The Bio Brief

What Is Movement Due to Growth?

• Some plant movements happen because of growth.
• These movements are:
  • Slow
  • Permanent
  • Directional
• Since growth occurs more on one side than the other, the plant appears to move.

Example 1: Tendrils in Pea Plant

• Tendrils help the plant climb and get support.
• Tendrils are sensitive to touch.

What happens when a tendril touches a support?

• The side touching the support grows slowly.
• The side away from the support grows faster.
• This uneven growth causes the tendril to coil around the support.

Flow Chart:

Tendril touches support
⬇
Unequal growth
⬇
Tendril curls
⬇
Plant gets support

Directional Growth Movements (Tropism)

Movement of plant parts in response to a stimulus is called tropism.

Types of Tropic Movements:

• Towards stimulus → Positive tropism
• Away from stimulus → Negative tropism

Phototropism (Response to Light)

• Shoots grow towards light → Positive phototropism
• Roots grow away from light → Negative phototropism

Why is this helpful?

• Shoots get more light for photosynthesis
• Roots remain in soil for water and minerals

Geotropism (Response to Gravity)

• Roots grow downwards → Positive geotropism
• Shoots grow upwards → Negative geotropism

Other Types of Tropism

Tropism	Stimulus	Example
Hydrotropism	Water	Roots grow towards water
Chemotropism	Chemicals	Pollen tube grows towards ovule

Simple Diagram (Text Form)

Phototropism:

Light →

Shoot bends towards light

Root bends away from light

Geotropism:

Shoot ↑

Root  ↓

(Gravity)

How Is Information Communicated in Plants?

Fast vs Slow Responses:

• Touch-me-not → Fast response
• Sunflower movement → Slow response
• Growth movements → Very slow

Electrical vs Chemical Signals

Electrical Signals:

• Very fast
• Limited to connected cells
• Cannot be continuous

Chemical Signals (Hormones):

• Slow
• Reach many cells
• Act for a longer time
• Used for growth and development

Plant Hormones (Phytohormones)

Plant hormones are chemical messengers that control growth and responses.

Important Plant Hormones:

1. Auxin

• Helps in cell elongation
• Produced at shoot tip
• Causes bending towards light

Auxin Flow Chart:

Light from one side
⬇
Auxin moves to shady side
⬇
Cells elongate more
⬇
Shoot bends towards light

2. Gibberellins

• Help in stem growth

3. Cytokinins

• Promote cell division
• Found in fruits and seeds

4. Abscisic Acid

• Inhibits growth
• Causes wilting of leaves
• Helps plants survive stress

Key Points to Remember

• Growth-based movement is slow and permanent
• Directional growth is called tropism
• Plant hormones control growth
• Auxin helps in bending towards light
• Abscisic acid stops growth