PhotosynthesisPhotosynthesis

Biology 2Biology 2D. MitchellD. Mitchell

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All life requires All life requires energyenergy Almost all energy for life is derived from the Almost all energy for life is derived from the

sun.sun. Energy from the sun enters living systems when Energy from the sun enters living systems when

plants, algae, and some bacteria absorb sunlight.plants, algae, and some bacteria absorb sunlight.

Organisms that can make their own food are called autotrophs (producers).

Examples – plants, algae, and some bacteriaExamples – plants, algae, and some bacteria

Heterotrophs (consumers)-must feed on autotrophs, one another, or organic wastes in order to obtain energy.-cannot make their own food.

Examples: other bacteria, many protists, fungi and animals.

PhotosynthesisPhotosynthesis Process by which plants, algae and some bacteria

use light energy to make organic compounds (sugar-glucose).

EQUATION FOREQUATION FOR PHOTOSYNTHESISPHOTOSYNTHESIS

6CO6CO22 + + 6H6H22OO

Light Light ENERGYENERGY

CC66HH1212OO66 ++ 6O6O22

CARBON CARBON DIOXIDEDIOXIDE WATERWATER GLUCOSEGLUCOSE OXYGEN OXYGEN

GasGas

Reactants Products

The equation is read six molecules of carbon dioxide is added to six molecules of water which yields one molecule of glucose and six

molecules of oxygen gas.

Photosynthesis takes place in the chloroplast of plants and the cytoplasm of bacteria.

•Chloroplasts are the specialized organelles in plants and some algae where photosynthesis occurs.

•Most chloroplasts are in leaf cells that are specialized for photosynthesis.

Parts of the chloroplast:Parts of the chloroplast:

1.1. Thylakoids: disc-shaped stacks Thylakoids: disc-shaped stacks (granum) inside the chloroplast.(granum) inside the chloroplast.

1.1. Stroma: dark fluid that Stroma: dark fluid that surrounds the grana inside the surrounds the grana inside the chloroplastchloroplast

Thylakoid membrane

Stroma (fluid)

Chloroplast

Pigments involved in Photosynthesis

The primary pigment - chlorophyll Plants contain two types of chlorophyll -

chlorophyll a and chlorophyll b

Each pigment absorbs certain wavelengths of light (red and blue) and reflects others (green and yellow).

Photosynthesis: The Process

•Occurs in 2 main phasesLight Dependent Reactions

•Photosystem II•Photosystem I

Light Independent (Calvin Cycle) Reactions

Light Dependent Reactions

•Occur in the thylakoids of the chloroplasts during times of light

•Purpose is to absorb sunlight and convert it to ATP that can be used in the Calvin cycle.

Light Dependent Reactions

•The pigments in the thylakoid space organize themselves into PHOTOSYSTEMS.

•Photosystems contain combinations of chlorophyll a and b, other pigments, and carotenoids that help pick up other wavelengths of light.

Photosystem II

•Photons split water molecules producing O2

•When chlorophyll is hit by light, the electron produced from the split is elevated to a higher energy level (it is "excited")

•The excited electron is then passed to a PRIMARY ELECTRON ACCEPTOR of the Electron Transport Chain as begins to travel down the ETC.

•Energy provided in the ETC is used to make ATP from ADP

Photosystem I

•Photons (again) boost electrons to a higher energy state

•Electrons travel down another electron transport chain,

•Energy is used to make NADPH from NADP.

Summary of Light Dependent

• Sunlight enters the chloroplast in the thylakoids. Pigments absorb the light energy and release excited electrons.

• Water molecules are split, ATP and NADPH are formed, and oxygen is released

And now what….

•The ATP and the NADPH of the light dependent reactions are used for the next main step, the Calvin cycle (Light independent reactions)

Light Independent Reactions

•USES Carbon dioxide (CO2) and the energy in ATP and NADPH

•CO2 is fixed/mixed with the Hydrogen ions to make glucose.

•Occurs in the stroma in the chloroplast

Calvin Benson Cycle

• the most common method of carbon-dioxide fixation

• function -to produce a single molecule of glucose (C6H12O6)

•3 phases:1.Carbon Fixation2.Reduction3.Regeneration of RuBP

Summary of Light Independent Reactions

Environmental factors that affect photosynthesis are:

•Light quality •Light intensity •Light Period •Carbon dioxide availability •Water availability