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Flashcards in Energy transfer & productivity Deck (13):

Where do ecosystems get their energy?

-the sun is the source of energy for ecosystems
-however as little as 1% of tis light energy may be captured by green plants and so made available to organisms in the food chain
-these organisms in turn pass on only a small fraction of the energy that they receive to each successive stage in the chain


How much energy do plants convert?

-between 1 and 3% of the suns energy available to them is converted into organic matter


Why is most of the suns energy not converted to organic matter by photosynthesis?

-over 90% of the sun's energy is reflected back into space by clouds and dust or absorbed by the atmosphere
-not all wavelengths of light can be absorbed and used for photosynthesis
-light may not fall on a chlorophyll molecule
-a factor such as low carbon dioxide levels, may limit the rate of photosynthesis


What is gross primary production?

-the total quantity of chemical energy store in plants biomass, in a given area or volume, in a given time is called the prose primary production or GPP


What is the nets primary production?

-plants use 20-50% of this energy in respiration
-the chemical energy store which is left when these losses to respiration have been taken into account, is called nets primary productivity or NPP


What is nets primary productions purpose?

-the nets primary production is available for plant growth and reproduction
-it is also available to other trophic levels in the ecosystem, such as consumers and decomposers
-usually less than 10% of this nets primary production in plants can be used by primary consumers for growth
-secondary and tertiary consumers are slightly more efficient, transferring p to about 20% of the energy from their prey into their own bodies


Why is there a low percentage of energy transferred at each trophic level?

-some of the organism is not consumed
-some parts are consumed but cannot be digested and are therefore lost in faeces
-some of the energy is lot in excretory materials such as urine
-some energy losses occur as heat from respiration and lost to the environment
-these losses are high in mammals and birds because of their high body temperature
-much energy is needed to maintain their body temperature when heat is constantly being lost to the environment


Why is energy transfer between trophic levels inefficient?

-most food chains only have four or five trophic levels because insufficient energy is available to support a large enough breeding population at trophic levels higher than these
-the total mass of organisms in a particular place is less at higher trophic levels
-the total amount of energy available is less at each level as one moved up the food chain


How do you calculate the efficiency of energy transfers?

-data shows the amount of energy available at each tropic level of a food chain
-the energy available is usually measured in kilojoules per square metre per year
-it is often useful to calculate the efficiency of the energy transfers between each trophic level of these food chains


What is the productivity and farming practices?

-many farming practiced are employed as methods of increasing yields by increasing the efficiency of energy transfer along the food chain
-any practice that reduces the respiratory losses in a human food chain will therefore reduce energy loss and increase yield


How does factory farming increase the energy conservation rate?

-movement is restricted and so less energy is used in muscle contraction
-the environment can be kept warm in order to reduce heat loss from the body most intensively reared species are warm-blooded
-feeding can be controlled so that the animals receive the optimum amount and type of food for maximum growth with no wastage
-feeding can be controlled so that the animals relieve the optimum amount and type of food for maximum growth with no wastage
-predators are excluded so that there is no loss to other organisms in the food web
-this is about converting the smallest possible quantity of food energy into greatest quantity of animal mass


how can we simplifying food webs to increase the efficiency of energy transfer?

-reducing or eliminating organisms which compete with the plant or animal being farmed
-weeds compete with crops for already limited resources such as water, mineral ions, carbon dioxide, space, and light so less is available for the crop plant
-insect pests may damage the leaves of crops, limiting their ability to photosynthesize and thus reducing their productivity
-many crops are now grown in mono-culture, and this enables insect and fungal pests to spread rapidly
-pests may cause disease so the animals may not grow rapidly, be unfit for human consumption or die
-all of which lead to reduced productivity


What is the aim of pest control?

- the aim of pest control is to simplify the food web and so limit the effect of pests on productivity to a commercially acceptable level
-in other words, to balance the cost of pest control with the benefits it brings
-the problem is that at least two different interests are involved: the farmer who has to satisfy our demand for cheap food while still making a living and the conservation of natural resources, which will enable us to continue to have food in the future
-the trick is to balance the two conflicting interests