Parenchyma:
Parenchyma is a type of simple permanent tissue found in plants. It is made up of living cells that have thin cell walls and large intercellular spaces. This tissue is responsible for various functions such as photosynthesis, storage, and secretion.

Characteristics of Parenchyma:
- Parenchyma cells are isodiametric in shape, meaning they have a similar diameter in all directions.
- They have a thin primary cell wall made up of cellulose.
- The cells are loosely packed, allowing for the movement of gases, water, and nutrients.
- Parenchyma cells can divide and differentiate into other types of cells if needed.
- They contain a large central vacuole that helps in storing water, nutrients, and waste products.

Types of Parenchyma:
1. Chlorenchyma: This type of parenchyma contains chloroplasts and is responsible for photosynthesis. It is found in the leaves of plants.
2. Aerenchyma: Aerenchyma parenchyma has large intercellular spaces filled with air. It helps in buoyancy and provides oxygen to the roots of aquatic plants.
3. Storage Parenchyma: This type of parenchyma stores various substances such as starch, oils, and proteins. It is found in fruits, seeds, and tubers.

Collenchyma:
Collenchyma is another type of simple permanent tissue found in plants, primarily in young plant parts like stems and petioles. It provides mechanical support to the plant and helps in withstanding bending forces.

Characteristics of Collenchyma:
- Collenchyma cells are elongated and have irregularly thickened cell walls.
- The cell walls are made up of cellulose, hemicellulose, and pectin, which provide strength and flexibility.
- The corners of the cells have thickenings called 'angles' or 'thickening bands' that give support to the plant.
- Collenchyma cells are living and have a protoplast containing a nucleus and other cell organelles.

Sclerenchyma:
Sclerenchyma is a type of complex permanent tissue found in plants. It provides mechanical strength and support to the plant. Sclerenchyma cells are dead at maturity and have thick, lignified cell walls.

Characteristics of Sclerenchyma:
- Sclerenchyma cells are elongated and have extremely thick, lignified cell walls.
- The cell walls contain a substance called lignin, which makes them hard and waterproof.
- The cells are dead at maturity and lack a protoplast.
- Sclerenchyma cells are highly specialized and occur in regions where support is required, such as the stems, roots, and veins of leaves.
- There are two types of sclerenchyma cells: fibers and sclereids. Fibers are long and slender, while sclereids are short and irregularly shaped.

Key Differences:
- Parenchyma cells have thin cell walls, while collenchyma and sclerenchyma cells have thickened cell walls.
- Collenchyma cells have irregularly thickened cell walls, while scleren