Explanation

Tube feet, respiratory tree, and papillae are all present in Holothuroidea, which are commonly known as sea cucumbers.

Holothuroidea is a class of echinoderms that includes various species of sea cucumbers.

Explanation

The formula for Intelligence Quotient (IQ) is:

$$text{IQ} = frac{text{Mental Age (MA)}}{text{Chronological Age (CA)}} times 100$$

Explanation

Iron is essential in making hemoglobin, a protein in red blood cells.

These red blood cells help carry oxygen throughout your body.

Explanation

The endosymbiont hypothesis suggests that mitochondria and chloroplasts originated as free-living bacteria that were engulfed by ancestral eukaryotic cells.

The presence of their own DNA and similarities with certain bacteria strongly support this hypothesis.

Explanation

Pneumatophores are specialized aerial roots found in mangrove species.

In some species, these roots are pencil-sized and peg whereas in some other species, they look like a knee.

These roots have numerous pores through which oxygen enters the underground tissues

Explanation

Soil salinity is measured using a conductivity meter, which assesses the electrical conductivity of the soil.

Explanation

The fetal presentation is the part of the fetus (such as the head, breech, or shoulder) that enters the birth canal first.

It is a crucial factor in determining the position and orientation of the fetus during labor. 

Explanation

The body wall of sponges is composed of two main layers: the pinacoderm and the choanoderm.

The pinacoderm is the outermost layer, made up of flat cells called pinacocytes, which cover the external surface of the sponge.

Explanation

Potassium ions play a crucial role in the conduction of nerve impulses.

They help in the repolarization phase of the action potential,

Allowing the nerve cell to reset its membrane potential after the transmission of an impulse

Explanation

Natural rubber is primarily composed of polyisoprene, a polymer made up of isoprene monomers.

Isoprene (2-methyl-1,3-butadiene) is a diene compound that polymerizes to form the long chains found in natural rubber.