Nutrition in Green Plants

Nutrition in Green Plants

By the end of this chapter, you will be able to:

(a) understand the meaning of autotrophic and heterotrophic nutrition.

(b) derive the meaning of the term photosynthesis and understand the process.

(c) perform experiments to investigate the factors that affect the rate of photosynthesis.

(d) appreciate the structures and adaptations that enable a leaf to carry out the process of photosynthesis.

Introduction

In this Chapter you are going to understand that plants manufacture their own food from water and carbon dioxide using energy from the sun.

Unlike animals which cannot animals for food. manufacture their own food depend on plants and other

4.1 Autotrophic and heterotrophic nutrition

Activity 4.1 Understanding the terms autotrophic and heterotrophic nutrition

Key question

How do plants and animals differ in their mode of nutrition?

What you need

• Biology textbooks

Computer with internet

What to do

1 In small groups research and find the meaning of the terms autotrophic and heterotrophic nutrition.

2 Discuss why autotrophs are the providers of all food.

3 Present your definitions of the terms and what you have discussed to the rest of class.

4.2 Photosynthesis

In the next activity, you are going to research about the meaning of photosynthesis. You must have noticed that we do not have to feed the plants in and around our homes, yet they continue to grow.

We have to feed the animals in our homes like pets, that is, dogs, cats, rabbits and other domestic animals like cattle, sheep, pigs, goats and chicken for proper growth.

The reason is that plants can manufacture their own food while animals cannot.

Activity 4.2 Finding out the term photosynthesis

Key question

What is photosynthesis?

What you need .

Biology textbooks

Computer with internet

What to do

1 In small groups discuss the meaning of the terms photo, then synthesis.

2 Research and find the equation for photosynthesis.

3 Discuss what plants need to carry out photosynthesis from the equation.

4 Present your findings to the class.

4.3 Factors affecting photosynthesis

In the next activity, you are going to design and carry out an experiment to show the need for light during photosynthesis. We already know that what is necessary is light, carbon dioxide, chlorophyll and water for plants to produce starch during photosynthesis.

We can use experiments to find out if plants need these four factors to produce starch during photosynthesis.

The principle behind the experiments is that starch is first removed from the plant leaves. This is done by placing the plant in the dark for a period of 2 days or more.

A leaf is then tested for starch to make sure all the starch has been completely removed (by the plant using it of course). Then the plant is given all conditions it requires for growth except one.

This is the function we want to investigate its effect on the process of photosynthesis. After some time (say 2 days) another leaf is tested for starch to find out if it has made some starch. If starch is not present, then we conclude that the factor missing was necessary for starch formation and hence photosynthesis. For comparison a control experiment is set up.

This is an experiment in which the (control) plant is given all the four factors and all conditions required for growth including the one we are investigating.

In the next three activities 4.3, 4.4 and 4.5 you are going to investigate the need for each of these factors one at a time.

Figure 4.2 Diagram of a leaf – the plant organ for photosynthesis

Activity 4.3 Finding out the need for light in the formation of starch

Key question

Is light necessary for photosynthesis?

What you need

A destarched potted plant

Aluminium foil or black paper strip or black tape

Paper clips

lodine solution

Dropper

Source of heat

Methylated spirit/ethanol

Beaker

Water

White tile/White paper/Petri dish

Test tube

Test tube holder

What to do

In your group, carry out of following instructions:

1 Cut a simple shape from a piece of aluminium foil or black paper and attach it to a leaf.

2 Put the leaf in sunlight for 3 hours. r

3 Remove the aluminium foil/black paper.

4 Test the leaf for the presence of starch as follows:

Heat water in a beaker until it boils.

Place the leaf in the boiling water for about 10 seconds.

Put off the flame. CAUTION Methylated spirit/ethanol catches fire easily!

Put methylated spirit/ethanol in a test tube to fill it halfway.

Place the leaf in the spirit/alcohol.

Figure 4.3 Testing a leaf starch

Place the test tube containing the leaf in spirit/alcohol in the hot water for 1 minute and notice what happens.

Place the leaf flat on a white tile/white piece of paper/ petri dish. Using a dropper put drops of iodine solution to cover the whole leaf surface leave for 3 minutes. • Wash any iodine solution with water.

1 Describe the appearance of the leaf after it has been tested for starch.

2 Make a drawing of the leaf to show its appearance, present your report to the rest of the class.

3 Write a report indicating the title, question, prediction, materials, procedure, record of results, analysis, of results Questions-How do you interprete the results? Which part of and conclusion. the leaf is the control experiment?

Activity 4.4 Finding out the need for chlorophyll in the formation of starch

Key question

Is chlorophyll necessary for photosynthesis?

What you need

Potted plant with variegated leaves

White tile/White paper/Petri dish

Test tubes

lodine solution

Stirring rod/dropper

Potted plant with variegated leaves

Source of heat

Methylated spirit/ethanol

Beaker

Water

Test tube holder

What to do

Nutrition in Green Plants In your groups carry out the following instructions: Remove one leaf from the plant and make a drawing of it taking note or the pattern of the green and white areas.

Test the leaf for starch following the procedure in activity 4.3.

3 Make a second drawing of the leaf alongside your first drawing to show areas coloured dark blue and those that are orange brown with iodine solution.

4 Write a report on the experiment using the following format: title, question, prediction, materials procedure, record of results, analysis of results and conclusion.

5 Present your report to the rest of the class.

Questions

1 Which parts of the leaf are stained dark blue and orange brown?

2 In which parts was starch formed or not formed?

3 How do you explain this in terms of chlorophyll distribution and photosynthesis?

Activity 4.5 Finding out the need for carbon dioxide in the formation of starch

Key question

• Is carbon dioxide necessary for photosynthesis?

What you need

• Methylated spirit / ethanol
• Test tubes lodine solution Source of heat.
• Retort stand with 2 clamps
• Plant with normal green leaves
• Test tube holder Sodium bicarbonate 63
• Beaker
• Water
• White tile
• Stirring rod / dropper
• Vaseline
• Two split cocks
• Two conical flasks

What to do

1. In your groups carry out the following instructions to show the need for carbon dioxide during photosynthesis.
2. Detach one leaf from the plant and test it for starch following the procedure in activity 4.3 to ensure no starch is present.
3. Enclose one leaf in a clear glass flask containing solid lime which will absorb carbon dioxide.
4. Enclose another leaf in a clear glass flask containing sodium bicarbonate solution which will release carbon dioxide. The leaf stalks should pass through a split cork which has been vaselined.
5. Support each flask with a clamp on a metal stand.
6. Put the plants in light for 3 hours.
7. Test each leaf for presence of starch and record your observation.
8. Write a report on experiments using the following format: title, question, prediction, materials procedure, record of results, analysis of results and conclusion.
9. Present your report to the rest of the class.

Questions

1. Which leaf is the control experiment?
2. Why are the split corks vase lined? Explain your results.

4.4 Structure of a leaf in relation to photosynthesis

Activity 4.6 Finding out the structures that enable a leaf to carry out the process of photosynthesis

Key question

• What structures enable a leaf to carry out photosynthesis?

What you need

• Leaves
• Hand lens
• Microscope
• Slides and cover slips / already prepared slides of leaves
• Biology textbooks / computer with internet

Figure 4.5 Internal structure of a leaf

What to do

1. In groups, collect leaves from the surrounding of the school.
2. Discuss the structure of the leaf.
3. Research on the leaf structure from internet / Biology textbooks.
4. Draw and label a large drawing of the leaf.
5. Observe the already mounted leaf on the microscope. The teacher will help you to observe the structure.
6. Compare what you have observed to the already drawn structure in the textbook / internet.
7. Use a suitable method to report your findings to the rest of the class.

There is no simple experiment which can be done to find out if water is necessary for photosynthesis. This is because we cannot remove all the water from the plant without killing it. These experiments confirm that carbon dioxide – light and chlorophyll are necessary for photosynthesis.

Chapter summary

In this chapter, you have learnt that:

• Plants make their own food from water and carbon dioxide using sunlight energy in the process of photosynthesis.
• Leaves are the organs for photosynthesis in plants and are adapted stomata and veins. For the process structurally by having chloroplasts, air spaces.
• They offer a large surface area for trapping sunlight by being numerous on the plant and arranged in such a way that they are in the best position to get maximum amount of light

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