Basics of Photosynthesis

Photosynthesis=process that produces 'food' in plants. 'food' it produces is glucose. Photosynthesis uses energy to change carbon dioixed + water into glucose +oxygen. Plants use this glucose for no. of things e.g making cell walls + proteins. 

Photosynthesis happens in chloroplasts in green plant cells - contain pigments like chlorophyll to absorb light. Energy transferred to chloroplasts from environment by light. Photosynthesis=endothermic - means energy is transferred from environment in process. 

Photosynthesis happens in leaves of all green plants - what leaves are for. Word equation for photosynthesis: carbon dioxide + water --(light)--> glucose + oxygen

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How plants use glucose

Glucose used for:

  • Respiration - plants use some of glucose for respiration. Respiration=occurs in all living things=where energy released from breakdown of glucose. Plants use this energy to convert rest of glucose into other substances which can use to build new cells + grow. To produce some of these substances plants also need to gather a few minerals from soil (nitrates)
  • Making cellulose - glucose converted to cellulose for making strong cell walls esp. in rapidly growing plant. These cell walls support + strengthen the cells
  • Making amino acids - in plant cells glucose combined with nitrate ions to make amino acids. Amino acids=building blocks which make up proteins. When amino acids joined together in particular sequence they make up particular protein
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Storage of glucose

Glucose can be converted into other substances for storage: 

  • Lipids - plants convert some of the glucose they produce into lipids (fats + oils). Plants store lipids in seeds.
  • Starch - plants can convert glucose to starch. Glucose=stored as starch so its ready for use when photosynthesis isn't happening as much e.g winter. In plants, starch stored as roots, stems, seeds + leaves. Starch=insoluble=better for storing glucose - a cell with lots glucose in would draw in lots of water + swell up.
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The rate of photosynthesis

Limiting factors in photosynthesis - rate affected by intensity of light, volume of CO2 + temp. All 3 things need to be at right level to allow plant to photosynthesise as quickly as possible. If any one of factors=too high/low it will become limiting factor. Means just factor which stopping photosynthesis happening any faster.

Which factor is limiting at particular time depends on environmental conditions:

  • at night= less light=light limiting factor
  • in winter=cold=low temp limiting factor
  • if warm + bright enough=amount of CO2 limiting factor
  • amount of chlorophyll=can be limiting factor
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Interpreting data on rate of photosynthesis

1.  Effect of light intensity - light provides energy for photosynthesis. Rate increases steadily with light intensity but only to certain point. Beyond that=won't make a difference - as light intensity increases, the rate will no longer increase. This is because is other limiting factor (e.g CO2/temp) not light. Photosynthesis hasn't stopped when graph levels off.

2. Effect of carbon dioxide level - CO2 is one of raw materials needed for photosynthesis. As with light intensity amount of CO2 will only increase rate of photosynthesis to a certain point. After this graph=flattens out = as amount of CO2 increases rate no longer increases. This shows CO2 no longer limiting factor. As long as light + CO2 plentiful in supply then factor limiting photosynthesis=temp.

3. Effect of temp - Enzymes=proteins which increase speed of chemical reaction in living things=enzymes increase rate of photosynthesis in plant cells. The speed at which enzymes work=affected by temp. If temp limiting factor=because too low - enzymes needed for photosynthesis work more slowly at low temps. But if plant=too hot enzymes=denatured (at 45 degrees)

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Interpreting data...


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Investigate Photosynthesis Rate

To investigate effect of light intensities on rate=need to measure rate. One way to do this involves aquatic plant (e.g Canadian pondweed). The rate at which plant produces oxygen=rate at which photosynthesising  - the faster the rate of O2 production, the faster the rate of photosynthesis.

Experiment= source of white light placed at specfic distance from plant. You should then leave plant for couple of minutes to adjust to new light intensity before starting experiment. When ready to start=the plant left to photosynthesise for set amount of time. As it photosynthesises, O2 released= collect in capillary tube.

At end of experiment, syringe is used to draw gas bubble in tube alongside ruler + length of gas bubble measured=proportional to volume of O2 produced. The experiment is repeated twice with light source at same distance + mean volume of O2 produced calculated. Then whole experiment repeated with light source at different distances from plant.

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Investigate Photosynthesis Rate...

Controlling variables - this experiment=investigating effect of different light intensities on rate - light intensity is the independent variable. The dependent variable is amount of O2 produced, which represented by length of bubble. Have to try to keep all other variables constant so=fair test. E.g if plant in flask, keep flask in water bath to keep temp constant.

Calculating rate of photosynthesis - can compare results at different light intensities by giving rate of photosynthesis as length of bubble per unit time e.g cm/min. To calculate rate= divide total length of bubble by time taken to produce it.

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Artificially controlling plant growth

Greenhouses - to artificially create ideal environment which maximises rate of plant growth is to use greenhouse. Commercial growers (people who grow plants for money) often grow large quantities of plants in commercial greenhouses. The following conditions can easily be managed in a greenhouse.

1. Temp - greenhouses help to trap Sun's heat and make sure that temp doesn't become limiting factor. Temp can be controlled in other ways too: farmer might use heater in winter + in summer greenhouses=too hot so farmers might use shades + ventilation to cool it down

2. Light - always needed for photosynthesis=farmers often supply artificial light after Sun goes down to give their plants more quality photosynthesis time

3. Carbon dioxide conc - farmers can also increase level of CO2 in greenhouse. Fairly common way is to use paraffin heater to heat greenhouse. As paraffin burns makes CO2 as by-product.

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Artificially controlling plant growth..(cont)

4. General health of plants - keeping plants enclosed in greenhouse also makes easier to keep them free from pests + diseases. Farmers can add fertilisers to soil as well to provide all minerals needed for healthy growth.

Greenhouse costs - contolling conditions in greenhouse=money - but if farmer can keep conditions just right for photosynthesis plants=grow much faster & decent crop can be harvested much more often, which can then be sold. 

It's important that farmer supplies just right amount of heat, light etc - enough to make plants grow well but not more than plants need as this=wasting money

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Aerobic Respiration

Respiration=process of transferring energy from glucose, which goes on in every cell = exothermic.

Aerobic respiration=respiration with energy=most efficient=most of aerobic respiration reactions in mitochondria. Equation = glucose + oxygen --> carbon dioxide + water

Following ways organism may use energy from respiration= organisms use energy to build up larger molecules from smaller one (amino acids to proteins), animals use energy to allow muscles to contract=movement & mammals + birds use energy to keep body temp steady.

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Anaerobic Respiration

When you do vigorous exercise + body can't supply enough O2 to muscles=start doing anaerobic respiration

Anaerobic=without oxygen=incomplete breakdown of glucose, making lactic acid. Word equation: glucose --> lactic acid

Anaerobic not as efficient as aerobic=glucose not fully oxidised (doesn't combine with oxygen). Anaerobic only useful in emergencies.

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Oxygen Debt

After anaerobic repsiration, when you stop exercising you'll have oxygen debt. Oxygen debt=amount of extra oxygen your body needs after exercise=have to "repay" oxygen you didn't get to muscles in time because lungs, heart + blood couldn't keep up with demand earlier on. This means have to keep breathing hard for a while after you stop=to get more oxygen into blood which is transported to muscle cells. Oxygen Debt=amount of extra O2 body needs after exercise to react with build up of lactic acid + remove it from cells.

Removing lactic acid - The extra oxygen repayed to oxygen debt=used to react with lactic acid to produce harmless CO2 + waterPulse + breathing rate=high whilst are high levels of lactic acid + CO2 to deliver more O2 to cells + take away CO2. Body=another way of coping with high level of lactic acid - blood that enters muscles transports lactic acid to liver. In liver, lactic acid=converted back to glucose.

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Anaerobic respiration in plants + yeast

Is slightly different to animals. Plants + yeast cells can respire without oxygen too but produce ethanol (alcohol) + carbon dioxide (instead of lactic acid). 

Word equation: glucose --> ethanol + carbon dioxide

Fermentation - anaerobic repsiration in yeast cells=fermentation. In food industry fermentation by yeast=great value as used to make bread + alcoholic drinks (beer + wine). In bread-making the carbon dioxide from fermentation that makes bread rise. In beer and wine-making, it's fermentation process that produces alcohol.

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Energy for exercise - muscle cells use oxygen to transfer energy from glucose (aerobic respiration), which is used to contract muscles.

When you exercise some of your muscles contract more frequently than normal=need more energy. Energy comes from increased respiration. The increase in respiration in your cells means you need to get more oxygen in them.

Therefore physical activityincreases your breathing rate + breath volume to meet demand for extra oxygen & increases your heart rate to make your blood flow more quickly, delivering more oxygen + glucose to cells for respiration + taking more CO2 away.

When you do really vigorous exercise, body can't supply oxygen to muscles quickly enough=anaerobic. This is not best way to respire=builds up lactic acid in muscles=painful. Long periods of exercise=muscle fatigue=get tired + stop contracting efficiently.

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Recovery Period

After anaerobic exercise stops=will be 'oxygen debt'. While 'debt' being 'repayed' = known as recovery period

Investigating effect of exercise - you can measure breathing rate by counting breaths + heart rate by taking pulse. E.g To take pulse put 2 fingers on inside of wrist + count no. of beats in 1 min. Can also count in 30s + double it. You could take pulse after:

  • sitting down for 5min
  • then after 5min of gentle walking
  • then again after 5min of slow jogging
  • then again after running for 5min

Your heart rate will increase the more intense the exercise is=body needs to get more O2 to muscles + take away CO2 from muscles. To reduce effect of random errors on results=do as group + plot average heart rate for each exercise.

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Metabolism=all chemical reactions happening in your body, not just in digestion.

In a cell=lots of chemical reactions happening all the time=controlled by enzymes. Many of these reactions linked together to form bigger reactions: reactant --(enzyme)--> product --(enzyme)--> product --(enzyme)-->product.

In some of these reactions, larger molecules=made from smaller ones. Overall these reactions=endothermic.(e.g lots of small glucose joined together to make starch, glycogen + cellulose)

In other reactions, larger molecules broken down into smaller ones. Overall these reactions=exothermic. (e.g excess protein broken down in reaction to produce Urea. Urea then excreted as urine)

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