Actually, the locomotor part of a hydra is not its tentacles. Hydras move by a remarkable way called "looping." They attach one end of their body to a surface and then release the other end, allowing it to move and attach again. This looping movement is facilitated by the contraction and expansion of the body, rather than the use of tentacles. Tentacles are specialized structures primarily used for feeding and defense in hydras.

Cats (and many other animals) have a layer of cells behind their retinas called the tapetum lucidum. This layer enhances night vision by reflecting light that passes through the retina back into the eyes. When light enters the eye, some of it is absorbed by the retina's cells, allowing the brain to process visual information. However, the tapetum lucidum reflects the remaining light back through the retina, giving the photoreceptor cells a second chance to detect the light. This reflection of light enhances their night vision capabilities and is what causes a cat's eyes to appear to glow in the dark or in low light conditions.

The term "Rh factor" is derived from the Rhesus monkey, in which the protein was first discovered. The Rh factor is a protein that can be present on the surface of red blood cells, and it is named after the Rhesus monkey because the protein was initially identified in Rhesus monkey blood during scientific experiments. The Rh factor is an important component in blood typing and can be either Rh-positive (presence of the protein) or Rh-negative (absence of the protein) in humans.

Mercury and Venus are the two planets in our solar system that do not have any natural satellites (moons).

female sterilization is commonly referred to as tubectomy. Tubectomy is a surgical procedure in which a woman's fallopian tubes are blocked, cut, or sealed to prevent eggs from reaching the uterus for fertilization. This method of permanent contraception is also known as tubal ligation.

Bile juice is produced by the liver and stored in the gallbladder, which is a small organ located beneath the liver. When needed, bile is released from the gallbladder into the small intestine to aid in the digestion and absorption of fats and fat-soluble vitamins. So, the correct answer is the liver secretes bile juice, and it is stored in the gallbladder before being released into the small intestine.

Vitamins A, D, E, and K are called the fat-soluble vitamins, because they are soluble in organic solvents and are absorbed and transported in a manner similar to that of fats. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitamin E, can cause nerve problems.

This is a fundamental constant in chemistry that represents the number of atoms or molecules in one mole of a substance. (Option 4 is correct) Its value is approximately 6.022 x 10²³, and it is denoted by the symbol "N_A". Avogadro's number is a key concept in stoichiometry. The branch of chemistry deals with the quantitative relationships between reactants and products in chemical reactions.