Revision class 8 science

1. Give reasons.

A. Cell wall is free permeable component of cell. 

B. Cell membrane is selectively or semi-permeable membrane.

C. Nucleus is the controller of the cell. 

D. Lysosome is the sucidial bag of the cell. 

E. Mitochondria is the power house of the cell. 

F. Atom is electrically neutral. 

G. The valency of magnesium is 2.

H. The valency of chlorine is 1.

I. Aluminum is a metal. 

J. Sulphur is a non-metal. 

K. Neon is an inert gas. 

L. Silicon is a metalloid. 

M. Every ores are minerals but every minerals are not ores. 

N. Force and motion are relative term. 

J. The acceleration of a body moving with uniform velocity is zero. 

K. The mechanical advantage of a second class lever is greater than 1.

L. The mechanical advantage of a third class lever is less than 1. 

M. The dams of the rivers are made wider. 

N. The speed of flow of water is greater in ground floor than that up of third floor.