Cell – Structure and functions
Important topics covered:
- Discovery of cell
- Cell theory
- Cell structure and function
- Types of cell
- Prokaryotic cell
- Eukaryotic cell
- Parts of cell
- Cell membrane
- Difference between plant and animal cell
Discovery of cell:
- Robert Hooke, in 1665 observed the slices of cork (bark of trees) under magnifying device.
- He observed that there were a number of compartment (box) like shape in the cork slice.
- These boxes or compartments looked like honeycomb.
- There were separating wall which separated the compartments.
- Hooke named them as cell.
- The cell he observed were dead cells.
- After 170 years of research by different biologists, the cell theory was proposed.
- It was first proposed by Matthias Jacob Schleiden and Theodore Schwann in 1838.
- Cells are the primary structural and functional units of life in a living organism.
- As bricks are the basic unit of a building, similarly cells together make the body of living organisms.
- Every living organism is made up of one or more cells.
- Cell contain cell organelle, plasma membrane, nucleus etc.
- Cells vary in their shape, size as well as functions.
- The size of the cell varies from 1 to 100 micrometre.
- The new cell is produced by cell division of the existing cell.
- The cells having genetic material is carried out to the next generation through reproduction.
- Cells are complex structures and carry out different substantial functions.
- Growth, repair, excretion, immunity, digestion are some of the processes carried out by cells.
Types of organisms:
There are two types of organisms on the basis of number of cells present in living organisms:
- Organisms containing single cells are unicellular organisms.
- All the life processes like respiration, digestion, excretion is carried out by that single cell.
- Amoeba and paramecium are examples of unicellular organisms.
- Living organisms made up of more than one cell are multicellular organisms.
- In these organisms, different life processes are carried out by a group of cells.
- Division of labour is seen in cells of multicellular organisms each group of cells is involved in doing a specific function.
- Humans, different animals, plants etc. are some example of multicellular organisms.
Facts to know about human cell
- Ovum in females is the largest whereas sperm cell is the smallest cell inside the human body.
- Brain contains nerve cells which are said to be neurons.
- Liver cells are said as Hepatocytes.
- Kidney cells are known to be nephrons.
Cell – structure and function:
There are trillions of cells present in living organisms. The cells vary in shape, size and function. Let’s discuss structures and function of cells.
Shape of cells:
- Generally, cells are elongated, round shaped or spherical.
- Some cells are long and pointed at its ends.
- A few of them are branched. As we see in case of neuron.
- Cell walls which are an additional covering of the cell give the shape to the cells of plants. It also provides rigidity.
- Amoeba cell has no definite shape.
Size of cells
- Bacteria contain the smallest cell with 0.1 to 0.5 micrometre.
- Egg of ostrich is the largest cell with dimension 170 mm x 130 mm.
- There is no dependency of cell size on the size of the organism.
Structure of cells:
- Many cells constitute tissue, many tissues come together to form organs and different organs together called organ system.
- Every organ in living organism performs different functions like digestion, absorption and assimilation.
- Plants too have different organs to perform particular functions like roots help in absorption of water and minerals.
Different parts of cell
- The cell membrane has cytoplasm and nucleus enclosed within it.
- The membrane is thin, elastic and delicate. is
- It is also called the plasma membrane.
- Cell membrane is living part of the cell.
- It is the protective layer around the cell.
- Also we call it selectively permeable membrane because selectively allows entry of some substances it prevents the entry of harmful material.
- It is also involved in checking the movement of substances in and out of the cell.
- In plants cell is covered with a thick layer which is called cell wall.
- Cell wall covering the cell membrane in plants helps in protection of plants against temperature, high wind speed, atmospheric moisture etc.
- The jelly-like substance present between the cell membrane and nucleus is cytoplasm.
- Various other components, or organelles of cells i.e. mitochondria, golgi bodies, ribosomes, etc. are present in the cytoplasm.
- It is located at the centre of the cell and is the most important component of the living organism.
- Also, it is a dense spherical organelle which can be seen with a microscope.
- Nucleus is surrounded by a porous nuclear membrane which separates cytoplasm and nucleus.
- It contains spherical body called nucleolus.
- Nucleus is also called storehouse of genes.
- Chromosomes are thread-like structures which are present here and can only be observed when cell divides.
- Genetic codes present in genes of chromosomes are responsible for the unique physical characteristics of an animal or a plant.
- The living content of cell is called protoplasm.
- Cells can’t survive without nucleus.
- Nucleus also controls the activities inside the cell.
- It also has a main role in inheritance.
Difference between plants and animal cells:
We can distinguish between plant and animal cell is given below.
|Cell wall is present.
|No cell wall is present.
|Nucleus is present inside the
cell at any position.
|Nucleus is present at the
centre of the cell.
|Plant cells contain plastids.
|Plastids are absent.
|At the centre of cytoplasm a
larger vacuole is present.
|A number of small vacuole is
present in the cytoplasm.
|Plant cells contain chloroplast
which is used in photosynthesis.
|Animal cell does not contain
|Plant cells are rigid due to cell wall.
|Animal cells are blobby.