6.3.1: Ecosystems and 6.3.2: Populations and sustainability

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) x100

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.