The Fundamental Unit Of Life

• In 1665, Robert Hooke, a British scientist discovered cells.
• He took a thin slice of cork from an oak tree and observed it under the microscope.
• He observed honeycomb-like compartments bounded by thick walls; hence, named them “cells”.

• The cell is called the structural unit of life because all the organisms are made up of cells.
• The cell is also known as the functional unit of life because all the things that an organism does are controlled by cells.
• Cells organise and form tissues, which form organs which further form organ systems that perform all the bodily functions.
• Hence a cell is the structural and functional unit of life.

• The cell membrane is also known as the plasma membrane.
• It is the outermost covering of the cell that separates the contents inside of the cell from its outside environment.
• Plasma membrane only allows some materials, like some small molecules and water molecules, to enter the cell or leave from the cell.
• Not everything that comes in contact with the cell membrane can enter the cell because of this.
• So, the plasma membrane is known as a selectively permeable membrane. It selects or chooses what goes in and out of the cell.

Diffusion is the process by which particles move from a region of higher concentration to a region of lower concentration, until uniform concentration is finally achieved. Carbon dioxide (CO₂) moves in and out of the cells by the process of diffusion.

Osmosis is a special type of diffusion. Osmosis is diffusion of water from the region of its higher concentration (pure water or dilute solution) to the region of its lower concentration (strong solution) though a semipermeable membrane. Water moves in and out of the cells by osmosis.

Both diffusion and osmosis are physical or mechanical processes and do not require spending of energy for their performance by the cells.They are both gradient dependent process.

2. Lack of organized nucleus, the genetic material present in the form of nucleoid. Nuclear membrane is absent.

4. Membrane-bound cell organelles such as mitochondria, plastids, Golgi apparatus, lysosomes, etc. are present in the cytoplasm.

Mitochondria and Plastids are two cell organelles that contain their own genetic material. They are also known as Semi-Autonomous organelles as they have their own DNA(Genetic Material) and Ribosomes.

Cell is the smallest unit of a life which is able to perform all basic functions of life. If the organisation of a cell is destroyed due to some physical and chemical influence, it will not able to perform all living functions like respiration, nutrition, excretion, etc. and the cell will ultimately die.

• Lysosomes are the waste disposal system of the cell.
• They help to keep the cell clean by digesting any foreign materials or worn out cell organelles.
• Lysosomes contain a powerful digestive enzyme capable of digesting all organic materials.
• Lysosomes are also known as "Suicide Bags" because whenever their is some disturbance in cell metabolism or when the cell gets damaged, the lysosomes burst themselves resulting in the digestion of their own cell by the digestive enzymes.

Ribosomes are the sites of protein synthesis. They are small and dense particles which occur freely in the cytosol or remain attached to the endoplasmic reticulum. They take part in the synthesis of proteins.

Difference between plant cell and animal cell:

• Plasma membrane is the outer covering of the cell.
• It is semi permeable in nature. This means that it allows only certain molecules to enter or leave the cell.
• If the plasma membrane is rutured, the cell content (the cytoplasm and organelles) will get displaced and the cell will die.
• No kind of cell uptake would be possible, this means no osmosis or diffusion.

If there was no Golgi apparatus in the cell, the following cell activities would be affected:

(i) Formation of lysosomes

(iii) The formation of cell plate and cell membrane
(iv) Storage, modification and packaging of products in vesicles

• The mitochondria are known as the powerhouse of the cell. (Singular: Mitochondrion; Plural: Mitochondria)
• Reason: ATP synthesis takes place in the mitochondria.
• ATP molecules (Adenosine Triphosphate) are the energy molecules.
• ATP molecules store and transport chemical energy within cells which they use to carry out the different processed.

The Lipids and Proteins that constitute the cell membrane are mainly synthesized in the Endoplasmic Reticulum.Their are two types of Endoplasmic Reticulum:-

1. Smooth Endoplasmic Reticulum:- Which is without the presence of ribosomes and is specialized for synthesizing lipids used in cell membrane.

2. Rough Endoplasmic Reticulum:- Which has Ribosomes attached on the outer surface and are specialized to synthesize proteins used in cell membrane

Amoeba obtains its food through the process of endocytosis. The plasma membrane of Amoeba is flexible, which help the amoeba to engulf its food particles and other material from its external environment. The flexible plasma membrane that an amoeba uses to capture its prey is known as pseudopodia. (meaning false legs)

Osmosis is a special case of diffusion of water molecules from a region of higher concentration to a region of lower concentration through a semi-permeable membrane. The below diagram shows osmosis:-

(i) Water gathers in the hollowed portion of unboiled potatoes B and C because the cells of potatoes gained water by endosmosis.
The water moveed inside the cell by osmosis(From higher concentration to Lower Concentration).

(ii) Potato cup A is necessary in the experiment as a ‘control’ for providing comparison with situations created in potato cups B, C and D.