photosynthesis Flashcards
what is light energy absorbed by?
chlorophyll
what kingdoms does photosynthesis occur in?
plants, and some bacteria/protoctista too
2.19 word equation for photosynthesis?
carbon dioxide + water —> glucose + oxygen
2.19 balanced chemical equation for photosynthesis?
6CO2 + 6H2O —> C6H12O6 + 6O2
2.22 what are nitrates (NO3 -) used for in plants?
they’re required to make amino acids (and so proteins), and nucleic acids (DNA and RNA)
2.22 what is magnesium (Mg) used for in plants?
required to make chlorophyll
what are phosphates (PO4 3-) used for in plants?
required to make nucleic acids (DNA and RNA); is part of cell membrane
symptoms of nitrates deficiency in plants?
stunted growth
symptoms of magnesium deficiency in plants?
yellow leaves
symptoms of phosphates deficiency in plants?
poor root growth; purple younger leaves
what is the limiting factor?
the factor which is in shortest supply
2.20 what are the factors affecting photosynthesis?
- the availability of the substrates for the reaction - carbon dioxide & water
- energy available to allow the reaction to occur - light intensity
- kinetic energy available to move substrate and enzyme molecules - increasing temperature increases kinetic energy
2.21 what are the adaptations of the upper epidermis?
it’s transparent, allowing light to penetrate to the mesophyll
2.21 how is the leaf specialised for photosynthesis?
-large surface area, thin, to maximise absorption of sunlight by photosynthetic cells
-this also increases number of stomata, so CO2 can diffuse quicker
2.21 what are palisade cells like?
-long, thin, tightly packed
-contain large numbers of chloroplasts
-this maximises absorption of sunlight energy
-palisade mesophyll is main site of photosynthesis
2.21 what do stomata do
-allow gases to diffuse into air spaces of leaf
-this provides a short diffusion distance for CO2
what’s the xylem
-transports water (absorbed in roots) to leaves
-this then provides short distance for water to diffuse into photosynthesising cells
what’s the phloem vessels do
transport sugars made in photosynthesis to other parts of the plant
2.20 understand how varying carbon dioxide concentration affects the rate of photosynthesis
- adding more CO2: reaction happens faster, as more molecules to collide w enzymes
- however, reach point when adding more CO2 has no effect - there’s a lack of energy
2.20 understand how varying light intensity affects the rate of photosynthesis
- by adding brighter light we inc rate of photosynthesis, as more energy for reaction to occur
- this doesn’t last forever, as at high light intensities a different factor is limiting (and so graph levels off)
2.20 understand how varying temperature affects the rate of photosynthesis
- inc temp speeds up reaction
- enzymes & substrates have more KE & collide more often
- however, at high temps rate of photosynthesis decreases & reaction stops
- this bc enzymes carrying out stages of photosynthesis have been denatured
2.23 practical: investigate photosynthesis, showing the production of starch and the requirements of light, carbon dioxide and chlorophyll (testing leaf for starch)
- take leaf that’s been destarched by placing in dark for 24 hrs
- leave it to photosynthesise outside for a day
- heat leaf in boiling water for 1 min (boiled w Bunsen burner) (this kills the tissue & breaks down cell walls)
- turn off Bunsen burner
- transfer leaf to test tube containing ethanol & place in the hot water for 5-10 mins - boil in ethanol (removes chlorophyll so colour change from iodine seen more clearly)
- rinse the leaf in cold water (to soften leaf tissue after being in ethanol)
- spread leaf out on white tile & cover in iodine solution
- only parts of leaf that produce starch will turn blue/black
2.23 practical: why do you need to destarch the leaf before/at the beginning of the practical?
ensures that any starch already present in leaves will be used up which means any starch in leaf you test was produced from glucose made in photosynthesis during experiment (won’t affect results of experiment)
2.23 practical: how can you vary the experiment to show the different conditions needed for photosynthesis?
- light required: 1 leaf covered w foil (or part of leaf covered); only the leaves (parts of leaf) exposed to light will produce starch & turn black
- chlorophyll required: a variegated leaf, in which white parts of leaf lacks chlorophyll, is used & starch only produced in green areas
- CO2 required: 1 leaf of plant enclosed in conical flask containing soda lime to absorb CO2, compared to 1 in flask w/o soda lime. only leaf w CO2 produces starch.
