What is a cell?

cell_cartoonA cell is a basic unit of life, everyone knows that. It is the smallest particle our very body is made up of. Each cell fulfills a specific purpose. Its structure is out of shape in animals and humans. In plants, cells are rigid and are commonly rectangular or are of similar shape.

What is the Protoplasm?

The Cytoplasm, the Plasma membrane and the Nucleus of the cell are altogether known as the protoplasm of a cell.

The Organelles found in a Cell:

Plasma Membrane:

This is an animal cell. The outside purple layer in the figure is called the plasma membrane which is semi permeable to specific substances such as food cell which has been cut into small cells by digestive system. It lets in small particles to strengthen it for chemical reactions. It basically is the protective barrier of the cell.


The inner part contains a gelatin substance consisting of mainly water and other minerals which create the cytoplasm. Inside the cytoplasm many chemical reactions occur which helps in everyday activities. Inside the cytoplasm other structures are also found.

Mitochondria and ATP:

The mitochondrion (plural – mitochondria) is an oval shaped structure which is mitochondriafigure1.jpginvolved in cell respiration. It is an organelle found inside the cell and has two membranes, an envalope, the outer membrane, made of porin, and the inner membrane shaped like a cristae. The cristea is shaped as such to increase its surface area to volume ratio. The outer membrane and the inner membrane are both specific in nature  causing certain substances to enter the mitochondria to begin breaking it for forming ATP (Adenosine Triphosphate). The space between the membranes is known as the intermembrane space. It is the power house of a cell.

 The Vacuole and Centrioles:

The animal cell also contains small bits of vacuole compared to large vacuoles found in plants. These don’t last long in animal cells. In plant cells the vacuoles are large structures comprising most of the cells and contains watery substance inside them as well as pigments, proteins, the cell sap and various other substances. The colour of the petal is due to the pigments found inside the vacuoles.

A pair of small structures found in cell is called centrioles which bring about cell division. These are mostly found in animal cells rather than in plant cells.

The Nucleus:

The next thing found in a cell is the nucleus. It is the brain of the cell which guides the cell and commands it to do different activities. It includes three main structures. The outer layer is covered with the two membranes which is called the nuclear envelop which forms a barrier between the cytoplasm and the contents of the nucleus.

The outer membrane is continuous with sac like structures called the endoplasmic reticulum. Inside its membrane is found the chromatin which contains hereditary information. The chromatin is a thread like structure which is made up of protein and deoxyribonucleic acid (DNA). The DNA is segmented into genes which contain hereditary information inherited from our parents as well as instructions for cell activity.

Ch1C1This is a detailed structure of the nucleus.

The nucleus of a cell also contains the nucleolus which forms proteins and ribosomes and RNA (ribonucleic acid).

All the structures found in the nucleus including the nuclear envelop forms the nucleoplasm (the protoplasm of the nucleus). The envalope seperates the nucleus contents from the cytoplasmic contents this is called cell compartmentalization. There are nuclear pores found on the envalope for exchange of substances between the nucleus and the cytoplasm.

plant_cellCell Wall

The cell wall is a rigid structure made of cellulose. It is freely permeable unlike the plasma membrane and absorbs all substances. The plant cell is normally larger than animal cell and has a fixed and definite shape due to the cell wall. During osmosis the cell wall prevents the cell from bursting.


Chloroplasts are large organelles found inside the plant cell, the chloroplast have grana inside them, these are called as such due to their grain like structure. These contain the substance chlorophyll. The chlorophyll absorb sunlight for the process of photosynthesis.

Endoplasmic Reticulum

The endoplasmic reticulum is a structure found continuous with the outer nucleur membrane, these look like sacs. There are 2 types of ER in a cell, the Rough Endoplasmic Reticulum (RER) and the Smooth Endoplasmic Reticulum (SER). The RER is known as such due the presence of ribosomes around it. The ribosomes form porteins which are sent into the sacs which are modified along the way. The SER is so called because it lacks the ribosomes surrounding the RER. These simply create steroids and lipids.

Tissues, Organs and Organ systems:

A cell does not carry out all the heavy duty work all by itself. As we all know that cells forms a group with other cells which serve the same purpose. These groups are known as tissues.

Examples of tissues in animals and humans are:

  • Nervous Tissue
  • Epithelial Tissue                                                                                              ec19dfb80ab59a5fc080b354fc937d78
  • Adipose Tissue
  • Muscle Tissue

Examples of tissues in plants are:

  • Vascular Tissue
  • Epidermal Tissue
  • Ground Tissue
  • Meristematic Tissue

Tissues further join together with another tissue with the same nature and purpose and form a group called the organ.

The most common examples of organs in animals are:

  • Stomach                                                                                             h9991275_001
  • Liver
  • Heart
  • Skin
  • Pancreas and many more.

Example of plant organs:

  • Leaves
  • Stems
  • Flower
  • Root

The organs are further grouped together into organ systems. Each organ system has organs working together to achieve the same purpose. There are 11 Organ systems in a human body.

Common examples of organ systems in animals are:

  • Digestive system                                                                                           K-digestive-275x267-enIL
  • Respiratory system
  • Excretory system

Examples of plant organ systems are:

  • Shoot system
  • And the Root system


When new cells are produced they may change their function and form new kinds of tissues. This process of change is known as Differentiation.

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