Organisation of an ecosystem

Question 1

Define habitat

Answer 1

The place in which an organism lives.

Question 2

Define population

Answer 2

A species that occupy the same habitat.

Question 3

What do food chains show?

Answer 3

Food chains show the feeding relationships of different organisms and the flow of energy between the organisms.

Question 4

Define biomass

Answer 4

The total dry mass of living material/organisms in an area.

Question 5

Define community

Answer 5

Populations of different species interacting in a habitat.

Question 6

What are trophic levels?

Answer 6

The stages in a food chain.

Question 7

What do arrows in a food chain represent?

Answer 7

The direction of biomass transfer.

Question 8

Describe a simple food chain

Answer 8

Producer - Primary consumer - Secondary consumer - Tertiary consumer

Question 9

What is a producer?

Answer 9

An organism which makes its own food.

Question 10

What types of organisms are primary producers?

Answer 10

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

Question 11

What is a primary consumer?

Answer 11

An organism that feeds on producers.

Question 12

What is a secondary consumer?

Answer 12

An organism which feeds on primary consumers.

Question 13

What is a tertiary consumer?

Answer 13

An organism that feeds on secondary consumers.

Question 14

What is a predator?

Answer 14

A consumer that kills and eats other animals.

Question 15

What is prey?

Answer 15

An animal that is killed and eaten by another animal.

Question 16

Describe the pattern of predators and prey in a stable community

Answer 16

The numbers of predators and prey rise and fall in cycles.

Question 17

Why are producers the first trophic level?

Answer 17

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

Question 18

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

Answer 18

Quadrat.

Question 19

What piece of apparatus is used to study the distribution of organisms across a gradient?

Answer 19

Belt transect.

Question 20

When considering the abundance of organisms, what is meant by ‘mean’?

Answer 20

The average number of organisms.

Question 21

How is the arithmetic mean calculated?

Answer 21

Sum of each number of each organism / total number of each type of organism

Question 22

When considering the abundance of different organisms, what is meant by ‘mode’?

Answer 22

The most populous organism.

Question 23

When considering the abundance of organisms, what is meant by the term ‘median’?

Answer 23

The organism that represents the middle value when the numbers of each organism are arranged from lowest to highest.

Question 24

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

Answer 24

• Organisms take in elements from their surroundings such as from the soil and air.
• Elements converted to complex molecules which become biomass.
• Elements transferred along a food chain.
• Elements returned to environment during excretion and decomposition of dead organisms.

Question 25

Give 3 molecules which are cycle through ecosystems

Answer 25

• Oxygen.
• Carbon dioxide.
• Water.

Question 26

Describe the carbon cycle

Answer 26

• 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.
• Carbon dioxide is released from respiration of decomposers that break down dead organisms.
• Dead organisms that are not broken down turn into fossils over millions of years, which can be burnt for fuel releasing carbon dioxide into the atmosphere.

Question 27

Why is the carbon cycle important?

Answer 27

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

Question 28

Describe the water cycle

Answer 28

• Water from lakes and oceans evaporate.
• 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 29

Why is the water cycle important?

Answer 29

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

Question 30

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

Answer 30

Microorganisms such as 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 (using mineral ions for growth).

Question 31

What is meant by decomposition?

Answer 31

The breakdown of dead materials into simple organic matter.

Question 32

How do decomposers break down dead matter?

Answer 32

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

Question 33

What are the 2 types of decomposition?

Answer 33

• Aerobic decomposition (with oxygen).

- Anaerobic decomposition (without oxygen).

Question 34

What factors affect the rate of decomposition?

Answer 34

• Oxygen availability.
• Temperature.
• Water content.

Question 35

Why is oxygen required for decomposition?

Answer 35

Most decomposers require oxygen for aerobic respiration.

Question 36

How does the availability of oxygen affect the rate of decomposition?

Answer 36

• As oxygen levels increase, the rate of decomposition increases.
• As oxygen levels decrease, the rate of decomposition decreases.

Question 37

Why can decomposition still occur the absence of oxygen?

Answer 37

Some decomposers respire anaerobically.

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

Question 38

How does soil water content affect the rate of decomposition?

Answer 38

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 39

Why does decomposition require water?

Answer 39

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

Question 40

How does temperature affect the rate of decomposition?

Answer 40

Decomposers release enzymes:

• Rate highest at 50°C (optimum temperature for enzymes).
• Lower temperatures, enzymes work too slow, rate decreases.
• High temperatures, enzymes denature decomposition stops.

Question 41

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

Answer 41

Rate of change = Change in value / change in time

Question 42

What is compost and manure?

Answer 42

Compost is decayed organic matter from dead plants and is nutrient-rich.
Manure is animal waste and is nutrient-rich.

Question 43

How is compost used?

Answer 43

Used as natural fertiliser to promote growth of crops or garden plants.

Question 44

Describe how biogas generators work

Answer 44

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