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- Physical Nature of Matter
Matter is made up of particles
Particles of matter are continuously moving
Particles of matter have space between them
Particles of matter attract each other
- Matter exists in three different states– solid, liquid and gas
- The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases.
- Mixtures are constituted by more than one kind of pure form of matter, known as a substance.
- A solution is a homogeneous mixture of two or more substances.
- Non-homogeneous systems, in which solids are dispersed in liquids, are called suspensions.
- An element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
- Law of constant proportions
In a chemical substance the elements are always present in definite proportions by mass.
- IUPAC (International Union of Pure and Applied Chemistry) approves names of elements.
- A molecule is defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance.
- An ion is a charged particle and can be negatively or positively charged. A negatively charged ion is called an ‘anion’ and the positively charged ion, a ‘cation’.
- The formula unit mass of a substance is a sum of the atomic masses of all atoms in a formula unit of a compound.
- Thomson’s model of an atom
(i) An atom consists of a positively charged sphere and the electrons are embedded in it.
(ii) The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral.
- Rutherford’s model of an atom
(i) There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus.
(ii) The electrons revolve around the nucleus in well-defined orbits.
(iii) The size of the nucleus is very small as compared to the size of the atom.
- The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. The cell membrane, therefore, is called a selectively permeable membrane.
- The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose.
- The nucleus has a double layered covering called nuclear membrane. The nuclear membrane has pores which allow the transfer of material from inside the nucleus to its outside, that is, to the cytoplasm. The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.
- The cytoplasm is the fluid content inside the plasma membrane. It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.
- Plant Tissues : The growth of plants occurs only in certain specific regions. This is because the dividing tissue, also known as meristematic tissue, is located only at these points. Depending on the region where they are present, meristematic tissues are classified as apical, lateral and intercalary
- Animal Tissues : On the basis of the functions they perform we can think of different types of animal tissues, such as epithelial tissue, connective tissue, muscular tissue and nervous tissue. Blood is a type of connective tissue, and muscle forms muscular tissue.
- Biologists, such as Ernst Haeckel (1894), Robert Whittaker (1959) and Carl Woese (1977) have tried to classify all living organisms into broad categories, called kingdoms.
- Further classification is done by naming the sub-groups at various levels as given in the following scheme:
Kingdom Phylum (for animals) / Division (for plants): Class – Order – Family – Genus – Species
- The system of scientific naming or nomenclature we use today was introduced by Carolus Linnaeus in the eighteenth century. The scientific name of an organism is the result of the process of classification which puts it along with the organisms it is most related to.