Flashcards in F215:03:03 Manipulating energy transfer Deck (43):
Define primary productivity
the total amount of energy fixed by photosynthesis
The net flux of carbon from the atmosphere to plants per unit time. It is a rate and can be measured in terms of energy per unit of time.
Give an example of a measurement that can measure primary productivity
What is net primary productivity?
the rate at which carbohydrate accumulates in the tissue of plants of an ecosystem and is measures in dry organic mass, such as kg ha-1yr-1
(rate of production of new biomass available for consumption of heterotrophs)
How is net primary productivity calculated?
Net primary productivity = primary productivity - respiratory heat loss
What % of sunlight energy that reaches Earth is used for photosynthesis
Less than 1%
What happens to all the sunlight that reaches earth that is not being used for photosynthesis?
It is reflected by clouds and the Earths surface
used to heat the Earths atmosphere
To evaporate water
Or is of the wrong wavelength so is not captured by the chlorophyll
What is the energy captured by leaves for photosynthesis known as?
What does R stand for?
When scientisist measures NPP 'in the field' what % is the actual levels for crop plants?
How can humans increase the NPP?
By manipulating environmental factors
By making energy conversion more efficient
By reducing energy loss
Increasing crop yields
How do light levels limit NPP?
As light level limits the rate of photosynthesis
How can light levels be increased to raise the NPP?
Some are planted earlier so the growing season is longer
Some are grown under light banks
How is a lack of water being prevented from reducing NPP?
Crops can be irrigated
Drought-resistance strains have been bred
Give 3 examples of drought-resistant strains being developed to increase the NPP of plants in places that lack water
barley in north africa
wheat in Australia
sugar beet in UK
How can temperature limit NPP?
As it limits the speed of chemical reactions in a plant
How have humans prevented temperature from limiting NPP as much?
By using green houses, which provide warmer temperatures for growing plants and therefore increase NPP
And planting crops early to provide a longer growing season helps to avoid the impact of temp on final yield
Why are crops planted earlier
So the growing season is longer
Allows more light to be harvested by the plants
helps avoid the impact of temp on the final yield
How can a lack of nutrients limit NPP?
As a lack of nutrients slows the rate of photosynthesis and growth
How do farmers prevent there becoming a lack of nutrients which would reduce the NPP?
Crop rotations can help
Particularly planting nitrogen fixing plants which replenishes nitrates in the soil
many crops have been bred to be more responsive high levels of fertiliser
What is crop rotation?
Growing a different crop in each field on a rotational cycle
Give two examples of nitrogen fixing plants
How can pests reduce the NPP of a crop?
as they eat the plantrs and reduce the amount of biomass and stored energy from the food chain and lower the yield
How have humans prevented pests from reducing the NPP of a crop?
By spraying the crops with pesticides
or some plants have been bred to be pest resistant
Or are genetically modified with a bacterial gene (Bt gene)
What does Bt stand for?
Give an example of when plants have been made to be pest resistant using Bt
In Bt-cotton in the USA, its resistant to bollworm and in maize against corn-borers
How do fungal diseases reduce NPP?
They cause root rot, damage to xylem vessels, damage foilage tubes ot damage flowers/fruit
How does root rot reduce NPP?
By reducing water absorption
How does damage to xylem vessels reduce NPP?
by interfering with water absorption
How does the damage of foilage roots reduce NPP?
interfering with the translocation of sugars
How does damage of flowers/fruits reduce the NPP?
interfers with reproduction
How do farmers prevent fungi from reducing NPP?
farmers spray crops with fungicides
Some have been bred to be resistant to fungal infections
Or genetically modified
Give an example of a plant that has been bred to be resistant to fungal infections
Rhizomania resistance in sugar beet
Give an example of how plants have been genetically modified to be resistant to fungal infections
potatoes have been genetically modified to be resistant to potato blight
How can weeds reduce NPP in crops?
They compete with plants for light, water, and nutrients
How do farmers prevent crops from having to compete with weeds for nutrients, water and light?
They spray herbicides on plants to kill the weeds
How efficient is the transfer of energy from producers to consumers?
Why dont primary consumers make full use of a plants biomass?
Some plants die
Consumers dont eat every part of the plant
they dont digest everything they eat, a lot is egested into their faeces
Even what it does digest, only a small amount is stored to use for growth, most is used to keep the animal alive
How do humans manipulate energy transfer from producer to consumer?
- Young animals invest a larger proportion of growth than an adult does, so they are killed earlier to reduce waste
- In the past, steroids have been used, but was outlawed by the EU years ago
- Selective breeding has been used to breed breeds with faster growth rates, increased egg/milk production
- Animals can be treated with antibiotics to reduce unnecessary loss of energy to parasites/pathogens
- mammals and birds waste alot of energy moving around to look for food, and keeping their body temperature stable.
As energy transfer is so inefficient, why don't we just eat the grain directly instead of feeding animals first?
As there are places where grain cannot be grown but animals can exist
Give an example of a place where animals can be grown but grain cant
Sheep can be bred on the mountainsides,
But they are usually infertile so cant be used to grow grain
Why is the balance between animal welfare and efficient food production so controversial?
As many people have serious concerns about modern farming practices.
Suggest which animals would be most efficient to farm:
endotherms like birds and mammals (with a constant body temp)
Ectotherms like worms, fish and reptiles (whose body term varies)
Ectotherms would be the most efficient, as they would not use energy to maintain body temp as endotherms need to.