1. Photosynthesis (2.9) IB Diploma Biology
Essential Idea: Photosynthesis transforms light energy into chemical potential energy that can be used by organisms

2. 2.9.1 Photosynthesis is the production of carbon compounds in cells using light energy.
Transformation of Light energy (sunlight) into Chemical energy (carbon compounds)

3. The LIGHT DEPENDENT Reactions
2.9.4 Oxygen is produced in photosynthesis from photolysis of water.
Photosynthesis occurs in two main stages in the chloroplasts of plant cells
In the first stage, light energy is used to split (lyse) water into oxygen and hydrogen and make some ATP
Oxygen gas is released into the atmosphere and Hydrogen atoms and ATP are the used to provide energy for the second stage of reactions
The LIGHT DEPENDENT Reactions

4. The LIGHT INDEPENDENT Reactions
2.9.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
In the second stage, energy from ATP and Hydrogen is used to transform Carbon dioxide into Carbohydrates
FUN FACT: The average tree absorbs 50 lbs of CO2 per year. Giant Redwoods can fix more than one TON of carbon in their lifetimes
Process known as Carbon Fixation
The enzyme Rubisco catalyzes this reaction series
The LIGHT INDEPENDENT Reactions
(aka the Calvin Cycle)

5. 2.9.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
Light Independent reactions occur in the Stroma
Light Dependent reactions occur in the Thylakoids

6. 2.9.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.

7. 2.9.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.

8. 2.9.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
Starch granules

9. 2.9.5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.

10. 2.9.2 Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.

11. 2.9.3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colors.

12. 2.9.3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colors.

13. 2.9.10 Draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

14. 2.9.10 Draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

15. 2.9.10 Draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

16. 2.9.10 Draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

17. Photosynthetic Pigments
When light meets matter, it may be reflected, transmitted, or absorbed. A pigment is a substance which absorbs specific wavelengths of visible light and reflects others.
Different pigments absorb photons of different wavelengths.
A leaf looks green because chlorophyll, the dominant pigment, absorbs red and blue light, while transmitting and reflecting green light.

18. Photosynthetic Pigments
Chlorophyll a, the primary photosynthetic pigment, absorbs best in the red and blue wavelengths, and least in the green. (green in color)
Chlorophyll b, with a slightly different structure than chlorophyll a, has a slightly different absorption spectrum (but also red and blue) and funnels the energy from these wavelengths to chlorophyll a. (green in color)
Carotenoids can funnel the energy from other wavelengths to chlorophyll a and also participate in photoprotection against wavelengths of light (ultraviolet) that could possibly damage the plant cells. (Yellow, orange, red in color)
Xanthophylls are another type of pigment which are involved in light absorption. (Red in color)
**Note- Chlorophyll b, the Cartotenoids and Xanthrophylls are known as accessory pigments, which absorb other wavelengths of light that Chlorophyll a cannot.

19. 2.9.9 Separation of photosynthetic pigments by chromatography.
Chromatography is an method of separating out different pigment molecules based on their solubility
It can be used to separate and distinguish chlorophyll and other accessory pigments, such as carotene and xanthophyll

20. 2.9.6 Temperature, light intensity, and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

21. 2.9.6 Temperature, light intensity, and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

22. 2.9.6 Temperature, light intensity, and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

23. 2.9.6 Temperature, light intensity, and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

24. 2.9.6 Temperature, light intensity, and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

25. 2.9.8 Design experiments to investigate limiting factors on photosynthesis.

26. 2.9.8 Design experiments to investigate limiting factors on photosynthesis.

27. Placing the plant in a closed space with water.
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Placing the plant in a closed space with water.
CO2 reacts with the water producing bicarbonate and hydrogen ions, which increases the acidity of the solution. Increased CO2 uptake -> increased pH -> increased rate of photosynthesis.

28. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Aquatic plants can submerged in water in a closed space with a gas syringe attached. Alternatively gas volume can be measured by displacing water in an inverted measuring cylinder or by simply counting bubbles.
Oxygen probes can be used with terrestrial plants kept in closed environments to measure increases in oxygen concentration.

29. starch levels in a plant (glucose is stored as starch)
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Glucose production can be (indirectly) measured by a change in a plant's dry biomass.
starch levels in a plant (glucose is stored as starch)
can be identified by staining with iodine solution, this can be quantitated using a colorimeter.

30. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?

31. The independent variable
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
The independent variable
Only one limiting factor should be investigated at a time
The range of values should reflect conditions experienced by the organism
The range of values should allow the limiting factor to range from values that restrict photosynthesis to values that allow photosynthesis to happen at it’s optimum rate.
The increments should be sufficiently in size that a trend can be clearly detected

32. Oxygen production per time unit is recommended.
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
Dependent variable
An accurate method for measuring the rate of photosynthesis needs to be used.
Oxygen production per time unit is recommended.
Leaf discs are a successful and easy way to measure oxygen generation by leaves

33. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
The control variables
These should include the limiting factors not being investigated.
Other key control variables should include any factor that affects a metabolic pathway controlled by enzymes, e.g. pH.
Ambient light should be considered as it affects the wavelength and intensity of light absorbed by the organism.
The values chosen for the control variables should be close to their optimum values so that the control variables do not limit photosynthesis. (If the control variables limit photosynthesis it may not be possible to see the impact of the limiting factor being investigated)

34. The control variables - Nature of Science
Nature of Science: Experimental design - controlling relevant variables in photosynthesis experiments is essential. (3.1)
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
The control variables - Nature of Science
Explain why it is essential to control the limiting factors not being investigated.
Evaluate which of the identified reasons are the most important.

35. Iron compounds in the oceans were oxidized:
2.9.A1 Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.
Primordial Earth had a reducing atmosphere that contained very low levels of oxygen gas (approx. 2%).
 Cyanobacteria (prokaryotes) containing chlorophyll first performed photosynthesis about 2.5 billion years ago.
Photosynthesis creates oxygen gas as a by-product (by the photolysis of water).
Oxygen levels remained at 2% until about 750 million years ago (mya). From 750 mya until the now there has been a significant rise to 20%.
Oxygen generation also allowed the formation of an ozone layer (O3). Ozone shielded the Earth from damaging levels of UV radiation. This, in turn, lead to the evolution of a wider range of organisms.
Iron compounds in the oceans were oxidized:
The insoluble iron oxides precipitated onto the seabed.
Time and further sedmentation has produced rocks with layers rich in iron ore called the banded iron formations.
Oxygen in the atmosphere lead to the production of oxidised compounds (e.g. CO2) in the oceans.

36. Known as the Great Oxidation Event
2.9.7 Changes to the Earth’s atmosphere, oceans, and rock deposition due to photosynthesis.
Early Earth’s reducing atmosphere contained negligible amounts of oxygen. The first prokaryotes emerged around 3.5 BYA, but it wasn’t until about 2.2 BYA that oxygen levels rose to 2%.
Known as the Great Oxidation Event
Thanks, Photosynthesis!!

37. 2.9.7 Changes to the Earth’s atmosphere, oceans, and rock deposition due to photosynthesis.
Thanks, Photosynthesis!
Oxygen rise caused drops in Methane and CO2 (GHGs!) which corresponded with Earth’s first glaciation. BRRR!

38. 2.9.7 Changes to the Earth’s atmosphere, oceans, and rock deposition due to photosynthesis.
Corresponding oxidation of dissolved iron in the oceans allowed iron ore to precipitate, forming bands across the seafloor and providing a source of iron and steel to this day
Thanks, Photosynthesis!

39. 2.9.7 Changes to the Earth’s atmosphere, oceans, and rock deposition due to photosynthesis.
Thanks, Photosynthesis!
…and Aerobic Respiration!
Oxygen rise to 20% atmospheric concentration around MYA allowed for the “Cambrian Explosion” of multicellular speciation

40. Bibliography / Acknowledgments
Jason de Nys
Chris Paine