The Fundamental Unit of Life – Parts of the Cell & their Functions (Part -3)

Parts of the Cell

• Cell Wall – only found in plant cells.
• Cell Membrane
• Protoplasm – includes Cytoplasm and Nucleus.

Cell Wall

• The cell wall is a outer covering of the Cell (Cell Membrane).
• It is Rigid and Freely-permeable.
• It is protective and supportive layer.
• Made out of Cellulose.

Functions of Cell Wall

• It provides shape and rigidity to the cell.
• Only found in Plant, fungi and bacteria cells.
• It protects the cell contents (protoplasm)
• It permits the cells to withstand very dilute external medium without bursting.

Cell Membrane

• Cell membrane encloses the protoplasm.
• It is flexible and semi-permeable.
• Made out of Lipid and Proteins.
• Three layered, consisting of central lipid layer sandwiched between two protein layers.

Functions of Cell Membrane

• Gives form (Shape & Size) to the cell.
• Maintains the individuality of the cell; i.e. separates the cell from the external surroundings.
• Keeps the cell contents in place
• Selectively permits (regulates) the flow of materials into and out of cell.
• Prevents mixing of the cell contents with extracellular materials.

Protoplasm

• The living material of Cell.
• First discovered by Purkinje.
• Consist of Cytoplasm & Nucleus

Cytoplasm

• The portion of the protoplasm excluding the nucleus is known as Cytoplasm.
• It is a semi-fluid jelly-like substance
• Various Organelles are present in it.

Nucleus

• Nucleus is the control centre of the cell, it controls and coordinates all the activities of the cell.
• It is roughly spherical in shape.
• Most cells have nucleus in it, the cells that doesn’t have a nucleus are calledEnucleate Cells. e.g.:- Red Blood Cells (RBC)
• The cells that have a single nucleus are called Uninucleate Cells.
• The cells that have more than one (multiple) nucleus’s are calledMultinucleate Cells.

Parts of Nucleus

• Nuclear Membrane       (Similar to Cell Membrane)
• Nucleoplasm
• Nucleolus
• Chromatin Network

Nuclear Membrane

• The membrane that bounds nucleus is known as Nuclear Membrane.
• It is double layered & porous
• Semi-permeable membrane
• It regulates the exchange of materials between Cytoplasm and Nucleoplasm.

Nucleoplasm 

• The part of protoplasm lying inside the nucleus, in which nucleoli & chromatin fibres are present.
• Semi-fluid Substance.

Nucleolus

• Nucleolus is a dense, spherical, darkly stained structure.
• It is the site of formation and store house of rRNA’s.

Chromatin Network/Nuclear Reticulum

• Chromatin Network/Reticulum is a group of chromatin fibres located inside the nucleus.
• They are only found during the resting stage of a cell.
• During the dividing stage, the network of Chromatin fibres separate out to form chromosomes.

Chromosomes

• Chromosomes are found in pairs
• They are made up of DNA’s & Proteins
• The segment of DNA which is responsible for specific hereditary character is known as Gene.

Classification of Cell’s based on the type of arrangement they have

• The cells that have well organised nucleus and cell organelles are called Eukaryotes. E.g.:- Amoeba, Paramecium
• Eu means True and Karyote means Nucleus.
• Eukaryotes have nuclear membrane, as well as membrane bound cell organelles.
•  The cells that do not have well organised nucleus and cell organelles are called Prokaryotes. E.g.:- Bacteria, Blue green algae
• Pro means Primitive (old) and Karyote means Nucleus. 
• Prokaryotes lack nuclear membrane and membrane bound cell organelles.
• The undefined nuclear region of Prokaryotic cell is called nucleoid.

Functions of Nucleus

• The nucleus controls all the cellular activities of the cell.
• The nucleus plays a vital role in Cell division.
• The nucleus carry as well as transmits hereditary characters.