Evidence of phototropism in the laboratory.

-The stems of this plant is bending towards the light.

2.81 Phototropism

Describe the positive Phototropism of stem.
- photo= light     tropism= growth and response   positive= towards the light
-with light coming from all directions the stem will grow forwards and upwards.
-with light coming from lateral (side) light source the stem will bend in growth towards the light.
-the light on the side causes movement to the other side (side with no light) of a compound known as Auxin. which is a hormone that causes growth and bending.

2.80 Geotropism

Describe the geotropic responses of roots and stems
-Geotropic    Geo= Gravity   Tropic= Growth response
-Embryonic root grows downwards (positive geotropism)
-Embryonic shoot grows upwards (negative geotropism)
-If you rotate the seed the shoot will grow upwards (negative tropism) and the root will grow downwards (positive tropism)

2.79 Plants and Stimuli

Understand that plants respond to Stimuli
- Stimuli: Changes in the environment. Examples- temperature and light changes.
-The plant has receptors which can detect stimuli and turn them into response- they take the form of growth.
-Growth and response to stimulus is called a tropism.
-Tropism that involves light is called phototropism.
-Tropism that involves gravity is called geotropism.
-The connection between receptor and response usually takes the form of plant hormones (plant growth regulators) example- auxim.

2.54 Transpiration

Recall that transpiration is the evaporation of water from the surface of the plant.
- H20 (water) turns into a Gas by evaporation from heat and light.
- Water is taken up in the root systems by osmosis.
- Water travels up through the stem out through petiole.
- Sunlight warms the leaf to create heat so water can change to gas.
- Water is then evaporated through the stomatal pores.
- Water leaves the leaf due to the diffusion from a high humidity (100%) to a lower humidity in the air.

2.53 Uptake of water

Explain how water is absorbed by root hair cells.
-Branching patterns of roots increases surface area- increases absorption of water.
-End of roots have root hairs which are epidermal cells (cells on surface of root)- increases surface area, more water is absorbed.
-Active transport of minerals encourages the plant to take up water by osmosis. (osmosis- water moves from dilute to concentrated region)
-Dilute region is the soil water surrounding the root hairs and the concentrated region is created by building up the minerals in the cell by active transport.
-Water moves across the cortex of the root to the xylem by osmosis.

potometer

 A Potometer is a device used for measuring the rate of water uptake of a leafy shoot.

root structure.

This photo comes from: http://extension.oregonstate.edu/mg/botany/roots.html

2.39 gas exchange in plants.