Cell and its structure

March 8, 2014
 Cell is a basic functional and structural unit of life. It was discovered by Robert Hooke in 1665.

Cell Theory

It states that
  • Body of all living organisms is composed of cells.
  • Each organism starts its life from single cell.
  • Each cell is made of pre-existing cell.
Some facts regarding cell
  • The smallest cell is Mycoplasma gallisepticum.
  • The biggest cell is egg of ostrich.
  • The longest cell is Neuron.
  • The biggest cell in human body is female sex organ ovum.

Types of cell

Cell is of two types:
Prokaryotic cell
Eukaryotic cell
It is primitive cell.
It is a complete cell.
It does not contain Nucleus.
It contain nucleus.
It contains Nucleoids and organelles like mitochondria, golgi bodies are absent.
It contains Nucleoids and organelles like mitochondria, golgi bodies.
For example: Bacteria, Arch Bacteria, Cyno Bacteria.
For example: Plant cell, Animal cell.
Ribosome is an organelle found in both Prokaryotic and Eukaryotic cell.

Part of cell

The various parts of cell are:
  • Cell wall: it is found only in plant cell. It is made up of cellulose. It provides rigidity to plants.
  • Plasma Membrane or cell membrane: It is the outer covering of animal cell. It is also found in plant cell. It is made up of phospholipids. It is selective permeable membrane.
  • Protoplasm: Entire fluid inside the plasma membrane is called protoplasm. It is divided into two parts:
    • Cytoplasm: it is the fluid outside nucleus and inside plasma membrane.
    • Nucleoplasm: it is the fluid inside nucleus.
  • Mitochondria: It is a rod shaped double layered organelle. It contain matrix. Matrix contains many enzymes which help in cellular respiration. It is a respiratory site in cellular respiration. It is also called power house of cell.
  • Lysosome:Lysosome contains many hydrolytic enzymes for digestion of waste material inside the cell. This cell may digest the entire cell, so it also called Suicidal bag.
  • Endoplasmic Reticulum (ER): It is a network connecting plasma membrane to nucleus. Its one side contains embedded ribosome also called rough or Ribosome endoplasmic Reticulum (RER). Its other side without ribosome is called smooth endoplasmic reticulum.
  • Ribosome: It is found in ER or cytoplasm inferior state. It helps in synthesis of protein.
  • Nucleus:It is a spherical shaped centrally located organelle. It contains nucleoplasm. Within nucleoplasm, there is Nucleolus which is called factory of ribosomes. Within nucleoplasm there are chromatids. Two chromatids join together at a point called centromere to form Chromosome.
    Different organisms have different number of chromosomes.
  • Gene: A bead like structure found in chromosome which is called Gene. It is carrier of genetic information from one generation to other in coded form. Gene is carrier of genetic information and chromosome id hereditary vehicle.
    Human contains 23 pairs of chromosome.

Cell division

There are two types of cell division:
Mitosis
Meiosis
This type of cell division occurs in somatic cell.
This type of cell division occurs in reproductive cell i.e. ova or sperm.
Due to mitosis, two daughter cells are produced having same number of chromosomes as parent cell.
Due to meiosis, four daughter cell are produced having half the number of chromosomes as in parent cell.
Uncontrolled mitosis causes cancer or tumor.