ecosystems and efficiency

Question 1

ecosystem definition

Answer 1

all of the living organisms that interact with each other in a defined area as well as non living factors present in that region.

Question 2

biotic factors

Answer 2

the living factors
e.g. competition

Question 3

abiotic factors

Answer 3

non-living factors
e.g. sunlight, temperature, water availability, oxygen availability, soil pH

Question 4

dynamic ecosystem meaning

Answer 4

changing all the time

Question 5

trophic level

Answer 5

stage in a chain of transfer of biomass and energy through organisms in an ecosystem

Question 6

food webs

Answer 6

system of interlinked food chains

Question 7

producer

Answer 7

organism that converts light energy into chemical energy by photosynthesis

Question 8

consumers

Answer 8

organisms that obtain their energy by feeding on other organisms

Question 9

decomposers

Answer 9

break down dead organisms releasing nutrients back into the ecosystem

Question 10

biomass

Answer 10

the mass of living material

Question 11

how much sunlight is converted into energy by producers

Answer 11

1-3%
- because not all of solar energy available is used for photosynthesis- 90% is reflected, some transmitted, some unusable
- other factors limit photosynthesis
- a proportion of energy is lost as its used for photosynthetic reactions

Question 12

how much energy is used for respiration by producers (respiratory loss)

Answer 12

20-50%
rest is converted into biomass

Question 13

why do consumers convert at most 10% of the biomass in their food to their own organic tissue

Answer 13

• not all of the biomass of an organism is eaten e.g. bones and roots
• some energy is transferred to the environment as metabolic heat as a result of movement/respiration
• some parts of an organism are eaten but indigestible so egested
• some energy is lost from the animal in urine

Question 14

formula to calculate efficiency of energy transfer

Answer 14

ecological efficiency= energy available after transfer/energy available before transfer x100

Question 15

formula for net production

Answer 15

net productivity= gross productivity- respiratory loss

Question 16

efficiency of energy transfer from sun to producer

Answer 16

• 1-3%
• because not all light energy can be absorbed and some is lost in photosynthesis

Question 17

efficiency of energy transfer from producer to consumer

Answer 17

• 5-10%
• because plants contain a high proportion of indigestible material e.g. cellulose

Question 18

efficiency of energy transfer from consumer to consumer

Answer 18

• 15-20%
• higher than from producer to consumer because animals contain a high proportion of relatively digestible meat

Question 19

how does agriculture affect ecosystems

Answer 19

it involves manipulating the environment to favour plant species that we can eat (crops) and to rear animals for food or their produce.
- plants and animals provided with abiotic conditions they need to thrive such as water and warmth
- competition from other species and predators are removed
-

Question 20

herbicides

Answer 20

kill weeds that compete with agricultural crops for energy
- so crops receive more energy so grow faster and larger, increasing productivity

Question 21

fungicides

Answer 21

kill fungal infections that damage agricultural crops
- so crops use more energy for growth and less for fighting infection so they grow faster and larger, increasing productivity

Question 22

insecticides

Answer 22

kill insect pests that eat and damage crops
- so less biomass lost from crops so they grow to be larger, increasing productivity

Question 23

natural predators

Answer 23

introduced to the ecosystem to eat the pest species
- crops lose less energy and biomass, increasing productivity

Question 24

fertilisers

Answer 24

chemicals that provide crops with minerals needed for growth e.g. nitrates
- this replaces the lost minerals from the soil so more energy used to grow, increasing efficiency of the energy conversion