Chapter 10

Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen

6 CO H 2 O + (light)  C 6 H 12 O O 2 Use of inorganic compounds to make organic sugar and oxygen Tells you what you need, but doesn’t tell you what happens

Light and Pigment The equation tells you what is needed, BUT not what happens Photosynthesis requires light and a substance called chlorophyll Found in chloroplasts Makes plants look green

Inside a Chloroplast The organelle where photosynthesis takes place Thylakoid Saclike photosynthetic membranes Grana (Granum) Stacks of thylakoids Photosystems Clusters of pigment and protein that absorb light energy Stroma Area outside of the thylakoid in the chloroplast

Stomata Specialized openings for the entrance/exit of gases Formed by guard cells Respond to water pressure Open – high water pressure or turgor pressure Closed – low water pressure

Consists of two stages Light reactions Convert light energy to chemical energy Dark reactions No light required

Light reaction responsibilities: Water is split Light energy absorbed is transferred to an electron carrier NADP + NADPH Oxygen is given off as a byproduct ATP is generated by chemiosmosis NO SUGAR PRODUCTION!

Dark reaction responsibilities: Calvin Cycle Uses CO 2 from the air to make organic molecules Uses NADPH to produce sugars Uses ATP in the production of sugars

Light is a form of energy Travels in wavelengths Most concerned with the visible light spectrum The amount of energy in a wavelength is inversely proportional to the wavelength Shorter wavelength = more energy

Light is absorbed by pigments Pigments in plants are called chlorophylls and carotenoids Chlorphyll a – violet/blue and red light Chlorophyll b – slightly different wavelengths from a Carotenoids – blue and green (appear yellow and orange)

Sunlight causes electrons to move from the ground state to the excited state Energy can not disappear Excited state is very unstable

Made up of chlorophyll and inorganic molecules Reactive center surrounded by light harvesting units Reactive center has a pair of chlorophyll a molecules Light harvesting molecules has chlorophyll a, b, and carotenoids

1. Light hits a pigment in Photosystem II-electron excited 2. Energy is transferred to the chlorophyll a electrons and then to the primary electron acceptor 3. Water splits to give 2 electrons, 2 H +, and 1 O atom 4. Excited electrons pass from primary electron acceptor of PS II to PS I via electron transport chain (ETC) 5. Energy is released from electrons falling back to ground state- used to make ATP 6. Light energy also being absorbed by PS I just like PS II 7. Excited electrons from PS I now travel through a second ETC 8. Electrons are now transferred to NADP + (reduction) to make NADPH

Certain bacteria do not use PS II Electrons cycle back to the cytochrome complex of first ETC Does not produce NADPH production or O 2 release, but there is ATP production Ex. Purple sulfur bacteria

Mitochondria Generates ATP Uses H + gradient for potential energy High energy electrons come from breakdown of organic molecules Chemiosmosis is used to tranfer chemical energy from food ATP Chloroplasts Generates ATP Uses H + gradient for potential energy Electrons come from water and become energized by light Transform light energy into chemical energy in ATP

Anabolic cycle Builds sugars from smaller molecules Consumes energy 3 Steps Carbon fixation Reduction Regeneration of RuBP Two cycles will result in 12 G3P which will exit independently and become glucose

Plants may need to modify photosynthesis in times of low CO 2 Instead of CO 2 using the plant will use O 2 in the Calvin cyle The result is a 2 carbon molecule Leaves the chloroplast and peroxisomes/mitochondria rearrange the split Photorespiration

Plants consume about 50% of the sugars they make to perform daily activities Produces about 160 billion metric tons of carbohydrates per year There is no chemical process on earth that can match the output of photosynthesis