1. Nature’s energy factory! Page 89 and 90
Photosynthesis
Nature’s energy factory!
Page 89 and 90

2. Basic overview
Photosynthesis is a process of capturing and transforming energy from the sun to make sugars that store chemical energy.
This process takes place inside plant cells, in a special organelle called the chloroplast.
There are two major steps in photosynthesis: the light-dependent reactions and the light-independent reactions.
In the light-dependent reactions (1-3), energy from the sun is captured. It is transferred across the thylakoid membranes where it is transferred to ATP and NADPH molecules that carry energy. Water is broken down and oxygen is released as a waste product.
In the light-independent reactions, carbon dioxide is broken down to build larger sugar molecules called glucose.

3. Step 1: Gathering ingredients
During the first step in photosynthesis, light from the sun is captured within the plant’s leaves.
Chloroplasts contain a stacks of pancake-like compartments called thylakoids. These thylakoids contain a pigment known as chlorophyll which is able to absorb some of the energy in visible light.
Water is brought up from the roots of the plant to the plant cells in the leaves.

4. Step 2: Electron transport chain
As light passes through the thylakoid membrane, the sun’s energy is transferred to free electrons that become available as water molecules are broken down into hydrogen ions, free electrons, and oxygen (a waste product).
The free electrons pass through a series of proteins in the thylakoid membrane called the electron transport chain. The hydrogen ions move inside the thylakoid.
The electrons combine with a molecule called NADP+ to create a molecule called NADPH. NADPH helps to store energy for use during the next step, the light- independent reations.

5. Step 3: Creating ATP (Chemical energy)
All the hydrogen ions that have been building up have created an uneven concentration gradient (more hydrogen ions inside the thylakoid than outside).
To correct this, the hydrogen ions flow out through a protein channel (diffuse).
As the ions flow through the protein channel, an enzyme called ATP synthase creates ATP, a type of chemical energy.

6. Reviewing steps 1-3 Steps 1-3 make up the light-dependent reactions.
During the light-dependent reactions, sunlight and energy are broken down to create ATP and NADPH, both of which contain the chemical energy needed later to make sugars.
Oxygen is given off as a waste product.

7. Step 4: the Calvin Cycle
Carbon dioxide is taken in through holes on the underside of the leaf called stomata and is also brought into the plant cells.
The carbons from the carbon dioxide are separated from the molecule and used to create six carbon molecules.
ATP and NADPH use their stored energy to break apart the six carbon molecules into high-energy three carbon molecules, which are used to make glucose through repeated cycles of The Calvin Cycle.
NADP and ADP are waste products and go back to assist with the light-dependent reactions.
Glucose is created.

8. Reviewing step 4 Steps 4 is the light-independent reactions.
In Step 4, the ATP and NADPH from the light-dependent reactions give energy to the carbon molecules from carbon dioxide.
This helps to create glucose, the final product form of chemical energy in photosynthesis.

9. Reactants and products
Light Dependent Reactions
Light Independent Reactions
REACTANTS
PRODUCTS
Light energy (from the sun)
ATP (carries energy)
ATP & NADPH (from the light dependent reactions)
Glucose
Water (from the roots)
NADPH (carries energy)
CO2 (from the air brought in by the stomata)
ADP & NADP+ (recycled to be used in the light dependent reactions again)
Oxygen (a waste product)