Current Affairs 7th Class

       Classification of Motion   Motion, on the basis of covered distance has been classified into two groups.               Uniform Motion (Uniform = Alike) If a body covers equal distances in equal interval of time, the body is said to be in the uniform motion. (Interval of time: Time duration or time difference)     In the above picture, speed of the car is constant at different interval of time. Therefore, it covers equal distances in equal interval of time. Thus the above shown car is in uniform motion.   Graphical Representation of the Uniform Motion     The above graph shows that the body covers the distance 20 m in every 5 minute. It means, the body covers equal distances in equal interval of time, therefore, the body is in uniform motion. Note: If motion of a body, on a distance time-graph, represents a straight line, it means the body is in uniform motion.                Non-Uniform Motion There are two conditions for a motion to be non- uniform: When a body covers unequal distances in equal interval of time. When a body covers equal distances in unequal interval of time.     In the above picture, speed of the car varies at different interval of time. Therefore, it covers unequal distances in equal interval of time. Thus the above shown car is in non-uniform motion.   Graphical Representation of the Non-Uniform Motion     The above graph shows, the body covers 20 meter in first 5 minute, 25 meter in next 5 minute, 15 meter in next 5 minute, and 20 meter in the last 5 minute. It means the body covers unequal distances in ‘equal interval of time. Thus the body is in non-uniform motion. Note: If motion of a body, on a distance time-graph, represents a curved line, it means the body has non-uniform motion     Questions 1 and 2 are based on the following graph           Graphical representation of motion of two different body has been shown in the above graph. Both the body are in......... (a) Uniform motion (b) Non-uniform motion (c) Periodic motion (d) Circular motion (e) None of these   Answer: (a)           Look at the above graph carefully and choose which one of the following bodies have greater speed? (a) Body A (b) Body B (c) Both the body have equal speed (d) All of these (e) None of these   Answer: (b)

       Rest and Motion   As we know, in this universe nothing is fixed at a single place. The galaxies are moving away from each other and universe is spreading. Therefore, everything is changing its position with respect to the time. Rest and Motion is the branch of Physics that deals with the position of a body. We will study the two different physical quantities "motion and rest" to describe the position of a body. In our day to day life, we often come across the terms rest and motion. In actual, in this universe nothing is in the rest. Earth moves around the Sun; Sun moves around the centre of the galaxy. Galaxies are moving away from each other and so on. The objects, which we see as in rest, actual are in motion. As the Earth is moving around the Sun, objects on the Earth are also moving along. However we use the terms rest and motion in physics and in our day to day life. The rest and motion are actually two different physical quantities, which are used to describe the position of an object with respect to the time and a reference point. If the object's position has changed with respect to the reference point, the object is said to be in the motion and if the object's position has not changed with respect to the reference point, the object is said to be in the rest.   Note: A reference point is essential to describe whether the object is in motion or in the rest and different reference point may give different result.     Let us describe the position of a person who is traveling from Delhi to Shimla by train. If we take Delhi station as a reference point, then he is in the motion; as in the beginning he was on the station and now he is away of the station. And if we take window of the train as a reference point, then the person is still at the same distance from the window as on Delhi station. So the person is in the rest. Therefore, whether an object is in rest or in motion depends on the reference point that the observer choose to describe object's position.   Let us take one more example: Suppose an object is at the distance of 5 m in east direction from a pole fixed on the ground. The object is said to be in motion:

• If the object's distance from the pole increases or decreases.
• The distance remains fixed and direction of the object changes.

And the object is in the rest: If neither distance nor direction of the object from the pole changes.               Classification of Motion There are four types of motion. Let us study them in detail     more...

       Sexual Reproduction   A sexual reproduction requires two individual of opposite sexes (male and female). An egg or ovum is called female gamete and a sperm is called male gamete. In sexual reproduction,' a male gamete fuses with a female gamete, which results in the development of new organism.                Sexual Reproduction in Flowering Plants A sexual reproduction requires two opposite sex cells male gamete and female gamete. When a flowering plant is mature to produce new plants sexually, it produces flowers, which contain the sex organs of the plant. There are some flowers, which contain only one sex organ (either male sex organ or female sex organ), called unisexual flower. And some flowers contain both type of sex organ, called bisexual flower. In the plants, the male sex organ is called stamen and the female sex organ is called carpel. Upper part of the stamen (male sex organ) is anther, which is joined with filament. Another contains pollen grains and pollen grains contain male gametes. Upper part of the carpel is stigma and lower part of the carpel is ovary. Ovary contains the ovule and ovule contains female gametes, called ova or eggs. Stigma receives the pollen grain from the anther and transfer it to the ovule, where fertilization takes place. This fertilized eggs grow into seeds, which develop into new plants after germination.                  Sexual Reproduction in Animals Animals are unicellular or in other word male sex cells and female sex cells are contained by two different bodies. Male contains male sex cells and female contains female sex cells. Male sex cells or male gametes are called sperm and female sex cells or female gametes are called ovum (plural ova) or egg. Male gamete fuses with the female gamete. Meeting of the male sex cell with the female sex cell is termed as fertilization. In some animals like human being, fertilization takes place inside the body, known as internal fertilization. And in some animals like frog, fertilization takes place outside the body, known as external fertilization. During the fertilization, nucleus of female sex cell fuses with the nucleus of male sex cell forming a single cell called zygote. This zygote goes on mitosis division. As the embryo goes on development, structural feature of the organism becomes clear. After 8 to 9 weeks of fertilization features of the organism can be recognized clearly. At this stage the embryo is known as foetus. The foetus grows and develops into a new baby.   What actually happens during the fertilization   We know that the nucleus of the human body cells contains 46 chromosomes. Whereas sex cells, i.e. sperm and. ova contains only 23 chromosomes and therefore they are called haploids. During the fertilization, more...

        Artificial Methods of Vegetative Propagation   We have developed many methods of vegetative propagation by which a new plant can be grown from a part of plant. There are three common methods of artificial vegetative propagation: Cutting Layering Grafting              Cutting In this method, a part of plant is cut and the cut portion is buried under the soil, which develops into a new plant.                Layering In this method, a branch of plant is pulled down and covered with soil in such a way that the tips of the branch remain exposed in air. After few days covered part develops roots and grows into new plants.                  Grafting Grafting is a method in which two stems of two different plants are joined together to grow as a single plant. In this method one stem is taken with root, called stock and other stem is taken without root, called scion.                 Look at the following table  

Artificial method of vegetative propagation	Name of the plants,
Cutting	Grapes, sugarcane, bananas, cactus, etc.
Layering	Rose, pear, strawberry, jasmine etc.
Grafting	Guava, mango lemon, Jasmine etc.

               In which one of the following method of vegetative propagation the terms "scion and stock" are used? (a) Cutting (b) Layering (c) Grafting (d) All of these (e) None of these   Answer: (c)          How many new young ones are produced in more...

       Mode of Reproduction   There are two types of reproduction: Sexual reproduction Asexual reproduction              Asexual Reproduction This type of reproduction has been continued since the beginning of life on earth. By asexual reproduction an organism alone can reproduce new offspring without the help of any sex partner. There are six different ways by which a life can alone give birth to young ones. These are: Fission Budding Spore formation Regeneration Fragmentation Vegetative propagation              Fission In this type of reproduction, body of a living organism divides into two or more than two, living organisms. When a living body divides into two new living bodies, it is called binary fission (bi means two). And, when a living body divides into more than two new living bodies, it is called multiple fission (multiple means many). This type of reproduction mainly takes place in unicellular organisms like amoeba, paramecium etc.                Budding In this method, a bud is appeared on the living organism. This bud grows and finally detaches from the body and develops into new young one. Organisms like hydra, yeast etc. produce their young ones by this method.                 Spore Formation In this method, parent plant produces spores inside a spore case. On bursting the spore case, spores are spread into air. When these spores find a suitable condition, they grow into new plants. Ex: fungi, bacteria etc.                Regeneration In this method, a part of body regains lost parts and develops into a full organism. Ex: hydra, planaria etc.               Fragmentation In this method, body of a multicellular organism splits into many pieces or fragments and each fragment develops into new organism. Ex: spirogyra, sea anemones etc.                  Vegetative Propagation In vegetative propagation method, a part of a plant like leaves, stem, or root grows into a new plant. It occurs only in plants. Actually leaves, stem, root all contain buds, which grow into plant on getting favorable condition.

         Reproduction   Life appeared on the earth about 3.8 billion year ago and is still continuing. This continuation of life has been made possible only by reproduction. Reproduction not only increases the number of the organisms, but also opens the way for the coming up of new organisms. As a result, the earth is filled with new species of animals and life form has becomes more complex. The term reproduction is used to mean the development of new life from the existing one. In another word, reproduction is a method by which organisms increase their number in the nature.

     Movement of Substance   The two basic requirement of each and every cell are:

• Availability of life substances (glucose and oxygen)
• Removal of waste products

  Multicellular life may be made up of trillions of cells. All cells are not in direct contact with air so that they can get air directly and can make food for themselves. Therefore, a transport system is required for supplying all the cells with glucose and oxygen and for removing waste products out of the body. Transportation is one of the most important metabolic functions of the body, without which multicellular life is not possible..

          Need of Transport System in Plants   Plants are made up of mainly three parts, i.e. root, stem and leaves. Leaves develop in upper part of plants so that they remain in directly contact with atmosphere to trap \[C{{O}_{2}}\] and sunlight. Roots develop in lower part of plants and remain underground to absorb water and minerals from the soil. These raw materials, obtained by different parts of plant, need to be get together in the leaves for the process of photosynthesis. So for transporting these materials from one part to another part, plants need a transport system..

       Transport System in Plant   Inside the plant body, mainly three types of materials are transported. These are water containing minerals, digested food, and hormones. In plants two systems are involved in transportation, namely: Xylem Phloem                 Transportation of Water and Minerals The system, which is responsible for transportation of water and minerals is called xylem. Let us know about the xylem..                Xylem Xylem is responsible for transportation of water and minerals. Water and mineral absorbed by the roots of a plant is transferred to the leaves by xylem. The transport system, xylem, is made up of two kinds of elements: Xylem vessels Tracheids                Xylem Vessels Xylem vessels are made up of long dead cells. In the xylem vessels, dead cellsare joined with each other. And at the joint, cell wall is broken down. Thus atube like structure is formed and water and minerals absorbed by the root hairget a way to reach to the leaves.                Tracheids Tracheids are also dead cells but they have the tapering ends rather than open. Therefore they do no form the vessels. The transportation of water from one dead cell to another occurs through pits present in their cell walls. Tracheids are water conducting tissues in only non-flowering plant.              Work of Root Hair The job of root hair is to absorb the water and to take it to xylem tube. Xylem tubes reach to every leaves of the plant. So when water enters into xylem, it is transported to the required parts.                        Which one of the following statements is not true? (a) Water enters into xylem vessels through root hairs (b) Root hairs lie in between soil particles (c) The cells of xylem vessels have tapering end (d) Cells of xylem vessels are joined with open ends (e) None of these   Answer: (C)           Transportation of water from one tracheid to another takes place through their tapering ends". Read the above statement and select by which one of the following options, "tapering end 'given in the statement should be replaced? (a) Vessels formed by the dead cells (b) Flat ends of the tracheid cells joined together (c) Pits present on the cell (d) Selectively permeable cell wall (e) None of these   Answer: (c)

       Transportation of Food and Hormones   The system, which is responsible for transportation of food and hormones is called phloem. Transportation of food is called translocation.            Phloem Phloem is made up of living cells. Like xylem vessels its cells also joins end to end. But the cell walls at the joint are not broken completely although they form sieve plates, which have small holes in them to pass the food materials. Thus by connecting cells one by one, phloem tube is formed. Phloem tubes lie throughout the body. So food and hormones enter into it and reach to the required cells.