Energy transfer & productivity

Question 1

Where do ecosystems get their energy?

Answer 1

• the sun is the source of energy for ecosystems
• however as little as 1% of tis light energy may be captured by green plants and so made available to organisms in the food chain
• these organisms in turn pass on only a small fraction of the energy that they receive to each successive stage in the chain

Question 2

How much energy do plants convert?

Answer 2

-between 1 and 3% of the suns energy available to them is converted into organic matter

Question 3

Why is most of the suns energy not converted to organic matter by photosynthesis?

Answer 3

• over 90% of the sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere
• not all wavelengths of light can be absorbed and used for photosynthesis
• light may not fall on a chlorophyll molecule
• a factor such as low carbon dioxide levels, may limit the rate of photosynthesis

Question 4

What is gross primary production?

Answer 4

-the total quantity of chemical energy store in plants biomass, in a given area or volume, in a given time is called the prose primary production or GPP

Question 5

What is the nets primary production?

Answer 5

• plants use 20-50% of this energy in respiration
• the chemical energy store which is left when these losses to respiration have been taken into account, is called nets primary productivity or NPP

Question 6

What is nets primary productions purpose?

Answer 6

• the nets primary production is available for plant growth and reproduction
• it is also available to other trophic levels in the ecosystem, such as consumers and decomposers
• usually less than 10% of this nets primary production in plants can be used by primary consumers for growth
• secondary and tertiary consumers are slightly more efficient, transferring p to about 20% of the energy from their prey into their own bodies

Question 7

Why is there a low percentage of energy transferred at each trophic level?

Answer 7

• some of the organism is not consumed
• some parts are consumed but cannot be digested and are therefore lost in faeces
• some of the energy is lot in excretory materials such as urine
• some energy losses occur as heat from respiration and lost to the environment
• these losses are high in mammals and birds because of their high body temperature
• much energy is needed to maintain their body temperature when heat is constantly being lost to the environment

Question 8

Why is energy transfer between trophic levels inefficient?

Answer 8

• most food chains only have four or five trophic levels because insufficient energy is available to support a large enough breeding population at trophic levels higher than these
• the total mass of organisms in a particular place is less at higher trophic levels
• the total amount of energy available is less at each level as one moved up the food chain

Question 9

How do you calculate the efficiency of energy transfers?

Answer 9

• data shows the amount of energy available at each tropic level of a food chain
• the energy available is usually measured in kilojoules per square metre per year
• it is often useful to calculate the efficiency of the energy transfers between each trophic level of these food chains

Question 10

What is the productivity and farming practices?

Answer 10

• many farming practiced are employed as methods of increasing yields by increasing the efficiency of energy transfer along the food chain
• any practice that reduces the respiratory losses in a human food chain will therefore reduce energy loss and increase yield

Question 11

How does factory farming increase the energy conservation rate?

Answer 11

• movement is restricted and so less energy is used in muscle contraction
• the environment can be kept warm in order to reduce heat loss from the body most intensively reared species are warm-blooded
• feeding can be controlled so that the animals receive the optimum amount and type of food for maximum growth with no wastage
• feeding can be controlled so that the animals relieve the optimum amount and type of food for maximum growth with no wastage
• predators are excluded so that there is no loss to other organisms in the food web
• this is about converting the smallest possible quantity of food energy into greatest quantity of animal mass

Question 12

how can we simplifying food webs to increase the efficiency of energy transfer?

Answer 12

• reducing or eliminating organisms which compete with the plant or animal being farmed
• weeds compete with crops for already limited resources such as water, mineral ions, carbon dioxide, space, and light so less is available for the crop plant
• insect pests may damage the leaves of crops, limiting their ability to photosynthesize and thus reducing their productivity
• many crops are now grown in mono-culture, and this enables insect and fungal pests to spread rapidly
• pests may cause disease so the animals may not grow rapidly, be unfit for human consumption or die
• all of which lead to reduced productivity

Question 13

What is the aim of pest control?

Answer 13

• the aim of pest control is to simplify the food web and so limit the effect of pests on productivity to a commercially acceptable level
• in other words, to balance the cost of pest control with the benefits it brings
• the problem is that at least two different interests are involved: the farmer who has to satisfy our demand for cheap food while still making a living and the conservation of natural resources, which will enable us to continue to have food in the future
• the trick is to balance the two conflicting interests