1. The Working Cell: Energy from Sunlight
Chapter 8

2. What process is this?

3. Photosynthesis uses light energy to make food
Photosynthesis is the opposite of cellular respiration

4. Photosynthesis is the process in which plants and other producers convert the energy of sunlight into energy stored in organic molecules
The cellular organelle in which photosynthesis takes place…
Chloroplast
Chloroplasts contain chlorophyll, a chemical compound that give the chloroplast a green color

7. In most plants leaves contain the most chloroplasts and are the major site of photosynthesis

8. Leaves have tiny pores, called stomata, throughout their surface which allow CO2 in and O2 out

9. Chloroplasts have an inner and outer membrane
Inside the inner membrane is a thick fluid called stroma
Suspended in the stroma are many disk-shaped sacs called thylakoids
A stack of thylakoids is called a grana

10. Photosynthesis occurs in two stages:
The light reactions = convert the energy in sunlight to chemical energy
The Calvin cycle = makes sugar from the atoms in carbon dioxide, hydrogen ions, and high-energy electrons

11. Overview of Photosynthesis

12. Electromagnetic energy= a form of energy that exhibits wavelike behavior as it travels through space
Visible light, microwaves, X rays
Wavelength= the shortest distance between equivalent points on a continuous wave

13. Electromagnetic spectrum = range of types of electromagnetic energy
The most important segment for life is a narrow band between 380 to 760nm…visible light
ROY G BIV
A particle of electromagnetic radiation is called a photon

15. Pigments= chemical compounds that determine a substance’s color
When light shines on a material that contains pigments, three things can happen:
Absorption
Transmission (goes through the material)
Reflection (bounces back)
Why do leaves look green?

16. Within the thylakoid membrane, chlorophyll and other molecules are arranged in clusters called photosystems
think solar panel!
Each photosystem contains a few hundred pigment molecules, including chlorophyll a,chlorophyll b, and carotenoids
Chlorophyll a, the dominant pigment, absorbs best in the red and blue wavelengths, and least in the green

17. Only chlorophyll a participates directly in the light reactions but accessory photosynthetic pigments absorb light and transfer energy to chlorophyll a.
Chlorophyll b, with a slightly different structure than chlorophyll a, has a slightly different absorption spectrum and funnels the energy from these wavelengths to chlorophyll a.
Carotenoids are pigments that range in color from pale yellow to deep red
they are involved in the color changes of leaves in the fall
they funnel the energy from other wavelengths to chlorophyll a.

19. Carotenoids

20. Photosynthesis Overview: Chlorophyll absorbs light ↓
Energy transferred to electrons
Energy level of electrons increased (unstable)
Carbohydrates, oxygen

21. Light Reactions

22. This leaves hydrogen ions and electrons
The light reactions involve two photosystems, photosystem I and photosystem II, connected by an electron transport chain
Photons of light, as well as water molecules, come into the thylakoid and strikes photosystem I
The oxygen is “sliced” off of the water molecule and is released through the stomata into the atmosphere
Called photolysis
This leaves hydrogen ions and electrons
The electrons are funneled to the electron transport chain

23. The electrons move from carrier to carrier within the electron chain
Each time an electron moves to the next carrier energy is produced
When the electrons exit the electron chain they move to photosystem II
Photosystem II is called the “NADPH producing system”
What is NADPH?
Nicotinamide Adenine Dinucleotide Phosphate
It’s a carrier molecule!!
What does it carry?
Electrons!!!

24. The electrons are carried by NADPH to the Calvin cycle
Now, back to the hydrogen ions…
The ETC produces energy by moving the electrons from carrier to carrier
This energy is used to pump hydrogen ions across the membrane from an area of low concentration to area of high concentration
Potential energy builds up and the hydrogen ions rush through the ATP synthase which produces what?
ATP
The ATP is then used in the Calvin Cycle

26. The Calvin cycle makes sugar from carbon dioxide
The light reactions produce oxygen, a very important product for life to exist
But life needs more…organic molecules!

27. The Calvin cycle Carbon enters as CO2
ATP and NADPH, from the light reactions, provide energy and electrons that are used to make the sugar
The sugar that is produced is called G3P, a smaller molecule than glucose (three carbons instead of 6 carbons)
G3P exits the cycle
G3P is the raw material that plants use to make glucose and other organic molecules

29. Summary of Photosynthesis
Overall equation for photosynthesis
Sunlight + 6 CO2 + 6 H2O   C6H O2
Light reactions
take place in thylakoid membrane
use light and water
convert light energy to the ATP and NADPH
product is oxygen
Calvin cycle
takes place in the stroma
Uses ATP and NADPH to convert carbon dioxide to sugar

30. Photosynthesis has a global impact
On a global scale, photosynthesis is the most important process to the welfare of life on Earth
Photosynthetic organisms make about 160 billion metric tons of organic material per year

31. Earth’s atmosphere
Carbon dioxide traps heat from the sun and prevents it from escaping back out into outer space
The greenhouse effect, keeps the world climate warm enough for life to exist
In recent years the amount of CO2 in the atmosphere has been rising