Key Concepts In this session we will focus on summarising what you need to know about: Photosynthesis the process

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1 GRADE 11 LIFE SCIENCES SESSION 1: PHOTOSYNTHESIS Key Concepts In this session we will focus on summarising what you need to know about: process of photosynthesis using words and symbols: importance of photosynthesis effects of variable amounts of light, carbon dioxide and temperature on the rate of photosynthesis The role of carbon dioxide enrichment, optimum light and optimum temperatures in greenhouse systems to improve crop Role of ATP as an important energy carrier in the cell Photosynthesis the process What is photosynthesis? Process whereby green plants use the radiant energy of the sun and carbon dioxide to manufacture their own food. chlorophyll Carbon dioxide+ Light + Water Sugar + Oxygen enzymes 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

2 Photosynthesis takes place mainly in the leaf. These contain chloroplasts, which are tiny objects containing chlorophyll. Cross-section through a leaf cell Photosynthesis occurs mainly in the palisade mesophyll, which contains chloroplasts, which are organelles containing chlorophyll.

3 Explain this organelle structurally suited for photosynthesis. The membrane is permeable to water and carbon dioxide The stroma contain enzymes for the photosynthesis dark phase. The stroma has ribosomes which manufacture enzymes. The lamella/thylakoids contain chlorophyll to trap radiant energy. The grana consist of stacks of thylakoids to increase the surface area to absorb sunlight.

4 Two reactions make up photosynthesis: 1.Light Reaction or Light Dependent Reaction - Produces energy from solar power (photons) in the form of ATP and NADPH. 2. Dark Phase/Calvin Cycle or Light Independent Reaction Uses energy (ATP and NADPH) from light reaction to make sugar (glucose). O 2 is released The Light phase Occurs in the Thylakoid membranes During the light reaction, there are two possible routes for electron flow: A. Cyclic Electron Flow Here the energy is used to form the energy carrier, ATP ADP + P ATP B. Noncyclic Electron Flow Here the energy is used to split water molecules into high energy hydrogen atoms and oxygen. The hydrogen atoms combine with coenzymes which take them to into the stroma for the dark phase. The oxygen is released into the atmosphere as a by-product. The Dark Phase Occurs in the stroma Carbon dioxide combines with the high energy hydrogen atoms in a series of reactions to form energy-rich carbohydrates like glucose and starch. The high energy hydrogen and ATP from the light phase provide the energy All reactions are controlled by enzymes.

5 A Summary of the process:

6 Question One 1.1 Why is photosynthesis important to organisms? Maintains the oxygen balance in the atmosphere. Maintains the carbon dioxide balance in the atmosphere. Production of food - all of our food comes directly or indirectly from photosynthesis. 1.2 Draw a labelled diagram to illustrate the general structure of the chloroplast. 1.3 A learner performed an investigation in which a green leafy twig from an aquatic plant was placed in a beaker containing sodium bicarbonate solution. The apparatus was exposed to a light source for a period of time and the intensity of light from the light source was increased at regular intervals. Gas bubbles were released. The number of gas bubbles released per minute was observed and recorded. The results of the investigation are shown in the table below. Study the table and answer the questions that follow. (Nated 2008 hgp1) Light intensity (lux) Number of gas bubbles released What is the aim of the experiment? Name the gas that is released in the investigation. What is the function of the sodium bicarbonate solution in this investigation? Explain the relationship between the light intensity and the number of gas bubbles released per minute as shown in the table. How would you set up a control for this investigation?

7 Factors limiting photosynthesis Three factors can limit the speed of photosynthesis - light intensity, carbon dioxide concentration and temperature. The following graphs illustrate this. Can you use the graphs to explain how each factor affects the rate of photosynthesis?

8 Maximising growth Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses. They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity they can use shade netting to reduce light The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too. Temperature can be increased by using heaters and reduced by using fans and/or shade nets. All the above create ideal conditions within the greenhouse and crop yield may improve.