Higher Biology Photosynthesis Mr G Davidson

Pigments and Light White light is a form of radiant energy it travels in the form of waves. These waves always travel in straight lines. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Pigments and Light White light can be split into its coloured component if it is passed through a glass prism: Red Orange Yellow Green Blue Indigo Violet. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Pigments and Light Each colour of the spectrum has a different wavelength The wavelength of light is measured in nanometres (nm) 1 nm = 10-9m (1/1,000,000,000th metre) red the longest – around 700 nm violet the shortest – around 400 nm Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Photosynthesis Visible white light from the sun is the source of energy for photosynthesis. Pigments in the leaf absorb light Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Photosynthesis When it strikes a green leaf light is absorbed by these pigments A small percentage of this is used in photosynthesis. The remainder of the light is either reflected from the leaf or transmitted through the leaf. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Photosynthesis Most leaves are green because they reflect green light and transmit green light. Each of the pigments present in a leaf absorbs light of certain wavelengths therefore if a plant has different pigments, it can absorb a wider range of wavelengths of light. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Absorption Spectrum Wavelength (nm) Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Photosynthesis The pigments found in plants depend largely on where the plant is to be found e.g. shady plants need more pigment than canopy plants Different sea weeds have a different range of pigments because of the reducing light intensity at greater depths of water. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Fate of Light Striking a Leaf 100 % Sunlight 83 % absorbed 5 % transmitted 12 % reflected Only a small percentage of absorbed light is used in photosynthesis Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Chloroplasts Granum Double unit membranes Lamella Stroma Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Chloroplast Structure Function Double unit membrane Enclose contents Granum Site of light dependent phase Stroma Site of carbon fixation Lamella Connect grana Starch grains Food Store Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Chloroplasts The light trapping pigments are to be found in the chloroplasts of plant cells. Chloroplasts are relatively large organelles found in the cytoplasm, each one surrounded by a double unit membrane. Inside the chloroplast are large starch grains which act as food stores. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Chloroplasts The main components of the chloroplast are grana which are interconnected by lamellae. The grana are composed of flattened discs containing the pigments, and are the site of the light reaction. The stroma is the site of carbon fixation and is the fluid part in the chloroplast. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Chemistry of Photosynthesis In the process of photosynthesis, raw materials carbon dioxide and water are assembled to make organic food molecules producing oxygen as a waste product. Carbon dioxide CO2 oxygen O2 glucose C6H12O6 Light Pigments water H2O Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Chloroplasts Photosynthesis occurs in two stages. The first stage requires light and is called the light reaction or photolysis. The second stage is a temperature dependent series of enzyme controlled reactions called carbon fixation or the Calvin Cycle. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Photolysis This is the trapping of sunlight energy by photosynthetic pigments to release chemical energy. The light energy splits water into hydrogen and oxygen, the oxygen then being released as a by-product. The hydrogen then combines with a hydrogen acceptor NAD to produce NADH2. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Photolysis At the same time, energy is also made available to convert ADP + Pi into the high energy molecule ATP. This is a process known as photophosphorylation. The NADH2 and ATP made by photolysis are passed to the carbon fixation stage. Photolysis occurs on the grana of the chloroplasts. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Photolysis NADH2 Carbon Fixation CO2 Sugar Water Photo- phosphorylation ATP Photolysis Sunlight Oxygen Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Calvin Cycle This is also referred to as carbon fixation. This stage is a series of enzyme controlled chemical reactions in the form of a cycle. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Calvin Cycle As the carbon dioxide enters carbon fixation, it combines with a 5 carbon ribulose biphosphate (RuBP) to form an unstable 6 carbon compound which immediately splits into two molecules of 3 carbon glycerate phosphate. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Calvin Cycle Glucose 5C 1C 3C 6C Triose phosphate Glycerate phosphate ATP ADP + Pi NAD NADH2 Triose phosphate Glycerate phosphate 6 Carbon compound CO2 RuBP Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Calvin Cycle Two molecules of glycerate phosphate are then converted via a triose phosphate into 6C sugar, using hydrogen and energy – both provided by photolysis. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Calvin Cycle Two molecules of triose phosphate are then used to make one molecule of 6 carbon glucose, which are then built to form starch or cellulose. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Calvin Cycle Not all triose phosphate molecules are used to make sugar, some are required to continue the cycle i.e. take it back to RuBP. In doing this 5 molecules of 3 carbon triose phosphate become 3 molecules of 5 carbon RuBP using energy from ATP and so the Calvin cycle is allowed to continue. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Limiting Factors Chemical reactions such as photosynthesis can be speeded up or slowed down depending on certain conditions. A condition which is able to limit the rate of a reaction is usually called a limiting factor. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Elodea Bubbler In the Elodea bubbler experiment we can alter light intensity, CO2 concentration and temperature, one at a time to show that they are all limiting factors. The rate of photosynthesis is measured by counting the bubbles of oxygen released in a specific time. Monday, 19 November 2018Monday, 19 November 2018 G Davidson

Elodea Bubbler 0.5% solution of sodium bicarbonate to provide a supply of CO2 Constant temperature Monday, 19 November 2018Monday, 19 November 2018 G Davidson