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What is a producer?

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.


What is a consumer?

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


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

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.


What is a trophic level?

The position of an organism in a food chain.


Give the energy gain percentage between each trophic level.

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


How does energy enter an ecosystem?

Sunlight is converted to chemical energy in photosynthesis.


Why is not all sunlight energy transferred to plants?

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


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

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.


What is the difference between excretion and egestion?

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


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

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


What is biomass?

The mass of living material (without water).


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

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


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

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.


How is net productivity calculated?

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


How is efficiency of energy transfer calculated?

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


How do you measure net productivity?

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.


What is an ecosystem?

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


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

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.


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

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.


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

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.


Define a decomposer (Saprotrophs).

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


Define a Detritivore.

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


How is carbon taken from the atmosphere?



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

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.


What are the important greenhouse gases?

Methane and carbon dioxide.


What is the role of limestone in the carbon cycle?

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.


Which processes remove carbon dioxide from the air?

Photosynthesis by plants. Dissolving in the oceans.


Which processes return carbon dioxide from the air?

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.


What mineral ions are released by the break down of chlorophyll/phospholipids/proteins/nucleic acids?

Chlorophyll - magnesium ions.
Phospholipids - phosphate ions.
Proteins - nitrate ions.
Nucleic acids - nitrate ions.


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

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