1. Introduction to Photosynthesis
Chapter 10 (Part 1)
Introduction to Photosynthesis
Ms. Day
AP Biology

2. The Process That Feeds the Biosphere
Photosynthesis
the process that converts solar energy into chemical energy
Light + CO2 + water  food
Who or What?
Plants and other autotrophs
They are producers of the biosphere

3. 2 Types of Autotrophs Chemoautotrophs
Use chemosynthesis to make “food”
Photoautotrophs
Use photosynthesis to make “food”

4. Plants, some bacteria and algae are photoautotrophs
Use energy of sun to make organic molecules from H2O and CO2
Some worms and bacteria are chemoautotrophs
Use energy from chemicals to make organic molecules

6. (b) Multicellular algae (c) Unicellular protist
Photosynthesis
Occurs in plants, algae, certain other protists, some **prokaryotes
These organisms use light energy to drive the
synthesis of organic molecules from carbon dioxideand (in most cases) water. They feed not onlythemselves, but the entire living world. (a) On
land, plants are the predominant producers of
food. In aquatic environments, photosynthetic
organisms include (b) multicellular algae, such
as this kelp; (c) some unicellular protists, such
as Euglena; (d) the prokaryotes called
cyanobacteria; and (e) other photosynthetic
prokaryotes, such as these purple sulfur
bacteria, which produce sulfur (spherical
globules) (c, d, e: LMs).
(a) Plants
(b) Multicellular algae
(c) Unicellular protist
10 m
40 m
(d) Cyanobacteria
1.5 m
(e) Pruple sulfur
bacteria
Figure 10.2

7. Autotrophs vs. Heterotrophs
Obtain their organic material from other organisms
They are consumers of the biosphere

8. Chloroplasts: The Sites of Photosynthesis in Plants
The leaves of plants-THEY’RE GREEN!!
major sites of photosynthesis
VeinH2O
Leaf cross section
Figure 10.3
Mesophyll (leaf tissue)
CO2 O2
Stomata
30-40 chloroplats
Stomata; Stoma (pl)
CO2 O2

9. Leaf Anatomy

10. Organelle where photosynthesis occurs
Chloroplasts
Organelle where photosynthesis occurs
Stroma
Dense fluid within chloroplast
Dark reaction occurs here
Thylakoids
Membranous sac (or “coin”) in stroma
Inside space called thylakoid space
Light reactions occur here
Grana (granum = singular)
Stack of thylakoids (“coins”)

14. The Equation for Photosynthesis
Photosynthesis converts light energy to the chemical energy of food
Overall chemical equation
**almost opposite of cell respiration
6 CO2 + 6 H2O + Light energy  C6H12O6 + 6 O2

15. Photosynthesis as a Redox Process
Photosynthesis is an endergonic redox process
Water is oxidized
carbon dioxide (CO2) is reduced
What is the source of energy?
Light
The light boosts the energy of e-s as they are moved from H20  C6H12O6 (glucose)

16. The Nature of Sunlight Light A form of electromagnetic energy
Travels in waves and particles
Particles are called photons
Wavelength
Distance between crests of waves
Determines type of energy light has (wavelength & energy are inversely proportionate)

17. The electromagnetic spectrum
The entire range of electromagnetic energy, or radiation
Gamma
rays
X-rays UV
Infrared
Micro-
waves
Radio
10–5 nm
10–3 nm
1 nm
103 nm
106 nm
1 m
103 m
380
450
500
550
600
650
700
750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy

18. The visible light spectrum
Includes the colors of light we can see (ROYGBV)
Includes the wavelengths that drive photosynthesis
When light hits matter  it is:
Absorbed
Reflected
Transmitted

19. BLACK  all colors are absorbed
Color we SEE = color most reflected by pigment; other colors (wavelengths) are absorbed
BLACK  all colors are absorbed
Light
Reflected
Chloroplast
Absorbed
light
Granum
Transmitted

20. How do the light reactions capture solar energy?
Photosynthetic Pigments
molecules that absorb visible light
different pigments absorb different wavelengths of light
Different pigments used in photosynthesis

21. Primary vs. Accessory Pigments
Primary Pigment
Chlorophyll a (most abundant)
Accessory (Antennae) Pigments
Chlorophyll b
Anthocyanins
Xanthophylls
Cartenoids

22. Photosynthetic pigments
Primary pigment = chlorophyll a 
takes direct part in light reactions
Accessory pigments
protect chlorophyll a from UV damage
absorb light at wavelengths that are not absorbed by chlorophyll a
Funnel e-s to chlorophyll a  help broaden absorption spectrum for photosynthesis (act as “antennae”)

23. The Two Stages of Photosynthesis: A Preview
The Light reactions
NEEDS LIGHT
A.k.a- Light Dependent Reactions
The Calvin cycle
A.k.a-
Dark Reactions
Light Independent Reactions
C3 pathway
DOES NOT NEED LIGHT

24. GOAL= Convert solar energy to chemical energy (ATP & NADPH)
The Light Reactions
Occur in the grana (& thylakoids)
GOAL= Convert solar energy to chemical energy (ATP & NADPH)
Chlorophyll absorbs solar energy
Splits water
release O2 (a by-product)
produce ATP (using chemiosmosis)
Forms NADPH from NADP+ (an e- acceptor/carrier)
Temporarily stores high energy e-’s
“Electron shuttle bus”

25. The Calvin Cycle GOAL= Use ATP & NADPH to convert CO2 into sugar
Occurs in the stroma
Forms SUGAR from carbon dioxide
Carbon fixation occurs (CO2 fixed carbon into sugars)
**Uses ATP and NADPH from light reactions

26. An overview of photosynthesis
H2O
CO2
Light
LIGHT REACTIONS
CALVIN
CYCLE
Chloroplast
[CH2O]
(sugar)
NADPH
NADP 
ADP
+ P O2
ATP
G3P