My Evidence of Phototropism in the laboratory

The stems of the plant are bending towards the light, this is an example of phototropism.

2.81 Phototropism

- Phototropism. Photo = Light. Tropism = Growth in response to light. "Positive" shows towards the light
- If light comes from all directions the stem will grow forwards and upwards
- If light comes from lateral light source the stem will start growing towards the light (bends to face) 
- Light on one side, causes movement of opposite side of a compound, Auxin (plant hormone). 
- Auxin cause more growth on the opposite then on the light side, causing it to bend 

2.80 Geotropism

- Geotropic. Geo = Gravity. Tropic = Growth response 
- Embryonic root grows downwards in a seed (Positive Geotropism) 
- It SHOULD grow upwards (Negative geotropism) 
- If you take the same seed but rotated the shoot then grows upwards (Negative) and the Embryonic root will grow downwards (Positive) 

2.79 Plants and Stimuli

- Stimuli are changes in the environment, Temperature or light. 
- Plants have receptors that detect stimuli and turn into response
- Response - Take form of growth - Tropism, involving light (phototropism)
                                                     - Tropism, involving Gravity (Geotropism) 
- Connection between Receptor and Response - takes form of Plant hormones (plant growth regulators). Example: Auxim 

2.55 Rate of Transpiration

- Transpiration is the loss of water through the leaf (caused by evaporation and diffusion through stomatal pore) 
- absorption of sunshine generates heat - transforms the water into heat 
- Concentration gradient for Water Vapour 
- if big difference then high rate of transpiration - factors: low humidity, high winds (wind blows away water vapour), high temperature (more evaporation), high light intensity ( higher rates of Photosynthesis) All result in FAST DIFFUSION 
- if small difference then low rate of transpiration - factors: high humidity, low wind speed (water vapour builds up around pore - gradient shallow), low temperature (less evaporation), low light intensity (rate of photosynthesis will be low and slow so water movement will be low and slow) 

2.54 Transpiration

- Evaporation (liquid  ---heat (sunlight) ---> gas) - through the stomatal pores 
- Water taken up in roots (osmosis) - travels up stem - out through petiole - evaporation in leaf 
- Sunlight warms the leaf allowing evaporation to take place so it can escape 
- Not all sunlight is absorbed by chloroplasts some absorbed by other cell structures creating heat 
- Water through xylem - moves through mesophyll - just above stomatal pore (little pocket) is where the phase change occurs from liquid to gas 
- Water vapor gas diffuses through the pores - steep diffusion gradient 

Potometer

A Potometer is a device used for measuring the rate of water uptake of a leafy shoot. The causes of this water uptake are photosynthesis and transpiration. You measure the volume of water by calculating the rate of movement of the air bubbles and hence the rate of transpiration. Using the formula: 

distance moved by air bubble/time take for the air bubble to move that distance. 

The units of measurement are cm/s.

Root Structure

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

2.53 Root Structure

- Branching pattern increases SA - increases absorption of water  
- End of root has root hairs - they are epidermal (cells on the surface of the root) cell wall is extended outwards (that is the root hair) - increases SA - abs. water
- Two different levels of increased SA - Tissue level and cellular level 
- Active transport against the concentration gradient and involving energy of minerals
- Plant actively concentrates the minerals in certain areas 
- Encourages plant to take up water by osmosis (water moves from dilute region - concentrated region) 
- Dilute region is soil water surrounding the root hairs. Concentrated region is created by building up the minerals in cells (achieved by active transport) 
- Water moves across cortex of the root to the xylem by osmosis