Tuesday, 29 March 2011

2.79, 2.80, 2.81 (Plants and stimuli, Geotropism, Phototropism)

2.79 main points:
  • Stimuli are changes in the environment (e.g. temperature changes and light changes)
  • Plants have receptors to which can detect these stimuli to create a responses
  • The responses often take before growth, this type of growth is called a tropism.
  • Two types of responses are: Phototropism (related to light) and Geotropism (related to gravity)
  • The connect between receptor and response is of plant hormones (e.g Auxin) 
2.80 main points:
  • Geo refers to gravity tropism refers to response of growth.
  • An example is a seed, if we observe a seed growing we can see seed growing downwards we can describe this as positive geotropism. 
  • If it grows upwards it is called negative geotropism.
  • If we rotate the seed around then geotropism will still happen.
2.81 main points:
  • Photo refers to light tropism refers to response of growth (grows towards light)
  • With uniform light growing all directions it will grow forward
  • With some places with light, it will grow towards the light called lateral light.
  • The hormones in the plant called Auxin leads plant to bend.

Tuesday, 22 March 2011

2.53 Roots

5 main points:

  • The root structure has a branching pattern, which increases the surface area for the absorption of water.
  • If you zoom in there are hairs on the end which is called root hair, which are epidermal cells (cells that are surface)
  • Root hair has an extension of the cell wall which increases the surface area to absorb water
  • Active transport against the concentration gradient takes in the mineral into the root.
  • In which roots get water by osmosis (water moves from dilute to concentrated), the dilute region (soil water surrounding the root) moves into the root (concentrated, building up the minerals in the cell). Water then moves across the cortex to the xylem by osmosis.

2.54 Transpiration

5 key points:

  • Transpiration is the evaporation of water from the surface of the plant through the stomatal pores.
  • Some light is absorbed by other structures in the leaf which creates heat and water is delivered to the leaf by xylem, and goes through the spongy mesophyll.
  • Liquid changes to a gas in the spongy mesophyll
  • It then diffuses out to the outside atmosphere at a fairly steep diffusion gradient.
  • Heat and light energy changes H2O to water vapor.