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The Invisible World and the Cell
- Tiny living things are around us
- They live in air, water and soil
- We need a microscope to see them
- These are called microorganisms
- The cell is the basic unit of life
- Lactobacillus turns milk to curd
- yeast helps make cakes
- bread mould spoils bread
- all living things are made of cells
- a cell is the basic structural unit
- and the functional unit of life
- Bacteria, fungi, virus and protozoa are some examples of microbes.
- Some microorganisms are useful and some are harmful.
- Science covers both the macroscopic and the microscopic world.
Electricity, Force and Pressure
- Electricity has heating and magnetic effects
- Heating effect lights bulbs and heaters
- Magnetic effect runs motors and MRI
- Force explains why objects move or stop
- Pressure tells how force spreads over an area
- heating effect boils water in a kettle
- magnetic effect rings an electric bell
- also powers a loudspeaker
- a ball stops rolling after a while
- a thrown ball comes back down
- force changes an object's shape
- The magnetic effect of current is used to create the magnetic field for MRI machines and to separate scrap metals.
- Pressure helps explain atmospheric pressure, how wind blows and how cyclones form.
- Knowledge of water pressure helps in designing dams.
Matter, Light and the Sky
- Matter exists as solid, liquid and gas
- It can be a pure substance or a mixture
- Light is a form of energy to see things
- Light reflects off mirrors and surfaces
- Reflected light lets us see the Moon
- air we breathe is a mixture
- water we drink is a compound
- iron sinks but a ship floats
- a magnifying glass makes things bigger
- we see different parts of the Moon
- this led to making calendars
- Most things around us are mixtures of pure substances like elements and compounds.
- Aryabhata, a famous mathematician and astronomer, explained the occurrence of eclipses.
- Aryabhata stated that the westward movement of the Sun and stars is due to the Earth's rotation on its axis.
Name the following: It occupies a very large volume and on expansion produces pressure.
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Explanation
- Steam occupies a larger volume and creates pressure on expansion, the idea behind the steam engine.
Name the following: The tiny creatures which are not visible to the naked eye.
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Explanation
- Microorganisms are so small that we need a microscope to see them.
Name the following: The loudspeaker and doorbell work on this principle.
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Explanation
- The magnetic effect of current is used in loudspeakers and electric doorbells.
Name the following: The different states of matter.
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Explanation
- Matter exists in three states — solid, liquid and gas.
Fill in the blank: A ________ is the basic structural and functional unit of life.
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Explanation
- All living things are made of cells, the basic unit of life.
State whether true or false: The fungus, bread mould curdles milk.
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Explanation
- Bread mould spoils bread; milk is curdled into curd by Lactobacillus bacteria.
State whether true or false: Force helps to move or stop an object.
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Explanation
- A force can move a stationary object and stop a moving one.
State whether true or false: We can see objects because they disperse light.
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Explanation
- We see objects because they reflect light into our eyes, not because they disperse it.
State whether true or false: The Earth rotates on its own axis.
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Explanation
- Aryabhata stated that the apparent westward movement of the Sun and stars is due to the Earth's rotation on its axis.
Which among the following states of matter occupy a greater volume?
- (a) steam
- (b) ice
- (c) water
- (d) snow
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Explanation
- Steam is a gas, which occupies a much larger volume than ice, water or snow.
The organism Lactobacillus is a:
- (a) virus
- (b) protozoa
- (c) bacteria
- (d) fungi
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Explanation
- Lactobacillus is a bacteria that helps convert milk into curd.
The heating effect of current is used to:
- (a) ring a doorbell
- (b) light bulbs
- (c) run MRI machine
- (d) power electric motor
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Explanation
- Light bulbs work on the heating effect; the others use the magnetic effect of current.
It sinks in water.
- (a) iceberg
- (b) ship
- (c) brick
- (d) piece of wood
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Explanation
- A brick is heavier than the water it displaces, so it sinks; the others float.
The Indian astronomer who explained eclipses:
- (a) Aryabhata
- (b) Acharya Jagadish Chandra Bose
- (c) Varahamihira
- (d) Megnad Saha
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Explanation
- Aryabhata, a famous mathematician and astronomer, explained the occurrence of eclipses.
