4.2 Energy Flow

Question 1

Ecosystem

Answer 1

A combination of the abiotic and biotic factors in a particular area

Question 2

What do most ecosystems rely on?

Answer 2

They rely on the supply of energy from sunlight however energy must be converted into usable forms

Question 3

Besides light, how else do some ecosystems gain energy?

Answer 3

Through chemicals in the surrounding environment in a process known as chemosynthesis

Question 4

How do producers capture light?

Answer 4

Through pigments called chlorophyll in reactions like photosynthesis

Question 5

Briefly outline photosynthesis

Answer 5

• Light breaks water into protons and electrons which transform CO2 and water into glucose and other carbon compounds
• Light energy is thus converted to chemical energy

Question 6

Saprotrophs

Answer 6

Organisms that feed on non-living/decaying organic matter

Question 7

Detritivores

Answer 7

They feed on organic waste of decomposed plants and animals

Question 8

How is energy generated in producers from carbon compounds?

Answer 8

In the form of ATP

Question 9

Examples of how energy can be used in cellular activities

Answer 9

• Nucleic acid and protein synthesis
• Ion exchange across membranes
• Cell division for reproduction, growth and repair
• Intra-cellular movement of cell components

Question 10

Why is heat lost when generating energy?

Answer 10

Organisms cannot covert heat to other forms of energy so they are released into immediate surroundings

Question 11

What happens to carbon compounds that are not immediately used up?

Answer 11

They end up as structural components which when consumed, transfer energy

Question 12

What are the different types of energy that can be created + examples

Answer 12

• Kinetic: Muscular contractions
• Electrical: Nerve impulses
• Light: Bioluminescence
• Chemical: Anabolism
• Sound: Communication

Question 13

Food chain

Answer 13

Model that shows how nutrients and energy are passed from producer to subsequent consumers. Shows direction of energy flow as well

Question 14

Why are producers and autotrophs the first organisms in the food chain?

Answer 14

They do not feed on anything and produce their own nutrition through solar or chemical energy

Question 15

Trophic level + example

Answer 15

Position of organisms in the food chain eg. producers are first trophic level and primary consumers are second

Question 16

Which trophic level are decomposers?

Answer 16

They are largely present at every level since they decompose any living matter

Question 17

Food webs

Answer 17

Interconnections that occur amongst food chains. Each organism may have or be several sources of nutrition for several other organisms

Question 18

Why is energy transfer never 100%?

Answer 18

• Food may not be entirely consumed (eg. bones)
• Some material is indigestible so they leave body through egestion
• Some energy is contained in waste material which becomes available to saprotrophs and decomposers

Question 19

What is the estimated energy transfer at each trophic level?

Answer 19

10-20%

Question 20

How does energy transfer explain predator’s diets?

Answer 20

Top predators receive less energy as they are at higher levels so they have to consume higher number of organisms to meet energy requirements

Question 21

Why are there fewer organisms at higher trophic levels?

Answer 21

There is a decrease in biomass as we move up and due to their diets, the food pyramid can only support a certain amount of organisms

Question 22

Biomass

Answer 22

Mass of all dried organic material which can be used as fuel in an ecosystem (dry weight per unit area)

Question 23

Energy pyramid

Answer 23

Model used to represent energy flow in a community

Question 24

How should trophic levels be drawn in energy pyramids?

Answer 24

They should be drawn to scale with size of bar representing energy available

Question 25

Units for energy pyramids

Answer 25

Kilojoules per square meter or megajoules

Question 26

Numbers pyramid

Answer 26

A model that depicts the number of individuals in each trophic level

Question 27

Why do some number pyramids have very thin bases?

Answer 27

An organism like a single tree may be able to support thousands of consumers due to its size

Question 28

Biomass pyramids

Answer 28

Another way to quantify and present ecosystem data. Represents amount of biomass at each level

Question 29

Why are biomass pyramids usually larger at the base?

Answer 29

They may have multiple producers as compared to consumers like grass

Question 30

Is energy and nutrients recyclable?

Answer 30

Energy is not recyclable and is instead in constant supply by the sun. Nutrients are finite and recyclable

Question 31

How are nutrients lost from the ecosystem?

Answer 31

Leaching, harvesting, sedimentation, erosion, burning etc.

Question 32

Explain flow of energy in an ecosystem

Answer 32

• Enters from sunlight
• Autotrophs capture sunlight
• Energy flows through trophic levels (approx. 10% available at each level)
• Energy is lost through assimilation, egestion, excretion or just by not being consumed
• Energy passes to decomposers, detritivores and saprotrophs as dead matter
• Heat energy is also lost to environment or through cell respiration

Question 33

Explain the flow of nutrients in ecosystems

Answer 33

• Nutrients are recycled within system
• Nutrients enter from rock weathering, decomposition of dead organisms
• Nutrients move through ecosystem by digestion of other organisms
• Nutrients can be absorbed by producers or plants
• Nutrients are then lost by leaching or sedimentation