Photosynthesis Notes

Photosynthesis

Autotrophs vs. Heterotrophs

Autotroph

Make their own

food

Example: Plants

Heterotroph

Obtain energy from

foods they eat

Example: Animals,

fungi

Autotrophs

Photosynthesis occurs within:

Some bacteria

Algae

Within leaves of plants

does NOT happen in ALL cells

Chemical EnergyEnergy – the ability to do work

Adenosine Triphosphate (ATP)

Adenine

Ribose

3 phosphate groups

ADP + P

Adenosine diphosphate + phosphate

Chemical Energy =

Adenosine Triphosphate

(ATP)

PhotosynthesisThe process of creating sugar

from CO2.

Consumes H2O and is powered

by light.

Photosynthesis Equation

Light

CO2 + H2O C6H12O6 + O2

carbon dioxide + water sugars + oxygen

6 6 6

Electromagnetic Spectrum

Absorption of Light by

Chlorophyll a and Chlorophyll b

Light and PigmentPlants gather the Sun’s energy

with light absorbing molecules

called pigments

Chlorophyll (Green)

chlorophyll a and chlorophyll b

Chloroplast

Stroma - Liquid

Granum – stack

of thylakoids

Thylakoid – contains chlorophyll

Photo SynthesisLight To make or create

Photosynthesis Part I:

Light Dependent ReactionsLocation: Thylakoid Membrane

Light-Dependent Reactions

Light-Dependent ReactionsLocation: Thylakoid Membrane

1. Photosystem II

Light energy absorbed by electrons and increases their energy level

Enzymes break up water molecules into: 2 electrons

2 hydrogen ions

1 oxygen atom

2. Electron Transport Chain

High-energy electrons move

hydrogen ions from the stroma

into the inner thylakoid space

Light-Dependent ReactionsLocation: Thylakoid Membrane

3. Photosystem I

Uses energy from light to re-energize the electrons.

NADP+ picks up electron and 2 H+

ions

Produces NADPH

Light-Dependent ReactionsLocation: Thylakoid Membrane

4. Hydrogen Ion Movement

Hydrogen ions move

across the thylakoid

membrane making the

inside positively charged

Light-Dependent ReactionsLocation: Thylakoid Membrane

5. ATP Formation

Hydrogen ions pass through ATP

synthase (protein)

Energy is converted from ADP

to ATP

Light-Dependent ReactionsLocation: Moves from Thylakoid to Stroma

Photosynthesis Part II:

Light Independent Reactionsa.k.a. Calvin Cycle

Location: Stroma

Calvin Cycle

Uses CO2, ATP and

NADPH to produce

high energy sugars

Calvin CycleLocation: Stroma

1. Carbon Fixation

6 CO2 combines with a

five-carbon sugar

Enzyme breaks down to

12 three-carbon molecules

2. Energy Input

ATP is broken down giving each

three-carbon molecule a

phosphate

NADPH gives up electrons to

provide more energy

Calvin CycleLocation: Stroma

3. Sugar Production

2 three-carbon molecules exit

cycle to be used by the plant

10 three-carbon molecules are

recycled

Calvin CycleLocation: Stroma

4.5-Carbon Molecule Regeneration

10 three-carbon molecules are converted back into 6 5-carbon molecules to be used in the next cycle

6 ATP molecules are used to complete this process

Calvin CycleLocation: Stroma

Factors Affecting Photosynthesis

Water

Plants in dry conditions have a waxy coating on the leaves that reduce water loss

Temperature

Photosynthesis depend on enzymes that function best between 0oC and 35oC

Light Intensity

Increasing light intensity increases the rate of photosynthesis

However, a plant has a maximum rate of photosynthesis that can be reached