Nutrition is the series of processes by which living things obtain foods and use them to provide energy and materials fortheir life activities. It is an anabolic process. (Building up process).

Nutrition in plants is an Autotrophic mode of nutrition (building complex organic substances from simple inorganic materials) Nutrition processes in green plants involve photosynthesis and mineral uptake and utilization.

Photosynthesis

Photosynthesis is the process by which green plants use carbon dioxide and waterto produce sugar in the presence ofchlorophyll using solar energy. Although the chemistry of photosynthesis can be summarized in the chemical equation:

6Co² + 6H → C⁶H¹²O⁶+6O²

Details of the process are really complex. lt involves two stages of reactions called lightand dark reactions.

Light Reaction (Photophase)

During the light reaction, light energy excites the electrons of chlorophyll and the accessory pigments. These excited electrons are passed along an electron transport chain, where some ofthe energy is captured inATP (Adenosine triphosphate) During the reaction, the bonds of water molecule are split, producing hydrogen and oxygen (Photolysis of water). The hydrogen is accepted by NADP (Nicotinamide Adenine Dinucleotide phosphate) thus fomwing NADPH. Oxygen is released as a bye product.

Dark Reaction

The dark reaction involves a process of carbon fixation, which occurs in the stoma in the mesophyll. During this process, the NADPH and ATP formed during the light reaction are used to power a complete series of reactions, which is catalyzed by enzymes in the stroma. In carbon fixation (dark reaction) carbon from molecules of carbon (IV) oxide combines with hydrogen from NADPHto form glucose.

Conditions and Materials Necessary for Photosynthesis

The presence of sunlight and chlorophyll are conditions necessary for photosynthesis. Carbondioxide and water are materials necessary in photosynthesis.

Leaves Adaptation to Photosynthesis

Although all the green parts of a plant can carry out photosynthesis, the leaves are the major photosynthetic organs. The following are its adaptive features for photosynthesis.

1. Numerous chloroplast— structures which contain chlorophyll.
2. The presence ofstomata and air spaces in leaves which provide pathways fordiffusions of oxygen into and carbondioxide out ofthe leaf.
3. Network of veins by which water circulates to cells of the leaf.
4. Flat broad surface of lea ves for adequa te sunlight receptivity.
5. The perpendicular positioning ofthe leaf to the sun with little overlapping.

Rates of photosynthesis can be affected by light intensity , temperature, relative humidity and amount of water available.

Fate of Photosynthetic Products and Importance of Photosynthesis to Life The products of photosynthesis are utilized in the following ways;

NUTRIENT CYCLES

The continuous movement or circulation of atoms of essential elements from the environment is called nutrient cycle.

A typical example of nutrient cycle in plants is Nitrogen Cycle. Nitrogen cycle is the natural continuous circulation of nitrogen atoms through the atmosphere, living things, soil and water in a cyclic manner.

General Questions

1. The diagram below(fig 8.3) is the internal structure of a leaf showing its transverse section, observe the structure and answer the questions that follow

1. Label the diagram in figure 8.3. for part tagged A B C and D
2. Identify and write the structures where photosynthesis occurs
   Teacher's attention required
3. What is the use of water in the substomatal air chamber
4. Distinguish between the palisade mesophyll and the spongy mesophyll
   Teacher's attention required

2. Write four structural modifications of the leaf for photosynthetic activities(I)

Teacher's attention required

3. Figure 8.1 shows apparatus for water culture experiment. Observe the diagram carefully and answer these questions Label the diagram according to the letters used

Teacher's attention required

4a. What is water culture experiment used for

4b. What is the function of the cuttonwool in the water culture experiment

5. and are the two products of photosynthesis.

6. The splitting of water during the light reaction in photosynthesis is called

7. in green parts of plants absorbs or captures energy from the sun for photosynthesis.

8. When a plant is kept in total darkness for a few days, its leaf when tested for starch will prove negative because

9. is necessary for photosynthesis.

10. There are leaves of plants that appear multi coloured with parts green and others yellow or white such leaves are called leaves.

11. A leaf that is yellow as a result of mineral deficiency is said to be

12. The conversion of atmospheric nitrogen to amino compounds and protein by the action of bacteria and fungi is called 13. During Nitrification Ammonia is converted to nitrite by Nitrosomonas bacteria while nitrites are converted to nitrates by bacteria.

PRACTICAL ACTIVITIES

Problems Under Investigation: To find out the bye products of photosynthesis.

Experiment (i): oxygen as one of the bye-products of photosynthesis.
Material / Apparatus required: Freshly collected water plant (example elodea) ,two test tubes, two beakers, sodium or potassium hydrogen trixocarbonate IV and water, filter funnel, lump of plasticine or clay, retort stand and clamp and wooden splint.

Procedure in steps
1. Place the plant under a glass filter funnel.
2. Rest the funnel securely on the beaker by means of plasticine, which has been inside a sink or bucket of water as shown in the diagram.
3. Fill a test tube with water and invert it over the arm of the funnel.
4. Remove the assembled apparatus from under water.
5. Add some sodium or potassium hydrogen trixocarbonate (IV) to the beaker of water. Stir gently until the trixocarbonate IV is dissolved. Label the apparatus A and leave it under sunlight for a few hours. Set up a similar experimental set up as a control but place it in the dark and label it as C.
6. After few hours test for the presence of oxygen in the test tubes using a glowing splint.

Questions:

1. State your observations on the surface of the leaves of the experiments
2. State your observation on inserting glowing splinter into test tube A and test tube B respectively.

Experiment 2: To find out if starch is a product of photosynthesis.

Materials /Apparatus required: Alcohol, iodine, test, tube beaker, water, white slab, petri-dish, Bunsen burner and tripod stand ,and leaves of a potted plant e.g. cocoyam leaf (the leaf in its plant must have been exposed to sunlight for hours.

Experimental procedure in steps:
1. Dip the leaf in boiling water for half a minute to kill the cells.
2. Dip the leaf in a hot alcohol, which is contained in a test tube being boiled by water bath as shown. Caution - Because of the inflammability of alcohol, care should be taken not to allow the test tube containing the alcohol to touch the bottom of the water bath. Also the test tube should be occasionally lifted out of water to avoid over heating as that can result to sudden spurting of the hot alcohol.
3. Dip the decolorized leaf in hot water to soften it and wash it in cold water to remove remaining traces of alcohol.
4. Place the leaf on a tile or petri dish and add drops of iodine solution to it

Questions

1. Record your observations

2. Briefly describe how you can set up a control experiment for experiment 2.

3. State two reasons why leaf cells has to be killed in boiling water.

4. Why must the leaf for experiment 2 be plucked after its plant has been exposed to sunlight for few hours?

5. What conclusions can you draw from the test and control Experiments 2.

6. State the food substance produced immediately during photosynthesis and why is the product not tested for in the leaf to show that photosynthesis has occurred.

PROBLEM UNDER INVESTIGATION :

Conditions necessary for photosynthesis.
Experiment 3
Materials required: Variegated leaf plucked after its plant has been exposed to sunlight for some hours, 70% ethanol,iodine solution, petri dishes, thin white sheet of paper, transparent sheet of paper and pencil.

Experimental procedure in steps:
1. Take the Variegated leaf and place a transparent sheet of paper over it on a table.
2. Draw the outline of the edges of the leaf. Also draw the outline of the green areas of the leaf.
3. Test the leaf for starch.
4. Place the traced drawing again over the leaf.

Questions

1. Write your observations in steps 3 and 4.

1. Steps 3
2. Steps 4

2. What was the role of caustic soda in the experiment?

3. Write the possible occurrence or observation in Step 4 if the caustic soda were replaced with sodium hydrogen trixocarbonate (IV) (sodium bicarbonate)

4. What conclusions can you draw from your observations in Steps 3 and 4.

5. In your practical notebook, draw a labeled diagram to show another way of carrying out Experiment 4

Experiment 5. To show that a certain factor is necessary for photosynthesis.

Materials/Apparatus required: Apotted plant, paper clips, two stripes of black paper, pair of scissors, materials and apparatus for testing the presence of starch in a leaf

Experimental procedure in steps:
1. Make a hole of any shape on the surface of the black paper strip.
2. Clip the paper strip with hole on the upper surface of a leaf of the potted plant.
3. Make sure the plant is well watered and is destarched.
4. Place the plant under sunlight for about 4 hours.
5. Detach the leaf to which has been clipped the black paperstrip with hole and test the leaf for starch after removing the paper.

Questions

1. Record your observation in Step 5

2. What factor is being shown to be necessary for photosynthesis from your observation in Experiment 5?

3. Why is it good to start the experiment early in the morning?

4. Label the diagrams of leaves in Experiment 5 (in the space above) showing the portions where there is starch and portions where there is no starch. Is the colour of the part where starch is not present green? If not how does the portion look like? (label it in the drawing)?

5. What is the use of black paper in the experiment?

PROJECT/CHALLENGE

1. Check up the experiments on plant growth performed by the Belgian Scientist Jan Baptist Van Helmont. Design an experiment to demonstrate his result using a fast growing plant.