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Photosynthesis A summary of what you should know.

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Presentation on theme: "Photosynthesis A summary of what you should know."— Presentation transcript:

1 photosynthesis A summary of what you should know

2 Revision of third form photosynthesis

3 Photosynthesis What happens to the glucose formed in photosynthesis? PHOTOSYNTHESIS GLUCOSE STARCH CELLULOSE LIPIDS PROTEINS CARBON DIOXIDE AND WATER Required to make plant cell walls. It is made of 100s of glucose molecules bonded together. Glucose is chemically converted to fatty acids and glycerol to make lipids, which are needed to make plant cell membranes and seed storage oils. Is used by roots and leaves to store excess glucose in an osmotically inactive form. It is made of 100s of glucose molecules. Using nitrate ions absorbed by plant roots, glucose is converted first to amino acids then to protein. The carbon dioxide can be used again in photosynthesis or may diffuse out of the leaf via the stomata respiration ATP

4 Factors necessary for photosynthesis Factors affecting the rate of photosynthesis light intensity The main external factors affecting the rate of photosynthesis are: Rate of photosynthesis temperature (degrees C) Heat energy increases kinetic energy. More collisions, with more force, thus the rate increases Enzyme protein denatures. They lose their catalytic ability to catalyse photosynthesis Optimum Increasing light intensity increases the energy entering chlorophyll and thus the amount of ATP and produced to drive photosynthesis The effect of light intensity on photosynthetic rate The effect of temperature on photosynthetic rate The rate is limited by another factor such as carbon dioxide concentration Light intensity limiting. light wavelength light intensity temperature carbon dioxide Notice how increasing the light intensity beyond a certain point causes no further increase in rate of photosynthesis. Something else is now holding the reaction back. Light is no longer the limiting factor. Photosynthetic sugar production is catalysed by enzymes. If the temperature is raised too high the enzymes denature and photosynthesis stops.

5 Factors necessary for photosynthesis Limiting factors 25 O C and 0.04% CO 2 25 O C and 0.4% CO 2 15 O C and 0.04% CO 2 Rate of photosynthesis Light intensity Rate of photosynthesis temperature (degrees C) High light intensity Low light intensity The effect of temperature and light At low light intensities increasing the temperature has little effect on the rate of photosynthesis. At high light intensities the rate of photosynthesis increases much more rapidly over the same temperature range. This is an example of the law of limiting factors. THE LAW OF LIMITING FACTORS If a process is influenced by more than 1 factor, the rate will be limited by the factor nearest its lowest value Here is another example of the law of limiting factors What 3 factors are limiting in regions A, B, C respectively? ANSWERS: At B temperature limiting At A CO2 limiting A B C At C light limiting

6 Plant mineral requirements Plants require small quantities of minerals for healthy growth Minerals are absorbed by the root hairs, either by diffusion or active transport, depending on their concentration in the soil – see next topic. The most important minerals for plants are: Nitrogen Potassium Magnesium Iron Phosphorous usually as nitrate, nitrite or ammonium ions, NO 3 -, NO 2 -, NH 4 + often in the form of phosphate ions, PO 4 - ions. in the form of K + ions. in the form of Mg 2+ ions in the form of Fe 2+ ions

7 Mineral requirements of plants Nitrogen (nitrate ions: Needed to make proteins and chlorophyll Deficiency: Poor growth and leaf yellowing NO 3 - Potassium: Helps enzymes in photosynthesis and respiration Deficiency: Yellow leaves with dead spots K+K+ Phosphorous: Required for photosynthesis and respiration Deficiency: Poor root growth and purple younger leaves PO 4 - Iron is required by the enzymes that make chlorophyll Deficiency: Leaf yellowing Fe 2+ Magnesium is required as part of the chlorophyll molecule Deficiency: Yellowing of leaves and poor growth Mg + REMEMBER THESE ARE REQUIRED IN IONIC FORM!

8 The photosynthesis word equation. That light energy is absorbed by chlorophyll in chloroplasts and used to make sugar from carbon dioxide. Oxygen is a bye-product. The rate of photosynthesis may by limited by: low temperature, shortage of carbon dioxide, shortage of light. The glucose produced in photosynthesis may be converted to insoluble starch. Start does not attract water by osmosis. The energy from respiration is used to build smaller molecules into larger ones, including: sugars into starch, sugars into cellulose for cell walls, sugars, nitrates and other nutrients into amino acids and then proteins. Sugars into lipids for seed storage. For healthy growth plants need mineral ions including: nitrate for protein synthesis, phosphate and potassium for photosynthesis and respiration. Symptoms shown by mineral ion-deficient plants include: Any 1 of light, temperature and carbon dioxide will be limiting the rate of photosynthesis at any particular time. WHAT YOU SHOULD KNOW AT THE END OF THIS UNIT Plant cells use some of the photosynthetic glucose for respiration. In addition, nitrates, absorbed by the roots, are needed for healthy growth. Stunted growth and yellow older leaves if nitrate ions are deficient Poor root growth and purple younger leaves if phosphate ions are deficient Yellow leaves with dead spots if potassium ions are deficient.

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