Energy and Ecosystems

Question 1

Biomass

Answer 1

mass of carbon/ dry mass of tissue in a given area, in a given time.

Question 2

How can the chemical energy stored in biomass be estimated?

Answer 2

using calorimetry

Question 3

What is GPP?

Answer 3

Gross Primary Production = chemical energy store in plant biomass, in a given area/ volume and time.

Question 4

What is NPP?

Answer 4

Net Primary Production =chemical energy store in plant biomass after respiratory losses (R, to environment) are taken into account

Question 5

What is R, and why does it occur?

Answer 5

Respiratory losses - as plants use some of their chemical energy store for respiration.

Question 6

Primary productivity of plants equation

Answer 6

NPP = GPP - R

Question 7

What is NPP available for?

Answer 7

NPP is energy available for plant growth and reproduction. It is also available to other trophic levels in an ecosystem - e.g. herbivores, decomposers.

Question 8

Food chain stages

Answer 8

Producer
↓
Primary consumer
↓
Secondary consumer
↓
Tertiary consumer

Question 9

What are saprobionts?

Answer 9

decomposers - break down material in dead organisms, releasing the compounds so they can be recycled. E.g. fungi, bacteria.

Question 10

Why is energy transfer from 1 trophic level to the next not 100% efficient? Give examples.

Answer 10

Some energy is transferred to the surroundings at each stage.
- Respiration/ movement: energy transferred to the surroundings as heat. Heat transfer is greater in organisms that regulate their body temperature (endotherms).

• In excretory materials: faeces, urine. Not all food can be digested.
• Not all of an organism is eaten - bones, roots

Question 11

Net production of consumers equation

Answer 11

N = I - (F+R)
I = chemical energy store in ingested food
F = chemical energy lost to the environment in faeces
R = respiratory losses to the environment

Question 12

How do farming practices aim to increase yield? 2 ways

Answer 12

By increasing the efficiency of energy transfer - by reducing respiratory losses from livestock and by simplifying food webs.

Question 13

How can simplifying food webs reduce energy losses to non-human food chains?

Answer 13

by removing organisms that compete with those being farmed. (Pest control.)

Question 14

How can reducing respiratory losses increase the efficiency of energy transfer?

Answer 14

• Using the smallest possible quantity of energy in food into the greatest possible quantity of animal biomass, which can be passed on to the next trophic level.
• As much energy as possible goes into growth.
• Factory farming increases energy conversion as movement is restricted, the environment can be kept warm, feeding can be controlled and predators are excluded.

Question 15

Pyramids of energy units

Answer 15

kJ m^-2 year^-1

Question 16

Why is nitrogen needed by living organisms?

Answer 16

to produce proteins, nucleic acids and ATP

Question 17

Name the key stages of the nitrogen cycle.

Answer 17

ammonification, nitrification, nitrogen fixation, denitrification, feeding, assimilation by plants

Question 18

Describe ammonification

Answer 18

The production of ammonia from organic N-containing compounds found in dead organisms and excretory materials.
Saprobionts feed on these materials, releasing ammonia, which forms ammonium ions in the soil. (non-living component).

Question 19

Describe nitrification, including the conditions needed.

Answer 19

2 stages:
Oxidation of ammonium ions, NH4+, to nitrite ions, NO2-
Oxidation of nitrite ions to nitrate ions NO3-.

Oxygen is needed for these reactions, so it is important for farmers to keep soil well aerated by ploughing.

Question 20

Role of bacteria in nitrification

Answer 20

Nitrifying bacteria

• obtain energy from chemical reactions involving ions - here, the conversion of ammonium ions, NH4+ to nitrate ions, NO3-. This is an oxidation reaction.

Question 21

Describe nitrogen fixation.

Answer 21

N2 gas is converted into nitrogen containing compounds.

Question 22

Role of bacteria in nitrogen fixation

Answer 22

nitrogen fixing bacteria live in the root nodules of leguminous plants and have a mutualistic relationship with the plant - they provide the plant with nitrogen compounds in return for carbohydrates.

Question 23

Describe denitrification and where it can occur.

Answer 23

Denitrifying bacteria convert nitrates to N2 gas. This occurs in anaerobic conditions, e.g. waterlogged soils.

Question 24

Why is denitrification bad?

Answer 24

It reduces the amount of nitrates in the soil which plants can use to make substances needed for growth.

Question 25

Why do living organisms need phosphates?

Answer 25

to make ATP, phospholipids and nucleic acids

Question 26

In what form does most phosphorus exist?

Answer 26

as phosphate ions, PO4 3-, in sedimentary rocks.

Question 27

Describe what happens in the phosphorus cycle after phosphate ions are released from rocks

Answer 27

• phosphate ions are released into the soil by weathering
• they are taken into plants via the roots
• transferred through the food chain as animals eat the plants and are eaten by other animals
• lost from animals in waste products
• saprobionts break down organic compounds in dead plants and animals and watses, releasing phosphate ions into the soil.

Question 28

Describe the aquatic part of the phosphorus cycle

Answer 28

• weathering of rocks releases phosphates into waterways (e.g. rivers).
• phosphates are taken up by aquatic producers (algae) and passed along the food chain.
• the wastes produced by sea birds contains a high proportion of phosphate ions.

Question 29

Role of mycorrhizae

Answer 29

Strands of fungi connected to plant roots which have a symbiotic relationship with plants - they increase the surface area of the plant root system, helping the plant absorb scarce ions like phosphate from the soil. also increase uptake of water.

Question 30

Describe the process of saprobiontic nutrition.

Answer 30

Saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need. This is extracellular digestion - organic molecules are broken down into inorganic ions.
Saprobiontic nutrition = obtaining nutrients from dead organic matter using extracellular digestion.

Question 31

Why are nutrients lost when crops are harvested?

Answer 31

mineral ions are taken up by crops but then removed as the crops are harvested and used for food - the plants do not die and decompose, as would naturally happen.

Question 32

Why are nutrients lost when animals are removed from land?

Answer 32

Animals eat grass and plants, taking in nutrients. When they are slaughtered or transferred, the nutrients aren’t replaced through their remains or waste products.

Question 33

What are the 2 types of fertiliser?

Answer 33

artificial and natural

Question 34

What are artificial fertilisers?

Answer 34

inorganic: they contain chemicals(compounds of nitrogen, phosphorus and potassium) mined from rocks or deposits, in the best ratio for a certain crop.

Question 35

What are natural fertilisers?

Answer 35

organic - dead or decaying animal or plant remains, animal wastes like manure

Question 36

How do fertilisers increase productivity?

Answer 36

Fertilisers contain the minerals needed by plants for growth. When these minerals are readily available to plants, they are likely to develop earlier and grow larger, hence increasing the rate of photosynthesis and crop productivity. ⇒ cheaper food.

Question 37

Disadvantages of artificial fertilisers

Answer 37

reduced species diversity - nitrogen-rich soils favour fast-growing plants, which could out-compete other species
leaching
eutrophication

Question 38

describe the process of eutrophication.

5 stages

Answer 38

1. mineral ions leach from fertilised fields and stimulate rapid algal growth in waterways.
2. large amounts of algae block light, preventing it from reaching plants below.
3. plants die as they are unable to photosynthesise enough.
4. saprobiontic bacteria feed on the dead plant matter. Increased numbers of bacteria reduce oxygen concentration of the water as they respire aerobically.
5. fish and other aquatic organisms die as O2 concs are too low.

Question 39

What is leaching?

Answer 39

when water-soluble compounds in the soil are washed away, into nearby waterways.

Question 40

Why does leaching occur?

Answer 40

when more fertiliser (containing inorganic ions) is applied than plants need or can use. Soluble inorganic ions dissolve in water and leach into waterways.

Question 41

What can leaching lead to?

Answer 41

eutrophication

Question 42

Why is leaching more likely with artificial than natural fertilisers?

Answer 42

Artificial fertilisers contain soluble inorganic ions which are likely to be leached if not used immediately.
In natural fertilisers, nitrogen and phosphorus are still in organic molecules which need to be decomposed by microorganisms before absorption by plants. Inorganic ions (from breakdown) are released into the soil more slowly, so leaching is less likely.

Question 43

Eutrophication

Answer 43

(d) 1.
2. Plants (cover surface and) block out light so plants (under surface) die;
3. Increase in (aerobic) bacteria / decomposers (which break down plants);
4. Bacteria / decomposers use up oxygen / reduce oxygen conc. in water;
5. In respiration;
6. Plants unable to photosynthesise so less oxygen produced;
Increased phosphate causes increase in plant growth / algal bloom;