Biomass Transfer Through An Ecosystem

Question 1

what is the source of energy of almost all ecosystems on earth?

Answer 1

the sun.

Question 2

what do food chains and food webs represent?

Answer 2

the transfer of biomass, and therefore energy, through the organisms in an ecosystem.

Question 3

what is each stage of the food chain known as?

Answer 3

trophic levels.

Question 4

what is the first trophic level?

Answer 4

a producer.

Question 5

what is a producer?

Answer 5

an organism that converts light energy into chemical energy by the process of photosynthesis.

Question 6

what are the rest of the trophic levels?

Answer 6

consumers

Question 7

what is a consumer?

Answer 7

organisms that obtain their energy by feeding on other organisms.

Question 8

what is a primary consumer?

Answer 8

an animal that eats a producer.

Question 9

why do food chains not have more trophic levels than a quaternary consumer?

Answer 9

there is often not sufficient biomass and stored energy left to support further organisms.

Question 10

what do decomposers do?

Answer 10

break down dead organisms and release nutrients back into the ecosystem.

Question 11

what is the format of a pyramid food chain?

Answer 11

• the size of each tier represents the number of organisms at each trophic level.
• the producers are placed at the bottom and trophic levels are added above.

Question 12

what is biomass?

Answer 12

the mass of living material present in a particular place or in particular organisms.

Question 13

why is biomass an important measure in the study of food chains/webs ?

Answer 13

it can be equated to energy content.

Question 14

how do you calculate the biomass at each trophic level?

Answer 14

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

Question 15

what is the issue of pyramids of biomass?

Answer 15

it only represents the biomass present at a particular moment in time and does not take into account seasonal changes.

Question 16

what is the easiest way to measure biomass?

Answer 16

to measure the mass of fresh material present.

Question 17

what is the issue with measuring the mass of fresh material present to calculate biomass?

Answer 17

water content must be discounted and the presence of varying amounts of water in different organisms akes the technique unreliable unless very large samples are used. Instead, scientists often calculate dry mass.

Question 18

what is the issue with calculating dry mass of an organism?

Answer 18

organisms have to be killed in order to be dried (inhumane). As a result, only a small sample size is taken to minimise destruction of organisms but this may not be representative of whole populations.

Question 19

what is biomass measured in for areas of land?

Answer 19

grams per square metre (gm^-2)

Question 20

what is biomass measured in for areas of water?

Answer 20

grams per cubic metre (gm^-3)

Question 21

why is the biomass in each trophic level nearly always less than the trophic level before?

Answer 21

biomass consists of all the cells and tissues of the organism, including carbohydrates and carbon compounds the organisms contain. when animals eat, only a small proportion of the food they ingest is converted into new tissue - it is only this part of the biomass which is available for the net trophic level to eat.

Question 22

what is the energy available at each level measured in?

Answer 22

kilojoules per metre squared per year (kJm^-2 yr^-1). this is to allow for changes in photosynthetic production and consumer feeding patterns throughout the year.

Question 23

what is ecological efficiency?

Answer 23

the efficiency with which biomass is transferred from one trophic level to the next.

Question 24

what percentage of sunlight to producers convert into chemcial energy?

Answer 24

1-3%

Question 25

why do plants only convert 1-3% of sunlight into chemical energy?

Answer 25

• not all of the solar energy available is used for photosynthesis (around 90% is reflected.)
• other factors may limit photosynthesis.
• a proportion of the energy is lost as it is used for photosynthesis.

Question 26

what is gross production?

Answer 26

the total solar energy that plants convert to organic matter.

Question 27

how much of the gross production is used for respiration?

Answer 27

20-50%

Question 28

what is the net production?

Answer 28

the energy available to the next trophic level.

Question 29

how do you calculate net production?

Answer 29

net production = gross production - respiratory losses.

Question 30

how much of the biomass in food is converted to their own organic tissue?

Answer 30

at most 10%

Question 31

why is only 10% of biomass in food converted to organic tissue?

Answer 31

• not all the biomass of the organisms is eaten (plant roots or animal bones)
• some energy is transferred to the environment as metabolic heat, as a result of movement and respiration.
• some parts of the organism are eaten but are indigestible
• some energy is lost from the animal in excretory in excretory materials such as urine.

Question 32

how do you calculate the ecological efficiency?

Answer 32

(energy or biomass available after the transfer / energy or biomass available before the transfer ) x 100.

Question 33

how does agriculture manipulate the environment to favour plant species?

Answer 33

plants and animals are provided with the abiotic conditions they need to thrive (adequate watering and warmth) , competition from other species is removed (pesticides) and the threat of predators is removed (fences to exclude predators)

Question 34

what are the three trophic levels in farming animals for human consumption?

Answer 34

• producer (animal feed)
• primary consumers (livestock)
• secondary consumers (humans)

Question 35

what are the two trophic levels in farming plants for human consumption?

Answer 35

• producers (crops)
• primary consumers (humans)

Question 36

what are sea urchins?

Answer 36

marine invertebrates that feed on kelp (type of seaweed.)

Question 37

why are kelp forests disrupted in areas where sea urchins are abundant?

Answer 37

urchins eat the kelps’ holdfast which anchors the kelp to the seabed. the rest of the plant floats away resulting in an urchin barren ecosystem, which contains so little biomass of seaweed that species cannot survive.

Question 38

what animal feeds on sea urchins?

Answer 38

sea otters.

Question 39

what benefit do sea otters have on the kelp ecosystem?

Answer 39

they keep sea urchin levels low, therefore keeping the kelp forests intact.

Question 40

when was the ecological balance of otters, urchins, and kelp disrupted?

Answer 40

during the 19th century.

Question 41

what happened when sea otters were wiped out by excessive hunting for otter fur?

Answer 41

urchin numbers grew rapidly and kelp forests were destroyed.