20 Organisms and their environment

Question 1

Define ecology

Answer 1

the study of organisms in their environment

Question 2

Define a habitat

Answer 2

the place where an organism lives

Question 3

Define a population

Answer 3

a group of organisms of one species, living in the same area, at the same time

Question 4

Define a community

Answer 4

all of the populations of different species in an ecosystem

Question 5

Define an ecosystem

Answer 5

a unit containing the community of organisms and their environment, interacting together

Question 6

Define a food chain

Answer 6

the transfer of energy from one organism to the next, beginning with a producer

Question 7

Define a food web

Answer 7

a network of interconnected food chains

Question 8

Define a producer

Answer 8

an organism that makes its own food using energy from sunlight, through photosynthesis

Question 9

Define a consumer

Answer 9

an organism that gets its energy by feeding on other organisms

Question 10

Define a herbivore

Answer 10

an animal that gets its energy by eating plants

Question 11

Define a carnivore

Answer 11

an animal that gets its energy by eating other animals

Question 12

Define a decomposer

Answer 12

an organism that gets its energy from dead or waste organic material

Question 13

What is the advantage of using a pyramid of biomass rather than a pyramid of numbers?

Answer 13

a more accurate representation of the energy flow through a food chain as the organisms sizes are taken into account

Question 14

Define a trophic level

Answer 14

the position of an organism in a food chain, food web, or ecological pyramid

Question 15

What is the advantage of using a pyramid of energy rather than pyramids of numbers or biomass?

Answer 15

the rate of production of the organism over a period of time is taken into account

Question 16

Why is the transfer of energy from one trophic level to another not efficient?

Answer 16

Energy released from food is lost as heat energy to the environment during respiration. Hence only about 10% of the energy is transferred at each trophic level

Question 17

Explain, in terms of energy loss, why food chains usually have fewer than five trophic levels?

Answer 17

As energy is passed along the food chain, some of it is lost to the environment as heat energy. Hence there is less energy available at higher trophic levels. The loss of energy limits the length of food chains as there is not enough energy to support a fifth trophic level

Question 18

Why is it more efficient for humans to eat crop plants than to eat livestock that have fed on crop plants?

Answer 18

nearer to the beginning of the food chain hence more energy available

Question 19

Describe the carbon cycle

Answer 19

1. When plants photosynthesise, carbon atoms in carbon dioxide become part of the glucose and starch molecules in a plant
2. When the plant respires, some of the glucose is broken down by the plant. The carbon in the glucose becomes part of a carbon dioxide molecule again and is released into the atmosphere
3. Animals eat some of the carbon in the plant. When the animals respire, some of the carbon is released back into the atmosphere as carbon dioxide
4. When a plant or animal dies, decomposers will feed on them. The carbon will become part of the decomposers bodies and when they respire, carbon dioxide is released back into the atmosphere again

Question 20

Describe a decomposer

Answer 20

An organism that gets its energy from dead or waste organic matter. They help to release carbon and nitrogen from dead organisms to be used again by living ones.

Question 21

Describe the nitrogen cycle

Answer 21

1. Lightning causes some of the nitrogen gas in air to combine with oxygen, forming nitrogen oxides through nitrogen fixation. The nitrogen oxides dissolve in rain and are washed into the soil as nitrate ions. The nitrogen ions are absorbed by plants.
2. Nitrogen-fixing bacteria that live in soil use nitrogen gas from the air spaces in the soil and combine it with other substances to form ammonium ions and other compounds. Once the nitrogen has been fixed, it can be used to make proteins in plants. Animals get their nitrogen in the form of proteins when they eat plants.
3. When animals or plants die, they decompose with the help of bacteria and fungi. The protein containing nitrogen is broken down into ammonium ions. Nitrifying bacteria convert the ammonium ions into nitrates through nitrification, to be used by plants again. Animals excrete nitrogenous waste material in the form of ammonia or urea from the deamination of excess amino acids. Nitrifying bacteria converts the ammonia into nitrates again.
4. Denitrifying bacteria undo the work done by nitrifying bacteria by converting nitrates and ammonium ions in soil into nitrogen gas which is released into the atmosphere.