energy and ecosystems (3.5.3)

Question 1

define biomass

Answer 1

Most of the sugars synthesised by plants are used by the plant as respiratory substrates. The rest are used to make other groups of biological molecules e.g. cellulose. These biological molecules form the biomass of the plants.

Question 2

what is a respiratory substrate

Answer 2

A respiratory substrate is simply a chemical that can be respired to produce ATP.

Question 3

how can you measure biomass

Answer 3

it can be measured in terms of
-mass of carbon or,
-dry mass of tissue
PER GIVEN AREA

Question 4

why is it important to measure the dry mass instead of the actual mass of tissue

Answer 4

It is important to study the dry mass of tissue, since water content can vary greatly between fresh samples.

Question 5

what does it mean when it says plants are photoautotrophs

Answer 5

means that plants can MAKE THEIR OWN ORGANIC COMPOUNDS using LIGHT energy and simple inorganic molecules
(-algae are also photoautotrophs)

Question 6

how can the chemical energy store in dry biomass be estimated

Answer 6

by a calorimeter

Question 7

describe the method used to estimate the chemical energy store in dry biomass

Answer 7

• Take a fresh sample of tissue and heat at 100 degrees- to boil off the water(can’t exceed this temp as it may burn the sample)
• weigh and heat in intervals until there is NO FURTHER CHANGE IN MASS
• sample then is burnt in pure oxygen within a container called a ‘bomb’
• The ‘bomb’ is surrounded with water which is made out of steel to ensure high heat conduction, as when combustion happens it causes a rise in temp of the water bath
• the water bath is fully surrounded by an insulating layer to reduce heat loss, and has a stirrer to evenly distribute the heat energy.
• The SPECIFIC HEAT CAPASITY can be used to calculate the energy released from the dry tissue

Question 8

Suggest why the GPP of the rainforest is greater than that of the pine forest. (2)

Answer 8

• higher LIGHT INTENSITY of rainforest gives greater rate of photosynthesis
• higher TEMPERATURE of rainforest gives greater rate of photosynthesis
• GREATER RAINFALL in rainforest gives greater rate of photosynthesis

Question 9

define what its meant by productivity

Answer 9

measuring chemical energy stored in biomass that has been produced in a given AREA and given TIME

Question 10

why does so little light energy end up as chemical energy in plants?

Answer 10

• light energy can be reflected
• chlorophyll can’t absorb all wavelengths
• light may miss the chlorophyll molecules
• factor such as; low carbon dioxide concentration or temperature may limit the rate of photosynthesis.

Question 11

why is the efficiency of energy transfer greater when an animal eats an animal, compared to an animal eating a plant? (2 marks)

Answer 11

• cellulose id difficult to digest- lost in faeces

- Meat is more protein-rich; protein is easier to digest