1. PHOTOSYNTHESIS
Topic 3.8
IB Biology
Miss Werba

2. CARBS, LIPIDS & PROTEINS 3.5 TRANSCRIPTION & TRANSLATION
TOPIC 3 - BIOCHEMISTRY
3.1 ELEMENTS & WATER
3.2
CARBS, LIPIDS & PROTEINS
3.3
DNA STRUCTURE
3.4
DNA REPLICATION
3.5 TRANSCRIPTION & TRANSLATION
3.6 ENZYMES
3.7 CELL RESPIRATION
3.8 PHOTOSYNTHESIS
J WERBA – IB BIOLOGY 2

3. THINGS TO COVER Photosynthesis Light & the electromagnetic spectrum
Chlorophyll
Absorption of light by chlorophyll
Light energy & photosynthesis
Synthesis of organic molecules
Measuring rate of photosynthesis
Factors affecting rate of reaction
J WERBA – IB BIOLOGY 3

4. ENERGY CONVERSION Command term = STATE
3.8.1
ENERGY CONVERSION Command term = STATE
Photosynthesis is used by plants and some other organisms (e.g. photosynthetic algae).
Photosynthesis involves the conversion of light energy into chemical energy (ATP)
The synthesis of organic compounds from inorganic sources in the presence of sunlight
J WERBA – IB BIOLOGY 4

5. LIGHT ENERGY Command term = STATE
3.8.2
LIGHT ENERGY Command term = STATE
Light from the Sun is composed of a range of wavelengths (colours)
Remember: ROY G BIV:
Red, Orange, Yellow, Green, Blue, Indigo, Violet
Light contains a range of wavelengths:
shortest - blue ≈ 400nm
longest - red ≈ 700nm
J WERBA – IB BIOLOGY 5

6. CHLOROPHYLL Command term = STATE
3.8.3
CHLOROPHYLL Command term = STATE
Chlorophyll is the main photosynthetic pigment.
It is located in the chloroplasts.
Chlorophyll absorbs light in the light-dependent stage of photosynthesis
There are different types of chlorophyll:
main one = chlorophyll a
When chlorophyll absorbs light energy, it releases electrons which are used to make ATP (chemical energy)
J WERBA – IB BIOLOGY 6

7. ABSORPTION OF LIGHT Chlorophyll absorbs mainly red and blue light
3.8.4
ABSORPTION OF LIGHT
Chlorophyll absorbs mainly red and blue light
Chlorophyll does not absorb (reflects) green light
Explains why most leaves are green
Changes in chlorophyll production responsible for colours of autumn leaves
Absorption spectrum: The spectrum of light absorbed by chlorophyll
Action spectrum: The spectrum of light used for photosynthesis
J WERBA – IB BIOLOGY 7

8. 3.8.4
ABSORPTION OF LIGHT
J WERBA – IB BIOLOGY 8

9. LIGHT-DEPENDENT REACTIONS Command term = STATE
3.8.5
LIGHT-DEPENDENT REACTIONS Command term = STATE
Light energy is required for the first stage of photosynthesis
Light energy is used to:
produce ATP
to split water molecules (photolysis) to form O2 and H+
J WERBA – IB BIOLOGY 9

10. LIGHT-DEPENDENT REACTIONS Command term = STATE
3.8.5
LIGHT-DEPENDENT REACTIONS Command term = STATE
Details:
Light stimulates chlorophyll to release electrons, which results in the production of ATP
Light energy also splits water molecules (photolysis), producing oxygen and hydrogen
The hydrogen is taken up by a hydrogen carrier (NADP+) to form NADPH
The splitting of water also releases electrons, which replace those lost by the chlorophyll
The ATP and hydrogen (NADPH) are taken to the site of the light independent reactions
J WERBA – IB BIOLOGY 10

11. LIGHT-INDEPENDENT STAGE Command term = STATE
3.8.6
LIGHT-INDEPENDENT STAGE Command term = STATE
ATP and hydrogen (from the photolysis of water) are used to fix carbon dioxide to make organic molecules.
J WERBA – IB BIOLOGY 11

12. LIGHT-INDEPENDENT REACTIONS Command term = STATE
3.8.6
LIGHT-INDEPENDENT REACTIONS Command term = STATE
Details:
ATP and hydrogen (carried by NADPH) are products of the light dependent reactions
They are used to fix carbon molecules together (add CO2 to basic carbon compounds)
This allows for the production of more complex organic molecules (e.g. sugars)
These organic molecules can then be stored to use in cellular respiration as required
J WERBA – IB BIOLOGY 12

13. MEASURING PHOTOSYNTHESIS
3.8.7
MEASURING PHOTOSYNTHESIS
Oxygen Production:
Investigate formation of air bubbles from submerged plant
Count number or volume of bubbles in time period
J WERBA – IB BIOLOGY 13

14. MEASURING PHOTOSYNTHESIS
3.8.7
MEASURING PHOTOSYNTHESIS
CO2 Uptake:
pH of water will rise as CO2 is absorbed from water
Investigate pH change in water with submerged plant
J WERBA – IB BIOLOGY 14

15. MEASURING PHOTOSYNTHESIS
3.8.7
MEASURING PHOTOSYNTHESIS
Change in Biomass (indirect):
Investigate weight change in a dehydrated plant
Dehydration ensures the change in biomass reflects a change in organic matter and not water content
Investigate glucose production by determining the change in starch levels in a plant
Starch can be identified via iodine staining and quantified using a colorimeter
J WERBA – IB BIOLOGY 15

16. LIMITING PHOTOSYNTHESIS
3.8.8
LIMITING PHOTOSYNTHESIS
J WERBA – IB BIOLOGY 16

17. LIMITING PHOTOSYNTHESIS
3.8.8
LIMITING PHOTOSYNTHESIS
Temperature:
Enzymes controlling photosynthesis are temperature sensitive
Increase temp  faster reaction - until enzymes denature
J WERBA – IB BIOLOGY 17

18. LIMITING PHOTOSYNTHESIS
3.8.8
LIMITING PHOTOSYNTHESIS
Light Intensity:
More light, more photosynthesis
Rate will plateau eventually when enzymes are working at maximum efficiency
Different wavelengths of light will have different effects on the rate of photosynthesis
J WERBA – IB BIOLOGY 18

19. LIMITING PHOTOSYNTHESIS
3.8.8
LIMITING PHOTOSYNTHESIS
CO2 Concentration:
Increase [CO2]  increase rate
Rate will plateau eventually when enzymes are working at maximum efficiency
J WERBA – IB BIOLOGY 19

20. Sample questions
Q1. Which type of light is least useful for photosynthesis in terrestrial plants? A. Blue B. Green C. White D. Red
J WERBA – IB BIOLOGY 20

21. Sample questions
Q2. A plant is exposed to increasing light intensity from very dim to bright light, while the carbon dioxide concentration and temperature are kept at an optimum level. What will happen to the rate of oxygen production? A. It will increase exponentially. B. It will remain constant. C. It will decrease to a minimum level. D. It will increase to a maximum level.
J WERBA – IB BIOLOGY 21

22. Sample questions
A1. B
A2. D
J WERBA – IB BIOLOGY 22

23. Sample questions
Q3. Outline how light energy is used and how organic molecules are made in photosynthesis.
(6 marks)
J WERBA – IB BIOLOGY 23

24. Sample questions A3. chlorophyll is the (main) photosynthetic pigment;
absorbs (mainly) red and blue light;
green light is reflected;
light energy absorbed is converted into chemical energy;
ATP produced;
water split;
to form oxygen and hydrogen;
ATP and hydrogen used to fix carbon dioxide to make organic molecules;
J WERBA – IB BIOLOGY 24