Key Area 3: Life on Earth

What is biodiversity?

Biodiversity is the variety of life found on Earth.

What is a species?

A species is a group of organisms that can interbreed to produce fertile offspring.

What does fertile mean?

Able to reproduce.

What is an ecosystem?

An ecosystem consists of all the organisms living in a particular area and the non-living components with which the organisms interact.

What is a habitat?

A habitat is the place where a living organism lives.

What is a population?

A population is all the organisms of one species found in a particular area.

What is a community?

A community is all the plants and animals in an ecosystem.

What is a producer?

A producer is a green plant that produces its own food by photosynthesis.

What is a consumer?

A consumer obtains energy by eating other organisms.

What is a herbivore?

An animal that eats plants only.

What is a carnivore?

An animal that eats animals only.

What is an omnivore?

An animal that eats both plants and animals.

What is a predator?

An animal that hunts, kills and eats other animals for food.

What is a prey?

Organisms that predators kill for food.

What does a food chain represent?

The energy transfer from one organism to another during feeding.

What do the arrows in a food chain show?

The direction of energy flow.

What is a food web?

A food web shows the energy flow through interconnected food chains in an ecosystem.

Why is an organism usually part of more than one food chain?

Because a producer is normally eaten by several animals, which in turn can be eaten by several different animals.

What happens when an organism is removed from a food web?

Other organisms in the food web can be affected because they are connected through feeding relationships.

What is a niche?

A niche is the role that an organism plays within a community.

What resources does a plant's niche relate to?

Light, temperature and nutrient availability.

What resources does an animal’s niche relate to?

Food, water and shelter.

What other things are involved in an organism’s niche?

Its interactions with other organisms, including food availability, habitat, competition and predation, as well as the conditions it can tolerate such as temperature.

What is competition?

Competition occurs when two or more members of a community need a particular resource that is in short supply.

What do green plants compete for?

Light, water, soil nutrients and root space.

What do animals compete for?

Water, food and habitat.

What is interspecific competition?

Competition between individuals of different species for one or a few of the resources they require.

What is intraspecific competition?

Competition between individuals of the same species for all the resources required.

Which type of competition is more intense?

Intraspecific competition.

Why is intraspecific competition more intense?

Individuals of the same species have the same niche, so they compete for exactly the same resources.

What are biotic factors?

Biotic factors are interactions associated with living organisms that can influence the distribution of organisms in an ecosystem.

Name 5 biotic factors.

Competition for resources, disease, food availability, grazing and predation.

What are abiotic factors?

Abiotic factors are non-living components of an ecosystem that can influence where organisms can live.

Name 4 abiotic factors.

Temperature, light intensity, soil moisture and pH.

How is temperature measured?

Using a thermometer or temperature probe.

How is light measured?

Using a light meter.

How is soil moisture measured?

Using a soil meter.

How is pH measured?

Using a pH meter or chemical test.

What are two errors when using a thermometer?

Not allowing the thermometer enough time to stabilise and not taking enough samples.

How can thermometer errors be reduced?

Allow the thermometer to stabilise before taking a reading and take more samples.

What are two errors when using a light meter?

Shading the light meter and changes in light intensity because of cloud cover.

How can errors with a light meter be reduced?

Avoid shading the light meter and take all measurements at the same time of day.

What are errors when using a moisture or pH meter?

Not cleaning the probe between readings, not pushing the probe deep enough into the ground and not taking enough samples.

How can moisture or pH meter errors be reduced?

Clean the probe between readings, push the probe deep into the ground and take more samples.

How can abiotic and biotic factors affect organisms?

They can affect the distribution of organisms and can cause an increase or decrease in biodiversity.

What are quadrats used for?

Estimating the abundance of plants or slow-moving animals.

Why should quadrats be placed randomly?

To obtain representative sampling of the ecosystem.

Why should many quadrat samples be taken?

To provide adequate replication and make the results more reliable.

What are three errors when using quadrats?

Too few samples, non-random placement and deciding whether a sample is "in or out".

How can quadrat errors be reduced?

Take more samples, ensure random placement and only count a square if more than half of the plant is in the square.

What are pitfall traps used for?

Sampling small invertebrates living on the ground.

What should the top of the pitfall trap be?

Level with the soil surface.

Why is a cover placed over a pitfall trap?

To keep out rain, make it dark and stop birds eating the trapped animals.

Why should pitfall traps be checked regularly?

To prevent animals escaping or being eaten before they are counted.

What are three errors with pitfall traps?

The sample may not represent the whole ecosystem, birds may eat trapped animals, and some animals may eat others.

How can pitfall-trap errors be reduced?

Take more samples, disguise the opening, and check the trap regularly or use a preserving liquid such as alcohol.

What are biological keys used for?

Identifying unknown organisms.

What are the two types of biological key mentioned?

Branching keys and paired-statement keys.

What is an indicator species?

A species whose presence or absence indicates environmental quality or levels of pollution.

What do mayfly nymphs, stonefly nymphs and dobsonfly larvae indicate?

Clean water with lots of oxygen.

What do freshwater shrimp and caddisfly larvae indicate?

Fairly clean water with some oxygen and low pollution levels.

What do water lice and bloodworms indicate?

High pollution levels and low oxygen.

What do rat-tailed maggots and sludge worms indicate?

Very high pollution and very little oxygen.

What happens to bacteria when pollution enters a river?

The number of bacteria increases because there is more food.

What happens to oxygen concentration when pollution enters a river?

Oxygen concentration decreases because more microorganisms are respiring aerobically.

What happens to biodiversity in polluted water?

Biodiversity decreases because fewer species can live in polluted water.

What is photosynthesis?

Photosynthesis is a series of enzyme-controlled reactions in a two-stage process.

What is the word equation for photosynthesis?

Carbon dioxide + water → sugar + oxygen.

What is needed for photosynthesis?

Light energy absorbed by chlorophyll.

Where does photosynthesis occur?

In chloroplasts containing chlorophyll.

What is the first stage of photosynthesis?

Light reactions.

What happens during the light reactions?

Light energy from the Sun is trapped by chlorophyll in chloroplasts and converted into chemical energy used to generate ATP.

What happens to water during the light reactions?

Water is split to produce hydrogen and oxygen.

What happens to the hydrogen produced?

It is used in stage 2, carbon fixation, to make sugar.

What happens to excess oxygen?

It diffuses out of the cell.

What is ATP?

ATP is the molecule generated from the light reactions and used in carbon fixation to make sugar.

What is the second stage of photosynthesis?

Carbon fixation.

What happens during carbon fixation?

It is a series of enzyme-controlled reactions in which hydrogen and ATP from the light reactions combine with carbon dioxide to produce sugar.

What two substances from the light reactions are used in carbon fixation?

Hydrogen and ATP.

What gas combines with hydrogen and ATP to produce sugar?

Carbon dioxide.

What can the chemical energy in sugar be used for?

Respiration, or it can be converted into starch for storage or cellulose for structure.

What are the three limiting factors of photosynthesis?

Light intensity, carbon dioxide concentration and temperature.

What is a limiting factor?

A factor in short supply that prevents photosynthesis occurring at its maximum rate.

What happens if a factor is limiting?

Photosynthesis occurs more slowly, less sugar is produced and plant growth is reduced.

What happens when light intensity increases while it is limiting?

The rate of photosynthesis increases.

What happens when increasing light intensity no longer increases photosynthesis?

Another factor, such as carbon dioxide concentration or temperature, is limiting.

What happens when temperature increases up to the optimum?

The rate of photosynthesis increases.

What happens when temperature rises above the optimum?

The rate of the reaction decreases because enzymes are denatured.

How is most energy lost when energy transfers between levels of a food chain?

As heat, movement or undigested materials.

How much energy is used for growth?

A very small quantity, approximately 10%.

Why is only a small amount of energy available to the next level?

Because the majority is lost as heat, movement or undigested materials.

What is a pyramid of energy?

A diagram showing the total energy in the bodies of organisms at each level in a food chain.

What happens to energy at each level of a food chain?

The energy decreases at each level.

What is a pyramid of numbers?

A diagram showing the total number of organisms at each stage in a food chain.

What usually happens to the number of organisms at each stage?

The numbers decrease at each stage.

Why can a pyramid of numbers be irregular?

The producer may be a single large plant, or the final consumer may be a large population of parasites.

Why does food production need to increase?

An increasing human population requires an increased food yield.

What can happen if food yield does not increase?

Malnutrition and starvation can occur.

What two methods can increase food yield?

Fertilisers and pesticides.

What do fertilisers provide?

Chemicals such as nitrates.