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  Access Answers to NCERT Class 9 Science Chapter 5 – The Fundamental Unit Of Life (All in text and Exercise Questions solved) Exercise-5.1 Page: 59 1. Who discovered cells, and how? Solution: in 1665, Robert Hooke discovered cells while examining a thin slice of cork through a self-designed microscope. He observed that the cork resembled the structure of a honeycomb consisting of numerous tiny compartments. The minuscule boxes are referred to as cells. 2. Why is the cell called the structural and functional unit of life? Solution: Cells form the structure of an entity. A group of cells form a tissue, further an organ and ultimately an organ system. They perform fundamental functions and life processes such as respiration, digestion, excretion etc in both unicellular and multicellular entities. They perform all the activities independently. Hence, cells are referred to as structural and fundamental units of life. Exercise-5.2.1 Page: 61 3. How do substances like CO...

   Class 10 :- Chapter 1 Force   Chapter 2 Work, Energy and Power Chapter 3 Machines Chapter 4 Refraction of Light at Plane Surfaces   Chapter 5 Refraction through Lens Chapter 6 Spectrum Chapter 7 Sound Chapter 8 Current Electricity Chapter 9 Electrical Power and Household Circuits Chapter 10 Electro-magnetism Chapter 11 Calorimetry Chapter 12 Radioactivity

  Selina ICSE Solutions for Class 10 Physics Chapter 12 Radioactivity Exercise 12(A) Solution 1. Three constituent of an atom are: Electrons: mass is 9.1 x 10 -31  kg, charge is -1.6 x 10 -19 C Neutron: mass is 1.6749 x 10 -27  kg, charge is zero. Protons: mass is 1.6726 x 10 -27  kg, charge is +1.6 x 10 -19  C Solution 2. Atomic number  – the number of protons in the nucleus is called atomic number. Mass number  – the total number of nucleons in the nucleus is called mass number. Solution 3. The nucleus at the centre of atom, whose size is of the order of 10 -15  m to 10 -14  m. The size of a nucleus is 10 -5  to 10 -4  times the size of an atom. It consists of protons and neutrons. If Z is the atomic number and A is the mass number of an atom, then the atom contains Z number of electrons; Z number of protons and A – Z number of neutrons. The atom is specified by the symbol  Z X A  where X is the chemical symbol...