Class 11 Biology Notes Chapter 4 (Chapter 4) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 4, Animal Kingdom. This is a crucial chapter, not just for your Class 11 understanding, but also forms a significant base for various government exams with a Biology component. We need to understand how animals are classified and the key features of each group.

Chapter 4: Animal Kingdom - Detailed Notes for Exam Preparation

I. Basis of Classification

Understanding why animals are grouped the way they are is fundamental. Classification is based on common fundamental features:

1. Levels of Organisation:

   • Cellular Level: Cells are arranged as loose aggregates. Basic division of labour. (e.g., Phylum Porifera)
   • Tissue Level: Cells performing the same function are arranged into tissues. (e.g., Phylum Coelenterata, Ctenophora)
   • Organ Level: Tissues are grouped together to form organs, each specialized for a particular function. (e.g., Phylum Platyhelminthes)
   • Organ System Level: Organs associate to form functional systems (e.g., digestive system, circulatory system). This is seen in higher phyla. (e.g., Aschelminthes to Chordata)
   • Note: Complexity of systems (e.g., digestive - incomplete vs complete; circulatory - open vs closed) is also a basis.

2. Symmetry: Arrangement of body parts around a central axis.

   • Asymmetrical: Body cannot be divided into equal halves through any plane. (e.g., Most Porifera)
   • Radial Symmetry: Body can be divided into identical halves by any plane passing through the central axis. (e.g., Coelenterata, Ctenophora, Adult Echinodermata)
   • Bilateral Symmetry: Body can be divided into identical left and right halves by only one plane. Associated with cephalization (formation of a head). (e.g., Platyhelminthes to Chordata, Larval Echinodermata)

3. Germ Layers: Layers of cells formed during embryonic development.

   • Diploblastic: Cells arranged in two embryonic layers - external Ectoderm and internal Endoderm. An undifferentiated layer, Mesoglea, may be present in between. (e.g., Porifera, Coelenterata, Ctenophora)
   • Triploblastic: Three embryonic layers develop - Ectoderm, Mesoderm (middle layer), and Endoderm. Mesoderm gives rise to most organs. (e.g., Platyhelminthes to Chordata)

4. Coelom (Body Cavity): The nature of the cavity between the body wall and the gut wall. Its presence/absence is very important.

   • Acoelomates: No body cavity present between the body wall and gut wall. The space is filled with matrix (parenchyma). (e.g., Platyhelminthes)
   • Pseudocoelomates: Body cavity is present, but it is not lined by mesoderm. Mesoderm is present as scattered pouches. (e.g., Aschelminthes)
   • Coelomates: Possess a true coelom - a cavity lined by mesoderm on all sides. Allows organs to be better accommodated and organized. (e.g., Annelida to Chordata)

5. Segmentation (Metamerism): Body is externally and internally divided into segments with serial repetition of at least some organs. (e.g., Annelida, Arthropoda, Chordata)

6. Notochord: A mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals.

   • Non-Chordates: Animals without a notochord. (Phyla Porifera to Echinodermata)
   • Chordates: Animals possessing a notochord at some stage of their life. (Phylum Chordata)

II. Classification of Animals (Phylum-wise Key Features & Examples)

(Focus on distinguishing features, unique characteristics, and common examples)

III. Phylum Chordata - Further Classification

Chordata is divided into three subphyla: Urochordata, Cephalochordata, and Vertebrata.

• Urochordata (Tunicata): Notochord only in larval tail. (Ascidia, Salpa)
• Cephalochordata: Notochord head to tail, persistent throughout life. (Branchiostoma / Amphioxus)
• Vertebrata: Notochord replaced by vertebral column (backbone) in adults. Have a ventral muscular heart, kidneys, paired appendages.

Subphylum Vertebrata - Classes:

1. Class Cyclostomata: (Jawless fish) Ectoparasites; Sucking circular mouth; No scales/paired fins; Cartilaginous skeleton; 6-15 pairs of gill slits. (Petromyzon - Lamprey, Myxine - Hagfish).
2. Class Chondrichthyes: (Cartilaginous fishes) Marine; Cartilaginous endoskeleton; Ventral mouth; Placoid scales; Gill slits without operculum; No air bladder; Mostly viviparous. (Scoliodon - Dogfish, Pristis - Sawfish, Trygon - Sting ray, Torpedo - Electric ray).
3. Class Osteichthyes: (Bony fishes) Marine & Freshwater; Bony endoskeleton; Terminal mouth; Cycloid/Ctenoid scales; 4 pairs of gills covered by operculum; Air bladder present; Mostly oviparous. (Labeo - Rohu, Catla, Clarias - Magur, Hippocampus - Seahorse, Exocoetus - Flying fish).
4. Class Amphibia: Live on land & water; 2 pairs of limbs; Moist skin (respiration); Tympanum represents ear; 3-chambered heart; Cold-blooded (Poikilotherm); External fertilization; Indirect development (larva). (Bufo - Toad, Rana - Frog, Salamandra, Ichthyophis - Limbless).
5. Class Reptilia: Mostly terrestrial; Dry, cornified skin with scales/scutes; Crawling locomotion; Tympanum; 3-chambered heart (4 in crocodiles); Cold-blooded (Poikilotherm); Internal fertilization; Oviparous; Direct development. (Chelone - Turtle, Testudo - Tortoise, Chameleon, Lizards, Snakes, Crocodiles).
6. Class Aves: (Birds) Feathers; Forelimbs modified into wings; Beak; Pneumatic (hollow) bones; 4-chambered heart; Warm-blooded (Homeotherm); Lungs with air sacs; Internal fertilization; Oviparous; Direct development. (Corvus - Crow, Columba - Pigeon, Pavo - Peacock, Struthio - Ostrich).
7. Class Mammalia: Mammary glands; Hair; External ears (pinnae); Heterodont teeth; 4-chambered heart; Warm-blooded (Homeotherm); Lungs; Internal fertilization; Viviparous (mostly, exception: Platypus); Direct development. (Ornithorhynchus - Platypus, Kangaroo, Whale, Dolphin, Tiger, Humans).

Key Points for Exams:

• Know the basis of classification thoroughly.
• Memorize unique features of each phylum (e.g., water canal system, cnidoblasts, comb plates, flame cells, jointed appendages, water vascular system).
• Be able to differentiate between closely related groups (e.g., Chondrichthyes vs Osteichthyes, Reptiles vs Amphibians).
• Remember common examples for each phylum/class.
• Pay attention to terms like Diploblastic/Triploblastic, Acoelomate/Pseudocoelomate/Coelomate, Radial/Bilateral symmetry, Open/Closed circulation, Poikilotherm/Homeotherm.
• Note exceptions (e.g., flightless birds, oviparous mammals).

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on Chapter 4 for your practice:

1. Which of the following phyla exhibits a pseudocoelom?
   (a) Platyhelminthes
   (b) Annelida
   (c) Aschelminthes
   (d) Mollusca

2. The characteristic feature of Phylum Porifera, involving pores and chambers for water flow, is known as the:
   (a) Gastro-vascular system
   (b) Water vascular system
   (c) Canal system
   (d) Respiratory system

3. Bioluminescence is a well-marked feature in which of the following phyla?
   (a) Coelenterata
   (b) Platyhelminthes
   (c) Ctenophora
   (d) Hemichordata

4. Which feature distinguishes Osteichthyes from Chondrichthyes?
   (a) Presence of scales
   (b) Presence of an operculum covering the gills
   (c) Cartilaginous endoskeleton
   (d) Ventral mouth

5. Pneumatic bones, i.e., bones filled with air cavities, are characteristic of:
   (a) Amphibia
   (b) Reptilia
   (c) Aves
   (d) Mammalia

6. Balanoglossus belongs to which Phylum?
   (a) Echinodermata
   (b) Hemichordata
   (c) Urochordata
   (d) Cephalochordata

7. Animals that are diploblastic and exhibit radial symmetry belong to:
   (a) Porifera and Coelenterata
   (b) Coelenterata and Ctenophora
   (c) Ctenophora and Platyhelminthes
   (d) Porifera and Echinodermata

8. Flame cells (protonephridia) are the primary excretory structures in:
   (a) Annelida
   (b) Mollusca
   (c) Platyhelminthes
   (d) Arthropoda

9. Which of the following is NOT one of the fundamental characteristics of Phylum Chordata present at some stage of life?
   (a) Notochord
   (b) Dorsal hollow nerve cord
   (c) Vertebral column
   (d) Pharyngeal gill slits

10. The most unique mammalian characteristic is:
    (a) Presence of lungs
    (b) Being homeothermic (warm-blooded)
    (c) Presence of mammary glands
    (d) Having a four-chambered heart

Answer Key for MCQs:

1. (c) Aschelminthes
2. (c) Canal system
3. (c) Ctenophora
4. (b) Presence of an operculum covering the gills
5. (c) Aves
6. (b) Hemichordata
7. (b) Coelenterata and Ctenophora
8. (c) Platyhelminthes
9. (c) Vertebral column (This develops in Vertebrates, replacing the notochord, but isn't a fundamental chordate feature present in all chordates at some stage).
10. (c) Presence of mammary glands

Study these notes carefully, focusing on the distinguishing features and examples. Understanding the 'why' behind the classification will help you remember the details better. Good luck with your preparation!