Topic 19

Question 1

“What is the main source of energy in biological systems?

Answer 1

The sun

Question 2

Describe the flow of energy in biological systems

Answer 2

“Light energy from the sun is trapped by photosynthetic organisms
Energy is stored as chemical energy in organisms
Energy is eventually lost to the environment”

Question 3

What is a food chain?

Answer 3

A way of showing the flow of energy between organisms starting with a producer

Question 4

How is energy transferred between organisms in a food chain?

Answer 4

By ingestion (organisms eating other organisms)

Question 5

What is a trophic level?

Answer 5

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

Question 6

Why are biomass transfers not 100% efficient?

Answer 6

“Energy is lost through:
Egestion (removal of faeces)
Excretion (removal of waste products e.g. urine)
Respiration
The production of inedible bones and shells”

Question 7

Why do food chains usually have fewer than 5 trophic levels?

Answer 7

Biomass transfers are not 100% efficient and so there is often not enough energy to support 5 trophic levels

Question 8

Why is it most efficient to supply plants as food for humans?

Answer 8

“Using the plants as food for livestock wastes energy as the biomass transfers are not 100% efficient
Eating plant transfers can maximise the amount of energy gained as there is only one transfer”

Question 9

What is a food web?

Answer 9

Multiple interconnected food chains

Question 10

What is a producer?

Answer 10

An organism that makes its own food (usually through photosynthesis)

Question 11

What is a consumer?

Answer 11

An organism that gets its energy by eating other organisms

Question 12

What is a primary consumer?

Answer 12

An organism that feeds on producers

Question 13

What is a secondary consumer?

Answer 13

An organism that feeds on primary consumers

Question 14

What is a tertiary consumer?

Answer 14

An organism that feeds on secondary consumers

Question 15

What are herbivores?

Answer 15

Herbivores are animals that only eat plants

Question 16

What are carnivores?

Answer 16

Organisms that mainly eat animals

Question 17

What are decomposers?

Answer 17

Organisms that get Theo energy from dead/waste organic material

Question 18

Explain the impact humans have on food chains and webs by overharvesting certain species

Answer 18

Many organisms rely on other organisms for food, overharvesting can reduce the amount of food available for other animals

Question 19

Explain the impact humans have on food chains and webs by introducing other species into a habitat

Answer 19

Introducing new organisms increases competition and can interfere with the food chain, causing organisms who cannot compete to die

Question 20

What is a pyramid of numbers?

Answer 20

A pyramid of numbers shows the number of organisms at each trophic level

Question 21

What is a biomass pyramid?

Answer 21

A pyramid that shows the total dry mass of organisms at each trophic level

Question 22

Why is a pyramid of biomass a better way of representing a food chain than a pyramid of numbers?

Answer 22

Pyramids of biomass take into account the size of the organisms and are less easily misinterpreted

Question 23

Describe the carbon cycle

Answer 23

1) Carbon present in atmosphere as CO2
2) CO2 taken by planks in photosynthesis & transferred to other molecules (eg. proteins & carbohydrates)
3) molecules (w/ C) passed on through food chains during feeding
4) C returned to atmosphere through
-respiration
-decomposition
-burned fossil fuel or combustion or deforestation

Question 24

State the effect of burning fossil fuels on carbon dioxide concentration in the environment

Answer 24

Burning fossil fuels releases more carbon dioxide into the atmosphere, increasing the concentration of CO2

Question 25

State the effect of deforestation on carbon dioxide concentration in the environment

Answer 25

“Trees take in carbon dioxide during photosynthesis (decreasing the atmospheric carbon dioxide concentration)
Cutting down trees prevents this and so the atmospheric carbon dioxide concentration does not decrease”

Question 26

Briefly describe how nitrogen is cycled through an ecosystem

Answer 26

“Nitrogen is fixed by lightning and bacteria
Decomposers break proteins / urea down into ammonium ions
Nitrifying bacteria convert ammonia, ions into nitrites and nitrates
Plants absorb nitrate ions
Denitrifying bacteria release nitrogen back to the atmosphere”

Question 27

What is deamination?

Answer 27

The removal of the amine group in an amino acid

Question 28

State 4 roles of bacteria in the nitrogen cycle

Answer 28

“Decomposition
Nitrification
Denitrification
Nitrogen fixation”

Question 29

Define population

Answer 29

A species that occupy the same habitat at the same time

Question 30

Define community

Answer 30

All the different populations in an ecosystem

Question 31

Define ecosystem

Answer 31

Both the community and their physical environment e.g. a pond

Question 32

State 3 factors that affect population growth rates

Answer 32

Disease, Predation, Availability of food

Question 33

Describe and explain the lag phase in population growth

Answer 33

Population size increases slowly at the beginning as there are few individuals so reproduction rate is slow

Question 34

Describe and explain the log phase in population growth

Answer 34

The growth of the population is increasing at a fast (exponential) rate- many individuals and lots of resources available

Question 35

Describe and explain the stationary phase in population growth

Answer 35

The amount of births and deaths are equal so population size does not increase- resources are limited so population does not increase further

Question 36

Describe and explain the death phase in population growth

Answer 36

Once the resources begin to be used up, organisms begin to compete for resources and organisms will die as resources become scarce and toxins build up