1. Chpt. 11: Photosynthesis

2. Autotrophic Organisms: are organisms that make their
own food – producers.
Majority of autotrophs are green plants and they make
their food by a process called photosynthesis.

3. Equation for photosynthesis: 6CO2 + 6H2O + Light C6H12O6 + 6O2
Photosynthesis: is the process by which plants make food and oxygen using carbon dioxide from the atmosphere, water from the soil and energy from the sun.
Equation for photosynthesis:
6CO2 + 6H2O + Light C6H12O6 + 6O2
Carbon Water Glucose Oxygen
Dioxide
Chlorophyll

4. Photosynthesis:
cells need energy to carry out their reactions
light (sun) provides this source of energy.
energy provided by the breakdown of Adenosine
TriPhosphate (ATP).
Light Energy ATP Glucose

5. Role of Photosynthesis:
plants use photosynthesis to make food.
animals get their food from plants.
photosynthesis produces oxygen (O2) needed for
respiration.
responsible for forming fossil fuels.

6. Role of photosynthesis:
Priestly’s experiment. A plant in a closed jar died and a mouse in another closed jar died, but when plant and mouse were put together, both lived.

7. Location of Photosynthesis:
Photosynthesis depends on chlorophyll which is located
in structures called chloroplasts.
Chloroplasts concentrated in cells in the upper surfaces
of leaves.
Chloroplasts are also present in the green stems of
some plants.

8. Factors necessary for photosynthesis:
Chlorophyll:
- green pigment found in grana of chloroplasts.
- made with magnesium.
- absorbs light and converts it into glucose.
2. Light:
- comes directly from the sun.
3. Carbon Dioxide (CO2):
- comes from the atmosphere through the stomata of the leaf.
- also comes from plant during respiration.

9. Factors necessary for photosynthesis:
4. Water:
comes from the soil.
taken up through the roots and transported via the xylem to the leaves.
5. Temperature:
- Photosynthesis is controlled by enzymes that work best at 25oC.
at approx. 50oC most enzymes are denatured.

10. Stages in Photosynthesis:
Stage 1: Light is absorbed
Stage 2: Water is split
Stage 3: Products are produced (protons, electrons ad oxygen)
Stage 4: Light energises electrons
Stage 5: Glucose is formed

11. 1. CHLOROPHYLL ABSORBS THE LIGHT ENERGY CAUSING ELECTRONS TO LEAVE THE CHLOROPHYLL AND TO PASS THROUGH A SERIES OF ELECTRON CARRIERS
2. WATER MOLECULES SPLIT INTO H+ IONS (PROTONS) AND OH- IONS. THE H+ IONS ACCEPT THE ELECTRONS TO BECOME H ATOMS, THIS PROCESS IS REFERRED TO AS PHOTOLYSIS
3. THE OH- IONS RELEASE THEIR ELECTRONS, WHICH ARE CARRIED BACK TO THE CHOLROPHYLL

12. Products of photosynthesis:
4. THE OH GROUPS COMBINE TO FORM H20 AND 0 ATOMS. THE OXYGEN ATOMS ESCAPE FROM THE LEAF INTO THE ATMOSPHERE AS 02 MOLECULES, OR USED INSIDE THE LEAF FOR RESPIRATION
5. THE HYDROGEN ATOMS ARE COMBINED WITH CO2 TO FORM GLUCOSE
Products of photosynthesis:
Glucose - food
Oxygen – used for respiration

13. 4.
OH (+OH)
EC4
EC3 E-
sunlight
H20
OH- 3.
EC5
H2O 2. E-
Chlorophyll
molecule 1. H+ E- E- E-
glucose
Electron carrier 1
EC2 5.
CO2

14. 6CO2 + 6H20 -------------- C6H12O6 + 602
CATALYSTS
SUNLIGHT
6CO2 + 6H  C6H12O
CHLOROPHYLL

15. What happens to the glucose?
Can be converted to starch and stored for later
use
Moved to another part of the plant to give
energy( respiration)
Changed to lipids or protein
Can be used to make cellulose for new cell
walls for growth

16. Environmental Factors
Environmental factors effecting the rate of photosynthesis are:
Light intensity*
Temperature
CO2 concentration
* need to know experiment

17. Experiment: To investigate the influence of light intensity on the rate of photosynthesis.
Plants can only photosynthesise in the light
At night photosynthesis cannot take place
By using artificial light at night we can increase the hours
of photosynthesis
In winter daylight is often weak , artificial lamps can
supplement the light and increase the rate of
photosynthesis
Example – in green houses

18. Experiment: To investigate the influence of light intensity on the rate of photosynthesis.
As the light intensity increases the rate of photosynthesis will also increase provided there is no shortage of CO2 and if the temperature is maintained at approx 250C
If you vary the light intensity (by moving the light) the other factors are kept constant because CO2 concentration and temp also effects the rate of photosynthesis
Keep CO2 conc constant by adding sodium bicarbonate
Keep temp constant by using a water bath

19. Experiment: To investigate the influence of light intensity on the rate of photosynthesis.
Elodea ( Canadian pondweed ) used, the rate of photosynthesis is measured by the number of oxygen bubbles produced per unit time ( must allow time for plant to adjust to each condition)

20. Experiment: To investigate the influence of light intensity on the rate of photosynthesis.

21. Sodium bicarbonate runs out
Experiment: To investigate the influence of light intensity on the rate of photosynthesis.
Light saturation pt
Sodium bicarbonate runs out
No of bubbles
light
* Note: see experiment pg 107/108

22. Biochemistry of Photosynthesis
(Higher Level)
Structure of Chloroplast:
LAMELLA
INNER MEMBRANE
OUTER MEMBRANE
DNA

23. Photosynthesis takes place in 2 stages:
- the LIGHT STAGE( light dependent) occurs in the
GRANA of chloroplast
- the DARK STAGE ( light independent—occurs
whether light is present or not)
occurs in STROMA of chloroplast

24. LIGHT STAGE Events in the Light Stage: A) Light absorption
B) Light energy transferred to electrons
C) Electron flow – Pathway 1
D) Electron flow – Pathway 2

25. Each cluster consists of: - a variety of pigments
Light Absorption:
Light is absorbed by a range of pigment clusters found in the chloroplast (almost all colours of light are absorbed but green is normally reflected)
Each cluster consists of:
- a variety of pigments
- a chlorophyll molecule *(specially placed)
- an electron acceptor
Electron acceptor
Chlorophyll molecule
Pigments
Pigment Cluster

26. B. Light Energy Transferred to Electrons:
The pigment cluster absorbs as much light energy as possible and passes it to the reaction centre chlorophyll molecule. This light energy is trapped by the chlorophyll molecule and passed to an electron.
This energy causes the electron to become energised.
The energised electron is passed to the electron acceptor which can then send it on one of two pathways.

27. C. Electron Flow – Pathway 1:
In pathway 1 the electrons pass from the first electron acceptor to a series of other electron acceptors (electron carriers) and back again to the chlorophyll
As the electrons are passed around they lose energy
This energy is used to join a phosphate (P) to ADP to form high energy ATP and water (Chpt. 10: energy carriers):
ADP + Energy + P ATP + Water
The addition of phosphate to ADP in this way is called
photophosphorylation
Because the electron travels in a cycle and returns to its
original chlorophyll this process is called Cyclic
Photophosphorylation (e- recycling)

28. D. Electron Flow – Pathway 2:
2 high energy electrons at a time are passed from chlorophyll to the electron acceptor and then along another series of electron acceptors (electron carriers)
In this case the electrons do not return to the original chlorophyll
They lose energy as they pass from electron acceptor to electron acceptor and this energy is used to make more ATP
Eventually the 2 electrons are passed to combine with NADP+ to form NADP- :
NADP electrons (2e-) NADP-

29. D. Electron Flow – Pathway 2:
The chlorophyll molecule is now short of electrons and gains more from the splitting of water. Electrons pass, two at a time, from a water molecule to chlorophyll
2H2O H+ + 4e- + O2
The splitting of water using light energy is called Photolysis
Light Energy
The H+ ions are attracted to NADP- and combine with it to form NADPH which is used in the DARK stage of photosynthesis.
Because the electrons start at a chlorophyll and finish at NADPH and form ATP on their way this pathway is known as Non cyclic photophosphorylation (no e- recycling)

30. Photolysis The splitting of water

31. End Products of the Light Stage
There are 3 end products of the light stage
ATP - this will provide energy for the dark stage
2. NADPH - this will provide protons and energised electrons for the dark stage
Oxygen is made when water is split – can be used for respiration or be released into the atmosphere
* Note: water is also produced to hydrate cytoplasm of cells

32. CYCLIC PHOTOPHOSPHORYLATION NON-CYCLIC PHOTOPHOSPHORYLATION
Light Stages
ATP
ADP + P
ATP
CE 3
CE 2
CE 1 O2
ADP + P
4OH- ions
CE 2
ATP
Chlorophyll molecule
CYCLIC PHOTOPHOSPHORYLATION
2H2O
NON-CYCLIC PHOTOPHOSPHORYLATION
CE I
ADP + P e-
4H+ ions
Electron acceptor
NADP+
2e-
NADPH (used in dark stage)
NADP-
excited e-
Pathway 2 (non-cyclic)
e- start with water and end up with NADPH
Pathway 1 (cyclic)
e- flow from chlorophyll back to chlorophyll

33. DARK STAGE (Calvin Cycle)
This may also be called the light independent stage as it can occur in the light but does not need to use it
It takes place in the stroma of the chloroplast
It is controlled by enzymes and therefore can be affected by temperature

34. Carbon dioxide from the air enters the chloroplast where it combines with protons (H+) and electrons to form glucose.
This process requires energy, protons and electrons:
- it obtains energy from the breaking down of:
ATP (produced in light stage) into ADP + P
- it obtains hydrogen ions and electrons from the
breaking down of:
NADPH (produced in light stage) into NADP+ +
2 electrons H+
Remember the addition of electrons to anything is known as reduction
Carbon Dioxide is reduced to glucose

35. Remember the addition of electrons to anything is known as reduction, thus,
Carbon Dioxide is reduced to glucose
The NADP+ , the ADP and P return to the light stage
to reform NADPH and ATP for the dark stage

36. The Dark Stage C6H1206 ATP ADP + P + ENERGY
NADP+ returns to light stage
ADP + P + ENERGY
The
Dark Stage
NADPH
From light stage
C6H1206
Carbohydrate is formed
CO2 from atmosphere

37. Summary
2 stages
The light dependent stage which converts H2O, NADP+, ADP + P into NADPH, ATP and O2 using chlorophyll and sunlight
The light independent stage which converts CO2 into glucose using NADPH and ATP. This process generates NADP+, ADP + P which can be reused in the light dependent stage

38. Differences between the light and dark stage
LIGHT STAGE DARK STAGE
Occurs in the grana Occurs in stroma
Light dependent Light independent
ATP produced ATP used up
NADPH produced NADPH used up
O2 is produced CO2 is used up
Chlorophyll molecule Chlorophyll not involved
is involved