method of marking is used so that it doesn’t harm the organism. A second random known number of individuals are captured. The number of marked individuals recaptured is recorded and then they are released. Population size can then be calculated from this data using the formula below.
Counting number of species caught in net sweeps/ traps (for mobile species that cannot be marked). Trap, sweep nets or stun individuals using a chemical. Number of individuals caught counted and classified then recorded.

Question 52

What techniques could be used for measuring distribution? (Systematic sampling).

Answer 52

Line / belt transect. Set up a line between two points. Place a quadrat at regular intervals along the transect and record the abundance of each species.

Question 53

How do you calculate estimated population size from mark-release-recapture data?

Answer 53

(Total number of individuals in first sample X total number of individuals in second sample) / number of marked individuals recaptured

Question 54

What conditions are needed for mark-release-recapture investigations to give reliable results?

Answer 54

Marking not removed.
No immigration/emigration.
Sufficient time for marked individuals to mix with the population.
No births/deaths.
Sampling method is the same.

Question 55

How can you ensure reliable survey results when sampling animals?

Answer 55

Random samples – no bias involved.
Larger sample size.
Larger sample area.
Smaller quadrat.
Same technique in each habitat.
Random number generator generating coordinates for quadrat placement.
Control/ note abiotic variables.

Question 56

Explain the role of pioneer plants in succession.

Answer 56

Stabilise the environment.
Soil development.
Increase availability of water – hold more water.
Some carry out nitrogen fixation – increase minerals/nutrients available.

Question 57

Give two ways in which deflected succession would be caused.

Answer 57

Grazing, mowing, burning.

Question 58

Define the term climax community.

Answer 58

Final stage in succession – community in equilibrium with the environment.

Question 59

How could you investigate the distribution & abundance of a species in an ecosystem?

Answer 59

Set sample grid. Use of quadrat of suitable size. Choose systematic method – belt or line transect. Repeat line transects / use quadrats (of appropriate size) at regular intervals – random number generator. Identification of species – using a key/book. Record both presence & absence of species. Count number of plants - calculate % of species frequency. Measure % cover of plants. Analyse data using a kite diagram or plot a graph. Carry out statistical test – Spearmans rank.