plant nutrition photosynthesis ➔ process by which plants manufacture carbohydrates from raw materials using energy from light: ➔ happens in chlorophyll ➔ transfers light energy into chemical energy for the synthesis of carbohydrates (i.e. glucose) ➔ glucose is then either converted to sucrose for transport around the plant or starch for storage ➔ glucose is too reactive to be transported around the plant on its own. There it has to be converted to sucrose first ➔ glucose cannot be stored due to its reactivity, so therefore it must be converted to starch first limiting factors ➔ something present in the environment in such a short supply that it restricts life processes investigations ➔ prove the necessity of chlorophyll, light, and carbon dioxide. ➔ take a functioning plant and deprive it of each of these factors individually and prove that the plant stops photosynthesizing when these factors are absent. ➔ de-starch all plants by leaving the plants in the dark for 48 hours. *during this period the plants will be unable to photosynthesize and therefore use up all its starch for respiration, so at the start of experiments, all plants will have absolutely no starch in them. starch test ➔ Boil the leaf in water ➔ Boil the leaf in ethanol ➔ Rinse the leaf in water ➔ Add iodine solution effect of light on photosynthesis ➔ partially cover the leaves of the plant and leave it under sunlight (covered areas will be deprived of light whereas the rest will be exposed) ➔ starch test after a few hours. ➔ results should show that the covered areas have a negative starch test (no photosynthesis) whereas the exposed areas have a positive star effect of carbon dioxide on photosynthesis ➔ place a test plant in a container with a carbon dioxide absorber (sodium hydroxide) and a control plant with a producer (sodium bicarbonate). ➔ starch test is then carried out after several hours. ➔ results should show that the test plant has a negative result whereas the control plant has a positive one. effect of chlorophyll on photosynthesis ➔ use a plant with variegated leaves (some parts of the leaf have chlorophyll whereas other parts do not, and they are whiter) ➔ carry out a starch test after several hours. ➔ results should show that parts of the leaf without chlorophyll will show negative results whereas the parts that do have chlorophyll will show a positive result. effect of factors on the rate of photosynthesis light intensity ➔ Rate of photosynthesis increases with light intensity until it plateaus. ➔ graph plateaus because something else becomes the limiting factor. carbon dioxide concentration ➔ rate of photosynthesis increases with increasing carbon dioxide concentration. ➔ at a certain point the graph will plateau. temperature ➔ rate of photosynthesis increases with temperature until the graph reverses and eventually drops down to zero. ➔ this is because high temperatures will denature enzymes that are required for photosynthesis. mineral requirements nitrate ions ➔ used in building amino acids (which eventually become proteins). ➔ nitrate ion deficiency would slow down the growth of the plant, the stem would weaken, and the lower leaves will turn yellow-ish and the upper leaves will become pale green as they die off. magnesium ions ➔ required to make chlorophyll. ➔ magnesium ion deficiency causes lack of chlorophyll, and leaves turn yellow and plant growth will slow down due to reduced photosynthesis. leaf structure cuticle: ➔ made of wax which waterproofs the leaf upper epidermis: ➔ barrier against disease organisms. ➔ cells are thin and transparent to allow light to enter the leaf. palisade mesophyll: ➔ main site of photosynthesis. ➔ cells are long and packed with chloroplasts to trap light energy. ➔ receive carbon dioxide via diffusion from air spaces in the spongy mesophyll spongy mesophyll: ➔ cells are spherical and loosely packed. ➔ contain chloroplasts but not as many as the palisade layer. ➔ loose packing creates air spaces and this allows gas exchange vascular bundle: ➔ contains xylem and phloem. ➔ xylem bring water and minerals to the leaf. ➔ phloem transport sugars and amino acids away from the leaf to the rest of the plant (translocation) Lower epidermis: ➔ protective layer. ➔ contains the stomata. stomata: ➔ gaps in the underside of the leaf, surrounded by a pair of guard cells. ➔ guard cells control whether the stoma is open or closed.
