B4

Question 1

What is an ecosystem?

Answer 1

All of the organisms living in an area, as well as all the non-living conditions eg. Soil quality, available of water and temperature

Question 2

How are materials through biotic and abiotic components of ecosystems?

Answer 2

Living things are made of elements which they take from the environment, eg. Carbon. They turn them into complex compounds (eg. Protein) that make up living organisms. Animals take these in when they eat plants. These elements are recycled - they return to the environment through waste products or when organisms die.

Question 3

What process causes Carbon to leave the air?

Answer 3

Photosynthesis - the entire carbon cycle is “powered” by it. Green plants use the carbon from CO2 in the air to make carbohydrates, fats and proteins.

Question 4

How does carbon pass from plants to animals?

Answer 4

When animals eat plants, the carbon compounds pass to the animals.

Question 5

What is one process which plants and animals perform which returns carbon to the air?

Answer 5

Respiration

Question 6

How is carbon released from animal and plant waste?

Answer 6

When plants and animals decompose, they’re broken down by microorganisms, such as bacteria and fungi. These decomposers release CO2 back into the air by respiration.

Question 7

What is combustion and how does it release carbon into the air?

Answer 7

When fossil fuels (oil, coal and gas) are extracted from the ground, they can be burned. This is called combustion and it releases CO2 back into the air.

Question 8

How much nitrogen gas does the atmosphere contain?

Answer 8

78% - it is very unreactive and so it can’t be used directly by plants or animals. Nitrogen is needed for making proteins for growth, so living organisms have to get it somehow.

Question 9

What is nitrogen fixation?

Answer 9

The process of turning unreactive Nitrogen gas from the air into nitrates which plants can use. There are 2 ways that this can happen: lightning (there’s so much energy in a bolt of lightning that it makes nitrogen react with oxygen in the air to create nitrates) and nitrogen-fixing bacteria.

Question 10

What do decomposers do in the nitrogen cycle?

Answer 10

They decompose proteins in rotting plants and animals and urea in animal waste and turn them into ammonia, which go on to form ammonium ions.

Question 11

What does Nitrifying Bacteria do?

Answer 11

It’s a type of bacteria which turns ammonium ions into nitrates.

Question 12

What does Nitrogen-Fixing Bacteria do?

Answer 12

It turns nitrogen gas in the air into nitrates which plants can use.

Question 13

What does Denitrifying Bacteria do?

Answer 13

It’s a type of bacteria which turns nitrates back into nitrogen gas. They’re often found in waterlogged soils.

Question 14

What does the sun do in the water cycle?

Answer 14

It evaporates water from the land and sea, turning it into water vapour.

Question 15

What happens to water vapour in the water cycle?

Answer 15

It is carried upwards (as warm air rises). When it gets higher up it cools and condenses to form clouds.

Question 16

What is precipitation?

Answer 16

It is when water falls from clouds (usually rain) and is returned to the land or sea.

Question 17

What do decomposers do?

Answer 17

They break down waste products and dead organisms, and are mostly bacteria and fungi.

Question 18

How does oxygen availability affect decomposers?

Answer 18

Decomposers need oxygen for aerobic respiration so the rate of decomposition increases where there is lots of oxygen available. When there is low oxygen levels, the rate of decomposition is slower.

Question 19

How does temperature affect decomposers?

Answer 19

Most decomposers work best in warm conditions - ther ate of decomposition is highest at around 50 degrees celsius. This is because they contain enzymes, which digest the dead/waste material. The rate of enzyme-controlled reactions varies with temperature - if it is too low, the enzymes work slower and if it is too high, the enzymes denature and the reactions stop.

Question 20

How does water content affect decomposers?

Answer 20

Decomposers need water to survive, so the rate of decomposition increases in moist conditions. However, waterlogged soils don’t contain much oxygen so the rate decreases if there is too much water.

Question 21

What is the individual level of an ecosystem?

Answer 21

A single organism.

Question 22

What is the population level of an ecosystem?

Answer 22

All the organisms of one species in a habitat.

Question 23

What is the community level of an ecosystem?

Answer 23

All the organisms (different species) living in a habitat.

Question 24

What do organisms have to do in order to survive and reproduce?

Answer 24

They have to compete with other species (and members of their own species) for the resources needed for their survival.

Question 25

Which abiotic factors affect communities?

Answer 25

Temperature, moisture level, light intensity and pH of the soil.

Question 26

Which biotic factors affect communities?

Answer 26

Availability of food and number of predators.

Question 27

What happens to the population of predators when the population of prey increases?

Answer 27

It increases because there is more food available for the predators to hunt/feed on.

Question 28

What happens to population of prey when the number of predators increases?

Answer 28

It decreases because the increased number of predators means that more of them are being hunted for food.

Question 29

Why are predator-prey cycles out of phase with each other?

Answer 29

It takes a while for one population to respond to the changes in another population. Eg. when the number of rabbits goes up, the number of foxes doesn’t increase immediately as it takes time for them to reproduce.

Question 30

What do predator-prey cycles show?

Answer 30

How interdependent different populations are.

Question 31

What is a parasite?

Answer 31

It is an organism which lives off a host. They take what hey need to survive, without giving anything back. This often harms the host - making it a win-lose situation.

Question 32

What are examples of parasites?

Answer 32

Tapeworms absorb lots of nutrients from a host, causing them to suffer from malnutrition. Fleas are parasites - dogs gain nothing from having them other than having lots of bites.

Question 33

What is mutualism?

Answer 33

A relationship between two organisms in which they both benefit - making it a win-win situation.

Question 34

What are examples of mutualism?

Answer 34

Clownfish live among the poisonous tentacles of sea anemones. They are the only fish which can survive the toxins, so they are protected from their predators. In return, the clownfish help protect the anemones by eating parasites which could harm them. Lots of plants are pollinated by insects, allowing them to reproduce. In reutnr, the insects get nectar.

Question 35

How does a food chain work?

Answer 35

They always start with a producer (a plant). They produce their own food using energy from the sun. Producers are eaten by primary consumers, which are then eaten by secondary consumers. In some cases, they are eaten by tertiary consumers. All of these organisms eventually die and are eaten by decomposers. Each stage of a food chain is a trophic level.

Question 36

What is a food web?

Answer 36

Multiple food chains which are linked together.

Question 37

What does a bar on a pyramid of biomass show?

Answer 37

The dry mass of living material at that stage of the food chain - how much all of the organisms at each level would weigh if you combined them. Biomass pyramids are almost always pyramid-shaped because biomass is lost at each stage in a food chain.

Question 38

What does a bar on a pyramid of numbers show?

Answer 38

They show the number of organisms at a stage of the food chain. This m).

Question 39

What is some glucose used for in a plant?

Answer 39

To create biological molecules, such as cellulose. These molecules make up the plant’s biomass - the mass of living material.

Question 40

Why is the majority of biomass not transferred from one trophic level to another?

Answer 40

Animals use some of the biomass which they consume for respiration to provide energy for movement, keeping warm, etc. Biomass is also lost from the food chain through egestion and excretion. This is why there are rarely food chains with more than 5 stages.

Question 41

How can you calculate the efficiency of biomass transfer?

Answer 41

(Biomass available to the next level / biomass that was available to the previous level) x 100