Populations, Sustainability And Ecosystems

Question 1

Define ecosystem.

Answer 1

All the living organisms found in one area, and the non-living aspects of their environment. Can range in size e.g. rock pool, tree, field. Known as ‘dynamic’ as they depend on interactions between biotic and abiotic factors.

Question 2

Describe biotic and abiotic factors, giving examples.

Answer 2

Biotic= living features of an ecosystem e.g. predators, disease.
Abiotic= non-living features of an ecosystem e.g. light, temperature.

Question 3

What is biomass and how is it transferred? How can we measure this?

Answer 3

The total weight of living matter in a certain area, transferred up trophic levels through consumption. Can be measured in terms of mass of carbon, or dry mass of tissue.

Question 4

Give the formula for efficiency of biomass transfer.

Answer 4

Efficiency = (biomass transferred/biomass intake) x 100

Question 5

How can human activities affect biomass transfer?

Answer 5

● Light, water, temperature maximised.
● Increased nutrients in soil.
● Pests and weeds removed.
● Growth rates boosted through
steroids, selective breeding, etc.

Question 6

Outline the roles of microorganisms in the nitrogen cycle.

Answer 6

● Nitrogen-fixing bacteria e.g. Rhizobium in roots and Azotobacter in soil, convert gaseous nitrogen into ammonia.
● Nitrifying bacteria e.g. Nitrosomonas convert
ammonium compounds into nitrites.
Nitrobacter then convert nitrites to nitrates.

Question 7

Outline the role of organisms in the carbon cycle

Answer 7

● Respiration of plants and animals add carbon dioxide into the atmosphere.
● Photosynthesis of plants removes carbon dioxide from the atmosphere.
● Decomposers (microorganisms) decay plant and animal material into carbon dioxide.

Question 8

What is meant by primary succession?

Answer 8

Where an area previously devoid of life is colonised by a community of organisms.

Question 9

Summarise the process of primary succession.

Answer 9

● Pioneer species, able to survive harsh conditions, colonise the area.
● They die, decompose, and add nutrients to the ground.
● Over time, this allows more complex organisms to survive.

Question 10

What is the climax community and how is it reached?

Answer 10

The final stage of succession, where the ecosystem is balanced and stable. It is reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing.

Question 11

What is deflected succession?

Answer 11

Where succession is interrupted, usually by human interference.

Question 12

What is sampling?

Answer 12

Selecting a group of individuals that will represent the whole target population. Allows us to measure the distribution and abundance of organisms.

Question 13

Give methods of sampling and explain how they are used.

Answer 13

● Quadrats= used in small areas. Randomly or regularly placed across habitat. Frequency or % cover calculated.
● Transects= used in larger areas. Sample taken along a line that crosses the habitat. Can be combined with quadrats in the form of a belt transect.

Question 14

Define carrying capacity.

Answer 14

The maximum population size that a habitat can support, defined by the presence of limiting factors.

Question 15

Give factors that limit the maximum size of a population.

Answer 15

● Food ● ● Water ● ● Light ● ● Oxygen ● ● Nesting sites Shelter Parasites Predators

Question 16

Describe the pattern of a typical predator-prey relationship in terms of population change.

Answer 16

● Prey is eaten by predator, resulting in predator population increasing and prey population decreasing.
● Fewer prey means increased competition for food, so predator population decreases.
● Fewer predators means more prey survives, and the cycle begins again.

Question 17

What is meant by intraspecific and interspecific competition?

Answer 17

Intraspecific= competition between organisms of the same species.
Interspecific= competition between organisms of different species.

Question 18

Differentiate between conservation and preservation

Answer 18

● Conservation= maintains biodiversity of a habitat by allowing sustainable use of the resources there.
● Preservation= maintains biodiversity of a habitat by minimising human impact.

Question 19

Give reasons why we conserve and preserve habitats.

Answer 19

● Economic= food source, natural pest control, boosts tourism.
● Social= many organisms can be used in medicine, aesthetics.
● Ethical= we have a responsibility to maintain habitats for future generations.

Question 20

Define sustainability.

Answer 20

Using resources in a way that also maintains them for future generations.

Question 21

What methods allow sustainable use of an ecosystem’s resources?

Answer 21

● Timber production= coppicing to encourage growth, replacing felled trees, selective cutting.
● Fishing= stocks not depleted, no
overfishing, can continue indefinitely.

Question 22

Give an example of how the conflict between conservation and human needs can be balanced.

Answer 22

Terai region (Nepal). Over-exploited for use in fuel. Locals now have a responsibility to look after the forest. ‘Corridors’ placed to enable migration.

Question 23

Give an example of how human effects are controlled in sensitive ecosystems.

Answer 23

Galapagos islands. Many species endangered due to hunting and tourism. New species introduced, but caused damage to native species. Trying to find a balance.