Cell- structure and functions...............BCDP

Cell is the basic fundamental and structural unit of life. All living organisms areade up of one or more cells.

Microscope is an instrument used to see objects which are too small to be seen through our Naked eyes. 

Cells are highly organised and all their functions an regulated. It is not just the rate of cell division that is controlled, but also the rate of cell death. If cells are longer needed, they commit suicide by activating an intracellular death program. This process is called programmed cell death or apoptosis.

Robert Hooke in 1665 observed the slices of cork under a microscope, he coined the name as cell.

Anton Van Leeuwenhook invented microscope 

Mathias Schleiden proposed that all plants are made up of cells.

Cell theory was proposed by Schleiden and Schwann.

The main postulates of cell theory are:

• All living organisms are composed of one or more cells.

 • Cell is the basic unit of structure, function, and organisation in all organisms.

• All cells come from pre-existing, living cells.

• All living cells do not have cell walls. It is present only in plants, fungi and bacteria.

Amoeba and WBCs have cell membranes and can change their shapes. WBCs use pseudopodia to engulf pathogens during phagocytosis, while amoeba uses pseudopodia for locomotion and engulfing food Amoeba is a unicellular organism and can exist independently. WBCs, on the other hand, are incapable of independent existence. 

Phagocytosis is a process of which amoeba ingests or engulfs food particles with the help of pseudopodia, It is the process which helps the amoeba to obtain nutrients. 

Types of cells on basis of number 

Multicellular Organisms made of more than one cell are called multicellular 

Unicellular The single celled organisms are called unicellular 

The shape and size of the cell depends upon the function they perform. 

Every human being starts with just one cell, this cell develops into tissues, then into organs and finally a full grown human being. 

An average adult have about 1 trillion cells in their body.

The smallest cell is 0.1-0.5 μ micrometer in bacteria.

The largest cell measuring 170mm × 130mm, is of egg of an ostrich. 

Organelles specialised structure within the cells is called organelles

Cell membrane 

The outer covering of cell 

The plasma membrane is made up of two layers of phospholipids 

The plasma membrane is fluid in nature and has many proteins embedded in it. 

Because it is fluid in nature and has proteins embedded in it, it is said to have a fluid mosaic model. 

The plasma membrane regulates the entry and exit of particles across the cell membrane by diffusion and osmosis. 

Cell wall in plants 

Cell Wall is only found in plants not in animals

The cell wall is located outside the cell membrane. It consists mainly of cellulose and may also contain lignin, which makes it more rigid. The cell wall shapes, supports, and protects the cell. It prevents the cell from absorbing too much water and bursting. It also keeps large, damaging molecules out of the cell.

Cytoplasm 

The cytoplasm is the semifluid material inside the cell's plasma membrane, it prevents the other organelles moving here and there and keeps them still, organelles seems to be floating in cytoplasm. 

1) In prokaryotes, all of the cell's functions take place directly in the cytoplasm.

2) In eukaryotes, all of the cell's functions take place within organelles in their cytoplasm.

Nucleus 

Nucleus is called the headquarters of the cell.

Inside the nucleus there is Nucleolus which has chromosomes, inside chromosomes there is  DNA .

Robert Brown coined the term nucleus in 1831

Chromosomes are thread-like structures present inside the nucleus of the cell. They are made up of the genetic material DNA, which is involved in the transmission of characters from parents to offsprings.

When a cell is not dividing i.e. at the 'resting stage, DNA inside the nucleus is present in the form of chromatin. During cell division, the thread like chromatin condenses to form chromosomes.

Golgi Apparatus

The Golgi apparatus is a sac-like structure which modifies proteins and transports them to their target sites in the cell or sometimes outside the cell through vesicles.

Lysosomes 

Lysosome is known as the suicidal bag of the cell. When a lysosome tries to kill a pathogen, it first fuses with it. This fusion forms a structure called phagosome. Inside the phagosome, the digestive enzymes of the lysosome digest the pathogen and then release the debris out of it. 

Plastids 

Plastids are small organelles in plants which contain various pigments. Chloroplast is a plastid that contains the green-coloured pigment chlorophyll. Therefore, chloroplasts are organelles which impart green colour to the leaves.

Mitochondria 

The power house of the cell

Respiration inside a cell, it releases ATP - Adenosine Triphosphate currency of cell 

Cristae are folds inside mitochondria, this increases the surface area to produce more energy (ATP) 

Mitochondria has its own small amount of DNA 

Muscle and nerve cells have a large number of mitochondria 

ATP is the energy currency of the cell 

Vacuole , mostly present in plants, very less of none in animals 

The vacuole is the cell organelle that stores excess water and gives support and rigidity to a plant cell. It occupies about 80% of the plant cell volume.

So that's it for today, hope you learned more facts and definitions

SSA 

SAI GROUP