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Learn about the process of photosynthesis, its factors and products, and how substances enter plants for photosynthesis. Understand why photosynthesis is critical and its connection to respiration.
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At the end of this unit you should: • Be able to describe the process of photosynthesis and why it’s needed. • Be able to name the factors needed for, and the products of, photosynthesis. • Be able to explain where the substances needed for photosynthesis come from and how they enter the plant. • Understand and know the word equation for photosynthesis. • Be able to explain what happens to the products of photosynthesis. • Be able to explain why photosynthesis is such a critical process to the world around us and the factors that can limit photosynthesis. • Be able to recognise and explain links between photosynthesis and respiration.
absorb biological chemical chlorophyll chloroplast energy hypothesis photosynthesis process respiration
LIGHTBULB QUESTION Photosynthesis is the most important reaction. Photosynthesis traps the sun’s energy to make food. Without food, respiration could not occur.
(a) In pairs, look at the images (a) and (b) in Fig. 05.01.01 and make a list of differences between the inputs and outputs in the images. • Image A Plant: • Plant is absorbing water through its roots from the soil • Taking in carbon dioxide from the air • Water is travelling from the roots through the stem to the leaves • Making food at the leaves/carrying out photosynthesis • Releasing oxygen into the air from the leaves
(a) In pairs, look at the images (a) and (b) in Fig. 05.01.01 and make a list of differences between the inputs and outputs in the images. • Image B Child: • The boy is taking in oxygen from the air • He is releasing carbon dioxide and water vapour into the air • The boy takes in food through the process of respiration
(b) State any similarities between the two images. Both are taking in and releasing a gas.
(c) If you were to think of one word that is involved in both, what would it be? Explain why you chose this word. Energy. Without energy, none of the processes in living things can take place.
LIGHTBULB QUESTION No, because when the plants photosynthesise they trap the suns energy and bring it in the food chains or food webs.
(a) Copy Table 05.01.01 and write beside each of the plant organs how it is involved in photosynthesis.
(b) Draw a diagram of a plant cell (see Unit 1.1) and indicate where photosynthesis occurs. Photosynthesis occurs in the chloroplast of a plant cell.
(c) Fig. 05.01.06 shows a daffodil. Sketch out this image and identify on your sketch where photosynthesis occurs. Add the words from the photosynthesis equation to the image. Photosynthesis: Carbon dioxide + Water Oxygen + Glucose Light Chlorophyll
(d) In your own words, explain the process of photosynthesis. Chlorophyll traps the light energy from the sun. Water is taken up from the roots and carbon dioxide into the leaves. A chemical reaction – photosynthesis – happens. Oxygen and food/glucose are produced.
Investigation 05.01.01: Revealing the different pigments in leaves Equipment: Some leaves from three different plants, some filter paper, a pencil, three beakers, a pair of scissors, a pestle and mortar, isopropyl alcohol, three straws, a glass rod, Sellotape or paper clip. Instructions: 1. Cut up enough leaves to quarter-fill a beaker. 2. Use the pestle and mortar to grind the leaves into a fine pulp. Clean and dry the pestle and mortar after each use – do not mix the different pulps. 3. Cut three strips of filter paper approximately 2.5 cm wide, and long enough to hang around a straw as shown in Fig. 05.01.08. 4. Draw a pencil line 2–3 cm from the bottom of each filter paper as shown.
Investigation 05.01.01: Revealing the different pigments in leaves Instructions: 5. Set the strips of paper aside. 6. Empty the pulp into beakers, a different beaker for each sample of leaf pulp. 7. Pour the alcohol over the pulp, making sure the alcohol level is above that of the pulp. (Do not use water.) 8. Stir with a glass rod until the alcohol changes colour. 9. Taking one of your strips of filter paper, roll the end that doesn’t have the pencil line on it around a straw and secure with Sellotape or a paper clip. Repeat with the other two strips.
Investigation 05.01.01: Revealing the different pigments in leaves Instructions: 10. Hang a strip of filter paper over each beaker, ensuring that the pencil line on the paper does not get covered with the liquid, as shown in Fig. 05.01.08. If your paper is too long, roll the paper around the straw again and secure with tape. (You do not want the end of the paper to get saturated.) 11. Wait approximately fifteen minutes or until you see colours move up to the top of the filter paper in each beaker. 12. Make a note of the different colours at the top of the paper and compare your results.
1. Do you think the leaves will have different pigment colours, or will they all be the same? Depending on the types of leaves sourced and the time of year. Generally the leaves will have different pigment colours.
2. If the leaves were from different types of trees, would the pigment colour results be the same or different? Justify your answer with an explanation. • Different types of trees have different leaves so therefore the pigment results may vary. The time of year may also be a factor in the results.
3. Suggest why you would not use water as a solvent. What might happen when it is added to the pulp? • The pigments within the leaves are not very soluble in water. There is water already in the leaves and more water may make the leaves soggy. The result of this would be that the actual pigment colours would not travel up the chromatography paper very well.
Investigation 05.01.02: Showing the limiting factors in photosynthesis (i) Varying the amount of light affects the growth of plants. • Equipment: Some cress seeds and cotton wool, some radish seeds and soil, sunlight or a lamp, some water, a graduated cylinder, a thermometer, a ruler, a results table. • Instructions: • Place the seeds on the cotton wool/in soil, and then add water to allow seeds to germinate. Students will have to decide how many sets of seeds and cotton wool they will use. • Put seeds in different places to vary the amount of light they receive: in cupboard to allow no light; covered by paper with holes to allow some light through; by a window or under a lamp to allow maximum light.
Investigation 05.01.02: Showing the limiting factors in photosynthesis (i) Varying the amount of light affects the growth of plants. Instructions: c) Students create a results table. d) Allow 3–4 days for growth to occur. e) Record results. Students should comment on colour of leaves, length of shoots, thickness or thinness of shoots. f) Students could use a thermometer to record the area temperature to ensure a fair test.
Investigation 05.01.02: Showing the limiting factors in photosynthesis (ii) Varying the amount of water affects the growth of plants. • Equipment: Some cress seeds and cotton wool, some radish seeds and soil, sunlight or a lamp, some water, a graduated cylinder, a thermometer, a ruler, a results table. • Instructions: • Place the seeds on cotton wool/in soil. • Add water to the seeds to allow germination to occur. • After two days of germination the students decide how much water to vary between their sets of seeds. For example: one set could get no water, the next a measured amount of water, the next double this and the next three times the amount of the second.
Investigation 05.01.02: Showing the limiting factors in photosynthesis (ii) Varying the amount of water affects the growth of plants. • Instructions: • Students create a results table. • Allow three–four days for growth to occur. • Record results. Students should comment on colour of leaves, length of shoots, thickness or thinness of shoots, whether the leaves look full or wilting.
Investigation 05.01.02: Showing the limiting factors in photosynthesis (iii)Varying the level of carbon dioxide affects the growth of plants. Equipment: Some pond weed, some sodium bicarbonate, a lamp, a boiling tube, a spatula, a paper clip, a results table. Instructions: a) Place a paper clip on the pond weed (so it doesn’t float) in the boiling tube and cover completely with water. (Students only need one boiling tube and one section of pond weed.) b) The boiling tube can be placed in a beaker or test tube rack. c) Students could use a thermometer to maintain the same temperature throughout the investigation.
Investigation 05.01.02: Showing the limiting factors in photosynthesis (iii)Varying the level of carbon dioxide affects the growth of plants. Instructions: d) A results table needs to be created noting the number of spatulas of sodium bicarbonate added and the number of bubbles produced. For example:
Investigation 05.01.02: Showing the limiting factors in photosynthesis (iii)Varying the level of carbon dioxide affects the growth of plants. Instructions: e) Place the boiling tube beside a lamp to increase the light intensity so the investigation is carried out more quickly. f) Count the number of bubbles within a specific period of time (the time factor should not change during the investigation). One minute is ideal. Record the answer. g) Add one spatula of sodium bicarbonate to the boiling tube. h) Count the number of bubbles. i) Add another spatula of sodium bicarbonate. j) Count the number of bubbles. k) Add another spatula of sodium bicarbonate, counting the number of bubbles again produced for one minute.
Investigation 05.01.02: Showing the limiting factors in photosynthesis (iv) A hypothesis of your own relating to the factors needed for photosynthesis. A suggestion might be to use different colours of filters on the lightbulb and see if this will change the rate of photosynthesis, the hypothesis being that ‘the rate of photosynthesis does not change/does change if coloured filters are used’. The support for this investigation would be that the rate of photosynthesis is related to the amount of light energy trapped and used. Does the coloured filters change the amount of light energy trapped? A control of the rate of photosynthesis of a normal bulb with no filter is needed in this investigation.
Investigation 05.01.02: Showing the limiting factors in photosynthesis 2. Draw a conclusion from your results. What happens when we limit the factors for photosynthesis? Example: • What happens with no light, a small amount of light, and enough light? • What happens with no water, a small amount, a large amount and too much? • What happens with a small amount of carbon dioxide, and greater amounts?
Investigation 05.01.02: Showing the limiting factors in photosynthesis 3. Compare your results with those of others in the class. There should be similar in trends even if the exact results and numbers are different.
How do you think the investigation you carried out will support the hypothesis you have chosen? • It will prove that each factor is needed in the right amounts for photosynthesis to occur and that reducing the factor can reduce the rate of photosynthesis. • Too much water will kill the plant. • A high amount of light intensity and carbon dioxide will only increase photosynthesis to a certain amount.
2. How did you ensure that a fair test was maintained during your investigation? • I only changed the factor that I was investigating and kept all others the same. • I used a graduated cylinder when measuring water for accuracy. • I used a spatula when measuring sodium bicarbonate for accuracy. • I used a thermometer to maintain the same temperature throughout the investigation.
3. Can you make a link between these problems of ensuring a fair test and the results you or a classmate found? • As we only changed one factor we ensured a fair test, if we changed more than one factor our results would not be correct as the test would not be fair. We used lab equipment to ensure accuracy, this also allowed our test to be fair and ensuring our results can be used in discussions and conclusions.
(a) Write out the word equations for photosynthesis and respiration. Place the chemical equation underneath each word equation. Light Photosynthesis: Carbon dioxide + Water Oxygen + Glucose CO2 + H2O O2 +C6H12O6 Chlorophyll Light Chlorophyll Respiration: Glucose + Oxygen = Carbon Dioxide + Water + Energy C6H12 O6 + O2= CO2 + H2O + Energy
(b) Make a list of the similarities and differences that you spotted between them. Similarities: Both involve a gas in the reaction. Differences: What one produces the other needs.
Copy and Complete In this unit I have learned that photosynthesis happens in plants. It allows plants to make food. This is food that we and other animals eat. The plant needs sunlight, chlorophyll, carbon dioxide and water to photosynthesise. The leaves take in carbon dioxide from the air, the roots take up water from the soil, and the chlorophyll is found in the leaves. When photosynthesis happens it produces oxygen and food. We call this food glucose or starch. We breathe in this oxygen and the plants use the food to grow or we eat the food from the plant. So we rely on plants to survive; without them we would not be able to live. Plants need the rightamounts of carbon dioxide and light to make the food. Too much or too little of either means the plant will not make food as quickly as it should.
1. Name the part of the plant where photosynthesis happens. Chloroplast.
2. Draw a diagram of a leaf as in Fig. 05.01.10 and label the arrows with the four materials needed for photosynthesis and the two materials that are produced. What is needed: Carbon dioxide, water, sunlight and chlorophyll. What is produced: Oxygen and glucose.
3. What pigment does the chloroplast have that allows photosynthesis to occur? Chlorophyll.
4. Sketch a graph of the results you would expect to see if a plant had reduced carbon dioxide levels over time. Use the following axes. Note: If the levels of carbon dioxide are high, then the rate of photosynthesis is high. When these levels decrease, so too does the rate. The x-axis on the graph refers to decreasing levels of carbon dioxide as referred to in question – some students may need this highlighted to them.
5. During the night the amount of light is low. Suggest what happens the rate of photosynthesis in a plant at night. The rate of photosynthesis decreases at night.
6. How do plants take in the essential minerals they need? Minerals are dissolved in the water in the soil and are taken up into the root with the water.
7. If you put a plant in a cupboard for two weeks and watered it regularly, would it still make food? Give a reason for your answer. No, it would become ‘de-starched’ or would not make food. Light, one of the four materials needed for photosynthesis, would be missing.
