Ecosystems, Nutrient Cycles & Succession

Question 1

How can carbon be added to the atmosphere?

Answer 1

1. Combustion
2. Respiration
3. From the sea

Question 2

How can carbon be removed from the atmosphere?

Answer 2

1. Photosynthesis
2. Dissolve into the sea

Question 3

Where is carbon found?

Answer 3

1. The atmosphere
2. Plants
3. Animals
4. Fossil fuels
5. Decomposers
6. The sea

Question 4

How does atmospheric carbon dioxide vary during the day?

Answer 4

Lowest in the day

Highest at night

Question 5

How does atmospheric carbon dioxide vary during the year?

Answer 5

Lowest in the summer

Highest in the winter

Question 6

What is global warming?

Answer 6

Increase in the average global temperature

Caused by the greenhouse effect

Question 7

How could global warming impact on crop yield?

Answer 7

Increase in carbon dioxide/temperature

⇒ Increase in rate of photosynthesis

⇒ Increased crop yield

Question 8

How might global warming affect pest species?

Answer 8

Might affect the life cycle of the pest species (e.g. shorter larval stage)

Could affect abundance/distribution of species

Question 9

How might global warming affect wild plants/animals?

Answer 9

Could affect the distribution/abundance of species

Question 10

What are the stages of the nitrogen cycle?

Answer 10

Nitrification

Denitrification

Nitrogen fixation

Ammonification

Absorption

Consumption

Death/excretion

Question 11

What is nitrogen fixing?

Answer 11

Nitrogen fixing bacteria convert nitrogen in the air into ammonium

Bacteria found in root nodules of leguminous plants and form mutualistic relationships

Question 12

What is nitrification?

Answer 12

Ammonium compounds are oxidised by nitrifying bacteria to nitrate ions

Question 13

What is ammonification?

Answer 13

Saprobiotic microorganisms convert dead organic matter and animal waste into ammonium compounds

Question 14

What is denitrification?

Answer 14

Occurs in anaerobic conditions, denitrifying bacteria use nitrate ions for respiration and release nitrogen

Question 15

What is the cause of eutrophication?

Answer 15

Nitrates in the soil leech into rivers

Question 16

Why are organic fertilisers less likely to cause eutrophication than artificial fertilisers?

Answer 16

Insoluble so less likely to leech

Needs to be broken down

Question 17

What is process of eutrophication?

Answer 17

1. Nitrates cause an algal bloom
2. This blocks out the light, plants can’t photosynthesise
3. Plants die and are broken down by saprobiotic bacteria
4. These bacteria respire aerobically, using oxygen
5. Aquatic animals die due to lack of oxygen
6. Anaerobic bacteria decompose the dead organisms making the water putrid

Question 18

What do fertilisers do?

Answer 18

Increase productivity

Question 19

How do fertilisers increase productivity?

Answer 19

Contain nitrogen in the form of nitrates:

1. Nitrogen present in DNA & proteins
2. Nitrogen increase height and leaf height

Question 20

Why is energy lost within a food chain/web?

Answer 20

Producers:

• Some of the Sun’s energy is absorbed/reflected by the atmosphere
• Not all wavelengths of light can be used in photosynthesis
• Not all the light falls on the chlorophyll/photosynthesising cells

Consumers:

• Some parts of the organism aren’t eaten
• Some parts cannot be digested
• Energy is lost by excretion (e.g. in urine/faeces)

Both:

• Energy is lost as heat due to respiration

Question 21

Answer 21

Question 22

Answer 22

Question 23

What are the three types of ecological pyramid and what are the associated units?

Answer 23

1. Pyramids of number: no units
2. Pyramids of biomass: kgm^-2 or kgm^-3
3. Pyramids of energy: kJm^-2year^-1 or kJm^-3year^-1

Question 24

What are the drawbacks of pyramids of number?

Answer 24

1. Size not taken into account
   
   • 1 large organism = 1 small organism
2. Impossible to represent accurately when there are large differences in numbers
3. Only considers one point in time

Question 25

What are the drawbacks of pyramids of biomass?

Answer 25

1. Organisms must be killed so samples are small * May not be representative 2. Different tissues contain different amounts of energy 3. Only considers one point in time

Question 26

What is the role of an agricultural ecosystem?

Answer 26

To produce food for humans, limiting the amount of energy lost between trophic levels

Question 27

What is a pest?

Answer 27

An organism which competes with humans for food or space or is a danger to health

Question 28

How are pest species controlled?

Answer 28

* Chemical pesticides * Biological controls

Question 29

What are the advantages of using biological controls?

Answer 29

1. Only requires one application because the organisms will reproduce 2. They are very specific 3. Maintains a low population of the pest 4. Pests do not develop resistance 5. No bioaccumulation (uses less chemicals)

Question 30

What are the advantages of using chemical pesticides?

Answer 30

1. Acts quickly 2. Can apply to a specific area (where it is required) 3. Kills most of pests (and a greater variety)

Question 31

What is an integrated system?

Answer 31

A combination of biological controls and chemical pesticides aimed at having the minimum impact on the environment

Question 32

In intensive rearing of livestock, how is net productivity maximised?

Answer 32

1. Restrict movement so less energy is lost due to muscle contraction 2. Keep in warm sheds to reduce heat losses 3. Fed concentrate so a higher proportion of the food is absorbed 4. Selectively bred for higher productivity 5. Slaughtered while still young so more energy transferred to biomass

Question 33

Describe the process of succession

Answer 33

1. Pioneer species colonise barren land 2. These species die and make the area less hostile 3. New species colonise and outcompete the pioneer species 4. This continues until a **climax community** is reached

Question 34

What are the adaptations of pioneer species?

Answer 34

1. Wind-borne species 2. Germinate quickly 3. Can photosynthesise 4. Withstand extreme conditions 5. Method of nitrogen fixation

Question 35

What is the purpose of conservation?

Answer 35

1. Maintain diversity 2. Maintain an ecosystem/habitat

Question 36

Why is conservation important?

Answer 36

1. Many species provide us with resources (e.g. drugs) 2. Ethical debates: species do not go extinct due to human activity 3. Help prevent climate change 4. Help prevent food chain disruption