B8 Photosynthesis

• chlorophyll is the green pigment in plants that absorbs light energy, so if a plant has less it wont be able to carry out as much photosynthesis. the level of chlorophyll in a plant can vary because of diseases like tobacco mosaic virus
• as light intensity increases, the rate of photosynthesis increases only until a certain point, hence why the graph we draw will increase and then plateau
• carbon dioxide levels also affect the rate of photosynthesis, as carbon dioxide is a reactant for photosynthesis, there more we have the higher the rate can be, but after a while the graph will plateau because something else will become the limiting factor
• the graph for temperature shows that an increase in temperature also increases the rate of photosynthesis because enzymes can work more quickly and molecules have more energy but only until a certain point. at a temperature too high (normally about 41 degrees) will cause the enzymes to denature so the rate will start to decrease
• leaves on plant adapt to maximise the rate of photosynthesis. most leaves have a large surface area for light to fall on, they are thin so the diffusion distances for gases are short, they contain chlorophyll in the chloroplasts to absorb light, they have guard cells that regulate gas exchange
• green plants and algae use light energy to make there own food in a process called photosynthesis.
• a plant needs carbon to dioxide, waer and light for photosynthesis to occur and makes glucose and oxygen as a result of photosynthesis so the word equation is carbon dioxide + water + (light) ---> glucose + oxygen (energy)
• photosynthesis takes place inside the chloroplasts because chloroplasts contain a green substance call chlorophyll which traps the light needed to make photosynthesis happen. this means that plants and algae can only carry out photosynthesis in the light
• photosynthesis is so important because without without it we wouldn't have food because it converts energy from the sun into chemical energy and photosynthesis also keeps the levels of carbon dioxide and oxygen balanced
• adaptations of leaves for photosynthesis include being thin, this provides a short diffusion distance for carbon dioxide to move into the leaf, they have large surface areas so maximise absorption, they contain chlorophyll to trap light.
• more adaptations of the leaf include having stomata which are small holes on the underside of the leaf that allow carbon dioxide and oxygen to move in and out of the leaf by diffusion, they have guard cells which open and close the stomata depending on the conditions and they have a network of tubes to transport water and food
• light intensity affects the rate of photosynthesis because without enough light the plant cannot photosynthesise quickly, to show this on a graph the rate of photosynthesis would increase then flatten out when another factor becomes too limited
• if the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase, the graph for this looks the same as the light intensity graph
• photosynthesis is an enzyme controlled reaction, this means that if the temperature is increased too much the enzymes will denature, causing the rate of photosynthesis to slow down
• chlorophyll absorbs the light energy required to convert carbon dioxide and water into glucose, chlorophyll is green so absorbs the red and blue parts of the electromagnetic spectrum
• the compensation point is when the rate of photosynthesis = the rate of respiration
• REQUIRED PRACTICAL

  1. set up a boiling tube containing 45cm of sodium hydrogencarbonate, allow the tube to stand and shake to remove any bubbles that could've formed
  2. cut a piece of pondweed of 8cm long and place in tube carefully
  3. position light source 10cm away from the light and then count the amount of bubbles that form
  4. calculate average per minute and repeat with different distances of light, then compare
• variables for the required practical are:

  independant = distance from light source

  dependant = the number of bubbles produced per minute

  control variables = concentration of sodium hydrogencarbonate, length of pondweed, type of pondweed, volume of sodium hydrogencarbonate
• plants use light for their source of energy, the reaction that plants use to utilise this light is called photosynthesis. because photosynthesis takes in energy, it is an endothermic reaction
• photosynthesis takes place in the leaves of the plant. leaves contain the green chemical chlorophyll, chlorophyll absorbs the light energy.
• in the first stage of photosynthesis. the plant takes in carbon dioxide and water into the leaf, light energy is the absorbed by chlorophyll. the light energy is then used to convert the carbon dioxide and water into the sugar glucose, oxygen is also produced
• if we increase the light intensity and the rate rate of photosynthesis also increases, this tells us that the light intensity was the limiting factor. photosynthesis was not as fast as it could've been because there was not enough light
• if we keep increasing the light intensity, there comes a point where the rate of photosynthesis no longer increases. this tells us that light intensity is no longer the limiting factor and something else is in short supply e.g. carbon dioxide in the air.
• the graph for the effects of carbon dioxide is the same shape as the light intensity graph
• as we increase carbon dioxide levels in the air, the rate of photosynthesis increases and it is the limiting factor. until the rate stops, and the limiting factor becomes something else
• leaves with patches of colour on them e.g. rose black spot, will have a lower rate of photosynthesis because they can trap less light energy than normal leaves
• as temperature increases, enzymes work at a higher rate. until a certain temperature, where the enzymes denature so the rate of photosynthesis decreases
• in photosynthesis, carbon dioxide and water are chemically reacted using the energy from light
• glucose from photosynthesis can be used to release energy in respiration. glucose is only produced in the day when there is light, but plant cells respire all the time, including at night
• glucose produced by photosynthesis is to produce the insoluble storage molecule starch. the starch can be converted back into glucose by the plant when it is needed e.g. at night
• glucose from photosynthesis can also be converted into fats and oils. fats and oils are used by the plant as a storage form of energy
• plant cells are enclosed in a cell wall, cell walls contain the molecule cellulose which give the cell strength. this cellulose is made from the glucose produced by photosynthesis
• glucose produced in photosynthesis is used to produce amino acids. amino acids are used by the plant to synthesise proteins
• to make amino acids from glucose, plants need to absorb nitrate ions from the soil
• limiting factors of photosynthesis include carbon dioxide concentration, the temperature, light intensity and chlorophyll in the leaves.
• when the concentration of carbon dioxide increases, the rate of photosynthesis increases, telling us that carbon dioxide concentration was the limiting factor
• farmers aim to increase the rate of photosynthesis as this increases the yield of the crops they produce. to do this they light and heat their greenhouses, and add extra carbon dioxide. this can be expensive so the extra cost has to be justified by the increase in yield
• some gardeners use oil burners as they release heat and carbon dioxide at the same time
• a limiting factor is one that when increased, increases the rate of reaction