Saturday, September 13, 2008

Lab 9 Transipration

What causes the movement of water?

- The movement of water is caused by many factors such as:

~ Osmosis


~ Root pressure


~ Transpiration


~ Cohesion-Tension


Osmosis- is when water enters through the root cells. The water potential outside the root is higher than inside. This is because dissolved minerals contribute to the lower water potential decreasing the osmotic presssure.


Root pressure- is when water enters the xylem cells increasing osmotic pressure producing root pressure.


Transpiration- is when water moves from mesophyll cells to air spaces and out the stomata. This occurs because water potential is higher in mesophyll cells and lower in dry air spaces of leaf.


Cohesion- Tension- Cohension is the attraction of like molecules, witch form weak hydrogen bonds between polar water molecules. As cohension occurs water molecules are pulled up from the roots to the leafs. This transpirational pull of water decreases the pressure potential, resulting in negative water potential, or tension.



  • This is the most dominant mechanism for the movement of water.

Factors that effect transpirtaion rates?


~ Temperature


~ Humidity


~ Air movement


~ Light intensity


Temperature- is when the temperature of a liquid increases and the kinetic energy of water increases. As a result, liquid is converted to water vapor more rapidly.


Humidity- is an increase in the water potential of the surrounding air. In response, the rate of transpiration decreases.


Air movement- is the moving of recently evaporated water away from the leaf. As a result, humidity and water potential drop, and the rate of transpirtaion increases.


Light intensity- is when light is absorbed by the leaf, and some of the light energy is converted to heat. The transpiration rate increases with temperature.

I hope you guys feel good about your first in class essay!






1 comment:

SMABiology said...

This is good to have the components for lab 9. We will definitely need to revisit this section before the exam.