Ernest Rutherford showed (1919) that nitrogen under alpha-particle bombardment ejects what appear to be hydrogen nuclei. By 1920 he had accepted the hydrogen nucleus as an elementary particle, naming it proton.

Discovery of Electrons, Protons and Neutrons

James Chadwick

The story begins in 1932, with the discovery of the neutron by Sir James Chadwick, an English physicist. Until 1932, the atom was known to consist of a positively charged nucleus surrounded by enough negatively charged electrons to make the atom electrically neutral.

1897

Nucleus. The nucleus is small, round and membrane bound structure found in cell. The fluid inside the nucleus surrounded by nuclear membrane is called nucleoplasm. It controls the cell’s growth and reproduction because it contains cell’s hereditary information.

Chromosomes are thread-like structures present in the nucleus, which carries genetic information from one generation to another. In Eukaryotic cells, genetic material is present in the nucleus in chromosomes, which is made up of highly organized DNA molecules with histone proteins supporting its structure.

Mitochondria are round “tube-like” organelles that provide energy to a cell in the form of ATP (Adenosine Triphosphate) for performing different chemical activities for the sustainance of life. Fig. Structure of mitochondria. The mitochondria is also called powerhouse of the cell.

Functions of Nucleus are: * It directs and control all the activities . * It controls all the metabolic activities of the cell and regulates the cell cycle . * It helps in transmission of heredity characters from parents to offsprings .

The nucleus consists of the following main parts: (1) Nucleolemma or nuclear membrane (karyotheca) (2) Nuclear sap or karyolymph or nucleoplasm (3) Chromatin network or fibres (4) Nucleolus (5) Endosomes.

Some real-life examples of Plasmolysis are: Shrinkage of vegetables in hypertonic conditions. Blood cell shrinks when they are placed in the hypertonic conditions. During extreme coastal flooding, ocean water deposits salt onto land. Spraying of weedicides kills weeds in lawns, orchards and agricultural fields.

A ribosome, formed from two subunits locking together, functions to: (1) Translate encoded information from the cell nucleus provided by messenger ribonucleic acid (mRNA), (2) Link together amino acids selected and collected from the cytoplasm by transfer ribonucleic acid (tRNA).

There are two types of ribosomes, free and fixed (also known as membrane bound). They are identical in structure but differ in locations within the cell. Free ribosomes are located in the cytosol and are able to move throughout the cell, whereas fixed ribosomes are attached to the rER.

A ribosome is a complex molecular machine found inside the living cells that produce proteins from amino acids during the process called protein synthesis or translation. Ribosomes are specialized cell organelles and found in both prokaryotic and eukaryotic cells.

The cytoplasm is the semi-viscous ground substance of the cell. All the volume of such substance outside the nucleus and inside the plasma membrane is cytoplasm. It is sometimes described as the non-nuclear content of the protoplasm. All the cellular contents in prokaryotes are contained within the cell’s cytoplasm.

In cell biology, the cytoplasm is a highly viscous (gel-like) substance enclosed within the cell membrane. It’s composed of water (about 85 percent), proteins (10 to 15 percent), lipids (2 to 4 percent), nucleic acids, inorganic salts and polysaccharides in smaller amounts.

All cells have a plasma membrane, ribosomes, cytoplasm, and DNA.