Biology Class 9 Notes- Chapter 7

INVERTEBRATA

QNo.1: What are invertebrates?

Ans. Phylum Invertebrata belongs to Kingdom Animalia. The animals which do not have back bone in their bodies are called invertebrates. They are smaller in size but greater in number than vertebrates. They are divided into many phyla.

QNo.2: Define Phylum Protozoa.

Ans. Phylum protozoa belongs to Kingdom Protoctista (Protista), consists of unicellular, microscopic, animal like organisms. They occur either as free living (e.g. amoeba, paramecium, euglena etc.), which are found in fresh and marine water or as parasites (e.g. plasmodium, Entamoeba histolytica). E. histolytica cause dysentery and plasmodium cause malaria.

            PARAMECIUM: Paramecium live in fresh water pond. Its surface is covered by thousands of hair like cilia which help in locomotion. Paramecium has two nuclei 1) Macronucleus: which is larger in size and 2) Micronucleus: Which is smaller in size. Cell membrane is covered by non-living pellicle which provides it a definite shape.

QNo.3: Define Phylum Porifera.

Ans. Porifera are multicellular organisms. Their body consists of loose aggregates of cells and lack any kind of tissues. Their body has numerous pores or ostia. They are commonly called as sponges. All sponges are aquatic and sessile. Surrounding water enters the hollow space inside the body through ostia where inner cells of sponges filter out the microscopic food particles. The water then leaves the sponge body through osculum.

            Sponges have an internal skeleton of spicules formed of calcium carbonate of silica.  The common examples of sponges are Sycon, Venus flower basket and bath sponge.

SYCON: It has flask-like shape and needle shaped spicules made up of calcium carbonate. It is found in colonial form, live in shallow water in sea, being attached to solid objects like rocks. The free end of flask has a single large opening the osculum.

QNo.4: Define Phylum Cnidaria (Coelenterata).

Ans. Coelenterates are aquatic (marine and fresh water) animals. Their cells form tissues. They are diploblastic (cells arranged in two layers), outer layer called ectoderm and inner layer called endoderm. In between these two layers jelly-like, non-living mesoglea is present. Many of coelenterates are sessile e.g. corals, while others are motile e.g. jelly-fish. They occur either as free living as single (hydra) or in the form of colony, for example, Obella and Physalia.

HYDRA: Hydra is a fresh water coelenterate which can be better seen with a microscope. Its body is cylindrical with many thread like tentacles and mouth is at its one end. Tentacles and ectoderm bear poisonous, stinging cells for defense and paralyzing the prey. The tentacles are used to capture the prey. Mouth opens into a hollow space (coelenteron, lies inside the body). The prey is digested in coelenteron. The posterior end of hydra is kept attached to some object in water.

JELLY FISH: It swim freely in sea water. They have umbrella like body with thicker body walls. The mouth is located in center of center of downside of umbrella. Mouth is attached with four long arms, each arm ha stinging cells. The arms are used for capturing small animals.

QNo.5: Define Phylum Platyhelminthes.

Ans. Platyhelminthes are commonly called flat-worms because of their flat body. They occur mostly as parasites of animals (e.g. Liver fluke, Tape worms), some are free living (e.g. Planaria, which lives in streams). They are triploblastic because there is a middle layer of cells in between ectoderm and endoderm.

LIVER FLUKE: It is a flat leaf shaped organism about 3 cm in length. It is parasite in liver of sheep, goat and cattle. It attaches itself with host with the help of two suckers (one around the mouth at anterior tip and other on the ventral side of body). It has a bifurcated digestive system. Anus is absent in them. They have both male and female reproductive organs.

QNo.6: Define Phylum Nematoda.

Ans. Nematoda (round worms) have long, smooth and cylindrical body, which is pointed ate both ends. The body is un-segmented. They have complete and one way digestive system with mouth at anterior end and anus at posterior end.

They are free living as well as parasites of animals, man and plants. Ascaris lumbricoides (Human round worm) lives in intestine of man. Male is slightly smaller than female.

QNo.7: Define Phylum Annelida.

Ans. Annelids have elongated, segmented (external and internal) body. Many organs are repeated in every segment of body. They live in water as well as on land. Most of them are free living (e.g. earth worm) while few are ectoparasites (e.g. leech). Respiration occurs through general body surface. They have advanced closed type circulatory system i.e. blood circulate in blood vessels and pumped by number of simple hearts.

QNo.8: Define Phylum Arthropoda.

Ans. This the largest phylum of Kingdom Animalia. They have jointed limbs (legs). Their body is covered with exoskeleton made up of chitin. They occur on land as well as in water. The body of arthropod is divisible into three parts; an anterior head, middle thorax and posterior abdomen.

For example: Scorpions, spiders, crabs, prawns, centipedes and insects.

INSECTS: Insects are most abundant animals on earth. They all have three pairs of legs, two pairs of wings and one pair of sensory hair-like antenna. Many insects such as mosquito, house fly, butterfly and cockroach have appendages for food handling.

QNo.9: Define metamorphosis and its types.

Ans. Many insects such as mosquitos hatch out of their eggs in a premature form and pass through different stages of development to reach the adult stage. This phenomenon is called metamorphosis. There are two types of metamorphosis.

1) Complete metamorphosis:

            In complete metamorphosis the larva, which hatches out of egg is morphologically completely different from adult. Then it encloses itself in a cover to become pupa. After development the pupa comes out of its capsule and becomes adult. Thus insect passes through these stages i.e. egg        larva        pupa        adult. Complete metamorphosis occurs in butterflies, mosquitoes, housefly etc.

2) Incomplete metamorphosis:

            In this type nymph (young one) which emerges out of egg is a miniature young one which closely resembles the adult, except it lacks wings and reproductive organs are immature. After complete development of wings and maturity of reproductive organs the nymph becomes adult. It occurs in grass-hopper, cockroach and termite etc.

QNo.10: Write a note on Phylum Mollusca.

Ans. Animals of this group have soft, fleshy body enclosed in thin fleshy cover called mentle. Most molluscs are covered by a hard and nonliving shell made up of calcium carbonate. They mostly occur in water but some are found on land. A fleshy FOOT is given out of shell on the ventral side of body. It helps in locomotion.

            Common examples of molluscs are snail, pearl oyster, squid, octopus and mussel.

SNAIL:They have spirally coiled shells. They are commonly seen in lawns and gardens.

MUSSELS:They live in fresh water. Shell is composed of two plates joined together by hinge joint.

QNo.11: Write a note on Phylum Echinodermata.

Ans. Members of this phylum have rough and spiny skin. They live only in the sea. They are pentamerous and have unique WATER VASCULAR SYSTEM which pump the external water throughout their bodies. A soft TUBE FEET enables the animal to glide over the rocks in water. They do not have head, eyes and brain. Common examples are star-fish, sand-dollar, sea-cucumber, sea-urchins etc.

STAR-FISH:It has plate like central disc with five or more arms.

SEA-URCHINS:It has ball-like body without arms. Its body is covered externally by long spines.