Science
(a) Name the group of organisms which form in the first trophic level of all food chains. Why are they called so ?
(b) Why are the human beings most adversely affected by bio-magnification ?
(c) State one ill-effect of the absence of decomposers from a natural ecosystem.
Answer
(a) The group of organisms which form the first trophic level of all food chains are producers. They are called so because they are the only one to change the light energy of sun to chemical energy of food. The same energy goes to other trophic levels in food chains
(b) Bio-magnification refers to progressive accumulation of chemicals at each trophic level. Human beings are most adversely affected by bio-magnification because they are at the top of any food chain. Therefore, the maximum concentration of these chemicals get accumulated in human bodies.
(c) Without decomposers, the organic matter would not be efficiently broken down and recycled into essential nutrients, leading to the accumulation of dead organic matter in the ecosystem. This will disrupt the natural recycling of nutrients, negatively impacting soil fertility, promoting disease, and hindering the overall health and functioning of the ecosystem.
Related Questions
(i) Define Electric Power and write its SI unit.
(ii) Two bulbs rated 100 W; 220 V and 60 W; 220 V are connected in parallel to an electric mains of 220 V. Find the current drawn by the bulbs from the mains.
(i) State Joule's law of heating. Express it mathematically when an appliance of resistance R is connected to a source of voltage V and the current I flows through the appliance for a time t.
(ii) A 5 Ω resistor is connected across a battery of 6 volts. Calculate the energy that dissipates as heat in 10 s.
The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.
(a) Why is a pair of sex chromosomes in human beings called a mismatched pair in terms of type and size ?
(b) Out of male or female, which of them has a perfect pair of sex chromosomes ? In case of a perfect pair, will the gametes produced be of the same kind or of a different kind ?
(c) (i) Name two animals whose sex is not genetically determined. Explain the process of their sex determination.
OR
(ii) With the help of a flowchart only, show how sex is genetically determined in human beings.
A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.
(a) Draw a diagram to show this pattern of iron filings.
(b) Draw the magnetic field lines of a bar magnet showing the poles of the bar magnet as well as the direction of the magnetic field lines.
(c) (i) How is the direction of magnetic field at a point determined using the field lines ? Why do two magnetic field lines not cross each other ?
OR
(ii) How are the magnetic field lines of a bar magnet drawn using a small compass needle ? Draw one magnetic field line each on both sides of the magnet.