Cells and Their Organelles

When using a microscope to magnify a section of tissue from any organism, you will observe that it is composed of units known as cells. The cell is a basic structural and functional unit of an organism.

Multicellular organisms, such as animals and plants, exhibit a complex organisation. For instance, the human body is comprised of approximately 30 trillion cells. In contrast, some organisms, like amoebae, consist of a single cell. Cells come in various shapes and sizes, each equipped with specialised functions that contribute to the overall functioning of living systems. Different functions of a cell can be assigned to specialised compartments called organelles.

Cells can be categorised as eukaryotic or prokaryotic. Two large groups of organisms, bacteria and archaea have prokaryotic cells, while all other organisms have eukaryotic cells. Take a look at the diagram below and try to identify two major similarities and one difference between prokaryotic and eukaryotic cells.

All cells share common characteristics, one of the most notable being the presence of a plasma membrane and ribosomes. The cell membrane serves to control what goes in and out of the cell. The ribosomes perform the synthesis of proteins.

The major difference is the presence of a nucleus and other membrane-enclosed organelles in eukaryotic cells. Membranes separate such organelles from the rest of the cell in order to maintain conditions (e.g. pH or concentration of some molecules) optimised to perform particular tasks. A jelly-like substance surrounding the organelles is called cytosol.

The functions of major organelles that can be found in most eukaryotic cells are described in the table below.

Plant cells have some organelles distinguishing them from animal cells.

Prokaryotic cells have no nucleus and other membrane-bound organelles. Many prokaryotes are surrounded by two membranes (gram-negative bacteria).

Summary

The video below provides a summary of the topic and some additional details: