Class 7 General Science NCERT Based - 3 - Free MCQ Practice Test with solutions,

• A vertical section through different layers of the soil is called the soil profile. Each layer differs in feel (texture), colour, depth and chemical composition. These layers are referred to as horizons.

• The uppermost horizon is generally dark in colour as it is rich in humus and minerals.

• The humus makes the soil fertile and provides nutrients to growing plants. This layer is generally soft, porous and can retain more water. It is called the topsoil or the Horizon. This provides shelter for many living organisms such as worms, rodents, moles and beetles.

• The roots of small plants are embedded entirely in the topsoil. The next layer has a lesser amount of humus but more of minerals. This layer is generally harder and more compact and is called the B-horizon or the middle layer.

• The third layer is the C-horizon, which is made up of small lumps of rocks with cracks and crevices. Below this layer is the bedrock, which is hard and difficult to dig with a spade.

• The best topsoil for growing plants is loam. Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. Silt occurs as a deposit in river beds. The size of the silt particles is between those of sand and clay.

• The loamy soil also has humus in it. It has the right water holding capacity for the growth of plants.

• Clayey soil and loamy soil are suitable for growing wheat, gram and paddy, as they have good amounts of humus in them; while cotton is grown in sandy soil and loamy soil, which facilitate quick draining of water.

• 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.

• Blood is the fluid which flows in blood vessels. It transports substances like digested food from the small intestine to the other parts of the body.

• It carries oxygen from the lungs to the cells of the body. It also transports waste for removal from the body.

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.

1. Blood circulation was discovered by an English physician, William Harvey.

2. Blood, blood vessels and heart are all part of the human circulatory system.

3. Blood transports substances like digested food from the small intestine to the other parts of the body. It carries oxygen from the lungs to the cells of the body.

4. There are two types of blood vessels present in the body – arteries and veins. Arteries carry oxygen-rich blood from the heart to all parts of the body. Since the blood flow is rapid and at a high pressure, the arteries have thick elastic walls.

5. Veins are the vessels which carry carbon dioxide-rich blood from all parts of the body back to the heart. The veins have thin walls. There are valves present in veins which allow blood to flow only towards the heart.

6. The heart is an organ which beats continuously to act as a pump for the transport of blood, which carries other substances with it.

7. The renal is part of the Excretory system in humans and not the circulatory system.

• There are several ways by which plants produce their offspring. These are categorised into two types: A. Asexual B. Sexual reproduction.

• In asexual reproduction plants can give rise to new plants without seeds, whereas in sexual reproduction new plants are obtained from seeds.

• Vegetative propagation It is a type of asexual reproduction in which new plants are produced from roots, stems, leaves and buds. Plants produced by vegetative propagation take less time to grow and bear flowers and fruits earlier than those produced from seeds.

• The new plants are exact copies of the parent plant, as they are produced from a single parent.

1. Yeast is a unicellular organism in which reproduction is done through budding.The small bulb-like projection coming out from the yeast cell is called a bud. The bud gradually grows and gets detached from the parent cell and forms a new yeast cell. The new yeast cell grows, matures and produces more yeast cells.

2. The process of reproduction in algae is done by fragmentation. In this process, the algae (such as spirogyra) breaks up into two or more fragments. These fragments or pieces grow into new individuals.

3. Plants such as moss and ferns, also reproduce by means of spores. When spores are released they keep floating in the air reaching long distances. Under favourable conditions, a spore germinates and develops into a new individual.

• Since pollen grains are light, they can be carried by wind or water. Insects visit flowers and carry away pollen on their bodies. Some of the pollen lands on the stigma of a flower of the same kind.

• The transfer of pollen from the anther to the stigma of a flower is called pollination. If the pollen lands on the stigma of the same flower or another flower of the same plant, it is called self-pollination.

• When the pollen of a flower lands on the stigma of a flower of a different plant of the same kind, it is called cross-pollination.

• 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.

• The wire gets hot when an electric current passes through it. This is the heating effect of the electric current. Oersted observed the deflection of the compass needle every time the current was passed through the wire.

• So, when electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current.

• 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.

• Plane mirrors are simply flat mirrors without curves. Because these can be found almost anywhere, the average person is incredibly familiar with them (even if they don't know the technical term).

• While the first manmade mirrors were made from intensely polished bronze, silver and other metals, today most mirrors are made from glass sheets finished with a thin layer of aluminum.

• That said, plane mirrors can be made from liquid as well: Gallium and mercury can be used for this purpose. Regardless of material construction, however, all flat mirrors function the same way.

• They reflect rays of light, producing an image. Characteristics of the image formed by a plane mirror : • It is virtual • It is erect and of same size as the object • The distance of an object from the plane mirror is the same as the distance of image from the plane mirror.

• One of the important characteristics of the image is that it is laterally inverted. It means if you raise your left hand it would appear in the plane mirror that you have raised your right hand.

• Concave mirrors are used for many purposes. Doctors use concave mirrors for examining eyes, ears, nose and throat. Concave mirrors are also used by dentists to see an enlarged image of the teeth.

• The reflectors of torches, headlights of cars and scooters are concave in shape. Convex mirror is used as side mirrors in automobiles. Convex mirrors can form images of objects spread over a large area. So, these help the drivers to see the traffic behind them.

• A convex lens can form images that are real, inverted, and larger than the object. However, this happens only when the object is between the lens and the focal point.
• A concave lens always forms images that are virtual, erect, and smaller than the object. This is true for all positions of the object.

The correct assertion is about the concave lens. Therefore, Assertion 2 is correct.

• When a ray of light approaches a smooth polished surface and the light ray bounces back, it is called the reflection of light. The incident light ray which lands upon the surface is said to be reflected off the surface.

• The ray that bounces back is called the reflected ray. If a perpendicular were to be drawn on a reflecting surface, it would be called normal. The figure below shows the reflection of an incident beam on a plane mirror.

• Image formation on a mirror is caused by reflection. Refraction and diffraction have no role to play in it.

• 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).

Anti-shoplifting devices often use convex mirrors. These mirrors are helpful for the following reasons:

• Wide Field of View: Convex mirrors can cover a larger area compared to other types of mirrors.
• Security: They help store personnel monitor large sections of the store, making it harder for shoplifters to steal unnoticed.
• Cost-effective: Convex mirrors are a simple and affordable security measure.