Organisms and their environment | 19

Question 1

Producer

Answer 1

an organism which converts light energy to chemical energy in order to produce its own nutrients.

Question 2

Consumer

Answer 2

an organism which gets energy from feeding on other animals or plants.

Question 3

Food chain

Answer 3

a diagram which shows the order of energy transfer through feeding in an ecosystem.

Question 4

Food web

Answer 4

a diagram showing how different food chains interact with each other.

Question 5

Trophic level

Answer 5

the trophic level of an organism refers to its position in the food chain, food web, pyramid of numbers or pyramid of biomass.

Question 6

Pyramid of numbers

Answer 6

shows the number of organisms in each trophic level of a food chain

Question 7

Pyramid of biomass

Answer 7

shows the total mass of organisms in each trophic level of a food chain

Question 8

Biomass

Answer 8

the total mass of living material

Question 9

Herbivore

Answer 9

organisms which feed on plants

Question 10

Carnivore

Answer 10

organisms which feed on animals

Question 11

Decomposer

Answer 11

organisms which break down decaying organic material to feed on

Question 12

Describe the flow of energy in biological systems

Answer 12

Energy is introduced into biological systems as light energy which is absorbed by plants, where the Sun is the principal source of energy.

This energy is then transferred to chemical energy and can pass to other organisms through feeding. When these animals die, they are broken down by decomposers which return their nutrients to the soil

Question 13

Describe the process of the food chain

Answer 13

A food chain shows the order of energy transfer between organisms.

Food chains start with producers, which are plants which convert light energy from the Sun to chemical energy.

Organisms which feed on plants, or other animals, are known as consumers.

Plants are eaten by herbivores, which gain nutrients from the plants that are used for growth.

This consumer is then eaten by another animal which gains the nutrients from the first.

Each of these organisms has its own trophic level.

Consumers are classed as primary, secondary, tertiary or quaternary, depending on their position in the food chain.

Question 14

Why is energy being passed through trophic levels inefficient

Answer 14

Not all animal and plant material can be digested to gain energy from, e.g. fur and bones.

Energy is lost through excretion and decay

Energy is used in other processes, e.g. movement and keeping warm.

This means that organisms later on in the food chain gain less energy from their food than organisms earlier on, as energy is lost at each level.

Consequently, organisms later in the food chain must eat a larger amount to gain enough energy for survival.

For this reason, there are usually not more than five trophic levels as too much energy would be lost to sustain another.

This is also why it is more efficient for humans to eat plants rather than animals, as there are more stages in the food chain if animals are present

Question 15

Explain the pyramid of biomass and numbers

Answer 15

A pyramid of numbers can be used to show the number of organisms in each trophic level.

This is similar to a pyramid of biomass, which measures the total biomass of all the organisms at each level.

A pyramid of biomass tends to have a true pyramid shape as biomass is lost in each level which corresponds to the energy lost.

A pyramid of biomass therefore is more useful as it gives an indication of the amount of energy being passed on at each stage of the food chain

Question 16

How do humans impact the food chain

Answer 16

Humans alter food webs through over-harvesting food species and introducing foreign species to habitats.

Question 17

Explain over harvesting

Answer 17

Over-harvesting will damage food chains as other organisms which consume these organisms will not have enough food to survive, meaning that many of them will die.

when one trophic level is damaged, all that follow are also impacted as the amount of food for them decreases.

Question 18

Explain why introducing a foregien species to a food web is bad

Answer 18

Introducing foreign species can cause the food chain to die out as there is now competition for resources, which could damage existing species by interfering with the food chain.

An example of this is cane toads, which were introduced to Australia to eat pests. Due to their toxic skin, they have destroyed many native species and damaged habitats, especially water habitats, where the biodiversity has been reduced.

This has had a negative effect on the bird population which preyed on animals living in these areas.

This shows that when one trophic level is damaged, all that follow are also impacted as the amount of food for them decreases.

Question 19

Explain the carbon cycle

Answer 19

1. Carbon is present in the atmosphere in the form of carbon dioxide, which makes up about 0.04% of the air.
2. Carbon dioxide is taken in by plants during photosynthesis. Here, the carbon is transferred from carbon dioxide to other molecules such as proteins and carbohydrates.
3. These molecules are passed through the food chain when feeding occurs, hence carbon is also passed between the trophic levels.
4. Carbon is returned to the atmosphere during respiration, which releases carbon dioxide, and during decomposition.

Question 20

Explain carbon being made into fossil fuels

Answer 20

Carbon can be trapped in dead organisms when decomposition does not occur.

These organisms become fossilized over thousands of years to form fossil fuel.

When this fossil fuel is burned, large amounts of carbon dioxide is released back into the atmosphere.

This, along with the effect of deforestation, leads to the amount of carbon dioxide in the atmosphere increasing, which causes global warming.

Question 21

Explain the water cycle

Answer 21

1. Water evaporates from bodies of water such as lakes and rivers to form water vapour (gas). It also is released from plants during transpiration.
2. This water vapour rises upwards and begins to cool. When it cools, condensation occurs, turning the vapour back into liquid water which forms clouds.
3. When the cloud becomes too heavy, water falls from the cloud as precipitation (rain, snow, hail etc.).
4. This water is then taken up by plants and animals, or returns to a body of water, so that the cycle can continue

Question 22

Explain the nitrogen cycle

Answer 22

1. Nitrogen gas is present in the air. This nitrogen is fixed (converted to useable nitrate ions) by nitrogen-fixing bacteria which live on the root nodules of some plants, or by lightning.
2. Plants absorb these nitrate ions and use them to make other molecules, such as amino acids and proteins.
3. These molecules are passed through the food chain via feeding.
4. Nitrogen is returned to the soil in the form of ammonia when decomposition occurs, or in the form of urea, which is excreted from organisms after deamination occurs.

If this decomposition occurs in anaerobic conditions (without oxygen) then denitrifying bacteria can break down nitrates and return nitrogen gas to the atmosphere.

Question 23

Why is nitrogen important to organisms

Answer 23

Nitrogen is another element which is key to biological lifeforms.

Nitrogen is used to make

• Amino Acids
• DNA
  -ATP (molecule that releases energy)

Microorganisms are key to the nitrogen cycle as they help to convert nitrogen to different forms so that it can be used.

Question 24

Population

Answer 24

A group of organisms of the same species living together in one habitat.

Question 25

Community

Answer 25

Populations of many different species living together in one ecosystem make up a community

Question 26

Ecosystem

Answer 26

A system in a specific area which contains a variety of living organisms which work together within the environment.

Question 27

Factors affecting population growth

Answer 27

Food supply - if there is a large amount of food, organisms can breed more successfully. If there is a food shortage, there is a higher death rate which results in a slow or negative population growth.

Predation - organisms which have lots of predators will have a slower rate of population growth as more will be killed by predators.

Disease - disease can reduce the population by killing organisms. In densely populated areas, disease can spread quickly, thus a large proportion of the population may be wiped out

Question 28

Sigmond Curve

Answer 28

Characteristic growth pattern of a population when there is plenty of fodd

A - lag phase - population is small , no large population increase

B - Exponential phase - Continued doubling of population explodes population

growth rate starts to go down

C - Stationary - phase - resources are limited , death rate is equal to reproduction rate

D - death pase - death rate is higher and population falls

Question 29

Abiotic and biotic limiting factors

Answer 29

Abiotic - rainfall , temprature , light intensity

Biotic - leaves eating , fungal diseases