Energy Transfers in and Between Organisms: Energy and Ecosystems - Measuring Biomass

Question 1

Define the term biomass

Answer 1

• The mass of living material in an organism

Question 2

How can biomass be measured?

Answer 2

• Mass of carbon an organism contains

- I.e Dry mass of its tissue per unit area

Question 3

What is dry mass?

Answer 3

• Mass of the organism with the water removed

Question 4

How is dry mass measured?

Answer 4

• A sample of the organism is dried, often with an oven using a low temperature until sample reaches a constant mass
• This value can be scaled up to give the total dry mass (biomass) of the total population in the area being investigated

Question 5

What are the typical units for biomass?

Answer 5

• kg m^-2 yr^-1

Question 6

Why is time quoted in the units?

Answer 6

• Biomass changes over time

Question 7

How can you estimate the amount of energy stored in biomass?

Answer 7

• Burn the biomass in a calorimeter
• A sample of dry biomass is burnt and energy is released to heat a known volume of water
• The change in temperature of the water is used to calculate the chemical energy of the biomass

Question 8

How much energy is used to raise the temperature of 1kg of water by 1°C? (J/kg°C)

Answer 8

• 4200 Joules

- Or 4.2 Joules for 1g of water

Question 9

List some of the components of a bomb calorimeter

Answer 9

• Thermometer
• Insulated container
• Sealed bomb with oxygen
• Water
• Motorised stirrer

Question 10

What is the importance of the insulated container?

Answer 10

• To reduce heat loss to the environment by radiation

Question 11

Why is oxygen present in the sealed container?

Answer 11

• To allow complete combustion to occur

Question 12

Why is there a motorised stirrer?

Answer 12

• To evenly distribute heat

Question 13

What is gross primary production (GPP)?

Answer 13

• The total amount of chemical energy converted from light energy by plants, in a given area/volume and time

Question 14

What is respiratory loss?

Answer 14

• Heat that is lost to the environment when organisms respire

Question 15

Approximately how much of the gross primary production is lost to the environment due to respiration?

Answer 15

• 50%

Question 16

What is net chemical production (NPP)?

Answer 16

• The energy left in a plant after respiratory loss is subtracted from the gross primary production

Question 17

Give the equation that describes the relationship between GPP, R and NPP (NPP as subject)

Answer 17

• NPP = GPP - R

Question 18

What is primary production called when it is expressed as a rate?

Answer 18

• Primary productivity

Question 19

How is the net primary production used?

Answer 19

• NPP is energy available to the plant for growth and reproduction
• Also energy is available to organisms at the next stage in the food chain

Question 20

What is net production in consumers (N)?

Answer 20

• Net production (N) is the total chemical energy consumers store after energy losses have been subtracted from the chemical energy of the ingested food

Question 21

List the different ways energy is lost in plants and animals

Answer 21

• Not all energy is absorbed / material is indigestible
• Respiratory loss
• Excretion

Question 22

How is some energy not absorbed in plants?

Answer 22

• Some light misses the leaf and the chlorophyll

- Some wavelengths of light are not absorbed

Question 23

How does respiratory loss differ in plants and animals?

Answer 23

• Animals have a higher respiratory loss

- Animals move more, so more heat is generated from more metabolic reactions

Question 24

How is some energy not absorbed in animals?

Answer 24

• Animals may not eat the whole biomass (e.g roots)

- Some of biomass is indigestible (cellulose/fibre in humans) and is excreted

Question 25

What is the formula for calculating net production?

Answer 25

• N = I - (F+R)

• N = net production
• I = chemical energy in ingested food
• F = chemical energy lost in faeces and urine
• R = energy lost through respiration

Question 26

What is the net production of consumers also known as?

Answer 26

• Secondary production

Question 27

What is net production known as when expressed as a rate?

Answer 27

• Secondary productivity

Question 28

What is the formula of the efficiency of energy transfer?

Answer 28

• % efficiency of energy transfer = (net production of trophic level / net production of previous trophic level) x 100

Question 29

How does the efficiency of energy transfer differ across the food chain?

Answer 29

• As you move up a food chain (from producers to consumers) energy transfer usually becomes more efficient
• Higher proportion of plant biomass is indigestible or not eaten by consumers