Most Important Diagrams Class 11 Biology (Zoology) | NEET 2023 Biology Exam Preparation

The diagrams in Class 11 (Zoology) encompasses a wide range of topics from the animal kingdom to circulation, excretion and neural control. These diagrams have been organised chapter-wise below and are important in terms of NEET preparation. Every year, diagram-based questions have been a part of the NEET Biology section. Understanding important diagrams are vital in cracking this exam.

Here, let us take a look at a few important diagrams in class 11 zoology, through which you can visually conceptualise the topic.

Table of Contents:

• Animal Kingdom
• Structural Organisations in Animals
• Biomolecules
• Cell Cycle and Cell Division
• Digestion and Absorption
• Breathing and Exchange of Gases
• Body Fluid and Circulation
• Excretory Products and Their Elimination
• Locomotion and Movement
• Neural Control and Coordination

Animal Kingdom

The classification of the animal kingdom is based on certain salient features like the arrangement of cells, body symmetry, patterns of digestive system, nature of coelom, pattern of reproductive and circulatory systems. Thus animal kingdom can be broadly classified into the ones with bones (chordates) and the ones without bones (non-chordates).

1. Non-chordates include phylum Porifera, Cnidaria, Aschelminthes, Platyhelminthes, Annelida, Arthropoda, Mollusca, Hemichordata and Echinodermata.
2. Chordates include class Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia.

Salient Features of Different Phyla in the Animal Kingdom

There are no complex diagrams covered in this chapter except for the schematic diagram of animal kingdom classification. Understanding the salient features of each phylum is necessary to answer the image-based questions from this chapter.

Structural Organisations in Animals

The important diagrams in this chapter covers the morphology of animals like frogs, cockroaches and earthworms.

Alimentary Canal of Cockroach

The cockroach can be morphologically divided into head, thorax and abdomen. Likewise, their alimentary canal in the body cavity can be anatomically divided into foregut, midgut and hindgut. Below is the diagram of the cockroach’s digestive system with labelled parts. The location of Malpighian tubules, Hepatic caeca, Gizzard and Crop are important for NEET objectives.

Open circulatory system of cockroach

Cockroaches have a 13-chambered heart and an open circulatory system. The diagram of the heart and the surrounding sinuses are also important for the exam. Here, oxygenated blood reaches each chamber via slits called Ostia.

Biomolecules

This chapter talks about macromolecules like proteins, nucleic acids and polysaccharides and also briefs on enzymes and their functions. Enzymes are nothing but proteins which catalyse biochemical reactions in the cells.

Mechanism of Enzyme Action

Enzyme (E) binds with substrate (S) to form a transient ES complex. Enzymes usually decrease the activation energy that is required to start a reaction by providing a surface to the substrate. The graph representing the activation energy with and without enzymes is important for the exam. The ES complex is converted into a product which later splits into enzyme and product (P). This enzyme activity is affected by factors such as pH, temperature, the presence of inhibitors, the concentration of substrates, allosteric regulators, etc.

The macromolecular components of all enzymes consist of protein, except in the class of RNA catalysts called ribozymes. Also, the word ribozyme is derived from the ribonucleic acid enzyme.

Cell Cycle and Cell Division

A typical cell cycle is divided into two basic phases – Interphase and M phase (Mitosis phase). The interphase can be further divided into 3 phases – G1 phase (Gap 1), S phase (Synthesis) and G2 phase (Gap 2). The sequential order of cell division is to be remembered for the objective.

Digestion and Absorption

The digestive system begins with the mouth which leads to the oral cavity. The oral cavity comprises the tongue and different types of teeth. The number and type of teeth in each half of both jaws are represented by the dental formula.

Milk Teeth or Primary Dentition

Premolars are absent in the primary dentition of humans.

Permanent Dentition

Here, I represents incisors, C – canine, Pm – premolars and M – molars.

Breathing and Exchange of Gases

This chapter deals with the respiratory organs, breathing mechanisms and exchange of gases. Thus we can find important diagrams like structure of lungs, mechanism of inspiration and expiration, alveolus, oxygen transport curve and exchange of gases.

Transport of Gases between Tissue and Alveoli

The alveoli are made up of simple squamous epithelium and they are the primary sites of gas exchange. The epithelial cells of alveoli consist of type Ⅰ and type Ⅱ cells. The type Ⅱ cells of alveoli secrete a lipoprotein (surfactant) whose main role is to reduce the surface tension in the alveoli. The exchange of gases also occurs between tissues and blood. The oxygen and carbon dioxide are exchanged in these sites by simple diffusion mainly based on concentration or pressure gradient.

The exchange of gases happens down the concentration gradient from the region of higher concentration to lower. The partial pressure of oxygen (pO₂) is higher in the alveoli (104 mm Hg) compared to deoxygenated blood (40 mm Hg), which facilitates the diffusion of oxygen from the alveoli to the blood. Similarly, the partial pressure of carbon dioxide (pCO₂) in alveoli (40 mm Hg) is less compared to the blood coming from tissues (45 mm Hg), which facilitates the release of carbon dioxide in alveoli.

The diagram represents systemic veins carrying deoxygenated blood and systemic arteries carrying oxygenated blood. The partial pressure of carbon dioxide and oxygen (in mmHg) involved in diffusion is compared to the atmospheric air in the below table.

Body Fluid and Circulation

This chapter deals with various body fluids like blood and lymph, and the circulatory system. The diagram of blood cells and the structure of the heart are some common and important diagrams to be revised. Apart from that, the schematic representation or flow chart of double circulation can be asked in the exam.

Systemic circulation

• It carries oxygenated blood from the left ventricles to the aorta.
• Then the oxygen-rich blood is transferred to the capillaries for circulation.
• Later, the veins and venules collect the carbon dioxide-rich deoxygenated blood from various parts of the body.
• The deoxygenated blood is pumped back into the superior vena cava and then to the right atrium.
• From the right atrium, the blood is carried to the right ventricle for pulmonary circulation.

Pulmonary circulation

• The pulmonary artery collects the blood from the right ventricle and carries it to the lungs for oxygenation.
• Now the oxygenated blood is pumped back to the left atrium through the pulmonary vein which is then carried to the left ventricles.
• Again the left ventricles carry oxygenated blood to the aorta for systemic circulation.

Electrocardiograph

Electrocardiograph is the machine used to obtain the ECG (electrocardiogram). It is the graphical representation of electrical activity of the heart during a cardiac cycle.

Here, the P wave represents depolarization or electrical excitation of the atria. The QRS complex denotes ventricular contraction (depolarisation). Q marks the beginning of systole, which is followed by the higher amplitude R wave and the downward deflecting S wave. The T wave represents ventricular repolarisation or return of the ventricles from an excited to normal state.

Excretory Products and their Elimination

The human excretory system consists of a pair of kidneys, a urinary bladder, a pair of ureters and a urethra. The diagram of the urinary system, kidney and nephron are covered in this chapter.

Urine Formation: Reabsorption and Secretion

The nephron comprises two components – the renal corpuscle and the renal tubule. The renal corpuscle or Malpighian body consists of the glomerulus and Bowman’s capsule. The renal tubule is a tubular structure that comprises a proximal convoluted tubule (PCT), Henle’s loop, distal convoluted tubule (DCT) and collecting duct.

The renal corpuscle, PCT and DCT are present in the cortex region, whereas Henle’s loop mostly lies in the medulla.

• The PCT has simple cuboidal epithelium with microvilli covered brush borders to increase the surface area for reabsorption. Around 70-80% of reabsorption happens here.
• Minimum reabsorption happens in the ascending limb of Henle’s loop. This loop plays a vital role in the maintenance of high osmolarity of the fluid. Here, the ascending limb of the loop is impermeable to water and the descending limb is permeable to water.
• The conditional reabsorption of water and sodium happens in the DCT. Then comes the collecting duct where a large amount of water is reabsorbed to produce concentrated urine.

Locomotion and Movement

This chapter comprises diagrams related to muscles, muscle fibres and contractile proteins. Out of these, the most important one is the diagram representing the sliding filament theory. The theory states that muscle contraction happens by the sliding of thin filaments over thick filaments.

• Muscle contraction is initiated by a signal from the central nervous system through motor neurons. This signal causes the release of neurotransmitters.
• Acetylcholine at the synaptic cleft binds to receptors on the muscle fibre and leads to the depolarization of sarcolemma. This generates action potential in the sarcolemma which spreads through muscle fibres and causes the release of Ca²⁺ ions into the sarcoplasm.
• The Ca²⁺ ions bind to the troponin subunit and cause structural changes. Thus, the myosin-binding sites located on actin filaments become exposed.
• The myosin head also contains a binding site for ATP. ATP hydrolysis takes place by ATPase activity of the myosin head. Now the energised myosin head binds to the active binding sites on actin forming a cross bridge.

ATP = ADP + Pi + Energy

• The actin filament is pulled inwards towards the centre of the A-band and the Z-line attached to actin is also pulled inwards. This causes shortening or contraction of the sarcomere. Likewise, ADP and Pi are released from the myosin and thus it goes back to a relaxed state. A new ATP binds and breaks the cross-bridge.
• The whole cycle is repeated causing further muscle contraction. It continues till the calcium ions are pumped back to the sarcoplasmic cisternae which results in the masking of actin filaments. This makes the Z-lines come back to their original or relaxed position.

Also Check: MCQs on Sliding Filament Theory

Neural Control and Coordination

This final chapter of class 11 has many important diagrams like the sagittal section of the brain, structure of neuron, structure of ear, eye, schematic representation of reflex action and the diagram of axon terminal and synapses.

Structure of a Neuron

Neuron is a microscopic structure of the nervous system that is composed of the dendrites, cell body and axon. The cell body contains granular bodies known as Nissl’s granules. Branch-like structures that project out of the cell body and contain Nissl’s granules are called dendrites, whereas axons are long tubular structures that carry impulses away from the cell body to neuromuscular junction or synapse.

The axons can be either myelinated or unmyelinated. The myelinated neurons are covered by the myelin sheath that is formed by Schwann cells. The gaps between adjacent myelin sheaths are termed nodes of Ranvier. Whereas, unmyelinated neurons are also covered by Schwann cells but they do not form the myelin sheath.

The nerve impulses are transmitted from one neuron to another via synapses. The axon branch terminates in a bulb-like structure known as the synaptic knob that has synaptic vesicles containing neurotransmitters. Below is a labelled diagram representing the synapse.

Axon Terminal and Synapse

Membrane of a post-synaptic neuron and pre-synaptic neuron form a synapse that may or may not be separated by a gap called the synaptic cleft. The axon terminal has synaptic vesicles filled with neurotransmitters. The action potential stimulates the synaptic vesicles to release neurotransmitters in the synaptic cleft. These neurotransmitters get attached to their specific receptors on the postsynaptic membrane.

Sagittal section of the Human Brain

The human brain is protected inside the skull and is covered by cranial meninges called dura mater (outer layer), arachnoid (middle thin layer) and pia mater (inner layer). The brain can be distinguished into 3 parts – forebrain, midbrain and hindbrain.

The forebrain consists of the cerebrum, thalamus and hypothalamus. The right and left cerebral hemispheres are connected by a stretch of nerve fibres called the corpus callosum. The midbrain is present between the hypothalamus of the forebrain and the pons of the hindbrain. Finally, the hindbrain comprises the pons, cerebellum and medulla.

Eye Structure

The human eyeball is composed of 3 layers – sclera (external layer), retina (inner layer) and choroid (middle layer).

• The anterior portion of the sclera is called cornea.
• The choroid layer forms the thick ciliary body towards the anterior portion. This ciliary body continues forward to form an opaque and pigmented structure termed the iris. The aperture surrounding the iris is called the pupil.
• The eyeball has a transparent lens that is held in place by suspensory ligaments. The space between lens and cornea is called the aqueous chamber and it is filled with aqueous humour.
• Retina is the innermost layer that comprises two photoreceptor cells – rods and cones.
• The space between the retina and lens is the vitreous chamber and it is filled with vitreous humour.

Ear Structure

• The ear is distinguished into 3 regions – outer ear, middle ear and inner ear. The outer ear comprises the external auditory canal and pinna. This auditory canal extends up to the eardrum or tympanic membrane.
• The middle ear consists of 3 ossicles – malleus, stapes and incus. The middle ear is connected with the pharynx via the eustachian tube.
• The labyrinth or inner ear comprises 2 parts – a membranous labyrinth and a bony part. The membranous labyrinth is surrounded by perilymph and filled with endolymph. It also has a coiled portion called the cochlea.

The diagram showing the sectional view of cochlea is also important for the exam. It shows parts like the organ of Corti, Reissner’s membrane and basilar membrane. There is a vestibular apparatus present above the cochlea that helps in maintaining the equilibrium of the body.

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