Energy and ecosystems Flashcards
What is the main way energy enters an ecosystem?
Photosynthesis
Define autotrophic
Organisms able to build up organic compounds from simple molecules.
Define producer.
Photosynthetic organisms that build up complex organic compounds in the process of photosynthesis, from light, water CO2 and minerals.
Define heterotrophic.
Organisms that rely on an external source of organic compounds i.e. they have to take in organic compounds.
Define consumers.
Organisms that eat other organisms.
What are saprobionts?
Also known as decomposers, they break down complex organic compounds in dead organisms. Bacteria and fungi are decomposers.
Define biomass.
The total quantity or weight of organisms in a given area or volume. Units gm-2.
What are food chains?
They display the feeding relationship between organisms. Each level in a food chain is known as a tropic level, the arrows between tropic levels display the energy transfer within the food chain.
What are food webs?
Food chains do not occur in isolation and in a particular habitat many food chains can be linked together to form a food web.
The higher the diversity the more the complex the food web and this means that any one change in the food web will have less of an effect.
How is some energy from the sun lost?
Only about 1-3% of available sunlight energy is trapped in photosynthesis and converted to organic molecules. This is due to:
-Some of the light is reflected by the atmosphere
-Some of the light is the wrong wavelength
-Some light does not fall on chloroplasts and misses the chlorophyll
How is energy lost when consumers eat producers?
Only about 5-10% of energy in the organic molecules (biomass) of the producer is passed to the primary consumer. Due to:
- Some parts of plant being indigestible
- Not all the plant is eaten
How is energy lost when consumers eat consumers?
Only about 15-20% of energy in the organic molecules (biomass) of the primary consumer is passed to the secondary consumer. This is due to:
-Large amounts of the animal may be indigestible
-Not all of the animal may be eaten
-Some energy is lost in excretion such as energy lost in urine
-Energy lost in respiration and as heat to the environment.
Is energy transfer efficient?
Energy transfer is inefficient and results in large losses at each trophic level
Food chains are therefore usually no more than 4-5 trophic levels as there is not enough energy to support a breeding population at a higher trophic level.
What is the equation for net primary production?
NPP = GPP - R
Net primary production = gross primary production - respiration
Remaining glucose available as biomass = glucose produced during photosynthesis - glucose used in respiration
What is the equation for net production?
N = I - (F+R)
Net production = chemical energy stored in ingested food - (energy lost is faeces and urine + energy lot due to respiration)
How do you calculate percentage efficiency?
percentage efficiency = (energy available after transfer/energy available before transfer) x 100
Why does fresh mass vary?
It is dependent on the varying water content of organisms.
What is a limitation of using mass of carbon or dry mass?
The organism must be killed
How is dry biomass obtained?
Via drying out the same in an oven at 100C in order for the all the water to evaporate. The dry mass is determined when the mass is constant.
As dry biomass is measure per given area, in a given time a common unit would be per gram per square meter (gm-2).
What is calorimetry?
It is used to measure the energy stored in the dry biomass of an organism. The dry mass is burnt, within the bomb. The energy released is used to heat the surrounding water which can be measure in kJkg-1.
Explain why only a small proportion of the light reaching the leaves of the oak trees is used to produce new biomass. (3)
Wrong wavelength;
Does not hit chlorophyll/chloroplast;
Reflected;
Used for evaporation of water;
Explain why an increase in biomass can be taken as a measurement of net primary productivity. (2)
- Represents dry mass / mass of carbon;
2. Represents gross production minus respiratory losses;
Accept: NPP = GPP −R.
Accept: Chemical energy minus respiratory losses.
1 and 2. Chemical energy store minus respiratory losses = 2 marks.
What ways do farmers increase productivity/yield?
An increase in productivity is usually brought about by increasing the efficiency of energy conversion. Ways of doing this include:
· Using fertilisers
· Using chemical pesticides, biological agents or integrated systems to control pests
· Intensive rearing of domestic livestock.
Why are fertilisers needed?
As the levels of inorganic ions in the soil is reduced the productivity is reduced, this is because nitrogen is required to produce proteins and DNA, both of which are needed for growth. Soil which is not deficient in nitrates will produce plants that have a higher growth rate and as plants have a greater leaf area the rate of photosynthesis will increase increasing productivity. It is therefore important to replace the lost ions. This can be done by the use of fertilisers.
