5.3 - Energy and ecosystems

Question 1

Large areas of land have to be used to grow the plants to make biofuels. Ecologists have suggested that changes in land use could lead to a decrease in biodiversity. Suggest how changes in land use could lead to a decrease in biodiversity. (2)

Answer 1

• Removes species / fewer species / growth of single crop / single plant species / monoculture
• Removes habitats / fewer habitats / niches / only one habitat
• Removes variety of food sources / fewer food sources / only one food source

Question 2

In the investigation, the scientists used pigs of the same breed, with similar genotypes. Explain why. (2)

Answer 2

• Same breed so similar alleles
  ‘accept different alleles have different effects’
• Controls / removes variable / so genes not a factor / only temperature affects results / rate of growth affected by genes

Question 3

Define the term ‘trophic leveL’ as used in ecology. (2)

Answer 3

• A step in a food chain / food web
• Based on the feeding behaviour of an organism
  (Examples including producers, consumers)

Question 4

Livestock farmers can use the following methods to increase meat yields:
- Heated indoor sheds to rear livestock
- Use of artificial feed, bought commercially
Evaluate the use of these methods to allow farmers to manipulate energy transfers to their advantage when growing food for the meat industry. (6)

Answer 4

Advantages of heated sheds:
- Less respiratory loss of energy as heat
- Less movement of animals so more energy can be transferred to biomass
- Less risk of livestock loss to predators

Disadvantages of heated sheds:
- Expensive to build/heat
- Lack of movement leads to lack of muscle condition and inferior meat quality

Advantages of artificial feed:
- Regular input of the correct nutrients
- Feed can promote muscle growth

Disadvantages of artificial feed:
- Expensive (versus grazing)
- Livestock cannot be left unattended e.g. when grazing in fields
- Creates hazardous effluent which has to be treated

Question 5

Only around 1% of the light energy that reaches the Earth’s atmosphere is captured by plants and made available to other organisms in the food chain. Suggest reasons for this low value. (4)

Answer 5

• Energy is reflected back into space by clouds and atmospheric dust
• Energy is absorbed by the atmosphere
• Only certain wavelengths (of light) are absorbed during photosynthesis
• Light may fall away from a plant so can’t be absorbed
• Other factors such as low temperature may limit the rate of photosynthesis

Question 6

A typical oak tree has a mass of 15,000 kg and can be assumed to be 50% dry mass. Explain why the energy content of its biomass, measured in a calorimeter, can only be an estimate. (2)

Answer 6

• Different organs have different energy contents
• Difficult to quantify the energy content of a large organism from a small calorimeter sample
• Not all the biomass will combust fully in the calorimete
• Not all the energy given out as heat will be transferred to the water

Question 7

Methane is produced by microorganisms in the soil. The scientists found that rice fields that are flooded produce larger volumes of methane than rice dry fields. Suggest why. (2)

Answer 7

• Dry fields allow aerobic soil conditions / more oxygen to penetrate the soil / flooded fields promote anaerobic conditions / less oxygen
• Flooded fields have more active anaerobic microorganisms / respiration / unflooded fields have more active aerobic microorganisms / respiration

Question 8

Define the term biomass. (1)

Answer 8

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

Question 9

Biomass is usually measured using dry biomass. State why dry biomass is a more accurate measurement than wet biomass. (2)

Answer 9

• Organisms contain different amounts of water in their tissues
• (Dry biomass) enables comparisons to be made between different organisms / eliminates the differences between organisms that are due to tissue water content

Question 10

Describe how an organism’s dry biomass would be calculated. (2)

Answer 10

• Removing water (from a specimen) by heating / drying out in an oven at a low temperature to avoid burning
• Until the mass (of the specimen) stops decreasing / remains constant

Question 11

Define the term gross primary production. (1)

Answer 11

• The chemical energy store / light energy converted to chemical energy in plant biomass in a given area (or a given volume in an aquatic system)

Question 12

The process of converting solar energy into GPP is not 100% efficient. Suggest one reason why this might be the case. (1)

Answer 12

• Not all wavelengths of light are absorbed / some light reflects off leaves
• Some light passes through leaves
• Not all light falls on photosynthesising parts of the plant / not all light falls on the chloroplasts
• Another limiting factor (e.g. carbon dioxide) may limit the rate of photosynthesis

Question 13

It was suggested to the farmer that efficiency could be improved by keeping the cows inside a shed rather than letting them roam in the fields. Explain how keeping the cows inside a shed might improve the efficiency of cattle farming. (2)

Answer 13

• It reduces respiratory loss / increases the amount of energy stored in cow biomass
• It will be warmer inside a shed, so less energy will be lost in the form of heat
• The cows will move around less inside a shed so less energy will be required for movement
• Cows inside a shed can be fed special feed that reduces energy egested in waste/faeces / contains antibiotics that reduce energy used to fight off infection