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Question 1

What is the difference between a population, community, habitat and ecosystem?(2)

Answer 1

An ecosystem contains a variety of habitats. A habitat is the place where an organism lives.
All the organisms of a specific species found in an ecosystem at a certain time form the population of that species. The populations of all species found in an ecosystem and at a specific time form the community.

Question 2

Define Biodiversity.

Answer 2

The amount of variation shown by species in an ecosystem is called the biodiversity. It is about the number of different species as well as the relative abundance of each species.

Question 3

List some Biotic factors that affect an ecosystem.(4)

Answer 3

Availability of food and competition for food.
Predation
Parasitism
Disease
Presence of pollinating insects

Question 4

List some Abiotic factors that affect an ecosystem.(4)

Answer 4

Climate
Hours of daylight
Soil conditions
Pollution

Question 5

What is the name given to the different stages in a food chain?

Answer 5

Trophic levels.

Question 6

What are the two different types of ecological pyramids?(2)

Answer 6

Pyramids of numbers, which represent the numbers of organisms in each tropics level, irrespective of their mass.
Pyramids of biomass, which show the total mass of the organisms in each tropic level, irrespective of their numbers.

Question 7

What is biomass?

Answer 7

Biomass is the total mass of organisms. When referred to living organisms, this is called the fresh biomass. The dry biomass is more common, this is the mass of plant or animal after water has been removed.

Question 8

Why is it that only about 10% of energy is passed on from each trophic level?(3)

Answer 8

Some parts of the organism are not eaten(bones or roots). Some parts are not digested and so are not absorbed.
Some of the materials absorbed form excretory products.
Many of the materials are respired to release energy, with the loss of carbon dioxide and water.

Question 9

Describe the important processes in the Carbon cycle.(4)

Answer 9

Photosynthesis fixes carbon atoms from carbon dioxide into organic compounds(plants).
Feeding and assimilation pass carbon atoms already in organic compounds along food chains.
Respiration produces inorganic carbon dioxide from organic compounds.
Fossils might be formed when living things do not decay fully -
Combustion of fossil fuels releases carbon dioxide into the atmosphere.

Question 10

Describe the basic important processes in the Nitrogen cycle.(3)

Answer 10

Feeding and assimilation passes nitrogen atoms along food chains.
Decomposition by fungi and bacteria produces ammonia from the nitrogen in compounds.
The ammonia is oxidised first to nitrite and then to nitrate by nitrifying bacteria. This is called nitrification.

Question 11

What are 2 ways that nitrates are formed?(4)

Answer 11

Lightning converts nitrogen gas in the air into oxides of nitrogen.
These dissolve in rainwater, enter the soil and are converted into nitrates by nitrifying bacteria.
Humans also make nitrates industrially from nitrogen gas via the Haber(-Bosch) process. These nitrates are mainly used as fertilisers because they increase the rate of growth of crops.

Question 12

What are the processes that bacteria carry out that affect the amount of nitrate in the soil?(3)

Answer 12

Denitrifying bacteria use nitrates as an energy source and convert them into nitrogen gas. Reduces nitrate in soil.
Free-living nitrogen fixing bacteria in soil convert nitrogen gas into ammonia. When the bacteria die, their proteins decompose, releasing ammonia back to the soil.
Nitrogen fixing bacteria in root nodules also make ammonia but this is converted by the plant into amino acids.

Question 13

How can soil ions be controlled to improve yield of crop plants?(2)

Answer 13

Adding fertilisers to the soil or growing in a hydroponic culture.
This means extra mineral ions can be taken up and used to make proteins and other compounds for growth.

Question 14

How can soil structure be controlled to improve yield of crop plants?(2)

Answer 14

Ploughing fields to break up compacted soil; adding manure to improve drainage and aeration of heavy, clay soils.
Good aeration and drainage allow a better uptake of mineral ions and water.

Question 15

How can soil pH be controlled to improve yield of crop plants?(2)

Answer 15

Adding lime to acidic soils; few soils are too alkaline to need treatment.
Soil pH can affect crop growth as an unsuitable pH reduces uptake of mineral ions.

Question 16

Why do greenhouses and polytunnels provide very controlled conditions for plant growth?(3)

Answer 16

Transparent walls allow natural light for photosynthesis; during winter additional lighting gives the effect of a longer day.
Greenhouses heat up very quickly and even if the temperature outside is low they can be heated.
Carbon dioxide and water from the heaters are good for the plants.

Question 17

What are the main consequences of air pollution from Carbon Monoxide and Sulphur Dioxide?(4)

Answer 17

Carbon monoxide is poisonous because it combines with the haemoglobin in red blood cells preventing them from carrying oxygen.
It is released from car emissions.
Sulfur dioxide can mix with rain clouds to form dilute H2SO4 which falls as acid rain.
Sulfur dioxide forms from burning fossil fuels.

Question 18

How does Acid Rain damage the environment?(2)

Answer 18

Acid rain can cause a lake to become more acidic which has a severe effect on the lake’s ecosystem because many organisms are sensitive to changes in pH.
Acid rain can kill trees, by damaging leaves and releasing toxic substances from the soil.

Question 19

What are the 4 main greenhouse gases?(4)

Answer 19

Carbon dioxide; released through many processes.
Methane; increased release because of cattle rearing and rice growing.
Nitrous Oxide; increased release from soils after fertiliser use.
CFCs; man-made chemicals that were once used in aerosol sprays, arguably most damaging greenhouse gas because they damage ozone layer as well.

Question 20

What are the biological consequences for water pollution from fertilisers?(3)

Answer 20

Nitrates and phosphates are put onto fields as mineral fertilisers.
If too much fertiliser is applied and it rains afterwards, nitrates are easily leached into rivers and lakes.
The result is eutrophication which can cause serious damage to river and lake ecosystems.

Question 21

What are the biological consequences for water pollution from sewage?(2)

Answer 21

Sewage contains lots of phosphates from detergents. It also contains nitrates from urine and faeces.
These extra nutrients cause eutrophication.

Question 22

Describe and explain the steps of eutrophication?(4)

Answer 22

Extra nutrients most likely nitrates cause algae to grow fast and block out the light.
Plants can’t photosynthesise due to lack of light and start to die.
With more food available, microorganisms that feed on dead plants increase and use up all oxygen in water.
Organisms that need oxygen die, the algae soon die as well as the microorganisms.

Question 23

How can deforestation affect leaching?(2)

Answer 23

Trees take up nutrients from the soil before they can be washed away by rain, but return them to the soil when leaves die.
When trees are removed nutrients get leached away but don’t get replaced leaving infertile soil.

Question 24

How can deforestation affect soil erosion?(2)

Answer 24

Trees roots’ hold the soil together
When trees are removed, soil can be washed away by the rain leaving infertile ground.

Question 25

How can deforestation disturb evapotranspiration?(2)

Answer 25

Evapotranspiration are the processes of water evaporating from the Earth’s surface and from plant transpiration.
When trees are cut down, evapotranspiration is reduced, making the local climate drier.