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In the previous session, we learned that a cell is the basic unit of life. Now, imagine our body as a highly organised city, where each part performs a specific role to keep everything running smoothly. Just as buildings in a city differ in structure and function, cells in our bodies also vary in shape and structure to perform specialised tasks.
Different buildings in a city
Our body does not use identical cells everywhere. Instead, it uses different types of cells, each carefully designed for a particular function. This variation allows the body to perform complex activities efficiently.
Different types of cell size:
Cell size varies widely. Cell sizes can range from nanometers to micrometres. A smaller cell has more volume and surface area than a larger cell.
The smallest cell found is a mycoplasma cell or PPLO (Pleuro Pneumonia Like Organisms, which is about \(0.1micron\) in diameter.
Mycoplasma
The most longest are nerve cells, measuring about a meter in length.The longest part of a neuron is the axon.
Neuron
The Biggest Cell:
The yolk of an ostrich egg is a single, largest known cell measuring about \(130)\–\(170)\ mm in diameter, protected by a shell and nourished by egg white for its development.
Ostrich egg
Variation in Shape and Structure of Cells:
Cells differ in their shape, size, and internal structure depending on their role in the body.
Different types of cells according to their shapes
- Muscle cells are spindle-shaped and flexible, which helps them contract and relax for movement.
- Nerve cells (neurons) are long and branched, enabling them to transmit messages rapidly across the body.
- Cheek cells are thin and flat, forming a protective covering inside the mouth.
- Plant cells may be rectangular, oval, or tube-like, helping in support and transport of water and nutrients.
The structure of each cell directly supports its function, showing how form and function are closely related in living organisms.
Cells Work Together to Perform Functions:
Cells do not work in isolation. Instead, they coordinate with one another to carry out body processes.
Digestive system
- In the food pipe, muscle cells contract and relax in a wave-like motion to push food downward.
- In the stomach, muscle cells churn food, while other cells secrete digestive juices and acids.
- Different cell types divide work and function together, ensuring smooth digestion.
This cooperation among cells demonstrates the concept of division of labour, where each cell type performs a specific task for the benefit of the whole organism.
Levels of Organisation in Living Organisms:
A cell forms the basic unit. When many similar cells come together, they form a tissue. Different tissues then combine to create an organ. Several organs coordinate their activities to form an organ system, and all organ systems together make a complete organism.
Levels of Organisation
Every complex organism starts from a single cell called the egg, which divides repeatedly to form many specialised cells that organise into tissues, organs, and organ systems, ultimately giving rise to multicellular organisms such as humans, animals, and plants.
Cell theory
Life shows a clear pattern of specialisation, cooperation, and organisation, allowing even the smallest unit a cell to contribute to the functioning of an entire living being.
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