sensitivity
A- Sensitivity of plants
CHAPTER II

- Definition: Sensitivity of plants is the ability to respond appropriately to environmental stimuli.
- Features: Slow response, difficult to detect and less diverse.
- Classification: directional and application.
UNIT
23
DIRECTION
Picture 23.1. Growth of young plants are different lighting conditions.
I- DEFINITION
Definition
Direction is grow of plant with stimulation from one side of the environment.
2. Reason
Plant growth is different from the growth on either side of the organ (stem, root).
3. Classification
There are two main types of response in plants
+ If the growth of a plant is in direction of stimulus, it is called positive tropism.
+ If the growth of a plant is opposite direction or away from that of a stimulus, it is called negative stimulus.
II- TYPES OF DIRECTION
Ficture 23.4. Chemotropism
Ficture 23.5. Hydrotropism
Ficture 23.6. Thigmotropism
We have five types of direction
Ficture 23.2. Phototropism
Ficture 23.3. Geotropism
1. Phototropism
II- TYPES OF DIRECTION
- Growth movement shown by plants in response to light
Ficture 23.7. Phototropism
+ Shoots grow towards light → positive phototropism.
+ Roots grow away from light → negative photopism.
- Hormone auxin is formed in cells at the tip of the shoot and is then passed from cell to cell.
- The plant hormone auxin which do this by elongating the cells of the stem on the side that is farthest from the light.
- Light is used as energy for making food, a process called photosynthesis. 
2. Hydrotropism
Ficture: 23.8. Hydrotropism
- Growth movement shown by plants in response to water
+ Roots grow towards water → positive hydrotropism.
+ Shoots grow away from water→ negative hydrotropism.
- Plants use water to increase moisture and nutrients back and forth between the roots and leaves.
3. Geotropism
- Growth movement shown by plants in response to gravity
Form 23.7. Geotropism
+ Roots always grow downwards – in the direction of gravity → positive geotropism.
+ Shoots grow upwards away from gravity→ negative geotropism.
- Roots always grow good.
4. Chemotropism
Ficture 23.8. Chemotropism
- Growth movements are expessed by plants in response to chemistry (NPK Fertilizers)
- That help plants grow in a way that benefits the environment.
5. Thigmotropism
- The directional response of plants to touching an object: Thigmotropism.
Picture 23. 9. Thigmotropism
- Climbing plants – have weak stems and tendons to support its own weight like cucumber and bean. Make sure these plants can grow upwards.
- Towards the sunlight.
III- ROLE OF DIRECTION IN GROW PLANTS.
Role: Direction helps plant adapt when environment changes.
Application:
- Shaping.
- Watering.
- Fertilizing.
→ This make the root system grow as desired.
Create the tree.
THE END