DO NOW

What is the difference between an
autotroph and a heterotroph?

Why do plants need sunlight?

What gases are exchanged between
plants and animals?
Overview Of Photosynthesis
Objectives
To be able to list the inputs and outputs
of photosynthesis.
 To be able to identify the structures in a
chloroplast.
 To be able to summarize light-dependent
reactions.

Photosynthesis

Light energy ------> chemical energy

Used by autotrophs to produce food

All of our energy starts as light energy!
◦ Plants use sunlight to make food animals
eat plants other animals those animals
Photosynthetic Organisms
Go through Photosynthesis to produce
GLUCOSE…
 Autotrophs
 “Producers” in the food web
 Consist of plants, protists, cyanobacteria

Overall Chemical Equation
Phase Overview

1) Light dependent Reactions
◦ Light energy is absorbed and converted into
chemical energy in the form of ATP and
NADPH. (also produces Oxygen!)

2) Light Independent Reactions:(Calvin
Cycle)
◦ CO2 ATP and NADPH are used to make
glucose.
*Glucose is the basic building block for more complex sugars such as starch.*
Glucose
The Chloroplast
Structures within a chloroplast

Thylakoids:
 flattened sac-like membranes arranged in
stacks (stacks are called grana).
 Light-dependent reactions take place here.
 Electron transport occurs in the thylakoid
membrane

Stroma:
 Fluid filled space outside the grana.
 Light-independent reactions take place here.
Light Dependent Reactions

Step 1: Light energy reaches
photosytem II causing the water
molecule to split
H
H
O
H 2O
H+
+
O2
*H+ is released to the electron
transport system.
* O2 is given off as a byproduct.

Step 2: Light energy reaches
photosystem I and electrons flow from
photosystem II to photosystem I. (to
replace the electrons lost)

Step 3: Hydrogen ions (protons) are
pumped across the membrane as the
electrons fall. (think of a hyper child losing
energy)

Step 4: Electrons from photosystem I
move to a protein called ferrodoxin.
**Ferrodoxin = “helper”
protein**

Step 5: Ferrodoxin transfers electrons
to NADP+ forming NADPH. (We need
this for the next part of photosynthesis!)

Step 6: Hydrogen ions move through the
ATP Synthase because of the
concentration gradient, creating ATP.
(Chemiosmosis)
To Calvin Cycle
Light Dependent Reactions
Lets see it altogether now!
http://www.science.smith.edu/departments/
Biology/Bio231/ltrxn.html
Review!

What goes into a light dependent reaction?

What is the goal of a light dependent
reaction?

What is given off as a byproduct?

What is the name of the protein needed in a
light dependent reaction?
Do Now
In what part of the chloroplast do light
reactions occur?
 What are the outputs of light-dependent
reactions?
 What is the name of the cycle in lightindependent reactions?

Objectives
List the inputs and outputs of the Calvin
Cycle
 Define chemiosmosis and it’s role in
photosynthesis.
 Summarize light – independent reactions
 Perform chromatography to identify the
pigments of green leaves.

Calvin Cycle
Takes place in the stroma
 Uses NADPH and ATP from Phase I (light
dependent reactions)
 Needs CO2!!!
 Produces GLUCOSE 

Calvin Cycle
Functions like a sugar factory within a
chloroplast
 **Regenerates the starting material with
each turn

Calvin Cycle
Inputs
ATP
- NADPH
- CO2
-
Outputs
- Glucose
Calvin Cycle
Chemosynthesis
Mechanism in which ATP is produced as a
result from the flow of electrons down a
concentration gradient.
 Ex: Light reactions (H+ ions and ATP
synthase)

Alternative Pathways
Light and Water can limit the amount
of photosynthesis a plant can perform.
 Some plants develop alternate pathways
to maximize energy conservation.
 Ex: CAM and C4 plants.

C4 Plants
These plants minimize water lost
 Turn CO2 into a 4 carbon molecule instead of
a 3 carbon molecule
 Keeps stomata (plant cell pores) closed
during hot days
 Ex. Corn and Sugar Cane

CAM Plants
Occurs in water-conserving plants that
live in deserts, salt marshes, etc.
 CO2 only enters leaves at night
 Turns CO2 into a “storage molecule” until
needed later
 Ex. Orchids, cacti, pineapples

Description
9. The second phase of
photosynthesis, in which energy is
stored in glucose
10. Pathway(s) that help(s) plants
photosynthesize while minimizing water
loss
11. Pathway that allows carbon dioxide
to enter leaves only at night
12. Light-independent reactions
13. Uses the enzyme rubisco to convert
carbon dioxide into molecules that can
be used by the cell
14. Type of plant found in hot, dry
environments
Calvin
C4
CAM
Animation

http://www.science.smith.edu/department
s/Biology/Bio231/calvin.html
Do Now – True or False
1. The anaerobic pathway that follows glycolysis in the absence of
oxygen is fermentation.
2. The hydrogen necessary in the electron transport chain comes from
the splitting of carbon dioxide molecules.
3. Cellular respiration in eukaryotes is slightly more efficient than in
prokaryotes.
4. The Krebs cycle is sometimes called the TCA cycle or the citric acid
cycle.
5. Fermentation occurs in the mitochondria.
6. Skeletal muscle produces lactic acid when the body cannot supply
enough oxygen.
7. Alcohol fermentation is found in some bacteria and in humans.
8. The two pyruvate molecules formed during glycolysis result in two
Krebs cycles.
9. Electron transport is the first step in the breakdown of glucose.