Bio Chapter 8

Photosynthesis

Photosynthesis

The process of using light energy to make glucose from carbon dioxide and water

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂        

 delta G = +686 kcal/mol

Photosynthesis chemical equation

What is the purpose of photosynthesis?

to produce glucose to be used for anaerobic cellular respiration

Where does photosynthesis occur?

The chloroplasts

Stomata

sites of gas exchange

Mesophyll

contain chloroplasts 

Thylakoid

flattened sac inside chloroplasts that contain chlorophyll in its membrane

Granum

stacks of thylakoids

Stroma

fluid in the chloroplast

Pigment molecules

molecules that absorb light energy

How is light energy absorbed?

By boosting electrons to a higher energy level

Two stages of photosynthesis

light reactions, Calvin cycle

6CO₂ + 6H₂O + sunlight —> C₆H₁₂O₆ + 6O₂

photosynthesis formula

What type of reaction is photosnythesis?

Endergonic

carotenoids

accessory pigments that work in conjunction with chloroplasts

Where to light reactions occur?

the thylakoid membrane

What do light reactions produce?

ATP, NADPH and O2

Where does the Calvin cycle take place?

stroma

What does the Calvin cycle do?

It uses ATP, NADPH and CO2 to produce glucose

What happens in photosystem II? (4 steps)

Pigement molecules absorb energy from sunlight, Water is split into 2H and ½ O2, light energy excites an electron to a higher energy level, the electron is passed down an electron transport chain to photosystem I

What happens in Photosystem I? (4 steps)

Pigment molecules absorb energy from sunlight, the light energy excites an electron to a higher energy level, the electron is passed down a 2nd electron transport chain, the energy released is used by NADP to reduce it to NADPH

What does the Calvin Cycle produce

glucose

What is Carbon Fixation?

What is the purpose of PS I?

to generate ATP for the Calvin Cycle

Phases of the Calvin Cycle

Carbon Fixation, Reduction and Sugar Production, Regeneration of RuBP

What happens in Phase 1: Carbon Fixation?

The enzyme Rubisco attaches CO2 to the molecule RuBP

What happens in Phase 2: Reduction and Sugar Production?

3-PGA is reduced to G3P, ATP is used as a source of energy, and NADPH donates high energy electrons

What happens in Phase 3: Regeneration of RuBP?

Some G3P makes glucose and the rest is recycled to regenerate the RuBP acceptor. Requires 18 ATP and 12 NADPH

What is RuBP

an enzyme

Inputs and outputs of the Calvin Cycle

CO2 to glucose, 12 NADPH to 12 NADP, 18ATP

What is photorespiration?

when the enzyme Rubisco fixes O2 instead of CO2 and adds O2 to RuBP instead of CO2.

When does photorespiration occur and why?

In hot and dry conditions since it closes the stomata and therefore reduces water loss

What is a C3 plant? (90% of plants)

plants fix CO2 into a 3-carbon molecule and do not separate carbon fixation from the Calvin Cycle

What is a C4 plant? Examples

plants fix CO2 into a 4-carbon molecule and separates carbon fixation from the Calvin Cycle. Corn, Sugarcane