Energy Transfer

Question 1

Definition of trophic level

Answer 1

The position an organism occurs within an energy transfer

Question 2

Producers

Answer 2

Auto trophic- build up organic compounds (DNA/polypeptides) from simple molecules (glucose/nitrates) needed for growth

Question 3

Consumers

Answer 3

Heterotrophic- rely on an external source of organic compounds i.e. they have to take in organic compounds

Question 4

Saprobionts/Decomposers

Answer 4

Heterotrophic- break down complex organic compounds in dead organisms (fungi/bacteria)

Question 5

How many trophic levels are in a food chain?

Answer 5

• No more than 4/5
• energy lost at each trophic level = inefficient
• so not enough energy to support breeding population at higher trophic level

Question 6

Food webs

Answer 6

• food chains do not occur in isolation
• in habitats, many food chains linked together to form a food web

Question 7

Effect of complex food webs

Answer 7

• higher diversity
• more complex food web interactions
• closer to climax community
• any one change within web will have less effect on individual species

Question 8

Definition of biomass

Answer 8

total mass of organic material (carbon) in a specific area at a given time

Question 9

Fresh mass

Answer 9

• living
• easy to assess
• variable H2O content
• unreliable
• variable food indigested
  (wet)

Question 10

Dry mass

Answer 10

• dead
• difficult to assess
• small sample size
• unreliable
• situational
  (mass of carbon)

Question 11

Calculating energy stored in biomass

Answer 11

• bomb calorimeter
• chemical energy in biomass estimated using calorimetry
• sample of dry biomass combusted with a sealed chamber
• chamber surrounded by water bath, heat energy released causes temperature rise in water

Question 12

Bomb calorimetry features

Answer 12

Stirrer= distributes heat energy
water= high specific heat capacity
air= insoluble, reduces heat loss

Question 13

Respirometer Question
The student found that the coloured liquid moved 1.5 cm in 24 hours. The diameter of the lumen (hole) of the capillary tubing was 1 mm.

The volume of a capillary tubing is given by πr2l, where π is 3.14 and l = length.

Calculate the volume of gas produced in cm3 hour–1.

Answer = ____________________ cm3 hour–1

Answer 13

1. Correct answer in range of

4.9 × 10–4 to 4.91 × 10–4 = 2 marks;;

Accept any equivalent mathematical representation of this answer

2. Incorrect but shows division by 24 = 1 mark

OR

1175 to 1178 = 1 mark;

OR

49 = 1 mark;

Question 14

Suggest what you should do to ensure all water is removed from a tissue / sample.

Answer 14

Regularly weigh and Heat (less than 100 °C)
Until mass is constant

Question 15

Advantage of using dry mass not fresh to compare yield

Answer 15

• water content present will vary in fresh mass
• this issue will not affect dry

Question 16

Energy losses from the sun to the producer

Answer 16

1. some light energy is reflected
2. some light energy absorbed by gases/ water vapour in atmosphere
3. some light energy is the wrong wavelength
4. some light energy does not strike chlorophyll

Question 17

Define Gross Primary Productivity

Answer 17

Chemical energy store in plant biomass, in a given area or volume. (Rate of photosynthesis)

Question 18

Define Net Primary Production

Answer 18

• Chemical energy store in plant biomass after respiratory losses to the environment have been taken into account.
• NPP is available for new plant growth and reproduction
• kJ km–2 year–1

Question 19

NPP equation

Answer 19

NPP= GPP - R
(R= respiratory losses)

Question 20

Energy losses from the producer to the primary consumer

Answer 20

1. large amounts of plant may be indigestible
2. not all of the plant may be eaten (roots)
3. some energy lost in excretion such as energy lost in urine
4. energy lost in respiration and as heat to the environment

Question 21

Energy losses from the primary consumer to the secondary consumer

Answer 21

1. large amounts of animal may be indigestible
2. not all of animal may be eaten (bones)
3. some energy lost in excretion such as energy lost in urine
4. energy lost in respiration and as heat lost to the environment

Question 22

Net production of consumer equation

Answer 22

N = I - ( F + R )
N=net production
I=chemical energy store of ingested food
F=energy lost in faeces/urine
R=energy lost in respiration

Question 23

Calculating efficiency of energy transfer

Answer 23

% efficiency = energy available after transfer/energy available before x100

Question 24

Calculations up/down trophic levels

Answer 24

producer -> consumer
[energy x %/100 x %/100]

Question 25

Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer.

Answer 25

• Some light energy fails to strike/is reflected/not
• Efficiency of photosynthesis in plants is low
• Loss as heat
• Efficiency of transfer to consumers greater than transfer to producers
• Efficiency lower in older animals
• Carnivores use more of their food than herbivores

Question 26

Domestic livestock ethics

Answer 26

barn hens- closely packed together, increased chance of parasites being transmitted
-restricted movement, growth occurs at faster rate than natural
-antibiotic resistance, linked to intensive agriculture

Question 27

Explain how the intensive rearing of domestic livestock increases net productivity

Answer 27

• Slaughtered when still growing
• Fed on controlled diet
• Movement restricted so less respiratory loss
• heating so less heat loss

Question 28

You are given samples of water from three different rivers.

Describe how you would obtain a quantitative measurement of their cloudiness.

Answer 28

• Use of colorimeter;
• Measure the absorbance
• Example of how method can be standardised eg same volume of water, zeroing colorimeter, same wavelength of light

Question 29

The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur

Answer 29

• High concentration of carbon dioxide linked with darkness;
• No photosynthesis in dark
• In dark plants respire;
• In light net uptake of carbon dioxide by plants
• Decrease in carbon dioxide concentration with height;
• At ground level fewer leaves