Photosynthesis is the process in which the raw materials water and carbon dioxide are used to make glucose. Oxygen is produced as a by-product.
It takes place within the chloroplasts within the leaf. Chlorophyll is found here which is used to absorb light energy. This is an endothermic process.
Equation: 6CO2 + H2O -> C6H12O6 + O2Carbon dioxide + Water -> Glucose + Oxygen
Caption: : The chloroplasts are in the palisade cells
Slide 2
Limiting Factors
A limiting factor of photosynthesis is a factor that is stopping the process of photosynthesis from taking place faster
The limiting factors of photosynthesis are light, concentration of CO2 and temperature
All of these factors have an overall effect upon the rate of photosynthesis. The environmental conditions determine which factor is limiting
At night it is light
In winter it is temperature
If it is warm and bright enough then concentration of CO2 may be the limiting factor
Chlorophyll can also be a limiting factor. Amount of chlorophyll can be affected by disease (e.g. tobacco mosaic virus) or lack of nutrients.
These factors can cause chloroplasts to become damaged or not be able to produce enough chlorophyll
The rate of photosynthesis is therefore reduced as not as much light can be harnessed
Light provides the energy that is required for the process of photosynthesis
When light intensity is a limiting factor and light level is raised then the rate of photosynthesis increases steadily but up to a point
From this point onward either temperature of carbon dioxide concentration will be limiting
A light meter is used to get accurate results of light intensity
Caption: : Rate of photosynthesis against light intensity
Caption: : Rate of photosynthesis against carbon dioxide concentration
Carbon dioxide is one of the raw material needed for photosynthesis
The graph is similar to the light intensity graph because it is only the limiting factor up to a point
From that point onward the line flattens out as it is no longer the limiting factor
If light and carbon dioxide concentration are in perfect supply then temperature may be the limiting factor
Caption: : Rate of photosynthesis against temperature. The optimum temperature is located where the peak of the line is
Temperature is normally a limiting factor if it is too low
Enzymes (biological catalysts) are used in photosynthesis for various chemical reactions
Enzymes work slowly at lower temperatures but work very well at optimum temperatures
If the plant gets too hot however, the enzymes needed for photosynthesis and other reactions will be damaged and start to denature
If an enzyme is denatured then the shape of the active site will change which will cause the enzyme to slowly stop working
45*C is often the temperature at which this happens
Slide 6
Required Practical: Photosynthesis
Canadian pond-weed can be used to measure the effect of light intensity upon the rate of photosynthesis. The rate at which oxygen is produced corresponds to the rate of photosynthesis.
A lamp is placed at a specific distance from the pond-weed
The pond-weed is left to photosynthesise for a set amount of time. The oxygen released will collect in the capillary tubing
The syringe is used after the experiment to draw the gas in the tube up along the ruler to measure the length of the gas bubble. This is proportional to the volume of O2 produced
This experiment is repeated at different distances away from the pond-weed
Variables to be controlled: temperature, time pond-weed is left_______________________________________________________________________________This experiment can be used to test the effect of temperature using a water bath of different temperaturesThis experiment can also be used to test effect of carbon dioxide using different concentrations of sodium hydrogen carbonate dissolved in the water (it releases carbon dioxide)
When the lamp is moved away from the pond-weed the amount of light that reaches it decreases
As distance increases light intensity decreases. This is an inversely proportional relationship
The light intensity decreases in proportion to the square of the distance which is known as the inverse square law:The EquationLight intensity ∝ 1 / distance (d)^2This law shows that if you halve the distance the light intensity is four times greater. If you treble the distance then the light intensity will be nine times smaller.
Slide 9
Greenhouses
Greenhouses are used to artificially create an ideal environment for plants to grow
Greenhouses trap the sun's heat to ensure that temperature is not a limiting factor
In Winter a heater may be used to keep the temperatures at the ideal level
If it gets too hot then shades or ventilation may be used to cool the greenhouse down
Light is often supplied after the sun goes down at night to allow plants to photosynthesise for longer
Carbon dioxide levels are also regulated by farmers. Paraffin heaters heat the greenhouse as well as give off carbon dioxide as a by-product
Plants are kept away from pests and disease by keeping them enclosed within the greenhouse. Fertilisers are also used to ensure that the plants are able to get all the minerals they need from the soil
Money is needed for all of this. However, if the farmer is able to keep the conditions at the optimum level (no extra costs) then a decent from can be grown faster and can be harvested more often. An excess of light or carbon dioxide will be wasting money so the farmers need to be aware of this.
Glucose is used by plants in five different ways:
Respiration - Energy is trasferred from the glucose to enable the plant to carry out different processes such as converting the glucose into various substances
Making Cellulose - Glucose is converted into cellulose to make strong cell walls
Making Amino Acids - Glucose is combined with nitrate ions from the soil to make amino acids, which are then made into proteins
Stored as oils / Fats - Glucose is tuned into lipids (fats and oils) for storing in seeds
Stored as Starch - Glucose is converted into starch in order to store it in roots, stems and leaves. This is so that it is ready to use when photosynthesis is not happening such as in winter.
Starch is insoluble and so it is easier to store than glucose. A cell with lots of glucose would swell up as it is soluble in water.
Slide 12
Respiration
Respiration is the process of transferring energy from the breakdown of glucose. All living things (including plants) respire. Living things transfer energy from their food to every single cell in the body.
Respiration is an exothermic reaction as it transfers energy to the environment
Organisms use energy from respiration in different ways. In mammals, it is used for keeping body temperatures steady and allow muscles to contract. Another use of the energy is to build up larger molecules (e.g. proteins from amino acids)
There are many chemical reactions within cells which are happening all the time. These are controlled by enzymes
Many of these reactions are liked to form bigger reactions
In some reactions smaller molecules of glucose are joined to form starch
Lipid molecules are made from one molecule of glycerol and three fatty acids
Glucose is combined with nitrate ions to make amino acids which are then made into proteins
In some reactions larger molecules are broken down into smaller molecules
Glucose is broken down to release energy which powers other reactions
Excess protein is broken down to produce urea which is excreted through unimn