13.1 Ecologists Study Relationships
PHOTOSYNTHESIS
4.2 Overview of Photosynthesis
KEY CONCEPT
Photosynthesis is a series of chemical reactions that
transform light energy into chemical energy stored in food.
4.2 Overview of Photosynthesis
Chemical Equation of Photosynthesis
6CO2 + 6H2O
Carbon dioxide + Water
REACTANTS
Carbon dioxide
Water
Sunlight Energy
chlorophyll
Sunlight Energy
chlorophyll
C6H12O6 + 6O2
Glucose + Oxygen
PRODUCTS
Glucose (sugar)
Oxygen
4.2 Overview of Photosynthesis
4.2 Overview of Photosynthesis
CO2 diffuses into leaf cells through stomata pores
4.2 Overview of Photosynthesis
Water is absorbed by osmosis through the roots
4.2 Overview of Photosynthesis
In plants, Photosynthesis occurs in chloroplasts.
chloroplast
• Chloroplasts are green colored
organelles that contain the green
pigmented molecule chlorophyll
leaf cell
•Chloroplast = Organelle
•Chlorophyll= Molecule
leaf
4.2 Overview of Photosynthesis
Structure of the Chloroplast Organelle
1.) Thylakoids- coin shaped compartments
surrounded by a membrane
chloroplast
grana (thylakoids)
2.) Grana –
Stacks of coin shaped thylakoids
3.) Chlorophyll – light absorbing green
molecule in thylakoid membrane
4.) Stroma –
Fluid filled space between grana
stroma
4.2 Overview of Photosynthesis
There are Two Main Stages of Photosynthesis
1. Light-Dependent Reactions – Require Light Energy
2. Light-Independent Reactions – Do Not Require Light Energy
4.2 Overview of Photosynthesis
• Light-Dependent Reactions - capture energy from sunlight.
*Light energy is needed
*Water is needed
*Occur in the chlorophyll filled thylakoid membrane
*Produce molecules that provide E to Light Independent Rxns.
(ATP and NADPH – High Energy Molecules)
*Waste byproduct is Oxygen
4.2 Overview of Photosynthesis
Basic Steps of the Light Dependent Reactions
1. Light energy “excites” the electrons in the chlorophyll molecule.
2. “Excited”, high energy electrons are passed from one protein
molecule to another along the electron transport chain in the
thylakoid membrane and are picked up by two molecules:
NADP to form NADPH
High E molecules needed to
ADP to form ATP
power the Light Independent Rxns
3. Enzymes split the water molecule: H2O
2H+ + 2e- + O* The 2e- replace the electrons the chlorophyll molecule lost
* Oxygen gas is released
4.2 Overview of Photosynthesis
• Light-Independent Reactions (Calvin Cycle)
•
•
•
•
•
Do NOT require light energy – can happen in the dark
Requires ATP and NADPH as energy source
Occurs in the stroma
CO2 needed. CO2 enters through the leaf stomata by diffusion
Glucose molecules made
4.2 Overview of Photosynthesis
Basic Steps of the Light Independent Reactions (Calvin Cycle)
1. CO2 molecules diffuse across the stroma.
2. CO2 is rearranged using H+ and Energy from ATP and
NADPH to make glucose. Carbon gets ”fixed” into
organic compounds – Carbohydrates, Lipids, Proteins
4.2 Overview of Photosynthesis
• Light Dependent Reactions – Capture Light Energy
•
Light Independent Reactions - Make Sugars
4.2 Overview of Photosynthesis
• The equation for the overall process is:
6CO2 + 6H2O  C6H12O6 + 6O2
granum (stack of thylakoids)
1
chloroplast
6H2O
thylakoid
6CO2
3
6O2
2
energy
stroma (fluid outside the thylakoids)
1 six-carbon sugar
4
C6H12O6