Test: Class 9 General Science NCERT Based - 2 - UPSC MCQ

• Thomson atomic model was proposed by William Thomson in the year 1900. This model explained the description of an inner structure of the atom theoretically. It was strongly supported by Sir Joseph Thomson, who had discovered the electron earlier. During a cathode ray tube experiment, a negatively charged particle was discovered by J.J. Thomson. This experiment took place in the year 1897.

• Cathode ray tube is a vacuum tube. The negative particle was called an electron. Thomson assumed that an electron is two thousand times lighter than a proton and believed that an atom is made up of thousands of electrons.

• In this atomic structure model, he considered atoms surrounded by a cloud having positive as well as negative charges. The demonstration of the ionization of air by X-ray was also done by him together with Rutherford.

• They were the first to demonstrate it. Thomson’s model of an atom is similar to a plum pudding. Postulates of Thomson’s atomic model: Postulate 1: An atom consists of a positively charged sphere with electrons embedded in it Postulate 2: An atom as a whole is electrically neutral because the negative and positive charges are equal in magnitude Thomson atomic model is compared to watermelon.

• Lysosomes are an important cell organelle found within eukaryotic animal cells. Due to their peculiar function, they are also known as the “suicide bags” of the cell.

• The term was coined by Christian de Duve, a Belgian biologist, who discovered it and ultimately got a Nobel Prize in Medicine or Physiology in the year 1974. Lysosome Definition: “Lysosomes are sphere-shaped sacs filled with hydrolytic enzymes that have the capability to break down many types of biomolecules.” In other words, lysosomes are membranous organelles whose specific function is to breakdown cellular wastes and debris by engulfing it with hydrolytic enzymes.

• Lysosomes work as the waste discarding structures of the cell by processing undesirable materials and degrading them, both from the exterior of the cell and waste constituents inside the cell. But sometimes, the digestive enzymes may end up damaging the lysosomes themselves, and this can cause the cell to die.

• This is termed as autolysis, where “auto” means “self” and “lysis” means “the disintegration of the cell by the destruction of its cell membrane“. Hence, lysosomes are known as “Suicidal Bags” of the cell.

Connective Tissues: They are the group of tissues made up of cells separated by non-living material, called an extracellular matrix. This tissue gives shape to the organs and holds them in place.

For example, blood, bone, tendon, adipose, ligament and areolar tissues. There are three types of connective tissue:

• Fibrous Connective Tissue.

• Fluid Connective Tissue.

• Skeletal Connective Tissue.

Functions of Connective Tissue The connective tissue gives shape to the organs and holds them in place. It functions as the main supporting tissue of the body. Other important and the major functions of connective tissue in the body are:

1. Insulating.

2. Helps in binding the organs together and provides support.

3. Protects against the invasions of pathogens by their phagocytic activity.

4. Provides shape to the body, conserves body heat and also stores energy.

5. Involved in transporting nutrients, hormones, gases, wastes, and other substances within the body.

Function of Stomata in Plants:
Stomata, along with the guard cells, serve several important functions for plants. However, one of the functions listed is not served by stomata. Let's discuss each function in detail:
A: Exchange of gases, particularly CO₂ and O₂, with the atmosphere:
- Stomata facilitate the exchange of gases between the plant and the atmosphere.
- They allow the uptake of carbon dioxide (CO₂) required for photosynthesis and the release of oxygen (O₂) as a byproduct.
B: Loss of water in the form of vapors during transpiration:
- Transpiration is the process by which plants lose water through stomata.
- Stomata open to release water vapor, allowing the plant to cool down and maintain its temperature.
C: Helps to create pressure for the water to rise upward, by its process of transpiration:
- Transpiration creates a pulling force, known as transpirational pull, which helps in the movement of water and nutrients from roots to leaves.
- Stomata play a vital role in this process by releasing water vapor, which creates a negative pressure gradient that draws water upwards.
D: Helps the leaves to carry out the process of photosynthesis:
- Stomata allow the entry of carbon dioxide, which is essential for photosynthesis.
- During photosynthesis, plants convert carbon dioxide and sunlight into glucose and oxygen, which is stored as energy.
Answer: D - Helps the leaves to carry out the process of photosynthesis
The correct answer is option D. Stomata do play a significant role in photosynthesis by facilitating the entry of carbon dioxide.

Meristematic Tissue: They are the group of young cells, which consists of actively dividing cells and leads to increase in length and thickness of the plant. There are different types of meristematic tissues, which are classified on the basis of positions, functions, plane of divisions, origin and development. The three main types of meristematic tissues depending on the occurrence of the meristematic tissue on the plant body are

1. Apical Meristem.

2. Lateral Meristem.

3. Intercalary Meristem.

Functions of Meristematic Tissue

1. It is responsible for the growth of the new organs.

2. Involved in the movement of water and nutrition within the plants.

3. These tissues are responsible for both primary and secondary growth of the plant.

4. It is the outermost tissue, functions by providing protection from mechanical injury.

5. It gives rise to the epidermis layer, cortex, endodermis, ground tissue and vascular tissue.

• The open circulatory system is common to molluscs and arthropods. Open circulatory systems pump blood into a cavity (hemocoel) with the blood diffusing back to the circulatory system between cells.

• Blood is pumped by a heart into the body cavities, where blood surrounds the organs. This system lacks a true heart or capillaries. The blood found in these organisms is a mix of blood and an interstitial fluid called as hemolymph.

1. The average velocity of an object is its total displacement divided by the total time taken. In other words, it is the rate at which an object changes its position from one place to another. Average velocity is a Vector quantity. The SI unit is meters per second.

2. The distance travelled is the path taken by a body to get from an initial point to an end point in a given period of time, at a certain velocity. If the velocity is constant: Distance = time * velocity.

3. The average speed of an object is the total distance traveled by the object divided by the elapsed time to cover that distance. It's a scalar quantity which means it is defined only by magnitude. A related concept, average velocity, is a vector quantity. A vector quantity is defined by magnitude and direction.

4. If an object moves relative to a reference frame—for example, if a professor moves to the right relative to a whiteboard, or a passenger moves toward the rear of an airplane—then the object’s position changes. This change in position is known as displacement. The word displacement implies that an object has moved, or has been displaced. Displacement is defined to be the change in position of an object.

If the car is moving on a straight road than the displacement is always equal to the distance, when an object is moving in the a straight path (displacement is defined as the shortest distance covered by a body)