Presentation on theme: "Photosynthesis. Energy is the ability to do work Living things depend on energy. Organisms that make their own food = autotrophs Plants and some other."— Presentation transcript:
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 Adenosine triphosphate (ATP) – chemical compound used to store and release energy
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
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
Releasing energy The energy stored in ATP is used by breaking the chemical bonds between the second and third phosphate groups.
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
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)
Investigating Photosynthesis Where does the mass of a tree come from? Trees start as seedlings and grow into trees – Metasequoia (Dawn Redwood)
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-”?
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
Jan Ingenhousz’ Experiment 1779 – Ingenhousz, Dutch scientist Found that plants only produce oxygen when exposed to light Concludes plants need sunlight to produce oxygen
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 6CO 2 + H 2 O + Light C 6 H 12 O 6 + O 2
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.
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.
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.
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.
Inside a Chloroplast Photosynthesis takes place inside chloroplasts Contain saclike photosynthetic membranes called thylakoids. Thylakoids are arranged in stacks called grana.
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
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.
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
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
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 O 2 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
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
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
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.
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