Ecosystems

Question 1

What is an ecosyatem?

Answer 1

An ecosystem is made up of all of the living organisms that interact with each other in a given area.

Question 2

What are the names of the categories of factors that affect ecosystems?

Answer 2

Biotic and Abiotic

Question 3

What are biotic factors?

Answer 3

The living factors e.g. in a forest ecosystem, shrews and hedgehogs would be biotic

Question 4

What are abiotic factors?

Answer 4

Non living factors e.g. in a forest ecosystem the amout of rainfall is an abiotic factor.

Question 5

Why do we refer to ecosystems as dynamic?

Answer 5

Because they are constantly changing.

Question 6

What is a trophic level?

Answer 6

Each stage in the food chain is referred to as a trophic level.

Question 7

What are the different trophic levels called?

Answer 7

The first one is a producer
The second is primary consumer
The third is secondary consumer
The fourth is tertiary consumer

Question 8

What are decomposers?

Answer 8

Decomposers are organisms which break down dead organisms releasing nutrients back into ecosystems

Question 9

What is biomass?

Answer 9

The mass of living material present in a particular place or in particular organisms

Question 10

How do you measure biomass?

Answer 10

Multiply the biomass present in each organism by the number of organisms in that trophic level.

Question 11

How is biomass affected as you go up the food chain?

Answer 11

Biomass can equal energy content so when animals eat, only a small proportion of the food they ingest is converted to new tissue so it is only this part of the biomass which gets transferred therefore biomass in each level is always less than the level below.

Question 12

How do you calculate efficiency of biomass?

Answer 12

efficiency = biomass transferred/ biomass intake x 100

Question 13

How much energy originally present in sunlight becomes finally embodied as biomass in a tertiary consumer?

Answer 13

0.001%

Question 14

How can human activities influence biomass.

Answer 14

Agriculture allows plants and animals to have the optimum biotic and abiotic conditions to thrive e.g. adequate watering and warmth. It also reduces competition for survival. In doing this, agriculture is creating very small food chains so as much biomass as possible can be transferred to each level and eventually to humans

Question 15

What is meant by a decomposer?

Answer 15

An organism that feeds on or breaks down dead plant or animal matter. Usually microscopic fungi and bacteria but can also be larger fungi e.g. toadstools

Question 16

Whst is a detritivore?

Answer 16

An organism e.g. woodlice which helps speed up the decay process by feeding on dead and decaying material to break it down into smaller organic pieces which can increase surface area for decomposers to work on.

Question 17

Describe the carbon cycle.

Answer 17

• Carbon dioxide in the air is used for photosynthesis for plants, the plants respire giving some of the CO2 back. If the plant dies whilst no decomposers are around then over millions of years it will become a fossil if there is enough heat and pressure. If the plant gets eaten by an animal then the carbon passes to the animal.
  The animal respires releasing some CO2 and if the animal dies (same as with plants) the CO2 will be transferred to the decomposers and if there are no decomposers around then it can also end up as a fossil and used as fossil fuels. These fossil fuels are combusted releasing carbon back to the atmosphere. The carbon in animals and plants can be turned into rocks such as limestone which can then be released from volcanoes or weathered to dissolve the carbon in oceans which can then release it back into the atmosphere. The ocean also absorbs carbon from the atmosphere.

Question 18

What are the 4 stages of the nitrogen cycle?

Answer 18

Nitrogen fixation, ammonification, nitrification and denitrification.

Question 19

What happens during nitrogen fixation?

Answer 19

Nitrogen gas in the air can be combined with hydrogen to form ammonia, this is done by bacteria e.g. rhizobium and aotobacter). This allows the nitrogen to be absorbed by plants. Rhizobium live within the root nodules of leguminous plants e.g. peas beans and clovers where they have a mutualistic symbiotic relationship with plants which means they both benefit:
- the plant gains amino acids from rhizobium
- the bacteria gain carbohydrates produced by the plant in photosynthesis

Question 20

What happens during Nitrification?

Answer 20

Nitrification is the process by which ammonium compounds in the soil are converted into nitrogen containing molecules that can be used by plants. Nitrifying bacteria such as Nitrosomonas oxidise ammonium compounds into nitrites (NO2-). Nitrobacter (another genus of nitrifying bacteria ocidise nitrites into nitrates (NO3-). This process only occurs in aerobic conditions.

Question 21

What happens during denitrification?

Answer 21

If there is an absence of oxygen in the soil then denitrifying bacteria convert nitrates back into to nitrogen gas. This is denitrification. It only happens under anaerobic conditions and the bacteria use nitrates as a source of energy for respiration and nitrogen gas is released

Question 22

What happens during ammonification?

Answer 22

Ammonification is the name given to the process by which decomposers convert nitrogen containing molecules in dead organisms faeces and urine into ammonium compounds.

Question 23

What is meant by succession?

Answer 23

Succession is when a plant or animal species changes as a result of changes to the environment.

Question 24

What is primary succession?

Answer 24

Succession that occurs on an area of land that has been newly formed or exposed e.g. bare rock.

Question 25

What is secondary succession?

Answer 25

Succession that occurs on areas of land where soil is present, but it contains no plant or animal species. e.g. bare earth after a forest fire.

Question 26

Explain the process of primary succession.

Answer 26

Pioneer community:
- the colonisation of an inhospitable environment by organisms known as a pioneer species. e.g algae
- These species arrive as spores or seeds carried by the wind
Intermediate community:
- Over time, rock gets weathered into soil and the pioneer species die and decompose releasing organic products into this new soil. This is humus
- Humus supports the growth of secondary colonisers
- As environmental conditions continue to improve, new species of plant arrive ( tertiary colonisers) e.g. ferns
Climax community:
- The community reaches a stable state and will show very little change over time. There are a few dominant plant and animal species

Question 27

What happens to biodiversity as succession occurs?

Answer 27

Biodiversity generally increases as succession increases however the climax community is not always the most diverse. Biodiversity reaches its peak mid - succession. Then due to dominant species out - competing pioneer species and other species the less biodiverse the environment becomes.

Question 28

Explain deflected succession.

Answer 28

Human activity can stop succession and prevent the ecosystem from reaching natural climax community

Question 29

What is the final stage before succession is stopped artificially called?

Answer 29

Plagioclimax

Question 30

What can cause deflected succession?

Answer 30

Agriculture:
- Grazing and trampling of vegetation by domesticated animals
- Removing existing vegetation to plant crops
- Burning as a means of forest clearance