Content 14 Photosynthesis

Most common pigment in thylakoids is chlorophyll a which appears green in color.  Looking at the light spectrum above, select the color chlorophyll a will ABSORB to carry out photosynthesis.(options: Red, Yellow, orange, green, purple, blue)

Red, Yellow, orange, purple, blue

The apple shown in the diagram above is red in color.  What wavelength lights (in nm) is REFLECTED off the apple?

650-700 nm

Light dependent reaction

• Purpose: Convert solar energy into chemical energy.

• Location: Thylakoid membrane

• Inputs: Light, water (H₂O), NADP⁺, and ADP.

• Outputs: Oxygen (O₂), ATP, and NADPH.

• Key events:  Light energy excites electrons in chlorophyll. These high-energy electrons are transferred to the electron transport chain.  Electrons in chlorophyll are replenished by splitting of water.  The energy is used to produce ATP and NADPH, which store energy for the next stage.

light independent reaction (dark reaction, calvin cycle)

• Purpose: Use chemical energy (ATP and NADPH) to fix carbon and synthesize glucose.

• Location: Stroma of chloroplast.

• Inputs: Carbon dioxide (CO₂), ATP, and NADPH.

• Outputs: Glucose (or other sugars), NADP⁺, and ADP.

• Key events: CO₂ is fixed into organic molecules using the energy from ATP and electrons from NADPH, forming glucose precursors.

Summary

• Light Reactions (in thylakoids):
  Use sunlight and water to produce ATP, NADPH, and release O₂ through an electron transport chain.

• Dark Reactions / Calvin Cycle (in stroma):
  Use ATP, NADPH, and CO₂ to produce glucose and regenerate energy carriers (ADP, NADP⁺).

• Overall:
  Converts light energy into chemical energy stored in sugars, supporting plant growth and oxygen production.

a) The light reactions of photosynthesis occur in the_______ of the chloroplast

thylakoid membranes

The main pigments involved in capturing light energy are called ______, which appears in clusters called _________.

chlorophylls and photosystems

c) The process of transferring excited electrons through the thylakoid membrane is known as the

electron transport chain

d) As electrons are being passed through the electron transport chain, protons (H+ ions) are pumped into

thylakoid space

e) During the light reactions, _____ molecules are split, releasing electrons, to replenish _____ in the chlorophylls of photosystem II. This process also releases _____ and H+ ions as byproducts.

water, lost electrons, and oxygen

f) The electrons are eventually passed on to convert the energy carrier NADP+ to ______ which will be used in the Calvin Cycle to make sugar molecules.

NADPH

g) Protons flow back out to stroma from thylakoid space through _______, allowing it to make ATP, which will be used in the Calvin Cycle to make sugar molecules.

ATP Synthase

What enzyme incorporates carbon from CO₂ into molecules of the Calvin Cycle?

Rubisco

What “products” of light reaction are used to fuel the Calvin Cycle?

NADPH and ATP

Carbon from CO₂ is eventually incorporated into sugar molecules by Calvin Cycle. True or False?

true