ecosystems

Question 1

Ecosystem

Answer 1

includes all organisms living in a particular area as well as the abiotic factors of that particular environment

the distribution and abundance of organisms in a habitat is controlled by both biotic and abiotic factors

Question 2

Succession

Answer 2

• change of one community of organisms into the other

Question 3

Primary succession

Answer 3

an area of bare rock or previously devoid of life, is colonised by communities of organisms
the area is first colonised by pioneer species e.g. lichens, which are adapted to survive in such harsh conditions
as organisms die, they are decomposed by microorganisms forming humus which leads to soil making the environment more suitable for more complex organisms
overtime, the soil becomes richer enabling plants e.g. shrubs to survive

Question 4

Climax community

Answer 4

it’s a self-sustaining and stable community which is established in the final seral stage of succession

Question 5

Secondary succession

Answer 5

occurs in previously colonised areas in which an existing community has been cleared. E.g after forest fires. soil layer is already present, succession begins at a later stage

Question 6

Biomass and trophic levels

Answer 6

biomass is lost between successive trophic levels because…

1. not all of the organism is eaten (e.g bones)
2. not all of the eaten material is digested (excretion)
3. energy used in respiration
4. some energy lost in urine and urea
5. energy lost for movement and heat

Question 7

Efficiency of energy transfer

Answer 7

(energy or biomass post transfer/ energy or biomass before transfer) x 100

Question 8

Efficiency at producer levels

Answer 8

producers only convert 1-3% of sunlight to chemical energy
the total amount of solar energy converted to organic matter is the GROSS PRODUCTION
energy is used in respiration, the remaining = biomass
the energy available to next trophic Lebel is the NET PRODUCTION

*net production = gross production - respiratory losses

Question 9

Efficiency at consumer levels

Answer 9

10% of biomass in their food becomes their own

Question 10

Carbon cycle

Answer 10

• carbon is a component of all organic molecules

- it is recycles by photosynthesis, feeding, respiration and decomposition

Question 11

Nitrogen

Answer 11

essential component of metabolism, required for the synthesis of proteins and nucleic acids
nitrogen can not be used in its gas form so must be fixed in the form of ammonium ions or nitrates to be of any use to plants

Question 12

Nitrogen cycle

Answer 12

• N is fixed by bacteria such as Rhizobium (in root nodules of leguminous plants) because of symbiotic mutualistic relationship with the plant
• N gas is reduced to ammonium ions in ammonification
• ammonium ions are released by bacteria
• Nitrosomonas oxidise ammonium ions to nitrites (NO2-)
• Nitrobacter oxidised nitrites to nitrates (NO3-)
• plants absorb nitrates from soil
• denitrifying bacteria convert nitrates back to oxygen, nitrogen gas for respiration

Question 13

Limiting factors for carrying capacity

Answer 13

competition takes place when there is limited supply of…

1. food
2. water
3. light
4. oxygen
5. nesting sites
6. shelter
7. parasites and predators
8. carbon dioxide
9. mates

Question 14

Predator-prey relationships

Answer 14

• give rise to fluctuating population size

predator population grows 
more prey consumed 
prey decreases 
too little prey 
fewer predators 
prey increases
predator growth

Question 15

Conservation

Answer 15

• maintain or increase the biodiversity within a particular habitat (sustainably)

Question 16

Preservation

Answer 16

• maintain biodiversity levels and habitats by minimising the effects of human activities

Question 17

Reasons for Conservation

Answer 17

economic, social, ethical

• food
• medicine
• tourism
• water quality
• pollination of crops
• right to survive
• aesthetic reasons

Question 18

Coppicing

Answer 18

cutting down trees close to the ground to encourage new growth as stumps have good root systems

Question 19

Selective felling

Answer 19

felling only grown mature trees allowing younger trees to grow
replacing them with seeds

Question 20

Pollarding

Answer 20

form of coppicing, trees cut further up to prevent deer from eating new shoots

Question 21

Sustainable fishing

Answer 21

quotas - limits no. of certain species that can be caught in an area

nets with bigger mesh size - allows immature fish to escape so only mature fish are caught

seasonal fishing - protects breeding season

Question 22

Management of ecosystems

Answer 22

• control no. of tourists
• involve local communities
• educate local communities
• active management of vegetation
• control of introduction of species

Question 23

Galapagos islands

Answer 23

due to increase in tourism, demand for resources, energy has decreased in the GI
waste and pollution has increased
overfishing too
many non-native species have been introduced which outcompete native species

conservation projects:

• goat culling
• captive breeding
• limiting tourism in specific areas

Question 24

Equilibrium in succession

Answer 24

stable community

Question 25

Carrying capacity

Answer 25

maximum population size that an ecosystem an support

Question 26

Sustainability

Answer 26

using resources in a way that also maintains them for future generations

Question 27

Human influence on biomass

Answer 27

- increases biomass transfer favourable conditions e.g. water and temp are maximised increases soil nutrients and pests and weeds are removed

Question 28

Egestion vs excretion

Answer 28

``` excretion = waste products egestion = rid of undigested material ```

Question 29

Biomass

Answer 29

mass of living material present in a place or organism (dry)

Question 30

Trophic level

Answer 30

stage/position in food web