B4 Ecosystems

Question 1

Define Ecosystem.

Answer 1

All the living organisms and physical conditions in the area.

Question 2

Define Community.

Answer 2

All of the organisms in the ecosystem.

Question 3

Define Habitat

Answer 3

Area where an organism lives

Question 4

Define Consumers.

Answer 4

Organisms that eat others to gain energy.

Question 5

Define Decomposers.

Answer 5

A special group of consumers that feed on dead or decaying material.

Question 6

Define Population.

Answer 6

Total number of organisms of each species.

Question 7

Define Producers.

Answer 7

Organisms that make their own food by photosynthesis.

Question 8

Define the term ‘interdependence’.

Answer 8

Interdependence relates to living things that rely upon each other to survive.

Question 9

State four abiotic factors that affect communities.

Answer 9

• Moisture levels – water is required by all living things.
• Temperature – affects the rate of chemical reactions in organisms.
• Light intensity – necessary for photosynthesis. Change in light over seasons can affect flowering of certain plants too.
• Soil type – level of nutrients and ability to hold water, pH.
• Gas levels – humidity and temperature can affect the amount of oxygen in the air.
• Fire – can be devastating for some organisms, but necessary for others (e.g. Australian plants/Scotish gorse/Heathland control).

Question 10

State four biotic factors that affect communities.

Answer 10

• Number of predators
• Food availability
• Disease
• Human activity

Question 11

What are the three types of interdependence?

Answer 11

• Predation
• Mutualism
• Parasitism

Question 12

Define commensalism.

Answer 12

When one organism benefits from another organism, which is unaffected.

Question 13

Define competition.

Answer 13

When two organisms fight over a resource. Can occur between different species, or within the same species or family.

Question 14

What is parasitism?

Answer 14

• When one organism lives on or in another organism and takes nutrients from (feeds off) the other organism.
• This is benficial to the parasite but detrimental to the host.

Question 15

Wht is mutualism?

Answer 15

• When two organisms living closely together both benefit from each other.
• Two organisms that depend on each other

Question 16

Give four things animals compete for.

Answer 16

1. Mates
2. Space
3. Food
4. Water

Question 17

Give four things plants compete for.

Answer 17

1. Light
2. Water
3. Minerals
4. Space

Question 18

What is a primary consumer?

Answer 18

An organism that feeds on producers.

Question 19

What is a secondary consumer?

Answer 19

An organism that feeds on primary consumers.

Question 20

What is biomass?

Answer 20

The dry mass of all of the living organisms in an area.

Question 21

Why is dry mass used for biomass?

Answer 21

Because the wet mass varies as the amount of water in the organism varies.

Question 22

How do you calculate the efficiency of biomass transfer?

Answer 22

Eefficiency = (energy transferred / total energy available) x 100

Question 23

Why are biomass transfers not 100% efficient?

Answer 23

Energy is lost through:

• Egestion (removal of faeces)
• Excretion (removal of urine)
• Respiration
• Inedible bones / hair / shells / teeth / spines

Question 24

How does the efficiency of biomas transfers affect the number of levels in a biomass pyramid.

Answer 24

The less efficient the transfers, the lower the number of trophic levels and the fewer organisms in higher trophic levels.

Question 25

Name three molecules which are cycle through ecosystems.

Answer 25

1. Oxygen
2. Carbon dioxide
3. Water

Question 26

Describe how water is cycled through an ecosystem.

Answer 26

• Water evaporates from rivers and lakes and from transpiration
• Water condenses as clouds
• Water is returned through precipitation

Question 27

Describe how carbon is cycled through an ecosystem.

Answer 27

1. Carbon dioxide is fixed through photosynthesis
2. Respiration releases carbon dioxide
3. Decomposition releases carbon dioxide
4. Combustion releases carbon dioxide

Question 28

Describe how nitrogen is cycled through an ecosystem.

Answer 28

1. Nitrogen is fixed by lightening and nitrogen-fixing bacteria
2. Denitrifying bacteria release nitrites in soil into nirtogen in the air.
3. Denitrifying bacteria covert nitrates in soil into nitrites, and nitrites to ammonia.
4. Nitrifying bacteria convert ammonia in soil into nitrites, and nitrites to nitrates.
5. Nitrates in soil taken up by plants and combined with carbohydrates to make plant proteins.
6. Plant proteins either eaten by other animals to form animal protien or die and decompose to release ammonia into soil.
7. Animals excrete ammonia and die and decompose to release ammonia into soil.

Question 29

Why is recycling in ecosystems necessary?

Answer 29

• To create a continuous flow of nutrients
• To provide fresh water

Question 30

How would a descrease in oxygen availabilty affect the rate of decomposition?

Answer 30

• Lack of oxygen causes micro-organisms to respire anaerobically
• Anaerobic decay is slower that aerobic decay.

Question 31

How would a descrease in water availabilty affect the rate of decomposition?

Answer 31

• Decomposing microorganisms need water for chemical processes
• Te less water available, the slower the rate of these processes

Question 32

How would a change in temperature affect the rate of decomposition?

Answer 32

• A decrease in temperature slows the rate of decomposition reactions
• A large increase in temperature would denaute enzymes, slowing or even stopping decomposition

Question 33

What is the difference between a decomposer and a detritivore?

Answer 33

• Decomposers are microorganisms that breakdown dead organic matter (DOM) and organic waste upon a microscopic level
• Decomposers use external digestion to break DOM down.
• Detritivores are small animals that speed up decompositio by shredding DOM into very small pieces creating a larger surface area for decomposers to work upon.
• Detritivores use external digestion to break DOM down.