Key Points

The cell was first discovered by Robert Hooke in 1665 while observing a thin slice of cork. He saw honeycomb-like compartments which he called 'cells', a Latin word for 'a little room'.

Proposed by Schleiden and Schwann, the theory states all living things are composed of cells and the cell is the basic unit of life. Virchow later added that all cells arise from pre-existing cells.

The plasma membrane is the outer boundary of the cell, made of lipids and proteins. It is a selectively permeable membrane, meaning it controls the entry and exit of substances.

Diffusion is the movement of substances like oxygen or carbon dioxide from high to low concentration. Osmosis is the specific movement of water across a selectively permeable membrane.

In a hypotonic solution, a cell swells up by gaining water. In a hypertonic solution, it shrinks by losing water. In an isotonic solution, the cell size remains the same as there is no net water movement.

Present in plant cells, fungi, and bacteria, the cell wall is a rigid layer outside the plasma membrane. It provides structural strength and prevents the cell from bursting due to excessive water intake.

The nucleus is the control center of the cell, containing chromosomes which hold genetic information in the form of DNA. It is enclosed by a double-layered nuclear membrane in eukaryotes.

Prokaryotic cells lack a defined nucleus and membrane-bound organelles; their genetic material is in a nucleoid. Eukaryotic cells have a true nucleus and organelles like mitochondria enclosed in membranes.

The ER is a network of membranes. Rough ER (RER) has ribosomes and synthesizes proteins. Smooth ER (SER) synthesizes fats (lipids) and helps in detoxification.

The Golgi apparatus modifies, sorts, and packages materials synthesized in the cell, like proteins from the ER. It is also involved in the formation of lysosomes.

Known as 'suicide bags', lysosomes are membrane-bound sacs with powerful digestive enzymes. They act as the cell's waste disposal system by breaking down foreign material and worn-out organelles.

Mitochondria are the 'powerhouses of the cell'. They generate energy in the form of ATP (Adenosine triphosphate) through cellular respiration. They uniquely contain their own DNA and ribosomes.

Plastids are found only in plant cells. Chloroplasts are green plastids responsible for photosynthesis. Leucoplasts are white or colorless plastids that store starch, oils, and proteins.

Vacuoles are storage sacs for solid or liquid contents. Plant cells have a large central vacuole that maintains turgidity and stores substances like amino acids, sugars, and wastes.

There are two types of cell division. Mitosis results in two identical daughter cells and is used for growth and repair. Meiosis produces four gametes (sex cells) with half the number of chromosomes.

The flexibility of the cell membrane allows a cell to engulf food and other material from its environment. This process, called endocytosis, is how single-celled organisms like Amoeba obtain their food.