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What is photosynthesis? Plants make their own food by photosynthesis. This process 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”. What do green plants “put together” to make their food? Photosynthesis: raw materials The raw materials for photosynthesis come from the air and the soil. What are these raw materials called? What else do plants need to turn carbon dioxide and water into food? carbon dioxide water Photosynthesis: energy for the reaction Photosynthesis is a chemical reaction between carbon dioxide and water. Energy is needed for this reaction to take place. Where do plants get this energy from? light energy carbon dioxide water Photosynthesis: where it happens Plants use light energy from the Sun to power photosynthesis. light energy Where in the leaf does this reaction take place? Photosynthesis takes place in what part of plant cells? carbon dioxide water Photosynthesis: where it happens Photosynthesis takes place in plant cells with chloroplasts. light energy Chloroplasts contain the green chemical called chlorophyll. Chlorophyll absorbs the energy from sunlight that allows carbon dioxide and water to react. What are the products of this reaction? chlorophyll carbon dioxide water Photosynthesis: products of the reaction The products of the reaction between carbon dioxide and water are glucose and oxygen. light energy chlorophyll Which of these products is used by plants? What happens to the ‘waste’ product? carbon dioxide oxygen glucose water Photosynthesis: products of the reaction Glucose is the useful product for plants. Some glucose is used straightaway by plant cells, some is converted to starch for storage and later used for food. light energy chlorophyll carbon Oxygen is the ‘waste’ dioxide product. This gas is transported out of the leaf into the air. Why is this important for humans and other living things? oxygen glucose water Photosynthesis: summary Summarize the process of photosynthesis in one sentence. Photosynthesis is a chemical reaction that takes place in the chloroplasts in green plant cells, where light energy is used to convert carbon dioxide and water into glucose and oxygen. Photosynthesis is a chemical reaction which means it can also be summarized in a word equation. What is the word equation for this vital chemical reaction? Photosynthesis: word equation light energy carbon dioxide water glucose chlorophyll light energy chlorophyll carbon dioxide water oxygen glucose oxygen Photosynthesis: chemical formulae? Photosynthesis is a chemical reaction involving molecules. light energy carbon dioxide water glucose oxygen C6H12O6 O2 chlorophyll CO2 H2O The chemical formula of a glucose molecule is C6H12O6. What are the chemical formulae of the simple molecules that make up carbon dioxide, water and oxygen? !!!YOU MUST LEARN THIS EQUATION!!!! PHOTOSYNTHESIS Using Sunlight Energy Carbon Dioxide 6CO2 + Water 6H2O Glucose Absorbed by Chlorophyll These four things must all be present in order to make food by Photosynthesis C6H12O6 + Oxygen 6O2 Glucose sugar is made and stored as starch. Oxygen is given off as a waste product Leaves: maximizing photosynthesis Leaves are the most efficient solar panels on Earth! Why can they be called this? Light energy is absorbed by the chlorophyll in leaves and used to carry out photosynthesis. Leaves come in all shapes and sizes but what features do they have in common to maximize photosynthesis? Structure of a leaf How are leaves designed to maximize photosynthesis? Leaves are wide and flat Leaves are thin so gases to create a large surface can reach cells easily. area and absorb as much light as possible. Leaves have lots of veins to carry water to the cells and carry glucose away. Leaves have holes, called stomata, on their underside through which gases move in and out. Structure of a leaf activity Take a look inside a leaf What happens to the glucose? Photosynthesis and respiration Only green plants photosynthesize, but respiration occurs in the cells of all living things to release energy. Photosynthesis (energy needed) light energy carbon dioxide water glucose oxygen chlorophyll Respiration (energy released) carbon glucose oxygen dioxide water Compare the reactants, products and energy results of these two chemical reactions. How are they connected? Photosynthesis and respiration How will the amounts of oxygen and carbon dioxide in the air vary over 24 hours? amount of oxygen amount of gas in the air amount of carbon dioxide 12 a.m. 12 p.m. 12 a.m. What overall effect do photosynthesis and respiration have on the levels of oxygen and carbon dioxide in the air? The rate of photosynthesis Photosynthesis is a chemical reaction and so has a rate. light energy carbon dioxide water glucose oxygen chlorophyll Is the rate of photosynthesis always the same? The rate of photosynthesis varies depending on three main factors: light carbon dioxide temperature How do these factors affect the rate of photosynthesis? Light and the rate of photosynthesis Light energy has to be absorbed by chlorophyll for photosynthesis to take place. light energy carbon dioxide water glucose oxygen chlorophyll 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? Carbon dioxide and the rate of photosynthesis Carbon dioxide is one of the raw materials used by plants to make their food. light energy carbon dioxide water glucose oxygen chlorophyll The concentration of carbon dioxide in the air (0.03%) is actually quite low. 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 quicker. Temperature and the rate of photosynthesis Photosynthesis is controlled by enzymes. Enzymes usually work best at warmer temperatures. light energy carbon dioxide water glucose oxygen chlorophyll Why is the rate of photosynthesis slower on a sunny day in winter? If the temperature gets too hot (above 40 °C), plant enzymes begin to break down and are destroyed or denatured. Why does photosynthesis stop under such conditions? What is a limiting factor? 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 is the rate affected if one of these factors is restricted? 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. Photosynthesis and light – limiting factors rate of photosynthesis How does the amount of light affect the rate of photosynthesis on this labelled graph? 1 As the amount of light increases, so does the rate. The limiting factor is light. 2 Here, increasing the amount of light has no affect on the rate. The limiting factor is now carbon dioxide or temperature. 2 1 light intensity What must be increased for the rate to increase? Photosynthesis and carbon dioxide – limiting factors rate of photosynthesis How does the amount of carbon dioxide affect the rate of photosynthesis on this labelled graph? 1 As the amount of carbon dioxide goes up, so does the rate. The limiting factor is carbon dioxide. 2 Here, increasing the amount of carbon dioxide has no affect on the rate. Light or warmth is now the limiting factor. 2 1 concentration of carbon dioxide What must be increased for the rate to increase?