An Overview of Cell - 2

Ribosomes are non-membrane-bound organelles.

They are found in both prokaryotic and eukaryotic cells.

Ribosomes are responsible for protein synthesis.

Ribosomes are found freely in the cytoplasm.

They are also present inside chloroplasts and mitochondria.

Additionally, ribosomes are attached to the rough endoplasmic reticulum (Rough ER).

Animal cells contain a non-membrane-bound organelle called the centrosome.

The centrosome contains a pair of centrioles.

It helps in organising microtubules and spindle formation during cell division.

Cells show considerable variation in their size and shape.

They also differ in the activities they perform.

These differences are related to the specific functions of different cells.

Mycoplasmas are the smallest known living cells.

They measure approximately 0.3 μm in length.

Bacteria are generally larger and could measure 3 to 5 μm.

The egg of an ostrich is considered the largest isolated single cell.

It is large enough to be seen easily without a microscope.

Despite its large size, it is a single cell.

Human red blood cells (RBCs) are approximately 7.0 μm in diameter.

They are specialised cells responsible for transporting respiratory gases.

Their biconcave shape provides a large surface area for gas exchange.

Nerve cells, also called neurons, are some of the longest cells in the body.

Their long extensions help transmit nerve impulses over long distances.

They are specialised for communication within the nervous system.

Cells show a wide variety of shapes.

They may be disc-like, polygonal, columnar, cuboid, thread-like or irregular.

The shape of a cell is often related to the function it performs.

The shape of a cell is often related to its function.

Different cells have different shapes to perform specialised activities.

For example, nerve cells have long extensions to transmit nerve impulses.

Red blood cells (RBCs) have a round, biconcave disc shape.

The biconcave shape provides a larger surface area for gas exchange.

This shape also helps RBCs pass through narrow blood capillaries.

White blood cells (WBCs) have an amoeboid shape.

They can change their shape by forming temporary projections called pseudopodia.

This helps them move through tissues and engulf foreign particles.

Columnar epithelial cells are elongated and narrow.

They are taller than they are wide, giving them a column-like appearance.

They commonly perform absorption and secretion functions.

Nerve cells, also called neurons, have a branched and long shape.

Their long axons transmit nerve impulses over long distances.

Their branched dendrites receive signals from other cells.

Tracheids are elongated, tube-like cells found in the xylem of vascular plants.

They help in the conduction of water and minerals.

Their elongated shape facilitates the movement of water through the plant.

Mesophyll cells are found in the leaves of plants.

They are generally round or oval in shape.

They contain chloroplasts and perform photosynthesis.