Biology - Unit 4 - Energy Flow And Nutrient Cycles

Front 1

Essentially what is an ecosystem?

Back 1

All the biotic and abiotic factors of an environment.

Front 2

What is the main way energy enters an ecosystem?

Back 2

Through photosynthesis

Front 3

How is energy transferred in an ecosystem?

Back 3

When one animal eats another or eats a plant

Front 4

What are the different stages in an ecosystem food chain called?

Back 4

Trophic levels

Front 5

What do food chains show?

Back 5

Shows one line of energy transfer in an ecosystem

Front 6

What do food webs show?

Back 6

these show lots of food chains in an ecosystem which overlap.

Front 7

What happens to the energy locked in bones etc?

Back 7

This is recycled back into the ecosystem by microorganisms and decomposers.

Front 8

Commonly how much energy is not taken in by the plant out of initial 100%?

Back 8

About 60% of the energy available is taken in by the plant.

Front 9

Why is not all the energy transferred via trophic levels?

Back 9

Because around 90% of the total energy is lost in various ways (temp. movement etc).

Front 10

What is the net productivity equation?

Back 10

Net

Productivity = Gross prod - respiratory loss.

Front 11

What does each pyramid block represent?

Back 11

A trophic level.

Front 12

What does the area of a block on a pyramid represent?

Back 12

The size of the trophic level

Front 13

What are the three types of pyramid?

Back 13

Number, biomass, energy.

Front 14

What does a pyramid of number show?

Back 14

These show the number of organisms for each trophic level.

Not always pyramid shaped, there can be small numbers of organisms i.e trees.

Front 15

What does a pyramid of Biomass show?

Back 15

These show the amount of biomass at each trophic level, the dry mass at a single moment in time.

They usually always come out as a pyramid shape. (apart from with phytoplankton.)

Front 16

What does a pyramid of Energy show?

Back 16

These show the amount of energy available at each trophic level.

Always pyramid shaped.

Front 17

Is intensive farming more productive than natural ecosystems?

Back 17

Yes

Front 18

What is a natural ecosystem?

Back 18

An ecosystem which has not been changed by human activity.

Front 19

What is the energy input into a natural ecosystem?

Back 19

The amount of sunlight captured by the producers.

Front 20

Essentially what is intensive farming?

Back 20

Control of the abiotic and biotic conditions making it more favourable for livestock.

Front 21

What does intense farming increase essentially?

Back 21

There would be a greater net productivity.

Front 22

What are the three ways intensive farming methods increase productivity?

Back 22

1 - Increase the efficiency of energy conversion.

2 - They remove limiting factors (co2)

3 - They increase energy input, more energy for growth.

Front 23

What are the three main intensive farming practises used?

Back 23

Using chemical pesticides

Using biological agents

Using integrated systems

Front 24

What are pests in farming practises?

Back 24

Pests are organisms which reduce the productivity of the crops, by reducing the amount of energy available for growth.

Front 25

What are the advantages of using Chemical Pesticides?

Back 25

Herbicides kill weeds that compete with agricultural crops for energy. This reduces competition, meaning crops receive more energy, so grow faster and become larger, increasing productivity.

Fungicides kill fungal infections, that damage agricultural crops, more energy growth and les for fighting infection. Grow faster and larger incr productivity.

Insecticides kill insect pests that eat and damage crops, killing insect pests man less biomass is lost from crops, so grow larger meaning productivity is greater.

Front 26

What are the environmental issues with using pesticides?

Back 26

They may directly affect - damage or kill, non pest species e.g. butterflies.

Indirectly affect non pest species e.g. poisoning a secondary consumer who eat a lot of primary consumers containing the pesticide.

Front 27

What are the economic issues with using chemical pesticides.

Back 27

Chemical pesticides can be expensive, may not be profitable for farmers to use them.

Front 28

What are the advantages to using biological agents to increase productivity?

Back 28

Biological agents reduce the number of pests so crops lose less energy and biomass, therefore increasing productivity. Natural predators who are introduced eat the pest species (e.g. ladybirds eat greenfly). Parasites live in/ lay their eggs on a pest insect. These parasites kill the insect or reduce its ability to function, eggs hatch and kill the host. Pathogenic bacteria and viruses are used to kill pests, they can produce toxins which kill specific species.

Front 29

Which environmental issues are raised by the use of Biological Agents.

Back 29

The natural predators introduced to an ecosystem could become a pest species themselves.

Biological agents can affect (damage or kill) other non-pest species.

Front 30

What are the Economic issues raised with Biological Agents?

Back 30

Biological agents may be less cost-effective than chemical pesticides, they can increase the productivity of the plants by a very small amount and only for a short amount of time, with the same amount of money invested.

Front 31

What is an integrated system?

Back 31

Integrated systems use both chemical pesticides and biological agents.

Front 32

What are the advantages of using integrated systems?

Back 32

Using both chemical and biological agents could reduce pest numbers even more than one method alone. Also integrated systems could reduce overall costs especially if one method is particularly expensive. Integrated systems can reduce the environmental impact, because less would be used.

Front 33

What are the advantages of using natural and artificial fertilisers?

Back 33

Provide crops with the minerals for growth (nitrates). More energy from the ecosystem can be used for growth.

Front 34

What are the environmental factors which fertilizers cause?

Back 34

Fertilizers can cause eutrophication.

Changes in the balance of nutrients in the soil which can cause crops and other plants to die.

Front 35

What economic factors does the use of fertilizers cause?

Back 35

Farmers need to get the amount of fertilizer used just right, too much could cause eutrophication too little and crop productivity does not increase.

Front 36

What is the Carbon Cycle?

Back 36

The carbon cycle shows how carbon is passed on and recycled in an environment.

Front 37

What happens in the Carbon Cycle?

Back 37

1) Carbon from air is absorbed by plants which carry out photosynthesis and it becomes carbon compounds found in plant tissues.

2) Carbon is passed onto primary consumers when they eat the producers, it is then passed on to secondary and tertiary consumers when they eat each other.

3)Carbon compounds from dead organisms, are digested by microorganisms called decomposers, feeding on dead organic matter called saprobiontic nutrition.

4) Carbon is returned to the air when living organisms respire, which produces CO2.

5) If dead organisms end up where there are no decomposers the carbon compounds are eventually turned into fossil fuels, over millions of years.

6) The carbon in fossil fuels is released as it burns this is called combustion.

Front 38

Does respiration add or take CO2 from the air?

Back 38

Adds CO2.

Front 39

Does photosynthesis add or take CO2 from the air?

Back 39

Removes CO2.

Front 40

Factors of the daily changes in CO2 concentration with respiration and photosynthesis.

Back 40

Respiration occurs constantly day and night, photosynthesis can only occur during the day. CO2 concentration falls during the day as it is being removed as plants carry out photosynthesis. CO2 concentration increases at night because it is no longer being removed by photosynthesis. But it is still being added by organisms respiring CO2.

Front 41

What are the four processes involved in the Nitrogen Cycle?

Back 41

Nitrogen fixation

Nitrification

Denitrification

Ammonification

Front 42

What happens in the Nitrogen Cycle during Nitrogen fixation?

Back 42

This is where gas from the atmosphere is turned into ammonia by bacteria called Rhizobium. This ammonia can then be used by plants.

Rhizobium are found inside the root nodules of leguminous plants. They form a mutualistic relationship with the plants, they supply the plant with nitrogen compounds and the plant provides them with carbohydrates.

Front 43

What happens in the Nitrogen Cycle during Ammonification?

Back 43

This is where nitrogen compounds from dead organisms are turned into ammonium compounds by decomposers. Animal waste, also contains nitrogen compounds that are turned into ammonium compounds by decomposers.

Front 44

What happens in the Nitrogen Cycle during Nitrification?

Back 44

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

Front 45

What happens in the Nitrogen Cycle during Denitrification?

Back 45

Denitrification is where nitrates in the soil are converted into nitrogen gas by denitrifying bacteria. (use nitrates in the soil to respire releasing nitrogen) This happens under anaerobic conditions. ( where there is no oxygen).

Front 46

What does the Haber process produce?

Back 46

This produces ammonia from atmospheric nitrogen.

Front 47

What is leaching?

Back 47

This is where water - soluble compounds in the soil are washed away by rain or irrigation systems. Often washed into ponds and rivers, often causing eutrophication.

Front 48

What is Eutrophication?

Back 48

1) Nitrates leached from fertilizers stimulate the growth of algae in ponds and rivers.

2) Large amounts of algae block light from reaching the plants below.

3) Eventually the plants die as they are unable to photosynthesise.

4) Bacteria feed on the dead plant matter.

5) Increased numbers of bacteria decrease the oxygen concentration in the water by carrying our aerobic respiration.

6) Fish and other aquatic animals die because there is not enough dissolved oxygen.

Front 49

Name the type of bacteria which convert

nitrogen in the air into ammonium compounds;

nitrites into nitrates.

Back 49

nitrogen fixing

nitrifying

Front 50

Other than spreading fertilisers, describe and explain how one farming practice

results in addition of nitrogen-containing compounds to a field.

Back 50

growing legumes/ named legume;

ploughed in/allowed to decompose/nitrogen-fixing

spread/add manure/slurry;

Front 51

Describe and explain how one farming practice results in the removal of nitrogencontaining

compounds from a field.

Back 51

uptake of nitrates/ammonium compounds by crop;

bare soil/fallow in winter/hedge removal; leaching

Front 52

Explain the role of bacteria in making carbon in dead plant remains available to

plants.

Back 52

decomposers/ saprotrophs;

release enzymes and digest detritus/

substances found in detritus/ eq.;

absorb products of digestion/ suitable e.g. that relates to

candidates 2nd point;

respired and CO

2

released;

used by plants in photosynthesis/ enters leaves;

Front 53

Substances found in fallen leaves contain the elements carbon and nitrogen.

Explain how the activities of decomposers and nitrifying bacteria recycle the substances in

fallen leaves for re-use by the trees.

Back 53

(Decomposers): Secretaion/release of enzymes;

Digest/hydrolyse organic matter;

Absorption /’taken in’ – by named process

e.g. diffusion/active transport

Respiration

Release carbon dioxide;

Carbon dioxide used in photosynthesis;

Release ammonia/ammonium salts/ions/mineral salts / nutrients;

Aerobic/use of oxygen/by oxidation;

[ALLOW correct symbols]

Nitrates/nitrites/ammonium used in synthesis of amino acids/protein

/nucleic acids/other correct organic –N;

Front 54

Explain how the felling and burning of trees on a large scale could affect the concentration

of carbon dioxide in the atmosphere.

Back 54

Burning releases carbon dioxide

Less carbon dioxide removed by trees/less removed in photosynthesis;

Front 55

A large lake is surrounded by fields. These fields are separated from each other by hedges. One

hundred years ago the lake was a habitat for many plants, invertebrates and fish. Today the lake

has no fish and few plants or invertebrates.

Explain how increased use of inorganic fertilisers on the fields may have led to these

changes.

Back 55

run off/leaching of nutrients / nitrates;

leads to increased growth of algae / plants;

competition for light / effect of competition;

death of algae / plants;

increases food supply / increases microorganisms / decomposers;

respiration (of microorganisms) uses up oxygen / increases BOD;

fish / animals die due to lack of oxygen;

Front 56

Describe and explain the effect of Rhizobium bacteria on the growth of soybeans.

Back 56

Forms mutualistic/symbiotic union with soyabean / forms root nodules /

mutual benefits (/described);

makes ammonia/ammonium;

Front 57

Growing the same crop over a large area year after year is known as monoculture.

Explain why an outbreak of pests is more of a problem in monoculture than where a

mixture of crops is grown.

Back 57

eggs / larvae /weeds left in soil;

lots of / plentiful supply of the same food source for pest;

rapid growth/reproduction of pest/more pests;

need to re-apply pesticides/use different pesticides / resistance to

pesticides;

hence lower yield / more of crop affected;

Front 58

Insect pests have developed resistance to pesticides. If the resistance is due to a

single gene, explain how resistant insects could be produced when both parents are

susceptible to the pesticide.

Back 58

resistant allele is recessive;

parents must both be heterozygous/carriers;

produce an offspring which is homozygous recessive;

Front 59

Other than resistance, give two disadvantages of using pesticides.

Back 59

higher dose to have the same effect / develop tolerance;

kill natural enemies/predators of pest;

kill (beneficial) organisms (not a predator) / named;

hazard to user / enters water/food chain;

residue left on crop;

Front 60

The concentrations of carbon dioxide in the air at different heights above ground in a

forest changes over a period of 24 hours. Use your knowledge of photosynthesis to

describe these changes and explain why they occur.

Back 60

(a) 1. High concentration of carbon dioxide linked with night/darkness;

Accept: converse of low in day

2. No photosynthesis in dark/night/light required for photosynthesis

/light-dependent reaction;

Ignore references to rate of photosynthesis in day/night

Accept day = light

3. (In dark) plants (and other organisms) respire;

Must be a reference to plants or all organisms

4. In light net uptake of carbon dioxide by plants/plants use more

carbon dioxide than they produce/rate of photosynthesis greater

than rate of respiration;

Do not allow converse for this point

Accept description of compensation point

5. Decrease in carbon dioxide concentration with height_;

Accept: converse of increase closer to ground

6. At ground level fewer leaves/less photosynthesising

tissue/more animals/less light;

Front 61

Because the forest soil is often nutrient-poor, nitrogen-containing fertilisers may be applied

to ensure good crop yields. Use your knowledge of the nitrogen cycle to explain the

potential benefit of applying a fertiliser containing ammonium nitrate rather than one

containing potassium nitrate.

Back 61

1. ammonium nitrate contains more nitrogen per molecule

than potassium nitrate;

2. nitrate ions in fertiliser available/ absorbed immediately;

3. ammonium converted to nitrate;

4. by nitrifying bacteria/Nitrosomonas and Nitrobacter;

5. fertiliser would provide only the initial release of nitrate/

potassium nitrate;

Front 62

Explain how the decay of dead plants results in reduced oxygen concentration and

increased nitrate production.

Back 62

lower species diversity/number of species;

species tolerant to low oxygen thrive/species requiring high oxygen

die out;

Front 63

Insecticides are pesticides which kill insects. A low concentration of insecticide was

sprayed on the leaves of rose plants to kill greenfly which were feeding on the plants.

Ladybirds eat greenfly. One month after spraying, the concentration of insecticide in the

tissues of ladybirds was found to be higher than the concentration sprayed on the rose

plants. Explain why.

Back 63

greenflies take in (small mass of) insecticide from roses/leaves;

ladybirds eat large numbers of/more/many greenflies;

bioaccumulation idea / insecticide cannot be excreted/remains in

body/stored in fat/not broken down;

Front 64

In the presence of oxygen, respiration yields more ATP per molecule of glucose than

it does in the absence of oxygen. Explain why.

Back 64

Oxygen as terminal hydrogen/electron acceptor;

Operation of electron transport chain/ oxidative phosphorylation;

Fate of pyruvate;

Krebs cycle;

Significance of ATP formed in glycolysis;

Front 65

In China, the fern is cultivated and ploughed into fields to act as an organic fertiliser.

Explain how ploughing the fern plants into the soil results in an improvement in the

growth of the rice crop grown in these fields.

Back 65

Decomposers/ bacteria/fungi/ saprobionts (in fields);

Convert protein/organic nitrogen (in cells of fern) into

ammonium ions (allow ammonia);

Ammonium ions (ammonia) converted to nitrite;

Nitrite converted to nitrate;

By nitrifying bacteria / correctly named;

Nitrate used to form protein / amino acids in rice;

Link between application of fern and protein/cells of rice;

Decomposers respire (suitable substrate) and release Co2

Used in photosynthesis by rice;

Front 66

In these forests, nitrogen in dead leaves is made available to growing plants by the action

of bacteria. Describe the role of bacteria in making the nitrogen in dead leaves available to

growing plants.

Back 66

1. Saprobionts/saprophytes;

2. Digest/break down proteins/DNA/nitrogen-containing substances;

3. Extracellular digestion/release of enzymes;

4. Ammonia/ammonium produced;

5. Ammonia converted to nitrite to nitrate/ammonia to nitrate;

6. Nitrifying (bacteria)/ nitrification;

7. Oxidation;