1.1.1 Eukaryotes and Prokaryotes

Plant and animal cells (eukaryotic cells) are complex structures that make up the bodies of plants, animals, fungi, and protists. They possess a nucleus that contains genetic material, along with a cell membrane, cytoplasm, and various organelles that perform specific functions within the cell.

Structure of Eukaryotic Cells

• Cell Membrane: Both plant and animal cells are enveloped by a cell membrane, also known as the plasma membrane. The cell membrane acts as a barrier, regulating the movement of substances in and out of the cell.
• Cytoplasm: The cytoplasm is the gel-like substance that fills the cell, surrounding the organelles. It contains various molecules, enzymes, and organelles necessary for cellular processes.
• Nucleus: The nucleus is the most prominent organelle in eukaryotic cells and is enclosed within a nuclear membrane. It houses the cell’s genetic material, including DNA, which carries instructions for cellular activities.

In our exploration of cellular structures, we now turn our attention to bacterial cells (prokaryotic cells). Unlike eukaryotic cells found in plants and animals, bacterial cells are single-celled organisms that are simpler in structure. They lack a defined nucleus and membrane-bound organelles but possess unique features that allow them to thrive in diverse environments.

Structure of Prokaryotic Cells

• Cell Membrane: The cell membrane, also known as the plasma membrane, is a thin barrier surrounding the bacterial cell. It regulates the movement of substances in and out of the cell.
• Cytoplasm: The cytoplasm is a gel-like substance that fills the bacterial cell and houses various cellular components. It contains enzymes, ribosomes, and other molecules necessary for cellular processes.
• Cell Wall: Bacterial cells have a cell wall outside the cell membrane. The cell wall provides structural support and protection for the cell. Unlike the cellulose-based cell walls of plant cells, bacterial cell walls are composed of peptidoglycan or other materials.
• Genetic Material: The genetic material in bacterial cells consists of a single, circular DNA molecule known as the nucleoid. The nucleoid is not enclosed within a nucleus but is instead found within the cytoplasm. Additionally, bacteria may contain small rings of DNA called plasmids, which can carry extra genes.

Bacterial cells are significantly smaller in size compared to eukaryotic cells. Eukaryotic cells typically range from 10 to 100 micrometres (μm) in diameter. Prokaryotic cells, such as bacteria, are generally smaller, ranging from 1 to 5 micrometres (μm) in length.

The size of cells is measured using units such as centimetres (cm), millimetres (mm), micrometres (μm), nanometers (nm), and picometers (pm).

• A centimetre (cm) is equal to one hundredth of a metre (10^-2 m).
• A millimetre (mm) is equal to one thousandth of a metre (10^-3 m).
• A micrometre (μm) is equal to one millionth of a metre (10^-6 m).
• A nanometer (nm) is equal to one billionth of a metre (10^-9 m).
• A picometer (pm) is equal to one trillionth of a metre (10^-12 m).

Order of Magnitude Calculations

Orders of magnitude refer to the powers of 10 that indicate the scale or magnitude of a quantity. Moving up or down an order of magnitude means multiplying or dividing the quantity by a factor of 10.

Standard form is a way to express numbers as a product of a decimal number and a power of 10. It is written in the form: a × 10^b, where “a” is a number between 1 and 10, and “b” is the power of 10.

Suppose we want to compare the size of a eukaryotic cell (20 μm) and a bacterial cell (2 μm). We can round them to the nearest power of 10: 20 μm ≈ 10¹ μm and 2 μm ≈ 10⁰ μm. The difference in order of magnitude is 1, indicating that eukaryotic cells are approximately 10 times larger than bacterial cells.

Conclusion

Bacterial cells, as prokaryotes, are smaller and simpler in structure compared to eukaryotic cells. They lack a nucleus and membrane-bound organelles but possess essential components such as a cell membrane, cell wall, cytoplasm, and genetic material.