Photosynthesis is the Source of Your Energy Photosynthesis is the source of energy for

biological activity in almost all organisms on earth!! (producers and consumers alike)

Sunlight energy is absorbed by chlorophyll – found in chloroplasts

Plants also take in carbon dioxide from the air and water molecules from the soil

Light energy, CO2, and H2O are the raw materials used to make sugars.

Water molecules are split into hydrogen and oxygen.

The hydrogen is combined with the CO2 to make sugars.

The oxygen is released into the air as oxygen gas.

The process of photosynthesis can be

summarized by the following equation:

Light energy + 6 CO2 + 6 H2O→ C6H12O6 + 6 O2

carbon + water → Glucose + Oxygen

dioxide

Remember, photosynthesis is a process, catalyzed by many enzymes

Electrons can be removed from atoms and change energy levels when energy added (like energy from sun) Reduction = gaining electrons (gaining

energy) Oxidation = losing electrons (losing energy)

Redox reactions are used to capture and transfer energy in living systems

The electron transport system (ETS), located in the membranes of chloroplasts, uses redox reactions to transfer energized electrons to make ATP.

An electron transport system (ETS) generates energy to make ATP. High-energy electrons,

such as those made when light strikes a chlorophyll molecule, are passed from one carrier molecule to another along a chain, like a hot potato.

Every time the electron is passed, some of its energy is released and can be used to build an ATP.

These are redox reactions.

http://student.ccbcmd.edu/~gkaiser/biotutorials/energy/ets.html

Coenzymes help enzymes complete their reactions. Accept or give up electrons in redox reactions. They act as

electron shuttles Important coenzymes in photosynthesis are:

NADH and NADPH FADH

Coenzymes are derived from vitamins like niacin, riboflavin (B2)

Review Chapter 5.3

NADH

NADPH

FADH

Photosynthesis takes place in chloroplasts, organelles with a double membrane subdivided into two regions Thylakoids -

contain chlorophyll Grana - stacks of

thylakoids Stroma - Fluid-filled

space between thylakoids

Overview: http://www.phschool.com/science/biology_place/biocoach/photosynth/calvin1.html

There are 3 basic steps in the process of photosynthesis: Light-capturing events – thylakoid

membrane Light-dependent reactions Light-independent reactions

Photosynthesis uses the energy from visible light

Chlorophyll absorbs red, blue and violet light and reflects green.

In the thylakoids, light energy is absorbed by chlorophyll, producing excited electrons. Chlorophylls arranged into clusters in

thylakoid membranes to most efficiently excite and transfer electrons. Called Photosystems I and II

There are 3 basic steps in the process of photosynthesis: Light-capturing events – thylakoid membrane Light-dependent reactions – inside

thylakoid Light-independent reactions

Excited electrons are used to produce ATP and to split water molecules. Some electrons enter electron transport

system and produce ATP. Other electrons split water into hydrogen

and oxygen. Oxygen is released Hydrogen (and its electrons) are used to make

the coenzyme NADPH.

“Light reactions” yield - ATP- NADPH (reduced coenzyme)- O2

Light reactions worksheet

There are 3 basic steps in the process of photosynthesis: Light-capturing events – thylakoid membrane Light-dependent reactions – inside thylakoid Light-independent reactions – in the

stroma Also called “dark reactions,” since light is not

needed for them to take place.

ATP and NADPH from light reactions enter stroma and are used to assemble CO2 molecules (from the atmosphere) into sugars

There are many reactions in the process, called the Calvin Cycle, each catalyzed by an enzyme.

ADP and NADP+ are recycled to light-dependent reactions.

“Dark reactions” yield:- PGAL (3 carbon sugar)- H2O

Dark reactions worksheet

The products of photosynthesis (simple sugars) can be used for: Making ATP via cellular respiration Biosynthesis of amino acids, lipids, nucleic

acids Making other sugars or starch for storage or

plant growth

Animation: http://www.cix.co.uk/~argus/Dreambio/photosynthesis/photosynthesis%201.htm

Special adaptations In hot/dry conditions, plants close stomates to

conserve water. No more CO2 enters cells, no more O2 exits Photosynthesis shuts down, sugar production

decreases Bad for the plant, bad for us if these are food

crops Called C3 plants because the first product made

from “fixed” CO2 is the 3 carbon compound PGAL Includes plants like soybeans, wheat and rice

C4/CAM plants – sugarcane, corn, desert plants like cacti Stomates often closed during day to prevent

water loss Light-capturing, light-dependent reactions

continue as usual Carbon fixation and Calvin cycle separated

CO2 fixed onto a 4 Carbon compound during night (when stomates open)

CO2 released to Calvin cycle during day (when energy from light-dependent reactions available)

End of photosynthesis

Autotrophs manufacture their own organic molecules (like glucose), but they must also perform cellular respiration to obtain energy from food molecules.

Plants do both photosynthesis and cellular respiration.