Questions

Controlled railroad crossing includes warning signs, red lights and railway gates, whereas absence of all of these warning signs like red lights and gates includes uncontrolled railroad crossings. 

Cellular respiration is best associated with the organelle Mitochondrion.

Snow Leopard

Starting from letter 'S' add 5 in the clock wise direction to get the next letter in English alphabets.

Here S + 5 => 19 + 5 = 24 => X

X + 5 = 24 + 5 = 3 => C

Similarly, 

B + 5 = G

Enzymes are protein macromolecules. Enzymes are almost always made of proteins only. Proteins are large biopolymer molecules that are made up of repeating monomer units called amino acids. There are 20 different common amino acids that make up proteins like enzymes. Of these, nine amino acids are essential, which means you must get them from your diet.

Enzymes catalyze chemical reactions in biological systems. This means that they speed up the rate of the reaction.