6.5.3 manipulating transfer of biomass

Question 1

define gross primary productivity

Answer 1

rate at which plants convert light energy into chemical energy through photosynthesis

Question 2

why do humans manipulate environmental factors

Answer 2

• make energy conversion more efficient
• reduce energy loss
• increase amount of biomass incorporated into plants

Question 3

how can light levels be manipulated

Answer 3

• some crops planted early to provide longer growing season to harvest more light
• others grown under light banks

–> light level limits rate of photosynthesis = limits production of biomass

Question 4

how can watering plants be manipulated

Answer 4

• irrigating crops
• drought-resistant strains strains have been bred (eg. sugar beet in UK)

–> water is reactant in photosynthesis when glucose is produced

Question 5

how can temperature be manipulated

Answer 5

• growing plants in greenhouses provides warmer temperature = increases rate of photosynthesis & rate of production of biomass
• planting field crops early provides longer growing season & helps avoid impact of temperature on final yield

Question 6

how can nutrients be manipulated

Answer 6

• crop rotation = stops reduction in soil levels of inorganic materials (eg. nitrate, potassium)
• include nitrogen-fixing crop (eg. peas) in cycle replenishes nitrogen levels
• many crops bred to respond to high levels of fertiliser = provides ammonium, nitrate, potassium & phosphorous

Question 7

how can pests be manipulated

Answer 7

• spraying pesticides can help
• some plants bred to be pest-resistant or genetically modified with bacterial gene (Bt gene)

Question 8

how can fungi be manipulated

Answer 8

• spray crops with fungicides
• many crops bred to resist fungal infections
• eg. potatoes genetically modified to resist potato blight

Question 9

how can competition (from weeds) be manipulated

Answer 9

• use herbicides to kill weeds
• usually binds to enzyme = stops it from working & frequently leads to toxic build-up of enzyme’s substrate

Question 10

how can humans manipulate energy transfer (secondary productivity)

Answer 10

• harvesting animals just before adulthood minimises loss of energy in food chain as invests more energy into growth
• selective breeding used to produce improved animal breeds with faster growth rates, increased egg production & increased milk production
• animals may be treated with antibiotics to avoid unnecessary loss of energy to pathogens/parasites
• zero grazing for pig & cattle farming maximises energy allocated to muscle by stopping animals moving about, by supplying food to them, & keeping environmental temperature constant