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IB Biology HL Unit 2 Notes
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In-depth notes on IB Biology HL Unit 2 (2.1 to 2.9). Many sources are integrated into one set of notes to prepare for any exam questions!
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2.9 PhotosynthesisObjectives:
❏ Understanding:
❏ Photosynthesis is the production of carbon compounds in cells using light energy
❏ Visible light has a range of wavelengths with violet the shortest wavelength and red the longest
❏ Chlorophyll absorbs red and blue light most effectively and reflects green light more than other
colours
❏ Oxygen is produced in photosynthesis from photolysis of water
❏ Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide
❏ Temperature, light intensity and carbon dioxide concentration are possible limiting factors on
the rate of photosynthesis
❏ Applications:
❏ Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis
❏ Skills:
❏ Design of experiments to investigate limiting factors on photosynthesis
❏ Separation of photosynthesis pigments by chromatography
❏ Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis
❏ Nature of Science
❏ Experimental design: controlling relevant variables in photosynthesis experiments is essential
Photosynthesis:
- Photosynthesis = the process by which cells synthesise organic compounds (e.g. glucose) from inorganic
molecules (CO2 and H2O) in the presence of sunlight
- Reverse of cell respiration (catabolic breakdown)
- Energy conversion (light energy to chemical energy in carbon compounds)
- Requires a photosynthetic pigment (chlorophyll)
- Use light energy from the sun the create chemical energy (ATP)
- Energy used either:
- Directly by organism
- Used to synthesise organic compounds (e.g. glucose)
- Animals consume the organic compounds as food and release stored energy via cell respiration
, Chloroplasts:
- Plants have evolved a specialised organelle responsible for photosynthesis - chloroplasts
- Contains membrane sacs (thylakoids) arranged into stacks (grana)
- Membrane sacs contain chlorophyll (site of light dependent reactions)
- Surrounding fluid matrix is called stroma and contains carbon fixating enzymes
- Site of light independent reaction
Practical 4: Separating photosynthetic pigments by chromatography:
- Chromatography = experimental technique by which mixtures can be separated
- Mixture dissolved in a fluid (mobile phase) and passed through a static material (stationary phase)
- The different components of the mixture travel at different speeds (causing them to separate)
- Retardation factor can be calculated
- Rf value = distance component travels / distance solvent travels
- Two most common techniques for separating photosynthetic pigments:
1. Paper chromatography
a. Uses paper (cellulose) as stationary bed
2. Thin layer chromatography
a. Uses thin layer of adsorbent (e.g. silica gel)
b. Runs faster
c. Has better separation
- Photosynthetic organisms do not rely on a single pigment to absorb light (benefit from the combined action
of many)
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