The UPSC mains GS-3 paper syllabus has various subjects like Economics, Science and Technology. Science and technology in UPSC is mostly concerned with current Affairs. but it is necessary to understand the basics of science. Basics of Biology starts with Cells, This article will give aspirant an idea of the basics of Human body cells.


  • What are cells?
  • Types of Cells


Cells in the human body number in the trillions and come in all shapes and sizes.

These tiny structures are the basic unit of living organisms. Cells comprise tissues, tissues make up organs, organs form organ systems, and organ systems work together to create an organism and keep it alive.


In the living organisms there are two types of cellular organizations. If we look at very simple organisms like bacteria and blue-green algae, We will discover cells that have no defined nucleus, these are prokaryotes cells. The cells which have definite nucleus are known as eukaryote. But the things which both have in common is that there are compartments surrounded by some type of membranes. These are called cell membranes.

Cell membranes 

It is like a plastic bag with some tiny holes that bag holds all of the cell pieces and fluids inside the cell and keeps foreign particles outside the cell. The holes are there to let some things move in and out of the cell. Compounds called proteins and phospholipids make up most of the cell membrance.the phospholipids make the basic bag. The proteins are found around the holes and help move molecules in and out of the cell. Substances like Co2 and O2  can move across the cell membranes by a process called diffusion. Diffusion is a process of movements of substance from a region of high concentration to a region where its concentration is low. Water also obeys the law of diffusion. The movement of water molecules is called osmosis.


It is the fluid that fills a cell. Scientists used to call the fluid proto plasm.cytoplasm contain many specialized cell called organ cells. Each of these organ cells performs a specific function for the cell. Cell organells : Organells are living part of the cell have definite shape, structure and functions. To keep their function different from each other these organelles use membranes bound little structure with in them selves. Some of the important organells are :

Endoplasmic reticulum 

It is a network of tulsular membranes connected at one end to the nucleus and on the other to the plasma membranes. Endoplasmic reticular (ER) are two types:-rough endoplasmic reticular (RER) and Smooth endoplasmic reticulum (SER).

Functions of ER:

  • It forms the supporting skeleton frame work of the cell.
  • It provides a pathway for distribution of nuclear material.
  • It provides surface for various enzymatic reactions.


It synthesis protein, and ER sent these protein in various part of the cell. Where as SER helps in the manufacture of fats. Functions of these proteins and fats :

  • Protein and fat (lipid) help in building the cell membranes. This process is known as membranes biogenesis.
  • Some other protein and fat functions as enzymes and hormones.
  • SER plays a crucial role in detoxifying many poisons and drugs.

Golgi apparatus

It is found in most cell. It is another packaging organelle like the endoplasmic reticulum. It gathers simple molecules and combines them to make molecules that are more complex. It then takes those big molecules, packages them in vesicles and either stores them for faster use or sends them out of the cell. Other functions:

  • Its functions include the storage modifications and packaging of products in vesicles.
  • It is also the organ Elle that builds lysosomes (cells digestion machines).


It is a kind of waste disposal system of the cell.  It helps to keep the cell clean by digesting any foreign material.  Old organs cell end up in the lysosomes. When the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore lysosomes are also known as the “suicide ways” of the cell.


It is known as the power house of the cell. The energy required for various chemical activities headed for life is released by mitochondria in the form of ATP (adenosine-triphosphate) molecules.

  • ATP is known as the energy currency of the cell. The body uses energy are stored in ATP for making new chemical compounds and for mechanical work.
  • Mitochondria are strange organells in the sense that they have their own DNA and ribosomes, there fore mitochondria are able to make their own protein.
  • Mitochondria is absent in bacteria and the red blood cells of mammals and higher animals.


It is a micro-tubular structure; centrioles are concerned with cell division. It initiates cell division.


These are present only in plant cells. There are two types of plastids:-chromoplastes (colour plastides) and leucoplast (white or colourless plastids).

  • Chromoplast impart colour to flowers and fruits.

Each type of cell in the human body is specially equipped for its role. Cells of the digestive system, for instance, are vastly different in structure and function from cells of the skeletal system. Cells of the body depend on each other to keep the body functioning as a unit. There are hundreds of types of cells, but the following are the most common.


Stem Cells

Stem cells are unique in that they originate as unspecialized cells and have the ability to develop into specialized cells that can be used to build specific organs or tissues. Stem cells can divide and replicate many times in order to replenish and repair tissue. In the field of stem cell research, scientists take advantage of the renewal properties of these structures by utilizing them to generate cells for tissue repair, organ transplantation, and for the treatment of disease.

Bone Cells

One of the strongest cells in the body bone cells are connected through calcium and phosphate. These give your body strength and support in its skeletal system. There are many different types of bone cells in the body: Osteoclasts, Osteoblasts, and Osteocytes. Each cell plays a different part in the body and performs a different task. Osteoclasts aid in bone resorption releasing enzymes and acids to help the process of breaking down bones. Osteoblasts help form new bones by managing bone mineralization. Osteoblast cells form osteocytes which are found in the bone. These cells produce growth on the bone in response to strain and help keep calcium balanced. Without bone cells you wouldn’t have your skeletal system.

Blood Cells

From transporting oxygen throughout the body to fighting infection, blood cell activity is vital to life. Blood cells are produced by bone marrow. The three major types of cells in the blood are red blood cells, white blood cells, and platelets.

Blood cells are of course very important for our body! They transport oxygen through the body, fight infections, and are critical to our body. There are different types of blood cells in the body such as red blood cells, white blood cells, and platelets. Each of these cells perform a different task in the bloodstream. Red blood cells carry oxygen through the body while white blood cells fight off diseases and illnesses. Platelets clot the blood to prevent too much blood loss. For example when you cut your finger platelets come together to stop the cut from bleeding. Each of these three cells are produced through bone marrow.

Muscle Cells

Muscle cells form muscle tissue, which enables all bodily movement. The three types of muscle cells are skeletal, cardiac, and smooth. Skeletal muscle tissue attaches to bones to facilitates voluntary movement. These muscle cells are covered by connective tissue, which protects and supports muscle fiber bundles.

Cardiac muscle cells form involuntary muscle, or muscle that doesn't require conscious effort to operate, found in the heart. These cells aid in heart contraction and are joined to one another by intercalated discs that allow for heartbeat synchronization.

Smooth muscle tissue is not striated like cardiac and skeletal muscle. Smooth muscle is involuntary muscle that lines body cavities and forms the walls of many organs such as kidneys, intestines, blood vessels, and lung airways.

Fat Cells

Fat cells, also called adipocytes, are a major cell component of adipose tissue. Adipocytes contain droplets of stored fat (triglycerides) that can be used for energy. When fat is stored, its cells become round and swollen. When fat is used, its cells shrink. Adipose cells also have a critical endocrine function: they produce hormones that influence sex hormone metabolism, blood pressure regulation, insulin sensitivity, fat storage and use, blood clotting, and cell signaling.

Skin Cells

Your skin is made of multiple layers of skin cells including epithelial and connective tissue, along with a subcutaneous layer. The outermost layer is made of many different types of cells packed tightly together. These cells include: Keratinocytes, Merkel cells, Langerhans cells, and Melanocytes. As you may be able to guess Keratinocytes produce keratin proteins, which block your body from toxins. Merkel cells are what give you the ability to feel when you touch an item. Langerhans cells are antigens for the skin. If there is a cut that becomes infected these cells fight that infection for your body. Melanocytes produce the melanin giving your skin its color.

Your skin is the largest organ in your body. It protects you from dehydration, germs, damage, and stores fats and vitamins within.

Nerve Cells

Nerve cells or neurons are the most basic unit of the nervous system. Nerves send signals between the brain, spinal cord, and other body organs via nerve impulses. Structurally, a neuron consists of a cell body and nerve processes. The central cell body contains the neuron's nucleus, associated cytoplasm, and organelles. Nerve processes are "finger-like" projections (axons and dendrites) that extend from the cell body and transmit signals.

Cartilage Cells

Cartilage cells are all over the body forming a firm tissue essential to the structure of your body. Cartilage is a firm tissue found in between bones, in your ears and nose, and even between the vertebrae of your spinal cord. However, because there are no blood vessels in cartilage this tissue repairs much slower than most and nutrients are diffused from surrounding tissue. However, without cartilage much of the body would not be bendable and flexible.



Every part of your body is made of tiny building blocks called cells, which fit together like bricks in a wall. These are called tissues



Genetics forms one of the central pillars of biology and overlaps with many other areas, such as agriculture, medicine, and biotechnology.


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