Questions

Metal Aluminium is present in chocolate wrappers.

Because arteries have to have thick walls for use of protection. Its when you get to veins where the walls get thinner. And the use of the heart is to pump blood to all of the cells and organs in the body so it would be to transport blood away from the heart.

i.e. 

Arteries = Away from the Heart 
Veins = Back to the Heart.

Given two trains of length = 180 mts + 180 mts 

The distance is = Length of trains = 360 mts 

Speed = 58 - 50 = 8 kmph x 5/18 m/s

Then, Time = dis/speed = (360x18) / (8x5) = 162 sec.

A sarcomere is the basic unit of striated muscle tissue. It is the repeating unit between two Z lines.

Skeletal muscles are composed of tubular muscle cells (myocytes called muscle fibers or myofibers) which are formed in a process known as myogenesis. Muscle fibers contain numerous tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as alternating dark and light bands. Sarcomeres are composed of long, fibrous proteins as filaments that slide past each other when a muscle contracts or relaxes.

A muscle fiber from a biceps muscle may contain 100,000 sarcomeres.