Energy And Ecosystems

Question 0

Give an example of a food chain

Answer 0

Grass –> caterpillar –> toad –> grass snake –> stoat

Question 1

Define food chain

Answer 1

Description of a feeding relationship and showing direction of energy transfer

Question 2

Why is most of the sun’s energy not converted to organic matter by photosynthesis?

Answer 2

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 3

What is the gross production?

Answer 3

The total quantity of energy that the plants in a community convert to organic matter

Question 4

What is the net production?

Answer 4

The rate at which the plants store energy

Question 5

What is the equation for net production?

Answer 5

Net production= gross production - respiratory losses

Question 6

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

Answer 6

Some of the organism is not eaten
Some parts are eaten but cannot be digested and are therefore lost in faeces
Some of the energy is lost in excretory materials such as urine
Some energy losses occur as heat from respiration and directly from the body to the environment (high in mammals)

Question 7

The inefficiency of the energy transfer between trophic levels explains why…

Answer 7

Most food chains have only 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 (biomass) is less at higher trophic levels

The total amount of energy stored is less at each level as one moves up a food chain.

Question 8

What is the amount of energy available at a trophic level in a food chain measured in?

Answer 8

kJ m^-2 year^-1

Question 9

What is the equation for energy transfer between trophic levels?

Answer 9

Energy transfer= energy available after the transfer/ energy available before the transfer x100

Question 10

What are the drawbacks of using a number pyramid to describe a food chain?

Answer 10

No account is taken of size - one giant tree is treated the same as one tiny aphid. This means that sometimes the pyramid is not a pyramid at all or it is inverted.

The number of individuals can be so great that it is impossible represent them accurately on the same scale as other species in the food chain.

Question 11

Define biomass

Answer 11

Biomass is the total mass of the plants and/or animals in a particular place

Question 12

What is biomass measured in?

Answer 12

g m^-3

Question 13

What are the drawbacks of pyramids or numbers and biomass?

Answer 13

Only the organisms present at a particular time are shown so seasonal differences are not made apparent

Question 14

Which is the most accurate representation of the energy flow through a food chain?

Answer 14

Pyramid of energy

Question 15

Why are the results for energy much more reliable than for pyramids of biomass?

Answer 15

Two organisms of the same dry mass may store different amounts of energy.

Question 16

What is the unit used in energy pyramids?

Answer 16

kJ m^-2 year^-1

Question 17

Net productivity is important in agricultural ecosystems and is effected by two main factors:

Answer 17

The efficiency of the crop at carrying out photosynthesis. This is improved if all necessary conditions for photosynthesis are supplied.

The area of the ground covered by the leaves of the crop

Question 18

Define pest

Answer 18

An organism which competes with humans for food space, or is a danger to health

Question 19

Give two disadvantages of biological control

Answer 19

They do not act as quickly, so there is often some interval of time between introducing the control organism and a significant reduction in the pest population

A control organism may itself become a pest

Question 20

Give three comparisons between biological control and chemical pesticides

Answer 20

Biological control is very specific whereas chemical pesticides have some effect on non-target species

Once introduced biological control organisms reproduces itself whereas chemical pesticides must be reapplied and they are expensive

The pests do not become resistant to their predators but can become resistant to chemical pesticides so new ones have to be developed

Question 21

Give a few examples of what integrated control systems do

Answer 21

Choosing pest resistant animal or plant varieties

Hand picking pests out of an environment

Providing suitable habitats for natural predators of pests

Using pesticides and biological agents if necessary

Question 22

Intensive rearing involves keeping animals in confined places. Why?

Answer 22

Their event 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

Feeding can be controlled so that the animals receive 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

Question 23

Name two other means, other than intensive rearing, with increase the energy-conversion rate in domesticated animals.

Answer 23

Selective breeding of animals to produce varieties that are more efficient at converting the food they eat into body mass

Using hormones to increase growth rates