Ecosystems, Distrubition Of Organisms And Photosynthesis

Question 1

Define the terms species, biodiversity, population, producer, consumer, herbivore, carnivore, omnivore, predator, prey, food chain and food web.

Answer 1

 A species is a group of organisms which can interbreed and produce fertile offspring.
 Biodiversity is the range of species in an ecosystem.
 A population is a group of one species.
 A producer makes its own food by photosynthesis and a consumer eats other
animals or plants for food.
 A herbivore only eats plant matter, a carnivore only eats animal matter and an
omnivore eats both plant and animal matter.
 A predator is an animal which hunts another animal for food and prey is an animal
which is hunted by a predator.
 An ecosystem consists of all the organisms (the community) living in a particular
habitat and the non-living components with which the organisms interact.
 Food chains and food webs show feeding relationships.

Question 2

State that an ecosystem consists of all the organisms (the community) living in a particular habitat and the non-living components with which the organisms interact.

Question 3

Describe the effects of removal of organism(s) from a food web.

Answer 3

The removal of a species from a food web impacts on other organisms in the food
web.

Question 4

Define the term niche.

Answer 4

A niche is the role that an organism plays within a community. It relates to the
resources it requires in its ecosystem, such as light and nutrient availability and its
interactions with other organisms in the community.

Question 5

State that a niche involves competition and predation and the conditions an organism can tolerate such as temperature.

Question 6

State that competition in ecosystems occurs when resources are in short supply.

Question 7

Define the terms interspecific competition and intraspecific competition.

Answer 7

Interspecific competition occurs amongst individuals of different species for one or a
few of the resources they require.
Intraspecific competition occurs amongst individuals of the same species and is for
all resources required.

Question 8

State that intraspecific competition is more intense than interspecific competition

Question 9

Define the term biotic factors and give three examples.

Answer 9

Biotic factors are living factors such as competition for resources, disease, food availability, grazing and predation.

Question 10

Define the term abiotic factors and give three examples.

Answer 10

Abiotic factors are non-living factors such as light intensity, moisture, pH and temperature.

Question 11

Describe how abiotic factors such as light intensity, soil moisture, pH and temperature are measured and a possible source of error that could occur.

Answer 11

Light intensity is measured using a light meter, the sensor is held towards a light source and the reading is taken from the meter. A possible source of error is the sensor being covered so ensure it is not in the shade.
pH is measured using a pH meter and soil moisture is measured using a moisture meter, in both cases the probe is inserted into the ground and the reading is taken from the meter. A possible source of error is soil being left on the probe in between uses so ensure the probe is wiped between readings.

Question 12

Describe how plants and animals can be sampled using quadrats and pitfall traps and the limitations and possible errors.

Answer 12

Quadrats are used to sample plants and very slow moving animals, they are placed randomly on the ground and the number of squares containing the sampled organism are counted. It is important that an area is sampled with more than one quadrat.
Pitfall traps are used to sample invertebrates which live on the ground, a small pot is sunk into the ground and camouflaged with leaves. It is important to camouflage the trap to ensure the invertebrates do not avoid it.

Question 13

Define the term indicator species.

Answer 13

Indicator species are species that by their presence or absence indicate environmental quality/levels of pollution.

Question 14

Give the word summary of the process of photosynthesis.

Answer 14

Carbon dioxide and water are the raw materials of photosynthesis, light and chlorophyll are the requirements and glucose and oxygen are the products.

Question 15

Name the first stage of photosynthesis.

Answer 15

The first stage of photosynthesis is called the light reactions.

Question 16

Describe what happens during the first stage of photosynthesis.

Answer 16

During the light reactions the light energy from the sun is trapped by chlorophyll in
the chloroplasts and is converted into chemical energy which is used to generate
ATP. Water is split to produce hydrogen and oxygen. Oxygen diffuses from the cell.

Question 17

Name the second stage of photosynthesis.

Answer 17

The second stage of photosynthesis is called carbon fixation.

Question 18

Describe what happens during the second stage of photosynthesis

Answer 18

Carbon fixation is a series of enzyme-controlled reactions, which use hydrogen and
ATP (produced by the light reactions) with carbon dioxide to produce sugar.

Question 19

Sate that the chemical energy in sugar is available for respiration or the sugar can be converted into other substances, such as starch (storage) and cellulose (structural).

Question 20

Explain the term limiting factors.

Answer 20

A limiting factor is a factor which slows the rate of photosynthesis when it is absent
or in short supply, therefore slowing the rate of plant growth.

Question 21

Name the three limiting factors of photosynthesis.

Answer 21

The limiting factors of photosynthesis are light intensity, carbon dioxide
concentration and temperature.

Question 22

Describe three mechanisms by which energy is lost from a food chain/web in transfers from one level to the next.

Answer 22

In transfers from one level to the next in a food chain, the majority of the energy is lost as heat, movement or undigested materials.

Question 23

State that only a very small quantity of energy is used for growth and is therefore available at the next level in a food chain.

Question 24

Define the terms pyramid of numbers and pyramid of energy.

Answer 24

A pyramid of numbers shows the number of organisms at each level of a food chain.

A pyramid of energy shows the total quantity of available energy stored in the
organisms at each level in the food chain.

Question 25

State that irregular shapes of pyramids of numbers based on different body sizes can be represented as true pyramids of energy.

Question 26

An increasing human population requires more food yield what can this further involve?

Answer 26

Fertilisers and pesticides

Question 27

Describe the role of fertilisers and pesticides.

Answer 27

Fertilisers provide chemicals such as nitrates which increase crop yield.
Plants and animals which reduce crop yield can be killed by pesticides.

Question 28

Describe how plants obtain nitrates and why they require nitrates.

Answer 28

Nitrates dissolved in soil water are absorbed into plants. Nitrates are used to
produce amino acids which are synthesised into plant proteins.

Question 29

Explain how animals obtain their protein.

Answer 29

Animals consume plants or other animals to obtain amino acids for protein
synthesis.

Question 30

Describe the consequences of fertilisers leaching into freshwater ecosystems.

Answer 30

Fertilisers can leach into fresh water, adding extra, unwanted nitrates. This will
increase algal populations which can cause algal blooms. Algal blooms reduce light levels, killing aquatic plants. These dead plants, as well as dead algae, become food for bacteria which increase greatly in number. The bacteria use up large quantities of oxygen, reducing the oxygen availability for other organisms.

Question 31

State that genetically modified (GM) crops can be used to reduce the use of fertilisers.

Question 32

State that pesticides sprayed onto crops can accumulate in the bodies of organisms over time and as they are passed along food chains, toxicity increases and can reach lethal levels.

Question 33

Define the term biological control.

Answer 33

Biological control involves using a pests natural predator to control pest numbers.

Question 34

What are two alternatives that can be used instead of pesticides

Answer 34

Biological control and (GM) crops

Question 35

Define the term mutation.

Answer 35

A mutation is a random change to genetic material. Mutations may be neutral, confer an advantage or a disadvantage to survival.

Question 36

State that mutations may be neutral, confer an advantage or a disadvantage to survival; they are spontaneous and are the only source of new alleles.

Question 37

Name environmental factors which can increase the rate of mutation.

Answer 37

Environmental factors, such as radiation and some chemicals, can increase the rate
of mutation.

Question 38

State that new alleles produced by mutation can result in plants and animals becoming better adapted to their environment.

Question 39

State that variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions.

Question 40

Define the term adaptation.

Answer 40

An adaptation is an inherited characteristic that makes an organism well suited to
survival in its environment/niche.

Question 41

Define the term selection pressure.

Answer 41

Selection pressures are any factors which can affect the survival or reproduction of
an organism.

Question 42

Describe the process of natural selection.

Answer 42

Species produce more offspring than the environment can sustain. Natural selection
or survival of the fittest occurs when there are selection pressures. The best adapted individuals in a population survive to reproduce, passing on the favourable alleles that confer the selective advantage. These alleles increase in frequency within the population.

Question 43

Describe the process of speciation and describe three types of the isolation barriers

Answer 43

Speciation occurs after part of a population becomes isolated by an isolation barrier, which can be geographical (e.g. mountain), ecological (e.g. pH) or behavioural (e.g. timing of breeding). Different mutations occur in each sub-population. Natural selection selects for different mutations in each group, due to different selection pressures. Each sub-population evolves until they become so genetically different that they are two different species.