hello and welcome to another complete Cambridge IGCSE biology lesson where you'll learn absolutely everything you need to know on topic 6.1 photosynthesis as always we'll be following the Cambridge syllabus exactly and we'll cover absolutely everything you need to know if your final exam the topic 6.1 you need to describe and state the word equation for photosynthesis understand the role of chlorophyll understand how the carbohydrates produced by photosynthesis are used and stored and conduct and interpret several experiments relating to photosynthesis for extended you also need to State the balanced chemical equation and explain the limiting factors of photosynthesis all living organisms require food so that they have the raw materials to build new cells and the energy to sustain life animals digest their food and absorb nutrients internally while plants according to the theory of photosynthesis make their own using gases in the air and water and minerals in the soil so photosynthesis is defined as the process by which plants synthesize carbohydrates from raw materials using energy from light the chemical equation which you also need to know states that carbon dioxide and water combine to make glucose and oxygen in the presence of light energy and chlorophyll now chlorophyll is a green pigment found in the chloroplasts of leaf cells and is the substance that transfers energy from light into chemical energy for the synthesis of glucose carbon dioxide diffuses from the air through the stomata of the leaves and water is taken up by the roots and transported through xylem vessels to the leaves in the chloroplast chlorophyll absorbs light energy and uses it to split the water molecules into hydrogen and oxygen the oxygen diffuses out of the leaf and the hydrogen and carbon dioxide combine to form glucose the glucose can then be converted into other molecules like starch cellulose and amino acids next you need to know how the carbohydrates produced are used and stored in plants so the glucose produced through the process of photosynthesis is quickly converted into sucrose which is the food transport molecule of plants so sucrose is transported in phloem vessels to all the parts of the plant that don't photosynthesize like fruits Buds and Roots starch is an energy storage molecule meaning any sugar that isn't needed for respiration or the synthesis of other molecules is converted to starch it's stored within the starch granules of chloroplasts in the cells of stems and roots and in tubers which are specialized organs that hold large starch reserves some of the glucose produced is also used to synthesize a tough fibrous molecule called cellulose which comprises the freely permeable cell walls of plant cells glucose can also be used to provide energy through respiration oxygen which diffuses through the stomata reacts with glucose to release energy and the byproducts carbon dioxide and water finally nectar in flowers is made from a mixture of carbohydrate molecules including glucose fructose and sucrose flowering plants produce nectar and store it to attract insects for pollination now in addition to their requirement for water and carbon dioxide plants also need a supply of certain minerals including nitrogen and magnesium nitrogen ions combine with glucose to make amino acids which are subsequently joined together to build proteins and magnesium is essential for the production of the photosynthetic pigment chlorophyll next you need to know how to conduct and interpret several controlled experiments on photosynthesis including the different factors that make up the chemical equation we learned earlier many of these experiments involve testing for starch which is used as evidence of photosynthesis as it's made from glucose the main product of the process I'll run through the test now so that I don't need to repeat myself later oil some water in a beaker turn off the flame and using forceps dip a leaf into the water for around 30 seconds this breaks down the cells of the leaf and makes it more permeable submerge the leaf in ethanol in a test tube and boil to remove the chlorophyll this makes any change in color easier to see next dip the leaf in hot water to soften it spread it out on a white tile and apply a few drops of iodine solution in the presence of starch iodine changes color from brown to blue black so the parts containing star should be clear to C now that we know how to test the starch let's run through the experiments number one is chlorophyll necessary for photosynthesis for this one a variegated leaf with only patches of chlorophyll is used the white part of the leaf is the experiment as it has no chlorophyll and the green part is the control start by destarching the leaf while it's still on the plant by leaving it in darkness for two to three days or covering the leaf with foil no new sugars will be produced due to the lack of light and any existing starch in the leaf will be turned into sucrose and transported to other parts of the plant after being destarched expose the leaf for several hours you can then remove a leaf draw it carefully so that you have a record of where the chlorophyll is and then test it for starch as only the parts of the leaf containing chlorophyll change color we're able to conclude that chlorophyll is necessary for photosynthesis number two is light necessary for photosynthesis cut a shape from a piece of foil and fix it to a de-starch leaf that's still attached to the plant the cover part is the experiment as it receives no light and the exposed part is the control expose the plant to light for several hours remove the leaf and test for starch by applying iodine the exposed parts will turn blue and the cover parts will remain Brown showing that light is necessary for photosynthesis number three is carbon dioxide necessary for photosynthesis cover two de-starch plants with clear polythene bags place a dish of soda lime in one pot and a dish of sodium bicarbonate in the other plant a is the experiment as sodalime absorbs carbon dioxide and plant B is the control as sodium bicarbonate releases carbon dioxide expose both plants to light for several hours remove a leaf from each and test for starch the leaf that had no carbon dioxide remains Brown showing that no starch was produced and that carbon dioxide is indeed necessary for photosynthesis number four is oxygen produced by photosynthesis how cover an aquatic plant with a funnel in a beaker of water fill a test tube with water place it upside down over the stem of the funnel and expose the plant to light set up a control in the same way and place it in a dark cupboard gas collects in the test tube of the experiment to prove that its oxygen put a glowing splint into the tube and it will reignite number five investigate the effects of light and dark conditions on gas exchange in an aquatic plant clean three boiling tubes with distilled water and fill with hydrogen carbonate indicator solution Place three equal sized pieces of pondweed in tubes one and two and seal all three with Stoppers exposed tubes one and three to light for 24 hours and place tube 2 in a dark cupboard the solution in tube One turns purple indicating that carbon dioxide has been used up through photosynthesis the solution in tube 2 turns yellow indicating a net increase in carbon dioxide this is because carbon dioxide is not being used up by photosynthesis as there's no light while some is being being released as a byproduct of respiration finally the control does not change color showing that it's the plant that caused the solution to change and not some other variable number six investigate the effects of varying light intensity on the rate of photosynthesis mix sodium bicarbonate in a beaker of water to saturate the water with carbon dioxide take a piece of pond weed attached to a paper clip to stop it floating and place in the beaker place a lamp 10 centimeters away from the beaker and count the number of bubbles released by the plant in one minute then move the lamp 20 centimeters away give it some time to adjust to the new light intensity and count the bubbles again repeat this process for at least five distances calculate light intensity at each distance using the following equation and plot your results on a graph we find that more bubbles are released per minute at greater light intensities and this is due to an increase in the rate of photosynthesis number seven investigate the effects of varying temperature on the rate of photosynthesis for this one simply repeat the process for the previous experiment but instead of varying light intensity change the temperature each time by using an ice jacket and a hot plate we find that more oxygen bubbles are released per minute at higher temperatures as photosynthetic enzyme activity goes up as temperature increases number eight investigate the effects of varying carbon dioxide concentration on the rate of photosynthesis attach a syringe to a capillary tube remove the plunger and add two or three pieces of pondweed with the stems facing upwards place a finger over the end of the capillary tube fill the syringe with distilled water and push the plunger down so that no air is trapped and the meniscus and ruler are aligned set up a lamp at a fixed distance from the syringe and after three minutes measure how far the meniscus has moved repeat the process using different concentrations of sodium bicarbonate solution and plot your results on a graph the meniscus moves further at higher concentrations as more carbon dioxide results in a faster rate of photosynthesis and therefore the rate at which which oxygen is released by the plant okay so that's everything you need to know for the core section so we'll move on now to the extended content for extended you also need to be able to State the balanced chemical equation for photosynthesis so six carbon dioxide molecules combined with six water molecules in the presence of light energy and chlorophyll the products are one glucose molecule and six oxygen molecules finally you need to explain the limiting factors of photosynthesis in different environmental conditions so a limiting factor is something present in the environment that limits life processes due to its short supply with regards to photosynthesis any one of the external factors of light intensity temperature and carbon dioxide concentration can limit the effects of the other two for example we would expect photosynthesis to occur faster as light intensity increases however here the curve starts to Plateau suggesting that something other than light is limiting the rate of reaction it could be that there's not enough carbon dioxide in the environment or that 10 temperature is too low for the photosynthetic enzymes to function optimally equally in plants that grow on the forest floor it could be that a lack of light due to the canopy above limits the rate of photosynthesis in farming to reduce the effects of limiting factors on the growth of crops polytunnels or greenhouses are used in which temperatures are higher and carbon dioxide levels can be artificially increased well done you've just covered absolutely everything you need to know on topic 6.1 photosynthesis if you enjoyed this video I'd really appreciate your subscription and I'll see you next time for topic 6.2 Leaf structure