Echinoderms cannot control the osmolarity (concentration of dissolved solutes) of their body fluids, so the osmolarity is the same as the medium they are in. this explains why they

This explains why they water vascular systems.

Echinodermata are a group of marine organisms that are osmoconformers. This means that their body fluids are similar to their surrounding water in osmolarity, in other words their internal environment is osmotic to their external environment. So, Echinodermata don’t expend energy to expel water or salt from the body. Echinodermata have unique water vascular system that helps them in gas exchange, feeding, sensory reception and locomotion.  

Disadvantage of osmoconformers is that they are sensitive to changes in the osmolarity of their environment.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.