Current Affairs 9th Class

  Is Matter Around us Pure   Synopsis  
  • Chemistry deals with the study of matter. The matter around us is of two types: pure substances and mixtures.
  • A pure substance is homogeneous in nature and has a definite set of properties. The composition of pure substances cannot be changed by physical methods. Pure substances can be further classified as elements and compounds.
  • Elements: Pure substances in which molecules are composed of only one kind of atoms are called elements, e.g., silver, iron, oxygen, nitrogen, etc.
  • Compounds: Pure substances in which two or more elements combine chemically in a fixed proportion by weight are called compounds. For example, water (H,0) is considered as a pure substance even though it consists of two kinds of atoms, as it has a fixed number of hydrogen and oxygen atoms combined together chemically in a definite proportion by weight. Hydrogen and oxygen combine in a fixed ratio of 1:8 by weight to form water.
  • Mixtures: Mixtures are those substances which contain two or more kinds of molecules.
  • For example, sugar solution contains molecules of sugar and molecules of water. Mixtures can have their constituents either as an element, elements, a compound or only compounds.
  • Solutions/suspensions and colloids differ in the size of solute particles (or dispersed particles), the size of particles being minimum in solutions and maximum in suspensions.
  • A suspension is a heterogeneous mixture in which small particles of a solid are spread throughout a liquid without dissolving in it. Some common examples of suspensions are: chalk - water mixture, milk of magnesia, sand particles suspended in water.
  • A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions. The size of solute particles in a colloid are bigger than that of a true solution but smaller than those of a suspension.
  • The scattering of light by colloidal particles is known as Tyndall effect.
  • The colloids can be classified into the following seven groups.
          (i)  Sol                              (v) Foam           (ii) Solid sol                    (vi) Solid foam           (iii) Aerosol                     (vii) Gel           (iv) Emulsion    

  Atoms and Molecules   Synopsis    
  • The simplest form of matter which can neither be split into nor built up from two or more dissimilar substances is called an element.
  • An atom of an element is denoted by the symbol of that element.
  • An atom of an element also denotes the atomic mass possessed by that element.
  • Each atom of an element is characterised by its atomic number and mass number.
  • Atomic weight of an element in grams is called gram atomic weight or gram atom.
  • The smallest part of a substance that can exist independently is called a molecule.
  • An aggregation of two or more atoms of the same or different elements is called a molecule.
  • Molecules are characterised by their molecular weights.
  • Law of Conservation of Mass: In a chemical reaction, the sum of the masses of the reactants and the products remains constant.
  • Law of Definite Proportions: A chemical compound always consists of the same elements which combine in the same fixed ratio by weight.
  • Law of Multiple Proportions: When two elements combine to form two or more compounds, the different weights of one element which combine with a fixed weight of the other bear a simple integral ratio.
  • Molecular weight of a compound expressed in grams is called gram molecular weight or gram molecule.
  • A mole is the quantity of substance that contains the same number of particles as are present in 12 g of carbon (or) mole is the collection of Avogadro's number of particles.
  • Avogadro's number is \[6.023\times 1023\]. It is denoted by N.
  • Empirical formula is the ratio of atoms of various elements in a compound and it is derived from percentage composition.
  • Molecular formula represents the actual number of atoms of each element in a compound.
  • Molecular formula = (empirical formula) \[\times \] n, where W is a small whole number.
  • Number of moles
\[=\frac{Weight\,\,of\,\,asubs\tan ce\,\,in\,\,grams}{Grammolecular\,\,weight}=\frac{Number\,\,of\,\,molecules}{Avogadro's\,\,number}\]  
  • Number of moles of a gaseous substance
\[=\frac{Volume\,\,of\,\,the\,\,gas\,\,at\,\,STD\,\,}{Grammolar\,\,volume\,\,}\] Number of molecules = Number of moles \[\times \] Avogadro’s number    
  • Weight of a molecules \[\frac{Weight\,\,of\,\,the\,\,substace}{Grannikecykar\,\,weight}\times Avogadro'snumber\]
Atomic weight of gaseous element =\[\frac{Molecular\,\,weight}{Atomicity}\]        
  • Weight of the substance = Number of mole \[\times \] gram molecular weight

  Structure of the Atom   Synopsis  
  • Atoms are the building blocks of all matter. The word atom, meaning indivisible was coined by Greek philosopher Democritus. Scientists, then assumed that these are the smallest units of matter. The first theory about atom was put forward by Dalton.
  • Atom contains fundamental particles electrons, protons and neutrons.
  • Thomson's Model of an Atom
          (a) It is also known as water melon model or plum pudding model.          (b) Electrons are embedded in the positively charged mass distributed uniformly thoughout the atomic sphere.  
  • Demerits
  • It could not explain how both positive and negatively charged particles protect their identity being together.
  • Rutherford bombarded a - particles at very high speed to strike a thin 'Au' foil of 10-4 mm thickness.
          Note: An a-particle is a doubly Ionised 'He' nuclei  \[(H{{e}^{++}})\]  
  • Rutherford's model or planetary model of an atom
          (a) The entire positively charged particles are present in the centre of an atom called nucleus.              (b) Electrons revolve around the nucleus just as planets revolve around the sun. Hence, it is called as planetary model or solar model.              (c) Electrons revolve around the nucleus with a high speed to overcome the electrostatic force of attractions between protons and electrons.  
  • Bohr's Model of Atom
  • Neils Bohr overcame the difficulties which Rutherford model faced and proposed his atomic model based on Planck's quantum theory. It explained the origin of stationary orbits which also led to an entirely new concept of atomic structure.
          This theory is based on Planck's quantum theory and the postulates are as given below.           (a) Electrons revolve around the nucleus in definite, circular paths known as orbits or shells.           (b) Each orbit is associated with a definite amount of energy. Hence, they are known as stationary orbits.           (c) These shells are designated as K, L, M, N....... or 1, 2, 3, 4 .........           (d) As the size of the orbit number increases, energy of the orbit also increases.  
  • Atomic Number is the number of protons or electrons in an atom.
  • Mass Number is the sum of protons and neutrons present in the nucleus of an atom
  • Isotopes are atoms having the same atomic number but have different mass number
  • Isobars are atoms having the same mass number but different atomic number.

  Cell - The Fundamental Unit of Life   Synopsis  
  • The cell is the basic unit of life. Cells were first discovered by Robert Hooke in 1665 by the observation of a cork slice under microscope. The cell theory was proposed by Schleiden and Schwann.
  • Rudolf Virchow proposed that all cells originate from pre-existing cells. The outermost covering that separates the contents of the cell from its external environment is called the plasma membrane, which is selectively permeable and is made up of lipids and proteins.
  • Plant cells have a rigid outer covering in addition to the plasma membrane. It is called the cell wall and is composed of cellulose.
  • The Nucleus is covered by a double-layered nuclear membrane and is filled with nucleoplasm. It has chromosomes that are composed of DNA and proteins.
  • Cells which lack a nuclear membrane and cell membrane bound organelles are called
Prokaryotes and cells having a nuclear membrane are called Eukaryotes.  
  • The Cytoplasm is the fluid content inside the plasma membrane of a cell.
  • The Endoplasmic reticulum (ER) is a large network of membrane bound tubes and sheets.
There are two types of ER - RER (site of lipid-protein synthesis) and SER (site of synthesis and detoxification of poisons and drugs).  
  • Lysosomes are saclike, small, spherical, single membrane bound vesicles which contain enzymes. They keep the cell clean by digesting the foreign materials entering the cell. They are otherwise known as the suicidal bags of the cell
  • The Golgi complex is a stack of flattened sacs meant for the secretion of substances.
  • Mitochondria are the power houses of the cell which generate ATP that provide energy required for various chemical activities in a cell.
  • Ribosomes are responsible for protein synthesis in a cell. A chain of ribosomes is termed as a polyribosome or polysome.
  • Plastids are present only in plant cells. There are three types of plastids - chloroplasts, chloroplasts (coloured) and leucoplasts (white or colourless).
  • Vacuoles are storage structures for solid or liquid content which are filled with cell sap.
  • Diffusion is the movement of a gaseous substance from a region of higher concentration to a region of lower concentration.
  • Osmosis is the movement of water molecules from a solution of lower concentration to a solution of higher concentration across a partially permeable membrane.
  • The pressure of the water in the vacuole which keeps the plant cell firm or turgid is called the turgor pressure.

  Tissues   Synopsis  
  • A group of cells that are similar in structure and work together to perform a particular function is called a tissue
  • Most of plant tissues that are supportive are dead but provide mechanical strength whereas most of the animal tissues are living. Plant tissues can be classified as meristema tic and permanent tissues Meristema tic tissues are classified as apical (tip of stem and roots), lateral (girth of stem and root), intercalary meristems (internodes).
  • Cells formed by meristema tic tissue lose the ability to divide and form a permanent tissue, which is termed as differentiation
  • Permanent tissues, which consist of similar types of cells are called simple permanent tissues Parenchyma, collenchyma and sclerenchyma are some examples.
  • Parenchymatous cells are usually loosely packed with intercellular spaces (Chlorenchyma- performs photosynthesis, Aerenchyma - provides buoyancy).
  • The flexibility in plants is due to collenchyma. The cells of the tissue have very little intercellular spaces.
  • Sclerenchymatous tissue makes the plant hard and stiff due to the presence of lignin.
  • Epidermal layer of leaf consists of pores called stomata which are enclosed by two kidney shaped cells called guard cells Stomata help in transpiration and exchange of gases.
  • Older plants have a chemical called suberinin their walls that makes them impervious to gases and water.
  • Complex tissues are made up of more than one type of cells. Xylem and phloem are complex tissues. Xylem consists of tracheid’s, vessels, xylem parenchyma and xylem fibres.
  • It transports water and minerals vertically. Phloem is made up of sieve tubes, companion cells, phloem fibres and phloem parenchyma. It transports food from leaves to other parts of the plant.
  • The protective tissues in animal body are epithelial tissues. Cells in skin, lining of mouth, alveoli, etc. are some examples. The cells of these tissues are tightly packed with no intercellular spaces.
  • Simple squamous epithelium (flat) is present in oesophagus and lining of the mouth. Stratified squamous epithelium (many layers) is present in skin. Columnar epithelium is present in the inner lining of the intestine. Ciliated columnar epithelium (have cilia) is present in the respiratory tract. Cuboidal epithelium is present in the lining of kidney tubules, etc.
  • The cells of connective tissues are loosely spaced in a jelly like matrix. Blood and bones are connective tissues.
  • Blood has a fluid matrix called plasma which consists of RBC/ WBC and platelets
  • Two bones are connected by ligaments that are very elastic. Tendons are fibrous tissues, which connect more...

  Diversity in Living Organisms   Synopsis  
  • Classification helps us in exploring the diversity of life forms and systematic study of organisms.
  • Robert Whittaker (1959) proposed the '5-kingdom System' based on the cell structure, mode of nutrition and body organisation. The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia.
  • Scheme of classification is:
          Kingdom \[\to \] Phylum (or) Division \[\to \] Class \[\to \]Order\[\to \] Family \[\to \] Genus \[\to \] Species.  
  • Monerans do not have a defined nucleus. The mode of nutrition is either autotrophic or heterotrophic. e.g., cyanobacteria, mycoplasma, etc.
  • Protista includes unicellular eukaryotic organisms mode of nutrition is either autotrophic or heterotrophic. e.g., diatoms, protozoan, etc.
  • Fungi are saprophytic eukaryotic organisms. They have -cell walls made up of chitin. e.g., yeast and mushroom. Some fungi lead a symbiotic life with algae. e.g., lichens.
  • Plants that do not have a differentiated plant body belong to thalloptiyta. e.g.,. spirogyra, ulothrix,
  • Plants with a differentiated plant body without a specialized vascular tissue belong to e.g. moss, marchantia, etc.
  • In Pteridophyta the plant body is differentiated into roots, stem and leaves and has specialized vascular tissue, e.g., fern, marsilea, etc.
  • Thallophytes, bryophytes and pteridophytes are together called
  • Plants with well-differentiated reproductive tissues that ultimately bear seeds are called Phanero- gams(Gymnosperms and Angiosperms).
  • Gymnosperms bear naked seeds and are usually perennial/evergreen and woody, e.g., pine, deodar, etc.
  • Angiosperms bear seeds inside the fruit. Plants with seeds having a single cotyledon are called monocots. e.g., paddy
  • Plants having two cotyledons are called e.g., bean.
  • Organisms belonging to animalia are eukaryotic, multicellular, heterotrophic and mobile. They do not have a cell wall.
  • Porifera includes non-mobile animals having pores and are commonly called sponges.
  • Animals belonging to coelenterate show body design differentiation and have a cavity in the body.
  • The body is made up of two layers of cells, e.g., hydra, sea anemones/etc.
  • The body of platyhelminthes is bilaterally symmetrical with no true ceolom. e.g., planarians, liver fluke, etc.
  • The body of nematodes is triploblastic with pseudoceolom. e.g., ascaris, wuchereria, etc.
  • Annelid shave extensive organ differentiation in a segmented form. e.g., earthworms, leeches, Animals belonging to arthropoda have open circulatory system and jointed legs, e.g., prawns, spiders, crabs, etc.
  • In molluscans the ceolomic cavity is reduced, e.g., snails, mussel, etc.

  Health and Diseases   Synopsis  
  • Health is a state of complete physical, mental and social well-being and not merely an absence of disease.
  • Basic conditions required for good health include balanced diet, personal hygiene, clean food, water and air, exercise, no addictions and good economic conditions.
  • Health is influenced by genetic, environmental, economic status and psychological factors.
  • A sign of a disease is a change in the bodily function or structure that can be observed, e.g., rashes, swelling or glands, change in colour of the skin, etc.
  • Depending upon the duration of diseases, they are classified into acute and chronic diseases.
  • Acute diseases last for a short period of ti-me whereas chronic diseases last longer, sometimes even for a lifetime.
  • Diseases where microbes are the immediate causes are called infectious diseases (common cold) and those, which are mostly internal, are non-infectious diseases (cancer).
  • Infectious agents spread diseases through air, water, physical contact or vectors.
  • Infectious diseases are caused by viruses (influenza, AIDS, etc.), some of the bacteria (typhoid, anthrax, etc.), fungi (candidiosis, aspergillosis, etc.), protozoans (malaria, kala- azar, etc.).
  • An infectious disease that can be spread from one infected individual to another is called a communicable disease.
  • Animals which act as carriers for the spread of diseases are called vectors. Mosquitoes are the vectors for the spread of malaria.
  • The basic principle of prevention of infectious diseases is the availability of proper and sufficient food for everyone, public health and hygiene.
  • Human immune system recognizes the infectious microbes and responds to it with greater vigour when an individual is infected for the second time by the same microbe. This forms the basis for development of immunization.
  • Edward Jenner introduced vaccination against small pox in 1776.
  • Prevention of a disease is more desirable than its successful treatment. We need a strong immune system and balanced diet for the prevention of diseases.

  Improvement in Food Resources   Synopsis  
  • Food supplies all the required nutrients for the development, growth and health of the body.
  • Cereals like wheat, provide carbohydrates, pulses (grams) provide proteins and oil seeds provide fats.
  • Hybridization is the crossing between genetically dissimilar plants.
  • Improvement of agriculture is done for higher yield, biotic and abiotic resistance, improved quality grade, adaptability and other factors.
  • Macronutrients are those that are required in large quantities by the plants (N, R K, Ca, Mg,S, etc.).
  • Micronutrients are those that are required in small quantities (Mn, B, Zn, etc.).
  • Manure contains organic matter and supplies nutrients to the soil. It is prepared by the decomposition of animal excreta and plant waste.
  • The process in which waste material is decomposed is known as composting. Compost prepared by using earthworms is called vermin compost.
  • Organic farming is a farming system with minimal or no use of chemical fertilizers, herbicides, pesticides etc. and with a maximum input of organic manures, recycled farm waste and bio-agents with healthy cropping system.
  • Mixed cropping is growing two or more crops simultaneously on the same piece of land. For example wheat and mustard are often grown together.
  • Inter cropping is growing of two or more crops in the same field but in a definite pattern. For example maize and soya bean crops are grown alternately.
  • Milk producing animals are called milch animals and those that are used for farm labour are called draught animals.
  • Poultry is undertaken to increase the production of meat and eggs.
  • Five or six species of fish are raised (grown) in a single pond in order to reduce competition for food. This is called composite fish culture. For example catlas (surface feeders), rohas (middle zone) and mrigals (bottom feeders) are raised together.
  • Rearing of honeybees for honey and wax is called bee-keeping or apiculture.
  • Italian bees have high honey collection capacity.

  Natural Resources   Synopsis  
  • Life on earth depends on resources like soil, water, air and energy from the sun.
  • The outer crust of the earth is called the lithosphere.
  • The air that covers the earth like a blanket is called the atmosphere. It prevents the sudden increase in temperature during daytime.
  • The life supporting zone on earth is known as the biosphere. Living things constitute the biotic components and non-living things constitute the abiotic components of biosphere.
  • The hot air released from various biological activities consists of water vapour that can expand and cool. This cooling causes it to condense and form rain.
  • When the temperature of the air is low, precipitation may occur in the form of snow, sleet or hail.
  • When fossil fuels are burnt they release oxides of nitrogen and sulphur, which dissolve in rain and cause acid rain.
  • Presence of high levels of hydrocarbons forms (unburnt carbon particles) increases the content of harmful substances in air is called air pollution.
  • Water occupies a very large area of the earth surface. All cellular processes take place in water.
Water is one of the major resources that determines life on land. The availability of water decides the number of individuals that are able to survive in a particular area.  
  • Fertilizers, pesticides, sewage and chemical water released from factories and addition of undesirable substances to water can pollute it.
  • Removal of useful components and addition of harmful compounds/which affect the fertility of the soil, causes soil pollution.
  • Water evaporates and falls on the land as rain and later flows back into the sea via rivers. This is known as water cycle.
  • Carbon dioxide is kept constant in the atmosphere by the process of photosynthesis.
  • An increase in the percentage of carbon dioxide in the atmosphere increases the temperature globally. This is known as global warming.
  • Oxygen is returned to the atmosphere in only one major process, i.e., photosynthesis. Ozone is present in the upper layers of the atmosphere. It prevents harmful radiations from reaching the surface of earth.
    Chlorofluoro carbons or CFC react with ozone molecules and degrade it causing great harm to people on earth. We need to conserve our natural resources and use them in a sustainable manner.        

  Matter in our Surroundings   Synopsis  
  • Matter exists in three states, namely, in the solid, liquid and gaseous states.
  • The physical properties of solids are density, specific gravity, hardness, odour, colour, point/freezing point, viscosity, solubility and heat conduction.
Particles are arranged in a regular pattern. They are closely packed and have fixed positions. They do not move freely but only vibrate and spin around their fixed positions. They are held together by strong attractive forces and have the least amount of energy.  
  • The properties of liquids are surface tension, adhesion, cohesion, viscosity, buoyancy and
Vaporisation Particles are not arranged in a regular pattern. They are further apart and do not have fixed positions. They move freely and around one another. They are held together by attractive forces which are weaker than those in the a moderate amount of energy.  
  • They properties of gases are pressure, volume, temperature, kinetic energy and speed.
Particles are not arranged in a regular pattern. They widely spaced and do not have fixed positions. They move freely and randomly at high speeds. They have very weak attractive forces between them and have the greatest amount of energy.  
  • Gases possess the property of intermixing with one another through diffusion.
  • Heat can cause matter to change from one state to another.
  • The kinetic energy of particles depends on the heat and pressure of the matter. The energy Will determine the movement of particles in the matter.
  • As the state of matter of matter changes there is a transfer of energy, heat is either absorbed or released.
  • Changes in the states of matter are reversible processes.

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