5.2.4. CYTOPLASM

When we look at the temporary mounts of onion peel as well as human cheek cells, we can see a large region of each cell enclosed by the cell membrane. This region takes up very little stain. It is called the cytoplasm. The cytoplasm is the fluid content inside the plasma membrane. It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.

Cytoplasm is a jelly-like fluid found within the cell membrane. This area contains various structures called organelles, which are responsible for carrying out specific functions necessary for the cell's survival. For example, it can house mitochondria that generate energy, ribosomes that produce proteins, and many others that help the cell perform its roles efficiently.

Think of the cytoplasm like a busy city: the cell membrane is the city’s walls, protecting everything inside, while the cytoplasm is like the streets filled with buildings (organelles) where different work is being done. Just like how a city needs different buildings for different activities, a cell requires various organelles for its functions.

Cell organelles are enclosed by membranes. In prokaryotes, beside the absence of a defined nuclear region, the membrane-bound cell organelles are also absent. On the other hand, the eukaryotic cells have nuclear membrane as well as membrane-enclosed organelles.

Organelles within a cell, such as the nucleus, mitochondria, and endoplasmic reticulum, are enclosed by membranes that provide structure and contain the components needed for specific functions. Prokaryotic cells, which are simpler and smaller (like bacteria), lack these complex structures and membranes. In contrast, eukaryotic cells, which are more advanced (found in plants, animals, fungi), have various organelles each surrounded by membranes, allowing them to perform more complex tasks.

Imagine a factory: prokaryotic cells are like a small workshop with no separate rooms (organelles), while eukaryotic cells are like a large factory with different sections (organelle membranes) for assembling, packaging, and shipping products. Each section has its dedicated purpose to improve efficiency.

The significance of membranes can be illustrated with the example of viruses. Viruses lack any membranes and hence do not show characteristics of life until they enter a living body and use its cell machinery to multiply.

Membranes are crucial because they separate the interior of the cell from the environment, allowing controlled interaction with external substances. In the case of viruses, they are not considered living organisms when outside a host because they lack functional membranes and organelles. Once inside a living cell, they hijack the cell's machinery to replicate, demonstrating how membranes are essential for life.

Think of a house (the cell) that needs doors (membranes) to control who can come in and out. A virus is like a burglar who can't enter (or operate) until he finds an open door (a living host), highlighting the importance of membranes in protecting the cell and regulating what enters.

--