Plant Nutrition Summarized Notes

Introduction

In our previos post, we saw how living organisms are made up of different chemical substances, and that carbohydrates, proteins and fats are vital components of plants and animals. Where do these food substances come from? All the food eaten by animals comes from plants, but where do plants obtain their carbohydrates, proteins and fats? The answer is that green plants make these substances from simple raw materials. In this post, we will learn about how green plants make their own food and how they are adapted to make food.

The Leaf Structure
The leaf can be described as a glucose factory because its main function is to make glucose for the plant during photosynthesis. The structure of a leaf is designed in such a way that it is adapted to the process of photosynthesis. You will learn about adaptation of the leaf for photosynthesis later on in this post. The leaf is very thin, and has a large surface area to allow efficient exchange of gases. The leaf is made of layers of cells. A transparent layer of cells, known as the epidermis, covers the upper and lower surface of the leaf. These cells allow light to pass through, but protect the rest of the cells in the leaf. The cells of the upper epidermis often secrete a waxy substance, which covers them. This substance is called the cuticle, and it helps to stop water evaporating from the leaf. There is sometimes a cuticle on the underside of a leaf as well. Below is a figure stucture of a leaf.

The figure below is an example of a section through a part of a leaf

Refer to the figure above reading this:
• Cuticle: a waxy, waterproof layer secreted by the epidermis, covering the upper and lower epidermis. It stops water from evaporating from the leaf.
• Upper and lower epidermis: transparent layers of cells that protect the inner layers of the leaf. These layers are transparent because they do not have chloroplasts. This allows maximum penetration of sunlight into the mesophyll layer.
• Mesophyll layer: the middle layer of the leaf, situated between the two epidermises. It is divided into the palisade mesophyll layer and the spongy mesophyll layer.
-The palisade layer is the top of the mesophyll layer. The cells in the palisade layer are rectangular-shaped and arranged in a regular pattern, end-on, like a fence, hence the name 'palisade'. This ensures that there are few walls between the leaf surface and the chloroplasts inside the cells, to allow maximum absorption of sunlight by chlorophyll inside chloroplasts. This layer contains a vast number of chloroplasts, therefore most photosynthesis takes place here.
-The spongy mesophyll is the lower layer of the mesophyll. cells in this layer are rounder and loosely arranged with large air spaces between them, like a sponge, as the name implies. The presence of air spaces in the spongy layer allows for gaseous exchange by diffusion between the mesophyll cells and the air. This layer contains many chloroplasts, but not as many as in the palisade layer. Photosynthesis also takes place here.
• Vascular bundle (veins): tiny tubes called xylem vessels and phloem tubes. The xylem vessels carry water and minerals to the mesophyll cells, and the phloem tubes carry photosynthesised food to the parts of the plant where it is needed.
• Stomata: small pores on the leaf. In a typical leaf, most  stomata are found on the underside of the leaf in the lower epidermis. Stomata allow gaseous exchange (carbon dioxide to diffuse in and oxygen to diffuse out, and vice versa) and transpiration to take place. The opening and closing of the stomata is controlled by the guard cells on either side of the stomata. The guard cells, unlike other cells in the epidermis, contain few chloroplasts. Some photosynthesis takes place here. Figure below shows a surface view of the lower surface of the leaf, showing the closely fitting cells of the epidermis the oval holes are the stomata.

How Carbon Dioxide Enters The Leaf
Carbon dioxide needed for photosynthesis comes from the air around the leaf. It enters the leaf by diffusion through the stomata shown in Figure below. Once inside the air spaces of the leaf, carbon dioxide diffuses into the mesophyll cells across their cell surface membranes.

Adaptations Of The Leaf For Photosynthesis
To carry out photosynthesis efficiently, leaves need to be able to:
• absorb the maximum amount of light
• obtain adequate supplies of carbon dioxide and water
• have a transport system for carrying the products of photosynthesis to other parts of the plant.

How Leaves Absorb The Maximum Amount Of Light
In most plants, the flat surfaces of the leaves are arranged so that they do not overshadow each other. This ensures maximum exposure to light. Plants that grow in the shade often have larger leaves than plants that grow where there is more light. The leaf is covered with a thin layer of transparent epidermal cells that allow the light to pass through to the mesophyll cells below. The palisade mesophyll cells are arranged end-on, like upright bricks, to absorb as much light as possible.

How Carbon dioxide Enters The Leaf
Only about 0.04% or 400 ppm by volume of the air is carbon dioxide. The stem and leaf stalk hold the leaf up to the air and the large surface area of the leaf helps it to absorb as much carbon dioxide as possible. Carbon dioxide diffuses into the leaf through the stomata and then diffuses into the mesophyll cells where it is absorbed by the chloroplasts.

How Water Is Taken Into The Plant
You can see in the section through the leaf in Figure shared earlier in this post of a section through a leaf that the vascular bundles are near to the mesophyll cells. The xylem tubes supply water for photosynthesis and the phloem tubes take away the products of photosynthesis. The table below summarises how the structure of the leaf and the cells within the leaf are adapted to carry out photosynthesis.

Adaptation Of Leaves For Photosynthesis
Supported by stem and petiole -To expose as much of it as possible to sunlight and air.
Large surface area -To expose as much of it as possible to sunlight and air.
Thin -To allow sunlight to penetrate to all cells, to allow CO₂, to diffuse in and O₂, to diffuse out as quickly as possible.
Stomata in lower epidermis -To allow CO₂, and O₂, to diffuse in and out.
Air spaces in spongy mesophyll -To allow CO₂, and O₂, to diffuse to and from all cells.
No chloroplasts in epidermis -To allow sunlight to penetrate to mesophyll layer.
Chloroplasts containing chlorophyll present in mesophyll layer -To absorb sunlight to provide energy to combine CO₂, and H₂O.
Palisade cells arranged end-on -To keep as few cell walls as possible between sunlight and chlorophyll.
Chloroplasts in palisade cells arranged broadside-on, especially in dim light -To expose as much chlorophyll as possible to sunlight.
Chlorophyll arranged on flat membranes inside chloroplast -To expose as much chlorophyll as possible to sunlight.
Xylem Vessels within short distance of every mesophyl cell -To supply water to chloroplasts for photosynthesis.
Phloem tubes within short distance of every mesophyll cell -To take away organic products of photosynthesis.

The Importance Of Nitrates, Phosphates, Iron and Magnesium Ions In Plants
Plants need many other nutrients, apart from carbon, hydrogen and oxygen. Nutrients, such as nitrates, phosphates, iron and magnesium, are taken into plants as mineral ions dissolved in soil water, through the root hairs. All these minerals are essential for the healthy growth of the plant. You need to know the uses of four mineral ions in plants:
But before hand look at the figure below which shows the uptake of mineral ions

1. Nitrogen is a macro-nutrient Plants use it in the form of nitrates. Nitrate ions are needed by plants to make amino acids, which combine to form proteins, to make chlorophyll, to make nucleotides, which form nucleic acids and make some plant hormones, such as auxin.

3. Phosphorus is a macro-nutrient. Plants use it in the form of phosphates. Phosphates are needed for DNA and RNA, and energy transfer reactions. Phosphates are a component of cell membranes in the form of phospholipids. Phosphates are also used to form high-energy compounds like ATP.
4. Iron is a micro-nutrient. Plants absorb it in the form of ions. Iron is needed for chlorophyll production, formation of some enzymes, and it is a constituent of electron carriers.

*farmers often add manure or artificial fertilizers which contain these essential minerals to the soil to increase crop yield*

Uptake Of Mineral Ions
The mineral ions, such as nitrate ions, magnesium ions, iron and phosphate ions, are taken up into the root through the root hairs, by means of active transport. The concentration of minerals is less in the soil than in the root hair, and energy is required from the respiration process in the mitochondria of the cells. After active absorption, the mineral ions move by diffusion along the vacuole into and through the xylem, upto the leaves, as a result of transpiration pull and capillarity to all parts of the plant.

When mineral ions are in short supply, the plant may develop deficiency symptoms.
For example, a lack of nitrate ions in the soil means plants do not build up amino acids, which are normally converted to proteins. As a result, plants tend to have poor growth and yellow leaves.

A lack of magnesium or iron means plants do not synthesise chlorophyll, which is necessary for photosynthesis. As a result, plants tend to develop yellow leaves and appear stunted

However, if phosphate is in short supply, stunted growth occurs, affecting the roots and causing brown patches on the leaves and petioles. If plants have a shortage of iron, yellowing of upper leaves occurs (chlorosis).

Photosynthesis
Can you imagine a world without green plants and photosynthesis? There would be no food to eat and no oxygen to break down glucose and no animals. Animals cannot make their own food. They must eat food that was originally made by green plants during the process of photosynthesis. Plants take in two simple inorganic substances:
• carbon dioxide from the air
• water from the soil.

Using light energy from the sun, the carbon dioxide and water combine and form sugars such as glucose. Glucose is described as an organic substance because it is made by green plants. Water, carbon dioxide and sunlight are sometimes called raw materials. They are the 'ingredients' from which the plant makes food. At the same time, oxygen molecules are produced. The figure below shows a summary of photosynthesis.

By definition, photosynthesis is a process by which light energy is trapped by chlorophyll
in chloroplasts and used to reduce carbon dioxide to form carbohydrates. You can write a
simple word equation to summarise the process of photosynthesis:
• sunlight
• carbon dioxide + water
• chlorophyll
• glucose + oxygen
The balanced equation for photosynthesis is: 6CO₂ + 6H₂O + sunlight energy - C₆H₂O₆+ 6O₂
The sunlight energy has to be trapped by the leaf and then used in photosynthesis. In green plants, sunlight energy is trapped by a substance called chlorophyll, the pigment which makes plants look green. Chlorophyll is kept inside the chloroplast of plant cells arranged on a series of membranes. Spread out like this, it can trap the maximum amount of sunlight. By now, you should be able to give a full explanation of how photosynthesis happens:

• Raw materials, carbon dioxide and water, enter the plant.
• When sunlight falls on a chlorophyll molecule, the energy is absorbed.
• The chlorophyll molecules are activated to release the energy.
• Photosynthesis has two stages: a light-dependent phase and light-independent phase. The light-dependent phase is called photolysis, where water is split to give off oxygen gas as a by-product. This stage takes place in the presence of light energy. The light-independent stage is called the reduction phase, where carbon dioxide is reduced to glucose. This stage does not need light. Carbon dioxide combines with ATP (energy) and the hydrogen from the light-dependent phase, to release energy-rich carbohydrates, for example, glucose.

Sources Of Water And Carbon Dioxide And How They Enter The Leaf
Water is absorbed from the soil by the root hair cells from a higher water potential in the through the cortex and endodermis to the xylem. Water travels up the xylem by different forces, such as adhesion, cohesion, transpiration pull and root pressure into the leaf xylem. Water moves from the leaf xylem into the mesophyll cells and chloroplasts by osmosis.

Carbon dioxide makes up 0.04% of the air. Carbon dioxide enters the leaf from a high concentration in the atmosphere to a low concentration in the leaf by diffusion. Carbon dioxide enters the leaf through the stomata and diffuses into the air spaces, from the air spaces into the mesophyll cells, down the concentration gradient. Chloroplasts in the mesophyll cells absorb light energy from sunlight where it is trapped by the chlorophyll.

Investigations Into Photosynthesis
Here you will be looking at four investigations to show that light, carbon dioxide and chlorophyll are necessary for photosynthesis, and that oxygen is produced. In each of these investigations, two plants are used:
• One plant is the experimental plant that is given everything it needs, except for one substance, such as carbon dioxide.
• The other plant is the control plant that is given everything it needs, including the substance under investigation.
In each investigation, both plants are treated in exactly the same way. Any differences between them at the end of the investigation, therefore, must be because of the substance being tested. At the end of each investigation, we use iodine solution to test a leaf from the experimental plant and the control plant to see if starch has been made. lodine solution turns black when it reacts with starch. By comparing the leaves, we can find out which substances are necessary for photosynthesis.

Destarching A Plant
It is very important that the leaves you are testing should not have any starch in them at the beginning of the investigation. If they did, and you found that the leaves contained starch at the end of the experiment, you could not be sure that they had been photosynthesising. The starch might have been made before the experiment began. So, before doing any of these experiments, you must start with plants that have no starch. The easiest way to do this is to leave them in a dark cupboard for at least 24 hours. The plants cannot photosynthesise while they are in the cupboard because there is no light. They use up their stores of starch and are described as destarched. To be certain that they are thoroughly destarched, test a leaf for starch before you begin your experiment.

EXPERIMENT 1
PRACTICAL INVESTIGATOR: TESTING A LEAF FOR STARCH

This practical activity may take you about 30 to 40 minutes.
lodine solution is used to test for starch. A blue-black colour shows that starch is present. However, if you put iodine solution onto a leaf that contains starch, it will not immediately turn black. This is because the starch is right inside the chloroplasts. The iodine solution cannot get through the cell membranes to reach the starch and react with it. Another difficulty is that the green colour of the leaf and the brown iodine solution together can make it look black. This means that before testing a leaf for starch, you must break down the cell membranes, and get rid of the green colour (chlorophyll). To do this, you first need to break down the cell membranes by treating them with boiling water, before removing the chlorophyll by dissolving it with alcohol.

You will need:
• iodine solution and a dropper
• a green leaf
• a saucepan of boiling water
• a small heat-resistant bowl with methylated spirits
• a spoon or something similar to lift the hot leaf
• a white saucer or small plate.

Step 1
1. Remove a leaf from a plant and drop it into the boiling water. Leave it for about 30 seconds. The leaf is boiled in water for about two minutes to break down cell walls and to stop the action of enzymes within the leaf. It will also allow easier penetration by ethanol

Step 2
2. Turn off the heat supply. Use your forceps or spoon to carefully remove the soft leaf and drop it into the small bowl of methylated spirits. Put the small bowl into the large saucepan of hot water. Leave it until the leaf has lost its green colour. All the chlorophyll will have been dissolved from the leaf. The leaf is warmed in ethanol, until the leaf is colourless, to extract the chlorophyll that would mask observations later

Step 3
3. The leaf will now be brittle. Rinse or dip it in warm water to soften it and allow penetration by the iodine solution.

Step 4
4. Spread the leaf on a white tile or saucer and cover it with iodine solution. Observe any colour changes. Iodine shows a black colour. In your notebook, write a conclusion about the use of iodine solution and the presence of starch in a leaf.

 

EXPERIMENT 2
PRACTICAL INVESTIGATION: IS LIGHT NECESSARY FOR PHOTOSYNTHESIS?

This practical activity can be done over a few days.

You will need:
• a healthy geranium plant
• dark cupboard
• aluminium foil, black paper or black plastic
• white saucer or small plate
• iodine solution and dropper bottle
• large saucepan of boiling water
• small bowl of methylated spirits.

Method:
1. Destarch a healthy geranium plant, growing in a pot, by putting it in a dark cupboard for one day

2. Test one of its leaves, to determine that it does not contain any starch.

3. As shown in the figure, wrap a piece of aluminium foil or black paper firmly over both sides of a leaf on your plant. Make sure that both edges are held firmly together.

4. Leave the plant in a warm, sunny spot, near a window for a few days.

5. Remove the cover from your leaf, and test the leaf for starch.

6. Make a labelled drawing of the appearance of your leaf after testing for starch.

7. In your notebook, write a conclusion based on the results obtained.

EXPERIMENT 3
PRACTICAL INVESTIGATION: IS CARBON DIOXIDE NECESSARY FOR PHOTOSYNTHESIS?

Spend about 10 to 15 minutes on this activity.
To answer this question, carbon dioxide must be removed from the air around a leaf. One chemical that can remove carbon dioxide is a chemical called potassium hydroxide. The investigation was set up as shown. When the leaf without carbon dioxide was tested with iodine, the iodine solution did not change colour. When the leaf with carbon dioxide was tested with iodine, a black colour appeared.

Answer these questions in your notebook.
1. Why was potassium hydroxide used with one leaf, and water with the other?
2. What do your results suggest about carbon dioxide and photosynthesis? 

EXPERIMENT 4
PRACTICAL INVESTIGATION: IS CHLOROPHYLL NECESSARY FOR PHOTOSYNTHESIS?

This practical activity will take you about 30 minutes.

You will need:
• healthy plant with variegated leaves that has been in the sunlight for several hours
• apparatus for testing a leaf for the presence
of starch. *variegated- green and white areas on the same leaf the white areas have no chlorophyll*

Method:
1. In your notebook, make a drawing to show the pattern of green and white parts of the leaf, as shown in the figure.
2. Test one of the leaves for starch.
3. Make a drawing of your leaf after testing, as shown in the figure.

Answer these questions in your notebook.
1. What was the control in this experiment?
2. What do your results tell you about chlorophyll
and photosynthesis?

EXPERIMENT 5

PRACTICAL INVESTIGATION: IS OXYGEN PRODUCED DURING PHOTOSYNTHESIS?

Spend about 10 minutes on this activity.
Answer the questions in your notebook.
1. A learner set up the apparatus, as shown in the figure below. He made sure that the test-tube was completely full of water

2. He left the apparatus near a warm, sunny window for a few days.

3. He carefully removed the test-tube from the top of the funnel, allowing the water to run out, but not letting the gas escape.
4. He lit a wooden splint, and then blew it out so that it was just glowing. He carefully put it into the gas in the test-tube. It burst into flame showing that the gas was oxygen.

Answer these questions in your notebook.
1. Suggest why the test-tube was filled with water.
2. Why did the learner put the apparatus near a warm, sunny window?
3. Where did the oxygen come from that was collected in the test-tube?

Photosynthetic Pigments
The function of photosynthetic pigments is to absorb light energy and to convert it into chemical energy. The pigments are located on the chloroplast membranes. There are two types of pigments in flowering types:
• chlorophyll
• carotenoids.
Chromatography is a method that is used to separate coloured chemical compounds (pigments). Follow the steps below to see the different colours:

1. Use dried, powdered grass leaves and grind it in a mortar with a pestle. Add a small amount of propanone (acetone).
2. Filter the extract through glass wool, so that the solids are left behind.
3. "Load' the chromatogram (chromatography paper) just above the line of contact with the solvent (propanone). A tiny spot of pigment extract will be spotted. Allow it to dry. Repeat this process until a dark green spot is visible.
4. Lower the loaded chromatogram into the solvent, with the loaded spot just above the solvent. Running the chromatogram causes the pigments to separate as the solvent runs up the chromatogram.
5. The following pigments can be identified:
• carotene (yellow)
• chlorophyll A (blue-green)
• xanthophyll (yellow)
• chlorophyll B (green).

Simple Sugars (monosaccharides)
Sugar and Glucose are simple sugars, the molecular formula of the glucose molecule can be written as: C(2) H(12) O(2) *refer to our discussion about Biological Molecules on how we write the glucose molecule the keyboard can't allow me to write it as*

This means that the molecule contains six carbon atoms, twelve hydrogen atoms and six oxygen atoms. The glucose molecule is described as a simple sugar. It is very small, soluble and tastes sweet. When two glucose molecules join together, a larger molecule, maltose, is made, as shown in Figures below.

Simple Sugar

Complex sugar

Starch, Glycogen and Cellulose (polysaccharides)
Very large, complex molecules are made when many thousands of simple sugar molecules join in a long chain, as shown in the figure below. Examples of these large, complex molecules are starch, which is found inside plant cells, and glycogen, which is found in the liver and muscle cells of animals. Cellulose, which forms the cell wall in plants, is also a complex sugar molecule. Most of these complex carbohydrates are insoluble and do not have a sweet taste.

Glycosidic Bonds
In polysaccharides and disaccharides, the monosaccharide subunits are held together by a special type of chemical bond known as a glycosidic bond. These bonds are formed and broken during chemical reactions that occur all the time in cells. There are two types of reactions to consider: condensation and hydrolysis.
A condensation reaction occurs when two monosaccharide subunits combine, and a bond is formed when a molecule of water is removed.
subunit - OH + HO - subunit g subunit - subunit + HO(2) (bonded with O)
A hydrolysis reaction occurs when a large molecule, such as starch, is broken down into its subunits, such as glucose, and a bond is broken when a molecule of subunit - subunit + H(2)O g subunit - OH + HO - subunit (O unit broken)

Figure below shows how a glycosidic bond is formed between two monosaccharide subunits during a condensation reaction and how it is broken during hydrolysis.

How Glucose Is Used In The Plant
The glucose produced in photosynthesis may be used in a number of different ways:
• in the leaf as an energy source for respiration 

• changed into sucrose and translocated in the phloem tubes to the rest of the plant changed into starch; glucose is soluble and cannot be stored; it is converted to insoluble starch that can be stored elsewhere in the plan

• changed into other carbohydrates, such as cellulose (the structural component of cell walls), or into oils

• converted into proteins by reaction with mineral salts
• converted into chlorophyll and vitamins.

Limiting Factors Affect The Rate Of Photosynthesis
Limiting factors can be defined as any environmental factors that can slow down the rate of a reaction if they are in short supply. Many factors, such as light intensity, carbon dioxide and temperature, affect the rate of photosynthesis. If any of these factors are in short supply, it will cause the rate of photosynthesis to reduce from its optimum rate. The factor that is in short supply is the limiting factor. It limits the rate at which the reaction can take place. Low CO(2) decreases the rate of photosynthesis. Low light intensity decreases the rate of photosynthesis. Low or extremely high temperature will decrease the rate of photosynthesis. A lack of water will let the leaf become flaccid, which will lead to the stomata closing so that no water can evaporate out of the plant, which then leads to a lack of CO(2), thus photosynthesis decreases.

Limiting factors for photosynthesis include:
• light intensity (how bright or how dim the light is)
• carbon dioxide concentration
• temperature
• availability of water.

Measuring The Rate Of Photosynthesis
One of the easiest ways of measuring the rate of photosynthesis is to measure the rate of oxygen production. A plant such as Elodea, Canadian pondweed, is used in experiments such as this. The diagram in Experiment 5 shows the simplest method. You can count the number of bubbles of oxygen produced by the plant over a period of time. However, this method does not give an accurate measure of photosynthesis. Some of the oxygen produced by photosynthesis is used by the plant for respiration.

• Light as a limiting factor
If the investigation shown in Experiment 5 is carried out at different light intensities, the rate of photosynthesis, as measured by the rate of production of oxygen bubbles produces results as shown in the Figure below. You can see in the Figure above that, as light intensity increases, the rate of photosynthesis increases, until a point is reached when the plant is photosynthesising as fast as it can. This is marked as point B. At point B, even if the light becomes brighter, the plant cannot photosynthesise any faster. This is the optimum level of light. Light is added between points A and B on the curve. The rate of photosynthesis is limited by how much light is available. If the light intensity increases, then the rate of photosynthesis increases. Light is not a limiting factor between points B and C on the curve. If the light intensity was increased, the rate of photosynthesis would not increase. Very high light intensities may actually damage plants.

• Carbon dioxide as a limiting factor
If the experiment is repeated with the plant being given more carbon dioxide than in the original experiment, we see that the rate of photosynthesis will increase, as shown in the Figure below. This shows that carbon dioxide can also be a limiting factor. The more carbon dioxide a plant is given, the faster it can photosynthesise up to a point of 0.5%, which is the maximum. The maximum is the optimum carbon dioxide concentration. Sometimes, photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. Growers of greenhouse tomatoes recognise this and provide a carbon dioxide-enriched atmosphere for their plants.

-Increasing crop yield/productivity (greenhouses) at certain times of the year, plant growers grow crops, such as In parts of the world with low light intensity and low temperatures tomatoes, lettuce, and cucumbers, in greenhouses. Inside these sealed environments plant growers can increase the carbon dioxide concentration by burning of fuels. They can increase the temperature by using heaters or burning fuels. Artificial lighting can be used to improve and maximise crop production, and reflectors can be used to reflect light directly onto the plants. The Figure below shows a greenhouse.

• Temperature
Changes in temperature will have little effect on the reactions of the light-dependent stage because these are driven by light, not heat. However, the reactions of the light-independent stage are catalysed by enzymes, which like all enzymes are sensitive to temperature. The effect of temperature on these reactions is similar to its effects on other enzymes. The optimum temperature varies for each species, but many temperate plants have an optimum temperature between 25 °C and 30 °C.

EXPERIMENT 6
Practical investigation: Investigate the effect of changing light intensity on photosynthesis
In this activity, you will investigate the effect of increasing light intensity on the rate of photosynthesis of waterweed (keeping all other factors constant). The rate at which bubbles of oxygen are released by a waterweed is an indication of the rate at which it is photosynthesising.
Method:
1. Make sure that the waterweed is being exposed to white light (that is, no colour filter is being used).
2. Set the CO, concentration at 0.5 arbitrary units.
3. Set the light intensity at 1.0 arbitrary unit.
4. Allow the experiment to run for a period of 30 minutes.
5. Carry out five runs. Calculate and record the average number of bubbles released.
6. Keeping the CO(2), concentration at 0.5 arbitrary units, repeat procedures 4 and 5 at the following light intensities: 2.5, 4.0,5.5, 7.0, 8.5, and 10.0 arbitrary units.
7. Plot a graph of bubble count against light intensity.
8. What conclusions can you draw about the rate of photosynthesis in the waterweed and the light intensity to which it is exposed?

EXPERIMENT 7
Deactical investigation: Investigate the effect of increasing CO(2), concentration on photosynthesis ln this activity, you Will investigate the effect of increasing the CO(2) concentration on the rate of pnotosynthesis of waterweed (keeping all other factors constant).
Method:
1. Make sure that the watervweed is being exposed to white light.
2. Set the light intensity at 10.0 arbitrary units.
3. Set the CO, concentration at 0.1 arbitrary units.
4. Allow the experiment to run for a period of 30 minutes (fast forward' will save time).
5. Carry out five runs. Calculate and record the average number of bubbles released.
6. Keeping the light intensity at 10 arbitrary units, repeat procedures 4 and 5 at the following CO(2) concentrations: 0.2, 0.3, 0.4, and 0.5 arbitrary units.
7. Plot a graph of bubble count against CO(2) concentration.
8. What conclusions can you draw about the rate of photosynthesis of the waterweed and the concentration of CO(2), available to it?

EXPERIMENT 8
Practical investigation: Investigate the effect of different colours of light on the rate of photosynthesis
Method:
1. Set the light intensity at 6.0 arbitrary units.
2. Set the CO, concentration at 0.5 arbitrary units.
3. Select white light.
4. Carry out five runs and record the average number of bubbles released.
5. Select the red filter and repeat procedure 4 above.
6. Select the green filter and repeat procedure 4 above.
7. Draw a bar graph to compare the rates of photosynthesis of the waterweed under the different colours of light.
8. What conclusions can you draw about the effect of different colours of light on the rate of photosynthesis in the waterweed?

The end, posted by Mrs Smith Merlin.