Free Manipulating Biomass Transfers OCR A Level Biology revision notes – covering specification point 6.3.1(b).
Manipulating the Transfer of Biomass
Farming aims to maximise the productivity of biomass production, so biomass transfers will be manipulated to increase the yield of food produced from crops and livestock.
Biomass transfers can be manipulated at either the primary productivity or secondary productivity level:
- Primary productivity is manipulated by reducing the limiting factors for photosynthesis, so that the rate of biomass production in the first trophic level is increased.
- Secondary productivity is manipulated by reducing energy loss and usage from consumers, so that more biomass goes into growth.
Increasing Primary Productivity
Improving primary productivity in farming involves increasing the rate of photosynthesis in plants and reducing the biomass lost to disease, fungi and pests.
The table below outlines how some of the factors that limit photosynthesis are manipulated to increase primary productivity:
| Factor | Manipulation |
|---|---|
| Fungal diseases | Applying fungicides or growing disease-resistant varieties keeps leaves healthy and prevents the loss of photosynthetic tissue. |
| Light availability | Plants grown in a greenhouse can be grown under artificial light, or shading can be removed by removing competing plants or thinning crops so that more light can be absorbed for the light-dependent reaction. |
| Mineral ions/ nutrients | Applying fertilisers, or carrying out crop rotation with nitrogen-fixing legumes, supplies the mineral ions needed to build biomass (e.g. nitrate for amino acids, magnesium for chlorophyll). |
| Weeds | Removing weeds with herbicides, by hand, or through biological control reduces the competition for light, water and mineral ions. |
Increasing Secondary Productivity
Improving secondary productivity in farming involves increasing the efficiency of animals converting consumed plant biomass into new animal biomass.
The table below outlines how the factors that reduce the efficiency of secondary productivity are manipulated:
| Factor | Manipulation |
|---|---|
| Disease | Controlling the spread of diseases with hygiene, or using antibiotics or medicines, reduces the energy lost to the immune response. |
| Feed quality | High-quality, easily digestible feed increases the proportion of consumed biomass that is absorbed and incorporated into animal biomass, as it reduces the biomass lost in faeces. |
| Temperature | Keeping animals at an optimal temperature reduces energy loss through maintaining body temperature. |
| Movement | Restricting animal movement reduces the energy lost through respiration. |
It is important to note that many farming practices which increase the efficiency of secondary productivity raise ethical issues due to poor animal welfare. This is because the unnatural conditions animals may be kept in reduce the opportunity for them to express normal behaviours (e.g. moving around, socialising), and increase the prevalence of disease.