Energy And Ecosystems

Question 1

Trophic level

Answer 1

• the stage in a food chain where an organism is found

Question 2

What does it mean that plants are photoautotrophs?

Answer 2

• they can make their own organic compounds using light energy and simple inorganic molecules

Question 3

what are classed as heteroautotrophs?

Answer 3

• primary (herbivores) and secondary (carnivores and omnivores) consumers

Question 4

What are saprobionts?

Answer 4

• bacteria and fungi are decomposers that break down dead organic material and wastes from organisms at various other trophic levels

Question 5

Why do saprobionts play a critical role in the ecosystem?

Answer 5

• they help to release nutrients from material that can be recycled and used as building blocks by primary producers

Question 6

How much percentage of energy is transferred from one trophic level to the next?

Answer 6

• 10%

Question 7

What are the reasons to why only 10% of energy is passed along a food chain?

Answer 7

• respiration, energy lost in faeces, not all of the organism is eaten, some energy excreted in urine, some organisms die

Question 8

What do the inefficiency of energy transfers between trophic levels explain?

Answer 8

• why biomass decreases with each trophic level, why food chains usually only have four or five trophic levels (not enough biomass available to support higher trophic levels)

Question 9

What is biomass?

Answer 9

• the mass of carbon or mass of dry tissue in a given area at a given time

Question 10

What is the measurement of biomass?

Answer 10

• gm^-2 / gm^-3

Question 11

What is the issue with including water in a measurement of an organisms biomass?

Answer 11

• water content varies between fresh samples and need to dry out completely

Question 12

How would you determine the dry mass of a sample of plant material and why not heat over 100?

Answer 12

• heat to temp to evaporate water, weigh and heat until no further change in mass
• heating over 100 would burn the sample

Question 13

How can the chemical energy store in dry biomass be estimated?

Answer 13

• using a calorimeter

Question 14

How to use a calorimeter?

Answer 14

• take fresh sample of tissue and heat in oven at 100 degrees celcius to evaporate off all the water
• weigh and heat until no further change in mass
• put known mass of dried sample in calorimeter
• sample is burnt in pure oxygen within this device to achieve complete combustion

Question 15

Why should you weigh sample until no further change in mass?

Answer 15

• to ensure all water is evaporated

Question 16

What are the features on a calorimeter that would enable a valid measurement of heat energy released?

Answer 16

• stirrer (distributes heat energy), insulation (reduces loss or gain of heat), water has high specific heat capacity

Question 17

What is secondary production?

Answer 17

• chemical energy stored in consumer biomass in given area

Question 18

How can net secondary production of consumers be calculated?

Answer 18

• chemical energy stored in ingested food - (chemical energy lost in faeces and urine + respiratory losses)

Question 19

What is net primary productivity?

Answer 19

• total energy after respiratory losses available for plant growth and reproduction (less than ten percent passes to primary consumers)

Question 20

How to work out net primary productivity?

Answer 20

• gross primary production - respiratory losses

Question 21

How much percentage of gross primary production is lost in respiration?

Answer 21

• 50%

Question 22

What is gross primary production?

Answer 22

• total energy in given area, in given time fixed by plants and converted to biomass (about 40% of the total energy available at the start)

Question 23

What does productivity refer to?

Answer 23

• chemical energy stored in biomass that has been produced in a given area in a given time

Question 24

What units does productivity have?

Answer 24

• kJ ha^-1 year^-1

Question 25

What is 1 ha?

Answer 25

• 1 hectare = 10,000 m^2

Question 26

Why does so little light energy reaching a plant end up as chemical energy?

Answer 26

• sunlight can be reflected, not all wavelengths can be absorbed by chlorophyll, light may miss chlorophyll molecules, low carbon dioxide concentration or temperature may limit rate of photosynthesis

Question 27

Why the efficiency of energy transfer is greater when an animal eats an animal compared to animal eating plant?

Answer 27

• cellulose in plants is difficult to digest, meat is more protein rich and protein easier to digest

Question 28

Suggest and explain two ways of reducing respiratory losses within human food chain

Answer 28

• restrict animal movement so less respiration needed and less energy wasted, keep animals warm indoors so less energy needs to be released by respiration to help animals maintain body temperature