Class 10 Plant Hormones
Class 10 Plant Hormones
- Plant hormones are chemical compounds used by multicellular organisms for control and coordination. This is referred to as chemical coordination in plants.
- Plants use chemical communication because electrical impulses are limited, reaching only connected cells, and cells require time to reset before generating a new impulse. Chemical signals are slower but can potentially reach all cells of the body steadily and persistently, regardless of nervous connections.
- Different plant hormones help coordinate growth, development, and responses to the environment.
- Plant hormones are synthesized at locations away from where they act and then simply diffuse to the area of action.
Types of Plant Hormones and Their Roles
The sources describe several plant hormones, categorized by their general effect on growth:
1. Growth Promoting Hormones
| Hormone | Site of Synthesis/High Concentration | Primary Function | Specific Examples/Details |
|---|---|---|---|
| Auxin | Synthesized at the shoot tip. | Helps cells to grow longer. | When light comes from one side, auxin diffuses towards the shady side of the shoot. This concentration stimulates the cells on the shady side to grow longer, causing the plant to bend towards light (phototropism). |
| Gibberellins | Not specified in source. | Helps in the growth of the stem. | They function similarly to auxins in promoting stem growth. |
| Cytokinins | Present in greater concentration in areas of rapid cell division. | Promote cell division. | Found frequently in areas like fruits and seeds. |
2. Growth Inhibiting Hormone
| Hormone | Primary Function | Specific Examples/Details |
|---|---|---|
| Abscisic acid | Inhibits growth. | Its effects include the wilting of leaves. Plants require signals to stop growing, and abscisic acid provides this signal. |
Plant Coordination and Movement Context
- Plants show two different types of movement: one dependent on growth (which is directional) and one independent of growth (immediate response to stimuli). Growth-related movement of plants is typically slow.
- Directional movements, or tropic movements, are responses to environmental triggers like light or gravity.
- Phototropism: Shoots bend towards light, while roots bend away from light. Auxins play a role in this growth.
- Geotropism: The upward growth of shoots and downward growth of roots in response to gravity.
- For movements that are independent of growth, such as the leaves of the sensitive plant (Mimosa), information that a touch has occurred is communicated using electrical-chemical means from cell to cell, although plants lack specialized nervous tissue for conduction. Movement happens because plant cells change shape by changing the amount of water in them, leading to swelling or shrinking.