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  1. Photosynthesis

  2. Energy and Life • Energy is the ability to do work, and nearly everything you do requires energy, even while sleeping! • Chemical energy is the energy stored in chemical bonds, and energy can change form. • The most important chemicals to provide energy is ATP (adenosine triphosphate) • ATP is made up of an adenine, ribose and a phosphate group.

  3. Energy and Life cont. • Cells give off the energy stored in ATP by breaking its bonds. • ATP comes from food. • Heterotrophs must eat food to survive. • Autotrophs have the ability to make their own food. • They do this by the process of Photosynthesis.

  4. Photosynthesis: An Overview • For photosynthesis to take place autotrophs must capture light energy from the sun. • Energy from the sun travels in the form of light, which we see as white light, but this is actually a mixture of different wavelengths that span the colors of the rainbow. • Plants gather the suns energy with light absorbing molecules called pigments. • Chlorophyll is the most common, however it does not absorb green light it reflects it!

  5. Chloroplasts • Photosynthesis takes place inside the chloroplast. • These organelles hold many flat-bag shaped membranes called thylakoids, which are connected to one another and arranged in stacks. • These stacks are called grana. • Chlorophyll and other pigments are found there. • The liquid filled space around the thylakoids is known as the stroma.

  6. High Energy Electrons • Light is a form of energy, and anything that absorbs light takes in energy. • When chlorophyll takes in light, much of that energy is moved directly to its electrons. • This is what makes photosynthesis work. • Plants use NADP to carry the electrons changing it to NADPH and carries the electrons to other parts of the cell.

  7. Summary of Photosynthesis • In symbols • 6CO2 + 6H2O + Light = C6H12O6 + 6O2 • In words • Carbon dioxide + water + light = Glucose + Oxygen

  8. Light Dependent Reactions • The first set of reactions in photosynthesis are the light Dependent reactions. • The light Dependent reactions take place in the Thylakoids. • Here TP and NADPH is made, and Oxygen is released.

  9. Light Independent Reactions • In the light independent reactions plants use the ATP and NADPH made in the light dependent reactions to make high energy sugars. • During these reactions CO2 is taken from the air • These reactions take place in the stroma

  10. The Process of Photosynthesis • Remember there are two sets of reactions in Photosynthesis. • The light dependent reactions and the light independent reactions. • The LDR take place in the thylakoids, these baglike membranes hold groups of chlorophyll and proteins are known as photosystems. • Photosystems take in sunlight and use it to add energy to electrons. • There are 2 Photosystems.

  11. Photosystem 2 • The pigments of photosystem 2 absorb light energy and release high energy electrons. • These electrons get passed down the electron transport chain which is a group of carrier proteins • As light shines on the chlorophyll more and more electrons enter the electron transport chain. This happens when water molecules are broken down • This is when Oxygen is released.

  12. Photosystem 1 • The electrons lose energy when they are pumped across the membrane. • Photosystem 1 light gives them energy again. • Then they go through the electron transport chain and make NADP into NADPH which is used in the next set of reactions.

  13. SUMMARY of LDR • The light dependent reactions give off oxygen gas. • They also make ATP and NADPH. • These compounds are important for the cell. • They provide the energy needed to build sugars in the light independent reactions.

  14. Light Independent Reactions: Making Sugars • ATP and NADPH store energy but are not stable. • During the LIR also called the Calvin Cycle, plants produce high energy sugars • These sugars are stable and can store energy for a long time. • One of the reactants in the Calvin Cycle is Carbon Dioxide, which comes from the air. • An enzyme joins CO2 molecules that are already in the cell producing energy rich Carbohydrates.

  15. Sugar Production • With each turn of the cycle, a few carbohydrate molecules leave the cell which become the building blocks that plant cells use to make sugars, lipids, amino acids and other compounds. • The plant will use these compound to grow. • The rest of the high energy molecules stay in the cycle • Enzymes use ATP to change them to molecules that will join with the new CO2 Molecules and the cycle begins again.

  16. Summary of LIR • The Calvin cycle uses compounds made in the LDR and CO2 from the air to make sugars. • The plant uses the sugars to meet its energy needs and to build molecules needed for growth. • When you eat plants you get that energy stored in the plants. • The end results from the LDR and the LIR is the energy in sunlight is is changed to chemical energy to be used by the plant.

  17. Factors affecting Photosynthesis • Temperature: The higher the temperature the faster photosynthesis takes place. • Light: The more light or stronger the Light the faster the rate of Photosynthesis. • Water: The more water available the faster the rate of photosynthesis.

  18. Photosynthesis in Extreme conditions • Plants lose water in their leaves through tiny openings that let in CO2. • When it is hot these openings are closed to help retain water, but by doing this less CO2 enters • Some plants have very special adaptations to deal with extreme conditions

  19. C4 Plants • C4 plants have a special chemical pathway that gets carbon dioxide into the Calvin Cycle even when there is not a lot of CO2 Available. • This pathway uses extra ATP but allow plants to undergo photosynthesis when it is really Hot. • Corn and Sugar cane are examples of C4 Plants

  20. CAM Plants • CAM plants save water by taking air into their leaves only at night. • In the dark CO2 is used to make acids. • During the day these acids are turned back to CO2 for photosynthesis. • Some examples of CAM plants are Pineapple Trees, and most desert Cactus.