1. Photosynthesis – Lesson # 1
Introduction

2. Why study photosynthesis?
Practical reasons:
Photosynthetic organisms are autotrophs (they make their own food)
Without autotrophs, heterotrophs (organisms that eat other organisms) would not have a source of food/energy

3. Photosynthesis – What is it?
The conversion of light energy, carbon dioxide and water into high energy compounds (e.g. Glucose).
The general equation for photosynthesis is:
CO2(g) + H2O(l) + light energy  [CH2O](aq) + O2(g)
Photosynthesis can be thought of as the reverse of cellular respiration. Why ?

4. Where in a plant does photosynthesis take place?
(Cross section of a leaf)

5. Leaves – Getting the Raw Materials
Light passes through the upper epidermis to reach the mesophyll layers.
Water is absorbed by plant roots, and is delivered to the leaf via the vascular bundle.
Carbon Dioxide gets into the leaf through the stoma (see picture below)

6. Guard Cells and Stomata
Guard cells control the diameter of the stoma
The stoma opens during the day and closes at night (usually)
Sunlight activates a proton pump in the guard cells causing H+ to exit the cells.
The electrical potential of the cells becomes negative
K+ ions flow in to correct this difference
The influx of K+ ions draws water into the guard cell making them turgid
The swelling of the guard cells opens the stoma

7. Guard Cells and Stomata
See animation:
So what?

8. Photosynthesis - Overview
Photosynthesis takes place in the chloroplast.
The following structures inside the chloroplast are important:
thylakoids
stroma
Why are these structures important?
Photosynthesis is a 2 step process. Step 1 (the light reactions) occurs in the thylakoids. Step 2 (the Calvin Cycle) occurs in the stroma

9. Photosynthesis - Overview

10. Light Reactions - Overview
Light Reactions: light is absorbed by chlorophyll which drives the transfer of electrons to (NADP+). NADP+ is reduced to form NADPH.
ATP is also produced during the light reactions in a process known as photophosphorylation
Take home point: Light reactions produce ATP and NADPH which are used in the Calvin Cycle to make sugar. Oxygen is also produced (as a result of the water splitting) as a by-product.

11. Calvin Cycle - Overview
Calvin Cycle: begins with carbon fixation. The Calvin Cycle uses NADPH and ATP from the light reactions to reduce carbon dioxide to carbohydrates (e.g. Glucose).
The Calvin Cycle is sometimes referred to as the “light independent reactions”. Why?

12. Tomorrow: More detail on light reactions and Calvin Cycle
You need to work on a photosynthesis cheat sheet (4 pages) and have a format like this:
Light Reactions
CAM Plants
Calvin Cycle
C4 Plants

13. Homework Read section 3.1 in your text (pp 138-144)
Try questions 1, 2a, 4, and 5 on page 145 of your textbook
Wednesday: Quiz on Cellular Respiration (Can use cheat sheet)