Ecosystems

Question 1

Define ecosystem

Answer 1

All the living organisms that interact with each other and the physical factors in a defined area

Question 2

Define and give examples of biotic factors

Answer 2

Living factors. Food, space, breeding partners, size of populations

Question 3

Define and give examples of abiotic factors

Answer 3

Non living factors. Light, temperature, water availability, oxygen availability

Question 4

Define trophic level

Answer 4

Each stage in a food chain

Question 5

Define producer

Answer 5

An organism that converts light energy into chemical energy by photosynthesis

Question 6

Define consumer

Answer 6

Organisms that obtain energy by feeding on other organisms

Question 7

Define primary consumer

Answer 7

An animal that eats a producer

Question 8

Define biomass

Answer 8

Mass of living material present in a particular place or in particular organisms

Question 9

How do you calculate biomass at each trophic level?

Answer 9

Biomass present in each organism x total number of organisms in that trophic level

Question 10

How do you measure biomass?

Answer 10

Burn a sample of the organism in a calorimeter. This energy is used to heat a known volume of water. Calculate the change in temperature of the water. This can be used to calculate the energy in the sample. Should be measured in J or Kj

Question 11

Explain efficiency at producer level

Answer 11

○ 1-3% of sunlight converted
○ 90% reflected, some is transmitted through the leaf and some is of unusable wave length
○ Other limiting factors
○ A proportion is lost as it is used for photosynthetic reactions

Question 12

How do you calculate the energy available to the next trophic level?

Answer 12

Net production = gross production - respiratory losses

Question 13

Explain efficiency at consumer levels

Answer 13

○ 10% of biomass is converted to their own organic tissue
○ Not all food is consumed
○ Transferred as metabolic heat
○ Indigestible parts
○ Excretion

Question 14

How do humans manipulate biomass through ecosystems

Answer 14

○ Suitable abiotic conditions (warmth, watering, shelter)
○ Competition is removed
○ Threat of predators is removed
○ Reduction of trophic levels
○ Selective breeding

Question 15

Define a decomposer

Answer 15

An organism that feeds on dead matter and breaks down organic compounds into inorganic compounds

Question 16

Define saprobiotic nutrition

Answer 16

Obtaining nutrition from dead/waste organic material. Secreting enzymes onto dead matter which breaks down complex organic molecules into more soluble molecules.

Question 17

Define detritivores

Answer 17

They speed up decay process by feeding on detritus which breaks down organic matter into smaller pieces (increasing the surface area)

Question 18

Explain the roles of Azotobacter and Rhizobium

Answer 18

Combines nitrogen with hydrogen to form ammonia - nitrogen fixation
Azotobacter : free living soil bacterium
Rhizobium : live inside root nodules (which grow on leguminous plants)

Question 19

Why is the relationship between bacteria and plants described as mutualistic?

Answer 19

Plants gain amino acids from Rhizobium and bacteria gains carbohydrates from the plant during photosynthesis

Question 20

How does nitrification occur?

Answer 20

It occurs in well aerated soil
Nitrosomanas oxidises compounds into nitrites
* Nitrobacter* oxidises nitrites into nitrates
Nitrate ions are highly soluble therefore can enter plants

Question 21

What condition does denitrification happen under?

Answer 21

Anaerobic condition

Question 22

Nitrogen Cycle

Answer 22

Nitrogen gas -> Nitrogen fixation -> Organic Nitrogen -> Ammonification -> Ammonium -> Nitrification -> Nitrite/Nitrate -> Denitrification -> Nitrogen Gas

Question 23

Why do levels of carbon dioxide fluctuate?

Answer 23

Plants only photosynthesise during the day whereas respiration is constant
Higher in the winter than in the summer as photosynthesis happens less

Question 24

Define primary succession

Answer 24

Development of organisms on a newly formed area of land

Question 25

Define secondary succession

Answer 25

Development of organisms on an area of land with soil present but no species

Question 26

What causes primary succession to occur?

Answer 26

Volcanic eruption
Sand blown by wind
Silt and mud are deposited at river estuaries
Glaciers retreating

Question 27

Define seral stage

Answer 27

Each step in succession

Question 28

Describe the first stage of succession

Answer 28

Pioneer species - arrive by wind or droppings by birds
○ seeds germinate rapidly
○ produce large quantities of seeds or spores
○ photosynthesise rapidly
○ tolerance to extreme conditions
○ nitrogen fixation

Question 29

Define humus

Answer 29

Organic products released by decomposition of pioneer species

Question 30

Describe the intermediate community

Answer 30

Secondary colonisers use soil to dominate the area
As the conditions improve, new species arrive (Tertiary colonisers). At each stage, the soil becomes more nutrient rich

Question 31

What is the final seral stage called?

Answer 31

Climax community

Question 32

Describe the climax community

Answer 32

Few species will dominate, little changes over time, stable state

Question 33

Define plagioclimax

Answer 33

The final stage when succession is stopped artificially

Question 34

How to measure distribution of plants

Answer 34

Line transect - laying measuring tape down and taking samples at regular intervals
Belt transect - two parallel lines arenarked and samples are taken from the area in between

Question 35

How to measure plant abundance

Answer 35

Using a quadrat placed randomly

Question 36

How to measure animal abundance

Answer 36

Capture-mark-release-recapture