Class 9 General Science NCERT Based - 2 - Free MCQ Practice Test with solutions,

Very few bombarded α-particles on gold foil were deflected by sharp angles and therefore, it was concluded that the positive charge is concentrated in a very small volume of the atom called nucleus.

Most of the particles passed through the foil undeflected and was concluded that most of the space in an atom is empty.
A very few α-particles (approx. 1 in 12,000) were bounced back.
So option A is only incorrect statement.

• The chemical properties of an element are determined by the configuration of its electrons in orbit around its nucleus.

• The number of electrons in orbit is equal to the number of protons in the nucleus (each proton has an electrical charge of plus one, while each electron has the same charge only negative one).

• Since all atoms (of all elements are electrically neutral), the number of electrons in orbit around the nucleus equals the number of protons in those nuclei, so the electrical charges balance each other. It is the way that these electrons orbit the nucleus (according to definite laws) that determines each element’s chemical properties. See a Periodic Table of the Elements. The number of protons in the nucleus of an atom is its Atomic Number.

• 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.

• Avogadro's number, or Avogadro's constant, is the number of particles found in one mole of a substance. It is the number of atoms in exactly 12 grams of carbon-12. This experimentally determined value is approximately 6.0221 x 1023 particles per mole. Avogadro's number may be designated using the symbol L or NA.

• Note that Avogadro's number, on its own, is a dimensionless quantity. In chemistry and physics, Avogadro's number usually refers to a number of atoms, molecules, or ions, but it can be applied to any "particle." For example, 6.02 x 1023 elephants are the number of elephants in one mole of them.

• Atoms, molecules, and ions are much less massive than elephants, so there needed to be a large number to refer to a uniform quantity of them so that they could be compared relative to each other in chemical equations and reactions.

• A plant cell also has chloroplast , which afflicts the plant cells colours. An animal's cell DOES not have chloroplast .

• Osmosis is the diffusion of a solvent through a differentially permeable membrane. In biological systems, the solvent will usually be water.

• Osmosis will occur whenever the water concentrations are different on either side of a differentially permeable membrane. Osmosis can be defined as the movement of water molecules from a higher water concentration area to the area of less water concentration through a semipermeable membrane.

• In other words, it can be defined as the diffusion of water molecules through a semipermeable membrane. It is a special case of diffusion of water (High to low). For example, water in the roots of plants is transported through osmosis.

• 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.

1. Play a major role in sensory reception, excretion, filtration and other metabolic activities.

2. Provide mechanical strength and resistance to the underlying cells and tissue.

3. It is involved in the movement of materials through the process of filtration, diffusion and secretion.

4. Protects the internal organs against the invasions of pathogens, toxins, physical trauma, radiation, etc. Epithelial tissues are also involved in secreting hormones, enzymes, mucus and other products from ducts and transporting it to the circulatory system.

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.

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.

• Angiosperms are the largest group of plants on Earth. There are approximately 270,000 known species alive today.

• There's probably one nearby right now. Angiosperms include all plants that have flowers and account for approximately 80% of all known living plants.

• Example of an angiosperm: Carpel of Broomrape plant Characteristics: Angiosperms are able to grow in a variety of habitats. They can grow as trees, shrubs, bushes, herbs, and small flowering plants.

• 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. It is an unbranched, filamentous green algae occurring in the stagnant water so known as pond scum.

2. A mucilaginous covering or sheath is present which makes the surface slimy hence known as pond silk.

3. A double layered cell wall is present in which the outer wall is made of pectin and inner wall of cellulose.

4. A spirally coiled or ribbon shaped chloroplast with a number of pyrenoids is present.

5. Reproduction occurs both in vegetative and sexual methods.

6. Vegetative reproduction is by fragmentation.

7. Sexual reproduction takes place by conjugation.

8. Three types of conjugation are found in spirogyra.

They are

i. scalariform conjugation,

ii. Lateral conjugation,

iii. Self conjugation.

9. The lifecycle of the spirogyra is haplobiontic.

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.

• Uniform or constant acceleration is a type of motion in which the velocity of an object changes by an equal amount in every equal time period. A frequently cited example of uniform acceleration is that of an object in free fall in a uniform gravitational field.

• The acceleration of a falling body in the absence of resistances to motion is dependent only on the gravitational field strength g (also called acceleration due to gravity). By Newton's Second Law the force F_g acting on a body is given by: F_g = mg