IGCSE Biology : U2 : Nutrition in Plants
Nutrition in Plants :
Photosynthesis is an endothermic reaction in chloroplasts which produces glucose for the plant to use. Chloroplasts contain special pigment called chlorophyll which traps the energy from the sun and then uses it to turn water and carbon dioxide into sugar (Glucose) for the plant.
Photosynthesis = 6CO^2 + 6H^2O -> (Sunlight, chlorophyll) C^6H^12O^6+ 6O^2
Xylem = Water
Phloem = Food and nutrients
Plant cells in the
leaves are adapted to
contain a high number
of chloroplasts.
Leaves broad surface
face towards the sun
to increase the
surface area for light
absorption.
Leaves are thin to
allow for easy
diffusion of gases.
• The palisade cells and
spongy mesophyll in the
leaves contain a high
number of chloroplasts.
•Which part of the plant do
you think would have no
chloroplasts?
The structures in a chloroplast contain structures called thylakoid membranes which are impregnated with a pigment called chlorophyll. Chlorophyll absorbs light especially from red and blue wavelengths. Green light is reflected which gives the pigment and the plants there colour. Chlorophyll has a similar structure to haemoglobin, but with an atom of magnesium in the centre instead of iron.
Chloroplasts have a double membrane and inside and an outside one.They are around the size of a normal prokaryotic cell and is believed chloroplasts and mitochondria were once separate but were included in large eukaryotic cells. This is called endosymbiosis
Factors affecting the rate of photosynthesis :
Light Intensity
Amount of CO^2
Temperature
A limiting factor is a component of a reaction that is in its shortest supply so it prevents the rate of reaction increasing in other words set a limit on it eg. light intensity is limited when there it is a
Light intensity affect the rate of photosynthesis with increasing levels of light increasing the rate of reaction however it can hit a plateau if there is a limiting factor or if it has hit its max
If there is not a lot of carbon dioxide it can become a limiting factor as photosynthesis needs it even if it has endless amounts of other factors
The rate of photosynthesis will either slow down or stop complete if the temperature falls or exceeds the optimal range due to the enzymes denaturing
If there is an endless supply of carbon dioxide or light there is a chance that one of them will have a short supply and cause the rate of photosynthesis to plateau until it has enough
Increasing global temperature and Carbon dioxide levels can be positive and negative. If the temperature rises the enzymes could denature and cause the plant to not photosynthesis but the Carbon dioxide levels could increases the rate of photosynthesis however the photosynthesis wouldn't speed up due to denatured enzymes resulting in the plant to die
The concept of limiting factors in photosynthesis can be applied in agricultural practices as farmers know what they need to have and can see the limit for example if there is a low temperature which is causing the plants to photosynthesize slower they could move the plants to a greenhouse to bring up the temperature.
Photosynthesis Experiment:
heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)
add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in color)
wash with water to rehydrate and soften the leaf and spread onto a white tile
add iodine solution from a dropping pipette
For a test for light related to starch, have two plants put one in a cupboard and give light to another one then repeat the steps above and test for starch. The plant in the dark should not have starch.
For a test for CO2 related to starch, have a plant in a bell jar with soda lime. Leave for 2-3 days then test for starch.
Deficiency of nitrate cause stunted growth and yellow leaves
Magnesium is used to make chlorophyll which causes pale yellow leaves if missing