3.2.1a Functioning Ecosystems: Energy Transfer

Question 1

how does energy enter an ecosystem?

Answer 1

• ultimate source of energy = sunlight
• sunlight converted to chemical energy by photosynthesising organisms and passed as food between other organisms

Question 2

what is the photosynthesis equation?

Answer 2

carbon dioxide + water –> glucose + oxygen

Question 3

define producer

Answer 3

plant in the food chain - make food by photosynthesis - autotrophs

Question 4

define primary consumer

Answer 4

animals that eat the producer - heterotrophs

Question 5

define secondary consumer

Answer 5

eat animal material - carnivores - heterotrophs

Question 6

define tertiary consumer

Answer 6

eats secondary consumers - heterotrophs

Question 7

define quaternary consumers

Answer 7

eats tertiary consumers - heterotrophs

Question 8

define omnivore

Answer 8

eats both plants and meat

Question 9

define herbivore

Answer 9

eats plants

Question 10

define trophic level

Answer 10

position occupied by a group of organisms in a food chain

Question 11

define food chain

Answer 11

describes a feeding relationship between organisms

Question 12

define food web

Answer 12

many food chains linked together

Question 13

define carnivore

Answer 13

an animal that eats other animals and therefore is a secondary and tertiary consumer

Question 14

define biomass

Answer 14

the total mass (weight) of all living material in a specific area, habitat or region

Question 15

what is the key concept of energy flow in ecosystems?

Answer 15

nutrients are recycled, but energy flow is unidirectional and transferred

Question 16

what are food chains?

Answer 16

• a food chain shows how energy is passed through a series of animals
• the arrows in a food chain show the flow of energy
• as an organism is eaten, energy is transferred to the organism that it ate

Question 17

what is a food web?

Answer 17

• within most ecosystems, organisms feed upon a variety of resources and many food chains co-exist
• linkages form between different chains creating a complex network of connections
• A food web is a complex network of inter-related food chains

Question 18

what are pyramids of number?

Answer 18

• trophic levels are displayed as a series of steps of differing widths
• the width of each step in the pyramid is proportional to the numbers of organisms present at each level

Question 19

what are pyramids of biomass?

Answer 19

• representation of trophic levels with ecosystems in terms of total dry mass per square meter of area (known as biomass)
• a pyramid of biomass represents the total dry mass (in grams per square meter of area) of all the organisms in each trophic level at a particular time.

Question 20

what is the difference between pyramid of number vs biomass?

Answer 20

• the pyramid of biomass takes into account the size of organisms but it is only a ‘snapshot’ of the amount of material present at a given time

Question 21

what are pyramids of energy?

Answer 21

• constructed using energy values determined from a given area over a specified period of time for each trophic level (usually KJ/M62/yr)
• pyramids of energy represent the flow of energy through each trophic level over a specified period of time and provide a measure of productivity
• they therefore take into account seasonal fluctuations in productivity
• rule of thumb: 10% of biomass will be passed on between each trophic level

Question 22

what is the relationship between energy flow and energy loss?

Answer 22

• energy is transferred between trophic levels when one organism eats another
• these transfers are inefficient, and this inefficiency limits the length of food chains
• only a small proportion of the available energy is transferred from one trophic level to the next
• much energy is lost during the respiratory processes of each organism in the chain
• it is this energy loss, at each stage, which limits the length of food chains (number of trophic levels)

Question 23

what is the relationship between biomass and energy losses?

Answer 23

• the dry mass of living material (biomass) at each stage in a food chain, is less than it was at the previous stage
• the biomass and the chemical energy contained in the biomass is reduced at each trophic level because:
  - not all light energy is utilised to make biomass. Some is reflected and passes straight through the plant
  - some materials and energy are always lost in the organism’s waste materials
  - respiration supplies all the energy needs for living processes, including movement, growth and temperature regulation - this energy is not available to the next trophic level
  - not all the individual organisms in a trophic level will get eaten by organisms in the next level up and not all parts of the organism are eaten

Question 24

how much energy from the sun is utilised during photosynthesis?

Answer 24

1% to 5%

Question 25

what are the 3 ways that light energy is wasted (not absorbed by plants)?

Answer 25

1. the green light is reflected and lost (only red and blue regions used)
2. reflection from surfaces
3. passes through plant

Question 26

what is the formula for calculation photosynthetic efficiency (memorise)?

Answer 26

photosynthetic efficiency (%) = (gross primary product / light energy input) x 100

Question 27

define GPP

Answer 27

the rate at which solar energy is captured in sugar molecules during photosynthesis (energy captured per unit area per unit time).

Question 28

define NPP

Answer 28

the rate at which energy is stored as biomass by plants or other primary producers and made available to the consumers in the ecosystem

Question 29

what is secondary production?

Answer 29

• energy flow through consumer populations takes into account the fate of the energy consumed by the organisms in the food chain.
• the energy used to make new consumer tissue is called secondary production

Question 30

how can energy efficiency be calculated?

Answer 30

• approximately 10% of energy is passed on between each trophic level
  
  • at the top there is no energy left to pass on
• (small no. / big no.) x 100