5.3/5.4 - Energy Through Ecosystems

Question 1

1. By what process to plants synthesize sugars?

Answer 1

Photosynthesis

Question 2

2. What sort of biological molecules are made from these sugars?

Answer 2

Polysaccharides, e.g. cellulose, starch, lignin
Lipids
Proteins etc

Question 3

3. State 2 examples of units which could be used to measure ‘biomass’?

Answer 3

g / m2 / month

kg / km2 / year

Question 4

4. What is a definition of gross primary production?

What does the GPP primarily depend on?

Answer 4

• The total chemical energy stored in plant biomass, in a given area/volume, in a given time
• This depends on the rate of photosynthesis

Question 5

5. List the reasons why not all the energy is transferred from:
   • Sun  producer

Answer 5

• Some of the radiation from the sun is reflected or absorbed (e.g. by clouds and dust) before it reaches the plant
• Not all the light is the right wavelength to be absorbed by chlorophyll – so some is reflected
• Some light doesn’t hit the chlorophyll molecules
• There might be another factor limiting the rate of photosynthesis (e.g. CO2 concentration)
• Photosynthesis is not 100% efficient (so some of the energy which is absorbed is not converted into biomass)

Question 6

6. What is a definition of net primary production?

Answer 6

• The chemical energy stored in plant biomass after respiratory losses to the environment

Question 7

7. What is the equation that links NPP with GPP?

Answer 7

NPP = GPP - R

Question 8

st the reasons why not all the energy is transferred from:

• Producer  herbivore (primary consumer)

Answer 8

• The herbivore doesn’t eat all of the producer
• Some parts of the producer are indigestible (so it is lost in egestion)
• Some energy is lost in excretion

Question 9

• Herbivore  Carnivore

Answer 9

• Some energy from respiration is used to allow muscle contraction and movement
• Some energy from respiration is used to maintain body temperature – so it is lost as heat (only relevant for mammals)
• Some parts of herbivores are indigestible to carnivores, so lost in egestion
• Some energy is lost in excretion

Question 10

9. What is arable farming?

Answer 10

• Growing crops such as wheat, barley, oats etc

Question 11

10. What is livestock farming?

Answer 11

• Rearing animals e.g. cows, sheep, chickens, pigs etc

Question 12

11. How do farmers reduce energy losses to non-human food chains?

Answer 12

• Use pesticides to kill pests, so less of the crop is eaten by pests, meaning yield for harvest is higher

Question 13

12. How does the use of chemical pesticides increase the productivity of crops?

Answer 13

• Kills pests which would otherwise damage/eat crops therefore the crop has to expend less energy on repairing damaged parts and more can be used for growth

Question 14

13. How do farmers reduce respiratory losses within human food chains?

Answer 14

• Restrict movement of livestock so that less energy is used for muscle contraction
• Keep animals in warmed environments so less energy is used to maintain body temperature
• Give animals antibiotics, so less energy from the animals is expended on the immune system ‘fighting’ pathogens
• Give animals concentrated food, so less of the food is indigestible, therefore less energy is lost in egestion
• Slaughter animals while young, because as animals get older they do not grow as much so the food that they eat does not lead to increased biomass

 

Question 15

Draw out the nitrogen cycle in full (including the names of all processes and microorganisms involved)

Answer 15

0

Question 16

Draw out the phosphorus cycle in full

Answer 16

0

Question 17

What is a saprobiont?

Answer 17

microorganism which secretes hydrolytic enzymes. It then absorbs the products of digestion. This is called ‘extracellular digestion’

Question 18

What is a saprobiont’s role in the nitrogen cycle?

Answer 18

Use enzymes to decompose proteins/DNA/RNA/urea

Releasing ammonia/ammonium compounds/ ions

Question 19

What is are mycorrhizae

Answer 19

Fungi which associate with the roots of plants

Question 20

How do mycorrhizae facilitate the uptake of water and ions by plants?

Answer 20

• They extend out from the roots of plants increasing the area from which ions and water can be absorbed
(remember there are enough mycorrhizae associated with the roots of just one oak tree that if you straightened them all out it would be long enough to wrap around the whole world!!!)
• They are able to grow into rocks in the soil and extract phosphates which the plants would not be able to access otherwise

Question 21

Why does the use of fertiliser increase the productivity of crops?

Answer 21

Increases the amount of nutrients available to the crops (such as nitrates which are used for forming amino acids and proteins, phosphates and potassium). So nutrient availability is no longer a limiting factor

Question 22

Natural fertilisers

Answer 22

Natural fertilisers

e.g.
manure or compost • Nutrients are released more slowly (so less likely to cause leaching)
• Have a wider range of micronutrients
• Improve the structure of the soil •

Can carry/contain pathogens or pests
• Cannot control the contents
• Bulky so difficult to store / transport / apply (requires more heavy machinery)

Question 23

Artificial fertilisers

Answer 23

Artificial fertilisers • Can control the contents exactly
• easier to store / transport / apply (because less bulky) • can lead to leaching because nutrients are released more quickly
• has fewer micronutrients

Question 24

What is leaching? And in what situations/conditions might leaching be high?

Answer 24

• When chemicals drain away through the soil (and often end up in bodies of water)
• more leaching can be caused by
o more rainfall
o too much fertiliser being applied (so it cannot all be absorbed by the plants

Question 25

Describe the process of eutrophication

Answer 25

* increase in the concentration of nitrates/phosphates in the water * causes algal bloom * this blocks the light from reaching the plants beneath the surface * the plants beneath the surface cannot photosynthesise so they die * therefore the population on aerobic saprobiotic bacteria (decomposers) increases * these bacteria respire aerobically, so there is a higher biological oxygen demand * this causes the oxygen levels in the water to drop * so aerobic organisms (such as fish and also the aerobic bacteria) die * this allows populations of anaerobic bacteria to increase * the anaerobic bacteria produce toxins which make the water putrid