Photosynthesis

Capturing the Energy in Light  Photosyntheis- process by which energy from the sun is converted to organic molecules  Plants, algae, and some bacteria are photosynthetic  Autotrophs- make own food  Heterotrophs- consume food from outside sources

Photosynthesis  Biochemical pathway- series of chemical reactions in an organism  6CO 2 + 6H 2 O + light  C 6 H 12 O 2 + 6O 2  Pathway opposite to photosynthesis is cellular respiration (organic molecules broken down)  Together photosynthesis and cellular respiration form a cycle

Chloroplasts  Site of first part of photosynthesis, light reactions  Organelle with pigments to collect light, located on thylakoid (disks) membrane  Surrounded by two membranes  Contains stacks of disks called called grana  The area between the grana is called the stroma

Light  Light looks white but contains many colors, called the spectrum  Light travels as waves  Different wavelengths are different colors and can be absorbed by different pigments  Most common in chloroplasts are chlorophylls, particularly chlorophyll a and chlorophyll b  Chlorophylls reflect green light, that is why plants look green

Pigments  Chlorophyll a directly involved in photosynthesis  Accessory pigments- Help chlorophyll a capture light  chlorophyll b  carotenoids

Photosynthesis  Two Steps  Light-Dependent (Light) Reactions  In Thylakoid  Electron Transport Chain  Light-Independent Reactions  In Stroma  Calvin Cycle

Electron Transport Intro.  Part of Light Reactions  Clusters of pigments are called photosystems, chloroplasts use photosystem I and photosytem II  First pigments absorb light  Light is passed on until it reaches chlorophyll a, then electron transport occurs

Electron Transport  Light energy forces electrons to go to a higher energy state  Electrons leave chlorophyll a and go to a primary electron acceptor  Primary electron acceptor donates electrons to first molecule of electron transport chain  As electrons move along the chain they lose their energy  Energy from photosystem II used to move protons across the membrane  Energy from photosystem I used to combine electrons, protons and NADP+ to form NADPH  Water broken down to replace electrons

Chemiosmosis  Process used to make ATP  Uses protons from the breakdown of water to create a concentration gradient  Power of concentration gradient used by ATP Synthase to make more ATP