Photosynthesis Biology 2 D. Mitchell

All life requires energy. 2/25/2019 All life requires energy. Almost all energy for life is derived from the sun. Energy from the sun enters living systems when autotrophs absorb sunlight. .

Autotrophs (producers)-Organisms that can make their own food Autotrophs (producers)-Organisms that can make their own food. Examples – 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.

Photosynthesis Process by which plants, algae and some bacteria use light energy to make organic compounds (sugar-glucose).

EQUATION FOR PHOTOSYNTHESIS Light ENERGY 6CO2 + 6H2O C6H12O6 + 6O2 CARBON DIOXIDE WATER GLUCOSE OXYGEN Gas 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.

2/25/2019 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.

Thylakoids: disc-shaped stacks (granum) inside the chloroplast. Parts of the chloroplast: Thylakoids: disc-shaped stacks (granum) inside the chloroplast. Stroma: dark fluid that surrounds the grana inside the chloroplast

Chloroplast Thylakoid membrane Stroma (fluid)

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 phases Light 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.

Summary of Light Dependent Sunlight enters the chloroplast when pigments in the thylakoids absorb the light. Some excited electrons are released. Water molecules are split into H+ and Oxygen gas (O2) .

Summary of Light Dependent Some excited electrons pass to the Electron Transport Chain and travel across the thylakoid membranes. Energy provided in the ETCs is used to make ATP.

Some excited electrons travel down another electron transport chain. Energy is used to make NADPH

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), H+, 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

the most common method of carbon-dioxide fixation Calvin Benson Cycle the most common method of carbon-dioxide fixation function -to produce a single molecule of glucose (C6H12O6)

3 phases: Carbon Fixation Reduction Regeneration of RuBP

Summary of Light Independent Reactions Using ATP and NADPH from the light dependent reactions, Carbon dioxide (CO2) is used to make glucose (C6H12O6).

Environmental factors that affect photosynthesis are: Light quality Light intensity Light availability Carbon dioxide availability Water availability