C. Short answer questions
1. Why do animals need to move?
ind invertebrat
Answers
Answer:
Movement is a trademark in the life of animal life. Most animals have ways to move through their environment to catch food, escape from predators or find mates. Sessile animals have to move their surrounding water or air in order to catch food, usually by using their tentacles or by using beating cilia to generate water currents and capture small food particles. Most animal phyla include species that swim but whether living on land or in the sediments of sea floor and lakes, animals crawl, walk, run, hop or stay put. Locomotion requires energy, and most animals spent a considerable amount of their time expending energy to overcome the forces of friction and gravity that tend to keep them stationary.
The energetic cost of transport or any kind of movement is different depending on the surrounding environment. In the aquatic environment most animals are buoyant and overcoming gravity is less of a problem. Because water is a much denser medium than air the primary problem is resistance/friction, hence the most energy-efficient means of locomotion for aquatic organisms is their adaptation to a sleek, hydrodynamic shape. Most four-legged aquatic vertebrates use their legs as oars to push against the water. Fish swim by using their body and tail from side to side and aquatic mammals heave their body up and down. Invertebrates such as squid, scallops and some cnidarians are jet-propelled using water that they squirt in and out of certain body parts.
At the cellular level, all animal movement is based on two systems of cell motility; microtubules and microfilaments. Microtubules are responsible for the beating of cilia and the undulations of flagella and microfilaments are the contractile elements of muscle cells. But muscle contraction in itself cannot translate to movement in the animal unless the muscle has some kind of support to work against and that is some type of a skeleton.
Skeletons support and protect the animal body and are essential to movement. There are three types of skeletons: the endoskeleton, the exoskeleton and the hydrostatic skeleton. Most cnidarians, flatworms, nematodes and annelids have a hydrostatic skeleton that consists of fluid held under pressure in a closed body compartment. These animals can control their body form and movement by using muscles to change the shape of the fluid filled compartments. Hydrostatic skeletons are ideal for life in aquatic environments and they may protect internal organs from shocks and provide support for crawling and burrowing but they cannot support any form of terrestrial locomotion in which an animal’s body is held off the ground.
The exoskeleton is a hard encasement deposited on the surface of an animal. Most mollusks are enclosed in calcium carbonate shells secreted by a sheet like extension of the body wall, the mantle. Animals increase the diameter of the shell by adding to its outer layer. Arthropods have a joint exoskeleton, the cuticle. As the animal grows in size the exoskeleton of an arthropod must be periodically molted and replaced by a larger one.
An endoskeleton consists of hard supporting elements buried within the soft tissues of an animal. Sponges for example are reinforced by either hard spicules or consisting of inorganic material or soft fibers made of protein. Echinoderms have an endoskeleton of hard plates beneath the skin and sea urchins have a skeleton of tightly bound ossicles. Ossicles of sea stars are more loosely bound which allows the animal to change the shape of its arms. Chordates have endoskeletons consisting of cartilage, bone or both.
Invertebrates, the animal phyla without backbones, consist mainly of aquatic species with a few exemptions of earthworms and snails can be generally found on moist soil and vegetation.