How do Organisms Reproduce? — Science STD 10 — Question

A filamentous alga X is found in ponds, lakes and slow-moving streams. The filament of this alga simply breaks into two (or more) pieces on maturing and each piece then grows to become a complete new alga.

1. Name an alga which X is likely to be.
2. What is the colour of X?
3. What is the method of forming new algae by the breaking of parent alga known as?
4. An Amoeba also breaks up to form two daughter Amoebae. What is the difference in the splitting of Amoeba and splitting of this alga as a method of reproduction?
5. Name one marine animal which reproduces in the same way as alga X.

What are micelles? Why does it form when soap is added to water? Will a micelle be formed in other solvents such as ethanol also? State briefly how the formation of micelles help to clean the clothes having oily spots.

State the advantages and disadvantages of using solar cells.

Can the following groups of elements be classified as Dobereiner's triads?

1. Na, Si, Cl.
2. Be, Mg, Ca.

Give reason for your answer.

(Atomic masses: Be 9; Na 23; Mg 24; Si 28; Cl 35. 5; Ca 40)

1. Draw a ray diagram to show the formation of image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.
2. In the above ray diagram mark the object-distance (u) and the image-distance (v) with their proper signs (+ve or – ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.
3. Find the power of a convex lens which forms a real, and inverted image of magnification -1 of an object placed at a distance of 20cm from its optical centre.

How can three resistors of resistances 2 Ω, 3 Ω, and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω?

Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formula of A, B and C.

The human body contains a large number of cells A which are very long and branched, and look like electric wires. The longest branch of this cell is B whereas there are many small branches C. Any two A cells do not join to one another completely in the human body. There is a microscopic gap D between every pair of adjacent A cells through which electric impulses can pass by the release of a chemical substance.

1. What are cells A?
2. What is the name of (i) branch B, and (ii) branches C?
3. What is the microscopic gap D known as?
4. What is the function of cells like A in the human body?
5. The cells A are of three types. name the three types.