1. Introduction to Biology
Photosynthesis
Introduction to Biology

2. Photosynthesis Photo = “light”, Synthesis “to make”
Photosynthesis is using light energy to make organic compounds such as sugars.

3. Almost all plants are photoautotrophs.
Autotrophs are able to produce the molecules they need for life without eating anything.
Photoautotrophs use sunlight as their energy source.
Chemoautotrophs use non-living chemicals (like Hydrogen sulfide gas) as their energy source
Almost all plants are photoautotrophs.
Also includes algae(protists), and some bacteria.

4. LE 10-2 Plants Unicellular protist Purple sulfur bacteria
10 µm
Purple sulfur
bacteria
1.5 µm
Multicellular algae
Cyanobacteria
40 µm

5. Heterotrophs obtain their organic material by eating other organisms
Almost all heterotrophs, including humans, depend on photoautotrophs like plants for food and oxygen

6. Energy in Sunlight
Energy from the sun travels to Earth in the form of light.
Sunlight is a mixture of many different types of energy:
Ultraviolet: Invisible to us, causes sunburns
Visible Light: Wavelengths of light we can see,
Infrared: Energy in the form of heat

7. Energy
Our eyes see the different wavelengths of the visible spectrum as different colors: red, orange, yellow, green, blue, indigo, and violet.

8. Pigments
Plants gather the sun’s energy with light-absorbing molecules called pigments.
The plants’ principal pigment is chlorophyll.
Chlorophyll is a green pigment.
Plants are green because chlorophyll reflects green light and absorbs every other wavelength.

9. Pigments
Plant cells contain other pigments besides chlorophyll that increase the wavelengths absorbed.
These are called carotenoids.
During the summer, so much chlorophyll is produced that the green color overwhelms the other pigments.
When temperatures drop, the plants stop producing chlorophyll, and the other pigments may be seen.

10. Chloroplasts
Photosynthesis takes place inside organelles called chloroplasts.
Chloroplasts contain stacks called grana.
The grana contained stacked membranes called thylakoids, which are interconnected.

11. Chloroplasts Leaves are the major locations of photosynthesis
Their green color is from chlorophyll, the green pigment within chloroplasts
Light energy absorbed by chlorophyll drives the reactions needed to produce sugars from carbon dioxide.
The plant “breathes” through microscopic pores called stomata.
CO2 enters the leaf and O2 exits

12. Chloroplasts Pigments are located in the thylakoid membranes.
The fluid portion outside of the thylakoids is known as the stroma.

13. Photosynthesis Equation
Photosynthesis can be summarized in the following equation:

14. Stages of Photosynthesis
Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
The light reactions occur in the thylakoids of the chloroplast.
Splits water, releases O2, produces ATP and NADPH
The Calvin cycle occurs in the stroma of the chloroplast.
Forms sugar from CO2 using ATP and NADPH

15. LE 10-5_1
H2O
Light
LIGHT
REACTIONS
Chloroplast

16. LE 10-5_2
H2O
Light
LIGHT
REACTIONS
ATP
NADPH
Chloroplast O2

17. LE 10-5_3 H2O CO2 Light NADP+ ADP + CALVIN CYCLE LIGHT REACTIONS ATP
NADPH
Chloroplast
[CH2O]
(sugar) O2

18. ATP and NADPH Chloroplasts are solar-powered chemical factories
Their thylakoids transform light energy into the chemical energy of ATP and NADPH.
These are small energy-containing molecules that can be used to make glucose later.

19. LE 10-7 Light Reflected light Chloroplast Absorbed Granum light
Transmitted
light

20. Absorption of Sunlight
When chlorophyll absorbs light, it goes from a low-energy ground state to an high-energy excited state, which is unstable.
When excited electrons fall back to the ground state, photons are given off causing fluorescence.

21. Building Glucose
The Calvin cycle builds sugar from smaller molecules by using ATP and NADPH
Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P)
To make one G3P, the cycle must take place three times, using up three molecules of CO2