The cell (from Latin cella, meaning “small room” is the basic structural, functional, and biological unit of all known living organisms. Cells are the smallest unit of life that can replicate independently, and are often called the “building blocks of life”. The study of cells is called cell biology.
Cells consist of cytoplasm enclosed within a membrane , which contains many biomolecules such as proteins and
nucleic acids.  Organisms can be classified as unicellular (consisting of a single cell; including bacteria) or
multicellular (including plants and
animals). While the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion (10 13 ) cells.  Most plant and animal cells are visible only under the microscope, with dimensions between 1 and 100 micrometres .

The cell was discovered by Robert Hooke in 1665, who named the biological unit for its resemblance to cells inhabited by
Christian monks in a monastery.



To survive in a dynamic world, cells evolved mechanisms for adjusting their organic chemistry in response to signals indicating environmental modification.
The changes will take several forms, as well as changes within the activities of pre-existing enzymne molecules, changes within the rates of synthesis of latest protein molecules, and changes in membrane-transport processes.
Chemicals that might pass into cells, either by diffusion through the cell membrane or by the action of transport protein and will bind on to protein within the cell and modulate their activities

Passive Transport: Movement across the cell membrane that doesn’t need energy from the cell.
Concentration Gradient: A distinction within the concentration of a substance across an area.
Equilibrium: A condition within which the concentration of a substance is equal throughout an area.
Diffusion: The movement of a substance from a region of high concentration to a region of lower concentration caused by the random motions of particles of the substance.
Osmosis: The diffusion of water through a by selective semi permeable membrane.
Hypertonic Solution: A solution that causes a cell to shrink due to osmosis.
Hypotonic Solution: A solution that causes a cell to swell due to osmosis.
Isotonic Solution: A solution that produces no modification in cell volume due to osmosis.
Ion Channel: A transport protein w/a polar pore that ions can pass through
Carrier Proteins: A transport protein which will bind to a selected substance on one side of a membrane, and free it on the opposite side.


The Cell in its Environment-Physical and Biophysical Processes
Substances can move into and out of a cell through its semi-permeable cell membrane. There are three different processes through which materials can move in and out of a cell. They are:
• Through the process of diffusion,
• Through the process of osmosis and
• Through the process of active transport

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      Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body’s hereditary material and can make copies of themselves. Cells are limited in size by their surface area to volume ratio. A group of small cells has a relatively larger surface area than a single large cell of the same volume. This is important because the nutrients, oxygen, and other materials a cell requires must enter through it surface. As a cell grows larger at some point its surface area becomes too small to allow these materials to enter the cell quickly enough to meet the cell’s need CELL SHAPE: Cells come in a variety of shapes – depending on their function:- The neurones from your toes to your head are long and thin; Blood cells are rounded disks, so that they can flow smoothly. Cell Theory consists of three principles: a. All living things are composed of one or more cells. b. Cells are the basic units of structure and function in an organism. c. Cells come only from the replication of existing cells.
      Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell. Human cells contain the following major parts, listed in alphabetical order: Cytoplasm Within cells, the cytoplasm is made up of a jelly-like fluid (called the cytosol) and other structures that surround the nucleus. Cytoskeleton The cytoskeleton is a network of long fibers that make up the cell’s structural framework. The cytoskeleton has several critical functions, including determining cell shape, participating in cell division, and allowing cells to move. It also provides a track-like system that directs the movement of organelles and other substances within cells. Endoplasmic reticulum (ER) This organelle helps process molecules created by the cell. The endoplasmic reticulum also transports these molecules to their specific destinations either inside or outside the cell. Golgi apparatus The Golgi apparatus packages molecules processed by the endoplasmic reticulum to be transported out of the cell.
      Lysosomes and peroxisomes These organelles are the recycling center of the cell. They digest foreign bacteria that invade the cell, rid the cell of toxic substances, and recycle worn-out cell components.

      REFERENCE Introduction to the Cell: (September, 2005) Retrieve from Ch 1 – Cells.pdf (biologymad.com) What is a cell (February 22nd, 2021) Retrieve from What is a cell?: MedlinePlus Genetics

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