Question

briefly describe how a sea star performs the physiological functions of digestion, gas exchange, circulation, excretion and body support

Answer 1

Sea star is also known as "Asterias" and "The Starfish".

• Kingdom=Animalia
• Phylum=Echinodermata
• Class=Asteroidea

Star fish have various Physiological Functions such as:-

1) DIGESTIVE SYSTEM:-

The beginning of the process:- Starfish or sea star have a unique digestive system with a mouth at the center of their underside and an rectum on their upper surface. Food can be brought into the stomach through the mouth or, in many species, the cardiac stomach can be extended out through the mouth to digest food outside the body. They then use their tube feet to pass the food to the stomach.

The stomachs:- Some species use their water vascular system to open the shells of some mollusks and inject their stomachs into the shells. It then digests the mollusk in place. Partially digested food is passed to the inside of the starfish where digestion continues in the pyloric stomach. The sea star's arms are filled with digestive glands called pyloric caeca which help with digestion. These digestive glands secrete enzymes and absorb required vitamins from food.

The end of the process:- A small intestine runs from the secondary stomach to the rectum which is located in the central upper part of the body.

2) RESPIRATORY SYSTEM (GAS EXCHANGE):-There are various oragans involved to perform the function of gases exchange in a star fish such as,

i) Tube Feet- The oxygen travels through the tube feet into the water vascular system

ii) Papulae- Also known as the dermal gills or skin gills, help get exchange gases and get rid of nitrogen.

iii) Coelom- Canals that run through the starfish that fills with water. The Tube feet connect with the canals.

• The starfish or sea star has an Open Respiratory System because the oxygen is allowed to move freely in the water vascular system. Also the Carbon Dioxide that is released during respiration were roaming in the starfish.

Location of the gas exchange:- The Gas Exchange occurs at the folds of skin on the starfish’s dorsal side, exchanging oxygen, carbon dioxide, and nitrogen.

Ventilation Process :- The starfish’s ventilation process mostly focuses around the tube feet. There, the oxygen enters the starfish and the carbon dioxide leaves.

Respiratory gas transportation in sea star or starfish:-The starfish has a water vascular system in which the exchange between oxygen and carbon dioxide occurs.The tube feet of the starfish act like gills.The Oxygen enters the water vascular system through the tube feet as the carbon dioxide exists the body.

3) Circulation:- It occurs in three places:-

i) The perivisceral coelom

ii) The water vascular system ,and

iii) The hemal system

There are hemal channels formings rings around the central part of the body around the mouth, and a third ring around the digestive system .There are also radial hemal channnels running down the rays next to the gonads.The hemal system seems mostly organised to distribute nutrients from the digestive tract.   

4) Excretion:- The process of excretion, like many other of the Echinoderm's processes use it's water vascular system because it has no excretory organs. the unique system includes a series of internal canals connected to external body parts called the tube feet, this allows Echinoderm's to use their water vascular system for excretion and other processes (i.e. Respiration,Movement etc.)

5) Body support:-The typical body is made up of five arms that radiate from a small central body with a toothless mouth on the underside. The number of arms may vary greatly, as well as the size, from species to species.

The colors of the starfish range from yellow, orange, pink, and red, with a few that are gray, blue, green, or purple.

Plates covered with a thin layer of skin support the body wall of the starfish. Spines also project from the surface singly or in a group. Muscles at their base move each spine. The surface may have little pincer-like jaws mounted on a short stalk on three spines that are positioned close together. They are important in preventing the surface of the starfish from becoming encrusted with algae or other small organisms.

Starfish move by numerous tube feet arranged in rows along the underside of each arm. The muscles of the tube feet propel the starfish along in the water. At the tips of the feet are suction discs, which help secure the starfish to a rock or to its prey.

A starfish has very good regenerative powers and can easily grow back an arm or two if it has lost them. Starfish are carnivorous and feed on fish, crustaceans, worms, and mollusks. There is one species that feeds on coral polyps.

The female starfish releases millions of eggs into the sea. A larva hatches from the egg and from the larva, in about two months time, a young starfish will break free. This is just a very simplified version for one species. There are other species of the starfish that are totally different in their development.

Starfish can be found on most beaches. These starfish are usually dead or dying. They are very popular to collect and are used in decorations.