❖ CELL:-
The cell is the structural and functional unit of life, which means that the structure of our
body is made up of cells, and all the functions we perform are done by the cell.
• Cells, as the fundamental units of life, possess a complex structure that allows them to
carry out various functions necessary for the existence and functioning of living
organisms.
• Cells are capable of independent existence.
• Living beings can be:
o Unicellular organisms – Made up of a single cell. Example: Amoeba, bacteria, fungi,
paramecium, etc
o Multicellular organisms – Composed of multiple cells. Example: Humans, animals,
plants
• Cells come in various shapes and sizes, such as muscle cells, neuron cells, sperm cells, and
egg cells. Their combination forms an organism.
Characteristics of the Cell:
• Reproduction: Cells play a role in both sexual and asexual modes of reproduction.
• Cell structure: It includes topics such as the division of labour.
• Metabolism: Metabolism covers digestion, excretion, respiration, and blood circulation.
• Adaptation: There are two types of adaptation: short-term adaptation and long-term
adaptation.
Discovery of the Cell:
• Robert Hooke (1665): The discovery of the cell is credited to Robert Hooke, an English
scientist, who first observed cells in 1665.
o Hooke was examining a thin slice of cork under a microscope.
o The cork appeared to be made up of tiny, box-like structures, which he called "cells"
because they resembled the small rooms (cells) that monks lived in.
• Anton van Leeuwenhoek (1674): Anton van Leeuwenhoek, a Dutch scientist, made
significant improvements to the microscope.
o He was the first to observe live cells, including bacteria, red blood cells, and sperm
cells. He discovered free-living cells in pond water.
• Robert Brown (1831): In 1831, while examining orchid cells under a microscope,
Robert Brown observed a small, round structure inside the cell. He identified this
structure as the nucleus.
o He was the first to describe the nucleus and recognize its importance within the cell.
