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.