Plant Growth and Development Class 11 Handwritten Notes for Easy Revision

Understanding Plant Growth: Definitions and Phases

Plant growth refers to the irreversible increase in size and volume of a plant. It occurs through three main processes:

• Cell Division: New cells form in meristematic tissues.
• Cell Elongation: Cells increase in size.
• Cell Differentiation: Cells develop specialized functions.

Growth is broadly divided into two phases:

1. Primary Growth: Increases length, occurs at apical meristems. 2. Secondary Growth: Increases girth, occurs at lateral meristems.

Understanding these phases is crucial for Class 11 students to grasp how plants develop structurally over time.

Meristems: The Growth Engines of Plants

Meristems are regions of actively dividing cells responsible for plant growth. They are classified into:

• Apical Meristems: Located at shoot and root tips; responsible for primary growth.
• Lateral Meristems: Include vascular cambium and cork cambium; responsible for secondary growth.
• Intercalary Meristems: Found at the base of leaves or internodes; help in regrowth.

These meristems continuously produce new cells that differentiate into various tissues, enabling plants to grow and repair.

Example: The shoot apical meristem produces new leaves and stems, while the vascular cambium forms secondary xylem and phloem.

Role of Phytohormones in Plant Growth and Development

Phytohormones are natural plant hormones that regulate growth and development. The main types include:

Worked example:

If a plant is treated with auxins on its shaded side, it bends toward the light due to differential cell elongation, demonstrating phototropism.

Seed Germination: Conditions and Process

Seed germination is the process where a seed develops into a new plant. The essential conditions for germination are:

• Water: Activates enzymes and softens seed coat.
• Oxygen: Required for respiration.
• Suitable Temperature: Optimal range varies by species.

Stages of Germination:

1. Imbibition: Absorption of water by the dry seed. 2. Activation: Enzymes become active. 3. Growth: Radicle emerges, followed by plumule.

Formula for Germination Percentage:

$$ ext{Germination \\ Percentage} = \left(\frac{\text{Number of seeds germinated}}{\text{Total seeds}}\right) \times 100$$

This formula helps evaluate seed viability during experiments.

Photoperiodism and Vernalisation in Flowering

Flowering in plants depends on environmental cues like light and temperature.

• Photoperiodism: Plants respond to the length of day and night.
• Short-day plants: Flower when day length is shorter than a critical period.
• Long-day plants: Flower when day length exceeds a critical period.
• Day-neutral plants: Flower regardless of day length.

• Vernalisation: Exposure to low temperatures to induce flowering.

These mechanisms ensure flowering occurs at the right season, improving reproductive success.

Example: Wheat is a long-day plant requiring vernalisation to flower.

Comparison of Primary and Secondary Growth in Plants

Understanding the differences between primary and secondary growth is vital:

This table helps Class 11 students distinguish the two growth types clearly.