Chapter 19 - Organisms and their environment

Question 1

What is the principle energy source in biological systems?

Answer 1

The sun is the principal source of energy input to biological systems. Energy flows through living organisms starting with light energy from the sun and then it is transferred to chemical energy in organisms. This energy is eventually transferred to the environment. E.g. as heat.

Question 2

What is a food chain?

Answer 2

A food chain shows the transfer of energy from one organism to the next, beginning with a producer.

Question 3

What is a food web?

Answer 3

A food web is a network of interconnected food chains.

Question 4

What are producers?

Answer 4

Producers are organisms that produce their own organic nutrients usually from energy from sunlight. Plants are producers as they carry out photosynthesis to make glucose.

Question 5

What is a herbivore?

Answer 5

Herbivore is an animal that gets its energy by eating plants.

Question 6

What is a carnivore?

Answer 6

Carnivore is an animal that gets its energy by eating other animals.

Question 7

What are primary consumers?

Answer 7

Primary consumers are herbivores as they feed on plants.

Question 8

What are secondary consumers?

Answer 8

Secondary consumers are predators that feed on primary consumers.

Question 9

What are tertiary consumers?

Answer 9

Tertiary consumers are predators that feed on secondary consumers.

Question 10

What are decomposers?

Answer 10

Decomposers are bacteria and fungi that get their energy from feeding off dead and decaying organisms and undigested waste by secreting enzymes to break them down.

Question 11

What is a trophic level?

Answer 11

A trophic level is the position of an organism in a food chain, food web or ecological pyramid.

Question 12

What is a pyramid of numbers?

Answer 12

A pyramid of numbers show how may organisms are at each level of a food chain. They are not always pyramid shaped.

Question 13

What is a pyramid of biomass?

Answer 13

A pyramid of biomass shows how much dry mass the creatures at each level. These are always pyramid shaped. This is because the mass of organisms has to decrease as you go up a food chain.

Question 14

Why are pyramids of biomass more accurate than pyramids of numbers?

Answer 14

Pyramids of biomass provide a much better idea of the quantity of the plant or animal material at each level of as food chain and therefore are a better way of representing interdependence within the food chain.

Question 15

What is a pyramid of energy?

Answer 15

A pyramid of energy shows the amount of energy ‘passed on’ by being consumed through a food chain.

Question 16

How is energy lost through food chains?

Answer 16

Energy can be lost or used through making waste products, movement, heat and as undigested waste. 90% of energy is lost as heat and in undigested animals making energy transfer between levels not very efficient. This explains why food chains are rarely more than 5 organisms long as if they were any longer there would be barely any more energy to mass on. It would be more efficient for humans to eat plants than to eat livestock because crop plants have the most amount of energy.

Question 17

What processes are involved in the carbon cycle?

Answer 17

Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis.
It is passed on to animals and microorganisms by feeding.
It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration.
If animals and plants die in conditions where decomposing microorganisms are present, their bodies can be decomposed.
If animals and plants die in conditions where decomposing microorganisms are not present, the carbon can be converted over millions of years and significant pressure into fossil fuels.
When fossil fuels are burned, combustion, carbon dioxide is released into the atmosphere.

Question 18

What processes are involved in the nitrogen cycle?

Answer 18

Nitrogen gas in the air can be converted into a usable form using nitrogen fixing bacteria to convert N2 gas into ammonium compounds, which can then be converted into usable nitrates or by using lightning which can split the bond between the two N atoms, turning them into nitrous oxides like N2O and NO2 that dissolve in rainwater and leach into the soil.
Plants absorb nitrogen from the soil in the form of nitrates and use it to build proteins.
Animals eat the plant and get the nitrogen they need from the plant proteins. This nitrogen is passed up the food chain.
Waste (urine and faeces) from animals sends nitrogen back into the soil in the form of ammonium compounds. This process is called deamination.
The bodies of dead plants and animals’ decay and all the proteins inside them are broken down into ammonium compounds by decomposers.
The plants can’t absorb ammonium compounds so nitrifying bacteria convert the ammonium compounds to nitrites and then to nitrates which can be absorbed by plants.
Denitrifying bacteria takes nitrates out of the soil and converts them back to N2 gas. This process reduces soil fertility and is bad for plant growth. Denitrifying bacteria are anaerobic so aerating the soil can reduce the rate of denitrification.
During decomposition, microorganisms break down dead plants, animals and waste products, converting organic nitrogen into ammonia NH3 or ammonium ions NH4+ in a process called ammonification.
During nitrification, specific bacteria convert ammonia NH3 or ammonium ions NH4+ into nitrites NO2- and then into nitrates NO3-. This process allows plants to absorb nitrogen in a form they can use for growth.
During nitrogen fixation, certain bacteria convert atmospheric nitrogen N2 into ammonia NH3 which can then be used by plants. This process can occur in the soil or in the roots of certain plants.
Denitrification is the process where bacteria converts nitrates NO3- back into nitrogen gas N2 releasing it into the atmosphere and completing the nitrogen cycle. This process usually occurs in anaerobic conditions where oxygen is limited.

Question 19

What is a population?

Answer 19

A population is a group of organisms of one species, living in the same area, at the same time.

Question 20

What is a community?

Answer 20

A community is all of the populations of different species in an ecosystem.

Question 21

What is an ecosystem?

Answer 21

An ecosystem is a unit containing the community of organisms and their environment interacting together.

Question 22

What four factors affect population growth?

Answer 22

Population growth is affected by food supply, competition, predation and disease.

Question 23

Diagram of a sigmoid population growth curve

Answer 23

Question 24

What is the lag phase?

Answer 24

The lag phase occurs at the beginning when organisms are adapting to the environment before they are able to reproduce. At this stage, there are very few organisms, and so reproduction is not producing a larger number of offspring.

Question 25

What is the log/exponential phase?

Answer 25

The log phase or exponential phase occurs when food supply is abundant, birth rate is rapid, and death rate is low. Growth is exponential and only limited by the number of new individuals that can be reproduced.

Question 26

What is the stationary phase?

Answer 26

The stationary phase is when the population levels out due to a factor in the environment such as a nutrient, becoming limited as it is not being replenished. Birth rate and death rate are equal and will remain so until either the nutrient is replenished or becomes severely limited.

Question 27

What is the death phase?

Answer 27

The death phase is when the population decreases as death rate is now greater than birth rate. This is usually because food supply is short or metabolic wastes are produced by the population and have built up to toxic levels.