Photosynthesis• Converts solar energy into the chemical energy of a carbohydrate in

this way:• Solar energy + carbon dioxide + water → carbohydrate + oxygen• Photosynthetic organisms include plants, algae, and certain bacteria.• These organisms are called producers; they synthesize organic

molecules from raw materials.

Photosynthetic Organisms

Nearly all life is dependent on solar energy because:

1) Photosynthetic organisms use solar energy to produce organic nutrients.

2) Almost all organisms depend either directly or indirectly on these organic nutrients to sustain themselves.

3) Photosynthetic organisms provide food for other organisms, known as consumers.

4) The bodies of plants became the coal or other fossil fuels used today.

Structure and Function of Chloroplasts• Chloroplasts are the organelles that carry on

photosynthesis.• Mesophyll cells in the middle of a leaf house chloroplasts• Mesophyll cells are protected from drying out by a waxy

cuticle.• Pores called stomata allow CO2 and O2 to enter the leaf.

Visible Light• Radiant energy from the sun (solar energy) can be described in

terms of its wavelength and its energy content.

• The colors in visible light range from violet (the shortest wavelength and highest energy) to blue, green, yellow, orange, and red (the longest wavelength and lowest energy).

• Pigments (chlorophylls and carotenoids) found within photosynthesizing cells, are capable of absorbing various portions of visible light.

• Both chlorophyll a and chlorophyll b absorb violet, blue, and red light best.

• Leaves appear green because green light is reflected and only minimally absorbed.

Visible Light & Plants

•It is an oxidation-reduction reaction, or redox reaction for short.•Oxidation is the loss of electrons; hydrogen atoms are removed from glucose.•Reduction is the gain of electrons; oxygen atoms gain electrons.•Remember OIL RIG (oxidation is loss, reduction is gain)

Photosynthetic Reactions

Overview of Photosynthesis

• A simplified overall equation for photosynthesis is:

• Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2

• During photosynthesis, water molecules are oxidized; they lose electrons (e-) along with hydrogen ions (H+).

• Also, CO2 is reduced and gains electrons given up by H2O.

• Electrons from H2O are energized by the sun.

Two Sets of Reactions

• Photosynthesis is divided into two sets of reactions, as implied by the term “photosynthesis”:

• “Photo” refers to the light-dependent (needs light) reactions that capture energy from the sun • Photosystem II• Photosystem I

• “Synthesis” refers to the light-independent (does not need light) reactions that produce carbohydrate.• Calvin Cycle

Light-Dependent Reactions • During the light-dependent reactions, light energy is absorbed by

chlorophyll molecules. ATP and NADPH is produced.

• Inside the chloroplast, water is split to produce oxygen, hydrogen ions, and electrons, the starting ingredients for photosynthesis

Photosystem II• The electrons are excited by incoming light energy (from the sun).

These excited electrons are passed through a series of electron carriers. Energy from these excited electrons is used to pump hydrogen ions through the chloroplast

• An enzyme (ATP Synthase) uses the energy from these moving ions to generate ATP.

Light-Dependent Reactions Photosystem I• Electrons are excited by incoming light energy (from the sun). These

excited electrons are passed through a series of different electron carriers (called Photosystem I).

• As electrons pass down this chain, they combine with the molecule NADP+ to form NADPH

Electron Transport System

Light-Independent Reactions

• The light-independent reactions do not need light and consist of the Calvin cycle.

• During the Calvin Cycle, Carbon Dioxide (CO2) is taken up by the plant (from the atmosphere)

• During the Calvin cycle, ATP and NADPH (made from the light dependant reactions) add phosphates and electrons to CO2, and convert it to glyceraldehyde 3- phosphate, or G3P

• G3P is a type of sugar which a plant can easily convert to glucose. This glucose can then be used as a source of stored energy for the plant

The Calvin Cycle

Overview of Photosynthesis