NEET Animal Kingdom, Biomolecules, and Structural Organisation in Animals Notes by PW

Preparing these Biology chapters for NEET requires more than memorising characteristics and definitions. You need to understand how animals are classified, how biomolecules are formed and function, and how different tissues and organs are organised in animals. Regular revision of important examples, biological processes, structures and functions can help improve concept clarity and recall while solving questions.

Instead of switching between different resources for each chapter, you can use Physics Wallah notes covering Animal Kingdom, Biomolecules, and Structural Organisation in Animals. The notes bring important concepts and classifications together, helping you save revision time and focus on the information you need to recall for NEET questions.

Animal Kingdom: Core Classification Concepts

Levels of Organisation

Animals show different levels of organisation based on the complexity of their body structure. Porifera show the cellular level of organisation, where cells are loosely arranged and perform different functions. Cnidaria and Ctenophora show the tissue level of organisation. Platyhelminthes have an organ level of organisation, while Aschelminthes and higher groups show the organ-system level of organisation.

Understanding these levels can help you differentiate major animal groups during NEET revision.

Germ Layers, Symmetry and Coelom

Animals can be classified based on the number of germ layers, type of symmetry and the presence or absence of a body cavity.

Cnidarians and ctenophores are diploblastic and have two germ layers. Cnidarians generally show radial symmetry, while ctenophores also show radial symmetry.

Platyhelminthes are triploblastic, bilaterally symmetrical and acoelomate. Annelids are triploblastic, bilaterally symmetrical and coelomate. Chordates are also triploblastic, bilaterally symmetrical and coelomate.

An acoelomate animal does not have a body cavity between the body wall and digestive tract. A pseudocoelomate has a body cavity that is not completely lined by mesoderm, while a coelomate has a true coelom completely lined by mesoderm.

Symmetry in Animal Groups

Symmetry refers to the arrangement of body parts around a central axis or plane.

Cnidarians generally show radial symmetry. Ctenophores also show radial symmetry. Adult echinoderms are radially symmetrical, while their larvae are bilaterally symmetrical. Most sponges are asymmetrical, although some may show radial symmetry. Platyhelminthes and annelids show bilateral symmetry.

Important Phylum-Based Features

Several characteristic features and examples are important for NEET revision. Porifera show intracellular digestion. Obelia is associated with metagenesis. Fasciola has suckers, while Taenia has hooks and suckers for attachment. Nereis possesses parapodia. Cnidarians have nematocysts or cnidoblasts, while ctenophores have comb plates. Arthropods have a chitinous exoskeleton and an open circulatory system. Echinoderms possess a water vascular system, while Mollusca generally have a radula, although it is absent in some groups.

Porifera

Poriferans are commonly known as sponges. Their body contains numerous small pores called ostia through which water enters. Water eventually leaves through the osculum.

Choanocytes, also called collar cells, help create water currents and trap food particles. Digestion in sponges is intracellular. Their skeleton may contain spicules or spongin fibres, which provide support.

The water canal system is important for feeding, respiration, removal of waste and reproduction. Understanding the functions of ostia, osculum and choanocytes is important while revising Porifera.

Cnidaria and Ctenophora

Cnidarians possess specialised cells called cnidoblasts or cnidocytes. These cells contain nematocysts that help in defence, capturing prey and attachment.

Cnidarians commonly occur in two body forms. The polyp is generally sessile, while the medusa is free-swimming. In Hydra, the mouth is located on the hypostome. Cnidarians are found in both marine and freshwater environments.

Ctenophores are exclusively marine animals. They possess eight rows of comb plates, which help in locomotion. Many ctenophores are bioluminescent. Digestion involves both extracellular and intracellular processes, and most ctenophores are hermaphroditic and reproduce sexually.

Arthropoda and Chordata

Arthropods have a chitinous exoskeleton and jointed appendages. They generally possess an open circulatory system. Aquatic arthropods may have statocysts, which help in maintaining balance.

Chordates are identified by four major characteristics: a notochord, dorsal hollow nerve cord, pharyngeal gill slits and post-anal tail. Chordates have a ventral heart and a closed circulatory system.

All vertebrates are chordates, but all chordates are not vertebrates. Chordates are broadly divided into Urochordata, Cephalochordata and Vertebrata.

Vertebrate Classification

• Cyclostomata are jawless vertebrates with a circular sucking mouth. Many members are ectoparasitic.

• Chondrichthyes have a cartilaginous skeleton and placoid scales. They generally lack an operculum.

• Osteichthyes have a bony skeleton and generally possess an air bladder.

• Amphibians have moist skin and usually show external fertilisation. They can live both in aquatic and terrestrial environments.

• Reptiles have dry skin and are mostly oviparous. Their heart is generally three-chambered, although crocodiles have a four-chambered heart.

• Aves have feathers and an oil gland. They maintain a relatively constant body temperature.

• Mammals have hair and mammary glands. They also possess a muscular diaphragm.

Water Vascular System in Echinoderms

Echinoderms possess a characteristic water vascular system. It consists of a network of canals filled with fluid and helps in locomotion, food capture, respiration and other functions.

Biomolecules: Important NEET Concepts

Amino Acids and Zwitterions

Amino acids contain an amino group, carboxyl group, hydrogen atom and variable R group attached to the same carbon atom, except in special cases such as proline.

The R group determines the properties of different amino acids. In glycine, the R group is hydrogen. In alanine, it is a methyl group. In serine, it is a CH₂OH group, while tyrosine contains an aromatic ring with a hydroxyl group.

Amino acids can exist as zwitterions, in which the amino group carries a positive charge and the carboxyl group carries a negative charge.

Proteins and Their Structures

Proteins are polymers made up of amino acids. Their primary structure refers to the specific sequence of amino acids in a polypeptide chain.

The end of a polypeptide with a free amino group is called the N-terminal, while the end with a free carboxyl group is called the C-terminal.

Protein structure may be described at primary, secondary, tertiary and quaternary levels. Haemoglobin is an example of a protein with quaternary structure and contains two alpha and two beta chains.

Important Biomolecular Bonds

Different biomolecules contain characteristic linkages. Amino acids in proteins are joined by peptide bonds. Nucleotides in nucleic acids are connected through phosphodiester bonds. Monosaccharides in polysaccharides are joined by glycosidic bonds.

Many lipids contain ester linkages, formed between fatty acids and alcohols such as glycerol.

Carbohydrates, Lipids and Nucleic Acids

• Cellulose is a homopolysaccharide made of glucose units. Chitin is made of repeating units of N-acetylglucosamine.

• Lipids are generally not considered true polymers because they are not made by the repeated linking of identical monomer units in the same way as proteins or nucleic acids.

• DNA and RNA are polymers of nucleotides. Nitrogenous bases are divided into purines and pyrimidines. Adenine and guanine are purines, while cytosine, thymine and uracil are pyrimidines.

• A nitrogenous base attached to a sugar forms a nucleoside. When a phosphate group is also attached, it forms a nucleotide. For example, adenine is a nitrogenous base, adenosine is a nucleoside and adenylic acid is a nucleotide.

• Phenylalanine is an example of an amino acid.

Enzymes and Enzyme Inhibition

• Enzymes act as biological catalysts and increase the rate of biochemical reactions by lowering the activation energy required for the reaction.

• The basic enzyme-substrate process involves the binding of a substrate to the enzyme's active site, formation of an enzyme-substrate complex, conversion of the substrate into product and release of the product.

• In competitive inhibition, the inhibitor resembles the substrate and competes with it for the active site of the enzyme.

• Some RNA molecules can also act as catalysts and are called ribozymes.

• Catalase and peroxidase contain heme as a prosthetic group. The protein part of a conjugated enzyme is called the apoenzyme. The complete active enzyme formed when the apoenzyme combines with its required non-protein component is called the holoenzyme.

Structural Organisation in Animals

• Epithelial Tissue

• Epithelial tissue covers body surfaces and lines internal organs and cavities. Its cells are closely packed and have very little intercellular matrix. Epithelial tissue is generally avascular and receives nutrients through diffusion.

• Squamous epithelium consists of thin, flattened cells and is found in structures such as alveoli and blood vessels.

• Ciliated epithelium has cilia that help move substances and occurs in regions such as bronchioles and parts of the female reproductive tract.

• Columnar epithelium consists of elongated cells and is found in areas such as the stomach and intestine.

• Cuboidal epithelium consists of cube-shaped cells and occurs in structures such as nephron tubules and gland ducts.

• Goblet cells are specialised secretory epithelial cells. Their nucleus is generally located towards the basal region, while their secretion is released towards the apical surface.

Connective Tissue

• Connective tissue supports, connects and protects different parts of the body.

• Bone contains mineral salts and provides support and protection. Cartilage contains chondroitin sulfate and provides flexible support.

• Tendons connect muscles to bones, while ligaments connect bones to other bones.

• Adipose tissue stores fat and also helps in insulation and protection.

Muscular Tissue

• Muscular tissue is specialised for contraction and movement.

• Skeletal muscles are voluntary and striated. They are generally attached to bones and help produce body movements.

• Cardiac muscles are involuntary and striated. They contain intercalated discs, which help coordinate contraction between adjacent cardiac muscle cells.

• Smooth muscles are involuntary and non-striated. Their cells are generally spindle-shaped and are found in the walls of internal organs.

Neural Tissue

• Neural tissue contains neurons and neuroglia. Neurons receive and conduct nerve impulses, while neuroglial cells provide support and protection.

• Astrocytes help maintain the blood-brain barrier and provide support to neurons. Oligodendrocytes produce myelin in the central nervous system.

Frog: Key Features for NEET

• Frogs are poikilothermic animals, meaning their body temperature varies with the surrounding environment.

• Tadpoles are generally herbivorous and have a relatively long intestine, while adult frogs are carnivorous and have a shorter intestine.

• Frogs show external fertilisation and indirect development. Tadpoles undergo metamorphosis to become adult frogs.

• Frogs can respire through their skin and lungs. Cutaneous respiration is especially important when they are in water. During hibernation and aestivation, respiration through the skin becomes particularly important.

• On land, respiration occurs through the skin, buccal cavity and lungs.

• The blood returning from the body enters the sinus venosus through the venae cavae.

• Male frogs possess features such as copulatory pads, vocal sacs and Bidder's canal.

• The cloaca receives faecal matter, urine and reproductive products before they are discharged from the body.

Cockroach: Key Features for NEET

• The cockroach has 10 pairs of spiracles. Two pairs are present in the thoracic region and eight pairs are present in the abdominal region.

• The main excretory organs are the Malpighian tubules.

• The crop stores food, while the gizzard or proventriculus helps grind food. The gastric caeca are associated with digestion and secretion.

• The forewings are called tegmina and are leathery, while the hind wings are membranous and help in flight.

• Anal cerci are present in both male and female cockroaches on the tenth abdominal segment. Anal styles are present only in males.

• Cockroaches have mosaic vision because each compound eye contains numerous ommatidia.

• The foregut includes the pharynx, oesophagus, crop and gizzard.

• In male cockroaches, the genital pouch contains phallomeres and the male genital pore.

Important Questions

1. Genetic material of living organisms is a polymer. The reason is that genetic material of living organisms is made of amino acids in a linear manner.

Options:

• A. Both assertion and reason are correct, and reason explains the assertion.

• B. Assertion is correct, but reason is incorrect.

• C. Both assertion and reason are incorrect.

• D. Both assertion and reason are correct, but reason does not explain the assertion.

Answer: B. Assertion is correct, but reason is incorrect.

Explanation:
Genetic material such as DNA and RNA is made up of nucleotides, not amino acids. Amino acids are the building blocks of proteins.

2. Which of the following animals is correctly matched with its characteristic feature and the phylum to which it belongs?

Options:

• A. Euspongia – Extracellular digestion – Porifera

• B. Obelia – Absence of metagenesis – Cnidaria

• C. Fasciola – Hooks and suckers are present – Platyhelminthes

• D. Nereis – Parapodia help in swimming – Annelida

Answer: C. Fasciola – Hooks and suckers are present – Platyhelminthes

Explanation:
Fasciola belongs to Platyhelminthes and possesses hooks and suckers that help it attach to the host.

3. Which of the following statements is true with respect to Porifera?

Options:

• A. Water enters through a minute pore called osculum.

• B. Collar cells line the spongocoel and the canals.

• C. Body is supported by exoskeletal structures.

• D. Digestion is both intracellular and extracellular.

Answer: B. Collar cells line the spongocoel and the canals.

Explanation:
In Porifera, choanocytes or collar cells line the spongocoel and canal system. Water enters through ostia, and digestion is intracellular.

4. Read the following statements regarding amphibians and select the correct option:

• a) Most of them are tetrapods.

• b) Tympanum represents ear.

• c) Eyes have no eyelids.

• d) Skin is dry without scales.

• e) Urinary tract opens into cloaca.

Options:

• A. a, b, c only

• B. b, e only

• C. c, d only

• D. a, b, e only

Answer: D. a, b, e only

Explanation:
Amphibians are generally tetrapods, the tympanum represents the external ear, and the urinary tract opens into the cloaca. Their eyes have eyelids and their skin is generally moist.

5. On the basis of compound analysis of living tissue, which of the following organic compounds constitutes the maximum percentage of total cellular mass?

Options:

• A. Water

• B. Proteins

• C. Carbohydrates

• D. Lipids

Answer: B. Proteins

Explanation:
Although water accounts for the highest overall percentage of cellular mass, the question specifically asks about organic compounds. Among organic compounds, proteins constitute the maximum percentage.

6. In frog, which one of the following is present only in males?

Options:

• A. Adrenal gland

• B. Vasa efferentia

• C. Oviduct

• D. Both A and B

Answer: B. Vasa efferentia

Explanation:
Vasa efferentia are present only in male frogs and help transport sperm from the testes. Adrenal glands are present in both sexes, while the oviduct is present in females.

7. Given below are two statements:

• Statement-I: Goblet cells are unicellular glands.

• Statement-II: Earwax is the secretion of an exocrine gland.

Options:

• A. Statement-I is true but Statement-II is false.

• B. Statement-I is false but Statement-II is true.

• C. Both Statement-I and Statement-II are true.

• D. Both Statement-I and Statement-II are false.

Answer: C. Both Statement-I and Statement-II are true.

Explanation:
Goblet cells are unicellular exocrine glands that secrete mucus. Earwax is produced by ceruminous glands, which are exocrine glands.

8. Read the following and choose the correct options regarding the functions of cnidoblasts:

• a) Anchorage

• b) Defence

• c) Sperm transfer

• d) Reproduction

• e) Food capture

Options:

• A. a, c, d only

• B. b, d, e only

• C. a, b, e only

• D. b, c, d only

Answer: C. a, b, e only

Explanation:
Cnidoblasts or cnidocytes containing nematocysts help in anchorage, defence and food capture.

9. Which of the following pairs regarding cockroach structures is correctly matched?

Options:

• A. Labrum – Lower lip

• B. Hypopharynx – Tongue

• C. Tegmina – Hindwings

• D. Labium – Upper lip

Answer: B. Hypopharynx – Tongue

Explanation:
The hypopharynx is a median, tongue-like structure present within the mouthparts of a cockroach.

10. Select the wrong statement about the blood vascular system of cockroach.

Options:

• A. The heart lies along the mid-dorsal line of thorax and abdomen.

• B. Heart is differentiated into 13 funnel-shaped chambers.

• C. Heart chambers have ostia on either side.

• D. Blood flows from anterior to the posterior end of the heart.

Answer: D. Blood flows from anterior to the posterior end of the heart.

Explanation:
In cockroaches, haemolymph enters the heart through ostia and is pumped anteriorly, from the posterior towards the anterior end. Therefore, option D is the wrong statement.

Key Takeaways for NEET 2026

• Revise Animal Kingdom using important features such as symmetry, germ layers, coelom and levels of organisation.

• Remember the characteristic features of major phyla and important examples such as Porifera, Cnidaria, Arthropoda and Echinodermata.

• Focus on the distinguishing characteristics of vertebrate classes from Cyclostomata to Mammalia.

• Revise amino acids, proteins, carbohydrates, lipids, nucleic acids and important biomolecular bonds.

• Understand enzyme action, activation energy, competitive inhibition, apoenzymes and holoenzymes.

• Revise epithelial, connective, muscular and neural tissues along with their functions and examples.

• Focus on important anatomical and physiological features of frogs and cockroaches for NCERT-based questions.

Animal Kingdom, Biomolecules, and Structural Organisation in Animals cover important concepts that require regular revision of characteristics, comparisons, structures and functions. Revising NCERT-based examples along with biological processes, biomolecular bonds, tissue functions and animal features can help strengthen your Biology preparation. Physics Wallah covers these topics through concept-based learning and regular question practice, helping you revise key details and apply them effectively. 

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