Photosynthesis

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8.2 Photosynthesis: An Overview
Lesson Objectives


Explain the role of light and pigments in photosynthesis.


Explain the role of electron carrier moleculesin photosynthesis.


State the overall equation for photosynthesis.
Lesson Summary
Chlorophyll and Chloroplasts In eukaryotes, photosynthesis occurs in organelles called chloroplasts.Chloroplasts house light-absorbing chemicals.


Light is a form of energy. Sunlight is a mixture of all the different colors of visible light.


Light-absorbing molecules called pigments capture thesun’s energy.


Chlorophyll is the principal pigment in photosynthetic organisms. Chlorophyll absorbs blue-violet and red light but reflects green light.


Chloroplasts have a complex internalstructure that includes:
· thylakoids: saclike photosynthetic membranes that contain chlorophyll and other pigments and are arranged in stacks called grana.
· stroma: the fluid portion outside of thethylakoids.

High-Energy Electrons The energy in light raises some of the electrons in chlorophyll to higher energy levels. These high-energy electrons are used in photosynthesis.


Electroncarriers are used to transport the electrons from chlorophyll to other molecules during photosynthesis.


NADP+ is a compound that can accept and hold 2 high-energy electrons and 1 hydrogen ion.This process converts NADP+ into NADPH.

An Overview of Photosynthesis Usually summarized by a simple chemical reaction, photosynthesis is a complex process that involves two interdependent sets ofreactions.


The light-dependent reactions require light, light-absorbing pigments, and water to form NADPH, ATP, and oxygen.


The light-independent reactions do not use light energy. They usecarbon dioxide from the atmosphere, NADPH, and ATP to make energy-rich carbon compounds.

Chlorophyll and Chloroplasts
For Questions 1–6, complete each statement by writing the correct word or...