Energy and Ecosystems

Question 1

Define:
- Biomass
- Producers
- Consumers
- Decomposers

Answer 1

• Biomass - the total mass of living material in a specific area at any given time.
• Producers - photosynthetic organisms that manufacture organic substances using light energy, water, carbon dioxide and mineral ions.
• Consumers - organisms that obtain their energy by feeding on other organisms rather than using. light energy from the sun directly.
• Decomposers - (detrivores/saprobionts) group of organisms that break down the complex materials in dead organisms into simpler ones.

Question 2

Why is not all of the sun’s available energy converted into organic matter in plants?

Answer 2

• ≥ 90% of the sun’s energy is reflected back into space by clouds or dust, or absorbed by the atmosphere.
• not all wavelengths of light can be absorbed and used for photosynthesis.
• a factor such as low CO2 levels may limit rate of photosynthesis.

Question 3

Name 4 ways in which energy can be lost in food chains.

Answer 3

• some parts of the organism aren’t eaten.
• some parts are eaten but cannot be digested sour are lost in faeces.
• some of the energy is lost in excretory materials like urine.
• some energy losses occur as heat from respiration and directly from the body to the environment.

Question 4

Define:
- Gross production
- Net production

Answer 4

• The total quantity of energy that the plants in a community covert to organic matter.
• The rate at which plants store energy.

Question 5

Give the equation for calculating Net production in plants and consumers.

Answer 5

Plants: Net production = gross production - respiratory losses
Consumers: Net production = chemical energy consumed - (excretions + respiratory losses)

Question 6

Why can the overall energy transfer between trophic levels only reach 4 or 5 levels?

Answer 6

• The overall energy transfer is insufficient so unable to support large enough breeding populations at higher trophic levels,

Question 7

Name the four main stages of The Nitrogen Cycle.

Answer 7

1 - Ammonification - production of ammonia from organic nitrogen - containing compounds. Saprobionts feed on dead organisms, release ammonia, which forms ammonium ions in soil.
2 - Nitrification - conversion of ammonium ions to nitrate ions. Oxidation reaction so releases energy. 1st stage: oxidation of NH4+ to NO2-, 2nd stage: oxidation NO2- to NO3-.
3 - Nitrogen Fixation - nitrogen gas into nitrogen - containing compounds.
4 - DeNitrification - soils becomes waterlogged, anaerobic denitrifying bacteria, converts soil nitrates into gaseous nitrogen, lost in atmosphere.

Question 8

Name the bacteria/micro-organisms found during in The Nitrogen Cycle, and their roles.

Answer 8

• Nitrogen Fixation - free-living nitrogen fixing bacteria/mutalistic nitrogen fixing bacteria.
• DeNitrification - anaerobic denitrifying bacteria.
• Nitrification - Nitrifying bacteria.
• Ammonification - Saprobiontic micro-organisms.

Question 9

Why can gaseous nitrogen not be used by plants?

Answer 9

• Nitrogen gas is unreactive and not easily converted into other compounds. Most plants only take nitrogen up by active transport in the form of ammonia or nitrate ions.

Question 10

What is the role of mycorrhizae fungi in nutrient cycles?

Answer 10

• Naturally occurring fungus found in soil.
• Form a symbiotic relationship with roots of trees and other plants.
• Increase surface area of roots for increases absorption of nutrients from the soil.

Question 11

How do fertilisers increase productivity?

Answer 11

• they return the essential elements needed for growth/yield to the soil.
• (e.g:) nitrogen, phosphate and potassium.