What is a cell?

What is a cell in Biology/Science?

  • The basic unit of life is a cell.
  • Life needs a structural compartment separate from the external environment in which macromolecules can perform unique functions in a relatively constant internal environment.
  • Most of the living things are made up of cells. Cellshapes are different according to their functions.
    Plant and animal cells may be differ in size, shape, and structure (plant cells are usually bigger than animal cells).

plant cell and animal cell

Why are the Cells different in sizes?/ What do cells look like?

  • Different Cells range in different sizes, from a few micrometers to many centimeter.
  • The size of every cell is very minute or small because cells that are larger in size cannot work efficiently or actively. But small cells can transport the material into and outside the cell very actively.
  • A large surface-to-volume ratio is useful, as cell size rises or increases, the volume grows more quickly than the surface area.
  • The larger or bigger the surface area of a cell, the quickly a cell can get in substances and get rid of waste product.
  • While large or big internal volume comparative to surface area makes it more difficult to transport materials or substances into and out of the cells.

What are the special Features of a plant cell?

  • Cell wall is composed of cellulose which is firm and stiff so it gives and maintain the shape of the cell.
  • Cell wall is fully permeable.
  • Plant cell is also surrounded by a partially permeable membrane called cell membrane.
  • Green pigment called chlorophyll is present in chloroplast.
  • A big permanent central vacuole that take up a large part of the internal of plant cell. It contains cell sap that helps to maintain the turgidity of the cell.
  • Jelly like substance called Cytoplasm contains most of the dissolved substances and organelles like,Mitochondria, Endoplasmic Reticulum, golgi apparatus, Nucleus.
  • Starch which is a stored food present in cytoplasm in form of colourless grains.
  • Immediate food that is made in the result of photosynthesis is glucose while moving food is called sucrose and stored food is called starch.


feature of plant cells

What are the essential features of an animal cell?

  • Animal cell is an irregular in shape.
  • Cell wall is absent in animal cell.
  • It contains cell membrane which grips the cell together and controls the substances entering into and leaving out the cell.
  • Many small Vacuoles are present but they are temporary.
  • Cell is filled with jelly like substances and many chemical reactions take place here to carry out many essential life processes.
  • Chloroplast is absent.
  • Stored food is in form of glycogen.


feature of animal cells

Difference between cell wall and cell membrane:

  • Cell walls are permeable to salts and water, which can pass by diffusion. Cell wall in plants is made up of cellulose fibre, which is tough as well as flexible to some extent. Cellulose is the major element of cotton fiber and wood, and it is used in paper production. It is fully permeable for all the materials.cell wall is present in Bacterial and fungi cells but it is not made of cellulose.When water enters and fills the plant cell, turgor produced but cell wall prevent the cell bursting. Thus the cell wall has many important functions in a cell including protection, structure, and support. The cell wall sends signals for the cell to enter the cell cycle in order to divide and grow.


  •  Cell membrane The cell membrane is a organic or biological membrane that splits the inner life  of all cells from outer environment . The Cell membrane is composed  of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures.Cell membrane is partially permeable membrane to different substances. Water can pass through osmosis, from high concentration to low concentration, down the osmotic gradient. Permeability to water causes turgor in vacuole of plant cell. Salts and mineral ions can pass selectively through the process of active transport where energy is required.


What do mean by Differentiation in Biology?

Why the term differentiation is important in Biology?

Life in All the organisms initiate from a single or one cell. This single cell contains DNA that contain the gene coding for all the proteins that will be used by an adult in future.  If this cell expressed all of its proteins at one time it would not be useful or purposeful.  cell must divide constantly, so the cells must begin the process of cell differentiation as they  further divide. As the cell lines begin to emerge or appear,  the cells get more and more specific. Eventually, an entire organism is formed with hundreds of different cell types from this process of cell differentiation.

stem cells

Specialized cells, tissues, organs, and systems:

What are the Specialized cells?
· A specialized cell is aimed to do a specific work.
· Nerve cells that are the part of Nervous system have long fibres to carry massages from brain to body and from body to brain.
· Muscle cells can contract and relax.
· White blood cells attack bacteria.
· Platelets help clotting

Detail of some specialized cells are as follows:

Adaptation of  Root hair cells:

  • Long and narrow shape of the root hair cells is to increase the surface area to volume ratio for effective and quick absorption of water and mineral salts from soil into the roots.


Root hair cells


Adaptation of Red blood cell:

  • RBCs contain a red pigment called haemoglobin that allow the cell to transport oxygen from lungs to all the rest of the  parts of our
  • Circular biconcave shape to increase surface area to volume ratio so oxygen can diffuse into and out of the cell at a quicker or faster rate.
  • No nucleus is present in a mature RBC and because of its absence  it has enough space to contain haemoglobin.


Red blood cells

Adaptations of Xylem vessels:

  • Xylem vessels or tubes transport water and mineral salts from the roots to the stem and leaves.
  • No cross walls and protoplasm that enables water to move easily through the lumen.
  • Lignin strengthens the walls and prevents collapse of the vessel.
  • When bundled together, xylem vessels provide mechanical support to the plant.


Xylem vessels

What  are Tissues in biology?
· A Large numbers of specialized cells when composed together they form tissues.
· Muscles, blood and nerves are all the example of Tissue.
· Blood tissue contains many types of cells like, Red Cells for carrying oxygen to distribute in the body ,white cells for destroying harmful bacteria to make the immune system strong , and platelets that help in  clotting after cuts.

Four different types of tissues

What do you mean by Organs ?
· Various tissues get together and  make up a special Organ.
· Each organ has its own definite work.
· The heart in circulatory system, the stomach in digestive system and the brain in nervous system are all  the special Organs.
· The heart has to pump oxygenated blood all round the body. It is composed of
of Muscle tissues, Blood vessels like arteries,veins and capillaries and  sensory or motor Nerves
· Arteries and veins can be considered as  organs because  they consist of
several tissues.

images of different organs in the human body

What do you mean by Organ system:
When Many organs organized  then they group in  an Organ System. E.g. the Circulatory
system that carries oxygenated blood to all parts of the body which  is made up of muscular heart,arteries, veins, capillaries and blood.

circulation of blood from the heart

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