IV: 1, 2 - Energy flow, food chains and food webs

Question 1

What is the principal source of energy input to biological systems?

Answer 1

The Sun provides energy in two main forms: light and heat

Question 2

Describe the non-cyclical nature of energy flow

Answer 2

• Energy flow is not a cycle; it starts from the sun and then that energy is harnessed by plants which are eaten by animals which are eaten by other animals.
• At each step, energy is lost to the environment.

Question 3

Define

ecology

Answer 3

The study of inter-relationships in and between living and non-living factors in an ecosystem

Question 4

What are abiotic and biotic factors?

Answer 4

Abiotic factor: non-living factor in the environment, e.g. air, water, soil, light, climate

Biotic factor: living factor in the environment, e.g. plants and animals

Question 5

Define

food chain

Answer 5

A chart showing the flow of energy (food) from one organism to the next, beginning with a producer

e.g. mahogany tree → caterpillar → song bird → hawk

Question 6

Define

food web

Answer 6

A network of interconnected food chains showing the energy flow through part of an ecosystem

Question 7

Define

producer

Answer 7

An organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis

Question 8

Define

consumer

Answer 8

An organism that gets its energy by feeding on other organisms

Question 9

Define

herbivore

Answer 9

An animal that gets its energy by eating plants

Question 10

Define

carnivore

Answer 10

An animal that gets its energy by eating other animals

Question 11

Define

decomposer

Answer 11

An organism that gets its energy from dead or waste organic matter

Question 12

Define

ecosystem

Answer 12

A unit containing all of the organisms and their environment, interacting together, in a given area

e.g. a decomposing log or a lake

Question 13

Define

trophic level

Answer 13

The position of an organism in a food chain, food web or pyramid of biomass, numbers or energy

Question 14

Explain why food chains usually have fewer than five trophic levels

Answer 14

This is because energy transfer is inefficient

Only about 10% of energy is transferred between trophic levels, whilst the other 90% is lost

Question 15

Describe how energy may be lost between trophic levels

Answer 15

In plants:

• Only 1% of Sun’s energy falls on leaves, of which 5-8% is used by the producer
• Leaves do not trap all wavelengths of light
• Some light is reflected; some passes through leaves

In animals:

• Primary consumer only gets between 5-10% because some parts are indigestible (e.g. cellulose) and not eating the whole plant.
• Secondary consumer gets between 10-20% because animal matter is more digestible and has a higher energy value.
• Energy is lost through faeces, urine, respiration, movement, and heat loss

Question 16

Why may a food web become imbalanced?

Answer 16

• Disease
• Pollution
• Use of pesticides/insecticides
• Lack of resources (e.g. food)
• Emigration
• Over-predation
• Hunting

Question 17

Explain why humans eating plants is more efficient than humans eating animals

Answer 17

• We need only a couple of vegetables to have one meal, but to have meat we must feed the animal a lot of plant material in order to get far less meat.
• In the process of raising an animal, plants lose energy to environment, then animal loses energy to environment and does not use up all the plant material so it is very inefficient.

Generally, shorter food cains are more efficient, as fewer organisms lost energy and thus more energy is available for consumers higher up.

Question 18

What differences are there between pyramids of biomass and numbers?

Answer 18

Numbers:

• Shows number of each organism in a food chain.
• When moving up pyramid, number of individuals’ decreases
• Exceptions: when a large number of consumers feed on one producer, e.g. a tree

Biomass:

• Pyramid which shows the biomass
• number of individuals × their individual mass