The Symphony of Cells
How Plants and Animals Master the Division of Labour
Why Do We Need Tissues?
In single-celled organisms like Amoeba, one cell does it all—eating, breathing, and moving. But in multicellular organisms (like us!), there are millions of cells. To manage this chaos, nature uses the Division of Labour.
Definition of a Tissue:
A group of cells that are similar in structure and work together to achieve a particular function.
Plants and animals have very different lifestyles, so their tissues are designed differently. Plants are stationary and need support (often using dead cells), while animals are active and need high energy (using mostly living cells).
1. Meristematic Tissues
Unlike animals, plants grow continuously, but only in specific areas. This is thanks to Meristematic Tissue—the dividing tissue.
- Apical Meristem: Found at the tips of roots and stems (makes the plant taller).
- Lateral Meristem (Cambium): Found on the sides (makes the stem thicker).
- Intercalary Meristem: Located at the base of leaves or nodes.
2. Permanent Tissues
When meristematic cells stop dividing, they take a permanent shape and function. This process is called differentiation.
Simple Permanent
Made of one type of cell.
- Parenchyma: Stores food. If it has chlorophyll, it's Chlorenchyma. If it has air cavities (in aquatic plants), it's Aerenchyma.
- Collenchyma: Provides flexibility. Allows plants to bend without breaking.
- Sclerenchyma: Makes the plant hard and stiff (like the husk of a coconut). These cells are dead.
Complex Permanent
Made of more than one type of cell working as a unit.
- Xylem: Transports water and minerals from roots to leaves.
- Phloem: Transports food from leaves to other parts.
Note: The entire surface of a plant is covered by the Epidermis, which protects against water loss using a waxy coating and regulates gas exchange via pores called Stomata.
1. Epithelial Tissue
This is the covering or protective tissue. It forms a barrier to keep different body systems separate.
- Squamous: Thin and flat (lining of mouth, esophagus).
- Cuboidal: Cube-shaped (kidney tubules).
- Columnar: Pillar-like, often with cilia (intestine, respiratory tract).
2. Connective Tissue
The cells are loosely spaced and embedded in a matrix. This tissue binds and supports the body.
Fluid & Rigid
- Blood: A fluid matrix (plasma) transporting gases, food, and hormones.
- Bone: Hard matrix of calcium and phosphorus; provides framework.
- Cartilage: Smoothens bone surfaces at joints (also found in ear and nose).
Binding
- Ligaments: Connect bone to bone.
- Tendons: Connect muscle to bone.
- Areolar: Fills space inside organs, helps in repair.
- Adipose: Stores fat below the skin (insulation).
3. Muscular Tissue
Contains contractile proteins that help in movement.
- Striated (Skeletal): Voluntary muscles attached to bones.
- Smooth: Involuntary muscles (stomach, iris of eye).
- Cardiac: Involuntary rhythmic muscles of the heart.
4. Nervous Tissue
Specialized for receiving and transmitting stimuli rapidly.
- Neurons: The unit of nervous tissue. Consists of a cell body, dendrites (branches), and an axon (long tail).
- Found in the brain, spinal cord, and nerves.
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