Ch-5 The Fundamental Unit of Life: Cell

SUBJECT: BIOLOGY

CLASS :IX

Contents

• Cell Theory

• Types of Cell

• Components of Cell

Cell Theory

•Robert Hooke saw that the cork resembled the structure of a honeycomb consisting of many little compartments.

•Cork is a substance which comes from the bark of a tree. (This was in the year 1665 when Hooke made this chance observation through a self-designed microscope)

•Robert Hooke called these boxes cells

Cell

•Cells were first discovered by Robert Hooke in 1665

•Cell is a Latin word for ‘a little room’

•Cells represent the basic structural and functional unit of life.

•Organelles - small structures inside a cell with specific functions.

•All organisms are composed of one or more cells.

•All tissues & organs are composed of cells.

•There is no life without cells!

Types of Cells

• Cells are similar to factories with different laborers

and departments that work towards a common

objective.

• Various types of cells perform different functions.

Based on cellular structure, there are two types of cells:

•Prokaryotes•Eukaryotes

Prokaryotic

• Prokaryotic cells have no nucleus. Instead, some prokaryotes such as bacteria have a region within the cell where the genetic material is freely suspended. This region is called the nucleoid.

• The cell size ranges from 0.1 to 0.5 µm in diameter.

• They all are single-celled microorganisms. Examples include archaea, bacteria, and cyanobacteria.

• The hereditary material can either be DNA or RNA.

• Prokaryotes reproduce by binary fission, a form of sexual reproduction.

Eukaryotic• Eukaryotic cells are characterized by a true nucleus.

• The size of the cells ranges between 10–100 µm in diameter.

• This broad category involves plants, fungi, protozoan, and animals.

• The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in and out of the cells. It is also responsible for cell to cell communication.

• They reproduce sexually as well as asexually.

Components of Cells

•The plasma membrane surrounds the cell.

•The nucleus is the largest organelle.

•Double layered nuclear envelope.

Cell Model (Internet connection required to follow link)

Components of Cells

• Cytoplasm refers to the cellular material between

the cell membrane and nuclear envelope.

• Organelles such as the mitochondria, Golgi

complex, centrioles, and endoplasmic reticulum,

vacoules, ribosomes, chloroplast, lysosomes are

found in the cytoplasm.