8.3 Process of Photosynthesis

8.3 Process of Photosynthesis

Key Idea: What happens during light-dependent reactions?

Light-Dependent Reaction

Photosystem II (PS2)

Light energy absorbed by PS2 produces high-energy electrons

Water molecules are split to replace those electrons, releasing H⁺ ions and oxygen

Light-Dependent Reaction

Electron Transport Chain

High-energy electrons move down the electron transport chain, to photosystem I

Energy generated is use to pump H⁺ ions across the thylakoid membrane and into the thylakoid space​

Light-Dependent Reaction

Photosystem I (PS1)

Electrons are reenergized in PS1

A second electron transport chain then transfers these electrons to NADP⁺, producing NADPH​

Light-Dependent Reaction

Hydrogen Ion Movement and ATP Formation

As the thylakoid space fills up with H⁺ ions, the thylakoid membrane becomes positively charged

H⁺ ions pass back across the thylakoid membrane through ATP synthase

As ions pass through, the ATP synthase molecule rotates and the energy produced is used to convert ADP to ATP​

Summary of light-dependent reaction

Light, water, ADP+P, and NADP⁺ are turned into oxygen, ATP, and NADPH

Multiple Choice

Which of these is not a product of light-dependent reactions?

• Oxygen

• ATP

• NADPH

• Water

Key Idea: What happens during light-independent reactions?

Light-Independent Reactions

Calvin Cycle - Part 1

Six CO₂ molecules from the atmosphere are combined with six 5-carbon molecules to produce twelve 3-carbon compounds​

Light-Independent Reactions

Calvin Cycle - Part 2

Energy from ATP and NADPH are used to convert the 3-carbon molecules to higher-energy forms

Two of the 3-carbon molecules are removed from the cycle to prodcuce sugar​, lipids, amino acids, and other compounds

The rest of the 3-carbon molecules are converted back to 5-carbon forms which then start the cycle over again​

Multiple Choice

The light-independent reactions of photosynthesis are also known as the

• Calvin cycle

• sugar cycle

• carbon cycle

• ATP cycle

Key Idea: What factors affect photosynthesis?

Factors affecting photosynthesis

Temperature, Light, and Water

Photosynthesis uses enzymes that function best between 0^oC and 35^oC

More intense light increases rate of photosynthesis up to a certain point

​Shortage of water can slow/stop photosynthesis

Open Ended

Of the three factors that affect photosynthesis, which is the MOST IMPORTANT for photosynthesis?