Chapter 13

Question 1

What are producers in a food web

Answer 1

Plants

Question 2

How can the amount biomass be measured

Answer 2

Measured in terms of mass of carbon or dry mass of tissue per given area.

Question 3

Energy transfer

Answer 3

Between each trophic level in a food web the majority of the energy is lost due to respiration and excretion. The remaining energy is used to form the biomass.

Question 4

What is eutrophication

Answer 4

Eutrophication is when nitrates leached from fertilised fields stimulate growth of algae in pond.

Question 5

Eutrophication process

Answer 5

The excessive growth of algae creates a blanket on the surface of the water which blocks out light.

As a result plants below cannot photosynthesis and die.

Bacteria within the water feed and respire on the dead plant matter.

This results in an increase in bacteria, which are all respiring and using up the oxygen within the water.
Eventually, fish and other aquatic organisms die due to the lack of dissolved oxygen in the water.

Question 6

What is leaching

Answer 6

Leaching is when water-soluble compounds are washed away, often into rivers or ponds.

Question 7

What could happen if the nitrogen fertiliser leach into water

Answer 7

If nitrogen fertilisers leach into waterways it causes eutrophication.

Question 8

Natural fertilisers

Answer 8

Natural fertilisers are cheaper, and often free if the farmer owns animals.
However, the exact minerals and proportions cannot be controlled.

Question 9

Artificial fertilisers

Answer 9

Artificial fertilisers are chemicals created to contain exact proportions of minerals.

Inorganic substances are more water soluble, and therefore more of these ions dissolve in the water surrounding the soil.

Whilst this is an advantage to the plant for absorbing the nitrates and phosphates, the downside is that their high solubility means that larger quantities are washed away with rainfall and therefore have a greater impact on the environment.

Question 10

Fertilisers

Answer 10

Fertilisers are added to soil to replace the nitrate and phosphates ions lost when plants are harvested and removed from nutrient cycles as crops.
These fertilisers can be either:
• natural (manure)
• artificial (inorganic chemicals).

Question 11

The nitrogen cycle key processes

Answer 11

I. Saprobiotic nutrition and microbes
2. Ammonification
3. Nitrification
4. Nitrogen fixation
5. Denitrification

Question 12

What’s GPP

Answer 12

Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume. It is the total energy resulting from photosynthesis.

Question 13

What’s NPP

Answer 13

Net primary production (NPP) is the chemical energy store in plant biomass taking into account the energy that will be lost due to respiration (R).

Question 14

NPP calculation

Answer 14

NPP = GPP - R

The NPP is the energy left over that is available to the plant to create new biomass and therefore available to the next trophic level in a food web.

Question 15

NPP & gpp

Answer 15

How productive an ecosystem is depends on the abiotic and biotic factors. Plenty of water, light, warmth and green plants will maximise the rates of photosynthesis and therefore result in more carbohydrates being produced in the plants. This can be quantified using GPP and NPP.

Question 16

Net production of consumers

Answer 16

To work out the net production of consumers (N), such as animals, the formula below can be used:
N=I-F+R

= the chemical energy store in ingested food(energy in ingested food)
F = the chemical energy lost to the environment in faeces and urine (energy lost in faeces and urine)
R = respiratory losses.(energy lost in respiration)

Question 17

Rates of productivity

Answer 17

Rates of productivity are recorded using the units kJ ha-l year-I.
• kj is the unit for energy, but these units also includes per unit area and per year.
• It is recorded as per unit area to standardize the results to enable environments to be compared-it takes into account that different environments will vary in size.
• The units are also per year to take into account the impact seasons will have on rain, light and heat - it provides an annual average to allow fair comparisons between environments.

Question 18

THE IMPORTANCE OF THE NITROGEN
CYCLE

Answer 18

The air is 78% nitrogen, however plants and animals cannot obtain nitrogen through gas exchange.
• Nitrogen gas (N,) contains a triple bond. NEN
• Microorganisms are needed to convert nitrogen gas into nitrogen containing substances that plants and animals can absorb.

Question 19

Which biological molecules contain N

Answer 19

Proteins

ATP

Nucleic acids

Question 20

Why are mycorrhizae are beneficial for plant growth?

Answer 20

I. The fungi increase the surface area for water and mineral absorption
2. The mycorrhizae acts like a sponge so holds water and minerals around the roots.
3. This makes plants more drought resistant and able to take up more inorganic ions.

Their part in the nutrient cycles is therefore improving the uptake of relatively scarce ions, such as phosphate ions.

This is a mutualistic relationship.

Question 21

What are mycorrhizae

Answer 21

Mycorrhizae are fungal associations between plant roots and beneficial fungi

Question 22

What is phosphorous used for in organisms

Answer 22

• DNA/RNA
• АТР
• Phospholipid bilayer

It is therefore an essential element for life.

Question 23

Phosphorous cycle

Answer 23

This cycle is different to the carbon and nitrogen, in that phosphorus is not found as a gas and therefore not in the atmosphere.

Instead it is mainly found as a phosphate ion, in mineral form in sedimentary rocks.