Cytoplasm is a jelly like substance present between the cell membrane and the nucleus. Various components, or organelles are present in the cytoplasm. These are mitochondria, golgi bodies, ribosomes etc.

Kabbadi players rub their hands with soil to increase the friction so that they can grip the opposite team players firmly.

LED is a device or bulb which even glows at low or small current.

The sugar solution in distilled water will make it a good conductor of electricity and current can easily pass through it.

Since angle of incidence = angle of reflection. So, angle of incidence = 30°

The two ligaments which stretch across the larynx in such a way that it leaves a narrow slit between them for the passage of air, are known as vocal cords.

The stages in the life cycle of silkworm occursin following sequence:
Egg ⟶ Caterpillar ⟶ Pupa ⟶ Silkmoth
This drastic change in structure from caterpillar to silkmoth is called metamorphosis.

Reproduction is the biological process of formation of young ones of their own kind by living organisms.

Robert Hooke discovered cell on observation of cork slice.

Eukaryotes are organisms which contain well organised nucleus with nuclear membrane, e.g. humans.
Prokaryotes are those organisms which contain the primitive nucleus (unorganised) without nuclear membrane, e.g. bacteria, blue-green algae.

The advantages of electroplating are given below:
(i) It protects the metal from corrosion and rusting.
(ii) It is used to coat desired metal on other objects.
(iii) It can make more reactive metal like iron.
(iv) Coating of chromium on the metal gives luster to the objects.

Due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing. However, if the current through a circuit is too weak, the filament does not get heated sufficiently and it does not glow.

Sportsmen use shoes with spikes in order to avoid getting slip in the field. The spikes in the shoes increase the friction, so he/she can run on the ground easily.

There are two laws of reflection as below:
(i) The angle of incidence is equal to the angle of reflection.
(ii) Incident ray reflected ray and the normal drawn at the point of incidence to the reflecting surface, all lie in the same plane.

Given, number of oscillations = 10
Time taken = 20 s
As, we know that the number of oscillations per second is frequency.
\(\therefore frequency=\frac { Number\ of\ oscillations }{ Time\ taken } =\frac { 10 }{ 20 } =0.5Hz\\ \therefore time\ period=\frac { 1 }{ Frequency } =\frac { 1 }{ 0.5 } =2s\)

The cell organelles like mitochondria, Golgi complex, ribosomes, nucleus, etc carry out specific functions in a cell but they function only when present inside a living cell. They cannot act as independent units. Therefore, we do not call, cell organelles as the structural and functional units of living organisms.

Yes, music becomes noise sometimes, when it crosses the bearable range of sound for the ears.

Difference between internal fertilisation and external fertilisation are

Difference between a zygote and a foetus is

Factors affecting friction:
(i) It depends on the nature of surfaces in contact.
(ii) It is more between rough surfaces and less between smooth surfaces.
(iii) It depends on how hard the two surfaces press together.
(iv) It is independent of the area of contact.

Care of the eyes: It is necessary to take proper care of eyes. Few suggestions are as follows:
(i) If advised, use suitable spectacles.
(ii) Too little or too much light is bad for eyes. Insufficient light causes eye strain and headaches.
(iii) Do not look at the sun or a powerful light directly.
(iv) Never rub your eyes. If particles of dust go into your eyeswash your eyeswith cleanwater.
(v) Always read at the normal distance for vision. Do not read by bringing the book too close to your eyes or keeping it too far.

Nucleus is the most important component of the living cell. It is round or spherical in shape and situated in the centre of the cell. Nucleus is separated from cytoplasm by a membrane called nuclear membrane. This membrane is porous and allows the movement of materials between the cytoplasm and inner side of the nucleus. There is a small and spherical body in the nucleus. It is called nucleolus. Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. Nucleus also acts as a control centre of the activities of the cell.

When a fine powder sprinkled on the carrom board and a few drops of oil are poured on the hinges of a door, the door moves smoothly. A cycJe or a motor mechanic some times uses grease between the moving parts of the cycle. In all the above cases, our try was to reduce friction in order to increase efficiency.
Also, interlocking of irregularities is avoided to a great extent due to which the movement becomes smooth. The substances which reduce friction are called lubricants. In some machines, it may not be advisable to use oil as lubricant. There is an air cushion between the moving parts, that is used to reduce friction.

(a) Cytoplasm is the transparent, jelly-like substance that makes up most of the inside of a cell. It is present between the cell membrane and nucleus.
Various structures such as the nucleus, mitochondria are present in it. These are called organelles. Salts, proteins, sugars and other substances are dissolved in this fluid.
Function Most of the chemical reactions which keep the cell alive take place in the cytoplasm.
(b) The nucleus and the cytoplasm together make up the protoplasm which is called the living substance of the cell.
The main constituent elements of protoplasm are carbon, hydrogen, oxygen and nitrogen