Cell and cell organelles
Cell: A cell is the fundamental and structural unit of living organisms.
Cell Organelles:
● Cell wall -
It is the outermost covering of a plant cell. It is present only in plant cells. It is strong and
rigid. It is composed of cellulose, Lignin, Pectin, Suberin, Cutin. Depending on the function,
the amount of non-cellulosic compounds can be less. eg. The composition of lignin is going
to be higher in woody plants. And the composition of Pectin is higher in fruits.
● Structure of the cell wall:
There is a thin cementing layer between adjacent cells. This is called Middle lamella.
It is like an adhesive that sticks together adjacent cells. It is called Middle lamella because it
is in the middle of two joined cells. It is composed of calcium and magnesium pectates. It is
the outermost layer of the cell wall. After that comes the primary wall. It is a very thin, elastic
and flexible layer. It is composed of pectin, cellulose microfibrils, soluble protein and
hemicellulose.
● Cell membrane -
It is the outer crust covering in animal cells and the second covering in plant cells. Plasma
membrane is very choosy, it allows some substances to enter while preventing others so it is
also called to be selectively permeable. The widely accepted model is the Fluid Mosaic
Model. a) Fluid because all the components of the membrane are always moving and if it
stops moving it will stop functioning as well. b) Mosaic it refers to a pattern made of small
regular or irregular pieces held in place by covering a surface. It is called phospholipid.
However the big capsule-like component is protein, it helps in transport of substances inside
out of the cell membrane. A single tail-like component is called fatty acid tail
(non-polar/hydrophobic) in a collection of layers it is called phospholipid bilayer. Activities
that consume cellular energy:
Endocytosis - endo-entry, cyto-cell and sis - process. The movement of useful substances
inside the cell through the cell membrane.
Exocytosis - Exo-exit. The movement wastes substances outside the cell through the cell
membrane.
Diffusion - Entry or exit of small molecules like O2, CO2.
Osmosis - Movement of water from a region of higher concentration to a region of lower
concentration. The water content inside the cell is equal to the water content outside the cell,
then the water outside the cell is called the Isotonic Solution. Water doesn't go in or out. a)
The water content inside the cell is less than outside the cell. It is called a Hypotonic
solution. Water will move inside the cell. b) Water content inside the cell is less than outside
the cell. It is called a Hypertonic solution. Here the water will move outside the cell making it
shrivel and lose its shape. Turgor pressure.
● Nucleus -
It has a double layered membrane with small pores. It takes all the decisions for the cell. It
contains a nucleolus (nucleus of the nucleus). It makes decisions from the information that it
Cell: A cell is the fundamental and structural unit of living organisms.
Cell Organelles:
● Cell wall -
It is the outermost covering of a plant cell. It is present only in plant cells. It is strong and
rigid. It is composed of cellulose, Lignin, Pectin, Suberin, Cutin. Depending on the function,
the amount of non-cellulosic compounds can be less. eg. The composition of lignin is going
to be higher in woody plants. And the composition of Pectin is higher in fruits.
● Structure of the cell wall:
There is a thin cementing layer between adjacent cells. This is called Middle lamella.
It is like an adhesive that sticks together adjacent cells. It is called Middle lamella because it
is in the middle of two joined cells. It is composed of calcium and magnesium pectates. It is
the outermost layer of the cell wall. After that comes the primary wall. It is a very thin, elastic
and flexible layer. It is composed of pectin, cellulose microfibrils, soluble protein and
hemicellulose.
● Cell membrane -
It is the outer crust covering in animal cells and the second covering in plant cells. Plasma
membrane is very choosy, it allows some substances to enter while preventing others so it is
also called to be selectively permeable. The widely accepted model is the Fluid Mosaic
Model. a) Fluid because all the components of the membrane are always moving and if it
stops moving it will stop functioning as well. b) Mosaic it refers to a pattern made of small
regular or irregular pieces held in place by covering a surface. It is called phospholipid.
However the big capsule-like component is protein, it helps in transport of substances inside
out of the cell membrane. A single tail-like component is called fatty acid tail
(non-polar/hydrophobic) in a collection of layers it is called phospholipid bilayer. Activities
that consume cellular energy:
Endocytosis - endo-entry, cyto-cell and sis - process. The movement of useful substances
inside the cell through the cell membrane.
Exocytosis - Exo-exit. The movement wastes substances outside the cell through the cell
membrane.
Diffusion - Entry or exit of small molecules like O2, CO2.
Osmosis - Movement of water from a region of higher concentration to a region of lower
concentration. The water content inside the cell is equal to the water content outside the cell,
then the water outside the cell is called the Isotonic Solution. Water doesn't go in or out. a)
The water content inside the cell is less than outside the cell. It is called a Hypotonic
solution. Water will move inside the cell. b) Water content inside the cell is less than outside
the cell. It is called a Hypertonic solution. Here the water will move outside the cell making it
shrivel and lose its shape. Turgor pressure.
● Nucleus -
It has a double layered membrane with small pores. It takes all the decisions for the cell. It
contains a nucleolus (nucleus of the nucleus). It makes decisions from the information that it
