Photosynthesis

Overview

Autotrophs
depends on themselves to make their own food

Photoautotroph
make their own food by using light

Phototrophs are the producers of the biosphere because they produce its food supply.

Examples of phototrophs :-

Protist

Plants

Kelp, a large alga underwater.

Cyanobacteria(Prokaryotic), important producer in freshwater and marine ecosystem.

Chemoautotroph
make their own food by using chemicals

Hetotroph
depends on others food

Chloroplast

Definition

All green parts of a plant have chloroplast in their cells and can carry out photosynthesis.

In most plants the leaves have the most chloroplast about half a million (500,000) in a square millimeter.

The major sites of photosynthesis is the leaves.

Chloroplasts are concentrated in the cells of the mesophyll.

A typical mesophyll cell has about 30 to 40 chloroplasts.

Mesophyll is the green tissue in the interior of the leaf.

Stomata, are tiny pores allow carbon dioxide to enter the leaf and oxygen to exit the leaf.

Veins, deliver the water absorbed by roots to the leaf.
Leaves use it to export sugar to roots and other parts.

Membranes in the chloroplast form the framework where many of the reactions of photosynthesis occur.

Composed of

Stroma

In the chloroplast , an envelope of two membranes enclosed an inner compartment, which is filled with a thick fluid called stroma.

Grana

Thylakoids are connected in stacks called grana.

Thylakoids

is a system of interconnected membranous sacs.

which enclose another internal compartment, called the thylakoid space.

The thylakoids membrane also house much of the machinery that converts light energy to chemical energy.

Pigments

Chlorophyll

is a light absorbing pigment in the chloroplast.

Plays a central role in photosynthesis.

Built into the thylakoid membranes are the chlorophyll molecules that capture light energy.

There are two types of chlorophyll

Chlorophyll A, absorbs blue-violet and red light but reflect the green light.

Chlorophyll B, absorbs blue and orange light but reflect yellow green light.

Carotenoids

absorb excessive light that would damage chlorophyll.

Process

Redox process

CH2 is reduced to sugar.

Water molecules are oxidized, lose electrons.

Photosynthesis converts light energy to chemical energy and stores it in the chemical bonds of sugar molecules.

The two stages of photosynthesis

Light Reaction
Light-dependent reaction
stage 1

The light reaction occur in the thylakoid membrane.

The light reaction, convert light energy to chemical energy and released O2.

Water split providing a source of electrons and giving off O2 as by-product.

The light reaction generate ATP from ADP and a phosphate group.

The light reactions absorb solar energy and convert it to chemical energy stored in ATP and NADPH.

Calvin Cycle
Light-independent reaction
stage 2

The calvin cycle occur in the stroma of the chloroplast.

It is a cycle series of reactions that assembles sugar molecule using CO2 and the energy-rich products of the light reactions.

Each turn of the light independent cycle requires 1 (CO2) 3 (ATP) and 2 (NADPH).

It needs 6 turns of the cycle to make 1 molecule of glucose
because glucose has 6 carbon atom backbone.

The incorporation of carbon from CO2 into organic compounds is called carbon fixation.

After carbon fixation, enzyme of the cycle make sugar by further reducing the carbon compound.

NADPH provides the electron for reducing carbon in the Calvin cycle.

ATP provides chemical energy that powers several of the steps of the Calvin cycle.

The Calvin cycle sometimes referred to as the dark reaction.
because non of the steps requires light directly.

In most plants, the Calvin cycle occurs during daylight,

when light reaction power the Calvin cycle's sugar assembly line by supplying it with NADPH ans ATP

The chloroplast's sugar factory is the Calvin cycle.