Photosynthesis allows plants to convert sunlight, carbon dioxide and water into glucose and oxygen. It occurs in two phases within the chloroplast - the light dependent reactions where ATP and NADPH are produced, and the light independent Calvin cycle where glucose is assembled from carbon dioxide using ATP and NADPH. The overall equation is carbon dioxide + water + energy (sunlight) → glucose + oxygen.

1. Photosynthesis
Trapping the Sun’s Energy

2. Photosynthesis:
Life from Light and Air

3. Plants are energy producers
Like animals, plants need energy to live
unlike animals, plants don’t need to eat
food to make that energy
Plants make both FOOD & ENERGY
plants are producers
animals are consumers

4. Using light & air to grow plants
Photosynthesis
using sun’s energy to make ATP
using CO2 & water to make glucose (sugar)
occurs in chloroplasts
allows plants to grow
makes a waste product
(ATP) = used to build the sugar
oxygen (O2)
carbon sun
dioxide
+ water + energy
® glucose + oxygen
6CO2 6H2O C6H12O6 6O2 sun
energy + + ®
+

5. What do plants need to grow?
The “factory” for making
energy & sugars
chloroplast
Fuels
sunlight
carbon dioxide
water
The Helpers
H2O
enzymes
sugars
ATP
Make ATP!
Make sugar!
I can do it all…
And no one
even notices!
enzymes
CO2
sun

6. The chloroplast is the organelle in a
plant cell where photosynthesis occurs

7. Chloroplasts are only in plants
aanniimmaall cceellllss ppllaanntt cceellllss

8. What absorbs light in a plant?
Pigments are molecules that absorb
specific wavelengths of sunlight
Sunlight (white light) can be separated
into many different wavelengths- that
appear as colors
ROYGBIV

9. Most common pigment is chlorophyll
It absorbs every wavelength
except GREEN
Green gets reflected- that’s why
plants appear green to the human
eye.
There are other types of plant
pigments
ex. Carotene= orange
ex. Xanthophyll = yellow

10. Why do leaves turn colors in
the fall?
Chlorophylls are more abundant than
other pigments in the leaves.
As trees prepare to lose their leaves,
chlorophyll molecules break down,
revealing the other pigments that are
also in the leaf.

11. Photosynthesis has 2 phases;
1. Light Dependent Reactions
2. Light Independent Reactions
-aka Calvin Cycle

12. Let’s take a look at the structure of a chloroplast
since that’s where the action is.
Calvin cycle (light
independent) occur in
the stroma
Light Reactions
(light dependent)
occur in the
thylakoids

13. Overview of Photosynthesis

14. Phase 1:
Light Dependent Reactions
Require Sunlight

15. Steps to the Light Dependent Reaction
1. Light hits the chlorophyll molecules
in the thylakoid membrane of the
chloroplast.
2. Causes water to split.
a. H+ ions  Build up in the
thylakoid space
b. Electrons  move down the
electron transport chain
c. Oxygen  Released into the air
as a waste product

16. 11
22

17. 3. Electrons move down the electron
transport chain.

18. 4. The electron exits the electron
transport chain and binds with
NADP+ to make NADPH.
a. NADPH is like an electron bus,
shuttling electrons to the Calvin
Cycle.

20. 5. Chemiosmosis
Hydrogen ions (H+) diffuse from an
area of high concentration to an area
of lower concentration through ATP
synthase.
ATP synthase is like an ATP
turbine.
Its job is to attach a phosphate to
an ADP to make
ATP
ATP is transferred to the Calvin
Cycle

22. Light Dependent Reactions Recap:
Water was split
Oxygen was released as a
waste product
ATP and NADPH were
transferred to the Calvin Cycle
(Calvin Cycle is aka Light Independent Reactions)

23. Phase 2: The Calvin Cycle
• Light independent reaction: this
means it does NOT need light in
order to work.
• Takes place in the stroma (fluid) of
the chloroplast
Here

24. The Calvin Cycle

25. Stages of the Calvin Cycle
1. CO2 (carbon dioxide) enters the
chloroplast
a. The carbon in CO2 is added to a
5-carbon (RuBP) molecule to
form a 6-carbon molecule

26. Stages of the Calvin Cycle
2. The 6 carbon molecule is split into two
3-carbon molecules (called PGA)
a. ATP and NADPH help convert a molecule
of PGA into G3P.
b. During this reaction, ATP loses a
phosphate (turning it into ADP) and NADPH
loses its hydrogen (turning it into NADP+).
c. These molecules return to the light
dependent reaction.

27. Stages of the Calvin Cycle
3. After several rounds of the Calvin
Cycle, two molecules of G3P leave the
cycle to form glucose
Making glucose is the entire point
of photosynthesis!

28. Stages of the Calvin Cycle
4. Some G3P molecules reform
the 5-carbon sugar (RuBP)
with the help of rubisco and
energy from ATP
5. The cycle is ready to begin
again!

29. The Calvin Cycle

30. Calvin Cycle Recap
Light Independent Reaction
What is made?
Glucose
ADP
NADP+
What goes in?
Carbon Dioxide
ATP
NADPH

31. Remember- the point of photosynthesis
is for plants to make glucose.
Why is glucose so important?
Plants use it for…
Food (break it down during cellular respiration)
Making cell walls
Storing it as starch (to eat later)

32. Questions:
1. What is the formula for
photosynthesis?
2. In what organelle does
photosynthesis take place?
3. What is used by a plant during the
light dependent reactions?
4. What is released by a plant during the
light dependent reactions?

33. Questions:
5. What is used by a plant during the light
independent reactions?
6. What is released by a plant during the
light independent reactions?
7. What two things produced by light
independent reactions are used
during light dependent reactions?