4.2 Energy Flow

Question 1

Most ecosystems rely on light energy from

Answer 1

the sun

Question 2

Plants, algae, and cyanobacteria are photoautotrophs:

Answer 2

Use pigments such as chlorophyll to capture light energy and convert into chemical energy as carbon compounds

Question 3

In very few ecosystems the producers are chemoautotrophs:

Answer 3

volcanic vents on the ocean floor, which use energy from chemical processes

Question 4

Heterotrophs rely…

Answer 4

indirectly on sunlight

Question 5

Amount of energy supplied to ecosystems varies around the world:

Answer 5

I.e. Sahara desert → high intensity but few producers
I.e. California forests → lower intensity, but many producers

Question 6

Autotrophs use sunlight to

Answer 6

convert carbon dioxide into organic compounds (glucose)

Question 7

The light energy is transferred into

Answer 7

bonds (chemical energy) between the atoms in a carbohydrate molecule.

Question 8

Molecules can be converted into

Answer 8

carbohydrates, lipids, amino acids

Question 9

Glucose can be used in cell respiration for cell activities and energy can be lost

Answer 9

as heat

Question 10

Most of the energy is retained within

Answer 10

plant structure and is available to heterotrophs

Question 11

Trophic level:

Answer 11

feeding position of an organism in a food chain

Question 12

Energy stored in organic molecules (primarily carbohydrates and lipids) can be

Answer 12

transferred by cell respiration to ATP.
ATP in turn is used by cells to support their metabolism:
Building and breaking down molecules (anabolism and catabolism)
Homeostasis
Growth
Active transport
movement

Question 13

No energy transfer is 100% efficient:

Answer 13

‘wasted’ heat (thermal) energy is produced too.
Some exothermic reactions involved in making ATP
Heat is produced when ATP is used in cell activities

Question 14

Living organisms can perform various energy conversions:

Answer 14

Light → chemical = photosynthesis
Chemical → kinetic = muscle contraction
Chemical → electrical = nerve cells
They cannot convert heat energy into useful forms of energy

Question 15

Heat resulting from cell respiration is useful for organisms to

Answer 15

maintain body temperature

Question 16

Thermal energy released from the organism dissipates into the ecosystem and is eventually

Answer 16

lost from it.

Therefore ecosystems require a continuous supply of energy (e.g. sunlight) to persist.

Question 17

Biomass

Answer 17

total mass of a group of organisms

Question 18

Pyramids of Biomass

Answer 18

Because biomass contains carbon compounds (which contain chemical energy), biomass can be used to indirectly measure chemical energy

Question 19

Pyramids of Biomass Trend =

Answer 19

energy added to each successive trophic level is less (upright triangle)

Organisms use energy in cell activities
Energy lost as heat
Some parts of organism uneaten by consumer
Toxic waste organic molecules are excreted
Some ingested material is not absorbed and ends up being egested as waste

Question 20

Pyramids of Energy

Answer 20

Shows the flow of energy between trophic levels
Trend = energy added to each successive trophic level is less (upright triangle)

Measured in units of energy per unit area per unit time: kJ⦁m-2⦁y-1
Transfer of energy is never 100% efficient
Around 90% of energy is lost between trophic levels
Not ingested (eaten)
Not digested or assimilated
Excreted
Lost as heat from respiration
n.b. organisms vary in their efficiency of energy transfer; it maybe as high as 20% or as low as 5%.

Question 21

Drawing Pyramids of Energy

Answer 21

Pyramids of energy always get smaller at higher trophic levels due to the loss of energy.
Bars should be roughly drawn to scale, e.g. secondary consumers should be 1/10th the width of primary consumers.
The bottom level will always represent the producers, with subsequent levels representing consumers (primary, secondary, etc.)

Question 22

flow of energy in ecosystem

Answer 22

• energy enters from sunlight.
• autotrophs capture sunlight
• energy flows through tropic levels/energy levels
• energy transfer is around 10% from one level to the next
• energy lost due to materials not being consumed, assimilated, egested, excreted
• energy passes through decomposers, detrivores, saprotrophs in dead organic matter
• heat energy is loss through cell respiration

Question 23

flow of nutrients in ecosystem

Answer 23

• nutrients cycle within ecosystem/nutrients are recycled
• nutrients from weathering rocks enter ecosystem
• nutrients recycled from decomposition of dead organisms
• nutrients move through food chain by digestion of other organisms
• nutrients absorbed by producers/plants
• nutrients lost by leaching/sedimentation