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Boardworks GCSE Additional Science: Biology

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Presentation on theme: "Boardworks GCSE Additional Science: Biology"— Presentation transcript:

1 Boardworks GCSE Additional Science: Biology
Photosynthesis Photosynthesis

2 Boardworks GCSE Additional Science: Biology
Photosynthesis 2

3 How do plants get the food they need?
Boardworks GCSE Additional Science: Biology Photosynthesis All living organisms need food to grow and survive. This is because food provides raw materials for growth and energy for chemical reactions. Plants are known as producers because they provide food for many other organisms. Without plants, other organisms would have no raw materials for growth or energy. Unlike animals, plants cannot move very much, so how do they get the food that they need? 3

4 Boardworks GCSE Additional Science: Biology
Do plants eat soil? Boardworks GCSE Additional Science: Biology Photosynthesis It used to be thought that plants got their food from the soil. Greek scientists believed that plants increased in mass by taking in minerals from the soil. A scientist called Van Helmont performed an experiment to test this idea. He grew a willow tree and measured the mass of the soil, the tree and the water he added. Teacher notes Van Helmont ( ) was amongst the first scientists to carry out experiments and collect quantitative data in order to draw conclusions. He was correct in deducing that nutrients from the soil had little effect on a plant’s mass, and in concluding that some of the increase in mass came from the water, but he was not aware that carbon dioxide also contributed. After five years the plant had gained about 74 kilos but the mass of the soil was the same. He concluded that the tree's weight gain had come from water. Was he right? 4

5 Boardworks GCSE Additional Science: Biology
Oxygen from plants Boardworks GCSE Additional Science: Biology Photosynthesis Joseph Priestley discovered oxygen, and later showed that it was made by plants. He placed a mint plant and a candle in an enclosed space, and soon discovered that the candle went out when all of the oxygen was used up in combustion. He kept the container closed and relit the candle 27 days later. The candle was able to burn again. Priestley concluded that something must have been made by the plant that changed the air. The gaseous product was oxygen. 5

6 Boardworks GCSE Additional Science: Biology
Photosynthesis 6

7 What is photosynthesis?
Boardworks GCSE Additional Science: Biology Photosynthesis Plants make their own food by photosynthesis. A few micro-organisms can do this too. Photosynthesis is a chemical reaction that uses light energy. light energy The word photosynthesis comes from the Greek language: ‘photo’ means ‘light’ ‘synthesis’ means ‘putting together’. Photosynthesis just means ‘putting together with light’. 7

8 Boardworks GCSE Additional Science: Biology
Photosynthesis Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This five-stage interactive animation shows how photosynthesis occurs in leaves. At the end of the animation, you can view a summary of this process by clicking on “summary”. Suitable prompts could include: Start: What is so special about photosynthesis? Stage 1: Where in the plant does photosynthesis take place? Stage 2: Which material comes from the soil and which material comes from the air? Why does carbon dioxide enter the plant from underneath the leaf? Stage 3: What is the source of the light energy for photosynthesis? Stage 4: Where in the plant cell does photosynthesis take place? What is the name of the pigment that is needed for photosynthesis? Stage 5: What food is produced during photosynthesis? What gas is produced during photosynthesis? 8

9 Photosynthesis: summary
Boardworks GCSE Additional Science: Biology Photosynthesis How can the process of photosynthesis be summarized in one sentence? Photosynthesis is a chemical reaction that takes place in the chloroplasts of green plant cells, where light energy is used to convert carbon dioxide and water into glucose and oxygen. What is the word equation for this chemical reaction? light energy chlorophyll carbon dioxide + water oxygen glucose 9

10 Photosynthesis: word equation
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This drag and drop activity could be used as a plenary exercise to check students’ ability to identify the reactants, conditions and products of photosynthesis. 10

11 Symbol equation for photosynthesis
Boardworks GCSE Additional Science: Biology Photosynthesis The reaction of photosynthesis can be represented by the following equation: light energy chlorophyll carbon dioxide + water oxygen glucose What is the symbol equation for this reaction? light energy 6 CO2 + 6 H2O + C6H12O2 6 O2 The symbol equation is higher tier for OCR Gateway and OCR Twenty-first Century GCSE Additional Science. chlorophyll Is this a balanced symbol equation? How would you balance the equation? 11

12 Word equation to symbol equation
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This drag and drop activity could be used to extend the work on the photosynthesis equation, by providing practice of changing the word equation into a balanced symbol equation. It is important to highlight that chlorophyll and light energy are still represented by words in the symbol equation. 12

13 Photosynthesis equation quiz
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This multiple-choice quiz of ten questions could be used as a plenary activity to check students’ understanding of photosynthesis. To answer the questions, students select the appropriate component of the photosynthesis word equation. Mini-whiteboards could be used to make this a whole-class activity. 13

14 Boardworks GCSE Additional Science: Biology
Photosynthesis 14

15 How can you test for photosynthesis?
Boardworks GCSE Additional Science: Biology Photosynthesis The presence of starch in a leaf can be used to show that photosynthesis has taken place. After photosynthesis occurs, the glucose is often converted to starch for storage. Iodine is used to test for starch. It reacts with starch and changes colour from brown to blue-black. The starch test can be used to prove that photosynthesis needs light, carbon dioxide and chlorophyll to take place. How would you set up an experiment to test the conditions needed for photosynthesis? How would you make the experiment fair and reliable? 15

16 Testing leaves for starch
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This four-stage virtual experiment demonstrates how iodine can be used to test for starch. It could be used as a precursor to running the practical in the lab, or as a revision exercise. Suitable prompts include: Stage 1: Why is the leaf placed in boiling water? Stage 2: What does the warm alcohol do to the leaf? Stage 3: Why is the leaf placed in warm water? Stage 4: What colour change occurs if starch is present? 16

17 Is chlorophyll needed for photosynthesis?
Boardworks GCSE Additional Science: Biology Photosynthesis Chlorophyll cannot be removed from a plant without killing the plant. Instead, variegated leaves can be used to show chlorophyll is essential for photosynthesis. Variegated leaves have pale parts, which do not contain chlorophyll. The green parts of the leaf contain chlorophyll and are the control. Which areas will react with iodine? Only the green areas of the leaf react with the iodine and turn blue-black. Without chlorophyll, the pale areas have been unable to produce starch and do not turn blue-black. 17

18 Testing leaves for starch – activity
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This activity can be used as a plenary or revision exercise to test students’ understanding of the conditions required for photosynthesis. The activity consists of two parts: Students complete the final stage of the iodine test on five leaves Students identify the conditions of growth for each plant. It should be highlighted to students that before putting a plant in experiment conditions, the plant should be de-starched. This can be done by putting the plant in darkness for approximately two days. This means that starch present in the leaves has been produced during the experiment. 18

19 Where does the oxygen come from?
Boardworks GCSE Additional Science: Biology Photosynthesis The content in this activity is higher tier for OCR Gateway GCSE Additional Science. 19

20 Boardworks GCSE Additional Science: Biology
Photosynthesis 20

21 What is the rate of photosynthesis?
Boardworks GCSE Additional Science: Biology Photosynthesis Photosynthesis is a chemical reaction and so has a rate. Like many reactions, photosynthesis requires enzymes. Is the rate of photosynthesis always the same? Which factors do you think affect the rate of photosynthesis? light carbon dioxide temperature How do these factors affect the rate of photosynthesis? 21

22 How does light affect photosynthesis?
Boardworks GCSE Additional Science: Biology Photosynthesis Light energy has to be absorbed by chlorophyll for photosynthesis to take place. light energy chlorophyll carbon dioxide + water oxygen glucose The brighter the light, the more light energy there is, so will photosynthesis be faster or slower? More light energy means that photosynthesis will be faster. If light intensity is too high plant cells can be damaged. How is photosynthesis affected if this happens? 22

23 Investigating photosynthesis
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This virtual experiment illustrates how light intensity affects the rate of photosynthesis. It could be used as a precursor to running the practical in the lab, or as a revision exercise. When using this activity, it should be emphasized that more oxygen is being produced when the light intensity is increased. This is shown by the rate of production of gas bubbles. 23

24 Investigation photosynthesis – results
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This data handling activity investigates the effects of light and temperature on the rate of photosynthesis. Students are able to plot two graphs using experimental data and a line of best fit is automatically added to each graph. It could be used to compliment a practical in the lab, or as a revision exercise. While using the activity, it should be emphasized that two experiments were conducted, changing only one variable at a time. 24

25 Carbon dioxide and the rate of photosynthesis
Boardworks GCSE Additional Science: Biology Photosynthesis Carbon dioxide is one of the raw materials used by plants to make their food. light energy chlorophyll carbon dioxide + water oxygen glucose The concentration of carbon dioxide in the air is actually quite low (0.03%). Why is the concentration of carbon dioxide in commercial greenhouses often raised to about 0.1%? More carbon dioxide means more photosynthesis, so plants make more food and grow more quickly. 25

26 Does temperature affect photosynthesis?
Boardworks GCSE Additional Science: Biology Photosynthesis Photosynthesis is controlled by enzymes, which usually work best at warmer temperatures. Does increasing the temperature always increase the rate of photosynthesis? If it gets too hot (above 40 °C), the enzymes needed for photosynthesis begin to break down and are destroyed or denatured. The rate of photosynthesis decreases or even stops completely. Teacher notes You may wish to remind students that plants grow faster in the summer than in the winter. This is because they get more light and a warmer temperature. See the ‘Enzymes’ presentation for more information about temperature and enzymes. Photo credits: © 2007 Jupiterimages Corporation 26

27 What is a limiting factor?
Boardworks GCSE Additional Science: Biology Photosynthesis What is the ideal combination of factors for the maximum rate of photosynthesis? enough light enough carbon dioxide ideal temperature (not too hot or cold). How does restricting one of these facts affect the rate? If one of the factors is restricted, the rate of photosynthesis will be below the maximum possible rate. The restricted factor controls how quickly photosynthesis occurs and so limits the rate. It is called the limiting factor. 27

28 Light intensity and photosynthesis
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This animated graph illustrates the affect of light intensity on the rate of photosynthesis. It should be emphasized that after a certain point, other limiting factors will control the rate and further increasing light intensity will have no effect. This information is higher tier for OCR Gateway and OCR Twenty-first Century GCSE Additional Science. 28

29 Carbon dioxide and photosynthesis
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This animated graph illustrates the effect of carbon dioxide levels on the rate of photosynthesis. It should be emphasized that after a certain point, other limiting factors will control the rate and increasing carbon dioxide levels will have no effect. The similarities of the light intensity and carbon dioxide graphs could also be highlighted. This information is higher tier for OCR Gateway and OCR Twenty-first Century GCSE Additional Science. 29

30 Temperature and photosynthesis
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This animated graph illustrates the effect of temperature on the rate of photosynthesis. It should highlighted that, unlike carbon dioxide and light intensity, increasing the temperature above 45 ºC will cause the rate to decrease or stop completely. Students should be aware that photosynthesis is controlled by temperature-sensitive enzymes. At both stages of the graph, temperature is the limiting factor. See the ‘Enzymes’ presentation for more information about temperature and enzymes. This information is higher tier for OCR Gateway and OCR Twenty-first Century GCSE Additional Science. 30

31 Limiting factors – activity
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This labelling graphs activity could be used to check students’ understanding of factors that limit the rate of photosynthesis. It should be emphasized that each of the three factors could possibly limit photosynthesis. This information is higher tier for OCR Gateway and OCR Twenty-first Century GCSE Additional Science. 31

32 Limiting factors in a greenhouse
Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This simulation activity enables students to experiment with the conditions required for optimum plant growth. It could be used as a plenary activity to check students’ understanding of the factors that control photosynthesis, or as a revision exercise. This information is higher tier for OCR Gateway GCSE Additional Science. 32

33 Boardworks GCSE Additional Science: Biology
Photosynthesis The worksheet ‘Photosynthesis’ accompanies this presentation. 33

34 Boardworks GCSE Additional Science: Biology
Glossary Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes chlorophyll – The green pigment inside chloroplasts that is needed for photosynthesis to take place. chloroplast – The plant cell structure where photosynthesis occurs. glucose – A simple sugar, with the formula C6H12O6. Glucose is one of the products of photosynthesis. iodine – An element that can be used to test for starch. It reacts with starch and changes colour from brown to blue-black. isotope – Different atoms of the same element. They have the same number of protons and electrons, but a different number of neutrons. photosynthesis – The process by which plants use carbon dioxide and water to make glucose and oxygen in the presence of light and chlorophyll. variegated – A leaf containing areas without chlorophyll.

35 Boardworks GCSE Additional Science: Biology
Multiple-choice quiz Boardworks GCSE Additional Science: Biology Photosynthesis Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of photosynthesis. The question can be skipped through without answering by pressing the forward arrow. Students could be asked to complete the questions in their book and the activity could be concluded by completion on the IWB. 35


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