CBSE II Question Bank in Biology CLASS 11 Features Short Answer Type Questions Long Answer Type Questions Strictly Based on the Latest CBSE Term-wise Syllabus Case Study Based MCQs Chapter at a Glance Very Short Answer Type Questions
Comprehensive CBSE Question Bank in Biology Term–II (FOR CLASS XI)
Comprehensive CBSE Question Bank in Biology Term–II (FOR CLASS XI) (According to the Latest CBSE Examination Pattern) By Dr. J.P. Sharma M.Sc., Ph.D., FISST Ex-Head, Deptt. of Botany Hindu College, Sonepat (M.D. University, Rohtak) Haryana LAXMI PUBLICATIONS (P) LTD (An ISO 9001:2015 Company) BENGALURU • CHENNAI • GUWAHATI • HYDERABAD • JALANDHAR KOCHI • KOLKATA • LUCKNOW • MUMBAI • RANCHI NEW DELHI
Comprehensive CBSE QUESTION BANK IN BIOLOGY–XI (TERM-II) Copyright © by Laxmi Publications Pvt., Ltd. All rights reserved including those of translation into other languages. In accordance with the Copyright (Amendment) Act, 2012, no part of this publication may be reproduced, stored in a retrieval system, translated into any other language or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise. Any such act or scanning, uploading, and or electronic sharing of any part of this book without the permission of the publisher constitutes unlawful piracy and theft of the copyright holder’s intellectual property. If you would like to use material from the book (other than for review purposes), prior written permission must be obtained from the publishers. Printed and bound in India Typeset at Kalyani Computer Services, Delhi New Edition ISBN : 978-93-93738-11-0 Limits of Liability/Disclaimer of Warranty: The publisher and the author make no representation or warranties with respect to the accuracy or completeness of the contents of this work and speciﬁcally disclaim all warranties. The advice, strategies, and activities contained herein may not be suitable for every situation. In performing activities adult supervision must be sought. Likewise, common sense and care are essential to the conduct of any and all activities, whether described in this book or otherwise. Neither the publisher nor the author shall be liable or assumes any responsibility for any injuries or damages arising here from. The fact that an organization or Website if referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers must be aware that the Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. All trademarks, logos or any other mark such as Vibgyor, USP, Amanda, Golden Bells, Firewall Media, Mercury, Trinity, Laxmi appearing in this work are trademarks and intellectual property owned by or licensed to Laxmi Publications, its subsidiaries or afﬁliates. Notwithstanding this disclaimer, all other names and marks mentioned in this work are the trade names, trademarks or service marks of their respective owners. Bengaluru 080-26 75 69 30 Chennai 044-24 34 47 26 Branches Guwahati 0361-254 36 69 Hyderabad 040-27 55 53 83 Jalandhar 0181-222 12 72 Kochi 0484-405 13 03 Kolkata 033-40 04 77 79 Lucknow 0522-430 36 13 Published in India by Ranchi 0651-224 24 64 Laxmi Publications (P) Ltd. C—00000/021/12 Printed at : Ajit Printing Press, Delhi. (An ISO 9001:2015 Company) 113, GOLDEN HOUSE, GURUDWARA ROAD, DARYAGANJ, NEW DELHI - 110002, INDIA Telephone : 91-11-4353 2500, 4353 2501 www.laxmipublications.com [email protected]
Contents Chapters Pages Unit III: Cell: Structure and Function 1–18 Chapter 1. Cell Cycle and Division (NCERT Textbook Chapter-10)3–18 Unit IV: Plant Physiology 19–70 Chapter 2. Photosynthesis in Higher Plants (NCERT Textbook Chapter-13)21–42 Chapter 3. Respiration in Plants (NCERT Textbook Chapter-14)43–58 Chapter 4. Plant-Growth and Development (NCERT Textbook Chapter-15)59–70 Unit V: Human Physiology 71–192 Chapter 5. Breathing and Exchange of Gases (NCERT Textbook Chapter-17)73–89 Chapter 6. Body Fluids and Circulation (NCERT Textbook Chapter-18)90–115 Chapter 7. Excretory Products and their Elimination (NCERT Textbook Chapter-19)116–139 Chapter 8. Locomotion and Movement (NCERT Textbook Chapter-20)140–151 Chapter 9. Neural Control and Coordination (NCERT Textbook Chapter-21)152–169 Chapter 10. Chemical Coordination and Integration (NCERT Textbook Chapter-22)170–192
Syllabus Class XI (Code N. 044) (2021-22) Term–II Theory EVALUATION SCHEME Marks Units 05 III Term–II 12 IV Cell: Structure and Function: Chapter - 10 18 V Plant Physiology: Chapter - 13,14 and 15 35 Human Physiology: Chapter –17, 18, 19, 20, 21 and 22 Total THEORY TERM-II Unit-III Cell: Structure and Function Chapter-10: Cell Cycle and Cell Division Cell cycle, mitosis, meiosis and their significance Unit-IV Plant Physiology Chapter-13: Photosynthesis in Higher Plants Photosynthesis as a means of autotrophic nutrition; site of photosynthesis, pigments involved in photosynthesis (elementary idea); photochemical and biosynthetic phases of photosynthesis; cyclic and non-cyclic photophosphorylation; chemiosmotic hypothesis; photorespiration; C3 and C4 pathways; factors affecting photosynthesis. Chapter-14: Respiration in Plants Exchange of gases; cellular respiration-glycolysis, fermentation (anaerobic), TCA cycle and electron transport system (aerobic); energy relations - number of ATP molecules generated; amphibolic pathways; respiratory quotient. Chapter-15: Plant-Growth and Development Growth regulators-auxin, gibberellin, cytokinin, ethylene, ABA.
Unit-V Human Physiology Chapter-17: Breathing and Exchange of Gases Respiratory organs in animals (recall only); Respiratory system in humans; mechanism of breathing and its regulation in humans-exchange of gases, transport of gases and regulation of respiration, respiratory volume; disorders related to respiration-asthma, emphysema, occupational respiratory disorders. Chapter-18: Body Fluids and Circulation Composition of blood, blood groups, coagulation of blood; composition of lymph and its function; human circulatory system-Structure of human heart and blood vessels; cardiac cycle, cardiac output, ECG; double circulation; regulation of cardiac activity; disorders of circulatory system- hypertension, coronary artery disease, angina pectoris, heart failure. Chapter-19: Excretory Products and their Elimination Modes of excretion-ammonotelism, ureotelism, uricotelism; human excretory system – structure and function; urine formation, osmoregulation; regulation of kidney function- renin-angiotensin, atrial natriuretic factor, ADH and diabetes insipidus; role of other organs in excretion; disorders-uremia, renal failure, renal calculi, nephritis; dialysis and artificial kidney, kidney transplant. Chapter-20: Locomotion and Movement Skeletal muscle, contractile proteins and muscle contraction. Chapter-21: Neural Control and Coordination Neuron and nerves; Nervous system in humans-central nervous system; peripheral nervous system and visceral nervous system; generation and conduction of nerve impulse. Chapter-22: Chemical Coordination and Integration Endocrine glands and hormones; human endocrine system-hypothalamus, pituitary, pineal, thyroid, parathyroid, adrenal, pancreas, gonads; mechanism of hormone action (elementary idea); role of hormones as messengers and regulators, hypo-and hyperactivity and related disorders; dwarfism, acromegaly, cretinism, goiter, exophthalmic goiter, diabetes, Addison's disease. Note: Diseases related to all the human physiological systems to be taught in brief.
Unit IV Plant Physiology 2. Photosynthesis in Higher Plants 3. Respiration in Plants 4. Plant-Growth and Development
Chapter-2 Photosynthesis in Higher Plants (NCERT Textbook Chapter-13) Important Notes/Chapter at a Glance Green plants carry out ‘photosynthesis’ a physiochemical process by which they use light energy to derive synthesis or organic compounds. Photosynthesis is an enzyme regulated anabolic process in which carbohydrates (food) is synthesised in the chlorophyll containing cells of plants from CO2 and water with the help of sunlight as a source of energy. 6CO2 + 12H2O ChlLoirgohpthyll→ C6H12O6 + 6H2O + 6O2 Importance of Photosynthesis Photosynthesis is important for two reasons: (i) It is the primary source of all food on earth i.e. food for all living organisms. (ii) It is responsible for the release of O2 into the atmosphere. Experiments on Photosynthesis (i) When a variegated leaf is tested for starch, only green parts of the leaves show the presence of starch, indicating that chlorophyll is essential for photosynthesis. (ii) When a leaf that was partially covered with black paper tested for starch, only the part of the leaf exposed to light shows the presence of starch indicating that photosynthesis occurs in presence of light. (iii) In a half leaf experiment (Moll’s experiment) where a part of a leaf is enclosed in a test tube containing some KOH soaked cotton (which absorbs CO2) while the other half is exposed to air. On testing for starch, only exposed part of the leaf give the positive test. Early Experiments (Historical Prospective) Joseph Priestley (1770)–through a series of experiments hypothesised that of the plants restore to the air whatever breathing animals and burning candles remove. (a) (b) (c) (d) Priestley’s experiment.
22 Biology-XI Jan Ingenhousz (1730-1799)–showed that only the green parts of the plants could release oxygen and only in sunlight. Julius Von Sachs (1854)–provided evidence that glucose is produced when plants grow, and the same is stored as starch. — He also showed that the green substance (chlorophyll) is located in special bodies (chloroplasts) in plants. T.W. Engelmann (1730-1799)–using a prism, split light into its component parts and illuminated a green alga, Cladophora placed in a suspension of aerobic bacteria (the bacteria were used to detect the sites of O2 evolution). — He observed that the bacteria accumulated mainly in the region of blue and red light of spectrum. — Thus, he first described the action spectrum of photosynthesis; the action spectrum resembles roughly the absorption spectra of chlorophyll a and b. By the middle of the nineteenth century, the key features of photosynthesis were known and the total process then understood as: CO2 + H2O Light→ [CH2O] + O2 where [CH2O] represented a carbohydrate (e.g. glucose) Cornelius Von Niel (1897-1985)–conducted experiments on purple and green bacteria and demonstrated that photosynthesis is essentially a light dependent reaction in which a hydrogen donor reduces carbon dioxide to corbohydrates. — This can be expressed by the following reaction 2H2A + CO2 Light→ 2A + CH2O + H2O — In green plants H2O is the hydrogen donor and it is oxidised to O2. — Purple and green sulphur bacteria use H2S as hydrogen donor and so the oxidation product is sulphur. — Hence, he inferred that the O2 evolved by the green plants comes from water (H2O) and not from carbon dioxide (CO2). — This was later proved by using radioactive isotopes of oxygen in water (H218O). — Thus, the correct equation is represented as follows. 6CO2 + 12H2O Light→ C6H12O6 + 6H2O + 6O2 However, photosynthesis is not a single reaction, but a description of a multi-step process. Site of Photosynthesis Photosynthesis occurs in chloroplasts present in the mesophyll cells of leaves and other green parts of the plants. Within the chloroplast, there is the membranous system consisting of grana, the stroma lamellae, and the fluid stroma the pigments required for capturing solar energy to initiate photosynthesis are present in the membranes of granal and stromal lamellae.
Photosynthesis in Higher Plants 23 There is a clear division of labour within the chloroplasts: — The membrane system is responsible for trapping light energy and for the synthesis of ATP and NADPH; These events are directly light driven, and are called ‘light reactions’. — In stroma, the enzymatic reactions incorporate CO2 to synthesise sugar; These events are not directly light driven but are dependent on the products of light reactions (ATP and NADPH), and are referred as dark reactions. Pigments Involved in Photosynthesis The leaf pigments separated through paper chromatography, reveals that there are four pigments chlorophyll a (bright or blue green in the chromatogram), chlorophyll b (yellow green), xanthophylls (yellow) and carotenoids (yellow to yellow orange). Chlorophyll a is the main pigment associated with photosynthesis, while chlorophyll b, xanthophyll and carotenoids act as accessory pigments. The accessory pigments perform following roles: (i) They absorb a wide range of wavelength of incoming light and transfer the energy to chlorophyll a. (ii) They protect chlorophyll a from photo-oxidation. Photosynthetic pigments absorb lights of different wavelengths. The wavelength at which there is maximum absorption by chlorophyll a i.e. in the blue and the red regions, also shows higher rate of photosynthesis. Light Harvesting Complexes (Photosystems) The photosynthetic pigments are organised in the membrane system into two discrete light harvesting complexes (LHC), within the photosystem I (PSI) and photosystem II (PSII). Each photosystem has one specific chlorophyll a and hundreds of other pigment molecules bound to proteins. The single chlorophyll a forms the reaction centre, while the other pigment molecules form the light harvesting system, also called antennae. In PSI, the reaction chlorophyll a, has an absorption peak at 700 nm hence is called P700,while in PS II, it has absorption maxima at 680 nm, and is called P680. Process of Photosynthesis Photosynthesis occurs in two phases: (i) Photochemical phase or Light reaction, and (ii) Biosynthetic phase or Dark reaction. (i) Photochemical phase (Light reaction): The photochemical phase directly depends on light, and include– (a) light absorption, (b) photolysis of water (water splitting), (c) oxygen release and (d) the formation of high energy chemical intermediates, ATP and NADPH. Electron Transport — In PS II, the reaction centre chlorophyll a absorbs 680 nm wavelength (red light), which make the electrons to become excited.
24 Biology-XI — These electrons are taken up by the eletron acceptor that passes them to an electron transport system (ETS) consisting of cytochromes. — This movement of electron is down hill in terms of an oxidation-reduction (redox) potential scale. — Then the electron pass to PS I. — Simultaneously, electrons in the reaction centre of PSI are also excited, when the later receive light of wavelength 700 nm (red light); these electrons are transferred to another acceptor molecule and finally to NADP+ which is reduced to NADPH + H+ by the enzyme NADP+ reductase. — This is called the ‘Z-scheme’ due to its characterstic shape, formed when all the carrier are placed in a sequence on a redox potential scale. Splitting of Water (Photolysis of Water) — The electrons removed from PS II are made available by splitting of water (photolysis of water), in which water is split into protons, oxygen and electrons. 2H2O → 4H+ + O2 + 4e– — The electrons needed to replace those removed from photosystem I are provided by photosystem II. — The water splitting complex is associated with the PS II, which is located on the inner side of the membrane of the thylakoid. — The oxygen diffuses out of the chloroplast and is released into the atmosphere, while the protons accumulate in the lumen of thylakoids. Photophosphorylation — Photophosphorylation is the synthesis of ATP (a high energy compound) from ADP and inorganic phosphate (Pi) in presence of light; It occurs in two ways: (a) Non-cyclic photophosphorylation When the two photosystems – first PS II and then PS I, work in a series (as mentioned in z-scheme) it is called non-cyclic photophosphorylation and is responsible for the synthesis of ATP and NADPH. The two photosystems are connected through an electron transport chain.
Photosynthesis in Higher Plants 25 In this process, the electrons lost from PS II are transferred to PS I and do not return to PS II, hence, the process is non-cyclic. (b) Cyclic photophosphorylation W hen only PS I is functional, the electrons is circulated within PS I, and the phosphorylation occurs due to cyclic flow of electrons. It occurs in the stroma lamellae membranes, which lack PS II and NADP+ reductase enzyme. Thus, the excited electron does not pass on to NADP+ but is cycled back to the PSI complex through the electron transport chain and results only in the synthesis of ATP. C yclic photophosphorylation also occurs when only light of wavelengths beyond 680 nm are available for excitation. Chemiosmotic Hypothesis Chemiosmotic hypothesis explains the mechanism of ATP synthesis in chloroplasts. A TP synthesis is linked to the development of a proton gradient across the membranes of thylakoids. It results due to: (a) The splitting of water takes place on the inner side of the thylakoid membrane, the protons (H+) accumulate within the lumen of the thylakoids. (b) The primary electron acceptor is located towards the outer side of the membrane and transfers its electron to the hydrogen (H) carrier. — Hence, this molecule removes a proton from the stroma while transporting an electron, but it releases this proton on the inner side of the membrane (i.e. into the lumen), when it passes its electron to the electron carrier. (c) The enzyme NADP+ reductase, located on the stroma side of the membrane. — Along with the electrons coming from PS I, protons are also removed from stroma, to reduce NADP+ to NADPH + H+. The gradient is broken down due to the movement of protons across the membrane through the transmembrane channel consists of ATPase (ATP synthase); The ATPase enzyme consists of two parts – F0 and F1. (a) F0– is embedded in the membrane and forms a transmembrane channel that carries out facilitated diffusion of protons, and (b) F1– protudes on the outer surface of the thylakoid membrane towards the stroma. T he breakdown of the gradient provides enough energy to cause a conformational change in the F1 particle of the ATPase, to synthesize energy packed ATP molecules. C hemiosmosis requires (a) a membrane (b) a proton pump (c) a proton gradient and (d) ATP ase; Energy is used to pump protons across a membrane, to create a gradient or a high concentration of protons within the thylakoid lumen. (ii) Biosynthetic phase (Dark reaction): This phase of photosynthesis does not directly depend on the presence of light but is dependent on the products of light reaction i.e. ATP and NADPH, besides CO2 and H2O.
26 Biology-XI It occurs in the stroma of chloroplasts through a series of enzyme catalysed reactions, resulting in the synthesis of sugars (food). Malvin Calvin, using radioactive carbondioxide (14CO2) in algal photosynthesis discovered that the first CO2 fixation production was a 3C organic acid, 3-phosphoglyceric acid (PGA); He also worked out the complete biosynthetic pathway, named as ‘Calvin cycle’ after him. Later scientists also discovered another group of plants on which the first stable product of CO2 fixation was a 4C organic acid, oxaloacetic acid (OAA). Thus, CO2 assimilation during photosynthesis is of two types: (i) C3 pathway – in which the first product is a C3 acid (PGA) and the primary acceptor of CO2 is a 5C compound, ribulose biphosphate (RUBP). (ii) C4 pathway – in which the first product is a C4 acid (OAA) and the primary acceptor of CO2 is a 3C compound, phosphoenol pyruvate (PEP). H owever, Calvin cycle (calvin pathway) occurs in all photosynthetic plants; it does not matter whether they have C3 or C4 (or any other) pathways of photosynthesis. The Calvin Cycle (C3 pathway) — Calvin cycle proceeds in three stages as follows: (a) Carboxylation — Carboxylation is the fixation of CO2 into a stable organic intermediate. — CO2 combines with a 5C compound, ribulose 1, 5-biphosphate to form 2 molecules of 3PGA in presence of enzyme RUBP carboxylase. — This enzyme has an oxygenation activity, hence commonly called RUBP carboxylase-oxygenase (RUBISCO). (b) Reduction — I t involves a series of reactions that lead to the formation of carbohydrate (glucose) and utilises 2 molecules of ATP and 2 molecules of NADPH for reduction per CO2 molecule fixed. — For the formation of one molecule of glucose 6 molecules of CO2 and 6 turns of the cycle are required. (c) Regeneration — To continue the cycle, the CO2 acceptor molecule RUBP is formed from triose phosphate with the utilisation of one molecule of ATP. — H ence, for each CO2 molecule, a total of 3 molecules of ATP and 2 of NADPH are required. — What goes in and what comes out of the calvin cycle is as In Out 6 CO2 1 Glucose 18 ATP 18 ADP + 18 Pi 12 NADPH 12 NADP
Photosynthesis in Higher Plants 27 The C4 Pathway (Hatch and Slack Pathway) — The C4 pathway of CO2 fixation occurs in C4 plants (e.g. maize, sorghum) which are characterised by (a) a special type of leaf anatomy (Kranz anatomy), (b) Tolerate higher temperatures, (c) show response to highlight intensities, (d) lack photorespiration, and (e) greater productivity of biomass. Kranz Anatomy The bundle sheath in leaves consists of several layers of cells around the vascular bundles. The bundle sheath cells have a large number of chloroplasts. They have thick walls impervious to gaseous exchange and have intercellular spaces. — In C4 pathway, the primary CO2 acceptor is a 3C compound, phosphoenol pyruvate which is present in the mesophyll cells, and the enzyme responsible for this fixation (CO2 fixation) in PEP carboxylase or PEP case (the mesophyll cells lack RUBISCO enzyme). — Initially CO2 is fixed by phosphoenol pyruvate (PEP) in mesophyll cells, to a 4C compound, oxaloacetic acid (OAA) with the help of enzyme PEP carboxylase. — OAA is converted into malic acid (4C acid), which is transported to bundle sheath cells and is broken down to release CO2 and pyruvic acid (3C acid). — The CO2 released in the bundle sheath cells is now fixed through Calvin cycle with the help of enzyme RUBISCO. — This pathway is also named as Hatch and Slack pathway. Photorespiration P hotorespiration is the light induced oxidation of a part of RUBP to release CO2 without the formation of ATP (energy) in the green cells of the plants. In C3 plants, some O2 binds with the enzyme RUBISCO, and hence CO2 fixation is decreased. — In this process RUBP instead of being converted to 2 molecules of PGA, binds with O2 and forms one molecule of PGA and phosphoglycolate (a 2C compound). — Photorespiration is a wasteful process as (i) there is neither synthesis of sugar nor of ATP, and (ii) it results in the release of CO2 with the utilisation of ATP. — In C4 plants photorespiration does not occur as they have mechanism that increases the concentration of CO2 at the site of RUBISCO activity i.e. in the bundle sheath cells. — This ensures that the RUBISCO functions as a carboxylase minimising its oxygenase activity. Factors Affecting Photosynthesis The rate of photosynthesis is very important in determining the yield of crops. P hotosynthesis is affected by both internal (plants) and external (environmental) factors.
28 Biology-XI T he internal factors include (i) The number, size, age and orientation of leaves (ii) mesophyll cells (iii) chloroplasts and the amount of chlorophyll and (iv) internal CO2 concentration. T he external factors include (i) light (ii) CO2 concentration (iii) temperature and (iv) water. Law of Limiting Factors/ Blackman’s (1905) Law of Limiting Factors This law states that: — If a chemical process is affected by more than one factor then its rate will be determined by the factor which is nearest to its minimal value. — It is the factor which directly affects the process, if its quantity is changed. (i) Light — Three features of light i.e. intensity, quality and duration of exposure to light influence the rate of photosynthesis. — At low light intensities, there is a linear relationship between incident light and CO2 fixation; at higher light intensities, gradually the rate does not show further increase as other factors become limiting. — Light saturation occurs at 10 per cent of the full sunlight, hence (except for plants growing in shade) light is rarely a limiting factor in nature. — Light of higher intensities cause the breakdown of chlorophyll, and so decrease the rate of photosynthesis. (ii) Carbon dioxide concentration — The concentration of CO2 in the atmosphere is very low (0.03-0.04 per cent); an increase in CO2 concentration upto 0.05 per cent can increase in the rate of photosynthesis. — In C3 plants, the rate of photosynthesis increases with incerease in CO2 concentration and saturation occurs beyond 450 μl L–1. — In C4 plants, the saturation is reached at a concentration of about 360 μl L–1. — As the rate of photosynthesis of C3 plants increases with increase in CO2 concentration, the yield of some green house crops (such as tomatoes and bell paper) can be increased by growing them in CO2 enriched atmosphere. (iii) Temperature — The biosynthetic phase involving enzyme controlled reactions is more sensitive to temperature than the photochemical phase. — C3 plants have a low temperature optimum, while C4 plants have a higher temperature optimum. (iv) Water — Water is a reactant in light reaction, hence affect the rate of photosynthesis. — Water stress influences photosynthesis in two ways: (i) Causes the stomata to close and reduces the CO2 availability, and (ii) Makes leaves wilt reducing the surface area and their metabolic activity.
Chapter-4 Plant Growth and Development (NCERT Textbook Chapter-15) Important Notes/Chapter at a Glance PLANT GROWTH REGULATORS Characteristics Plant growth regulators (PGRs) are also called as plant growth substances, plant hormones or phytohormones. PGRs are small, simple molecules of diverse chemical composition, which are produced in small amounts and regulate growth and development in plants e.g., (i) indole compounds (indole -3- acetic acid or IAA) (ii) adenine derivatives (N6- furfurylamino purine, kinetin) (iii) derivatives of carotenoids (abscisic acid or ABA) (iv) terpenes (gibberellic acid or GA3) (v) gases (ethylene or C2 H4). Based on nature of action, PGRs can be broadly divided into two groups. (i) Growth promoters – PGRs that are involved in growth promoting activities, e.g., auxins, gibberellins and cytokinins. (ii) Growth inhibitors – PGRs that are involved in various growth inhibiting activities and also play important role in plant responses to wounds and stresses of biotic and abiotic origin, e.g., abscisic acid. — Ethylene, the gaseous PGR, could fit into either group, but largely has inhibitory action. Discovery of PGRs The discovery of most of the PGRs have been accidental. (i) Discovery of auxins — Charles Darwin and his son Francis Darwin observed that the coleoptiles of canary grass responded to unilateral illumination by growing towards the light source (phototropism). — After a series of experiments, it was concluded that the tip of coleoptile is the site of production of a substance that caused the bending of coleoptile. — F.W. Went isolated auxin from the tips of coleoptiles of oat seedlings. (ii) Discovery of Gibberellins — Bakane (foolish seedling), a disease of rice seedlings, was caused by a fungal pathogen Gibberella fujikuroi.
60 Biology-XI — E. Kurosawa found that the symptoms of the disease coluld be developed in uninfected seedlings by treating them with sterile filtrates of the fungus. — The active substances were later identified as gibberellic acid. (iii) Discovery of cytokinins — F. Skoog and his co-workers observed that tobacco callus could proliferate only if the medium contains in addition to auxin, the extracts from yeast, coconut milk or DNA. — Later, Miller and Skoog identified and crystallised the cytokinesis promoting substance and termed it as kinetin. (iv) Discovery of abscisic acid — Three independent researches (during mid 1960s) reported three kinds of growth inhibitors, namely (i) inhibitor-B, (ii) abscission-II and (iii) dormin. — Later all of them were found to be chemically identical and named as abscisic acid. (v) Discovery of ethylene — Cousins found that the ripened oranges released a volatile substance that hastened the ripening of the stored bananas. — Later this volatile substance was identified as ethylene. Physiological Effects and Applications of PGRs (i) Auxins — Auxins (Gk. auxin = to grow) was first isolated from human urine. — Indole 3-acetic acid (IAA) and indole butyric acid (IBA) are natural auxins i.e. they have been isolated from plants. — Auxins are generally produced by the growing apices of the stems and roots from where they migrate to region of their action. — Naphthalene acetic acid (NAA) and 2, 4-D (2, 4-dichlorophenoxy acetic acid) are synthetic auxins. Physiological Effects — Auxins help in cell division and cell enlargement. — They also control cell division in vascular cambium and xylem differentiation. — Auxins cause apical dominance i.e. growing apical bud inhibits the growh of the lateral (axillary) buds. — They prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits. Applications/Uses — Auxins help to initiate rooting in stem cuttings, hence are used in plant propagation. — They promote flowering e.g., in pineapple. — Decapitation of shoot (removal of shoot tips), overcomes apical dominance and results in the growth of lateral buds; It is practised in tea plantations and hedge making.
Plant Growth and Development 61 — Auxins are used to induce parthenocarpy (formation of fruits without fertilisation) e.g., in tomatoes. — They are widely used as herbicides/weedicides e.g., 2, 4-D widely used to kill dicotyledonous weeds in crop fields and to prepare weed free lawns (2.4 D does not kill mature monocotyledonous plants). (ii) Gibberellins — More than hundred gibberellins are reported from different organisms such as fungi and higher plants. — They are denoted as GA1, GA2, GA3 and so on; All GAs are acidic. — GA3 is the first gibberellin to be discovered and is the most intensively studied. Physiological Effects — Gibberellins cause elongation of internodes and promote bolting (internode elongation just prior to flowering) in rosette plants such as beet, cabbage etc. — They delay senescence but hastens the maturity period, leading to early seed production in conifers. — GA3 initiates synthesis of hydrolysing enzymes to mobilise the reserve food materials in germinating seeds. — They also break seed dormancy. Applications/Uses — Gibberellins are used to increase the length of grape stalk to increase the size of grapes. — They cause fruits like apple to elongate and improve its shape. — They delay senescence, hence can be used to leave the fruits on the trees longer so as to extend the market period. — GA3 is used to speed up malting process in brewing industry. — By increasing the length of stems in sugarcane, gibberellins increase the yield of sugarcane by about 20 tonnes per acre. — Spraying juvenile conifers with GA3 hastens their maturity and leads to early seed production. (iii) Cytokinins — Cytokinins were discovered as kinetin (a modified form of adenine- a purine) from the autoclaved herring sperm DNA. — Kinetin does not occur naturally in plants; Therefore, the search for natural substances with cytokinin like activities led to the discovery and isolation of ‘zeatin’ from corn-kernels and coconut milk. — Since then several naturally occurring cytokinins, and some synthetic compounds with cell division promoting activities have been identified. — Natural cytokinins are synthesised in regions of rapid cell division e.g., root apices, developing shoot buds, young fruits etc. Physiological Effect — Cytokinins help to produce new leaves and chloroplast in leaves. — They overcome apical dominance and hence promote lateral shoot growth and adventitious shoot formation. — They promote nutrient mobilisation which helps in the delay of leaf senescence.
62 Biology-XI Applications/Uses — They are used to make the lateral buds grow into branches. — They are used to keep fruits and cut flowers fresh for a longer time. (iv) Abscisic Acid (ABA) Physiological Effects — ABA acts as a general inhibitor of metabolism and plant growth. — It plays an important role in seed development, maturation and dormancy; By inducing dormancy, ABA helps seeds to withstand desiccation and other unfavourable conditions. — It stimulates the closure of stomata under intense radiations and water stress. — It increases the tolerance of plants to various kinds of stresses and hence, it is also called ‘stress hormone’. — ABA inhibits seed germination. — It stimulates abscission of leaves, flowers and fruits. — In most cases, ABA acts as an antagonist to GAS. Applications/Uses — Plant propagules like tubers can be treated with ABA to prevent their sprouting during storage. (v) Ethylene Physiological Effects — Ethylene is a simple gaseous PGR which is synthesised in large amounts in tissues undergoing senescence and ripening fruits. — It promotes horizontal growth of seedlings and swelling of the axis. — It induces apical hook formation in dicot seedlings. — It promotes senescence and abscission of leaves and flowers. — Ethylene enhances the rate of respiration during ripening of fruits; This phenomenon is called respiratory climatic. — It promotes root growth and root hair formation. — It promotes rapid elongation of internodes and petioles of deep water rice plants and helps the leaves to be above water level. Application/Uses — Ethylene regulates several physiological processes hence it is most widely used PGR in agriculture. — Ethaphon (a widely used compound as a source of ethylene) in aqueous solution is readily absorbed and transported within the plant release ethylene slowly. It hastens fruit ripening in tomatoes and apples. — It accelerates abscission in flowers and fruits hence is used for thinning of cotton, cherry, walnut etc. for improving the quality of the produce. — It promotes female flowers in cucumbers, thereby increases the yield.
Plant Growth and Development 63 Summary of functions of PGRs/Plant hormones PGRs/Plant Hormones Functions Auxins Apical dominance, cell elongation, prevent premature Gibberellins leaf and fruit falling, initiate rooting in stem cutting, Cytokinins as weedicides, induce parthenocarpy. Ethylene Delay senescence, speed up malting process, increase in length of axis (grape stalk), increase in length of Abscisic acid stem (sugarcane), bolting in beet, cabbages and many plants with rosette habit. Promote cell division, induce cell enlargment, reduce apical dominance, induce growth in auxillary buds, chlorophyll preservation, lateral shoot growth, adventitious root formation. Promotes senescence and abscission of leaf and fruits, promotes ripening of fruits, break seed and bud dormancy, initiate germination in peanut, sprouting of potato tuber, promotes root growth and root hair formation. Inhibit seed germination, stimulate closer of stomata, increase tolerance to various stresses, induce dormancy in seeds and buds, promotes ageing of leaf (senescence). In each phase of plant growth, differentiation and development, one or the other PGR has some role to play. Such roles could be individualistic, synergistic (complementary) or antagonistic (opposite). There are a number of events in the life of a plant, where more than one PGR interact to affect that event e.g., dormancy in seeds/buds, abscission, senescence, apical dominance etc. Many extrinsic factors such as temperature and light control plant growth and development via PGRs e.g., vernalisation, flowering, dormancy, seed germination, plant movements etc. Very Short Answer Type Questions 1. Name the plant growth regulators (PGRs) referred to as growth promoters. Ans. (i) Auxins (ii) gibberellins (iii) cytokinins. 2. Who discovered that the coleoptiles of canary grass responded to unilateral illumination by growing towards the light source? Ans. Charles Darwin and his son Francis Darwin.
64 Biology-XI 3. Who isolated auxin from tips of coleoptiles of oat seedlings? Ans. F.W. Went. 4. Write the cause of bakane (foolish seedling) disease of rice. Ans. Gibberella fujikuroi (a fungal pathogen). 5. Name the plant hormone which was first isolated from human urine. Ans. Auxin (IAA). 6. Write the full form of IAA. Ans. Indole 3-acetic acid. 7. Who discovered cytokinesis promoting active substance kinetin from coconut milk or DNA? Ans. Skoog and Millar. 8. Name two naturally occurring auxins. Ans. IAA (Indole 3-acetic acid) and IBA (Indole butyric acid). 9. Name any two synthetic auxins used in agricultural and horticultural practices. Ans. (i) NAA (napthalene acetic acid) and (ii) 2, 4-D (2, 4-dichlorophenoxy acetic acid). 10. Why do lateral buds start developing into branches when apical bud is removed? Ans. Removal of shoot tip/apical bud (decapitation) overcome/removes apical dominance, resulting in the growth of lateral buds. 11. A farmer observed some broad leaved weeds in a wheat crop farm. Which plant hormone would you suggest to remove them? Ans. 2, 4-D (2, 4-Dichlorophenoxy acetic acid). 12. Name the first discovered most extensively studied gibberellin. Ans. GA3. 13. Which plant hormone increases sugar yield by increasing the length of sugarcane stems? Ans. Gibberellins. 14. Why GA3 is used in brewing industry? Ans. GA3 speeds up the malting process (i.e. hydrolysis of starch into maltose) in cereals for fermentation. 15. What is meant by bolting in plants? Ans. Bolting refers to elongation of internodes just prior to flowering in rosette plants like beet, cabbage etc. 16. What was the source of kinetin, the first discovered cytokinin? Ans. The autoclaved herring sperm DNA. 17. Name the natural substance with cytokinin like activities isolated from cornkernels and coconut milk. Ans. Zeatin.
Unit V Human Physiology 5. Breathing and Exchange of Gases 6. Body Fluids and Circulation 7. Excretory Products and their Elimination 8. Locomotion and Movement 9. Neural Control and Coordination 10. Chemical Coordination and Integration
Chapter-5 Breathing and Exchange of Gases (NCERT Textbook Chapter-17) Important Notes/Chapter at a Glance The process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing, commonly known as respiration. Respiratory Organs The respiratory organs and the mechanism of breathing vary among different groups of animals and mainly depend on the habitat in which the animal live. The organs involved in respiration in different animals are: (i) General body surface–In lower invertebrates like poriferans (sponges), coelenterates, flatworm etc. exchange of gases occurs by simple diffusion over their entire body surface. (ii) Moist cuticle–In earthworms exchange of gases takes place through the moist cuticle. (iii) Trachae or tracheal tubes–Insect have a network of tubes called tracheal tubes to transport atmospheric air within the body. (iv) Gills–Gills are the respiratory organs in most aquatic arthropods, molluscs, hemichordates, cephalochordates, urochordates and some chordates like fishes and tadpoles of frogs/toads. (v) Lungs–All land vertebrates (reptiles, birds and mammals) have vascularised bags called lungs as respiratory organs. Human Respiratory System Human respiratory system consists of a pair of external nostrils, nasal cavity/ chamber, nasopharynx, larynx, trachea, bronchi, broncheoles and alveoli. The external nostrils present just above the upper lip, lead into the nasal chamber through the nasal passage. The nasal chamber opens into nasopharynx (a part of pharynx – the common passage for food and air). The nasopharynx opens through glottis of the larynx region into trachea. Larynx (also called sound box) is a cartilaginous box-like structure that helps in sound production. A thin elastic cartilaginous flap called epiglottis covers the glottis during swallowing to prevent the entry of food into the larynx. Trachea is a straight tube that extends upto mid-thoracic cavity and divides at the level of the 5th thoracic vertebra into a right and left primary bronchi. Each bronchi divides into a number of secondary and tertiary bronchi and ending up in very thin terminal bronchioles.
74 Biology-XI The trachea, primary, secondary and tertiary bronchi and initial bronchioles are provided with incomplete (c. shaped) cartilaginous rings. Each terminal bronchioles gives rise to a number of very thin irregular walled and vascularised bag-like structures called alveoli. The branching network of bronchi, bronchioles and alveoli constitute the lungs. Humans have two lungs, each of which is covered by a double layered pleura, and pleural fluid is present between them. Diagrammatic view of human respiratory system (Sectional view of the left lung is also shown) The outer pleural membrane is in close contact with the inner lining of the thoracic cavity, while the inner pleural membrane is in contact of lung surface. Based on functions, the respiratory system can be divided into two parts– (a) the conducting part and (b) the exchange part. (a) T he conducting part: The part starting with the external nostrils upto the terminal broncheoles, is known as the conducting part; It performs the following functions. (i) transports the atmospheric air to the alveoli. (ii) clears the air from foreign particles. (iii) humidifies the air, and (iv) also brings the air to the body temperature. (b) The exchange part: The alveoli and their ducts constitute the exchange part. — The exchange part is the site of actual diffusion of O2 and CO2 between blood and atmospheric air. Thoracic Chamber as an Airtight Chamber The lungs are situated in the thoracic chamber. The thoracic chamber is formed dorsally by the vertebral column, ventrally by sternum, laterally by the ribs and on the lower side by the dome shaped diaphragm, thus forming an airtight chamber. The set up of lungs in thorax is such that any change in the volume of the thoracic cavity will be reflected in the lung/pulmonary cavity. Such an arrangement is essential for breathing.
Breathing and Exchange of Gases 75 Steps of Respiration Respiration involves the following steps: (i) Breathing or pulmonary ventilation by which atmospheric air is drawn in and CO2 rich alveolar air is released out. (ii) Diffusion of gases (O2 and CO2) across the alveolar membrane. (iii) Transport of gases by the blood. (iv) Diffusion of O2 and CO2 between blood and tissues. (v) Utilisation of O2 by the cells for the catabolic reactions/oxidation and resultant release of CO2. Mechanism of Breathing Breathing involves two steps: (i) Inspiration, during which atmospheric air drawn into the lungs, and (ii) Expiration, during which alveolar air is released out. (i) Inspiration — Inspiration occurs when the intrapulmonary pressure is less than the atmospheric pressure (i.e. the intrapulmonary pressure is negative). — It is initiated by the contraction of diaphragm, which increases the volume of thoracic chamber in the anterio-posterior axis. — The contraction of external intercostal muscles lifts up the ribs and sternum, resulting an increase in the volume of thoracic chamber in the dorsoventral axis. Inspiration Expiration — The overall increase in the thoracic volume also increases the pulmonary volume. — This causes a decrease in the intrapulmonary pressure and forces the atmospheric air to move into the lungs. (ii) Expiration — Expiration occurs when the intrapulmonary pressure is higher than that of the atmosphere (i.e. intrapulmonary pressure is positive).
76 Biology-XI — Relaxation of the diaphragm and the intercostal muscles returns the diaphragm and sternum to their normal positions. — It reduces the thoracic volume and thereby the pulmonary volume. — This leads to an increase in intrapulmonary pressure slightly above the atmospheric pressure causing expulsion of the air from the lungs. The strength of inspiration and expiration can be increased with the help of additional muscles in the abdomen. Beathing Rate — On an average, a healthy human breathes 12–16 times/minute. Respiratory Volume — The volume of air involved in breathing movements can be measured by using a respirometer. — Such volumes helps in clinical assessment of lung functions. 1. T idal Volume (TV). It is the volume of air inspired or expired during normal respiration; It is approximately 500 mL for a healthy person. 2. Inspiratory Reserve Volume (IRV). It is additional volume of air, a person can inspire by a forcible inspiration. — It is 2500 mL to 3000 mL. 3. E xpiratory Reserve Volume (ERV). It is the additional volume of air, a person can expire by a forcible expiration. — It is about 1000 mL to 1100 mL. 4. R esidual Volume (RV). It is the volume of air remaining in the lungs even after a forcible expiration. — It is about 1100 mL to 1200 mL. Respiratory Capacities/Pulmonary Capacities Two or more respiratory volumes are considered together to measure pulmonary capaci- ties. Such capacities can be used in clinical diagnosis. 1. Inspiratory Capacity (IC). It is the total volume of air a person can inspire after normal expiration. — It includes tidal volume and inspiratory reserve volume (TV + IRV). 2. Expiratory Capacity (EC). It is the total volume of air a person can expire after normal inspiration. — It includes tidal volume and expiratory reserve volume (TV + ERV). 3. Functional Residual Capacity (FRC). It is the volume of air that will remain in the lungs after a normal expiration. — This includes ERV + RV. 4. Vital capacity. It is the maximum volume of air a person can breathe in after forced expiration, or — The maximum volume of air a person can breathe out after a forced inspiration. — It includes ERV, TV and IRV.
Breathing and Exchange of Gases 77 5. Total lung capacity. It is the total volume of air accomodated in the lungs at the end of forced expiration. — It includes RV, ERV, TV and IRV or Vital capacity + Residual volume. Exchange of Gases Diffusion of gases takes place from the region of higher partial pressure of a gas to its lower partial pressure. Exchange of gases (O2 and CO2) occurs at two sites in the body i.e. in the alveoli and the tissues. (i) In the alveoli — The alveoli are the primary sites of exchange of respiratory gases. — Oxygen and carbon dioxide are exchanged by simple diffusion depending upon the gradient of their partial pressures. — Solubility of the gases as well as the thickness of the membranes involved in diffusion are also important factors that can affect the rate of diffusion. — The partial pressures (in mm Hg) of O2 and CO2 at different parts involved in diffusion are listed below. Respiratory Atmospheric Alveoli Blood Blood Tissues Gas Air (Deoxygenated) (Oxygenated) 40 pO2 45 pCO2 159 104 40 95 0.3 40 45 40 Diagrammatic representation of exchange of gases at the alveolus and the body tissues with blood and transport of oxygen and carbon dioxide
78 Biology-XI — There is a concentration gradient for O2 from alveoli to blood and blood to tissue, and gradient for CO2 in opposite direction. i.e. from tissue to blood and blood to alveoli. — The solubility of CO2 is 20-25 times higher than that of O2, as a result the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher as compared to O2. — The diffusion membrane is made up of three major layers A diagram of a section of an alveolus with a pulmonary capillary. (i) The squamous epithelium of alveoli. (ii) The endothelium of alveolar capillaries. (iii) The basement membranes between them. — The total thickness of the membrane is about 0.2 mm. — All these factors are favourable for diffusion of O2 into the venous blood from the alveoli and diffusion of CO2 from the venous blood into the alveoli. (ii) In the tissues — In the metabolically active tissues, the pO2 is 40 mm Hg, whereas the arterial blood brought to the tissues has a pO2 of 95 mm Hg; O2 diffuses from the blood into the tissue cells. — In the tissues the pCO2 is about 45 mm Hg, which is higher than that of the blood (40 mm Hg); CO2 diffuses from the tissues into the blood. Transport of Gases The transport of respiratory gases (i.e. O2 and CO2) takes place through blood. (i) Transport of oxygen — About 97 per cent of O2 is transported by RBCs in the blood in the form of oxyhaemoglobin, and 3 per cent is carried in a dissolved state through plasma. — O2 binds with the Fe2+ ions of haemoglobin in a reversible manner to form oxyhaemoglobin. — Each haemoglobin molecule can carry four molecules of O2. — Binding of O2 with haemoglobin depends on: (i) partial pressure of O2 (pO2). (ii) partial pressure of CO2 (pCO2). (iii) H+ ion concentration, and (iv) temperature.
Breathing and Exchange of Gases 79 — In alveoli, there is (i) high pO2, (ii) low pCO2, (iii) low H+ ion concentration and (iv) low temperature, which favour binding of O2 with haemoglobin to form oxyhaemoglobin. — In tissues, there is (i) low pO2, (ii) high pCO2 , (iii) high H+ ion concentration, and (iv) high temperature, which favour dissociation of O2 from oxyhaemoglobin. — Every 100 mL of oxygenated blood can deliver about 5 mL of O2 to the tissue under normal physiological conditions. — When percentage saturation of haemoglobin with O2 is plotted against the pO2, a sigmoid curve is obtained; It is called oxygen dissociation curve. Oxygen dissociation curve (ii) Transport of carbon dioxide — About 20–25 per cent of CO2 is carried by haemoglobin as carbamino- haemoglobin. — This binding occurs when pO2 is low and pCO2 is high as in the tissue whereas, when the pCO2 is low and pO2 is high as in the alveoli, dissociation of CO2 from carbamino-haemoglobin takes place. — About 70 per cent of CO2 is carried as bicarbonates. — Erythrocytes have a high concentration of enzyme carbonic anhydrase which catalyse the following reaction in both directions. Carbonic Carbonic anhydrase anhydrase CO2 + H2O H2CO3 HCO3– + H+ — Some of the bicarbonate ions ( HCO3–) diffuse into the cytoplasm (in exchange of Cl– ions) and are carried in the form of sodium bicarbonate. — The remaining bicarbonate ions in the erythrocytes are carried as potassium bicarbonate. — At the alveolar site where pCO2 is low the reaction proceeds in the opposite direction leading to the formation of CO2 and H2O; Thus, CO2 trapped as bicarbonate at the tissue level and transported to the alveoli is released out as CO2. — About 7 per cent of CO2 is carried in a dissolved state through plasma. — Every 100 mL of deoxygenated blood delivers approximately 4 mL of CO2 to the alveoli.
Chapter-6 Body Fluids and Circulation (NCERT Textbook Chapter-18) Important Notes/Chapter at a Glance In living organisms, all the cells have to be provided with nutrients, O2 and other essential substances; and the wastes and harmful substances produced have to be removed continuously for healthy functioning of tissues. Simple organisms like sponges and coelenterates circulate water from their surroundings through their body cavities to facilitate the cells to exchange these substances. Complex organisms including humans use special fluids within their bodies to transport such materials. Blood and lymph (tissue fluid) are the fluids that are used by higher organisms to transport different materials within the body. Blood Blood is a special connective tissue consisting of a fluid matrix (plasma) and formed elements. Plasma Plasma is a straw coloured viscous fluid; it constitutes 55 per cent part of the blood. Plasma consists of water, proteins, minerals (Na+, Ca2+, Mg2+, HCO3–, Cl–etc.), nutrients (glucose, amino acids, lipids etc.), hormones and clotting factors (in an inactive form).
Body Fluids and Circulation 91 Water constitute 90–92 per cent of the plasma, and proteins constitute 6–8 per cent of it. The major proteins of the plasma and their functions are: (i) Fibrinogens—needed for clotting or coagulation of blood. (ii) Globulins—primarily involved in defense mechanisms of the body, and (iii) Albumins—help in osmotic balance. The minerals and nutrients present in plasma are always in transit in the body. Plasma without clotting factors is called serum. Formed Elements Erythrocytes, leucocytes and platelets are collectively called formed elements. They constitute nearly 45 per cent of the blood. Diagrammatic representation of formed elements in blood (i) Erythrocytes (Red blood cells or RBCs) RBCs are circular, biconcave disc-like and lack nucleus and cell organelles in most of the mammals. They are formed in bone marrow in the adults. A healthy adult man has on an average 5 to 5.5 millions of RBCs per mm3 of blood. They contain a red coloured iron containing complex protein haemoglobin. A healthy individual has 12–16 g of haemoglobin in every 100 mL of blood. Haemoglobin plays a significant role in transport of respiratory gases. RBCs have an average life span of 120 days, after which they are destroyed in the spleen (the graveyard of RBCs). (ii) Leucocytes (White blood cells or WBCs) WBCs are colourless due to the lack of haemoglobin. They are nucleated and their number is about 6000 to 8000 mm3 of the blood. WBCs are generally short lived. W BCs are broadly classified into two categories—(a) Granulocytes and (b) Agranulocytes. (a) Granulocytes These are WBCs with granular cytoplasm and polymorphic nucleus. They are of three types — Neutrophils, Eosinophils and Basophils.
92 Biology-XI Neutrophils Eosinophils Basophils 1. They are most 1. They are 2–3 per 1. They are the least abundant WBCs i.e. cent of the total among WBCs i.e. 60–65 per cent of leucocytes. 0.5–1 per cent of the the total leucocytes. total leucocytes. 2. They are phagocytic 2. They resist 2. They secrete his- cells which destroy infections and are tamine, serotonin, foreign organisms also associated heparin, etc. and entering the body. with allergic are involved in reactions. inflammatory reac- tions. (b) Agranulocytes These are WBCs with non-granular cytoplasm with rounded or bilobed nucleus. Agranulocytes are of two types — Monocytes and lymphocytes. Monocytes Lymphocytes They are 6–8 per cent of the They are 20–25 per cent of the total WBCs. total WBCs. They are phagocytic cells which They are of two types destroy foreign organisms B-lymphocytes (B-cells) and entering the body. T-lymphocytes (T-cells) and are responsible for immune responses. (iii) Thrombocytes (platelets) They are cell fragments produced from megakaryocytes (special cells in the bone marrow). There are 1,50,000–3,50,000 platelets per mm3 of the blood. Thrombocytes release a variety of substances involved in coagulation/clotting of blood. Reduction in their number may lead to excessive loss of blood from the body even in minor injuries. Blood Groups In human beings, two types of blood grouping – ABO grouping and Rh grouping are important and widely used all over the world. (i) ABO blood grouping The presence or absence of two surface antigens (i.e. chemicals that can induce immune response) on the RBCs is the basis of this blood grouping. These antigens are, antigen A and antigen B. Similarly, the plasma of different individuals contain/lack one or two antibodies (i.e. proteins produced in response of antigens). Different blood groups and antigens and antibodies present in these groups are given below.
Body Fluids and Circulation 93 Blood Groups Antigens on Antibodies in Donor’s A RBCs Plasma Group A anti - B A, O B B anti - A B, O AB (universal recipient) A, B nil AB, A, B, O O (universal donor) nil anti - A, B O During blood transfusion the blood of a donor has to be matched with the blood of recipient, to avoid problem of clumping (destruction of RBCs). (ii) Rh blood grouping — Another antigen, the Rh-antigen (first discovered in Rhesus monkeys) also present on the surface of RBC in majority (nearly 80 per cent) of humans. — The individuals having Rh-antigen are called Rh positive (Rh +ve) and those lacking it are called Rh negative (Rh –ve). — An Rh –ve person if exposed to Rh +ve blood, will form specific antibodies against the Rh antigens. — An Rh incompatibility (mismatching) is observed between the Rh –ve blood of a pregnant mother with Rh +ve blood of the foetus. — Rh antigens of the foetus do not exposed to Rh –ve blood of the mother in the first pregnancy, as the two blood (i.e. of the foetus and the mother) are well separated by the placenta. — However, during the first delivery, there is a possibility of exposure of the maternal blood to the Rh +ve blood from the foetus. — In such a case, the mother’s body prepares antibodies against Rh antigen in her blood. — As a result, in subsequent pregnancies, the Rh antibodies from the mother can pass into the blood of the foetus (Rh +ve) through placenta and destroy the foetal RBCs. — This could be fatal to the foetus or could cause severe anaemia and jaundice (called erythroblastosis foetalis). — This condition can be avoided by injecting anti-Rh antibodies to the mother immediately after the first delivery. Coagulation of Blood (Blood Clotting) When there is any injury, there is bleeding from the wound, but soon the blood stops flowing out. This happens, because the blood has a mechanism called blood coagulation or clotting, and a dark reddish brown scum is formed at the site of injury. A clot or coagulum is formed which mainly consists of a network of fibres called fibrin in which the dead and damaged corpuscles are trapped. The process occurs by a series of linked enzymic reactions (cascade process) involving a number of factors present in the plasma in an inactive state.
94 Biology-XI Lymph (Tissue Fluid) Lymph is a colourless fluid containing specialised lymphocytes. — As the blood passes through the capillaries, some water and many small water soluble substances move out into the spaces of the tissues; it is called interstitial fluid or tissue fluid. An elaborate network of vessels called lymphatic system collect this fluid and drain it back to the major veins. — The fluid present in the lymphatic system is called lymph. Lymph performs the following functions: (i) Lymph contains specialised lymphocytes, which are responsible for the immune responses of the body. (ii) It is also an important carrier for nutrients, hormones etc. (iii) The lymph present in the lacteals in the intestinal villi is involved in the absorption of fatty acids and glycerol. Circulatory Pathways The circulatory patterns are of following two types: (i) Open circulatory system—the blood is pumped by heart into open spaces or body cavities called sinuses e.g., in arthropods and molluscs. (ii) Closed circulatory system—the blood pumped by the heart is circulated through a closed network of blood vessels e.g., in annelids and chordates. — The closed circulatory system is more advantageous as the flow of the blood can be more precisely regulated. Types of Hearts All vertebrates possess a muscular heart, which may be 2, 3 or 4 chambered. (i) 2-chambered heart with an atrium and a ventricle is present in fishes. — It pumps out deoxygenated blood, which is oxygenated by the gills and supplied to the body parts and returned to the heart after deoxygenation (single circulation). (ii) 3-chambered heart with two atria and a single ventricle is present in amphibians and reptiles (except crocodiles). — Here, the left atrium receives oxygenated blood from the gills/lungs/skin and the right atrium gets the deoxygenated blood from other body parts. — The two types of blood get mixed up in the single ventricle, which pumps out mixed blood (incomplete double circulation). (iii) 4-chambered heart with two atria and two ventricle is present in crocodiles, birds and mammals. — Here, oxygenated and deoxygenated blood received by the left and right atria respectively, and passes on to the ventricles of the same sides. — The ventricles pump it out without any mixing up i.e. there are present two separate pathways of circulation (double circulation).
Body Fluids and Circulation 95 Human Circulatory System Human circulatory system, also called blood vascular system consists of: (i) a muscular chambered heart, (ii) a network of closed branching blood vessels, and (iii) blood, (the circulating fluid). Heart Human heart develops from mesoderm and lies in the thoracic cavity in between the two lungs, slightly tilted to the left. It has the size of a clenched fist. The heart is enclosed in a double walled sac, called pericardium; the narrow space between the two layers of pericardium, is filled with pericardial fluid. Internal Structure of Heart The human heart consists of four chambers; two relatively small upper chambers, the atria and two larger lower chambers, the ventricles. — The entire heart is made of cardiac muscles; the walls of ventricles are much thicker than that of the atria. Section of a human heart — The right and left atria are separated by a thin muscular wall called the inter-atrial septum, while the right and left ventricles are separated, by a thick inter-ventricular septum. — The atrium and ventricle of the same side are also separated by thick fibrous tissue called the atrio-ventricular septum. — Each of these septa has an opening through which the two chambers of the same side are connected.
96 Biology-XI — The opening between the right atrium and the right ventricle is guarded by a valve of three muscular flaps or cusps called the tricuspid valve, and the opening between the left atrium and the left ventricle is guarded by a bicuspid or mitral valve. — The openings of the right and the left ventricles into the pulmonary artery and the aorta respectively are guarded by the semilunar valves. — The valves in the heart allows the flow of blood only in one direction, i.e., from the atria to the ventricles and ventricles to the pulmonary artery or aorta. Nodal Tissue and Conductive System of the Heart The heart rhythm is maintained by a highly specialised excitatory and conductive system called cardiac musculature or the nodal tissue. It consists of a sinoatrial node (SAN or SA node), an atrioventricular node (AVN or AV node), the AV bundle and the purkinje fibres. SA node (also called pace maker) is a patch of musculature in the right upper corner of the right atrium. AV node (also called pace setter) is another mass of musculature in the lower left corner of the right atrium, close to the atrioventricular septum. A bundle of nodal fibres called atrioventricular bundle (AV bundle) arises from the AV node, passes through the atrioventricular septa and divides into a right and left bundles. These bundles give rise to minute fibres throughout ventricular musculature, and are called purkinje fibres; these fibres along with right and left bundles are known as bundle of His. Working of the Nodal Tissue The nodal musculature has the ability to generate action potentials without any external stimuli (i.e. autoexcitable). The SA node can generate the maximum number of action potentials, i.e., 70–75 min–1 (average 72 beats min–1). Since SA node is responsible for initiating and rhythmic contractile activity of the heart; it is called the pace maker. Cardiac Cycle The sequential event in the heart, which is cyclically repeated is called the cardiac cycle and it consists of systole and diastole of both the atria and ventricles is called cardiac cycle. During a heart beat there is contraction phase called the systole, while the relaxation phase is called the diastole; when both the atria and ventricles are in diastole or relaxed phase, it is referred as joint diastole. Joint Diastole During joint diastole, the tricuspid and bicuspid valves are open, blood from pulmonary veins and vena cava flows into the left and the right ventricles respectively, through the left and right atria. The semi-lunar valves remain closed at this stage.
Body Fluids and Circulation 97 Atrial Systole The SAN now generates an action potential which stimulates both the atria to undergo simultaneous contraction. As the atria contract, the flow of blood into ventricles increases to about 30 per cent. Ventricular Systole The action potential is conducted to the ventricular side by the AVN and AV bundle; from where, the bundle of His transmit it to the entire ventricular musculature. Consequently, the ventricles contract (ventricular systole) and the atria undergoes relaxation (atrial diastole coinciding with the ventricular systole). As ventricular systole increases, the ventricular pressure causes the closure of tricuspid and bicuspid valves (due to attempted back flow of blood into the atria) and forced open, the semi-lunar valves that guards the pulmonary artery (right side) and the aorta (left side). This allow the blood in the ventricles to flow through these vessels into the circulatory pathways. Ventricular Diastole The ventricles now relax (ventricular diastole) and the ventricular pressure falls causing the closure of semi-lunar valves which prevents the back flow of blood into the ventricles. As the ventricular pressure declines, the tricuspid and bicuspid valves open and blood starts flowing into the ventricles. The ventricles and atria are now again in a relaxed (joint diastole) state, as earlier. Heart Rate and Cardiac Output The heart beats about 72 times per minute i.e. many cardiac cycles occur in a minute. Thus, the duration of one cardiac cycle is about 0.8 seconds. The volume of blood pumped by each ventricle during a cardiac cycle, is called stroke volume; it is approximately 70 mL. The volume of blood pumped out by each ventricle per minute is called ‘cardiac output’ the stroke volume multiplied by the heart rate (no. of beats per minute) gives the cardiac output (70 × 72 = 5040 mL–1 i.e. about 5 litres min–1). The human body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output e.g., the cardiac output of an athlete will be much higher than an ordinary person. Heart Sounds During each cardiac cycle two prominent sounds — lub and dub are produced, which can be easily heard through a stethoscope; these are called heart sounds. The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves. (due to ventricular systole), whereas the second heart sound (dub) is associated with the closure of the semilunar valves (due to ventricular diastole).
98 Biology-XI Electrocardiogram (ECG) Electrocardiogram is a graphical representation of the electrical activity of the heart during a cardiac cycle. R P QS T Diagrammatic representation of a standard ECG The instrument or machine used to record an electrocardiogram is called electrocardiograph. To obtain a standard ECG a patient is connected to the machine with three electrical leads. One in each wrist and one to the left ankle, that monitor the heart function. Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart. In a ECG, P-wave represents the electrical excitation (depolarisation) of the atria, which leads to the contraction of both the atria. The QRS complex represents, the depolarisation of ventricles, which initiates ventricular contraction. The T-wave represents the return of ventricles from excited to normal state (repolari- sation). The end of T-wave marks the end of systole. By counting the QRS complex formed during the given time period, one can determine the rate of heart beat of an individual. Since normal ECG has a fixed pattern, any deviation from it indicates an abnormality or disorder of heart functioning. Double Circulation Schematic plan of blood circulation in human
Body Fluids and Circulation 99 The movement of blood follows two pathways. Pulmonary circulation and systemic circulation; thus making the circulation of blood a double circulation. (i) Pulmonary circulation The flow of deoxygenated blood from the right ventricle to the lungs and return of oxygenated blood from the lungs to left atrium is called pulmonary circulation. (ii) Systemic circulation The flow of oxygenated blood from the left ventricle to all parts of the body and deoxygenated blood from various body parts to the right atrium is called systemic circulation. Systemic circulation serves two important functions: (a) transports nutrients, O2 and other essential substances to the tissues. (b) takes CO2 and other harmful substances away for elimination. Circulation through Special Regions Coronary circulation and portal circulation are circulations through special regions and are the part of systemic circulation. (i) Coronary circulation A special coronary system of blood vessels (Coronary arteries and coronary veins) is present in our body. It is meant for the circulation of blood to and from the cardiac musculature/ the heart muscles (myocardium). (ii) Portal circulation A vein which collect blood from one organ and distributes the blood to some other organ, instead of sending it to the heart is called a portal vein. The portal vein along with the capillaries by which it supplies blood to a specific organ forms a portal system. e.g., Hepatic portal system– It is a unique vascular connection between the digestive tract and the liver. The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation; this enables the liver cells to obtain nutrients from the small intestine. Regulation of Cardiac Activity The normal functioning of heart is regulated intrinsically (i.e. autoregulated) by specialised muscles (nodal tissue). Hence the heart is called myogenic. A special nerve centre in the medulla oblongata can moderate the cardiac activity through autonomic nervous system (ANS). Neural signals through ANS can increase the rate of heart beat, the strength of ventricular contraction and so the cardiac output, whereas the parasympathetic neural signals (another component of ANS ), decrease the same. Hormones of adrenal medulla (adrenaline and noradrenaline) can also increase the cardiac output.
Chapter-9 Neural Control and Coordination (NCERT Textbook Chapter-21) Important Notes/Chapter at a Glance Coordination is the process through which two or more organs interact and complement the functions of one another. The neural system and the endocrine system together coordinate and integrate all the activities of the organs so that they function in a synchronised manner. The neural system provides an organised network of point to point connections for a quick coordination. The endocrine system provides chemical integration through hormones. Neural System The neural system of all animals is composed of highly specialised cells called neurons. The neurons can detect, receive and transmit different kinds of stimuli. The neural system is very simple in lower invertebrates; the vertebrates have a more developed neural system. Human Neural System The human neural system is divided as follows. Neural system Central neural system (CNS) Peripheral neural system (PNS) Brain Spinal cord Somatic/voluntary Autonomic/Involuntary neural system neural system Sympathetic Parasympathetic neural system neural system 1. Central Neural System (CNS) It includes the brain and the spinal cord; it is the site of information processing and control. 2. Peripheral Neural System (PNS) It comprises of all the nerves of the body arising from the CNS (brain and spinal cord).
Neural Control and Coordination 153 The PNS is further divided into two divisions: (i) Somatic neural system—It relays impulses from CNS to skeletal muscles. (ii) Autonomic neural system—It transmits impulses from CNS to the involuntary organs/visceral organs. The autonomic neural system is further classified into two types, i.e., sympathetic neural system and parasympathetic neural system. The nerve fibres of PNS are of two types: (a) A fferent nerve fibres—They transmit impulses from tissues/organs to the CNS. (b) E fferent nerve fibres—They transmit regulatory impulses from CNS to the peripheral tissues/organs. Neuron as Structural and Functional Unit of Neural System A neuron is a microscopic structure and consists of three major parts, namely cell body, dendrites and axon. Dendrites Nissl’s granules Cell body Nucleus Schwann cell Axon Myelin sheath Node of Ranvier Axon terminal Synaptic knob Structure of a neuron The cell body contains cytoplasm with a nucleus and certain granular bodies called Nissl’s granules. The dendrites are short fibrous outgrowth which branch repeatedly and project out of the cell body; They also contain Nissl’s granules and transmit impulses towards the cell body. The axon is a single long fibre like outgrowth arise from the cell body; It is branched at distal end and each branch of it terminates into a bulk-like structure called synaptic knob, that possesses synaptic vesicles containing chemicals called neurotransmitters. The axons transmit nerve impulses away from the cell body to a synapse or to a neuro muscular junction.
154 Biology-XI Types of Neurons Based on the number of axon and dendrites, the neurons are of three types i.e. (i) Multipolar — They possess one axon and two or more dendrites. — They are found in cerebral cortex. (ii) Bipolar — They possess one axon and one dendrites. — They are found in the retina of eye. (iii) Unipolar — Their cell body possesses one axon only. — They are found usually in the embryonic stage. Types of Axon Depending on the presence or absence of myelin sheath the axons are of two types (i) myelinated and (ii) non-myelinated. (i) Myelinated — The myelinated nerve fibres (axons) are enveloped with Schwann cells, which form a myelin sheath around the axon. — The myelin sheath is not continuous and the gaps between adjacent myelin sheaths are called nodes of Ranvier. — The myelinated nerve fibres are found in the brain and spinal cord. (ii) Non-myelinated (Unmyelinated) — A non-myelinated nerve fibres is enclosed by a Schwann cell that does not form a myelin sheath around the axon. — They are commonly found in autonomous and the somatic neural systems. Generation and Conduction of Nerve Impulse Neurons are excitable, because their membranes are in a polarised state i.e. there exists a potential differences across the membrane. The axonal membrane has different types of ion channels, which are selectively permeable to different ions; As a result a potential difference is created, which is responsible for the generation and conduction of nerve impulse. (i) Resting potential/Polarised membrane When a neuron is not conducting any impulse i.e. resting, the axonal membrane is called polarised; this is due to difference in concentration of ions across the axonal membrane. In resting stage, the axonal membrane is more permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+). The membrane is also impermeable to negatively charged proteins present in the axoplasm. Thus, the axoplasm inside the axon contains high concentration of K+ and negatively charged proteins, and low concentration of Na+.
Neural Control and Coordination 155 In contrast, the fluid outside the axon contains a low concentration of K+, and a high concentration of Na+, and thus form a concentration gradient across the axonal membrane. This ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3Na+ outwards for 2k+ into the cell. As a result, the outer surface of the axonal membrane is positively charged and the inner surface is negatively charged; The membrane is said to be polarised. The potential difference across the resting axonal membrane/polarised membranes is called resting potential. (ii) Action potential When a stimulus is applied at a site on a polarised membrane, the membrane at this site becomes freely permeable to Na+. This leads to rapid influx of Na+ followed by reversal of the polarity at this site i.e. the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. Now the membrane is said to be depolarised, and the electrical potential difference across the plasma membrane at this site is called action potential, which infact termed as nerve impulse. (iii) Conduction of nerve impulse At site immediately ahead of the site of stimulation, the axon, membrane has a positive charge on the outer surface and a negative charge on its inner surface. As a result, the current flows on the inner surface ahead and on the outer surface in opposite direction to complete the circuit of current flow, leading to depolarisation of the membrane at the site ahead of site of stimulation. The sequence is repeated along the length of axon and the impulse is conducted. Diagrammatic representation of impulse conduction through an axon (at points A and B) The depolarisation membrane is very rapid, so the conduction of nerve impulse along the entire length of axon occurs in fractions of second.
156 Biology-XI (iv) Repolarisation The stimulus induced rise in the permeability to Na+ extremely short lived. It is quickly followed by an increase in the permeability to K+, the K+ diffuses outside the membrane and restores the resting potential of the membrane at the site of stimulation, and the fibre becomes once more responsive for further stimulation. Transmission of Impulse The nerve impulse is transmitted from one neuron to another through junctions called synapses. There are two types of synapse namely, (i) electrical synapses, and (ii) chemical synapses. (i) Electrical synapses — At electrical synapse the membrane of pre and post synaptic neuron are in very close proximity. — The electrical current can flow directly from one neuron into the other across these synapses, like impulse conduction along the single axon. (ii) Chemical synapses — Here, the membrane of pre and post synaptic neuron are separated by a fluid filled space called synaptic cleft. Axon Axon terminal Synaptic vesicles Pre-synaptic Synapse membrane Synaptic cleft Post-synaptic membrane Receptors Neurotransmitters Diagram showing axon terminal and synapse. — Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. — The axon terminals contain synaptic vesicles, which are filled with neurotransmitters.
Read the Text Version
CBSE II Question Bank in Biology CLASS 11 Features Short Answer Type Questions Long Answer Type Questions Strictly Based on the Latest CBSE Term-wise Syllabus Case Study Based MCQs Chapter at a Glance Very Short Answer Type Questions