1. Ch. 8.1: Photosynthesis Overview
Plants use sunlight to make food (glucose).

2. Plants and Photosynthesis
Plants are autotrophs (producers) - make their own food.
Plant cells have chloroplasts which can capture light energy and convert it into chemical energy – stored in glucose.

3. Photosynthesis + + The Process H2O CO2 Energy Calvin Cycle Chloroplast
ATP and
NADPH2
Which splits
water
Light is Adsorbed By
Chlorophyll
Calvin Cycle
ADP
NADP
Chloroplast
Used Energy and is recycled. O2 +
C6H12O6
Light Reaction
Dark Reaction

4. Chemical Equation for Photosynthesis

5. Chloroplast – the Photosynthetic Organelle in Plant Cells

6. Chloroplast site of photosynthesis.
Chloroplasts are concentrated in the mesophyll tissue found in the leaf.
Mesophyll tissue is present right under the epidermis of the leaf and consists of Palisade tissue + spongy tissue.

7. Gases: Where Does the O2 Come From?
CO2 is taken into the leaf through stomata for photosynthesis.
O2 is released out of the leaf through stomata as a product of photosynthesis.
In order to determine whether the O2 gas product came from the reactant CO2 or from H2O, scientists used tracer (radio-isotopic) Oxygen, first in CO2 and then in H2O as follows:

8. Fate of Atoms in Photosynthesis
CO2  becomes part of glucose (C6H12O6)
H2O  is split into H and O; O2 is released as a gas; H’s become part of glucose.

9. Two Stages of Photosynthesis
Photosynthesis occurs in two stages.
Light reactions (during day-time only, in the thylakoid membrane)
Calvin Cycle (both day and night, in the stroma), which are linked together by NADPH and ATP.

10. Light Reaction
Light reaction – is dependent on light and occurs only during the day in nature.
Where: thylakoid membrane of the chloroplast.
Light reactions involve:
a) Splitting of water to produce O2 gas and H for glucose.
b) Production of
ATP = chem. Energy
NADPH (carries H, also energy).

11. Calvin Cycle
independent of light and occurs during the day and the night.
Where: stroma of the chloroplast.
Calvin Cycle involves the production of ‘food’ as glucose, by using CO2, ATP energy and NADPH.

12. Light Used in Photosynthesis
Chlorophyll pigments can absorb only some wavelengths of the visible light from the electromagnetic spectrum.
Visible light consists of the following colors or wavelengths in order of increasing wavelengths / decreasing energy:
Violet Blue  Green  Yellow  Orange Red.
Chloroplasts absorb mainly blue-violet and red-orange lights.
Green light is reflected and transmitted by green plants – hence, they appear green.

13. Light Photon = a discrete packet of light energy.
The shorter the wavelength, the greater the energy….and vice-versa.

14. Photosynthesis + + H2O CO2 Energy Calvin Cycle Chloroplast O2 C6H12O6
ATP = chemical energy
NADPH – carries Hydrogen
(NADP + H) +
H2O
CO2
Energy
ATP and
NADPH2
Which splits
water
Light is Adsorbed By
Chlorophyll
Calvin Cycle
ADP
NADP
Chloroplast
Used Energy and is recycled. O2 +
C6H12O6
Light Reaction
“Dark” Reaction

15. Photosynthesis and Cellular Respiration
Both Photosynthesis and Cellular Respiration are reverse of each other.
Photosynthesis is an endergonic reaction (energy required for rxn)
Cellular Respiration is an exergonic reaction (energy released during rxn)

16. The Flow Of Biological Energy
Photosynthesis cellular respiration
carbohydrates/
energy rich O2
chloroplast mitochondria
CO2 + H2O ATP for:
(energy poor) movement/cell activity