2.81 Photo-tropism

photo-->light
tropism-->growth response


Positive photo-tropism of stem
Positive -->towards light
Negative-->away from light


A stem will always grow TOWARDS the light
--> Positive photo-tropism



light causes movement of the opposite side
causes movement of auxin
causes more growth on the opposite side
causes bending

2.80 Geotropism

Geo-Gravity
Tropic-growth response


Take a seed:
Embrionic root-->grows downwards-->positive geotropisim
Embrionic shoot-->grows upwards (above surface)-->negative geotropism


Turn the seed on its side
Theshoot grows upwards- again negative
root--> Grows down -->positive

2.79 Plants and stimuli

Stimuli: Changes in the environment
E.G temperature/light changes


Plant has receptors which detect the stimuli
(link between receptors and response-->Plant hormones e.g Auxin)


The plant responds - usually with growth (called tropisms - e.g for light--> phototropism)

2.54 transpiration is the evaporation of water from surface of the leaf

1. Liguid H2O--Heat -->Gas H2O
2.(heat=sunlight-->converted to heat as absorbed by plants structure)
   -unit of light intensity- Lux

3.H2O (l) changes to H2O (g) right above the stomatal pore -
4.diffuses through Stomatal pore

Humidity:
-above Stomatal pore is 100%
-surrounding the leaf -usually less than 100%
-humid day-->low rate
-windy day-->Faster rate-->low humidity
sunny, dry, windy--> greatest increase in rate of transpiration
-

2.53 Root Structure

Root Structure

KEY POINTS:

• Branching pattern--> increased surface area/H2O absorption
• Root cells--> Epidermal cells-->on the surface-->increases surface area
• Root cells--> folded cell wall
• active transport of minerals-->Plant activley concentrates minerals at the base--> (movement of water from CONCENTRATED area to a DIUTE area) encourages plant to take up water by osmosis
• water is pulled through the xylem to the leaves

         --> a property of water is that if you pull one molecule the others will follow

Potometer

• Potometer--> measures Transpiration (water evaporating off the leaf)
• Insert a plant stem (with leaves) into a piece of plastic tubing
• Connect the tube to a length of glass tubing full of water and put a bung on it
• Make sure there is no air in the equipment -i.e set it up underwater
• Measure Transpiration by the movement of an air bubble.
• Allow a small amount of air into the class tube.
•  As water is taken up by the plant, the bubble will be seen to move along the tube, and marks made along the side of the tube allow the bubble's rate of progress to be measured.

IGCSE Plants

<a href="http://quizlet.com/4340982/plants-flash-cards/">Plants</a>