Ecosystems

Question 1

What is meant by the terms population, community, habitat and ecosystem?

Answer 1

Population: All the organisms of a particular species found in an ecosystem at any one time
Community: The population of all species found in a particular ecosystem
Habitat: places where specific organisms live
Ecosystem: distinct, self-supporting system of organisms interacting with each other and with a physical environment.

Question 2

Explain how quadrats can be used to sample the distribution of organisms in their habitats

Answer 2

A pair of random numbers is generated. These numbers are used as coordinates to position the quadrats in the large square. The numbers of each plant species present in the quadratic are counted. The process is then repeated for nine more quadrats. The tape measures are moved to another area and the process is repeated.

Question 3

Explain the names given to different trophic levels

Answer 3

Producer: plant which produces food materials by photosynthesis
Primary consumer: herbivore which eats the producer
Secondary consumer: Carnivore which eats the primary consumer
Tertiary consumer: eats the secondary consumer
Decomposer: breaks down organic material

Question 4

How are substances and energy transferred along a food chain?

Answer 4

Photosynthesis fixes sunlight energy into chemicals such as glucose and starch. Respiration releases energy from organic compounds such as glucose. Almost all other biological processes use the energy released in respiration. If energy from respiration is used to make new cells, then the energy remains fixed in molecules in that organism. It can be passed onto the next trophic level by feeding. If the energy is used for other processes then it will eventually escape as heat from the organism. Energy is therefore lost from food chains at each trophic level.

Question 5

Explain why only about 10% of energy is transferred from one trophic level to the next

Answer 5

Some parts of the food are not eaten.
Some parts are not digested so aren’t absorbed
Some materials absorbed form excretory products
Many of the materials are respired to release energy with the loss of carbon dioxide and water

Question 6

Describe the stages in the water cycle (Paper 2)

Answer 6

Heat from the sun evaporates water from the surface.
Plant transpiration and respiration of organisms also releases water vapour into the air.
When clouds rise over high ground, they cool and water condenses to form rain or snow.
This precipitation falls on the earth where it is taken up by animals or plants or enters rivers and flows to the sea to start the cycle again.

Question 7

Describe the stages in the carbon cycle

Answer 7

Photosynthesis fixes carbon atoms from carbon dioxide into organic compounds.
Feeding and assimilation pass carbon atoms already in organic compounds along food chains.
Respiration produces inorganic carbon dioxide from organic compounds as they are broken down to release energy.
Fossilisation takes place and fossil fuels are formed
Combustion of fossil fuels releases CO2 back into the atmosphere

Question 8

Describe the stages in the nitrogen cycle (Paper 2)

Answer 8

Feeding and assimilation passes nitrogen atoms already in organic compounds along food chains.
Putrefaction by decomposers produces ammonia from the nitrogen in compounds like DNA and proteins
The ammonia is oxidised first to nitrite and then to nitrate by nitrifying bacteria. This process is called nitrification.
Plant roots absorb the nitrates are they are combined with carbohydrates to form amino acids and then proteins.