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Photosynthesis

Photosynthesis. Energy is the ability to do work. Living things depend on energy. Organisms that make their own food = autotrophs Plants and some other organisms are able to use light energy from the sun to make food Organisms that cannot make their own food = heterotrophs. Chemical Energy.

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Photosynthesis

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  1. Photosynthesis

  2. Energy is the ability to do work • Living things depend on energy. • Organisms that make their own food = autotrophs • Plants and some other organisms are able to use light energy from the sun to make food • Organisms that cannot make their own food = heterotrophs

  3. Chemical Energy • Adenosine triphosphate (ATP) – chemical compound used to store and release energy

  4. ATP • ATP consists of adenine (A), ribose (a 5-carbon sugar, remember RNA?), and three phosphate groups. • The 3 phosphate groups hold high energy bonds

  5. ADP • ADP is adenosine diphosphate– meaning it has two phosphate groups instead of three • Cells can add a phosphate group to ADP to make ATP to store energy. • ATP is like a full battery. ADP is like a battery that needs recharging

  6. Releasing energy • The energy stored in ATP is used by breaking the chemical bonds between the second and third phosphate groups.

  7. Why ATP is important • Powers cell membrane sodium-potassium pump – vital for nervous system connections • Powers movement of organelles • Powers synthesis of proteins and nucleic acids • Powers responses to chemical signals • Firefly light (chemical = luciferin) is powered by ATP in a process called bioluminescence

  8. Firefly luciferin

  9. Photosynthesis Photosynthesis – plants use the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates (sugar and starch) and oxygen (as waste)

  10. Investigating Photosynthesis • Where does the mass of a tree come from? • Trees start as seedlings and grow into trees • Metasequoia (Dawn Redwood)

  11. Jan van Helmont’s Experiment • 1643 – Belgian physician – “Where does mass of tree come from?” • Watered plant for five years • Seedling grew into tree – over 75 kg (~200 lb) • Mass of soil didn’t change over five years • Concluded mass was from water • Water = “hydrate” part of carbohydrate, what about “carbo-”?

  12. Joseph Priestley’s Experiment • 1771 – Joseph Priestley, English minister • Lit candle, placed jar over candle, watched candle go out. • Concluded oxygen was needed for fire • Placed sprig of mint plant in jar • After a few days, the candle could be relighted and would stay lit for a while • Concluded plants produce oxygen

  13. Jan Ingenhousz’ Experiment • 1779 – Ingenhousz, Dutch scientist • Found that plants only produce oxygen when exposed to light • Concludes plants need sunlight to produce oxygen

  14. The Photosynthesis Equation • Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen Carbon dioxide + Water + Light  Sugar + Oxygen 6CO2 + H2O + Light  C6H12O6 + O2

  15. Light and Pigments • In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, which is a molecule in chloroplasts, an organelle in plant cells.

  16. Light and Pigments • Energy from the sun travels to Earth in the form of light. • Light is of various wavelengths. • Your eyes see the wavelengths as different colors.

  17. Light and Pigments • Plants gather the sun’s energy with light absorbing molecules called pigments. • Main pigment is chlorophyll – two types chlorophyll a and chlorophyll b.

  18. Light and Pigments • Chlorophyll readily absorbs light in the red and blue-violet regions of the spectrum. • Chlorophyll does not absorb light well in the green region – thus the leaves of plants appear green. • Because light is energy, the plants are absorbing the energy from that light.

  19. Inside a Chloroplast • Photosynthesis takes place inside chloroplasts • Contain saclike photosynthetic membranes called thylakoids. • Thylakoids are arranged in stacks called grana.

  20. Inside a Chloroplast • Chlorophyll and other pigments in the thylakoid membrane are organized into photosystems. • The region outside the thylakoid membrane is called the stroma. • Two reactions in photosynthesis: • Light-dependent: inside thylakoid membrane • Calvin cycle (Light-independent/dark): in stroma

  21. Chloroplast

  22. Electron Carriers • When sunlight strikes a leaf, it ‘excites’ electrons, meaning that they gain energy. • Plant cells use electron-carriers to move these high energy electrons (think of hot coals) – process called electron transport.

  23. Electron Carriers • NADP+ (Nicotinamide adenine dinucleotide phosphate) is an electron carrier. • NADP+ accepts and holds 2 high-energy electrons along with a hydrogen ion (H+) • When it is holding these, it is converted to NADPH. Now it can carry these electrons to chemical reactions elsewhere in cell

  24. Light-Dependent Reactions • Light-dependent reactions require light. • This is why plants need light to grow. • The light-dependent reactions of plant cells produce oxygen as a gas and convert ADP and NADP+ into the energy carriers ATP and NADPH

  25. Light-Dependent Reactions • Step 1: Pigments in photosystem II (discovered second, hence name) absorb light • High energy electrons passed on to electron transport chain (ETC) • Thylakoids break up water molecules to use 2 H+ ions and oxygen is released – source of O2 we breathe • Step 2: Electrons move through ETC from photosystem II to photosystem I • H+ ions moved from stroma to inner thylakoid • Step 3: Pigments in photosystem I use energy from light to energize electrons. NADP+ picks these up and H+ ions to become NAPH

  26. Light-Dependent Reactions (Cont.) • Step 4: As electron pass from chlorophyll to NAP+, H+ ions are pumped across membrane, providing energy to make ATP. • Step 5: An enzyme, ATP Synthase, helps H+ ions cross the membrane • ATP Synthase binds ADP and a phosphate group to produce ATP

  27. Confused yet?

  28. The Calvin Cycle (Light-Independent Reactions) • The ATP and NADPH formed by the light-dependent reactions have chemical energy but not enough to sustain plant. • During the Calvin Cycle, plants use that energy to make energy that can be stored = high-energy sugars

  29. Calvin Cycle (Light-Independent Reactions) • Step 1: 6 Carbon dioxide molecules enter cycle from atmosphere. Combine with six 5-carbon molecules = 12 3-carbon molecules • Step 2: 12 3-carbon molecules converted into high-energy forms. Energy to do this comes from ATP and NAPH produced earlier • Step 3: Two 3-carbon molecules removed from cycles to produce sugars for metabolism and growth in the form of sugars, lipids, and proteins. • Step 4: Remaining carbon molecules are recycled for later Calvin Cycles.

  30. Factors affecting Photosynthesis • Water • Plant adaptation – plants in dry conditions have a waxy coating on leaves to prevent water loss • Temperature • Intensity of Light • Maximum rate • Conifers in Winter may only occasionally carry out photosynthesis

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