Cells, The Basic Unit of Life

What differentiates the living from the non-living? What do the living have that the non-living do not have? They have cells, that make up you, me, elephants, banyan tree or the bacteria.

There are two types of living beings – Plants and Animals. Both types have their own type of cells. While there are many similarities, there are some differences as well.

Plant cell

They have a cell wall
Cell shape is rectangular
Nucleus is at side of cell
They have plastids
Have large vacuole
Have less number of mitochondria

Animal cell

They do not have cell wall
Cell shape is round or irregular
Nucleus is at the centre
They do not have plastids
Have more number of small vacuoles
Have more number of mitochondria

Parts of a cell

Plasma membrane

Outermost membrane
Allows things to enter or leave the cell by diffusion/osmosis
It also prevents from entering
Made up of lipids and proteins

Cell wall

Present only in plants
Made up of cellulose
Rigid, and able to withstand outside pressure

Nucleus

Dark, dot like structure
Plays important role in cell division
Contain chromosomes
Chromosomes contain DNA that have information about the organism, to be passed to the offspring

Cytoplasm

It is the fluid inside the plasma membrane
Contains cell organelles

Cell organelles

They are the parts having specific functions

Cell Organelles

Endoplasmic reticulum

There are two types – Smooth (SER), Rough (RER
RER creates proteins
SER creates lipids (fat molecules)
Proteins and lipids act as enzymes and hormones
ER transports materials to different parts of the cell

Golgi apparatus

They are flattened sacs parallel to each other
They pack the materials created by ER and supply to other parts of the cell
Store, modify and pack the products
Convert complex sugars to simple sugars
Create lysosomes

Lysosomes

Sacs filled with enzymes
Break down bacteria, food and foreign substances
Keep the cell clean by removing wastes
If damaged, lysosomes digest themselves

Mitochondria

Called the powerhouse of the cell
Have two membranes – Outer is porous, inner has folds
Provide energy to cell in the form of ATP molecules
Have their own DNA and ribosomes

Plastids

Present only in plant cells
Two types – Chromoplasts, Leucoplasts
Chromoplasts contain chlorophyll
Leucoplasts store oils, proteins and starch
Have their own DNA and ribosomes

Vacuoles

They are sacs for storing solid and liquid contents
Store amino acids, proteins, sugars
They are large in plants, small in animals

Cell Division

The process of creating new cells by the parent cell dividing itself to form daughter cells is called cell division. There are two types – Mitosis and Meiosis

Mitosis

Each mother cell divides to form two daughter cells
They have same number of chromosomes as mother cell
Daughter cells are exact replica as the mother cell
For growth and repair of tissues

Meiosis

Each mother cells divide to form four daughter cells
They have half the number of chromosomes as mother cell
Form gametes needed for reproduction

Movement of Components

Diffusion: Movement of gases (O₂ and CO₂) in and out of the cells
Osmosis: Movement of water in and out of the cells

Types of solutions related to osmosis

Hypotonic

There is more water outside the cell
Water enters the cell

Isotonic

Water concentration same in and out
No movement of water

Hypertonic

More water inside the cell
Water leaves the cell

Basic organisms like prokaryotes do not have a proper nucleus and organelle membranes, unlike the advanced eukaryotes.