Year 13 - Energy transfers

Question 1

Describe the reasons for low efficiency of energy transfer through ecosystems

Answer 1

• ​Some light is reflected​
• Some light is not the appropriate wavelength so not abosrbed​
• Some light misses chloroplasts​
• Energy lost as heat loss from respiration ​
• Energy lost by faeces as food is not digested​
• Excretion of urea

Question 2

Describe how intensive rearing of domestic livestock increases net production

Answer 2

​Slaughtered when still growing so more energy transferred to biomass tissue​

Fed on controlled diet so higher proportion of food digested and not lost in faeces​

Movement restricted so less heat lost from respiration ​

Kept warm inside so less heat loss to maintain body temperature​

Genetically selected for higher productivity.

Question 3

Describe the action of microorganisms in the nitrogen cycle

Answer 3

1. Mycorrhizae, in legumes root nodules and soil, facilitate the active uptake of nitrate ions and water into plants ​
2. Plants use nitrates to synthesise N containing polymers such as DNA and polypeptides ​
3. Plants die, or plants eaten and then animals die​
   ​ Ammonification during decomposition
4. Saprobionts convert protein, amino acids, DNA into ammonia ​
   ​ Nitrification
5. Nitrifying bacteria oxidise ammonia into nitrite and then into nitrate​
   ​Nitrogen Fixation
6. Nitrogen-fixing bacteria reduce nitrogen gas to ammonia​
   ​ Denitrification
7. Denitrifying bacteria convert nitrates to N2 gas when in anaerobic conditions such as waterlogged soil.

Question 4

Describe the phosphorus cycle whilst highlighting the role of microorganisms

Answer 4

1. Saprobionts decompose dead organisms and excreta ​
2. phosphate ions from phospholipids, DNA and RNA ​
3. Phosphate ions from waste and remains (guano, bones and shells)
4. Phosphate ions transported by streams, river lakes and oceans​
5. Form sedimentary rock ​
6. Weathering and erosion of rock helps phosphate ions dissolve in oceans, lakes and soils. ​
7. Phosphates become available for absorption by plants through active transport and incorporated into biomass. ​
8. Mycorrhizae, in fungi and root systems, facilitate the active uptake of ions and water into plants

Question 5

Describe the mutualistic relationship of mycorrhizae and plants

Answer 5

Mycorrhizae benefit plants by:​
- Increasing the total surface area of the plants root​
- Increasing the absorption of water​
- Increasing the absorption of mineral ions e.g. phosphates and nitrates

Question 6

Describe and explain the environmental impact of using fertilisers (/describe leaching and eutrophication)

Answer 6

• Reduced species diversity as plants adapted to high nitrate concentrations outcompete other species. ​
• Excess nitrate and phosphate (and other) ions are not taken up by the plants and leads to leaching. ​
• High concentrations of ions cause rapid growth of algae causing an algal bloom. ​
• Algae block light from penetrating water causing less photosynthesis ​
• Plants and algae die. ​
• Saprobionts decompose by secreting enzymes onto dead tissue for extracellular digestion. ​
• Increase respiration rate reducing oxygen concentration available to other aquatic life. ​
• Animals increase anaerobic respiration leading to release of toxins and death.

Question 7

Describe why succession eventually causes GPP/NPP to decrease

Answer 7

NPP = GPP – respiratory losses​

NPP decrease due to GPP decrease. ​

GPP decrease caused by large trees reducing sunlight to ground.​

This reduces photosynthesis in plants beneath​

This reduces production of organic molecules therefore less organic biomass.​

Additionally, reduction in biodiversity due to more competition for light in shaded areas.

Question 8

`1. In ecosystems, what do plants use to synthesise organic compounds? ​

2. How do plants use sugars synthesised in plants?​
3. Explain how increase in named biomass can be taken as a measurement of NPP and why it is can be an appropriate measurement​
4. Define GPP ​
5. Define R ​
6. Define NPP ​
7. Define net production of consumers​
8. State appropriate Gross productivity units

Answer 8

`1. aquatic/atmospheric CO2​

2. most for respiratory substrates, some for new biological molecules to form the biomass of plants. ​
3. Represents dry mass/mass of carbon ​
   -Represents GPP – R. (dry mass measures organic matter directly as water content varies).
4. Chemical energy store in plant biomass per area/volume ​
5. respiratory losses to the environment ​
6. chemical energy store in biomass after respiratory losses to the environment ​
   
   • NPP = GPP – R
7. N = I – (F + R) (N = net production of consumers,​ I = chemical energy store in ingested food, ​F = chemical energy lost to environment in faeces,​ R = respiratory losses). ​
8. Unit of energy, per area, per year. E.g. KJ per m2 per year​