Nitrogen/phosphate Cycles + Energy Transfers

Question 1

Define Biomass

Answer 1

Mass of carbon (organic compounds)

Question 2

Suggest what you should do to ensure all water is removed from a tissue/sample

Answer 2

Regularly weigh and reheat until mass is constant

Question 3

Define Gross Primary Productivity (GPP)

Answer 3

Chemical energy store in plant biomass, in a given area or volume

Question 4

Define Net Primary Productivity (NPP)

Answer 4

Chemical energy stores in plant biomass after respiratory losses have been taken into account

NPP is available for new plant growth and reproduction or available for other trophic levels in the ecosystem, such as herbivores and sacrobionts

Question 5

Define Net production of consumers

Answer 5

N= I- (F+R)

I represents the chemical energy store in ingested food

F represents the chemical energy lost to the environment in faeces and urine

R represents the respiratory losses to the environment

Question 6

What are the units for biomass?

Answer 6

kJ ha-1 year-1

Question 7

The percentage of the light energy trapped by the producers is very low. Give three reasons why

Answer 7

1) Reflected/absorbed by water vapour
2)Reflected from wrong wavelength
3) Does not strike chlorophyll

Question 8

In natural ecosystems, most of the light falling on producers is not used in photosynthesis

Suggest reasons why

Answer 8

1) Light energy is not absorbed
2) Light is the wrong wavelength
3) Light misses chlorophyll

Question 9

The biomass of primary consumers is less than the biomass of producers. Explain why

Answer 9

1) Loss of energy
2) In respiration
3) In excretion/urine
4) In indigestible parts

Question 10

Describe how and explain why the efficency of energy transfer is different at different stages in the transfer?

Answer 10

1) Some light energy fails to strike
2) Efficiency of photosynthesis in plants is low
3) Respiratory loss/faeces
4) Loss as heat
5) Efficiency is lower in older animals
6) Carnivores consume, digest & assimilate more of their food than herbivores

Question 11

Explain how the intensive rearing of domestic livestock increases net productivity

Answer 11

1) Slaughtered when still growing so more energy transferred to biomass
2) Fed on a controlled diet so a higher proportion of digested food absorbed
3) Movement restricted so less energy used
4) Kept inside so less heat loss
5) Genetically selected for high productivity

Question 12

Describe the role of saprobionts in the nitrogen cycle

Answer 12

1) Secrete enzymes to decompose proteins/DNA/RNA
2) Producing ammonia/ammonium lons:

Question 13

Explain how carbon-containing compounds present in the pine leaves that fall from the trees are absorbed and used for growth by saprobionts/fungi that live in the soil

Answer 13

1) Extracellular digestion
2) By secretion of hydrolytic/digestive enzymes
3) Absorption of digested/soluble products
4) Synthesis of structural compounds
5) Respiration provides energy for the growth of saprobionts

Question 14

What are saprobionts?

Answer 14

1) Fungi/Bacteria that secrete extracelluar enzymes to digest large insoluble organic matter
2) Absorb monomers for assimilation/ respiration

Question 15

Nitrogen compounds in the plants are made available for the main crop after ploughing in spring. Describe the role of microorganisms in this process

Answer 15

1) Proteins/amino acids broken down
2) Ammonification (release of ammonium compounds)
3) By saprobionts
4) Conversion to nitrates via nitrites
5) By nitrifying bacteria
6) Nitrates absorbed into roots via active transport

Question 16

The scientists used units of ug g-1 for the concentration of ammonia in soil

Suggest why, in this investigation, the scientists used these units

Answer 16

1) ug because very little ammonia in the soil
2) ug because avoids use of lots of decimal places

Question 17

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested

Answer 17

Amino acids and DNA

Question 18

Describe why phosphates are needed by a growing plant

Answer 18

Production of DNA, RNA, NADP, and phospholipids in cell membranes

Question 19

Describe how a lack of phosphates in the soil surrounding a plant can affect its growth

Potential essay link

Answer 19

1) Required to make ATP so less energy for growth;
2) Required to make nucleotides, so less DNA for cell division
3) Required to make RuBP/NADP, so less CO2 reduced into sugar,
4) Required to make phospholipids for membranes

Question 20

Outline the advantages of having Mycorrhizae growth near plants

Essay link

Answer 20

1) Mycorrhizae help plants to defend themselves, causing an increase in crop yield
2) Mycorrhizae help plants to take up nitrates/phosphates, causing an increase in crop yield

Question 21

You are given samples of water from three different rivers.

Describe how you would obtain a quantitative measurement of their cloudiness

Answer 21

1) Use of colorimeter
2) Measure the absorbance
3) To standardise method, use same volume of water/filter/shake the sample

Question 22

Describe the process of eutrophication

Answer 22

1) Nitrates/Phosphates/Ammonium ions flushed into the waterway (leaching)
2) Increased algal bloom
3) Light blocked out
4) Submerged aquatic plants are unable to photosynthesise and die
5) Increase in saprobionts so increases rate of aerobic respiration
6) Saprobionts die due to lack of oxygen (anoxic conditions)
7) Increase in anaerobic microorganisms that produce toxins

Question 23

NPP= ?

Answer 23

NPP= GPP - R