INTRODUCTION
All organisms are composed of structural and functional units of life called ‘cells’.
The body of some organisms like bacteria, protozoans and some algae is made up
of a single cell whereas the body of higher fungi, plants and animals are composed
of many cells. Human body is built of about one trillion cells.
Cells vary in size and structure as they are specialized to perform different functions.
But the basic components of the cell are common to all biological cells. This lesson
deals with the structure common to all types of the cells. You will also learn about
the kinds of cell division and the processes involved therein in this lesson.
OBJECTIVES
After completing this lesson, you will be able to : justify that cell is the basic structural and
functional unit of all organisms; list the components of the cell and state cell theory; differentiate
between prokaryotic and eukaryotic cells; differentiate between plant and animal cells;
illustrate the structure of plant and animal cells by drawing labelled diagrams; describe the structure
and functions of plasma membrane, cell wall, endoplasmic reticulum (ER), cilia, flagella, nucleus,
ribosomes, mitochondria, chloroplasts, golgi body, peroxisome, glyoxysome and lysosome;
describe the general importance of the cell molecules-water, mineral ions, carbohydrates, lipids,
amino acids, proteins, nucleotides, nucleic acids, enzymes, vitamins, hormones, steroids and
alkaloids; justify the need for cell division; describe various phases of cell cycle; explain the term
karyotype and mention the karyotype analysis and its
, THE CELL AND CELL THEORY
Landmarks in the study of a cell
Soon after Anton Van Leeuwenhoek invented the microscope, Robert Hooke in 1665 observed a piece of cork
under the microscope and found it to be made of small compartments which he called "cells" (Latin cell = small room).
In 1672, Leeuwenhoek observed bacteria, sperms and red blood corpuscles, all of which were cells. Much later, in
1831, Robert Brown, an Englishman observed that all cells had a centrally positioned body which he termed the
nucleus.
The cell theory
In 1838 M.J. Schleiden and Theodore Schwann formulated the "cell theory." Which
maintains that all organisms are composed of cells. cell is the structural and functional unit
of life, and cells arise from pre-existing cells.
The cells vary considerably, in shapes and sizes. Nerve cells of animals have long extensions. They
can be several centimeter in length. Muscle cells are elongated in shape. Egg of the ostrich is the
largest cell (75 mm). Some plant cells have thick walls. There is also wide variation in the number of
cells in different organisms.
All organisms are composed of structural and functional units of life called ‘cells’.
The body of some organisms like bacteria, protozoans and some algae is made up
of a single cell whereas the body of higher fungi, plants and animals are composed
of many cells. Human body is built of about one trillion cells.
Cells vary in size and structure as they are specialized to perform different functions.
But the basic components of the cell are common to all biological cells. This lesson
deals with the structure common to all types of the cells. You will also learn about
the kinds of cell division and the processes involved therein in this lesson.
OBJECTIVES
After completing this lesson, you will be able to : justify that cell is the basic structural and
functional unit of all organisms; list the components of the cell and state cell theory; differentiate
between prokaryotic and eukaryotic cells; differentiate between plant and animal cells;
illustrate the structure of plant and animal cells by drawing labelled diagrams; describe the structure
and functions of plasma membrane, cell wall, endoplasmic reticulum (ER), cilia, flagella, nucleus,
ribosomes, mitochondria, chloroplasts, golgi body, peroxisome, glyoxysome and lysosome;
describe the general importance of the cell molecules-water, mineral ions, carbohydrates, lipids,
amino acids, proteins, nucleotides, nucleic acids, enzymes, vitamins, hormones, steroids and
alkaloids; justify the need for cell division; describe various phases of cell cycle; explain the term
karyotype and mention the karyotype analysis and its
, THE CELL AND CELL THEORY
Landmarks in the study of a cell
Soon after Anton Van Leeuwenhoek invented the microscope, Robert Hooke in 1665 observed a piece of cork
under the microscope and found it to be made of small compartments which he called "cells" (Latin cell = small room).
In 1672, Leeuwenhoek observed bacteria, sperms and red blood corpuscles, all of which were cells. Much later, in
1831, Robert Brown, an Englishman observed that all cells had a centrally positioned body which he termed the
nucleus.
The cell theory
In 1838 M.J. Schleiden and Theodore Schwann formulated the "cell theory." Which
maintains that all organisms are composed of cells. cell is the structural and functional unit
of life, and cells arise from pre-existing cells.
The cells vary considerably, in shapes and sizes. Nerve cells of animals have long extensions. They
can be several centimeter in length. Muscle cells are elongated in shape. Egg of the ostrich is the
largest cell (75 mm). Some plant cells have thick walls. There is also wide variation in the number of
cells in different organisms.
