Cell Biology Fundamentals

Cell: The Unit of Life

• The cell is the fundamental structural and functional unit of all living beings.
• A cell is the smallest part of an organism capable of independent existence and performing essential functions of life.

Discovery of Cells

• Antony van Leeuwenhoek, a Dutch scientist, constructed the first microscope.
• Robert Hooke, an English scientist, developed a compound microscope and observed "box-like" compartments in a cork slice, which he named "cells".

Cell Theory

• Matthias Schleiden, a German botanist, discovered that every plant is made up of cells.
• Theodor Schwann, a German zoologist, discovered that all animals and plants are composed of cells.
• Rudolf Virchow added to the cell theory by stating that all cells arise from pre-existing cells.

Types of Cells

• Single-celled organisms: made up of just one cell, e.g. bacteria, yeast, amoeba.
• Few-celled organisms: made up of a few hundred or thousand cells, e.g. Spirogyra, Volvox.
• Multi-celled organisms: made up of millions and billions of cells, e.g. human beings, mango trees.

Size of Cells

• Cells are very small and can only be seen with a microscope.
• Smallest cells: bacteria (0.3-5.0 micrometre).
• Longest cells: nerve cells.
• Largest cells: birds' eggs, e.g. ostrich egg is the largest single cell.

Importance of Cell Size

• Small cell size allows for rapid communication between regions for effective functioning.
• Small cell size provides a large surface area/volume ratio for greater diffusion of substances in and out of the cell.

Cell Shapes and Functions

• Human red blood cells: circular and biconcave for passing through narrow capillaries and transporting oxygen.
• White blood cells: amoeboid for squeezing out through capillary walls.
• Nerve cells: long for conducting impulses from distant parts of the body to the brain and vice versa.
• Muscle cells: long and contractile for pulling or squeezing parts.
• Guard cells: bean-shaped for opening and closing stomatal pores in leaves.

Structure of a Cell

• Three essential parts: cell membrane, nucleus, and cytoplasm.
• Cell membrane (plasma membrane): a living membrane with fine pores, allowing selective permeability.
• Cell wall (in plant cells): a non-living, permeable structure providing shape and rigidity.

Cell Organelles

• Cytoplasm: a semi-liquid substance containing many damaged cells that can be rapidly destroyed by lysosomes.
• Centrosome (in animal cells): containing two centrioles, which develop into spindle fibers during cell division.
• Plastids (in plant cells): leucoplasts (colourless), chromoplasts (variously coloured), and chloroplasts (green-coloured).
• Non-living substances or cell inclusions: granules, vacuoles.

Nucleus

• A small, spherical mass located in the center of the cytoplasm.
• Nucleoplasm contains chromatin fibers.
• Prokaryotic cells: lack nuclear membrane, e.g. bacteria.
• Eukaryotic cells: have a double nuclear membrane, e.g. all other organisms.

Learn about the basic building blocks of life, cells, and their functions in living organisms. Discover how the invention of the microscope led to the discovery of cells.