biology p2 t6

• photosynthesis: the process in which plants and algae make their own food, transforming light energy into chemical energy. It is an endothermic reaction and takes place in chloroplasts.
• carbon dioxide + water produces oxygen + glucose
• 6CO2 + 6H2O produces C6H1206 + 602
• the limiting factors of photosynthesis are temperature, light intensity and carbon dioxide concentration.
• temperature increases the rate of photosynthesis. It continues to increase until it reaches it optimum, which is where the enzymes are the most effective. The enzymes then start to denature and the rate of photosynthesis decreases.
• the light intensity increases the rate of photosynthesis until another factor starts limiting.
• as carbon dioxide concentration increases, the rate of reaction increases until another factor starts limiting.
• to calculate the rate of photosynthesis you can measure the oxygen production of a plant.

  method:

  • place pondweed in a test tube full of water and seal with a bung.
  • place a lamp at a measured distance from the tube.
  • as it photosynthesises, measure the distance the bubble has moved to calculate the oxygen produced.
• core practical aim: to investigate the effect of light intensity on photosynthesis.
• core practical method:

  • place flasks with algae in them at set distances from a light source.
  • add an indicator solution and leave for 1 hour.
  • compare the colours to see a pH change.
• core practical results: the pH decreases as you get further from the light source. A purple colour means low levels of carbon dioxide and a yellow colour means high levels of carbon dioxide.
• the inverse square law:

  • light intensity is directly proportional to the rate of photosynthesis.
  • light intensity is inversely proportional to the square of the distance.
• root hair cell adaptions:

  • a larger surface area so it can absorb more water.
  • a thin cell wall which makes it easier for minerals and water to pass through.
  • lots of mitochondria to provide energy from respiration for the active transport.
• xylem cell adaptions:

  • they are dead cells with no cytoplasm which enables water to flow through.
  • lignin cell walls to withstand high water pressure.
  • tiny pores allowing water and mineral ions to enter and leave.
• phloem cell adaptions:

  • have a large central channel for sugar to flow through.
  • have holes in the cell walls to allow sugar to flow into the companion cells.
  • lots of mitochondria to provide energy to transport the sucrose.
• xylem cells transport water and mineral ions through transpiration.
• phloem cells transport sugars through translocation.
• stomata adaptions:

  • have guard cells to open and close it.
  • can close to minimise water loss and can open to increase evaporation and transpiration.
  • allow gas exchange to occur when they are open.
• thin leaves mean that carbon dioxide only has a short distance to travel to enter the leaf.
• a large surface area which allows the leaf to absorb more sunlight which maximises the rate of photosynthesis.
• a waxy cuticle prevents water loss by evaporation.
• translocation: the movement of sugars from the leaves to the rest of the plant. It occurs in the phloem.
• transpiration: water transport in plants set up by the evaporation of water from leaves.
• the factors effecting transpiration are temperature, humidity, wind and light intensity.
• an increase in temperature causes the particle to move faster meaning evaporation happens at a faster rate. This increases the rate of transpiration.
• an increase in humidity reduces the concentration gradient which reduces the rate of transpiration.
• an increase in wind lowers the amount of water vapor around the leaf which causes a steeper concentration gradient. This increases the rate of transpiration.
• an increase in light intensity increases the rate of photosynthesis meaning more water can evaporate. This increase the rate of transpiration.
• transpiration can be measured using a potometer.
• hormones: chemicals inside plants that control growth.
• phototropism: a growth movement in response to light.
• gravitropism: a growth movement in response to gravity.
• auxin: a hormone involved in phototropic and gravitropic responses in plants.
• shoots are positively phototropic and negatively gravitropic.
• roots are negatively phototropic and positively gravitropic.
• auxins can be used as weed killers, as rooting powders and to promote growth in tissue culture.
• ethene exposure can cause fruit to ripen.
• gibberellins allow seed germination to occur by breaking seed dormancy. It can also increase the yields of fruit and help to make seedless fruit.