photosynthesis 2.18, 2.19, 2.20, 2.21, 2.22, 2.23 Flashcards
what’s the word equation for photosynthesis?
carbon dioxide + water > (light energy and chlorophyll) > glucose + oxygen
what’s the balanced chemical equation for photosynthesis?
6CO2 + 6H20 > C6H12O6 +6O2
what are five things that plants use from the glucose produced from photosynthesis?
chlorophyll
lipids (to make cell membranes etc)
amino acids
DNA
carbohydrates (cellulose, fructose, starch for storage, sucrose for transport)
why do plants need mineral ion nitrates (NO3-)?
to make amino acids (proteins) and nucleic acids (DNA and RNA)
why do plants need the mineral ion magnesium (Mg)?
to make chlorophyll
why do plants need mineral ion phosphates (PO4,3-)?
needed to make nucleic acids (DNA and RNA) and part of cell membrane
what three factors affect the rate of photosynthesis?
availability of the substances needed for reaction (carbon dioxide and water)
energy availability (light intensity)
kinetic energy available to move substrate and enzyme molecules (increasing temperature and increasing kinetic energy)
what is the factor that is in shortest supply called?
limiting factor
the effects of temperature on photosynthesis and enzymes?
as temperature increases speeds up the reaction
the enzyme and substrate have more kinetic energy so they move faster and there are more successful collisions
however, when the temperature meets a certain temp the shape of the active site changes the enzyme denatures and the active site is no longer complementary to the substrate
therefore rate of photosynthesis decreases and reaction stopos
list the structure of a leaf from the top, downwards:
cuticle
upper epidermis
palisade mesophyll
xylem and phloem
spongy mesophyll
lower epidermis
stomata and guard cells
how is the leaf specialised for photosynthesis?
large surface area and thin - maximises light absorption and increases number of stomata so carbon can diffuse quicker
how is the upper epidermis specialised for photosynthesis?
transparent so light can penetrate the mesophyll
how are the palisade cells specialised for photosynthesis?
long, thin and tightly packed
contain large amounts of chloroplasts, maximising the absorption of sunlight energy
palisade mesophyll is the main site of photosynthesis
how are the stomata specialised for photosynthesis?
allow gases to diffuse into air spaces of the leaf providing a short diffusion distance for CO2
practical:
photosynthesis experiment of chlorophyll and starch
shows that chlorophyll is needed for photosynthesis
- take a leaf that’s variegated (some bits green, some white) and destarched (place in dark for 24 hours)
- heat in boiling water for 1 minute stopping any chemical reactions and waxy cuticle
- transfer leaf to a test tube containing ethanol and place test tube in hot water, this gets rid of any chlorophyll
- to soften ethanol leaf place it in hot water and rinse leaf
- place leaf on a white tile and cover it in an iodine solution
the leaf will turn blue-black to show starch is present
practical
rate of photosynthesis with factors that affect it
equipment: pondweed, a beaker of water, ruler, light source
number of bubbles released from the stalk in 1 minute is counted
distance of the light source can be varied to see the effect of changing light intensity
improvements of method:
- put pondweed in a test tube and then in a beaker with a thermometer to act as a water bath, this reduces the temperature change
- collect gas in an inverted measuring cylinder to measure the volume of oxygen evolved
what is photosynthesis?
process that produces food in plants
when plants use simple molecules (CO2 and H2O) to make glucose and O2
requires light energy, which is absorbed by chlorophyll
occurs in plants and some bacteria and protoctista
what happens if a plant is deficient in nitrates (NO3-)?
if deficient stunted growth
what happens if a plant is deficient in magnesium (Mg)?
if deficient yellow leaves
what happens if a plant is deficient in phosphates (PO4 3-)?
if deficient poor root growth, purple younger leaves
what happens to rate of photosynthesis as you add more carbon dioxide?
by adding more carbon dioxide the reaction can happen faster as there are more molecules to collide with enzymes
however, there is a point where adding more CO2 has no effect as there is a lack of energy
what happens to the rate of photosynthesis in a brighter light?
by adding a brighter light we increase the rate of photosynthesis as there is more energy for the reaction to occur
how is the xylem specialised for photosynthesis?
the xylem transports water (absorbed in the roots) into the leaves
providing a short distance for water to diffuse into the photosynthesising cells
how is the phloem specialised for photosynthesis?
phloem vessels transport sugars made in photosynthesis to other parts of the plant
how can the photosynthesis experiment of chlorophyll and starch be adapted to show that light is required?
to show that light is required one leaf is covered by foil (or part of the leaf), and only the leaves exposed to light will produce starch and turn black
how can the photosynthesis experiment of chlorophyll and starch be adapted to show that carbon dioxide is required?
to show that carbon dioxide is required one leaf of a plant is enclosed in a conical flask containing soda lime to absorb the carbon dioxide and this leaf is compared to another enclosed flask but without the soda lime
only the leaf that had access to carbon dioxide produces starch
why do plants need potassium?
to help the enzymes needed for photosynthesis and respiration
what happens if a plant is deficient in potassium?
if deficient plants will have poor flower and fruit growth and discoloured leaves
