4. Plant Nutrition

4.1 Photosynthesis

1 . Photosynthesis:

  • It is the process of making food by using carbon dioxide, water, with the help of sunlight and chlorophyll by green plants.

2 . Photosynthesis required:

  • Carbon dioxide(CO2),
  • Water,
  • Chlorophyll,
  • Sunlight


Word Equation for photosynthesis:


Chemical equation for photosynthesis:


3 . Factors affecting the rate of photosynthesis:

1) Light intensity (The strength of light)

Fig 4.1 Graph of rate of photosynthesis against light intensity


A) Between regions A and B, an increase in the brightness of light increases the rate of photosynthesis.

B) This indicates that the speed at which photosynthesis is taking place is limited by the amount of light available.

C) At higher light intensities (i.e. after point C) a further increase in light intensity would not increase the rate of photosynthesis.

D) This implies that the photosynthetic process is receiving the maximum amount of light it can make use of.

E) Hence, an increase in light intensity will not increase the rate.


2) Temperature

Fig.4.2 Effect of temperature on the rate of photosynthesis

A) At low temperature, photosynthesis is inactive.

B) As the temperature increase, the rate of photosynthesis also increase.

C) At optimum temperature, photosynthesis is in its most active state.

D) Above optimum temperature, the rate of photosynthesis decreases.

E) At extreme temperature, photosynthesis stops, because the enzymes involved in this process are denatured.


Since photosynthesis can be affected negatively by heat, enzymes must be involved.


3) Concentration of CO2.

A) As there are more CO2, the faster the rate of photosynthesis.

B) CO2 concentration cannot exceed 0.03%, because that is the amount of CO2 in the air.

C) It can only exceed 0.03% under experimental conditions.


4 . Importance of photosynthesis:

  • It reduces the amount of  CO2 in the air which is the main cause of global warming.
  • It produces oxygen to support other organisms for doing respiration.
  • It produces food which is the source of energy of other organism and itself

5 . The leaf:

Fig.4.3 The external structure of a leaf


Fig.4.4 The internal structure of a leaf


6 . The important features about leaves:

  • The cells in the palisade layer are packed with chloroplasts which contain lots of chlorophyll. This is where the photosynthesis goes on.
  • The palisade and spongy layers are full of air spaces to allow CO2 to reach the palisade cells.
  • The cells in the epidermis make wax which covers the leaf structures, especially the top surface. This is to prevent water loss.
  • The lower surface is full of biddy little holes called stomata. They are there to let CO2 in. They also allow water to escape -this is how the transpiration stream comes about.
  • Xylem and phloem vessels cover the whole leaf like tiny “veins”, to deliver water to every part of the leaf and then to take away the food produced by the leaf.

7 . The stomata:

  • Stomata closes automatically when supplies of water from the roots start to dry up.
  • The guard cells control this. When water is scarce, they become flaccid, and they change shape, which closes the stomatal pores.
  • This prevents any more water being lost, but also stops CO2 getting in, so the photosynthesis stops as well.


4.2 Plant Mineral Nutrition
1 . Nitrogen:Plants need nitrogen to make proteins. They got nitrogen from the compounds of nitrogen from the soil. •

  • Plants need nitrogen to make proteins. They got nitrogen from the compounds of nitrogen from the soil.

2 . Magnesium:

  • Important for making chlorophyll.

3 . Plants lacking of magnesium:

  • They will have leaves not healthily green

4 . 

5 . 

6 . Plants lacking of nitrogen:

  • They will not grow properly.


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