Chapter 6 Photosynthesis Section 6.1

Energy Processes for Life Autotrophs manufacture their own food from inorganic substances Autotrophs manufacture their own food from inorganic substances Use photosynthesis to convert light energy from the sun into chemical energy Use photosynthesis to convert light energy from the sun into chemical energy

Heterotrophs cannot manufacture their own food Heterotrophs cannot manufacture their own food Must obtain food by eating autotrophs or other heterotrophs Must obtain food by eating autotrophs or other heterotrophs

Photosynthesis Involves a complex series of chemical reactions in which the product of one reaction is consumed in the next reaction Involves a complex series of chemical reactions in which the product of one reaction is consumed in the next reaction Biochemical pathway Biochemical pathway

6CO 2 + 6H 2 O + solar energy  C 6 H 12 O 6 + 6O 2 Solar energy drives a series of chemical reactions that require carbon dioxide and water

Light Absorption in Chloroplasts Light reactions- the initial reactions in photosynthesis Light reactions- the initial reactions in photosynthesis Begin with the absorption of light in chloroplasts Begin with the absorption of light in chloroplasts

Chloroplasts Each chloroplast is surrounded by a pair of membranes Each chloroplast is surrounded by a pair of membranes Inside the membranes are stacks of thylakoids Inside the membranes are stacks of thylakoids The stacks are called grana The stacks are called grana The fluid surrounding the grana is called stroma The fluid surrounding the grana is called stroma

Light and Pigments Visible spectrum- white light can be separated into an array of colors when passed through a prism Visible spectrum- white light can be separated into an array of colors when passed through a prism ROY G. BIV ROY G. BIV

Light Light travels in waves Light travels in waves The distance from the crest of one wave to the crest of another wave is called a wavelength The distance from the crest of one wave to the crest of another wave is called a wavelength

Chloroplast Pigments Pigments- compounds that absorb light Pigments- compounds that absorb light Chlorophyll a – absorbs more red light Chlorophyll a – absorbs more red light Chlorophyll b – absorbs more blue light Chlorophyll b – absorbs more blue light Carotenoids – absorbs more green light Carotenoids – absorbs more green light

Only chlorophyll a is directly involved in the light reactions of photosynthesis Only chlorophyll a is directly involved in the light reactions of photosynthesis Chlorophyll b assists chlorophyll a in capturing light energy (accessory pigment) Chlorophyll b assists chlorophyll a in capturing light energy (accessory pigment)

In the leaves of a plant, chlorophylls are abundant In the leaves of a plant, chlorophylls are abundant In Fall, plants lose their chlorophylls and their leaves take on the color of the carotenoids In Fall, plants lose their chlorophylls and their leaves take on the color of the carotenoids

Electron Transport Each cluster of pigment molecules is a photosystem Each cluster of pigment molecules is a photosystem Two types of photosystems: photosystem I & photosystem II Two types of photosystems: photosystem I & photosystem II

Light Reactions 1. light energy excites electrons in chlorophyll a molecules of photosystem II 1. light energy excites electrons in chlorophyll a molecules of photosystem II 2. These electrons move to a primary electron acceptor 2. These electrons move to a primary electron acceptor 3. The electrons are then transferred along a series of molecules called an electron transport chain 3. The electrons are then transferred along a series of molecules called an electron transport chain

4. light excites electrons in chlorophyll a molecules of photosystem I. As these electrons move to another primary electron acceptor, they are replaced by electrons from photosystem II 4. light excites electrons in chlorophyll a molecules of photosystem I. As these electrons move to another primary electron acceptor, they are replaced by electrons from photosystem II 5. The electrons from photosystem I are transferred along a second electron transport chain. At the end of this chain, they combine with NADP + and H + to make NADPH 5. The electrons from photosystem I are transferred along a second electron transport chain. At the end of this chain, they combine with NADP + and H + to make NADPH

Restoring Photosystem II Replacement electrons come from water molecules Replacement electrons come from water molecules An enzyme inside the thylakoid splits water molecules into protons, electrons, and oxygen An enzyme inside the thylakoid splits water molecules into protons, electrons, and oxygen 2H 2 O  4H + + 4e - + O 2 2H 2 O  4H + + 4e - + O 2

Chemiosmosis Synthesis of ATP Synthesis of ATP Depends on a concentration gradient of protons across a thylakoid membrane Depends on a concentration gradient of protons across a thylakoid membrane The concentration of protons is higher inside the thylakoid The concentration of protons is higher inside the thylakoid

ATP synthase makes ATP by adding a phosphate group to ADP ATP synthase makes ATP by adding a phosphate group to ADP ATP synthase functions as a carrier protein ATP synthase functions as a carrier protein