Chapter 8 - Photosynthesis

8.1 – Energy and Life

All activities performed by a cell require energy (the ability to do work)

Cells must obtain and use energy

ATP

Most energy in a cell is stored and released by adenosine triphosphate (ATP)

Structure

Adenine molecule, ribose (sugar) molecule, and three phosphate groups

Energy is stored and released from the phosphate group bonds

ATP does not store

energy when it is in

the form of ADP

(only 2 phosphates)

ATP stores energy when

it has all three phosphates.

It’s like a fully charged

battery.

Energy is stored when a phosphate group is added to adenosine diphosphate (ADP)

ADP + p + energy ATP

Energy is released when a phosphate group is removed

ATP ADP + p + energy

Energy can be continuously added and released this way

Used to power many functions in cell

Active transport

Movement (muscle cells)

Chemical reactions

ATP does not store energy for long periods of time

Molecules such as sugar (glucose) are produced to store energy

Stored energy is used to produce ATP when needed

How organisms obtain energy

Heterotrophs – organisms that obtain food by eating other organisms (animals, fungi)

Autotrophs – organisms that can make their own food (plants, algae)

Photosynthesis – sunlight energy is used to produce glucose (sugar)

Energy in sunlight is converted into chemical energy

Chemosynthesis – inorganic chemicals are used to produce food

Chapter 8 - Photosynthesis

8.2 – Photosynthesis: An Overview

Light and pigments

Different colors of sunlight (energy) travel at specific wavelengths of light

Pigments – molecules that absorb specific colors of light

Chlorophyll – absorbs all light except green, which is reflected (so, plants appear green)

Carotenoids (Carotene) - an accessory pigment in plants that absorbs all light except for red, orange, or yellow (usually seen in Autumn leaves)

The Chloroplast

Structure

Grana - Stacks of membrane sacks (singular = Granum)

Thylakoid – the membrane sacks of grana

Chlorophyll is located on membrane of thylakoid, where light absorption occurs

Stroma – Internal space surrounding grana

Structure of the chloroplast

Functions of photosynthetic

structures

Chapter 8 - Photosynthesis

8.3 – Photosynthesis

The Process

2 Steps:

1. Light-dependent reactions – uses sunlight to produce two energy carriers: NADPH and ATP

2. Light-independent reactions – uses carbon dioxide (CO2) to produce glucose, using energy from NADPH and ATP (from

step 1)

1. Light-dependent Reactions

Requires sunlight to work

Occurs on the membrane of the thylakoid in the chloroplast

Clusters of chlorophyll, called photosystems, absorb sunlight and excite electrons

Electrons were provided when H2O was broken down to form O2, which is then released as a waste

Electrons are passed along a chain of molecules

Energy from this is used to produce 2 molecules:

NADPH is made from NADP+

ATP is made from ADP

2. Light-independent reactions

Occurs in the stroma (open space) of the chloroplast

Does not require sunlight

Also called the Calvin Cycle

Continuous chain of chemical reactions in

which energy is used to convert CO2 into glucose

CO2 enters cycle and is combined with a 5-carbon sugar

Molecules are then rearranged using energy from the NADPH and ATP made during the light-dependent reactions

By the end of the cycle, some carbon molecules are used to make glucose, while the rest continue the Calvin cycle

Overall Reaction: (you must know this equation!)

(sunlight)

6 CO2 + 6 H2O ----> C6H12O6 + 6 O2

Light-Dependent Reactions:

http://www.youtube.com/watch?v=hj_WKgnL6MI

8.3 Worksheet Light-Dependent Reactions

Summary

Photosystem II PSII absorbs light, which increases electron energy. Electrons are passed to the Electron Transport Chain. Water is broken down to replace the lost electrons. H+ and O2

Electron Transport Chain

Energy from electrons is used by proteins in ETC to pump H+ ions from the stroma into the thylakoid space. Electrons are passed to PSI.

Photosystem I Energy in electrons declined, so light is absorbed again to reenergize electrons. Electrons are passed down another ETC, where NADP+ picks up the electrons and H+ ions to become NADPH.

Hydrogen Ion Movement and ATP Formation

H+ ions were building up in thylakoid space. Concentration (charge gradient) causes H+ ions to diffuse out of thylakoid through ATP synthase, which generates production of ATP.

How does ATP synthase produce ATP?

H+ ions pass though the enzyme, causing ATP synthase to rotate. This produces the energy needed to bind ADP to a phosphate group, to produce ATP.

When sunlight excites electrons in chlorophyll, how do the electrons change?

The electrons take on a great deal of energy, which causes them to move to a higher energy level.

What does the Calvin cycle use to produce sugars?

They use CO2 and energy from ATP and NADPH from the light-dependent reactions to make sugar.