1 CfE Higher Biology 3.1b(i) Photosynthesis

2 Key areas: 3.1b Plant growth i) Photosynthesis ●Photosynthesis captures light energy to produce carbohydrates. ●Fates of light that are not absorbed by a leaf. ●Absorption and action spectrums and the roles of pigments. ●Energy capture and photolysis. ●The process of carbon fixation (Calvin Cycle) ii) Plant productivity ●Net assimilation is the increase in dry mass of a plant due to photosynthesis minus the loss from respiration. ●Productivity is the rate of generation of new bio as per unit area of leaf per unit of time. ●Biological yield of a crop is the total plant biomass produced. ●Economic yield is the mass of the desired product. ●Harvest index is calculated by dry mass of the economic yield /dry mass of biological yield.

3 Photosynthesis The process in which green plants trap light energy and use it to make carbohydrates. When this light energy strikes the pigments in green plants it can be: 1. Absorbed 2. Reflected 3. Transmitted This light is known as 'visible light' on the radiation spectrum. The narrow band of wavelengths that it covers can range from 380 nm nm

4 PHOTOSYNTHESIS Most of the light will be absorbed, but it is not all used for photosynthesis. Some will be lost through: 1. RADIATION 2. HEAT Sunlight 100% Absorbed Transmitted 5% Reflected 15%

5 The spectrum of visible light Philip Ronan/Wikimedia Commons

6 Absorption Spectrum A spectrometer can be used to measure the the absorption of each wavelength of light by the pigments found in green plants. Chlorophyll a & b absorb mainly blue and red light. The other pigments and sometimes known as 'accessory pigments' as they absorb other colours of light and pass the energy on to chlorophyll. Reference image: ass/bio1151/Locked/media/ch10/10 _09PhotosynthWavelength.jpg ass/bio1151/Locked/media/ch10/10 _09PhotosynthWavelength.jpg

7 The action spectra shows how effective different wavelengths of light are being used in photosynthesis. This ability of a plant to use all these wavelengths of light in some way is crucial. Action Spectrum Reference image: hysiology/images/actabs.gif hysiology/images/actabs.gif

8 Practical opportunities Investigation the action spectra of photosynthesis. Extraction and separation of leaf pigments using thin layer chromatography.

9 Now use your results to calculate the Rf Value Reference image: s/img51.jpg s/img51.jpg

10 Chloroplasts Chloroplasts are found in many green plants and algae. The are surrounded by a double membrane Inside this membrane is a central space called the stroma containing many important enzymes for photosynthesis. The stroma also contains grana which contain the photosythetic pigments in a large surface area for light absorption. Lamellae are the network of membranes that run between the grana

11 Photolysis Photolysis occurs in the grana. This is the first stage of photosynthesis and is often know as the light dependant stage. Once the light energy is absorbed it is converted to chemical energy The light energy splits a molecule of water into; 1. Hydrogen 2. Oxygen The oxygen is released back into the atmosphere (diffusion) The hydrogen can not be left on it ’ s own, so it combines with a hydrogen acceptor NADP. Once this happens it is known as the ‘ reduced hydrogen acceptor ’ or NADPH 2

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13 Carbon Fixation/ Calvin Cycle RuBisCO is an enzyme that 'fixes' carbon dioxide in the Calvin Cycle. This carbon dioxide enters the cycle and attaches to RuBP. The product formed from this reaction is G3P (glyceraldehyde-3- phosphate) G3P Can be converted into glucose Can be regenerated into RuBP Can be synthesised into STARCH or CELLULOSE

14 The Calvin Cycle By Mike Jones (Own work) [CC BY-SA 3.0 ( or GFDL ( via Wikimedia Commons

15 The rate of Photosynthesis Oxygen is released from photosynthesis as a by-product. The rate of oxygen production can be used to determine the rate of photosynthesis by counting the number of bubbles released. This is the easiest method, but you could also use ….. 1.Uptake of carbon dioxide 2.Production of Carbohydrate It is important to understand that photosynthesis is affected by : LIGHT INTENSITY TEMPERATURE CARBON DIOXIDE CONCENTRATION