➤ Cell is the smallest structural and functional unit of life.
➤ All living organisms are composed of cells.
➤ All vital metabolic activities of organisms occur inside the cell.

➤ Cytology is the branch of biology that deals with the study of cells.
➤ “Cyto” means cell and “logy” means study.
➤ It includes study of cell structure, function, and organelles.

➤ Robert Hooke observed thin slices of cork under a microscope in 1665.
➤ He discovered dead cells and named them “cells.”
➤ Because of this work, Hooke is known as the Father of Cytology.

➤ Antonie van Leeuwenhoek first observed living cells in 1674.
➤ He used a simple microscope to examine pond water.
➤ He observed microorganisms which he called animalcules.

➤ Matthias Schleiden and Theodor Schwann proposed the Cell Theory (1838-1839).
➤ It states that all living organisms are made of cells.
➤ The cell is the basic unit of life.

➤ In 1855 Rudolf Virchow proposed “Omnis cellula e cellula.”
➤ It means new cells arise from pre-existing cells.
➤ This concept completed the modern cell theory.

➤ Viruses do not follow the cell theory.
➤ They lack cellular structure (no cytoplasm or organelles).
➤ They contain only DNA or RNA enclosed in a protein coat (capsid).
➤ Viruses can reproduce only inside a host cell, so they are considered semi-living.

➤ The ovum (egg cell) is the largest cell in the human body.
➤ It contains large amounts of cytoplasm and nutrients.
➤ It is visible to the naked eye.

➤ Sperm is the smallest cell in the human body.
➤ It has a head, middle piece, and tail.
➤ The tail helps the sperm move towards the ovum for fertilization.

➤ The ostrich egg is the largest cell found in nature.
➤ It is a single cell that can be several centimeters in diameter.
➤ It contains nutrients required for the development of the embryo.

➤ The cell membrane is also called the plasma membrane.
➤ It forms the outer boundary of animal cells.
➤ In plant cells, it lies just beneath the cell wall.

➤ The cell membrane is composed mainly of proteins and lipids.
➤ Approximately 50% proteins and 50% lipids.
➤ Lipids form a phospholipid bilayer that maintains membrane structure.

➤ The cell membrane is selectively permeable.
➤ It controls the movement of substances in and out of the cell.
➤ Only specific molecules can pass through the membrane.

➤ Diffusion is the movement of molecules from higher concentration to lower concentration.
➤ It occurs spontaneously without using cellular energy.
➤ Example: spread of incense smell in air.

➤ Diffusion occurs in all states of matter.
➤ The rate of diffusion follows: Gases > Liquids > Solids.
➤ This happens because gas molecules move more freely.

➤ Osmosis is the movement of water molecules through a semi-permeable membrane.
➤ Water moves from higher water concentration to lower water concentration.
➤ Osmosis does not require energy.

➤ Active transport moves molecules from lower concentration to higher concentration.
➤ It requires cellular energy (ATP).
➤ This process helps maintain cellular balance.

➤ A hypotonic solution has less solute and more water than the cell.
➤ Water enters the cell through osmosis.
➤ The cell swells and may burst (turgidity).

➤ A hypertonic solution has more solute and less water than the cell.
➤ Water moves out of the cell by osmosis.
➤ The cell shrinks, a process called plasmolysis.

➤ In an isotonic solution, the solute concentration inside and outside the cell is equal.
➤ There is no net movement of water.
➤ Therefore, the cell size remains unchanged.

➤ The cell wall is present in plant cells, bacteria, fungi, and algae.
➤ It is absent in animal cells.
➤ It provides rigidity, protection, and structural support to the cell.

➤ The plant cell wall is mainly composed of cellulose.
➤ Cellulose provides strength and rigidity to plant cells.
➤ It helps maintain the shape of the cell.

➤ Cytoplasm is the fluid present between the plasma membrane and nuclear membrane.
➤ It contains cell organelles such as mitochondria and ribosomes.
➤ It is the site of many metabolic reactions.

➤ Cytosol is the water-based fluid portion of the cytoplasm.
➤ It contains dissolved nutrients, ions, and enzymes.
➤ Many biochemical reactions occur in cytosol.

➤ The nucleus was discovered by Robert Brown in 1831.
➤ It is usually located near the center of the cell.
➤ It controls the activities of the cell.