Photosynthesis

By: John McKenzie

Honors Biology

Photosynthesis

• The conversion of light energy to chemical energy that is stored in glucose or other organic compounds; occurs in plants, algae, and certain prokaryotes.

Overview

• To produce sugar, plants only need water, carbon dioxide and light energy. Photosynthesis takes place in the chloroplasts, specifically using chlorophyll, and processing oxygen through the stomates

• Photosynthesis takes place primarily in leaves, rarely in any other part of the plant. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, and the stomates

Definitions

• Autotrophs- self-feeders only in the sense that they sustain themselves without eating or decomposing other organisms

• Heterotrophs- unable to make their own food, they live on compounds produced by other organisms

• Chlorophyll- the green pigment located within the chloroplasts

• Mesophyll- the tissue in the interior of the leaf

• Stoma- a microscopic pore in a plant that allows oxygen to enter and exit

Photosynthesis in Nature

• Plants and other autotrophs are the producers of the biosphere

• Chloroplasts are the sites of photosynthesis in plants

The Pathways of Photosynthesis

• Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis: science as a process

• The light reactions and the Calvin cycle cooperate in converting light energy to the chemical energy of food: an overview

• The light reactions convert solar energy to the chemical energy of ATP and NADPH: a closer look

• The Calvin cycle uses ATP and NADPH to convert CO2 to sugar: a closer look

• Alternative mechanisms of carbon fixation have evolved in hot, arid climates

• Photosynthesis is the biosphere's metabolic foundation: a review

Chemical Reactions

• The overall chemical reaction involved in photosynthesis is:

6CO2 + 6H2O (+ light energy)

C6H12O6 + 6O2.

• This is the main source of the O2 (Oxygen)

we breathe

Chlorophyll

• There are two types of chlorophyll: chlorophyll a and chlorophyll b

• Chlorophyll a is the green pigment in the chloroplasts

• The only difference between the two is that chlorophyll b is slightly different in color due to the slight structural difference and amount of absorption

The Calvin Cycle

• During, the Calvin cycle, starting material is regenerated after molecules enter and leave the cycle

• In the Calvin cycle, carbon enters in the form of CO2, and

is respirated as sugar

• “The cycle spends ATP as an energy source and consumes NADPH

as reducing power for adding high-energy electrons to make the

sugar”

How Photosynthesis Works

• In the first stage, the light-dependent reaction, the chloroplast takes in light energy and converts it into chemical energy contained in NADPH and ATP, these two molecules are also used in the second stage of photosynthesis

• In the second stage is called the light-independent reaction or the dark reaction, NADPH provides the hydrogen atoms that help form glucose, or sugar used for energy, and ATP provides the energy for this and other reactions used to break down glucose. These two stages reflect the literal meaning of the term photosynthesis, to build with light.

A Review of Photosynthesis

• Photosynthesis splits light and is absorbed in a plants for energy

• Photosynthesis is all plants main source of energy and oxygen

• “No other chemical process on the planet can match the output of photosynthesis. And no process is more important than photosynthesis to the welfare of life on Earth”