4.2 Energy Flow

Question 1

What does it mean if an organism is photoautotrophic? give examples

Answer 1

All green plants, and some bacteria, are photoautotrophic – they use sunlight as a source of energy

Question 2

What is the initial source for most communities?

Answer 2

This makes light the initial source of energy for almost all communities

Question 3

What is an exception to a community that uses sunlight as its primary energy source?

Answer 3

In a few ecosystems the producers are chemoautotrophic bacteria, which use energy derived from chemical processes

Question 4

What process makes use of light energy?

Answer 4

Light energy is absorbed by photoautotrophs and is converted into chemical energy via photosynthesis

Question 5

What is light energy used for?

Answer 5

This light energy is used to make organic compounds (e.g. sugars) from inorganic sources (e.g. CO2)

Question 6

Why do heterotrophs consume autotrophs?

Answer 6

Heterotrophs ingest these organic compounds in order to derive their chemical energy (ATP)

Question 7

What happens when organic compounds are broken down?

Answer 7

When organic compounds are broken down via cell respiration, ATP is produced to fuel metabolic processes

Question 8

What is light energy converted into?

Answer 8

Energy enters most ecosystems as sunlight, where it is converted into chemical energy by producers (via photosynthesis)

Question 9

How is chemical energy stored?

Answer 9

This chemical energy is stored in carbon compounds (organic molecules) and is transferred to heterotrophs via feeding

Question 10

What is a trophic level?

Answer 10

The position an organism occupies within a feeding sequence is known as a trophic level

Question 11

What occupies the first trophic level?

Answer 11

Producers always occupy the first trophic level in a feeding sequence

Question 12

What occupies the second trophic level?

Answer 12

Primary consumers feed on producers and hence occupy the second trophic level

Question 13

What occupies the consequent trophic levels (2+)?

Answer 13

Further consumers (e.g. secondary, tertiary, etc.) may occupy subsequent trophic levels

Question 14

What is a food chain?

Answer 14

A food chain shows the linear feeding relationships between species in a community

Question 15

What do arrows in a food chain represent?

Answer 15

Arrows represent the transfer of energy and matter as one organism is eaten by another (arrows point in direction of energy flow)

Question 16

What is the sequence of organisms in a food chain?

Answer 16

The first organism in a food chain is always a producer, followed by consumers (primary, secondary, tertiary, etc.)

Question 17

How can energy stored in organic molecules be released?

Answer 17

Energy stored in organic molecules (e.g. sugars and lipids) can be released by cell respiration to produce ATP

Question 18

What is ATP used for?

Answer 18

This ATP is then used to fuel metabolic reactions required for growth and homeostasis

Question 19

What is a by-product of respiration?

Answer 19

A by-product of these chemical reactions is heat (thermal energy), which is released from the organism

Question 20

In what ways can energy be lost?

Answer 20

Not all energy stored in organic molecules is transferred via heterotrophic feeding – some of the chemical energy is lost by:

Being excreted as part of the organism’s faeces
Remaining unconsumed as the uneaten portions of the food

Question 21

Into what 3 forms can energy produced by an organism be converted into?

Answer 21

kinetic, electrical and light energy

Question 22

What is an example of a use of kinetic energy?

Answer 22

during muscular contractions

Question 23

What is an example of a use of electrical energy?

Answer 23

during the transmission of nerve impulses

Question 24

What is an example of a use of light energy?

Answer 24

producing bioluminescence

Question 25

What type of reaction are the reactions in a food chain?

Answer 25

Living organisms cannot turn this heat into other forms of usable energy

Question 26

What is the consequence of these reactions being exothermic?

Answer 26

This heat energy is released from the organism and is lost from the ecosystem (unlike nutrients, which are recycled)

Question 27

What does the constant loss of energy from an ecosystem result in?

Answer 27

Hence ecosystems require a continuous influx of energy from an external source (such as the sun)

Question 28

What percentage of energy transformations are efficient?

Answer 28

Typically energy transformations are ~10% efficient, with about 90% of available energy lost between trophic levels

Question 29

What does the amount of energy transferred depend on?

Answer 29

The amount of energy transferred depends on how efficiently organisms can capture and use energy (usually between 5 – 20%)

Question 30

What does the loss of energy between trophic levels say about higher trophic levels?

Answer 30

As energy is lost between trophic levels, higher trophic levels store less energy as carbon compounds and so have less biomass

Question 31

What is biomass?

Answer 31

Biomass is the total mass of a group of organisms – consisting of the carbon compounds contained in the cells and tissues

Question 32

How can scientists measure the amount of energy added to organisms?

Answer 32

Because carbon compounds store energy, scientists can measure the amount of energy added to organisms as biomass

Question 33

How does biomass change along food chains and why?

Answer 33

Biomass diminishes along food chains with the loss of carbon dioxide, water and waste products (e.g. urea) to the environment

Question 34

Can there be an unlimited number of trophic levels? why?

Answer 34

Because energy and biomass is lost between each level of a food chain, the number of potential trophic levels are limited

Question 35

How much energy do higher trophic levels receive? What does this result in?

Answer 35

Higher trophic levels receive less energy / biomass from feeding and so need to eat larger quantities to obtain sufficient amounts

Question 36

How is energy lost by these higher trophic level organisms?

Answer 36

Because higher trophic levels need to eat more, they expend more energy (and biomass) hunting for food

Question 37

Why aren’t there more trophic levels?

Answer 37

If the energy required to hunt food exceeds the energy available from the food eaten, the trophic level becomes unviable

Question 38

What is a pyramid of energy?

Answer 38

A pyramid of energy is a graphical representation of the amount of energy at each trophic level of a food chain

Question 39

What is the unit of a pyramid of energy?

Answer 39

They are expressed in units of energy per area per time (e.g. kJ m–2 year–1)

Question 40

Do pyramids of energy always have the same general structure?

Answer 40

YES

Pyramids of energy will never appear inverted as some of the energy stored in one source is always lost upon transfer

Question 41

What is the rough change in size in pyramids of energy?

Answer 41

Each level should be roughly one tenth of the size of the preceding level (as energy transformations are ~10% efficient)

Question 42

What will the bottom level of a pyramid of energy usually represent?

Answer 42

The bottom level will always represent the producers, with subsequent levels representing consumers (primary, secondary, etc.)