Biology - how plants produce food.

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  • Created by: Jodie
  • Created on: 27-04-11 17:55


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Carbon Dioxide + water (+light energy) = glucose + oxygen

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Photosynthesis in detail

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  • Light energy is absorbed by the chlorophyll, which is found in the chloroplasts of the plant cell.
  • this light energy is then used to convert Carbon Dioxide from the air, and water from the soil, into Glucose.
  • this is a chemical reaction, which produces oxygen.
  • some of the Glucose produced during photosynthesis is used immediantly by the plant cells.
  • some of the glucose is converted to starch for storage.
  • iodine is used on plants to test for starch. it is yellowy brown and turns dark blue when it reacts with starch.
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Leaf Adaptations.

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plant leaves = perfectly adapted for photosynthesis

  • Leaves are broad = big surface area for light to fall on
  • chlorophyll in the chloroplasts enable the leaves to absorb light energy.
  • air spaces which enable carbon dioxide to enter the cell and oxygen to leave.
  • Veins - bring water to the cells in the leaves.
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 Limiting factors are factors that limit the rate of photosynthesis.

they are:  Light,     Temperature   &   Carbon Dioxide Levels.

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Light - Limiting factor

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Plenty of light = lots of photosynthesis

Very Little Light = photosynthesis will stop.

Most plants = The brighter the light the faster the rate of photosynthesis.


( Hence, why photosynthesis occurs more in the summer than the winter)

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Temperature - Limiting Factor

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Temperature effects all the chemical reactions in a plant. ( so of course Photosynthesis!)

increase in temperature = increase in rate of photosynthesis. as the reaction speeds up.

BUT. photosynthesis is controlled by enzymes.

so temperature cannot be too high, or else these enzymes will be denatured.

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Carbon Dioxide Levels - Limiting Factor.

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Increase Carbon Dioxide Levels = Increase in the rate of photosynthesis.

Carbon Dioxide is needed for the plants to produce Glucose.

Carbon dioxide is often the most limiting factor, as there is only 0.04% in the atmosphere.


In a laboratory or green house, carbon dioxide levels can be artificially increased.


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Plants Using Glucose

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Glucose is produced during photosynthesis.

Some of glucose = used immediantly by the plant cells, for respiration and for energy ( for cell functions, growth and reproduction )

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Plants using Glucose - Respiration

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Plant Cells respire all the time.

  • They use Oxygen to break down glucose in order to provide energy for their cells.
  • Water and carbon Dioxide = the waste products of this.

Energy released in respiration = used to turn smaller molecules into bigger molecules.

Plants build up sugars into complex carbohydrates and cellulose ( to make new plant cell walls )

some of the energy produced by respiration = used to combine sugars with other soil nutrients in order to produce Amino Acids. which are then built up as protein and used in the cells.

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Plants using Glucose - Transport and storage

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Food produced by photosynthesis = moved around the plant via a transport system. there are two the Phloem and the Xylem.

The Phloem is made of living tissue. it transports Sugars ( that were made by photosynthesis) from the leaves to the rest of the plant.

The Xylem is a transport tissue that carries water and mineral ions from the soil to the rest of the plant.


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Glucose & Starch

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Glucose is converted into starch for storage.

Glucose = soluable ( dissolves in water )  and therefore would affect the balance of water in a plant if it stored large amounts of it.

Starch = insoluable ( does not dissolve in water ) and therefore enables the plant to store large amounts of it, without it's water balance being affected.

Main energy store in plants = Starch, which is found everywhere in the plant.  It is stored in the leaves - to provide energy for when its dark or light levels are low.

Starch can also be stored in Bulbs and Tubers.

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Plants needing NITRATES.

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Plants need minerals and vitamins for healthy growth.

Plants need Nitrates because: Photosynthesis only produces carbyohydrates, and a plant also needs protein to act as Enzymes and to make up the cytoplasm and the membranes.

Nitrates are needed, as proteins are made up of amino acids ( which contain carbon hydrogen oxygen and nitrogen ). Plants find Nitrates in the soil.

the nitrates are dissolved in wter and taken up into the plant via the roots.

Symptoms of Nitrate Deficiency: Stunted growth. ( So it's small. )


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Plants needing MAGNESIUM.

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Plants need Magnesium to make Chlorophyll.

Magnesium = vital as chlorophyll = vital for photosynthesis to occur.

Symptoms of Magnesium defiency: pale and yellowish areas on leaves. ( due to a lack of chlorophyll. )

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