7.2

Question 1

define population

Answer 1

A species that occupy the same habitat.

Question 2

Define habitat

Answer 2

The place in which an organism lives.

Question 3

Define community

Answer 3

Populations of different species

interacting.

Question 4

Define ecosystem

Answer 4

The interactions between the biotic and

abiotic factors in an area

Question 5

Define biomass

Answer 5

The total mass of living material

Question 6

Describe a simple food chain

Answer 6

producer → primary consumer →

secondary consumer → tertiary consumer.

Question 7

What is a producer?

Answer 7

An organism that makes its own food

Question 8

What types of organisms are primary

producers?

Answer 8

Photosynthetic organisms like green
plants and algae that trap energy from
the sun.

Question 9

What is a primary consumer?

Answer 9

An organism that feeds on producers.

Question 10

What is a secondary consumer?

Answer 10

An organism that feeds on primary

consumers.

Question 11

What is a tertiary consumer?

Answer 11

An organism that feeds on secondary

consumers.

Question 12

What is a predator?

Answer 12

A consumer that kills and eats other

animals.

Question 13

What is prey?

Answer 13

An animal that is killed and eaten by

another animal.

Question 14

Describe the pattern of predators and prey in a

stable community

Answer 14

The numbers of predators and prey rise

and fall in cycles.

Question 15

Why are producers the first trophic level?

Answer 15

● Producers provide all biomass for the food
chain (production of glucose via
photosynthesis).
● The rest of the food chain involves the transfer
of this biomass.

Question 16

What piece of apparatus is used to
measure the abundance and distribution
of organisms in an area?

Answer 16

quadrat

Question 17

Describe how materials cycle through
the living and non-living components of
an ecosystem

Answer 17

● Organisms take in elements from their surroundings e.g. soil, air.

● Elements converted to complex molecules which become biomass.

● Elements transferred along food chains.

● Elements returned to environment during excretion and
decomposition of dead organisms.

Question 18

Give 3 molecules which are cycled through

ecosystems

Answer 18

Oxygen, carbon dioxide and water.

Question 19

Describe the carbon cycle

Answer 19

• Plants fix carbon dioxide into organic molecules during
  photosynthesis.
• The organic carbon-containing molecules are passed onto organisms
  that eat the plants.
• Carbon dioxide is released back into the atmosphere by respiration
  from animals and plants.
• Burning fossil fuels also releases carbon dioxide into the atmosphere.

Question 20

Why is the carbon cycle important?

Answer 20

Carbon-containing molecules such as
glucose are important for living
organisms to grow and provide energy
for vital functions within cells.

Question 21

Describe the water cycle

Answer 21

• Water from lakes and oceans evaporates.
• The evaporated water condenses into clouds and returns
  to earth as precipitation.
• The water from precipitation is useful for life on land.
• The water then returns to rivers and oceans through
  surface runoff

Question 22

Why is the water cycle important?

Answer 22

Living organisms require water and the
water cycle provides organisms on land
with a continuous supply of water

Question 23

Why are microorganisms important for
the cycling of materials through an
ecosystem?

Answer 23

Microorganisms (bacteria and fungi) return carbon to the
environment by releasing carbon dioxide through
respiration while they decompose dead matter. The
decomposition of dead matter in soil returns mineral ions to
the environment for other organisms to use e.g. plants use
mineral ions for growth.

Question 24

What is meant by decomposition?

Answer 24

The breakdown of dead materials into

simpler organic matter

Question 25

How do decomposers break down dead matter?

Answer 25

Decomposers release enzymes which
catalyse the breakdown of dead material
into smaller molecules.

Question 26

What are the two types of

decomposition?

Answer 26

Aerobic decomposition (with oxygen)

Anaerobic decomposition (without
oxygen)

Question 27

What factors affect the rate of decomposition?

Answer 27

● Oxygen availability

● Temperature

● Water content

Question 28

Why is oxygen required for decomposition?

Answer 28

Most decomposers require oxygen for

aerobic respiration.

Question 29

How does the availability of oxygen

affect the rate of decomposition?

Answer 29

● As oxygen levels increase, the rate of
decomposition increases.

● As oxygen levels decrease, the rate of
decomposition decreases.

Question 30

Why can decomposition still occur in the absence of

oxygen?

Answer 30

Some decomposers respire anaerobically.*

*However, the rate of decomposition is slower as
anaerobic respiration produces less energy.

Question 31

How does soil water content affect the

rate of decomposition?

Answer 31

Decomposers require water to survive:

● In moist conditions the rate of decomposition is high.

● In waterlogged soils there is little oxygen for
respiration so the rate of decomposition decreases

Question 32

Why does decomposition require water?

Answer 32

Water is required for the secretion of
enzymes and absorption of dissolved
molecules

Question 33

How does temperature affect the rate of

decomposition?

Answer 33

Decomposers release enzymes:

● Rate highest at 50°C (optimum temperature for enzymes).

● Lower temperatures, enzymes work too slowly, rate decreases.

● High temperatures, enzymes denature, decomposition stops.

Question 34

How is the rate of change calculated
when considering the decay of biological
material?

Answer 34

Rate of change =
Change in value / Change in time

Where value is a measurable variable associated with
the decay of the material

Question 35

What is compost?

Answer 35

The nutrient-rich product of the rapid
decay of waste biological material (dead
plants and animal waste) in optimum
conditions set by gardeners and farmers.

Question 36

How is compost used?

Answer 36

Used as natural fertiliser to promote

growth of crops or garden plants.

Question 37

Describe how biogas generators work

Answer 37

Biogas generators provide methane gas
for fuel through anaerobic decomposition
that occurs in animal waste.

Question 38

Name 5 greenhouse gases

Answer 38

• Water vapour
• Carbon dioxide
• Nitrous oxide
• Methane
• CFCs

Question 39

Give 3 human activities that contribute to

greenhouse gases

Answer 39

• Burning fossil fuels
• Deforestation
• Large scale livestock farming

Question 40

How do greenhouse gases lead to global

warming?

Answer 40

• Greenhouse gases allow heat from the
  sun to enter the atmosphere.
• The gases act as a ‘blanket’ and trap
  the heat in the atmosphere.

Question 41

State 3 negative consequences of global warming

Answer 41

• Sea level rise caused by melting icebergs.
• Disrupted farming and agriculture.
• Increased spread of diseases in warmer
  climates