1. Biology – Premed Windsor University School of Medicine
photosynthesis

2. LEARNING OBJECTIVES By the end of this lecture you will be able to:
Understand that ENERGY can be transformed from one form to another.
Know that energy exist in two forms; free energy - available for doing work or as heat - a form unavailable for doing work.
Appreciate that the Sun provides most of the energy needed for life on Earth.
Explain why photosynthesis is so important to energy and material flow for life on earth.
Know why plants tend to be green in appearance.
Equate the organelle of photosynthesis in eukaryotes with the chloroplast.
Describe the organization of the chloroplast.
Understand that photosynthesis is a two fold process composed of the light-dependent reactions (i.e., light reactions) and the light independent reactions (i.e. Calvin Cycle or Dark Reactions).
Tell where the light reactions and the CO2 fixation reactions occur in the chloroplast.
Define chlorophylls giving their basic composition and structure.
Draw the absorption spectrum of chlorophyll and compare it to the action spectrum of photosynthesis.
Define the Reaction Centers and Antennae and describe how it operates.
Describe cyclic photophosphorylation of photosynthesis.
Describe noncyclic photophosphorylation of photosynthesis.

3. What is Photosynthesis?
The process of photosynthesis is a chemical reaction. It is the most important chemical reaction on our planet.

4. AN OVERVIEW OF PHOTOSYNTHESIS
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
A process in which light energy is stored in the bonds of glucose for later use
Carbon dioxide
Water
Glucose
Oxygen gas
PHOTOSYNTHESIS

5. Terminology Autotrophs - Can make their own food (“Self-feeders”)
Heterotrophs – Can not make their own food
Light-dependent Photosynthesis - Requires light for photosynthetic process to complete
Light-independent Photosynthesis – Does NOT require light for photosynthetic process to complete

6. THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

7. THE BASICS OF PHOTOSYNTHESIS
Almost all plants are photosynthetic autotrophs, some bacteria and protists
Autotrophs generate their own organic matter through photosynthesis
Sunlight energy is transformed to energy stored in the form of chemical bonds
(c) Euglena
(d) Cyanobacteria
(b) Kelp
(a) Mosses, ferns, and
flowering plants

8. Light Energy Harvested by Plants & Other Photosynthetic Autotrophs
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

9. What is the equation for the chemical reaction of photosynthesis?
Six molecules of carbon dioxide react with six molecules of water to form 1 molecule of glucose and six molecules of oxygen.

10. Describe Photosynthesis
The process of changing light energy to chemical energy
Energy stored as sugar
Occurs in plants and some algae
Plants need light energy, CO2, and H2O
Takes place in the chloroplasts, using chlorophyll, the green pigment in plants

11. What happens during photosynthesis?
Plants capture light energy and use that energy to make glucose
Sunlight provides the energy needed by chlorophyll to change molecules of carbon dioxide and water into glucose
Oxygen is also released in this reaction

12. What happens during photosynthesis?
Carbon dioxide enters the leaf through holes called stomata
CO2 combines with the stored energy in the chloroplasts through a chemical reaction to make glucose
The sugar is moved through tubes in the leaf to the roots, stems and fruits of the plants
Some of the sugar is used right away by the plant for energy; some are stored as starch; and some are built into plant tissue

13. Why is this important to us?
We cannot make our own food (glucose, energy), we must get our food from plants.
Plants are the first step in the food chain.
The oxygen released during photosynthesis is necessary for all living things.

14. WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts
The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

15. THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED
Chloroplasts absorb light energy and convert it to chemical energy
Reflected
light
Light
Absorbed
light
Transmitted
light
Chloroplast

16. AN OVERVIEW OF PHOTOSYNTHESIS
The light reactions convert solar energy to chemical energy
Produce ATP & NADPH
Light
Chloroplast
NADP
ADP
+ P
The Calvin cycle makes sugar from carbon dioxide
ATP generated by the light reactions provides the energy for sugar synthesis
The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose
Calvin
cycle
Light
reactions

17. Chloroplasts: Sites of Photosynthesis
Occurs in chloroplasts, organelles in certain plants
All green plant parts have chloroplasts and carry out photosynthesis
The leaves have the most chloroplasts
The green color comes from chlorophyll in the chloroplasts
The pigments absorb light energy

18. Photosynthesis occurs in chloroplasts
In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts
A chloroplast contains:
stroma, a fluid
grana, stacks of thylakoids
The thylakoids contain chlorophyll
Chlorophyll is the green pigment that captures light for photosynthesis

19. The location and structure of chloroplasts
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Inner membrane
Grana
Stroma
Thylakoid compartment
Stroma
Thylakoid

20. Chloroplast Pigments Chlorophyll a Chlorophyll b Carotenoids
Chloroplasts contain several pigments
Chlorophyll a
Chlorophyll b
Carotenoids
Figure 7.7

21. Plants produce O2 gas by splitting H2O
The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)

22. Review: Photosynthesis uses light energy to make food molecules
A summary of the chemical processes of photosynthesis
Chloroplast
Light
Photosystem II Electron transport chains Photosystem I
CALVIN CYCLE
Stroma
Electrons
Cellular respiration
Cellulose
Starch
Other organic compounds
LIGHT REACTIONS
CALVIN CYCLE

23. What is Cellular Respiration?
The release of chemical energy for use by cells.
Once the energy that was in sunlight is changed into chemical energy by photosynthesis, an organism has to transform the chemical energy into a form that can be used by the organism.
This process is called cellular respiration.

24. Describe Cellular Respiration
The breakdown of glucose molecules to release energy
Takes place in all living things
Is a step by step process

25. What is the chemical equation for cellular respiration?

26. It's not that easy bein' green… but it is essential for life on earth!