Sample Material of Our Online Coaching Programme
Subject: General Science
Topic: The Animal Kingdom
There are many different types of animals in the world. Many
animals are quite similar to each other. Others are quite different. Animals can
be classified based on their similarities. Invertebrates Animals without a
Backboneor Spinal Column: Vertebrates Animals with a Backbone or Spinal Column:
(All these are those animals are in the phyla Chordata and the subphyla
Of the million or more animal species in the world, more than
98% are invertebrates. Invertebrates don’t have an internal skeleton made of
bone. Many invertebrates have a fluid-filled, hydrostatic skeleton, like the
jelly fish or worm. Others have a hard outer shell, like insects and
crustaceans. There are many types of invertebrates. The most common
invertebrates include the protozoa, annelids, echinoderms, mollusks and
arthropods. Arthropods include insects, crustaceans and arachnids.
Protozoa are simple, single-celled animals. They are the
smallest of all animals. Most protozoa are microscopic in size, and can only be
seen under a microscope. However, they do breathe, move and reproduce like
There are several types of protozoa. The amoebas are clear,
shapeless cells. Flagellates have a body shape looking like a hair. Although we
can’t see them, protozoa do a lot for us. Protozoa play a useful role in the
food chain as a source of food for fish and other animals. Some protozoa are
helpful to humans by eating dangerous bacteria. Unfortunately, other protozoa
are parasites and can be harmful to humans by transmitting disease.
Protozoa eat tiny algae and bacteria. Some protozoa absorb food through their
cell membrane. Others surround and engulf their food or have openings to collect
food. They digest their food in stomach-like compartments called vacuoles.
Protozoa take in oxygen and give off carbon dioxide through the cell membrane.
Protozoa reproduces by splitting in half.
(II) WORMS AND LEECHES
There are about 9,000 species of Annelids known today,
including worms and leeches. They can be found almost anywhere in the world.
Annelids have existed on Earth for over 120 million years. Annelids have bodies
that are divided into segments. They have very well-developed internal organs.
One common characteristic of annelids is that they don’t have any limbs. Some
annelids may have long bristles. Others have shorter bristles and seem smooth,
like the earthworm. There are many types of worms. Commonly known worms include
earthworms, roundworms and flatworms. Most worms are small, measuring fractions
of an inch to several inches long. Other worms, such as the ribbon worm, can
grow up to 100 feet in length. Some worms are considered parasites, in that they
live inside the human body.
Mollusks were among the first inhabitants of the Earth.
Fossils of mollusks have been found in rocks and date back over 500 million
years. Mollusk fossils are usually well preserved because of their hard shell.
Most mollusks have a soft, skin-like organ covered with a hard outside shell.
Some mollusks live on land, such as the snail and slug. Other mollusks live in
water, such as the oyster, mussel, clam, squid and octopus.
Land living mollusks, like the snail, move slowly on a flat sole called a foot.
Ocean living mollusks move or swim by jet propulsion. They propel themselves by
ejecting water from their body. For example, the squid ejects water from a
cavity within its body, and the scallop ejects water to move by clamping its
shell closed. Other ocean living mollusks, like the oyster, attach themselves to
rocks or other surfaces, and can’t move. They feed by filtering small food
particles from water that flows through them. Snail and Slug The snail family
consists of marine snails and land snails all over the world. Land snails live
in many habitats from gardens and woodlands, to deserts and mountains. Marine
snails are native to all the worlds oceans and seas, and many freshwater rivers
and lakes. Along with slug, snails make up the gastropod class of the mollusk
phylum. Snails have an external shell, large enough to withdraw their body into
it. Gastropods without a shell are known as slugs.