7th Class

Structures and Functions of the Living Body   All animals and plants have different organs to perform various functions. Each part of the body of an animal or plant is different in structure. The organs, however, function in coordination with one another.   SPECIFIC PARTS OF PLANTS

• Plants have two main systems: (i) the root system (ii) the shoot system

  The Root System The root system grows mainly underground. Root systems are of two types: (i) Tap root system (ii) Fibrous root system (i) Tap root system: It is a main root and grows vertically down into the soil. The tap root gives out branches. For example, pea, neem, mango. (ii) Fibrous root system: Some plants do not have main root. They have many fibre-like roots. These are called fibrous roots. These roots spread out in the soil and give firm support to the plant. For example, more...

Elements, Compounds and Mixtures  

• Matter can be classified into elements, compounds and mixtures. These, in turn, are made of small particles such as molecules and atoms.
• Elements: When a substance is made of only one kind of atoms, it is called an element. For example, copper, gold, silver, iron, are all elements. Similarly, oxygen is a gaseous element made of oxygen molecules and each oxygen molecule is made of two oxygen atoms. Hydrogen, nitrogen, chlorine are other examples of gaseous elements.
• Compounds: When two or more atoms combine in a fixed ratio, they produce compounds. They can be broken down into the elements from which they are made. Water is an example of a compound. Each water molecule is made of two atoms of hydrogen and one atom of oxygen. Thus on analysing water, we find two different types of atoms, those of hydrogen and oxygen. more...

Heat Energy  

• Energy is the ability to do work. When an object has the ability to do work, it is said that it has energy.
  • Heat is a form of energy and has the ability to do work.
  • Heat energy can also be converted to other forms. For example:
• When charcoal (coal of wood) is burnt, it emits light. In this way, heat energy produces light.
• The heat energy in a firecracker produces both sound and light.
• In a hot air balloon, the hot gases are lighter than the surrounding air. They rise and are capable of lifting heavy masses. Here heat energy is used to produce mechanical energy.
• A steam engine converts heat energy into mechanical energy and powers the train.
• Other forms of energy can also be converted to heat energy. For example,
• The heat (heat energy) produced from the mechanical more...

Transfer of Heat  

• When hot objects are kept away from a source of heat, they cool down. For example, when milk is removed from a burning stove, it starts cooling down. This is because the hot milk releases part of its heat energy to the surrounding air and cools down. The surrounding air absorbs the heat from it and heats up. Of course, the increase in temperature of the air is so less that it can hardly be detected. But, if we dip a spoon in the milk, we can quickly detect the rise in the temperature of the spoon. This is called transfer of heat.
• Heat from a hot body is transferred to a cold body in three different ways: (i) conduction (ii) convection (iii) radiation

(i) Conduction: In a solid, the molecules are closely packed. When one end of the solid is heated, the molecules more...

Light and Shadows   LIGHT

• Light is needed to see things. We may shave eyesight, but we cannot see anything without light. We need a source of light to make objects visible to us.

  SOURCE OF LIGHT

• An object that gives out light is called a source of light. These sources of light can be categorised in two ways:

(i) Natural sources of light: Sun, moon, stars, glow-worm are some examples of natural sources of light. (ii) Artifical sources of light: Candle, oil lamp, gas lamp, torch, electric bulb are some example of artificial sources of light.

• Some light sources are brighter than the others. For example, a candle is brighter than a firefly.
• The modem internationally accepted unit of brightness of a source is lumen (1 watt is equal to about 700 lumen).
• Light from a source more...

Mirrors and Reflection of Light  

• An object acts in three ways to the light that falls on it. It may allow the light to pass through, it may completely cut off the light from passing by absorbing the light, or, the object may scatter the light incident on it.

  REFLECTION OF LIGHT  

• The light beam (1) above the mirror consists of unstopped light rays. Light beam (2) defines the length of the shadow. Rays (3), (4), (5) and (6) are stopped by the mirror.
• Instead of passing through, the mirror surface bounces light rays like a smooth wall bounces a ball.
• The light rays falling on a mirror are scattered back. This scattering back is called reflection.
• The reflection of light from a smooth and an uneven surface is different, as the smooth more...

Sound  

• We hear many sounds around us. For example, the sound of buses and cars running on the street, the chirping of birds on the trees, the rustling of leaves in the breeze, the sound of rain falling on the roof and the sound of thunder in the monsoon.
• In each case, the sound is produced when the object undergoes a rapid to-and-fro motion. Such motion is called vibration or oscillation. In some cases, the vibrations are easily visible to our naked eyes such as the rustling of tree leaves. But in some cases, they are so small that we feel them with our palms. For example, we can feel the vibrations of a transistor, radio or television by placing our hands on the speaker. If we grab the vibrating tree leaves, their vibrations stop and so does the sound.

  VIBRATIONS OR OSCILLATIONS more...

Motion and Time   Synopsis  

• Change in the position of a particle with respect to time and a fixed place (observer) is known as motion.

 

• The rate of change of position in unit time interval is known as speed. Speed is also the distance covered by an object in unit time. Speed is relative and the same body can be said to be moving fast or slow when compared to different things.

   

• The S.I. unit of distance is metre (m) and that of time is second(s), therefore the unit of speed is metre per second (m/s or m s'1). The C.G.S. unit of speed is cm/s or cm s1.

 

• A more...

  Image   Learning Objectives  

• Images
• Concept of Mirror Image
• Concept of Water Image

  Images   The reflection of an object as seen in a surface is called Image. Image of an object is similar to the object but it may be inverted or laterally inverted.   Concept of Mirror Image   Image of an object as seen in a mirror is called mirror image or reflection of an object. The left of the object appears right and right appears as left in the image. This phenomenon is called lateral inversion. For example, mirror image of K =                Some more...

  Number System   Learning Objectives  

• Number Line
• Fractions and Decimals
• Rational Number

    Number Line       Number line is a model that helps us visualise adding and subtracting of integers. A number line is a picture of a straight Sine on which every point is assumed to correspond to a real number and every real number to a point.   Absolute Value Absolute value means to think only about how far a number is from zero.                             more...