Biology: 3.5 Population size and ecosystems

Question 1

Define ecosystems

Answer 1

A characteristic community of interdependent species and their habitat.

Question 2

Define environment

Answer 2

The physical and biological factors along with their chemical interactions that affect an organism or a group of organisms.

Question 3

What is an autotrophic plant?

Answer 3

A plant that carries out photosynthesis and can synthesise all the organic molecules they need from simple inorganic molecules using light as an energy source.

Question 4

What is a heterotrophic organism?

Answer 4

An animal that requires a source of organic food and rely on a source of chemical energy obtained from the food they eat.

Question 5

What is the LAG phase?

Answer 5

A period of slow growth as the organism adapts to its new environment.

Question 6

What is the LOG phase.

Answer 6

It is also known as the exponential growth phase, population doubles in unit time.

Question 7

What is the stationary phase?

Answer 7

During this period there is little change in number.

Question 8

What is the death phase?

Answer 8

Population numbers decrease.

Question 9

What is meant by the carrying capacity?

Answer 9

Maximum population size of a given species an environment can sustain.

Question 10

Spraying pesticide can also kill natural predators and parasites more effectively than killing the pest and natural predators of other pest species can be killed. What is the consequence of this?

Answer 10

In the absence of natural predators, pest populations increase rapidly and become greater problems than before applying the pesticide.

Question 11

Overuse of pesticide causes artificial selection - some individuals may have a mutation making them resistant to the pesticide. These survive and pass on the mutation to their offspring - others without the mutation die. What is the consequence of this?

Answer 11

Eventually, the pesticide becomes ineffective and increasing doses are used killing more natural predators and parasites and further selecting against non-resistant individuals.

Question 12

What is the consequence of bioaccumulation of the pesticides in animals and also humans leading to ill-health, reduced fertility and even death.

Answer 12

Loss of biodiversity, disruption of food chains and damage to humans.

Question 13

What is the difference between pyramids of numbers and pyramids of biomass.

Answer 13

Pyramids of numbers show the numbers of organisms at each trophic level. Biomass shows the mass of biological material (biomass) available at each trophic level for a set period of time.

Question 14

What is detritus?

Answer 14

It is a dead particulate organic material. Typically includes the bodies or fragments of microorganisms which act to decompose the material.

Question 15

What is humus?

Answer 15

Decaying organic matter in soil. (retains water)

Question 16

How do producers lose energy?

Answer 16

1: Plants respiring
2: >90% of the sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere.
3: Not all wavelengths of light can be absorbed and used for photosynthesis.
4: Light may not fall on a chlorophyll molecule.
5: A limiting factor such as low CO2 levels, may limit the rate of photosynthesis.

Question 17

What is the equation for Net Primary Activity?

Answer 17

Net primary activity = Gross primary activity - Respiratory losses.

Question 18

How do primary consumers lose energy?

Answer 18

1: Some energy losses occur as heat from respiration. Much energy is needed to maintain their body temperature when heat is being constantly lost to the environment.
2: Incomplete digestion - faeces still contain some energy.

Question 19

What is photosynthesis?

Answer 19

The main natural process that removes CO2 from the atmosphere and the only natural process that adds O2 to the atmosphere.

Question 20

What is respiration?

Answer 20

All living organisms release CO2 when they respire, including plants, animals and bacteria.

Question 21

What is decomposition?

Answer 21

Fungi and bacteria cause the decay of dead material - they release minerals into the soil and CO2 into the air through respiration. (Saprotrophic mode of nutrition)

Question 22

What is fossilisation?

Answer 22

Organic remains become fossilised - anaerobic conditions that led to the formation of coal, natural gas and oil.

Question 23

What are direct emissions?

Answer 23

They result from the burning of fossil fuels and production of plastics etc.

Question 24

What are indirect emissions?

Answer 24

They result from the use of energy in manufacture or services.

Question 25

What is putrefaction?

Answer 25

The initial decay of organic compounds found in plants and animals and also in the excreta and egesta of animals.
Amino groups are converted to ammonia in this stage.

Question 26

Describe nitrification.

Answer 26

Ammonia converted into soluble ions that can be absorbed by plants from the soil.
Nitrosomonas species of bacteria can convert ammonia and ammonium salts into nitrites.
Nitrobacter species of bacteria convert nitrites into nitrates.
Both of these types of bacteria are aerobic.

Question 27

What is nitrogen fixation?

Answer 27

Some species of bacteria living in the soil and in the roots of leguminous plants can absorb and fix nitrogen.
Free living bacteria: azotobacter
In root nodules of peas etc: Rhizobium.

Question 28

What is denitrification?

Answer 28

Under anaerobic conditions some bacteria break down nitrates and ammonium ions to N2 using energy from the breakdown of these ions.
Denitrifying bacteria is more likely to live in waterlogged soils, sewage, and at the bottom of ponds where oxygen is in short supply.

Question 29

How does ploughing and drainage increase fertility of the soil?

Answer 29

Ploughing helps drainage of soil and introduces air into the soil. This makes sure there are nitrates in the soil which fix the nitrogen.

Question 30

Explain eutrophication.

Answer 30

1: Excess fertiliser can be washed into waterways and can cause eutrophication.
2: When phosphates and nitrates enter ponds and lakes, the concentration of the minerals builds up and causes plant life in and on the water to increase in number of algal bloom.
3: Light can’t penetrate the water and the plants die.
4: Bacteria decompose the dead plants and use up the oxygen from the water for aerobic respiration.
5: Fewer plants and therefore less oxygen produced through photosynthesis.
6: Fish die as there is no longer an oxygen supply.

Question 31

What is ecological succession?

Answer 31

The change in species present in an ecosystem over time.

Question 32

What is primary succession?

Answer 32

A type of ecological succession, it occurs in an environment where there is no soil eg after a volcanic eruption.

Question 33

Describe the process of primary succession.

Answer 33

• Pioneer species initially claim the newly made inhabited area.
• Eventually a climax community takes over which is a stable community and can remain for many of years.

Question 34

What happens in secondary succession?

Answer 34

Plants recolonize an area that has been cleared through eg., fire, deforestation, or an abandoned garden.

Question 35

What is a sere?

Answer 35

Each stage in an ecological succession.