Test: Class 7 General Science NCERT Based - 3 - UPSC MCQ

• During heavy exercise, fast running , cycling, walking for many hours or heavy weight lifting, the demand for energy is high.

• But the supply of oxygen to produce the energy is limited. Then anaerobic respiration takes place in the muscle cells to fulfil the demand of energy. The partial breakdown of glucose produces lactic acid.

• The accumulation of lactic acid causes muscle cramps. We can get relief from cramps after a hot water bath or a massage. Hot water bath or massage improves circulation of blood.

• As a result, the supply of oxygen to the muscle cells increases. The increase in the supply of oxygen results in the complete breakdown of lactic acid into carbon dioxide and water.

• Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs.

• The taking in of air rich in oxygen into the body is called inhalation and giving out of air rich in carbon dioxide is known as exhalation. Inhaled air contains 21% oxygen and 0.04% carbon dioxide, while the exhaled air contains 16.4% oxygen and 4.4% carbon dioxide.

The correct option is:

1. 1 and 2 Only

Explanation:

1. Assertion 1: The process of breakdown of food in the cell with the release of energy is called cellular respiration.

   • This statement is correct. Cellular respiration refers to the metabolic process by which cells break down organic molecules, such as glucose, to produce energy in the form of adenosine triphosphate (ATP).

2. Assertion 2: In the cell, the food (glucose) is broken down into carbon dioxide and water using oxygen.

   • This statement is also correct. In aerobic cellular respiration, glucose is oxidized (broken down) in the presence of oxygen to produce carbon dioxide, water, and ATP.

3. Assertion 3: Food can also be broken down without using oxygen. This is called aerobic respiration.

   • This statement is incorrect. The correct term for the breakdown of food without using oxygen is anaerobic respiration, not aerobic respiration. Aerobic respiration specifically requires oxygen for the breakdown of food molecules.

1. Red blood cells (RBC)

2. White blood cells (WBC)

3. Platelets Red blood cells transport oxygen to all the parts of the body and ultimately to all the cells.White blood cells fight against germs that may enter our body, while the clot is formed because of the presence of another type of cells in the blood, called platelets.

• The device which measures the distance covered by the vehicle is called an odometer.

• Speedometer records the speed directly in km/h.

• Accelerometer is an instrument for measuring the acceleration of a moving or vibrating body.

• Altimeter is an instrument for determining altitude attained, especially a barometric or radar device fitted in an aircraft.

• Electric current is defined as the rate of flow of negative charges of the conductor. In other words, the continuous flow of electrons in an electric circuit is called an electric current. The conducting material consists of a large number of free electrons which move from one atom to the other at random.

• Since the charge is measured in coulombs and time in seconds, so the unit of electric current is coulomb/Sec (C/s) or amperes (A). The amperes is the SI unit of the conductor. The I is the symbolic representation of the current.

• Electric potential, the amount of work needed to move a unit charge from a reference point to a specific point against an electric field.

• Typically, the reference point is Earth, although any point beyond the influence of the electric field charge can be used.

• The potential energy for a positive charge increases when it moves against an electric field and decreases when it moves with the electric field; the opposite is true for a negative charge.

• Unless the unit charge crosses a changing magnetic field, its potential at any given point does not depend on the path taken. Although the concept of electric potential is useful in understanding electrical phenomena, only differences in potential energy are measurable.

• If an electric field is defined as the force per unit charge, then by analogy an electric potential can be thought of as the potential energy per unit charge. Therefore, the work done in moving a unit charge from one point to another (e.g., within an electric circuit) is equal to the difference in potential energies at each point.

• In the International System of Units (SI), electric potential is expressed in units of joules per coulomb (i.e., volts), and differences in potential energy are measured with a voltmeter.

• Push or pull of an object is considered a force. Push and pull come from the objects interacting with one another. Terms like stretch and squeeze can also be used to denote force.

• In Physics, force is defined as: The push or pull on an object with mass that causes it to change its velocity. Force is an external agent capable of changing the state of rest or motion of a particular body.

• It has a magnitude and a direction. The direction towards which the force is applied is known as the direction of the force, and the application of force is the point where force is applied.

• The Force can be measured using a spring balance. The SI unit of force is Newton(N). In physics, motion is defined as the change in position with respect to time. In simpler words, motion refers to the movement of a body. Typically, motion can either be described as:

  1. Change in speed

  2. Change in direction

  The Force has different effects and here are some of them.

  • Force can make a body which is at rest to move.

  • It can stop a moving body or slow it down.

  • It can accelerate the speed of a moving body.

  • It can also change the direction of a moving body along with its shape and size.

• Refraction is the bending of a wave when it enters a medium where its speed is different. We can define it as:Refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium Refraction of light is one of the most usually observed phenomena which includes refraction of light through prism, but other waves like sound waves and water waves also experience refraction.

• Laws of Refraction of Light: Laws of refraction state that:

  1. The incident ray, refracted ray, and the normal to the interface of two media at the point of incidence all lie on the same plane.

  2. The ratio of sine of angle of incidence to the sine of angle of refraction is a constant.

  This is also known as Snell’s law of refraction.

• Once light has been produced, it will keep travelling in a straight line until it hits something else. Shadows are evidence of light travelling in straight lines.

• An object blocks light so that it can’t reach the surface where we see the shadow. Light fills up all of the space before it hits the object, but the whole region between the object and the surface is in shadow.

• Shadows don’t appear totally dark because there is still some light reaching the surface that has been reflected off other objects. Once light has hit another surface or particles, it is then absorbed, reflected (bounces off), scattered (bounces off in all directions), refracted (direction and speed changes) or transmitted (passes straight through).