1. Photosynthesis: Capturing Energy
Chapter 8
Photosynthesis:
Capturing Energy

2. Photosynthesis is the process by which plants, some bacteria, and some protists use the energy from sunlight to produce sugar.
Cellular respiration then converts sugar into ATP, the "fuel" used by all living things.

3. Photosynthesis Conversion of light energy to chemical bond energy
Associated with the green pigment, chlorophyll
Equation:

4. Plants Plants are the only photosynthetic organisms that have leaves.
A leaf is basically a solar collector full of photosynthetic cells.

5. Leaves
Water enters the root and is transported up to the leaves through specialized plant cells known as xylem.
Land plants (which risk drying out) have structures called stomata that allow for gas exchange.
However, while open, water still escapes.

6. Leaf Structure

7. Leaf Stomata

8. Light Light is composed of small particles that travel as waves
Radiation varies in wavelength
Red – longer wavelengths
Violet – shorter wavelengths

10. Light Light can also behave as particles
Photons – packets of energy
When a molecule absorbs a photon of light energy, one electron is energized

11. Chlorophyll Chlorophyll is a pigment
Pigment is any substance that absorbs light.
Chlorophyll – green pigment common to all photosynthetic cells
Color is from the wavelength of light reflected
Different types of chlorophyll
Accessory pigments – absorb different wavelengths of light

12. Pigments All photosynthetic organisms have chlorophyll a
Chlorophyll a absorbs its energy from Violet-Blue and Red-Orange wavelengths
Green/Yellow is reflected
Accessory pigments: chlorophyll b, carotenoids – absorb other wavelengths

14. Chloroplasts Have a double membrane
Inner membrane encloses the stroma (area between membranes)
Thylakoids are a third set of membranes enclosing the thylakoid interior space
Stacks of thylakoids = grana
Chlorophyll and other pigments located in the thylakoid membranes

16. Prokaryotes lack chloroplasts
Thylakoids are still present, but without chloroplast structures
Thylakoid membranes are formed from infoldings of the plasma membrane

17. Photosynthesis Divided into 2 reactions:
Light Dependent Reactions - thylakoid
Carbon fixation/Calvin Cycle (Light Independent) – stroma

18. Light-Dependent Reactions
Light excites the electrons in chlorophyll a to a higher energy state
In a series of reactions the energy is converted (along an electron transport process) into ATP and NADPH.
Water is split in the process, releasing oxygen as a by-product of the reaction.
The ATP and NADPH are used to make C-C bonds in the Light Independent Process (Dark Reactions)

19. Calvin Cycle (Light Independent Reactions)
Not driven by light
Use products from Light Dependent reactions
CO2 is captured and modified with the addition of Hydrogen to form carbohydrates