Topic 12 - Energy and Ecosystems

Question 1

Define biomass

Answer 1

Total mass of living material.

Question 2

Define producer

Answer 2

Organism that synthesises organic molecules from simple inorganic ones.

Question 3

Define primary consumer

Answer 3

2nd trophic level, eat producers, herbivores.

Question 4

Define secondary consumer

Answer 4

Eat primary consumer.

Question 5

Define tertiary consumer

Answer 5

Eat secondary consumer, usually top of food chain.

Question 6

Define saprobiont

Answer 6

Digest food externally and then absorb the products.

Question 7

What happens to all the energy passing through an ecosystem?

Answer 7

Eventually lost as heat.

Question 8

How would a calorimeter be used to measure the chemical energy store in a recently collected sample of plant matter?

Answer 8

1) Sample is dried by heating it. Removed from oven, weighed at regular intervals until weight is at a constant mass.
2) Placed in a cup, and ignited in an oxygen rich atmosphere.
3) Heat from combustion is transferred to the water.
4) The thermometer measures the temperature of the water.

Question 9

What is the general rule about energy?

Answer 9

It cannot be created or destroyed, only changed from one form to another.

Question 10

Define gross production

Answer 10

The total quantity of energy that the plants in a community converts to organic matter.

Question 11

Define respiratory losses

Answer 11

Plants use 20% to 50% of the gross production energy for respiration, leaving little to be stored.

Question 12

Define net production

Answer 12

The rate at which the plant stores energy.

Question 13

What are some reasons why there is a low percentage of energy transferred at each trophic level?

Answer 13

• Part of the organism not eaten.
• Some parts are eaten but cannot be digested, lost in faeces.
• Some energy excreted, e.g. urine, faeces.
• Some energy lost as heat from respiration.

Question 14

How do you calculate net production?

Answer 14

Net production = chemical energy store of ingested food - (energy lost in faeces and urine + energy lost in respiration)

Question 15

Describe and explain roles of phosphorous in the structure and function of biological molecules.

Answer 15

• Found in phospholipids, they are a component of the phosphate head.
• RNA -> component of sugar phosphate backbone. Joins nucleotides.
• ATP -> In inorganic phosphate group. Lowers activation energy.

Question 16

What is the phosphorous cycle?

Answer 16

• Slower than nitrogen cycle.
• Main reservoir in mineral form.
• NO gas phase.
• Originate in the sea, brought to the surface by geological uplifting of rocks.
• Weathering and erosion of rocks allows phosphate to be released.

Question 17

What is Mycorrhizae?

Answer 17

• Type of fungi that grows around roots of some plants.
• Assists plants with uptake of water and inorganic ions.
• Highly specific to plant species, evolved with them.
• Mutualistic relationship -> both gain a nutritional advantage from each other.
• Have microscopic threads called hyphae, which grow on and into the root tissues, increasing the surface area for the plant.
• Mycorrhizae also saprobiotic -> their hyphae secrete enzymes that hydrolyse biological molecules in leaf litter, releasing ions that can be transported to the plant roots.

Question 18

What are the four stages of the nitrogen cycle?

Answer 18

1) Nitrogen fixation.
2) Ammonification.
3) Nitrification.
4) Denitrification.

Question 19

What is nitrogen fixation?

Answer 19

Process that causes nitrogen molecules found in atmosphere to break apart so nitrogen atoms can combine with other atoms. Occurs by:
- Atmospheric fixation
- Industrial fixation
- Biological fixation by nitrogen fixing bacteria that reduce atmospheric nitrogen with ammonia and make it available to an ecosystem.

Question 20

What is ammonification?

Answer 20

The production of ammonia from organic ammonium-containing compounds (urea).
- Saprobiotic organisms break down (amino acids) from dead animals and waste into ammonia, which is converted into ammonium ions.
- This is where nitrogen enters the non-living component of the ecosystem.

Question 21

What is nitrification?

Answer 21

Aerobic nitrifying bacteria:
- Oxidise ammonium ions to form nitrite ions.
- Another group oxidise nitrite ions to nitrate ions, which can be absorbed (by active transport) into the roots hairs of plants.

Question 22

What is denitrification?

Answer 22

Anaerobic denitrifying bacteria use the nitrate ions as an alternative to oxygen, reducing nitrate to nitrogen gas.
- Denitrification increases in waterlogged soils as less oxygen is present in the soil, creating anaerobic conditions.

Question 23

What are artificial fertilisers?

Answer 23

• Inorganic.
• Rich in nitrogen, phosphorous, and potassium.
• Guaranteed composition.
• Smaller amounts needed as concentrated.

Question 24

What are natural fertilisers?

Answer 24

• Organic.
• Adds organic matter to crop so may improve soil structure and reduce soil erosion.
• Releases nutrients over a long period of time.
• Usually manure, fishmeal, compost, bonemeal.