C astlehead H igh S chool Photosynthesis Intermediate 2 How plants make food

C astlehead H igh S chool What is photosynthesis? The word photo means light and synthesis means to build up The word photo means light and synthesis means to build up Photosynthesis is the process whereby green plants make glucose Photosynthesis is the process whereby green plants make glucose

C astlehead H igh S chool What does the plant need ? For photosynthesis to take place a plant needs For photosynthesis to take place a plant needs Carbon dioxide from the air Carbon dioxide from the air Light from the sun Light from the sun Water from the soil Water from the soil Chlorophyll from the leaves Chlorophyll from the leaves

C astlehead H igh S chool Testing for photosynthesis We can check for evidence of photosynthesis by testing a leaf for starch. We can check for evidence of photosynthesis by testing a leaf for starch. 1. Boil the leaf in water (bursts cells) 2. Boil the leaf in alcohol (removes chlorophyll) 3. Dip leaf in hot water (softens the leaf) 4. Put leaf in iodine solution (turns blue black if starch is present)

C astlehead H igh S chool Test for Starch Boil for 1 MinuteWarm in Ethanol Testing a leaf for Starch Wash in Water

C astlehead H igh S chool Testing your knowledge A variegated leaf is covered with a strip of metal foil then the leaf is tested for starch. Which diagram shows the correct result. A variegated leaf is covered with a strip of metal foil then the leaf is tested for starch. Which diagram shows the correct result. Metal foil Blue Black Starch present Orange No Starch present A BCD

C astlehead H igh S chool Word Equation for Photosynthesis Carbon Dioxide +WaterGlucose+Oxygen CO 2 H2OH2OC 6 H 12 O 6 O2O2 Light energy Raw MaterialsProducts

C astlehead H igh S chool Stages of Photosynthesis 1st Stage - PHOTOLYSIS 1st Stage - PHOTOLYSIS Light energy Absorbed by Chlorophyll WATER ADP + Pi ATP HYDROGEN + OXYGEN Only HYDROGEN and ATP go on to the second stage

C astlehead H igh S chool 2 nd Stage Carbon Fixation HYDROGEN ATP ADP + Pi GLUCOSE Starch Cellulose + CARBON DIOXIDE (from the air)

C astlehead H igh S chool Glucose What happens to the glucose? Cellulose made up of parallel chains of glucose to form tough fibres used to make cell walls For energy in respiration Starch made up of coiled chains of glucose to form starch grains. Can be converted back when glucose is needed by plant.

C astlehead H igh S chool Limiting Factors Carbon Dioxide Concentration - Carbon Dioxide Concentration - Less Carbon Dioxide means less glucose can be made. Light Intensity - More light means more energy Temperature - Temperature - Warmth increases the rate that enzymes work, however, high temperature denatures enzymes. Low temperatures slow reactions. If any of these are in short supply, they cut down or LIMIT the rate of photosynthesis.

C astlehead H igh S chool Measuring the rate of photosynthesis

C astlehead H igh S chool Rate of Photosynthesis If we move the lamp back and forwards we can change the light intensity

C astlehead H igh S chool Light Intensity Rate of Photosynthesis Light Intensity CO 2 readily available and warmth If light is increased photosynthesis will increase up to a certain point. After this something else becomes the limiting factor e.g. CO 2

C astlehead H igh S chool Limiting Factors Level of CO 2 What is the limiting factor at point X? What is the limiting factor at point Y? X Y Rate of Photosynthesis

C astlehead H igh S chool More to do! Go to Go to and do lesson numbers and do lesson numbers 49. Photosynthesis 50. The Role of the Leaf in Photosynthesis 51. Rate of Photosynthesis 52. Testing a Leaf for Starch 53. Experiments to see if Chlorophyll and Light are Needed to Make Starch 54. The Uses of Glucose 49. Photosynthesis 50. The Role of the Leaf in Photosynthesis 51. Rate of Photosynthesis 52. Testing a Leaf for Starch 53. Experiments to see if Chlorophyll and Light are Needed to Make Starch 54. The Uses of Glucose