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Animal Kingdom – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 4. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Animals are classified by levels of organisation, symmetry, germ layers, body cavity (coelom) and segmentation into phyla from Porifera to Chordata.

Basis of classification

Organisation: cellular (sponges), tissue (cnidarians), organ and organ-system levels.
Symmetry: asymmetrical, radial (cnidarians, adult echinoderms), bilateral.
Coelom: acoelomate (flatworms), pseudocoelomate (roundworms), coelomate (annelids onwards).

Phyla

Porifera (canal system), Cnidaria (cnidoblasts), Ctenophora (comb plates), Platyhelminthes (flame cells), Aschelminthes, Annelida (metameric segmentation), Arthropoda (largest phylum), Mollusca, Echinodermata (water vascular system), Hemichordata.
Chordates have a notochord, dorsal hollow nerve cord and pharyngeal gill slits.
Vertebrate classes: Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, Mammalia.

Key terms

Coelom: body cavity lined by mesoderm
Notochord: rod-like supporting structure on the dorsal side of chordates
Metamerism: division of the body into repeated segments, each with a set of organs, as in earthworm

Important questions with answers

What is the difference between diploblastic and triploblastic animals?2 marks

Diploblastic animals have two germ layers (ectoderm and endoderm), with an undifferentiated mesoglea between (cnidarians). Triploblastic animals have a third layer, the mesoderm (flatworms to chordates).

Give three characteristic features of Chondrichthyes and Osteichthyes each.3 marks

Chondrichthyes: cartilaginous endoskeleton; gill slits without operculum; placoid scales; no air bladder, so they swim constantly (shark, Scoliodon). Osteichthyes: bony endoskeleton; gills covered by an operculum; cycloid or ctenoid scales; air bladder for buoyancy (Labeo rohita, Catla).

Compare Amphibia, Reptilia, Aves and Mammalia on heart, skin, body temperature and reproduction.5 marks

Amphibia: 3-chambered heart; moist, glandular skin without scales; cold-blooded; external fertilisation, eggs laid in water (frog). Reptilia: usually 3-chambered heart (4 in crocodiles); dry skin with scales; cold-blooded; internal fertilisation, shelled eggs on land (lizard, snake). Aves: 4-chambered heart; feathers, no glands except oil gland; warm-blooded; internal fertilisation, eggs with hard shells, pneumatic bones for flight (crow, pigeon). Mammalia: 4-chambered heart; hair and mammary, sweat and oil glands; warm-blooded; mostly viviparous, young fed on milk (human, whale).

Quick revision

Water vascular system = Echinodermata.
Flame cells = Platyhelminthes.
Mammals have mammary glands and hair.

Exam tips

Arthropoda is the largest phylum; Mollusca is the second largest.
Make a one-line card for each phylum: level of organisation, symmetry, germ layers, coelom, segmentation, two examples.

Practice MCQs

The largest phylum of animals is
1. Mollusca
2. Chordata
3. Arthropoda
4. Annelida
Show answer
Answer: (c) Arthropoda. Insects.
Sponges belong to
1. Cnidaria
2. Porifera
3. Annelida
4. Mollusca
Show answer
Answer: (b) Porifera. Pore bearers.
Water vascular system is a feature of
1. Mollusca
2. Echinodermata
3. Arthropoda
4. Annelida
Show answer
Answer: (b) Echinodermata. Starfish.
Roundworms are
1. acoelomate
2. pseudocoelomate
3. coelomate
4. haemocoelic only
Show answer
Answer: (b) pseudocoelomate. False coelom.
Which animal is a mammal that lays eggs
1. bat
2. whale
3. platypus
4. kangaroo
Show answer
Answer: (c) platypus. Monotreme.
Flame cells for excretion are found in
1. Platyhelminthes
2. Annelida
3. Cnidaria
4. Arthropoda
Show answer
Answer: (a) Platyhelminthes. Flatworms.
Which is NOT a chordate feature
1. notochord
2. dorsal hollow nerve cord
3. pharyngeal gill slits
4. ventral solid nerve cord
Show answer
Answer: (d) ventral solid nerve cord. Non-chordates have ventral cord.
Animals with an open circulatory system include
1. earthworm
2. cockroach
3. frog
4. human
Show answer
Answer: (b) cockroach. Arthropods have haemocoel.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.