Energy and Ecosystems (Chapter 13)

Question 1

Describe Nitrogen Fixation

Answer 1

N2 gas in the air fixed by Nitrogen Fixing Bacteria (free-living or mutualistic) converted to ammonia then ammonium ions.

Question 2

Describe Nitrification

Answer 2

Nitrifying bacteria convert ammonium ions to nitrite then nitrate in an oxidation reaction. Taken in by plants through roots and used to make proteins, DNA etc.

Question 3

Describe Ammonification

Answer 3

Saprobionts break down proteins in dead plants and animals to amino acids and then ammonia. They release enzymes for extracellular digestion to break down proteins and absorb nutrients by diffusion. This is called saprobiotic nutrients.

Question 4

Describe Denitrification

Answer 4

Anaerobic denitrifying bacteria convert nitrate to N2 gas.

Question 5

What is the use of ploughing?

Answer 5

Increases oxygen in soil as nitrifying, saprophytic, and nitrogen-fixing bacteria use O2.

Question 6

What are Mycorrhizae?

Answer 6

Fungi which help a plant to take up water and inorganic ions through the roots of a plant and the mycorrhizae receive amino acids from the plant in return (mutualistic relationship).

Question 7

What do fertilisers do (nitrogen example)?

Answer 7

Increase nutrients in soil e.g. nitrates > more protein made > more growth > biggger leaves > more photosynthesis.

Question 8

What are natural fertilisers and pros and cons?

Answer 8

Made of dead and decaying plants and animals or waste e.g. manure, slurry, bone meal.

Cheaper, less soluble so less leaching but smell bad.

Question 9

What are artificial fertilisers and pros and cons?

Answer 9

Mind from rock deposits and converted to different forms and blended for different balances for different plants.

More concentrated so less needed but expensive and more soluble.

Question 10

Describe Leaching

Answer 10

Nutrients removed from soil by being dissolved into water and washed into rivers and can lead to eutrophication.

Question 11

Describe the process of Eutrophication

Answer 11

1) Increase in nitrate causes ‘algal bloom’.
2) Algae blocks light so lower plants die.
3) Saprophytes break down dead plant material.
4) Saprophytes use up oxygen in respiration.
5) Fish die due to a lack of oxygen.

Question 12

Why isn’t most of the sun’s energy made into organic matter?

Answer 12

• Light reflected
• Wrong wavelength
• Light misses chlorophyll molecule
• Respiration of producer

Question 13

Why are pyramids of energy always pyramid shape?

Answer 13

Energy is lost between each trophic level in respiration/heat/excretory substances, movement

Question 14

What is energy flow measured in for pyramids of energy?

Answer 14

kJm^-2

Question 15

How is net productivity calculated?

Answer 15

net productivity = gross productivity - respiratory losses

Question 16

What is net productivity affected by?

Answer 16

Area of ground covered by leaves and inefficiency of the crop at carrying out photosynthesis.

Question 17

How is energy transfer (% efficiency calculated)?

Answer 17

(Energy available after transfer/Energy available before transfer) X 100

Question 18

Define biomass

Answer 18

The total mass of living material in a specific area at a given time.

Question 19

What is biomass measured in?

Answer 19

mass of carbon or dry mass of tissue per given area per given time

Question 20

How is the problem of varying water in a sample of biomass overcome?

Answer 20

Using dry biomass (organism must be killed) by recording mass and reheating until a constant mass has been reached.

Question 21

What is the aim of agricultural ecosystems?

Answer 21

Aim to improve productivity.

Question 22

What are the problems with pyramids of numbers?

Answer 22

• Doesn’t account for size of organism
• Hard to show on a scale
• Doesn’t account for seasonal differences.

Question 23

Why does lowering the temperature affect the conversion of food to biomass?

Answer 23

Lose more heat/more respiration/more heat used in respiration.

Question 24

What methods are used to improve productivity?

Answer 24

• Adding fertilisers
• Using pesticides
• Using greenhouses/irrigation systems
• Ploughing - improves drainage and increases oxygen for saprophytes in N cycle
• Covering crops with nets (protects from birds)
• Intensive farming
• Selective breeding

Question 25

How is chemical energy storage estimated?

Answer 25

Calorimetry

Question 26

What is intensive farming and how is it maximised?

Answer 26

Aims to convert the smallest amounts of food into the most animal mass.

• Restricted movement of animals (less energy for muscle contraction)
• Kept warm (less heat loss form animal)
• No predators (No food lost to food chain)
• Feeding controlled (the optimum amount of food and type for growth)

Question 27

Define biomass

Answer 27

The total mass of living materials.