B4-Bioenergetics

• What does photosynthesis use energy for?

  Uses energy to change carbon dioxide and water into glucose and oxygen.
• Where does photosynthesis happen?

  -In chloroplasts-green plant cells which contain pigments like chlorophyll that absorb light

  -Energy is transferred to the chloroplasts from the environment by light.
• Is photosynthesis exothermic or endothermic?

  Photosynthesis is endothermic since energy is transferred from the environment in the process.
• What is the word equation

  Carbon dioxide + water --light--> glucose + oxygen
• What is the symbol equation for

  6CO2 + 6H2O ------> C6H12O6 + 6O2
• What do plants use glucose?

  1. for respiration

  2. making cellulose

  3. making amino acids

  4. stored as oils or fats

  5. stored as starch
• How do plants use glucose for respiration?

  This transfers energy from glucose which enables the plants to convert the rest of the glucose into various other useful substances
• How do plants use glucose to make cellulose?

  Glucose is converted into cellulose for making strong plant cell walls
• How do plants use glucose to make amino acids?

  Glucose is combined with nitrate ions to make amino acids, which are then made into proteins
• How do plants store glucose as oils and fats?

  Glucose is turned into lipids for storing in seeds
• How do plants store glucose as starch?

  Glucose is turned into starch and stored in the roots, stems and leaves, ready for use when photosynthesis isn't happening, like in the winter.
• Why is starch better for storage than glucose?

  -It is insoluble which makes it better than glucose for storage.

  -A cell with glucose would draw in water and cause cells to swell.
• What are the factors affecting the rate of photosynthesis?

  -Light intensity

  -CO2 concentration

  -Temperature
• What is a limiting factor in terms of photosynthesis?

  Could be any out of temperature,CO2 concentration levels and light intensity-which just means its stopping photosynthesis from happening any faster.
• How do we know which factor is limiting at a particular time?

  We look at the environmental conditions-

  -At night its pretty obvious that light is the limiting factor.

  -In winter, often the temperature

  -IF it is warm enough and bright enough it is often the CO2 concentration which is limiting.
• What can also be a limiting factor of photosynthesis besides the big 3?

  -Chlorophyll-The amount of chlorophyll in a plant can be affected by disease (e.g infection with the tobacco mosaic virus) or environmental stress such as lack of nutrients.

  -These factors can cause chloroplasts to become damaged or to not make enough chlorophyll.

  -This means the rate of photosynthesis is reduced because they cant absorb as much light.
• Describe the graph of the effect of light on photosynthesis

  -Light provides energy needed for photosynthesis

  -As the light level is raised,the rate of photosynthesis increases steadily but only up to a certain point.

  -Beyond that,it won't make much difference-as light intensity increases, the rate will no longer increase-this is because it'll be either the temperature or the CO2 level which is not the limiting factor, not the light.
• How can we change the light intensity in a lab?

  Changed by moving a lamp closer to or further away from your plant.
• How do we get the right graph results from the experiment of light intensity?

  measure the light intensity using a light metre or do some maths with results.
• Describe the graph of the effect of CO2 concentration on photosynthesis

  -CO2 is one of the raw materials needed for photosynthesis

  -As with light intensity, the amount of CO2 will only increase the rate of photosynthesis up to a point.

  -After thistle graph flattens out as the amount of CO2 increases, the rate no longer increases.This shows that CO2 is no longer the limiting factor
• Describe the graph of the effect of temperature on photosynthesis


  -Usually, if the temperature is the limiting factor it is because it is too low-the enzymes needed for photosynthesis work are slowly at low temperatures.

  -But if the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be damaged.

  -This is because at around 45 degrees
• Describe a graph where both light intensity and temperature affect the rate of photosynthesis


  -At the start, both of the lines show that as the light intensity increases, the rate of photosynthesis, increases steadily.

  -But the lines level off when light is no longer the limiting factor.

  -The line at a higher temperature levels off at a higher point than the one at 15 degrees showing that temperature must have been a limiting factor at 15 degrees.
• Describe a method of using Canadian pondweed to measure the effect of light intensity on the rate of photosynthesis

  -The rate at which the pondweed produces oxygen corresponds to the rate at which it is photosynthesising-the faster the rate if oxygen production, the faster the rate of photosynthesis.

  1)A source of white light is placed at a specific distance from the pondweed.

  2)The pondweed is left to photosynthesise for a set amount of time.As it photosynthesises the oxygen released will collect in the capillary tube.

  3)At the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured.This is proportional to the volume of O2 produced.
• How do we ensure that light intensity experiment is a fair test?

  -Any other factors must be controlled such as temperature and the time the pondweed is left to photosynthesise

  -The experiment must be repeated twice with the light source at the same distance and the mean volume of O2 produced is calculated

  -Then we repeat this experiment which the light source at different distances from the pondweed.
• How can the apparatus above be altered to measure the effect of temperature or CO2 on photosynthesis?

  -Put in water bath at a set temperature or a measured amount of sodium hydrogencarbonate can be dissolved in the water-giving off CO2-then can be tested with different temperature of water and concentrations etc.
• How are the distance and light intensity in photosynthesis related?

  -Inversely proportional to each other

  -Light intensity decreases in proportion to the square of the distance.

  This means that it fits the inverse square law.
• What is the inverse square law in photosynthesis?

  light intensity= 1/d squared
• What is the most common way to artificially create the ideal environment for plants?

  Growing them in greenhouses
• How are greenhouses beneficial in photosynthesis?


  -Greenhouses help to trap the Suns heat and make sure that the temperature does not become limiting.

  -In winter farmer or gardener might use a heater as well, to keep the temperature at the ideal level.

  -In summer, it could get too hot hot, so they might use shades and ventilation to cool things down.
• How do farmer maintain the required conditions in greenhouses for photosynthesis?

  -Often use artificial light after the sun goes down to give their plants more quality photosynthesis time.

  -Also increase the level of carbon dioxide by using a paraffin heater to heat the greenhouse.As the paraffin burns, it makes the carbon dioxide a by-product.

  -Keeping plants enclosed in greenhouses also make it easier to keep them, free from pests and diseases.The farmer can add fertilisers to the soil as well, to provide ask the minerals needed for healthy grow.
• What is a downside of greenhouses?


  Expensive

  If we give more than the plant needs it is wasting money.
• What does the use of greenhouses lead to?

  Farmer can keep the conditions just right for photosynthesis, the plants will grow much faster and a decent crop can be harvested much more often, which can then be sold.
• What does respiration transfer?

  Respiration transfers energy that the cell needs to work-this energy is used for all living processes.
• What is respiration?


  Respiration is the process used by all living organisms to release energy from organic molecules. Respiration is how all living things get energy from food.
• Is respiration exothermic


  Exothermic - transfers energy to the environment
• How do organisms use the energy transferred by respiration?

  1)To build up larger molecules from smaller ones-like proteins from amino acids

  2)In animals-used to allow the muscles to contract

  3)In mammals and birds-the energy is used to keep their body temperature steady in closer surroundings.
• What are controlled by enzymes?

  Chemical reactions happening in a cell.
• What are examples of reactions that turn small molecules into larger ones?

  -Lots of small glucose molecules are joined together in reactions to form starch, glycogen and cellulose.

  -Lipid molecules are each made from one molecule of glycerol and three fatty acids

  -Glucose combines with nitrate ions to make amino acids-then made into proteins
• What are examples of reactions where larger molecules are broken down into smaller ones?

  -Glucose is broken down in respiration.Respiration transfers energy to power all the reactions in the body than make molecules.

  -Excess protein is broken down in a reaction to produce urea. Urea is then excreted in urine
• What is metabolism?


  sum of all reactions in the body or in a cell.