How ecosystems work

Question 1

Biomass

Answer 1

• mass of organisms

Question 2

Productivity

Answer 2

• rate at which materials are produced

- energy transferred to a trophic level

Question 3

Why does biomass of grass in ungrazed area decrease?

Answer 3

• reduced photosynthesis due to long leaves blocking light
• greater competition for water, nutrients, minerals
• leaves dying

Question 4

Why are there low levels of primary productivity in grazed area?

Answer 4

• larger number of animals trample grass
• overgrazing
• grass unable to recover
• little photosynthesis takes place
• to much excretion

Question 5

How fall in predators affects food chain / grassland productivity

Answer 5

• decrease in predators results in an increase in predators’ prey, e.g. herbivores, fewer are killed
• this leads to overgrazing by increased number of herbivores
• reduction in producers, less primary productivity
• less food for herbivores, herbivores die
• increase in other carnivores

Question 6

How changes in % of dead organic matter changes the number of species

Answer 6

• less organic matter, fewer nutrients
• unstable substrate
• few species can tolerate conditions
• pioneer species colonise
• increased organic matter suits more species
• increased competition
• climax community established, fewer species where good soil is

Question 7

Climax community

Answer 7

• plant community that no longer changes in specie composition
• due to succession
• dominant species most abundant

Question 8

Net primary production (NPP)

Answer 8

• rate of production of new biomass
• that is available to the next tropic level
• NPP = GPP - respiration

Question 9

Why only a small % of the light energy falling onto a leaf is converted into chemical energy

Answer 9

• light reflected away from leaf
• some light passes straight through leaf
• plant cannot use all wavelengths of light
• photosynthesis is not efficient

Question 10

Why only 10% of energy locked up in secondary consumers is transferred to tertiary consumers

Answer 10

• secondary consumers respire / loss as heat
• they lose energy when they move around
• not all of them are eaten
• they have indigestible parts
• decomposition of secondary consumers

Question 11

Why decomposers have greatest energy transferring in

Answer 11

• they obtain energy from all trophic levels

Question 12

Why is slash and burn farming considered unsustainable

Answer 12

• after a long time total biomass has not returned to original
• fewer roots could lead to less water retention
• fewer roots will lead to more soil erosion
• leaf litter is loer so there will be less nutrients

Question 13

How biodiversity could change by the practice of slash and burn

Answer 13

• change in habitats
• more light allowed in
• exposure to wind (loss of shelter from wind)
• exposure to light changes plant populations
• may lead to soil erosion
• plants cannot get established
• animals might migrate
• changes in plants causes changes in types of animals

Question 14

Plagioclimax

Answer 14

• a sub climax

- factor e.g. grazing that maintains the subclimax

Question 15

How a grazed grassland could develop into a woodland community

Answer 15

• remove grazer
• allow different species to colonise
• competitive effects, change in soil
• will go through several stages
• succession occurs
• climax community established
• change in specie composition

Question 16

Factor that could affect population size of predator

Answer 16

• climate
• territory size
• diseases
• predation
• water/food supply

Question 17

Gross primary productivity

Answer 17

• Chemical energy fixed/ carbohydrates stored in producers by photosynthesis
• the rate at which producers capture ad store a given amount of chemical energy as biomass in a given length of time

Question 18

Role of decomposers in food chain

Answer 18

• decompose dead remains
• using external digestion
• to release nutrients (nitrates)

Question 19

Why is productivity lower in colder areas than tropical areas

Answer 19

• temperature lower
• slower enzyme activity
• shorter growing season, less sunlight
• less photosynthesis
• less water

Question 20

Ways energy is lost

Answer 20

• respiration
• faeces/indigestible material
• nitrogenous waste

Question 21

Why are food chains of limited length

Answer 21

• small proportion reaches next level

- insufficient energy to support another level

Question 22

Why is it important that compost is not allowed to become water logged or compacted

Answer 22

• compact gives rise to anaerobic conditions
• aerobic respiration not possible
• denitrifying organisms break nitrogen containing into nitrogen

Question 23

Reasons for causes of desertification

Answer 23

• overgrazing
• lack of rainfall
• climate change, e.g global warming

Question 24

Explain the process of desertification

Answer 24

• loss of vegetation due to overgrazing
• trampling compacts soil and removes plants
• soil is exposed to wind and sun
• soil blown away, evaporation of water from soil
• loss of roots loosens soil

Question 25

Way to prevent desertification

Answer 25

• put in a barrier, e.g. hedges, to reduce wind speed and provide shelter
• use plants that are drought resistant, these plants can survive
• plant fuel crop, sustainable
• rain water harvesting, irrigate land
• control grazing, e.g. density of animals to prevent loss of vegetation cover
• supply water to live stock

Question 26

Biotic factor

Answer 26

• involve other living organisms

Question 27

Abiotic factor

Answer 27

• involve physical/chemical non-living things

Question 28

Explain why GPP increases greater than NPP

Answer 28

• more energy is used in metabolism in bigger plants
• for protein synthesis and flower initiation
• herbivores cannot digest all parts
• more photosynthesis tissue

Question 29

Relationship between GPP, NPP and respiration

Answer 29

• GPP - NPP = R

- biomass production reduced by respiration

Question 30

Why only a proportion of the organic material, formed using CO2, will become plant tissues

Answer 30

• respiration of some of the organic material

- energy is required for synthesis of molecules, movement and active transport

Question 31

Abiotic factors that can affect gross primary production

Answer 31

• light intensity, duration, wavelength
• temperature
• CO2 concentration
• pH

Question 32

Why does oxygen uptake increase for dead plant material

Answer 32

• dead plant material is decomposed
• by the action of microorganism
• which respire aerobically
• more dead material provides more nutrients which leads to an increase in microorganism

Question 33

Why might there be a high number of predators

Answer 33

• GPP increases
• indicating high plant population
• plants releases O2 by photosynthesis
• more plants mean more herbivores
• more food for predators

Question 34

How plant species vary as a result of succession

Answer 34

• difference communities at different distances
• few species near beach, more further away as organic matter increases with distance, increasing number of niches
• pioneer species colonise empty inorganic surfaces, penetrating rock breaking it up, allowing organic material to accumulate
• increased organic matter results in increased water retention, mineral content
• less hostile conditions, larger plants can be supported
• better adapted plants out compete others, dominant specie is usually largest and most abundant
• eventually climax community is reached. specie range is constant and dominated by a few species

Question 35

Explain the difference between abiotic and biotic factors

Answer 35

• biotic factors involve organisms and abiotic factors are physical/chemical non-living factors