Inside the nucleoplasm a tangled mass of thread-like structures is called chromatin. They are formed of an acid called Deoxyribonucleic Acid (DNA) and proteins. When a cell starts to divide, the tangled mass of chromatin condense into long threads and finally, rod-like bodies called chromosomes. The chromosomes contain stretches of DNA which carry information for protein synthesis. A gene is called the hereditary unit and DNA is called the hereditary material. A chromatid is one copy of duplicated chromosome which is generally joined to the other copy by a centromere.

The pores present on the nuclear membrane allow transport of water-soluble molecules across the nuclear envelope. RNA and ribosomes move out of the nucleus, whereas carbohydrates, lipids and proteins move into the nucleus.

Golgi apparatus or Golgi complexes are bodies present in both animal and plant cells. 

The Golgi bodies put together the macromolecules like lipids and proteins like digestive enzymes and membrane proteins after they are synthesized in the cells. 

Therefore, the cells which secrete more digestive enzymes have a larger number of golgi bodies to bundle up the synthesized products.

Animals do not have rigid walls because cell walls are incompatible with the way in which an animal moves and grow. The flaccid cell membrane provides the animal cell freedom of mobility and formation of different tissues which is not present in plants.

• The simple permanent tissues are made of similar cells performing similar functions.
• These are the basic packaging tissues in the plants.

The physical quantity which corresponds to the rate of change of displacement is velocity.

The SI unit of velocity is m/s.

Velocity = Displacement / Time.

The physical quantity which corresponds to the rate of change of velocity is acceleration.

The SI unit of acceleration is m/s².

Acceleration = Change in velocity / Time.

Catalysts are substances including solid, liquid and gases that increase the rate of a chemical reactions and are vital to the chemical industry. They allow the efficient production of many chemicals and are used in a vast range of industrial applications including fine chemicals, refinery operations, edible oils, pharmaceuticals and polymers. Specific applications include the reduction of environmental emissions and the production of low sulphur fuels.

A pure substance consists of a single type of particles. In other words, a substance is a pure single form of matter. As we look around, we can see that most of the matter around us exist as mixtures of two or more pure components, for example, sea water, minerals, soil etc. are all mixtures. Mixture of two or more substances with one phase only, i.e. having no distinct boundary of constituent particles are called solution. For example, solution of sugar and water, solution of salt and water, lemonade, soft drinks, etc. ... Solute: Substance which is present in smaller quantity in a mixture is called solute.

Microvilli  are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, cellular adhesion, and mechanotransduction. Microvilli are most often found in the small intestine, on the surface of egg cells, as well as on white blood cells. In the intestine, they work in conjunction with villi to absorb more nutrients and more material because they expand the surface area of the intestine.

Nucleus

• The nucleus is small, round and membrane bound structure found in cell.
• The fluid inside the nucleus surrounded by nuclear membrane is called nucleoplasm.
• It controls the cell’s growth and reproduction because it contains cell's hereditary information.
• It is covered by dual layer called nuclear membrane.
• The nuclear membrane contains pores due to which materials can travel both inside the nucleus from its outer surrounding i.e. cytoplasm.

U= initial velocity= 80 km/h = 22.2 m/s
v= final velocity = 60 km/h = 16.7 m/s
t= time = 5 s
a= acceleration = ?
a=v-u/t
a= 16.7-22.2/5
a= -5.5/5
Therefore, a=-1.1 m/s2

Abdul, while driving to school, computes the average speed for his trip to be `20 km h^(-1)`. On his. Abdul, while driving to school, computes the average speed for his trip to be `20 km h^(-1)`. On his return trip along the same route, there is less traffic and the average speed is `30 km h^(-1)`

Pure substances are substances that are made up of only one kind of particles and has a fixed or constant structure.

Pure substances are further classified as elements and compounds.

A non-membranous cell organelle is ribosome. Ribosomes are extremely small, round bodies found either in the free state in the cytoplasm or attached to the surface of the ER.They are composed of ribonucleoproteic (ribonucleic acid and protein) .The main function of ribosomes is to act as a platform for the synthesis of proteins.

The second law of motion states that the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force.

The  quantity  of  motion  in  a  body depends  on  the product of mass  and  velocity  of  the  body termed as momentum.

The momentum (p) of a body is defined as the product of its mass (m) and velocity (v) and has the same direction as that of the velocity. Its SI unit is kilogram metre per second (kg m s−¹).

Momentum = mass × velocity

p = m × v

Momentum has both magnitude as well as direction; hence it is a vector quantity.

Momentum of a body at rest is zero.

Assertion: The momentum (p) of a body is defined as the product of its mass (m) and velocity (v) and has the same direction as that of the velocity.

Reason: Its SI unit is kilogram metre per second (kg m s−¹).

Both A and R are true and R is the correct explanation of assertion.

Both A and R are true but R is not the correct explanation of assertion.

A is true but R is false.

A is false but R is true.

• Mathematical Formulation of Second Law of Motion:

Suppose an object of mass, m is moving along a straight line with an initial velocity, u. It is uniformly accelerated to velocity, v in time, t by the application of a constant force, F throughout the time, t. The initial and final momentum of the object will be, p1 = mu and p2 = mv respectively.

The change in momentum ∝ p2 – p1

∝ mv – mu

∝ m × (v – u).

The rate of change of momentum ∝ m × (v – u)/t

Or, the applied force,

F ∝ m × (v – u)/t

F = km × (v – u)/t

= kma

Here, a = [(v – u)/t ] is the acceleration, which is the rate of change of velocity. The quantity, k is a constant of proportionality.

The SI unit of mass and acceleration are kg and ms-2.

One unit of force is defined as the amount that produces an acceleration of 1 ms-2  in an object of 1 kg mass.

1 unit of force = k × (1 kg) × (1 ms-2).

The unit of force is kg ms-2 or newton, which has the symbol N. The second law of motion gives us a method to measure the force acting on an object as a product of its mass and acceleration.

Isotopes are variants of a particular element with different a different number of neutrons. For example, the two isotopes of Uranium are, ²³⁵₉₂ U and ²³⁹₉₂ U. 

Isobars are elements that have the same number of nucleons (sum of protons and neutrons). The series of elements with 40 Mass number serves as a good example; ⁴⁰₁₆S, ⁴⁰₁₇Cl, ⁴⁰₁₈Ar, ⁴⁰₁₉K, and ⁴⁰₂₀Ca. 

Isotones are atoms that have the same neutron number but different proton number. For example, ³⁶₁₆S, ³⁷₁₇Cl, ³⁸₁₈Ar, ³⁹₁₉K and ⁴⁰₂₀Ca are all isotones of 20 since they all contain 20 neutrons.

The Cell theory says that the cells form the fundamental structural and functional units of all living organisms; proposed in 1838 by Matthias Schleiden and by Theodor Schwann.

The mass per unit volume of a substance is called density (density = mass/volume). As the volume of a substance increases, its density decreases.

Liquids have a lower density than that of solids. Water is also a liquid so it should also have less density than that of solid that is ice.

Though ice is solid, it has a cage-like structure hence there are a large number of empty spaces between its particles. These spaces are larger as compared to the spaces present between the particles of water. Thus for a given mass of water, the volume of ice is greater than that of water. Hence, the density of ice is less than that of water. A substance with lower density than water can float on water. Therefore, ice floats on water.