Observing Onion Cells ( virtual lab)
04 January, 2024

Observing Onion Cells ( virtual lab)



Cells are the smallest units of life in all living organisms, playing a crucial role in facilitating various vital activities such as digestion, movement, growth, and reproduction.


Importance of Cells:

Cells vary in their functions; for instance, plant cells assist in the transportation of water and salts, while white blood cells in humans and most animals help resist diseases. Despite these differences, plant cells, white blood cells, and all other cells share several common aspects.


Cell Theory:

In 1665, scientist Robert Hooke discovered cells after inventing the microscope. During his examination of a thin section of cork, he observed stacked chambers, which he named cells (see Figure 1). In the 17th and 18th centuries, scientists examined various living organisms using microscopes, leading to the development of the cell theory, consisting of three main ideas:


1. All living organisms are composed of one or more cells.

2. The cell is the basic unit of life where vital activities occur.

3. All cells arise from similar cells.


Microscopic Cells:

All living organisms are made up of cells, and bacteria are the smallest living organisms (see Figure 2). Bacteria consist of only one cell.


How many cells make up bacteria?

Large living organisms are composed of multiple cells that collaborate to perform vital activities. Most living organisms around us are multicellular. For example, your body consists of more than 10 trillion cells.



Scientists began studying cells over 300 years ago. Advancements in microscope manufacturing have allowed for the examination of cell differences. Modern microscopes, commonly used in schools, are compound light microscopes. They magnify images of tiny objects. In this type of microscope, light passes through the object first, then through two or more lenses. The lens closest to the viewer's eye is called the eyepiece lens, while the lens closest to the object being magnified is called the objective lens. The compound microscope's magnification depends on the power of both lenses: the eyepiece and the objective. If you examine either of these lenses, you will notice an "x" followed by a number, indicating its magnification power. For instance, a 10x objective lens means it magnifies the object ten times. To calculate the compound microscope's magnification power, multiply the eyepiece lens's magnification by the objective lens's magnification.


What are cells made of?

Despite their small size, cells consist of smaller parts, each with a specific function. Cells can be likened to a bakery, requiring various equipment, energy, and raw materials, much like wheat, water, and sugar. The cell's operations are overseen by the cell manager, determining plans for workers and the stages of manufacturing and selling bakery products.


Inside the Cell:

The cell operates similarly to a bakery, as it requires various equipment for its functions. Despite being small, the cell contains parts that store materials, such as water and nutrients, within vesicles in the cytoplasm. The cell is enclosed by a plasma membrane, acting as a flexible barrier between the cell and its environment, regulating the passage of materials.


Outside the Cell:

Similar to the walls of a bakery, the plasma membrane surrounds and protects cell components. This membrane serves as a flexible barrier, separating the cell from its surrounding environment and regulating the movement of materials in and out of the cell. Some cells, like plant, algae, and fungal cells, are surrounded by a cell wall outside the plasma membrane, providing support and protection.


Inside the Cytoplasm:

The cell is filled with a semi-gelatinous fluid called cytoplasm, constituting two-thirds water and containing various chemicals necessary for cell functions. Most vital activities occur within the cytoplasm, resembling the operational area in a bakery.



All cells, except bacterial cells, contain organelles, as seen in Figures 3 and 4. Organelles are specialized structures capable of movement within the cytoplasm and perform essential life processes. Organelles can be compared to employees in a bakery, each having a specific function. In bacterial cells, most life activities occur in the cytoplasm.


The Nucleus:

Similar to how a bakery manager plans and oversees operations, the cell's genetic material, housed within the nucleus, regulates most cell activities. The genetic material is carried on chromosomes in the form of a complex chemical called deoxyribonucleic acid (DNA), which determines the living organism's characteristics, such as plant leaf shape or human eye colour.



In conclusion, cells are the fundamental building blocks of life in all living organisms. They exhibit diversity in their functions, contributing to vital activities crucial for an organism's survival. The cell theory, developed over centuries, has revolutionized our understanding of life. Observing cells under a microscope has allowed scientists to delve into their intricacies, discovering the minute details of their structure and functions. Understanding this basic unit of life reveals the mysteries and depths of the biological world, advancing knowledge and progress in the field of life sciences.


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