8. Cell-Structure and functions Science class 8 in English Medium ncert book solutions Chapter Review

Chapter Review:

• The structural and functional unit of the living organism is called cell.

• Cells were first observed in cork by Robert Hooke in 1665.

• The smallest living part of an organism is a ‘cell’.

• Cells exhibit variety of shapes and sizes.

• The organism which is made of only one cell that is called unicellular organism. Ex : amoeba and paramecium. 

• The organism which is made of more than one cell are called multi cellular organism. Ex : human and tree. 

• A tissue is a group of similar cells having a specific function

• The nucleus contains thread-like structures called chromosomes. 

• Genes control the transfer of hereditary characteristic from parent to offspring; it is carried by the chromosomes. 

• Green colour plastid is called chloroplast.

• The nerve cell receives and transfers messages, thereby helping to
  control and coordinate the working of different parts of the body.

• The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest
  cell measuring 170 mm ×130 mm, is the egg of an ostrich.

• Gene is a unit of inheritance in living organisms. It controls the transfer of a hereditary characteristic from parents to offspring.

• Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane.

• The cells having nuclear material without nuclear membrane are termed prokaryotic cells.Examples are bacteria and blue green algae.

• The cells, like onion cells and cheek cells having well organised nucleus with a nuclear membrane are designated as eukaryotic cells.

• They are scattered in the cytoplasm of the leaf cells. These are called plastids.

• Coloured bodies called plastids are found in the plant cells only.

• Green plastids containing chlorophyll are called chloroplasts.