B8 - photosynthesis RP Flashcards
what is the purpose of the photosynthesis required practical
a piece of pondweed is usually used as it is easy to observe/measure the oxygen output (bubbles)
what is the risk assessment for the photosynthesis required practical
- hot lamp - could burn yourself or others - keep a safe distance away
- water and lamp - spill water on lamp - keep water away from lamp
- pondweed species - can invade species - dispose of carefully
what is the method for the photosynthesis required practical
- place a piece of pondweed in a large beaker of water
- shine a light at it using a lamp at a specific distance away
- record the number of bubbles of gas coming out of the pondweed in one minute
- repeat this with the lamp at different distances from the pondweed
the closer the lamp to the pondweed the more light energy the plant receives, so the number of bubbles in 1 minute increases (meaning the rate of photosynthesis increases) there may be a point at which the rate levels off as a factor other than light is limiting the rate
what is the independent variable of the photosynthesis required practical
light intensity
what is the dependent variable of the photosynthesis required practical
number of bubbles produced in 1 minute
what are the control variables of the photosynthesis required practical
- temperature of water
- carbon dioxide concentration
- pondweed used
why do you leave the lamp at each distance for a few minutes before taking a measurement in the photosynthesis required practical
the pondweed needs to acclimatise to the new light intensity (reach a steady rate of photosynthesis)
what are some sources of error in the photosynthesis required practical
- miscounting bubbles if they are coming out quickly - recording the bubbles and watching it slowed down would help
- the bubbles aren’t all the same size - measuring the volume of gas release in a syringe would be more accurate
