Energy Flow And Nutrient Cycles

Question 1

How is energy transferred through ecosystems?

Answer 1

Energy enters an ecosystem by photosynthesis. Plants convert sunlight energy into a form which can be used by other organisms. This energy is transferred when organisms eat other organisms, e.g. Primary consumers eat producers.

Question 2

What do the arrows show in a food web or food chain?

Answer 2

The arrows show the direction of energy transfer.

Question 3

Why is energy transfer between the trophic levels inefficient?

Answer 3

Around 90% of energy is not transferred to the next trophic level. This is because some energy is not taken in by organisms in the first place, e.g. Plants cant use all the light energy because some is the wrong wavelength, etc. Also, some parts of food cannot be eaten, e.g. Bones, etc. Also, some parts of food come out as waste. E.g. Faeces. Some energy which is taken up is used by the animals for respiration, muscle contraction, etc.

Question 4

What is net productivity?

Answer 4

Net productivity is the amount of energy that is available to the next trophic level.

Question 5

How is net productivity calculated?

Answer 5

Net productivity =

gross productivity - respiratory loss

Question 6

What are pyramids of numbers and what do they show?

Answer 6

Pyramids of numbers show the number of organisms in each trophic level. They may not be pyramid shaped because large numbers of primary consumers (e.g. Caterpillars) can eat one tree (producer).

Question 7

What are pyramids of biomass and what do they show?

Answer 7

Pyramids of biomass show the amount of biomass in each trophic level at a single moment in time. They are always pyramid shaped except for one exception.

Question 8

What is the exception when a pyramid of biomass is not pyramid shaped?

Answer 8

Plant plankton can have a smaller biomass than animal plankton in an ocean ecosystem. This is because there is a small amount of them at a given moment in time. However, they have a short life span and reproduce very quickly so there is a lot of them over a period of time.

Question 9

What are pyramids of energy and what do they show?

Answer 9

Pyramids of energy show the amount of energy available in each trophic level in kilojoules per square metre per year. (kJm-2 yr-1).
They are always pyramid shaped.

Question 10

Why are intensive farming systems more productive than natural ecosystems?

Answer 10

Intensive farming involves changing an ecosystem by controlling the biotic and abiotic conditions, e.g. Keeping animals in a heated barn so they don’t use energy for maintaining their body temperature.

Question 11

How can farmers increase productivity of intensive farming?

Answer 11

They can increase the efficiency of energy conversion so more energy is used for growth and less is used for other activities, e.g. Maintaining body temperature. They can increase energy input so more energy is added to the ecosystem so there is more energy for growth. E.g. Give the animals more food.

Question 12

How does use of chemical pesticides increase productivity?

Answer 12

Herbicides kill weeds that compete with crops for energy, so the crops receive more energy and so grow faster and larger.
Fungicides kill fungal infections that damage crops, so crops use more energy for growth and less for fighting infection so the grow faster and larger.
Insecticides kill insects that eat crops, so less biomass of crops is lost so they can grow larger.

Question 13

What are 3 chemical pesticides that can be used on crops?

Answer 13

Herbicides, fungicides and insecticides.

Question 14

What are the environmental issues of using chemical pesticides?

Answer 14

Pesticides can damage or kill non pest species, e.g. Butterflies.
They can affect other animals on the food chain, e.g. If a secondary consumer eats lots of primary consumers which contain a small amount of pesticide, the secondary consumer may be poisoned.

Question 15

What are the economic issues of using pesticides?

Answer 15

Chemical pesticides are expensive, so it may not be profitable for farmers to use them. E.g. The cost of pesticides may be greater than the extra money they would make from the extra productivity.

Question 16

How does the use of biological agents increase productivity?

Answer 16

Biological agents reduce the number of pests, so crops lose less energy and biomass, which increases productivity.

Question 17

What are some examples of biological agents?

Answer 17

Natural predators - can be introduced into ecosystems to eat a pest species.
Bacteria or viruses can be used to kill pests.
Parasites cans be used to live in a pest, the parasite can kill the insect.

Question 18

What are the environmental issues of using biological agents?

Answer 18

If a natural predator is introduced into an ecosystem the predator may become a pest itself.
Biological agents can damage or kill non pets species.

Question 19

What are economic issues of using biological agents?

Answer 19

They may be less cost effective than chemical pesticides, e.g. They don’t have an as fast short term effect. So they tend to increase productivity less than chemical pesticides in the short term.

Question 20

What are integrated systems?

Answer 20

Integrated systems are farms which use both chemical pesticides and biological agents.

Question 21

What are the advantages of integrated systems?

Answer 21

The combined effect of using both can reduce pest numbers even more than using one method alone, so productivity is increased even more.
Interested systems can reduce cost if one method is very expensive. E.g. You could use the expensive method less as the 2 methods are being used together.
They can reduce environmental impacts of pesticides as less is needed to be used.

Question 22

What are fertilisers?

Answer 22

Fertilisers are chemicals that provide crops with minerals which are needed for growth, e.g. Nitrates.

Question 23

Why do farmers use fertilisers?

Answer 23

Fertilisers are used because crops use minerals when they grow. So minerals are a limiting factor of growth. Therefore, if you add a fertiliser it replaces minerals in the soil, so they can be used by plants. So more energy from the ecosystem is used for growth.

Question 24

What are natural fertilisers?

Answer 24

Natural fertilisers are made from organic matter, e.g. Manure.

Question 25

What are artificial fertilisers?

Answer 25

Artificial fertilisers are inorganic, e.g. They contain chemicals such as ammonium nitrate.

Question 26

What are the environmental issues of using fertilisers?

Answer 26

They can be washed into rivers and kill fish and plant life. (Eutrophication).
Also, they can change the balance of nutrients in the soil and if there is too much of a certain nutrient it cans causes crops and other plants to die.

Question 27

What are economic issues of using fertilisers?

Answer 27

Farmers must get the amount of fertiliser they use correct because if the use too much they waste money and the excess fertiliser could get washed into rivers. If they use too little fertiliser they won’t increase there productivity enough, so they won’t make enough money from selling the crop.

Question 28

How does intensive rearing of animals increase productivity?

Answer 28

Animals are kept in warm, indoor pens so there movement is restricted and less energy is wasted maintaining their body temperature. The animals can also be given food which is higher in energy so more energy is available for growth.

Question 29

What is the benefit of intensive rearing of livestock?

Answer 29

More food can be produced in a shorter space of time.

Question 30

What are the ethical issues of intensive rearing of livestock?

Answer 30

Some people believe that the conditions animals are kept in causes them pain, distress and restricts their natural behaviour, so it shouldn’t be done.

Question 31

What happens in the carbon cycle?

Answer 31

Carbon (in there form of CO2 from air or water) is absorbed by plants when they photosynthesise. This carbons become carbons compounds in plant tissue. The carbon is passed onto primary consumers when they eat the plants, and secondary consumers when they eat primary consumers, etc. When organisms continuing carbon die, they are decomposed by saprobiotic microorganisms. This returns the carbon to the air as organisms respire, which produces CO2. If dead organic matter is not decomposed, it turns into fossil fuels over millions of years. When fossil fuels are burned, CO2 is released (combustion).

Question 32

Describe the daily change in CO2 concentration.

Answer 32

Respiration happens constantly throughout the day and night, which produces CO2. Photosynthesis can only take place in daylight hours. Therefore, the CO2 concentration falls during the day, as it is removed from the atmosphere by photosynthesising plants. The CO2 concentration increases at night because photosynthesis cannot happen at night, so CO2 isn’t removed, but all organisms are still respiring, which adds CO2 to the atmosphere.

Question 33

Describe the yearly change in CO2 concentration.

Answer 33

Most plant growth and photosynthesis happens in summer as that is when the light intensity is greatest. Therefore, more photosynthesis occurs in summer. CO2 concentration falls in summer because more CO2 is removed from the atmosphere by photosynthesising plants. CO2 concentration increases throughout autumn and winter and there is less light intensity, so less photosynthesis can happen and therefore less CO2 is removed from the atmosphere.

Question 34

What is the greenhouse effect and how does it cause global warming?

Answer 34

The greenhouse effect is when greenhouse gases, e.g. CO2 block energy from going out into space. This energy reflects back towards earth and is trapped in the atmosphere. Therefore, less energy is lost to space and the Earth warms up.

Question 35

Why is the CO2 concentration is the atmosphere increasing?

Answer 35

In the last 200 years CO2 concentration has increased rapidly. It is increasing because more fossil fuels, e.g. Gas, oil and coal are being burnt in power stations, cars, etc. Burning fossil fuels releases CO2 into the atmosphere. Also, things which store carbon are being destroyed, e.g. Trees. If the trees are burnt down CO2 is released from combustion and if the trees are decomposed, saprobiotic microorganisms break down the carbon compounds and respire.

Question 36

Why is methane concentration in the atmosphere increasing?

Answer 36

More methane is being released into the atmosphere because more fossil fuels are being extracted, there is more decaying waste and more cattle, which give off methane as a waste gas. Also methane can be released from natural stores, such as frozen ground. If temperatures increase these stores can thaw and release lots of methane into the atmosphere.

Question 37

What are 2 greenhouse gases?

Answer 37

Carbon dioxide and methane.

Question 38

How does global warming affect crop yield?

Answer 38

An increasing CO2 concentration can cause a higher crop yield as CO2 is a limiting factor of photosynthesis. Therefore, increasing CO2 concentration means crops grow faster and so increases crop yield.

Question 39

How does global warming affect insect pests?

Answer 39

Some species can become more abundant, e.g. If there are warmer and wetter conditions there can be an increase in the number of Mosquitos. Also, some insects can become less abundant, e.g. Some insects can only survive in specific temperature ranges so if it gets too hot fewer insects will survive.

Question 40

How does global warming affect wild animals and plants?

Answer 40

Some species will become more widely distributed, e.g. Species which thrive in a warm environment will become more widely distributed as there are more warmer environments. Some species will become less widely distributed, e.g. Species which need cold temperatures will be less widely distributed as there are less cold environments. Global warming can affect the numbers of plants and animals, e.g. Some species are becoming more abundant and some species are becoming less abundant.

Question 41

What is nitrogen fixation?

Answer 41

Nitrogen fixation is when nitrogen gas in the atmosphere is turned into ammonia by bacteria which live in the root nodules of plants.

Question 42

What is ammonification?

Answer 42

Ammonification is when nitrogen compounds from dead organisms are turned into ammonium compounds by decomposers.

Question 43

What is nitrification?

Answer 43

Nitrification is when ammonium compounds in the soil are changed into nitrogen compounds which can be used by plants by nitrifying bacteria. Nitrifying bacteria change ammonium compounds into nitrites and then nitrites into nitrates.

Question 44

What is denitrification?

Answer 44

Denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria. The denitrifying bacteria use the nitrates to respire and produce nitrogen gas. This only happens where there is no oxygen.

Question 45

What is leeching?

Answer 45

Leeching is when water soluble compounds in the soil are washed away, e.g. By rain.

Question 46

How is eutrophication caused?

Answer 46

Nitrogen fertilisers can be washed into rivers by rain.

Question 47

What happens during eutrophication?

Answer 47

Fertilisers that are applied to fields can be washed into rivers and ponds by rain. Nitrates in the fertiliser causes the algae to grow. Large amounts of algae block light from reaching plants below the surface. The plants below die because they don’t get enough light or photosynthesise. Bacteria feed on the dead plants. The bacteria respire which reduces the oxygen concentration of the river. Fish die because they isn’t enough oxygen in the water.

Question 48

What are trophic levels?

Answer 48

Trophic levels are the stages of the food chain, e.g. Produces, primary consumers, etc.