Energy and Ecosystems

Question 1

What is a trophic Level ?

Answer 1

Trophic levels describe the position of an organism in a food chain, web or pyramid.

Question 2

Why do most food chains only have four or five trophic levels ?

Answer 2

There is insufficient energy available to support a large population higher than 4-5 levels.
The total mass of all the organisms is less at higher trophic levels.
The total amount of energy stored is less at each level up the food chain.

Question 3

What do farmers do to food webs to reduce energy loss ?

Answer 3

They simplify food webs.

Question 4

What is Biomass ?

Answer 4

Total mass of living material in a specific area at a given time.

Question 5

What are the units of Biomass ?

Answer 5

Kg yr-1 or kg m-2 yr-1

Question 6

What can Biomass be measured in terms of ?

Answer 6

The dry mass of an organism or tissue in a given area in a given time.
The mass of carbon that an organism or tissue contains.

Question 7

What is dry mass ?

Answer 7

Is the mass of the organism or tissue after all the water has been removed.

Question 8

What can be used to estimate the chemical energy store in dry mass ?

Answer 8

Calorimetry

Question 9

Describe the process of Calorimetry.

Answer 9

This involves burning the sample of dry biomass in a calorimeter.
The burning sample heats a known volume of water.
The change in temperature of the water provides an estimate of the chemical energy the sample contains.

Question 10

How can Dry mass of a plant sample be found ?

Answer 10

Heat the sample in a crucible to evaporate the water until the mass remains constant.

Question 11

Why might the energy transferred to consumers be low ?

Answer 11

Some of the organisms not consumed.
Some parts are consumed but cannot be digested and are therefore lost in faeces.

Question 12

What is Net Primary Production ?

Answer 12

NPP is the chemical energy store in plant biomass in a given area or volume in a given time after respiratory losses have been taken into account.

Question 13

How is Net primary production calculated ?

Answer 13

GPP - R

Question 14

How is Net production of consumers calculated ?

Answer 14

N = I - (F + R )

I = Chemical energy store inside ingested food
F = Chemical energy lost to the environment through excretion of urine or faeces
R is respiratory losses to the environment.

Question 15

Why is Net primary production important ?

Answer 15

It represents the energy that is available to organisms at higher trophic levels in the ecosystem such as primary consumers.

Question 16

What is Gross Primary productivity ?

Answer 16

Is the chemical energy store in plant biomass in a given area of volume in a given time.

Question 17

What are the units of Gross primary productivity ?

Answer 17

units of energy / mass per unit area per unit time ( kg km-2 yr -1 )

Question 18

Describe primary production.

Answer 18

During photosynthesis primary producers such as plants and algae convert light energy into biological molecules. The storing of this chemical energy in the biomass of primary producers is known as primary production.

Question 19

Describe secondary production

Answer 19

The chemical energy stored as biomass during primary production is available to organisms in higher trophic levels in the ecosystem.
These organisms are known as consumers.
When consumers ingest producers, the chemical energy in the biomass of the producers is transferred to the consumers, the consumers also store this chemical energy in their biomass.

Question 20

what is the rate of primary production known as ?

Answer 20

primary productivity

Question 21

What are the units of primary and secondary productivity ?

Answer 21

units of mass per unit area per unit time ( g m-2 day -1) or J m–2 day–1 (joules per square metre per day)

Question 22

What are the limitations of calorimetry to estimate chemical energy store in plant biomass ?

Answer 22

• It can take a long time to fully dry out a plant sample to find its mass
• precise equipment is needed which may not be available
• the more simple and basic the calorimeter the less accurate the estimate will be for the chemical energy contained within the plant sample.

Question 23

What is the role of decomposers in ecosystems ?

Answer 23

they break down dead plant and animal material ( in the process gaining the chemical energy still stored in the dead matter )

Question 24

How do decomposers break down organisms ?

Answer 24

They use extracellular digestion
- Secreting enzymes on the surface of the dead organism.
These enzymes break down the dead matter into small soluble food molecules. These molecules are then absorbed by the decomposers.

Question 25

Why is decomposition important ?

Answer 25

Helps to release organic nutrients back into the environment which are essential for the growth of plants and other producers.

Question 26

How can the efficiency of energy transfer at each trophic level be calculated ?

Answer 26

Energy available after the transfer/ Energy available before the transfer x100

Question 27

How do farmers simplify food webs ?

Answer 27

Using pest control

Question 28

What are 3 examples of pest control

Answer 28

Insecticides
Herbicides
Biological agents

Question 29

What do insecticides do ?

Answer 29

Kill insect pests that eat and damage crops reducing the NPP of crops.

Question 30

What do herbicides do ?

Answer 30

kill weeds that compete with crops for sunlight and water, reducing the NPP of crops

Question 31

what are biological agents used for ?

Answer 31

Biological agents are used to reduce the number of pests

Question 32

give an example of an biological agent

Answer 32

pathogenic bacteria and viruses that kill caterpillars

Question 33

To increase the Net production of livestock (e.g cattle ) they are kept in pens where their movement is restricted. Why does this increase Net production ?

Answer 33

less energy is lost through respiration.

Question 34

Keeping livestock indoors and in heated pens also increases net production. How does this work ?

Answer 34

This lowers the energy lost through respiration.
Respiration rate is increased when animals need to generate heat to stay warm.

Question 35

Why is increasing net production of livestock beneficial ?

Answer 35

This means more energy is available for human consumption.
it also means that more food can be produced in a given period of time, sometimes at a lower cost.
Increased profit for farmers.

Question 36

How is Biomass produced in plants?

Answer 36

Sugars are synthesised by plants in photosynthesis.
Most of these sugars produced by plants are used as respiratory substrates.
The remaining sugars are used to make other groups of biological molecules such as starch, cellulose, lipids and proteins.
These different groups of biological molecules make up the biomass of plants.

Question 37

State why dry biomass is a more accurate measurement than wet biomass

Answer 37

Organisms contain different amounts of water in their tissues;
(Dry biomass) enables comparisons to be made between different organisms

Question 38

Give ways in which plants used the molecules produced in photosynthesis.

Answer 38

(Sugars are used as a) respiratory substrate
(Sugars are converted to starch for) energy storage
(Sugars are converted to cellulose for) building cell walls;
(Sugars are converted into lipids for) building cell membranes
protein synthesis;

Question 39

Explain how keeping cows in a shed may increase the efficiency of energy transfer.

Answer 39

It reduces respiratory loss
The cows will move around less inside a shed SO less energy will be required for movement