Energy Transfer Through An Ecosystem

Question 1

Explain the process of energy transfers through ecosystems

Answer 1

1. The main route by which energy enters an ecosystem is photosynthesis
2. During photosynthesis plants convert sunlight energy into a form that can be used by other organisms (producers). They store energy as biomass, which is the mass of living material
3. After producers store sunlight energy as biomass, it is transferred along the food chain through biomass transfers
4. Energy is transferred through living organisms of an ecosystem when organisms eat other organisms. Producers are eaten by primary consumers, and primary consumers are eaten by secondary consumers etc
5. So food chains and food webs show how energy is transferred through an ecosystem, with food chains showing simple lines of transfer, and food webs showing lots of food chains and how they overlap
6. Energy trapped in the things that can’t be eaten e.g bones, faeces, gets recycled back into the ecosystem by decomposers

Question 2

Explain why not all energy gets transferred to the next trophic level of the food chain

Answer 2

-(around 90% of the energy is lost in various ways)

Some of the available energy is never taken in by the organisms in the first place:

• plants can’t use all the light energy that reaches their leaves e.g some is the wrong wavelength, some is reflected, some passes straight through the leaves
• some sunlight can’t be used because it hits part of the plant that can’t photosynthesis e.g bark of a tree
• some parts of food e.g roots or bones aren’t eaten by organisms so the energy isn’t taken in, it passes to decomposers
• some parts of food are indigestible so pass through organisms and come out of waste e.g faeces, so is passed to decomposers

The rest of the available energy is taken in (known as the gross productivity), but not all of this is available to the next trophic level either:

• 30% of the total energy available is lost to the environment when organisms use energy produced from respiration for movement or body heat = respiratory loss
• 10% of the total energy available becomes biomass- this is called the net productivity

Net productivity is the amount of energy that’s available to the next trophic level. The flow of energy transfer continues at the next trophic level, the process starts again from the beginning

Question 3

How is net productivity calculated?

Answer 3

net productivity = gross productivity - respiratory loss

Question 4

Explain some of the farming methods that can increase crop productivity by increasing the transfer of energy through an ecosystem

Answer 4

1. herbicides kill weeds that compete with agriculture crops for energy, allowing for the crops to receive more energy to grow faster and bigger
2. fungicides kill fungal infections that damage agricultural crops, so they use more energy for growth and less for fighting infection, growing faster and bigger
3. insecticides kill insect pests that eat and damage crops, so less biomass is lost from crops so they grow larger
4. fertilisers are chemicals that provide crops with minerals needed for growth, as they replace lost minerals allowing more energy from the ecosystem to be used to grow

Question 5

Explain some of the ways animal productivity can increase by increasing the transfer of energy

Answer 5

1. animals may be kept in warm, indoor pens where there movement is restricted, so less energy is wasted keeping warm and moving around
2. animals may be given feed that’s higher in energy than their natural food, increasing energy input so more energy is available for growth

Question 6

What is the advantage and disadvantage to enhancing productivity

Answer 6

Advantage:
-more food can be produced in a shorter space of time, often at lower costs

Disadvantage:
-ethical issues- the conditions that the intensively reared animals are kept in could cause pain, distress, or restricts natural behaviour