2.9: Photosynthesis
Teaching time: 3 hours Practical time: 1 hour
key vocabulary
Prior learning and retrieval practice
Review 2.1 molecules to metabolism
Review 2.3 Carbohydrates & Lipids
Photosyntheis introduction
Essential idea: Photosynthesis uses the energy in sunlight to produce the chemical energy needed for life.
U1: Photosynthesis is the production of carbon compounds in cells using light energy.
Exercise 1: Watch the video and connect-extend-challenge
A1: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.
Exercise 2: Read the relevant section of your of your textbook and connect-extend-challenge.
Outline how earth's atmosphere, oceans and rock depositions changed due to photosynthesis
The light spectrum
U2: Visible light has a range of wavelengths with violet the shortest wavelength and red the longest. Guidance from the syllabus: Students should know that visible light has wavelengths between 400 and 700 nanometres, but they are not expected to recall the wavelengths of specific colours of light.
Exercise 3: Answer these questions:
What is the range of wavelengths that visible light is composed of?
How many meters is one nm?
What colours do the longest and shortest wavelengths correspond to?
S1: Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
Exercise 4: Draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
The process of photosynthesis
U3: Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.
U4: Oxygen is produced in photosynthesis from the photolysis of water.
U5: Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
Exercise 5: Explain the the process of photosynthesis with reference to chlorophyll, photolysis, light independent and light dependent reactions
Factors affecting photosynthesis
U6: Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.
Exercise 6: Explain how each of the above limiting factors effects photosynthesis. What do we mean by the term limiting?
Photosynthetic investigations
S2: Design of experiments to investigate the effect of limiting factors on photosynthesis.
NoS: Experimental design—controlling relevant variables in photosynthesis experiments is essential. (3.1)
Exercise 7: Design an experiment to investigate the effect of one limiting factor on photosynthesis
Guidance from the syllabus: Water free of dissolved carbon dioxide for photosynthesis experiments can be produced by boiling and cooling water.
Separating photosynthetic pigments (practical 4)
S3: Separation of photosynthetic pigments by chromatograph. (Practical 4)
Paper chromatography can be used to separate photosynthetic pigments but thin layer chromatography gives better results.
