Topic 4 - Bioenergetics Flashcards
what is photosynthesis?
it uses energy to change carbon dioxide and water into glucose and oxygen.
where does photosynthesis happen?
it takes place in chloroplasts in green plant cells - they contain pigments like chlorophyll that absorb light. energy is transferred to the chloroplasts from the environment by light
what kind of reaction is photosynthesis?
endothermic, this means energy is transferred from the environment into the place of reaction in the process
what is the word equation for photosynthesis?
carbon dioxide + water —-light—-> glucose + oxygen
what is the symbol equation for photosynthesis?
6CO₂ + 6H₂O ———light———-> C6H12O6 + 6O₂
what do plants make glucose for?
for respiration making cellulose making amino acids stored as oils or fats stored as starch
what happens when 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
why do plants use glucose for making cellulose?
glucose is converted into cellulose for making strong plant cell walls
how do plants use glucose for making amino acids?
glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into proteins
how do plants use glucose for storing as oils or fats?
glucose is turned into lipids (fats and oils) for storing in seeds
how do plants use glucose for storing as starch?
glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn’t happening, like in winter. starch is insoluble which makes it much better for storing than glucose, a cell with loads of glucose would draw in lots of water and swell up
what affects the rate of photosynthesis?
intensity of light, concentration of CO2 and temperature. they all have a combined affect on the rate of photosynthesis but any of these could be a limiting factor
whats a limiting factor?
this means that the factor is stopping photosynthesis from happening any faster
the factor of photosynthesis that is limiting at one time depends on:
the environmental conditions: at night, light is the limiting factor in winter, it's the temperature if its warm and bright enough, CO2 is usually limiting chlorophyll can also be limiting
how can chlorophyll be a limiting factor of photosynthesis?
the amount of chlorophyll in a plant can be affected by disease or environmental stress (lack of nutrients). these factors can cause chloroplasts to become damaged or to not make enough chlorophyll. so rate of photosynthesis is reduced because they can’t absorb as much light
what are the 3 important graphs for rate of photosynthesis?
not enough light slows down rate of photosynthesis
too little carbon dioxide also slows it down
the temperature has to be just right
what does the graph for rate of photosynthesis when light intensity increases look like?
light provides energy for photosynthesis, as light level increases, rate of photosynthesis increases, to a point. beyond that light intensity won’t increase rate of photosynthesis, this is because CO2 or temperature will be a limiting factor.
how can an experiment for lights affect on photosynthesis be conducted?
in a lab you can change light intensity by moving a lamp closer or further from a plant, but if you plot the rate of photosynthesis against the distance of the lamp from plant the shape of the graph will be weird, instead a light meter should be used
what does the graph for rate of photosynthesis when light intensity increases look like?
the amount of CO2 will only increase the rate of photosynthesis until it is no longer a limiting factor, then the graph will flatten out.
what does it mean when temperature is the limiting factor?
usually its because its too low, the enzymes needed for photosynthesis work more slowly at low temperatures, but if its too hot the enzymes will become damaged (this is usually 45*C
how can a graph show more than 1 limiting factor?
a graph for light intensity against rate of reaction can be used except the temperatures are labelled on each line, so that both lines increase are directly proportional until the one for the lowest temperature levels off and the higher temperature can level off later
what can be used to measure the effect of light intensity on rate of photosynthesis?
Canadian pond weed. the rate at which the pond weed produces oxygen corresponds to the rate at which its photosynthesising, the faster the rate of oxygen production the faster the rate of photosynthesis
how can an experiment be carried out using a lamp to increase photosynthesis in a plant?
a source of white light is placed a specific distance from the pond weed, it is left to photosynthesise and as it does the oxygen released is collected in the capillary tube. at the end of the experiment a syringe is used to draw the bubble along the tube up to a ruler. the length of the bubble is measured and it is proportional to the oxygen produced by the plant.
repeat the experiment with the lamp at different distances
what are the control variables for measuring photosynthesis with a lamp experiment?
any variables that could affect the results should be controlled e.g. the temperature and the time that the pond weed is left to photosynthesise
what should be done to increase accuracy for the measuring photosynthesis with a lamp experiment?
the experiment is repeated twice with the lamp at the same distance and the mean volume of O2 produced is calculated
what experiments can be used to show how temperature or CO2 affects photosynthesis?
the test tube of pond weed can be put in water baths at different set temperatures, or a different measured amounts of sodium hydrocarbonate(which releases CO2) can be dissolved in the water
how are light intensity and distance related?
in the experiment the further away the lamp was from the pant the lower the light intensity, so light and distance are inversely proportional, but with the inverse square law
what is the inverse square law of light intensity and distance?
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light intensity ∝ distance (d²)