Why can a plant make its own food but an animal cannot?
What is needed for photosynthesis to happen?
How do plants make food and store food?
Why do plants need so much water?
Can plants live in the dark?
Why are plants mostly green?
Teachers are encouraged to make a large circle on the wall using large arrows that can be cut from blue or even black plastic bags. Then cut out white letters to say "Photosynthesis" in the centre of the circle and stick large posters on the arrows to say:
Plants absorb carbon dioxide
Plants release oxygen
Animals breathe in oxygen
Animals breathe out carbon dioxide
Perhaps cut out pictures of plants or get learners to make plants and animals in Art and stick them next to the specific labels they illustrate. Create a glossary by placing words relating to the topic around the classroom. Tell the learners that they are going to be plant investigators, and that their job is to find out what the words mean, and how they relate to plants and photosynthesis.
When introducing this topic remind them of the work on interdependence they covered in Gr. 5. Discuss how animals and plants are interdependent upon each other - plants produce food and oxygen for animals, while animals - when they die - decay, replacing nutrients in the soil for plants, and releasing carbon into the air to continue the carbon cycle.
Plants and food
Green plants are just like factories! They make food for themselves and every animal on earth using sunlight energy, water and the gas carbon dioxide. They also recycle the air and make oxygen for us to breathe.
Scientists have found out exactly how plants are able to do all all these things. Let's take a closer look at how scientists did this and see how plants make food for themselves and us.
What happens in a factory? Why do you think we can say plants are like factories?
A factory is a place where goods or products are made/assembled/manufactured and then delivered to other places to be used. Plants are therefore like factories as they use raw products to make new products (food).
Why can we say that plants make food for themselves and every animal on earth?
Plants make food for themselves and plants are the beginning of the food chain, therefore all other animals, whether herbivores which eat plants directly, or carnivores which eat the herbivores, depend on plants for food.
The process of photosynthesis
Photosynthesis is the process that plants use to change the energy from sunlight into energy for food. Plants change light energy from the sun into food energy. Photosynthesis happens in all green parts of a plant. Leaves are usually the greenest parts. So plants do this mostly in their leaves.
There are some important requirements for photosynthesis to happen:
1. Chlorophyll: Chlorophyll is a green substance that plants use to capture light energy from the sun. Chlorophyll is very important. Without chlorophyll plants cannot use the sunlight energy to make food. Also, oxygen levels in the air will go down. If that happens plants and animals will suffocate.
As a fun activity, take learners outside to see if there are other colours found in leaves, and not just the green pigment chlorophyll. Although green chlorophyll is predominant, there are also yellow, orange and purple pigments found in leaves, especially in autumn when the leaves change colour. In the body, the pigment melanin, is the main determinant of skin colour and it is also found in hair and the iris in the eye.
2. Sunlight: Sunlight has energy. Plants use this energy to make sugars from water and carbon dioxide.
3. Water: The roots of a plant absorb water and nutrients from the soil. Water is a solvent in all living things. Dissolved substances are moved around the body to where they are needed. Just like you, plants have veins for this movement. They move minerals from the roots upwards. They move sugars from the leaves downwards. Photosynthesis can only happen in a water solution. Water is also important because it provides support to the plant to keep it upright. Like you, plants have skeletons. But unlike you many plants have water skeletons!
In the second term in Matter and Materials, learners will do more on mixtures, solutions and dissolving, and this will therefore make sense. Refer back to this section when you are doing solutions and discussing water as a solvent.
4. Carbon dioxide: The plant absorbs or takes in carbon dioxide from the air through little holes. These holes are found all over the plant, mostly under the leaves.
5. Soil: The soil provides mineral nutrients and water for the plant that are necessary during photosynthesis. Soil also provides anchorage to the plant, otherwise the plant cannot stand up straight.
Plants use chlorophyll, sunlight, water and carbon dioxide to make food. Here is a simple illustration to show how this process occurs:
Chlorophyll captures the sunlight energy.
This energy splits the water into hydrogen and oxygen.
The oxygen is released into the air.
The hydrogen is used with the carbon dioxide to make glucose (sugars).
The sugars are moved from the leaves to other parts of the plants where they are stored.
The water in the plant veins carries the sugars. When the sugars reach the storage parts they are changed into starch.
Plants can store the starch in these places:
leaves (cabbage, spinach, lettuce)
fruit (apples, banana, peaches)
stem (sugar cane)
seeds (wheat or mealies)
flowers (nasturtiums, broccoli and cauliflower)
roots (carrots or beetroot)
Starch is insoluble in water which is why plants store starch and not glucose, which is soluble in water. Refer back to this section when doing soluble and insoluble substances in the second term.
Dramatise the process of photosynthesis
Prepare beforehand by collecting the different materials needed. The characters need different colours to identify themselves as what they are, possibly some t-shirts that they can pull over their clothes, or else a scarf or ribbon or coloured piece of paper to pin onto their front. You will also need tin foil, glitter and string for the roots. For the animals, you can make masks out of paper plates with the eyes cut out, and tied around the head with a piece of string. Learners can draw animal faces on the front.
Your teacher will explain to you how to act out the process of photosynthesis.
Characters needed for this dramatisation:
Narrator to describe the process. This can be a teacher or a learner. It might be a good idea to make short notes from the information above to remember in what order everything is happening.
Sun - this learner can dress in yellow and perhaps get some old tin foil or shiny paper to decorate their head or body to show the light and heat energy that the sun produces.
Plants - a few learners can dress in green and perhaps tie a few strings to their feet to represent roots. They need to hold some rice or shiny glitter in their hands or their pockets to show that the water evaporates after photosynthesis.
Rain / water - a few learners can dress in blue and perhaps have some rice, shiny glitter, small pieces of tin foil or something similar to represent the rain falling.
Carbon dioxide - attach signs to the learner's chests that say 'Carbon dioxide' and dress in purple.
Oxygen - attach signs to the learner's chests that say 'Oxygen' and dress in orange.
Glucose energy as fruit and vegetables - dress up or make posters from scrap cardboard to show large carrots, apples, potatoes, or something similar.
Some learners need to be animals who breathe out carbon dioxide and eat the plants. You can make masks out of paper plates with eyes cut out.
The dramatisation: When the dramatisation starts, the glucose and oxygen actors sit quietly in small groups around the plants with their heads down, not looking at the audience.
The narrator introduces the play and explains the different processes as these occur.
The sun shines in the centre of the stage and can turn and/or raise their arms to show the sunlight radiating from it.
The plants stand away from the sun and the rainwater actors can 'water' them by gently throwing the rice or similar little objects over their heads. Then sit down around the plants.
The carbon dioxide actors run from the animals and circle the plants, and then sit down around the plants.
Now the oxygen and glucose actors rise and run around the plants, and then run to the animals to show they are receiving oxygen and food.
You might want to repeat this a few times to show that this cycle continues.
Why do plants die when there is a drought?
There are many processes which shut down without water, photosynthesis being one of them. Plants cannot photosynthesise sunlight without water. If they cannot photosynthesise they cannot create glucose to support life processes within the plant. If the plant cannot support its own life processes it dies. The plant also loses its support from the water in the veins acting as a 'skeleton'.
Design a poster for your Gr. 4 friends to explain the process of photosynthesis to them. You can use sentences and short paragraphs but make sure you use many illustrations.
Soil was looked at in Gr. 5 Earth and Beyond, especially the particles of soil and which types of soil plants grow best in. However, it would be useful to also emphasise soil in this section and have a discussion on what makes up soil, namely organic and inorganic material, water, air, rocks and sand. Where possible, bring examples of different soil types to class (such as loam soil, clay, beach sand) and get the learners to touch and feel the soil and explore what makes up soil.
Food from photosynthesis
Photosynthesis is the process inside plants that changes the energy from the sun's light into a form of energy that animals can eat and use to carry out their life processes.
Plants changes the glucose into starch, for example mealies (mealies and maize flour), rice (rice flour and rice) and wheat (flour).
Plants then store this food in different parts of the plant that an animal will eat. They can store it in their leaves, stems or roots, flowers, fruits or seeds.
Look at the images below of different plant products. For each image, identify which part of that plant we eat (for example: When we eat an apple, are we eating the leaf, the stem, the root, the fruit or the seed of the plant?) Use the space below to draw a table for your answers.
Part that we eat
We know that plants make glucose (a sugar) but they store starch. Let's now find out what the difference is.
Difference between a starch and a sugar
Prepare beforehand: Prepare at least 10 different plant products in advance of this lesson and mark each item from 1 - 10. Cut up fruit/potato/sweets into bite-sized cubes. Place flour/cooked rice/etc. into bowls. Use teaspoons to taste the flour/cooked rice/etc.
IMPORTANT: Before doing this activity find out if any of the learners have any allergies to these foods and if learners with diabetes are allowed to eat/taste the fruit/sweets.
cooked rice, potato, bread
sugar cane, if possible
Work in pairs.
One partner must be blindfolded.
On a piece of paper list the numbers 1 - 10.
The other partner must let the blindfolded partner taste each of the foods marked 1 - 10. If it is a flour, use a teaspoon to spoon the flour into your partner's mouth. If it is a kernel like a rice or mealie kernel, or a cube of fruit, put it in the palm of their hand and let them eat it themselves.
After each taste your blindfolded partner must guess if it is a sugar or a starch based on the taste.
Record your partners answers on the piece of paper containing the numbers 1 - 10.
Swap with your partner and repeat the test.
While learners are swapping with their blindfolded partners, rearrange the foods with the numbers to ensure fairness. The aim of the test is not to establish the exact name of the fruits and foods but to establish that taste is not a suitable method to test for sugar or starch. Generally sugars are sweet and starches are not, but not always.
Was it easy to distinguish between the sugar and the starch each time? Which foods did you find difficult to classify?
What can you say about the difference between a starch and a sugar based on taste?
Sugars are sweet, starches are not.
Using TASTE to check if a food is a sugar or a starch is not very reliable.
There is a special test that scientists use to see if a food product is a starch or not. It is called the iodine starch test.
Iodine solution is a special solution that is normally a brown liquid.
Iodine is what we call an indicator.
When iodine solution is dropped on starch, the iodine and starch combine and produce a blue colour. We use this to test whether there is starch in a food product.
Let's see how this works!
The iodine starch test
Note: There will be NO tasting in this activity.
the same foods used in the taste test (they should be marked 1 - 10 )
include some other foods such as cheese and a boiled egg
Write the food or plant product that you chose in the first column below.
You are going to test whether this food product is a starch or not. When the iodine solution turns blue-black you will know it is a starch.
Explanation for starch turning blue-black when iodine is placed on it: Starch is composed of polymers of glucose. Long linear chains are amylose. Amylose coils into a structure resembling a tube with a hollow core. Certain molecules, including iodine, can lodge inside the core. The complex of iodine stuck inside the amylose coil produces a characteristic blue-black colour. The starch itself is not altered. NB: This explanation is not necessary for learners, but do say that the iodine reacts with the starch to form a blue-black colour.
Use a dropper and drop iodine solution onto each food group.
Put a tick next to the food product that turns blue-black - this is a starch. Put a cross next to the food product that stays brown - this is not a starch.
Name of Food Product
Starch or not?
Which test do you think is more accurate to test for starch - the taste test or the iodine starch test?
Did the animal products, such as cheese and boiled egg, contain starch? Why do you think so?
Animals do not produce or store starch. Starch is only stored in plant products.
Animals do store carbohydrates, but not in the form of starch. Only plants produce and store starch. Animals store glucose in the form of glycogen.
Plants and air
All animals and plants need oxygen to live and carry out their life processes.
Animals breathe in oxygen and breathe out carbon dioxide, all through the day and the night. Oxygen is used to release energy from food inside the body, which is used for the life processes.
Do you remember what the seven life processes of living things are? Write them down below.
Just like animals, plants also use oxygen throughout the day and the night. Oxygen is necessary for plant growth and the development of new plants, seeds, leaves and shoots for example. Plants, therefore, also produce carbon dioxide as a 'waste product' once the oxygen has been used.
Plants do not photosynthesise through the night because there is no sunlight energy available to do that. This means that plants only need carbon dioxide during the day, for photosynthesis.
This cycle of using and producing both oxygen and carbon dioxide is very important to life on Earth.
The oxygen and carbon dioxide cycle
Carefully study the following illustration.
Answer the questions that follow.
Make a list of living organisms that produce both oxygen and carbon dioxide in this picture.
Tree, reeds, water plants, and shrubs on the bank
Identify three living organisms that cannot produce oxygen in this picture.
Fish, duiker (buck), squirrel, dragonfly
Predict what you think would happen if all the animals were removed from this habitat.
Probably not much would change as the leaves that decay would still give off carbon dioxide for the plants to use, as well as the carbon dioxide that the plants produce themselves.
What two life processes are involved in the carbon dioxide/oxygen cycle?
breathing in oxygen and giving off carbon dioxide
Complete this cycle by filling in the missing information for the two arrows on the left hand side of the illustration. Supply the labels for arrows 1 and 2.
Arrow 1: Plants produce oxygen
Arrow 2: Animals breathe out carbon dioxide
Explain why animals would not survive if all the plants on earth were to suddenly die.
Animals need oxygen for their cells to work and to carry out life processes.
If animals do not have oxygen they cannot carry out the life processes and will die.
Plants also produce food from the sun that animals need to eat for energy to carry out the life processes.
Why do we say the oxygen and carbon dioxide are in a cycle?
For life on Earth to continue, there needs to be an unlimited supply of carbon dioxide and oxygen. It is in a cycle to ensure that similar amounts of both are produced.
Plants produce their own food (glucose) by a process called photosynthesis.
Photosynthesis takes place mainly in the leaves.
During photosynthesis the plant uses chlorophyll, sunlight energy, carbon dioxide (from the atmosphere) and water to make glucose.
Plants change some of the glucose (sugar) into starch which they store in their leaves, stems and roots, flowers, fruits and seeds.
Animals take in oxygen from the air and produce carbon dioxide when they breathe.
Plants recycle carbon dioxide and make oxygen during the process of photosynthesis.
List the four things that are vitally important for plants and photosynthesis.
Choose words from the word box to complete the following sentences. Write the sentences out in full.
organic and inorganic material
sand and rocks
The process when the green parts of plants make food is named _____.
Water and minerals are absorbed by the _____ of plants.
Soil is made up of _____, _____, _____, _____.
The process when the green parts of plants make food is named photosynthesis.
Water and minerals are absorbed by the roots of plants.
Soil is made up of organic and inorganic material, water, air,sand and rocks.
The seedlings that were planted in the newspaper cuttings or cotton wool did not grow very well at all, even though they had sunlight and water. What could they not get from the newspaper or cotton wool that plants normally get from soil?
Nutrients and minerals
Where does photosynthesis usually take place? Explain your answer.
Photosynthesis usually takes place in the leaves. The leaves are green as they contain chlorophyll. Leaves also face the sunlight and are exposed to the most sun to drive the process of photosynthesis.
Do you think photosynthesis takes place at night? Explain your answer.
No, it will not take place. At night there is no sunlight energy to drive the process of photosynthesis.
What is the name given to the sugar that plants produce during photosynthesis?
What do plants store glucose as? List some places where it is stored.
Starch, stored in leaves, stems, roots, flowers, seeds, fruits.