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Showing posts from January, 2021

WHAT ARE CELLS MADE OF?

How was trade done earlier?

  The Stone Age man was not aware of any trading. They hunted for their own requirements, later they started cultivating fields. When the wild animals became scarce in a particular area or the crop was bad, tribes moved forwards. Eventually, people came across the other groups that cultivated and produced different things--an exchange of goods started. For the exchange of goods, the value of the goods had to be determined. This could not be done without numbers, measures, and weights. Scales and calculating devices such as the Abacus were invented, the trading activity expanded and a real triangular trade arose.   Who invented the numbers? The first written number system is about 5o0o years old and comes from the Sumerians in Mesopotamia. But man wanted to specify quantities even much earlier: of the animals killed or of mushrooms. In the beginning, man counted using the finger joints on each hand. Even today, young children are taught to count on their fingers. It is known about

Why are we thrown forward when brakes are applied?

  Objects fall because the mass of the Earth attracts them. The force that pulls us towards the center of the Earth is known as gravitation. It keeps us on the ground and the satellites in their orbits. This force of attraction is much less on the Moon than on the Earth-only one-sixth. For this reason, the astronauts bounce when they walk on the moon because they experience weightlessness. In the state of weightlessness, we do not feel any force of gravity and do not feel any weight. However, we feel the forces acting on us on the Earth, when we fall from a height or when we are thrown forward when brakes are applied.   What is mass, weight, and density? All objects have a mass. Because of the force of attraction on the Earth, an object has a weight. This is the force with which the body-that is, the mass of the body-is attracted. The force of gravity on the Moon is just one-sixth of that on the Earth. A person who weighs 60 kg on the Earth weighs only 10 kg on the Moon. The dens

Are Bacteria and Viruses Animals or Plants?

  How many plant species are there? Today, scientists are aware of around 320,000-500,000 different species of plants, but they estimate this number to be much higher. Many of the known trees and flowers come from Asia, while other species of plants thrive in the tropical rain forests. Some plants have adapted to live in or below water, whereas some have adapted to live in the desert areas. Algae, lichen, and moss also belong to the plant kingdom.   How do we differentiate between plant species? Earlier the scientists differentiated between plants mainly by their appearance. Today, plants are classified according to their evolution, i.e., on the basis that all members of a group must have shared a common ancestor more recently than they have with any species outside the group. Thus, the plants are broadly classified as those containing chlorophyll (the green plants) and those without chlorophyll. The green plants include the green algae and the land plants, which grow towards l