Biyo-Tek Günlüğüm…

Introduction to Cells

Cells of different organisms and even cells within the same organism are very diverse in terms of shape, size, and internal organization.

One theme that occurs again and again throughout biology is that form follows function.

Cell Shape

The diversity in cell shapes reflects the different functions of cells.

Each cell has a shape designed to allow the cell to perform its function effectively.

Cell Size

Cells differ not only in their shape but also in their size.

A few types of cells are large enough to be seen by the unaided human eye.

(For example, the nerve cells that extend from a giraffe’s spinal cord to its foot can be 2 m)

Common Cell Features

Cells share common structural features, including:

• an outer boundary called the cell membrane
• interior substance called cytoplasm
• structural support called the cytoskeletongenetic material in the form of DNA
• cellular structures that make proteins, called ribosomes

Plasma Membrane

The cell’s outer boundary, called the plasma membrane (or the cell membrane), covers a cell’s surface and acts as a barrier

between the inside and the outside of a cell. All materials enter or exit through the plasma membrane.

Cytoplasm

The region of the cell that is within the plasma membrane and that includes the fluid, the cytoskeleton, and all of the organelles except

the nucleus is called the cytoplasm. The part of the cytoplasm that includes molecules and small particles, such as ribosomes, but not

membrane-bound organelles is the cytosol.

Genetic Material

Cells carry coded information in the form of DNA for regulating their functions and reproducing themselves.

The DNA in some types of cells floats freely inside the cell. Other cells have a membrane- bound organelle that contains a cell’s DNA.

This membranebound structure is called the nucleus.

Here is a typical animal cell:

THE ULTRASTRUCTURE OF A CELL IS STUDIED IN GRADE 10