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Leigh Fauber

on 10 December 2013

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Transcript of Photosynthesis:

An Overview

Light-Dependent Reaction
Anatomy of a Leaf
**About half a million chloroplasts in a chunk of leaf with a top surface area of 1 mm2. A typical mesophyll cell contains about 30-40 chloroplasts.
Carbon dioxide enters the leaf and oxygen exits by way of microscopic pores called stomata (from the Greek meaning “mouth”).
Water is absorbed by the roots and delivered to the leaves in veins. Leaves also use veins to export sugar to roots and other nonphotosynthetic parts of the plant.
Chloroplasts have two membranes surrounding a dense fluid called the
Within the stroma is a third membrane system, made up of sacs called thylakoids. Thylakoid sacs can be stacked into columns called grana (singular, granum).
Thylakoids house chlorophyll pigments, which absorb light energy.
The thylakoid is where photosynthesis takes place because this is where the chlorophyll is located. It is the light energy that is abosrbed by chlorophyll that drives the process of photosynthesis and it is what gives plants their characteristic green color.
What is energy?
Types of Energy
ADP = Adenosine Diphosphate
ATP = Adenonsine Triphosphate
The Process of Photosynthesis
Endothermic Reaction
Photosynthesis is an endothermic reaction. This process absorbs light energy in order to break the bonds between the carbon dioxide molecule and water molecule. The absorbed solar energy is greater than the energy released then the new bonds are created in the glucose and oxygen molecules.
Two Types of Reactions within Photosynthesis
Light-Dependent Reactions:
These reactions require light energy in order for them to work. This is the first step in photosynthesis.

Light-Independent Reactions:

These reactions do NOT require energy in order to work.
Chemical Energy: ATP & ADP
Where do these reactions take place?
Role of Water
Water is required in this reaction as a source of electrons and hydrogen ions.

Enzymes on the inner surface of the thylakoid break up each water molecule into 2 electrons, 2 hydrogen ions and 1 oxygen atom.

These electrons replace the ones that were lost to the electron-transport chain.
What happens when solar energy is absorbed?
Chlorophyll absorbs sunlight and gives off high-energy electrons, which are passed to a series of electron carriers embedded in the thylakoid membrane.
This is the first step in the process of photosynthesis.
Hydrogen ions, some left behind by splitting of water and some pumped in from stroma build up a negative space in the stroma relative to the positive space in the thylakoid.
As the hydrogen ions leave the thylakoid, they spin this protein channel called ATP synthase. This makes ADP bind with a phosphate group to make ATP!
Role of Hydrogen Ions
Energy Conversions in Photosynthesis
The process of photosynthesis involves 3 energy conversions:
1) absorption of light energy
2) conversion of light energy into chemical energy
3) storage of chemical energy in the form of sugars

Factors Affecting Photosynthesis
Light Intensity
Carbon Dioxide Levels

The ATP produced in the light-dependent reactions drive the Calvin Cycle.
The part of photosynthesis, which takes place in the stroma, uses carbon dioxide gas to make more stable energy compounds like glucose.
The Calvin Cycle:
Light Independent Reaction
Full transcript