NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants

NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants

Topics and Subtopics in NCERT Solutions for Class 11 Biology Chapter 6 Anatomy of Flowering Plants:

Section Name Topic Name
6 Anatomy of Flowering Plants
6.1 The Tissues
6.2 The Tissue System
6.3 Anatomy of Dicotyledonous and Monocotyledonous Plants
6.4 Secondary Growth
6.5 Summary

NCRT TEXTBOOK QUESTIONS SOLVED

1.State the location and function of different types of meristems.
Soln. Meristems are of three types on the basis of their location in plant body:
(i) Apical meristem: It is present at the apices of root and shoot and is responsible for increase in length.
(ii)Intercalary meristem: It is present at the bases of leaves above the nodes or below the nodes and is responsible for elongation of the organs.
(iii)Lateral meristem : It is present on lateral side and is responsible for increase in girth or diameter.

2.Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Soln. Yes, I agree with this statement. Cork cambium cuts off cells both on its outer side and inner side. The cells cut off on outer side form cork and cells cut off on inner side form secondary cortex. The cells of cork are dead whereas those of secondary cortex are living.

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3.Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?
Soln. Secondary growth is the formation of secondary tissues from lateral meristems. It is found in dicots only. It increases the diameter of the stem. Secondary tissues are formed by two types of lateral meristems, vascular cambium and cork cambium. Vascular cambium produces secondary vascular tissues while cork cambium forms periderm.The vascular bundles in dicot stem are conjoint, collateral, open and are arranged in a ring. The cambium present between xylem and phloem in vascular bundles is called fascicular or intrafascicular cambium. Besides this, some cells of medullary rays also become meristematic and this is called interfascicular cambium. Both these cambia collectively constitute complete ring of vascular cambium. This ring of vascular cambium divides periclinally to cut off cells both on inner side and outer side. The cells cuts off on outer side are secondary phloem and inner side are secondary xylem. Amount of secondary xylem cut off is more than secondary phloem and thus with the formation of secondary tissue, increase in girth or diameter occurs. The structure of secondary xylem and secondary phloem is similar to that of primary xylem and primary phloem. With the increase in secondary tissue, the primary xylem and primary phloem get crushed. The ray initials of vascular cambium ring divide by tangential divisions and add new cells. These new cells produced on both the sides of ray initials remain meristematic for sometime and then differentiate into parenchymatous cells of rays. The rays, produced by vascular cambium in between the secondary xylem and secondary phloem, are called secondary medullary rays. They are usually one to few layers in thickness and one to several layers in height. The medullary rays form the radial systejn responsible for radial conduction of solutes. They maintain connection between pith and cortex There is a marked difference in activity of cambium with change in season. In spring, the activity of cambium is more and hence the wood elements are larger in size with wide lumen. The activity of cambium is less during autumn and the wood elements are smaller in size with narrow lumen. Spring wood and autumn wood of a year constitute annual ring.
In order to increase in girth and prevent harm on the rupturing of the outer ground tissues due to the formation of secondary vascular tissues, dicot stems produce a cork cambium or phellogen in the outer cortical cells. Phellogen cells divide on both the outer side as well as the inner side to form secondary tissues. The secondary tissue formed on the inner side is called secondary cortex while the tissue formed on outer side is called cork.
NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants Q3
Significance of secondary growth is as
follows:
(i) It adds to the girth of the plant thus provides support to increasing weight of aerial parts due to growth.
(ii)It’ produces a corky bark around the tree trunk that protects the interior from abrasion, heat, cold and infection.
(iii)It adds new vascular tissues for replacing old non-functioning one as well as for meeting increased demand for long distance transport of sap and organic nutrients.

4.Draw illustrations to bring out the anatomical difference between
(a) Monocot root and dicot root
(b) Monocot stem and dicot stem
Soln.(a) Differences between monocot root and dicot root are illustrated in the following figure and table.
NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants Q4
NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants Q4.1
(b) Differences between monocot and dicot stems are illustrated in the following figure and table.
NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants Q4.2

NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants Q4.3

5.Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem ? Give reasons.
Soln. Vascular bundles in dicot stem are arranged in a ring whereas in monocot stem vascular bundles are scattered throughout the ground tissue. On the basis of arrangement of vascular bundles it can be ascertained
whether the young stem is dicot or monocot. Besides undifferentiated ground tissue, sclerenchymatous hypodermis, oval or circular vascular bundles with Y shaped xylem are other differentiating features of monocot stem.

6.The transverse section of a plant material shows the following anatomical features – (a) the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheath, (b) phloem parenchyma is absent. What will you identify it as?
Soln. The plant material is identified as monocot stem.

7.Why are xylem and phloem called complex tissues?
Soln. A group of different types of cells which perform common function is called complex tissue. Xylem and phloem are called complex tissues as all cells that work as a unit for a common function have different structural organisation. Xylem has four types of cells-tracheids, vessels, xylem parenchyma and xylem fibres. Phloem consists of sieve tube elements, companion cells, phloem parenchyma and phloem fibres. Xylem is associated with conduction of water and minerals from roots to top of plants and phloem is responsible for transport of organic food.

8.What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.
Soln.Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange. Each stoma is composed*of two bean shaped cells known as guard cells which enclose stomatal pore. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialised in their shape and size and are known as subsidiary cells. The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.
NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants Q8
9.Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
Soln. The three basic tissue systems in flowering plants are epidermal tissue system, ground tissue system and vascular tissue system.
Epidermal tissue system comprises epidermal cells, stomata, trichomes and hairs.
Ground tissue system consists of cortex, endodermis, pericycle, pith and medullary rays, in the primary roots and stems. In¬leaves, the ground tissue consists of thin walled chloroplast containing cells and is called mesophyll.
The vascular tissue system consists of complex tissues, the phloem and the xylem.

10.How is the study of plant anatomy useful to us?
Soln. Study of internal structures of plants is called plant anatomy. Study of plant anatomy is useful:
-for solving taxonomic problems.
-for knowing homology and analogy of various plant groups.
-to differentiate the superior and inferior, standard and substandard or specified and unspecified woods.
-in establishing purity and correct identity of plant parts in pharmacognosy (science connected with sources, characteristics and possible medicinal uses).
-in knowing the structural peculiarities of different groups of plants.

11 .What is periderm? How does periderm formation take place in the dicot stems?
Soln. phelloderm, phellogen and phellem together constitute the periderm. Periderm is protective in function.Dicot stems produce cork cambium or phellogen in the outer cortical cells. Phellogen cells divide on both the outer side as well as the inner side to form secondary tissues. The secondary tissue produced on the inner side of the phellogen is called secondary cortex or phelloderm. On the outer side phellogen produces cork or phellem.

12.Describe the internal structure of a dorsiventral leaf with the help of labelled diagram.
Soln.
NCERT Solutions For Class 11 Biology Anatomy of Flowering Plants Q12
Dorsiventral leaves are found in dicots. The important anatomical features of dorsiventral leaves are discussed below:
(a) Upper epidermis : This is generally outermost single layer made of parenchymatous cells. The epidermal cells have sometimes outgrowths called papillae, e.g., in Gladiolus. The epidermal cells are devoid of chloroplast and stomata are absent on upper epidermis.
(b) Lower epidermis : It is just like upper epidermis but here stomata are present. Chloroplasts are absent in lower epidermis also, except the guard cells of stomata.
(c)Mesophyll: In between upper and lower epidermis mesophyll tissue is present which can be divided into two regions:
(i)Palisade parenchyma : These are elongated columnar cells without intercellular spaces. These have chloroplast in them and are generally arranged in two layers.
(ii)Spongy parenchyma : It is found below palisade parenchyma and are spherical or oval with intercellular spaces. They also have chloroplasts but number of chloroplasts is more in palisade parenchyma than spongy parenchyma.
(d)Vascular bundles : Vascular bundles are. generally found at the boundary between the palisade and the spongy regions. The vascular bundle in midrib region is largest. Vascular bundles are conjoint, collateral and closed. Each vascular bundle is surrounded by a bundle sheath of parenchymatous cells. In the vascular bundle, xylem is present towards upper epidermis and phloem towards lower epidermis. Further in xylem, protoxylem is towards upper epidermis.

NCERT Solutions For Class 11 Biology Chemical Coordination and Integration

NCERT Solutions For Class 11 Biology Chemical Coordination and Integration

Topics and Subtopics in NCERT Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration:

Section Name Topic Name
22 Chemical Coordination and Integration
22.1 Endocrine Glands and Hormones
22.2 Human Endocrine System
22.3 Hormones of Heart, Kidney and Gastrointestinal Tract
22.4 Mechanism of Hormone Action
22.5 Summary

NCERT Solutions Class 11 BiologyBiology Sample Papers

NCERT TEXTBOOK QUESTIONS FROM SOLVED

1. Define the following:
(a) Exocrine gland,
(b) Endocrine gland,
(c) Hormone.
Solution:
(a) Exocrine gland is a gland that pours its secretion on the surface or into a particular region by means of ducts for performing a metabolic activity, e.g., sebaceous glands, sweat glands, salivary glands and intestinal glands.
(b) Endocrine gland is an isolated gland (separates even from epithelium forming it) which secretes informational molecules or hormones that are poured into venous blood or lymph for reaching the target organ because the gland is not connected with the target organ by any duct. Therefore endocrine gland is also called ductless gland e.g. thyroid gland.
(c) Hormone is a substance that is manu-factured and secreted in very small quantities into the blood stream by an endocrine gland or a specialized nerve cell and regulates the growth or functioning of a specific tissue organ in a distant part of the body e.g insulin.

2. Diagrammatically indicate the location of the various endocrine glands in our body.
Solution:
NCERT Solutions For Class 11 Biology Chemical Coordination and Integration Q2

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3. List the hormones secreted by the following:
(a) Hypothalamus
(b) Pituitary
(c) Thyroid
(d) Parathyroid
(e) Adrenal
(f) Pancreas
(g) Testis
(h) Ovary
(i) Thymus
(j) Atrium
(k) Kidney
(l) G-l Tract.
Solution:
(a) Two types of hormones are produced by hypothalamus : releasing hormones (that stimulate secretion of pituitary hormones) and inhibiting hormones (that inhibit secretion of pituitary hormones).
These hormones are:

  1. Thyrotrophin-releasing hormone Adreno-
  2. corticotrophin-releasing hormone
  3. Follicle-stimulating hormone-releasing hormone
  4. Luteinizing hormone-releasing hormone
  5. Growth hormone-releasing hormone
  6. Growth inhibiting hormone
  7. Prolactin releasing hormone
  8. Prolactin inhibiting hormone
  9. Melanocyte stimulating hormone¬releasing hormone
  10. Melanocyte stimulating hormone- inhibiting hormone.

(b) Different parts of pituitary secrete different hormones.
Hormones secreted by anterior lobe of pituitary are:

  1. Follicle stimulating hormone
  2. Luteinizing hormone
  3. Thyroid stimulating hormone
  4. Adrenocorticotrophic hormone
  5. Somatotrophic or Growth hormone
  6. Prolactin hormone or Luteotrophic hormone.
    Middle (intermediate) lobe of pituitary : Melanocyte stimulating hormone.
    Posterior lobe of pituitary:
    (i) Oxytocin
    (ii) Vasopressin or antidiuretic hormone.

(c) Thyroid secretes 3 hormones:

  1. Thyroxine or tetraiodothyronine
  2. Triiodothyronine
  3. Calcitonin.

(d) Parathyroid gland secretes a single hormone called parathormone (PTH) or Collip’s hormone.

(e) Adrenal glands have two regions, namely, outer adrenal cortex and inner adrenal medulla. Both these regions secrete different hormones.
Hormones of adrenal cortex are grouped into three categories:

  1. Glucocorticoids, e.g., cortisol
  2. Mineralocorticoids, e.g., aldosterone
  3. Sexcorticoids e.g testosterone. Adrenal medulla secretes two hormones
    (i) Epinephrine (adrenaline)
    (ii)Nor-epinephrine (nor-adrenaline).

(f) Pancreas secretes following hormones:

  1. Insulin
  2. Glucagon
  3. Somatostatin.

(g) Testis secretes androgens such as testosterone.

(h) Ovary secretes:

  1. Estrogens such as estradiol
  2. Progesterone
  3. Relaxin.

(i) Thymus secretes thymosin hormone.

(j) Atrium secretes atrial natriuretic factor (ANF).

(k) Kidney secretes:
(i) Renin (ii) Erythropoetin

(l) G.I. tract secretes :

  1. Gastrin
  2. Secretin
  3. Cholecystokinin
  4. Enterocrinin
  5. Duocrinin
  6. Villikinin.

4. Fill in the blanks:
Hormones                                           Target gland
(a) Hypothalamic hormones        ………………..
(b) Thyrotrophin (TSH)                 ………………..
(c) Corticotrophin (ACH)              ………………..
(d) Gonadotrophins (LH, FSH)   ………………..
(e) Melanotrophin (MSH)              ………………..
Solution:
(a) Pituitary
(b) Thyroid
(c) Adrenal cortex
(d) Gonads -Testes in male and ovaries in female
(e) Skin.

5. Write short notes on the functions of the following hormones:
(a) Parathyroid hormones (PTH)
(b) Thyroid hormones
(c) Thymosin
(d) Androgens
(e) Estrogens
(f) Insulin and Glucagon.
Solution:
(a) Parathyroid hormone increases the level of calcium and decreases the level of phosphate in the blood.
(b) Thyroid gland secretes three hormones: thyroxine, triiodothyronin and calcitonin. Thyroxine and triiodothyronin control the general metabolism of the body, promote growth of body tissues and stimulates tissue differentiation. Calcitonin regulates the concentration of calcium in the blood.
(c) Thymosin is secreted by thymus. It accelerates cell division, stimulates the development and differentiation of T-lymphocytes and also hastens attainment of sexual maturity.
(d) Androgens are secreted by testis. They stimulate the development of male reproductive system, formation of sperms, development of male accessory sex characters and also determines the male sexual behaviour and the sex urge.
(e) Estrogens are secreted by ovaries. They stimulate the female reproductive tract to grow to full size and become functional, differentiation of ova and development of accessory sex characters.
(f) Insulin is secreted by the |3-cells of the pancreas. It lowers blood glucose level, and promotes synthesis of proteins and fats. Glucagon is secreted by the a-cells of the pancreas. It increases the level of glucose in the blood.

6. Give example(s) of
(a) Hyperglycemic hormone and hypoglyce-mic hormone
(b) Hypercalcemic hormone
(c) Gonadotrophic hormones
(d) Progestational hormone
(e) Blood pressure lowering hormone
(f) Androgens and estrogens.
Solution:
(a)Glucagon, Insulin
(b) Parathormone (PTH)
(c) Follicle stimulating hormone (FSH) and Luteinizing hormone (LH)
(d) Progesterone
(e) Atrial natriuretic factor
(f) Testosterone and Estradiol.

7. Which hormonal deficiency is responsible for the following:
(a) Diabetes meilitus
(b) Goitre
(c) Cretinism.
Solution:
(a) Insulin
(b) Thyroxine and Triiodothyronine
(c) Thyroxine and Triiodothyronine.

8. Briefly mention the mechanism of action of FSH.
Solution: (Folliclestimulatinghormone)being glycoprotein is insoluble in lipids, therefore,
cannot enter the target cells. It binds to the specific receptor molecules located on the surface of the cell membrane to form hormone – receptor complex. This complex causes the release of an enzyme adenylate cyclase from the receptor site. This enzyme forms the cell cyclic adenosine monophosphate (cAMP) from ATP. The cAMP activates the existing enzyme system of the cell. This accelerates the metabolic reactions in the cell. The hormone is called the first messenger and the cAMP is termed the second messenger. The hormone- receptor complex changes the permeability of the cell membrane to facilitate the passage of materials through it. This increases the activities of the cell as it receives the desired materials.

9. Match the following :
Column I         Column II
(a) T4              (i) Hypothalamus
(b) PTH          (ii)Thyroid
(c) GnRH      (iii)Pituitary
(d) LH            (iv) Parathyroid.
Solution:
(a) – (ii); (b) – (iv); (c) – (i); (d) – (iii)

NCERT Solutions For Class 11 Biology Neural Control and Coordination

NCERT Solutions For Class 11 Biology Neural Control and Coordination

Topics and Subtopics in NCERT Solutions for Class 11 Biology Chapter 21 Neural Control and Coordination:

Section Name Topic Name
21 Neural Control and Coordination
21.1 Neural System
21.2 Human Neural System
21.3 Neuron as Structural and Functional Unit of Neural System
21.4 Central Neural System
21.5 Reflex Action and Reflex Arc
21.6 Sensory Reception and Processing
21.7 Summary

NCERT Solutions Class 11 BiologyBiology Sample Papers

NCERT TEXTBOOK QUESTIONS FROM SOLVED

1. Briefly describe the structure of the following:
(a) Brain (b) Eye (c) Ear
Solution: (a) Brain: The brain acts as control and command system of the body. It is protected by skull and is covered by three meninges. It is divisible into three main regions: forebrain, midbrain and hindbrain.
(i) Forebrain – It consists of three regions:
(a) Olfactory lobes: These are a pair of very small, solid club-shaped bodies which are widely separated from each
other. They are fully covered by cerebral hemispheres.
(b) Cerebrum – It is the largest and most complex of all the parts of human brain. A deep cleft divides the cerebrum into right and left cerebral hemispheres, connected by myelinated fibres, the corpus callosum.
(c) Diencephalon – It encloses a slit-like cavity, the third ventricle. The thin roof of this cavity is known as the epithalamus, the thick right and left sides as the thalami, and floor as the hypothalamus.
(ii) Midbrain – It is located between thalamus/ hypothalamus of forebrain and pons of hindbrain. Its upper surface has two pairs of rounded protrusious called corpora quadrigemina and two bundles of fibres called crura cerebri.
(iii) Hindbrain – It consists of:
(a) Cerebellum – The second largest part of the human brain is the cerebellum. It consists of two lateral cerebellar hemispheres and central worm-shaped part, the vermis. The cerebellum has its grey matter on the outside, comprising three layers of cells and fibres. It also has Golgi cells, basket cells and granule cells.
(b) Pons varolii – An oval mass, called the pons varolii, lies above the medulla oblongata. It consists mainly of nerve fibres which interconnect different regions of the brain.
(c) Medulla oblongata – It extends from the pons varolii above and is continuous with the spinal cord below. The mid brain, pons varolii and medulla oblongata are collectively called brain stem.

(b) Eye: Eye is a hollow spherical structure composed of three coats:
– Outer fibrous coat
– Middle vascular coat
– Inner nervous coat
(i) Fibrous coat: It is thick and protects the eyeball. It has two distinct regions – sclera and cornea. Sclera covers most of the eye ball. The sclera or white of the eye contains many collagen fibres. Cornea is a transparent portion that forms the anterior one – sixth of the eyeball. The cornea is avascular (i.e., lacks blood supply).
(ii)Vascular coat: It comprises of 3 regions : choroid, iris, ciliary body.
(a) Choroid : It lies adjacent to sclera and contains numerous blood vessels and pigmented cells.
(b) Iris: The iris is a circular muscular diaphragm containing the pigment giving eye its colour. It extends from the ciliary body across the eyeball in front of the lens. It 2. has an opening in the centre called the pupil.
It contains two types of smooth muscles, circular muscles (sphincters) and radial muscles (dilators), of ectodermal origin.
(c) Ciliary body: Behind the peripheral margin of the iris, the vascular coat is thickened to form the ciliary body. It is composed of the ciliary muscles and the ciliary processes.
(iii) Nervous coat: It consists of retina which is neural and sensory layer of an eye ball. It consists of three layers; ganglion cells, bipolar cells and photoreceptor cells (rods and cones).
Lens: It is a transparent, biconvex, elastic structure that bends light waves as they pass through its surface. It is composed of epithelial cells that have large amounts of clear cytoplasm in the form of fibres.
Chambers of eyeball: The lens, suspensory ligament and ciliary body divide the eye into an anterior aqueous chamber and a posterior vitreous chamber which are filled with aqueous humour and vitreous humour respectively.

(c) Ear: There are three portions in an ear:
(i) External ear: It further has 2 regions: pinna and external auditory canal or meatus.
(a) Pinna: The pinna is a projecting elastic cartilage covered with skin. Its most prominent outer ridge is called the helix. The lobule is the soft pliable part at its lower end composed of fibrous and adipose tissue richly supplied with blood capillaries. It is sensitive as well as effective in collecting sound waves.
(b) External auditory canal: It is an S-shaped tube leading inward from the pinna. It is a tubular passage supported by cartilage in its exterior part and by bone in its interior part.
(ii) Middle ear: It consists of 3 small bones called ear ossicles – malleus, incus and stapes, which are attached to one another and increase efficiency of transmission of sound waves to inner ear.
(iii) Internal ear: It consists of bony and

2. Compare the following:
(a) Central neural system (CNS) and Peripheral neural system (PNS).
(b) Resting potential and action potential.
(c) Choroid and retina.
Solution: (a) CNS: It lies along the mid-dorsal axis of the body. It is a hollow, dorsally placed structure and comprises of brain and spinal cord. It is a centre of information processing and control.
PNS: Nerves arising from the central nervous system constitute the peripheral nervous system. It carries information to and from the CNS. It includes spinal nerves and cranial nerves.
(b) Resting potential: Outside the plasma membrane of a nerve fibre is the extracellular fluid which is positively charged with respect to the cell contents inside the plasma membrane. A resting nerve fibre shows a potential difference between inside and outside of this plasma membrane. This difference in the electrical charges across the plasma membrane is called the ‘resting potential’. A membrane with resting potential across it, is said to be electrically polarized. Action potential : Action potential is another name of nerve impulse. The contents inside a cell at the excited state becomes positively charged with respect to extracellular fluid outside it. This change in polarity across the plasma membrane is known as an action potential. The membrane with reversed polarity across it is said to be depolarized.
(c) Choroid: Choroid lies adjacent to the sclera and contains numerous blood vessels that supply nutrients and oxygen to the other tissues especially of retina. It contains abundant pigment cells and is dark brown in colour.
Retina: It is the neural and sensory layer of the eye ball. It is a very delicate coat and lines the whole of the vascular coat. Its external surface is in contact with the choroid and its internal surface with vitreous humour. It contains ganglion cells, bipolar cells and photoreceptor cells. membranous labyrinth. Membranous labyrinth consists of three semicircular ducts, utricle, saccule and cochlea.

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3. Explain the following processes:
(a) Polarisation of the membrane of a nerve fibre.
(b) Depolarisation of the membrane of a nerve fibre.
(c) Conduction of a nerve impulse along a nerve fibre.
(d) Transmission of a nerve impulse across a chemical synapse.
Solution: (a) Polarisation of the membrane of a nerve fibre : In the resting (not conducting impulse) nerve fibre the plasma membrane separates two solution of different chemical composition but having approximately the same total number of ions. In the external medium (tissue fluid), sodium ions (Na+) and Cl– ions predominate, whereas within the fibre (intracellular fluid) potassium ions (K+) predominate. The differential flow of the positively charged ions and the inability of the negatively charged organic (protein) ions within the nerve fibre to pass out cause an increasing positive charge on the outside of the membrane and negative charge on the inside of the membrane. This makes the membrane of the resting nerve fibre polarized, extracellular fluid outside being electropositive (positively charged) with respect to the cell contents inside it.
(b) Depolarisation of the membrane of a nerve fibre: During depolarisation, the activation gates of Na channels open, and the K channels remain closed. Na+ rush into the axon. Entry of sodium ions leads to depolarisation (reversal of polarity) of the nerve membrane, so that the nerve fibre contents become electropositive with respect to the extracellular fluid.
(c) Conduction of a nerve impulse along a nerve fibre: Nervous system transmits information as a series of nerve impulses. A nerve impulse is the movement of an action potential as a wave through a nerve fibre. Action potentials are propagated, that is, self-generated along the axon. The events that set up an action potential at one spot on the nerve fibre also transmit it along the entire length of the nerve fibre. The action potential then moves to the neighbouring region of the nerve fibre till it covers the whole length of the fibre.
(d) Transmission of a nerve impulse across a chemical synapse: At a chemical synapse, the membranes of the pre- and post- synaptic neurons are separated by a fluid- filled space called synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. The axon terminals contain vesicles filled with these neurotransmitters. When an impulse (action potential) arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and burst to release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post- synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.

4. Draw labelled diagrams of the following:
(a) Neuron (b) Brain
(c) Eye (d) Ear
Solution: (a)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q4
(b)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q4.1
(c)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q4.2
(d)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q4.3

5. Write short notes on the following:
(a) Neural coordination (b) Forebrain
(c) Midbrain                       (d) Hindbrain
(e) Retina                             (f) Ear ossicles
(g) Cochlea                          (h) Organ of Corti
(i) Synapse
Solution: (a) Neural coordination : When higher animals respond to various stimuli, each response to a specific stimulus generally involves many organs (parts) of their bodies. Therefore, it is necessary that all the concerned organs (parts) of the body should work in a systematic manner to produce the response. The working together of various organs (parts) of the body of multicelullar organism in a proper manner to complement the functions of each other is called coordination. This is achieved by three overlapping processes of nervous system-sensory input, integration and motor output.
(b) Forebrain: It consists of: Olfactory lobes, the paired structures concerned with the sense of smell. Cerebrum which is the largest and most complex of all the parts of the human brain. It is divided by a cleft into left and right cerebral hemispheres which are connected by a large bundle of myelinated fibres the. corpus callosum. The outer cover of cerebral hemisphere is called cerebral cortex. It consists of sensory and motor areas. Hypothalamus region of forebrain contains centres which control body temperature, hunger and also contains group of neurosecretory cells.
(c) Midbrain: The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passess through the midbrain. The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina. Midbrain and hindbrain form the brain stem.
(d) Hindbrain: The hindbrain comprises pons, cerebellum and medulla. Pons consists of fibre tracts that interconnect different regions of the brain. Cerebellum has very convoluted surface in order to provide the additional space of many more neurons. The medulla of the brain is connected to the spinal cord. The medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions.
(e) Retina: Retina is the inner layer of an eye and it contains three layers of cells-from inside to outside – ganglion cells, bipolar cells and photoreceptor cells. There are two types of photoreceptor cells, namely, rods and cones. These cells contain the light-sensitive proteins called the photopigments. The daylight (photopic) vision and colour vision are functions of cones and the twilight (scotopic) vision is the function of the rods. The rods contain a purplish-red protein called the rhodopsin or visual purple, which contains a derivative of Vitamin A. In the human eye, there are three types of cones which possess their own characteristic photopigments that respond to red, green and blue lights. The sensations of different colours are produced by various combinations of these cones and their photopigments. When these cones are stimulated equally, a sensation of white light is produced.
(f) Ear ossicles : There is a small flexible chain of three small bones called as ear ossicles – the malleus (hammer shaped), the incus (anvil shaped) and the stapes (stirrup shaped) in the middle ear. Malleus is attached to the tympanic membrane on one side and incus on the other side. Incus in turn is connected with the stapes. Malleus is the largest ossicle, however stapes is the smallest ossicle.
(g) Cochlea : It is the main hearing organ which is connected with saccule. It is a spirally coiled tube that resembles a snail shell in appearance. It tapers from a broad base to an almost pointed apex.
(h) Organ of Corti: It is a structure located on the basilar membrane which contains hair cells that act as auditory receptors. The hair cells are present in rows on the internal side of the organ of Corti.
(i) Synapse : It is the junction between the axon of one neuron and the dendrite or cyton of another neuron for transmission of nerve impulse.

6. Give a brief account of
(a) Mechanism of synaptic transmission.
(b) Mechanism of vision.
(c) Mechanism of hearing.
Solution: (a) Mechanism of synaptic transmission: Refer answer 3 (d)
(a) Mechanism of vision: The light rays in visible wavelength focused on the retina through the cornea and lens generate potentials (impulses) in rods and cones. Light induces
dissociation of the retinal from opsin resulting in changes in the structure of the opsin. This causes membrane permeability changes. As a result, potential differences are generated in the photoreceptor cells. This produces a signal that generates action potentials in the ganglion cells through the bipolar cells. These action potentials (impulses) are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analysed and the image formed on the retina is recognised based on earlier memory and experience.
(b) Mechanism of hearing : The external ear receives sound waves and directs them to the ear drum. The ear drum vibrates in response to the sound waves and these vibrations are transmitted through the ear ossicles (malleus, incus and stapes) to the oval window. The vibrations are passed through the oval window on to the fluid of the cochlea, where they generate waves in the lymphs. The waves in the lymphs induce a ripple in the basilar membrane. These movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane. As a result, nerve impulses are generated in the associated afferent neurons. These impulses are transmitted by the afferent fibres via auditory nerves to the auditory cortex of the brain, where the impulses are analysed and the sound is recognised.

7. Answer briefly.
(a) How do you perceive the colour of an object?
(b) Which part of our body helps us in maintaining the body balance?
(c) How does the eye regulate the amount of light that falls on the retina?
Solution: (a)In humans, colour vision results from the activity of cone cells, a type of photoreceptor cells. In the human eye, there are three types of cones which possess their own characteristic photopigments that respond to red, green and blue lights. The sensations of different colours are produced by various combinations of these cones and their photopigments. When these cones are stimulated equally, sensation of white light is produced. Yellow light, for instance, stimulates green’and red cones approximately to equal extent, and this is interpreted by the brain as yellow colour.
(b) Ears (cristae and maculae present in internal ears).
(c) The iris contains two sets of smooth muscles – sphincters and dilators. These muscles regulate the amount of light entering the eyeball by varying the size of pupil. Contraction of sphincter muscles makes the pupil smaller in bright light so that less light enters the eye. Contraction of dilator muscles widens the pupil in dim light so that more light goes in eye to fall on retina.

8. Explain the following.
(a) Role of Na+ in the generation of action potential.
(b) Mechanism of generation of light-induced impulse in the retina.
(c) Mechanism through which a sound produces a nerve impulse in the inner ear.
Solution: (a) The action potential is largely determined by Na+ ions. The action potential results from the following sequential events
(i) Disturbance caused to the membrane of a nerve fibre by a stimulus results in leakage of  Na+ into the nerve fibre.
(ii) Entry of Na+ lowers the trans-membrane potential difference.
(iii) Decrease in potential difference makes the membrane more permeable to Na+ than to K+ ions so that more Na+ enter the fibre than K+ leave it.
(iv) Accumulation of Na+ in the nerve fibre initiates depolarisation (action potential), making the axonic contents positively charged relative to the extracellular fluid.
(v) With continued addition of Na+ the potential reaches zero and then plus 40-50 millivolts. This is the peak of action potential.
(vi) Permeability of a depolarised membrane to Na+ then rapidly drops, there are now as many Na+ on the inside of the membrane as on the outside.
(b) Refer answer 6 (b)
(c) Refer answer 6 (c)

9. Differentiate between
(a) Myelinated and non-myelinated axons
(b) Dendrites and axons
(c) Rods and cones
(d) Thalamus and Hypothalamus
(e) Cerebrum and Cerebellum
Solution: (a) Differences between myelinated and non-myelinated axons are as follows:
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q9
(b) Axon and dendrites can be differentiated as follows:
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q9.1

NCERT Solutions For Class 11 Biology Neural Control and Coordination Q9.2
(c) The differences between rods and cones are as follows:
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q9.3
(d) Thalamus and hypothalamus can be differentiated as follows:
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q9.4
(e) Cerebrum and cerebellum can be differentiated as follows:
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q9.5

10. Answer the following.
(a) Which part of the ear determines the pitch ofa sound?
(b) Which part of the human brain is the most developed?
(c) Which part of our central neural system acts as a master clock?
Solution: (a) The receptor cells in the organ of Corti (Internal ear).
(b) Cerebrum (cerebral hemispheres).
(c) Pineal gland present in diencephalon of forebrain acts as a master clock, which maintains biological rhythm.

11. The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the
(a) fovea (b) iris
(c) blind spot (d) optic chiasma
Solution: (c) blind spot

12. Distinguish between
(a) Afferent neurons and efferent neurons
(b) Impulse conduction in myelinated nerve fibre and unmyelinated nerve fibre
(c) Aqueous humour and vitreous humour
(d) Blind spot and yellow spot
(e) Cranial nerves and spinal nerves
Solution: (a)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q12
(b) Refer answer 9(a)
(c)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q12.1

NCERT Solutions For Class 11 Biology Neural Control and Coordination Q12.2
(d)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q12.3
(e)
NCERT Solutions For Class 11 Biology Neural Control and Coordination Q12.4

NCERT Solutions For Class 11 Biology Locomotion and Movement

NCERT Solutions For Class 11 Biology Locomotion and Movement

Topics and Subtopics in NCERT Solutions for Class 11 Biology Chapter 20 Locomotion and Movement:

Section Name Topic Name
20 Locomotion and Movement
20.1 Types of Movement
20.2 Muscle
20.3 Skeletal System
20.4 Joints
20.5 Disorders of Muscular and Skeletal System
20.1 Summary

NCERT Solutions Class 11 BiologyBiology Sample Papers

NCERT TEXTBOOK QUESTIONS FROM SOLVED

1. Draw the diagram of a sarcomere of skeletal muscle showing different regions.
Solution: 
NCERT Solutions For Class 11 Biology Locomotion and Movement Q1

2. Define sliding filament theory of muscle contraction.
Solution: According to sliding filament theory of muscle contraction, the actin and myosin filaments slide past each other with the help of cross-bridges to reduce the length of the sarcomeres.

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3. Describe the important steps in muscle contraction.
Solution: Mechanism of muscle contraction is explainei by sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the th’ ck filaments. As a nerve impulse reaches the terminal end of the axon, synaptic vesicles fuse with the axon membrane and release a chemical transmitter, acetylcholine and binds to receptor sites of the motor end plate. When depolarization of the motor end plate reaches a certain level, it creates an action potential. An action potential (impulse) passes from the motor end plate over the sarcolemma and then into the T-tubules and sarcoplasmic reticulum and stimulates the sarcoplasmic reticulum to release calcium ions into the sarcoplasm. The calcium ions bind to troponin causing a change in its shape and position. This in turn alters shape and the position of tropomyosin, to which troponin binds. This shift exposes the active sites on the F-actin molecules. Myosin cross-bridges are then able to bind to these active sites. The heads of myosin molecules project laterally from thick myofilaments towards the surrounding thin myofilaments. These heads are called cross bridges. The head of each myosin molecule contains an enzyme mysoin ATPase. In the presence of myosin ATPase,Ca++ and Mg++ ions, ATP breaks down into ADP and inorganic phosphate, releasing energy in the head.
Energy from ATP causes energized myosin cross bridges to bind to actin.
NCERT Solutions For Class 11 Biology Locomotion and Movement Q3
The energized cross-bridges move, causing thin myofilaments to slide along the thick myofilaments.

4. Write true or false. If false change the statement so that it is true.
(a) Actin is present in thin filament.
(b) H-zone of striated muscle fibre represents both thick and thin filaments.
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body.
Solution: (a) True
(b) False – H-Zone of striated muscle fibres represents only thick filaments.
(c) True
(d) False – There are 12 pairs of ribs in man.
(e) True

5. Write the differences between:
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle
Solution: (a) Actin filaments and myosin filaments can be differentiated as follows:
NCERT Solutions For Class 11 Biology Locomotion and Movement Q5
(b) Differences between red muscle fibres and white muscle fibres are given in the following table:
NCERT Solutions For Class 11 Biology Locomotion and Movement Q5.1

NCERT Solutions For Class 11 Biology Locomotion and Movement Q5.2

NCERT Solutions For Class 11 Biology Locomotion and Movement Q5.3
(c) Differences between pectoral and pelvic girdles are given in the following table:
NCERT Solutions For Class 11 Biology Locomotion and Movement Q5.4

6. Match Column I with Column II:
Column I                            Column II
(a) Smooth muscle          (i) Myoglobin
(b) Tropomyosin             (ii) Thin filament
(c) Red muscle                (iii) Sutures
(d) Skull                            (iv) Involuntary
Solution.(a) – (iv), (b)-(ii), (c)-(i), (d)-(iii)

7. What are the different types of movements exhibited by the cells of human body?
Solution: The cells of human body show three types of movements: amoeboid, ciliary and muscular.
Amoeboid movements: These are found in leucocytes of blood and phagocytes of certain body organs. In such cells, movements are brought with the help of temporary finger-like cytoplasmic projections, called pseudopodia or false feet. So it is also called pseudopodial movement. These pseudopodia are formed by flow of cytoplasm, called cyclosis (simplest form of movement), and cytoskeletal structures like microfilaments.
Ciliary movements: Large number of our internal tubular organs are lined by ciliated epithelium. For instance, the cilia of the cells lining the trachea, oviducts and vasa efferentia propel dust particles, eggs and sperms respectively by their coordinated movements in specific directions in these organs. Muscular movements: These are brought about by the action of skeleton, joints and muscles. These are of two types: movements of body parts and locomotion.

8. How do you distinguish between a skeletal muscle and a cardiac muscle?
Solution: We can distinguish between a skeletal muscle and a cardiac muscle on the basis of the features discussed in the following table:
NCERT Solutions For Class 11 Biology Locomotion and Movement Q8

9. Name the type of joint between the following:
(a) atlas/axis
(b) carpal/metacarpal of thumb
(c) between phalanges
(d) femur/acetabulum
(e) between cranial bones
(f) between pubic bones in the pelvic girdle
Solution: (a) Pivot joint
(b) Saddle joint
(c) Hinge joint
(d) Ball and socket joint
(e) Fibrous joint
(f) Cartilaginous joint

10. Fill in the blank spaces:
(a) All mammals (except a few) have……. cervical vertebra.
(b) The number of phalanges in each limb of human is…….
(c) Thin filament of myofibril contains two ‘F’ actins and two other proteins namely…….and…….
(d) In a muscle fibre Ca++ is stored in …….
(e)…….and…….pairs of ribs are called floating ribs.
(f) The human cranium is made of……. bones.
Solution: (a) 7
(b) 14
(c) tropomyosin, troponin
(d) sarcoplasmic reticulum
(e) 11th and 12th
(f) 8

NCERT Solutions For Class 11 Biology Digestion and Absorption

NCERT Solutions For Class 11 Biology Digestion and Absorption

Topics and Subtopics in NCERT Solutions for Class 11 Biology Chapter 16 Digestion and Absorption:

Section Name Topic Name
16 Digestion and Absorption
16.1 Digestive System
16.2 Digestion of Food
16.3 Absorption of Digested Products
16.4 Disorders of Digestive System
16.5 Summary

NCERT TEXTBOOK QUESTIONS FROM SOLVED

1. Choose the correct answer among the following:
(a) Gastric juice contains
(i) pepsin, lipase and rennin
(ii) trypsin, lipase and rennin
(iii) trypsin, pepsin and lipase
(iv) trypsin, pepsin and rennin.
(b) Succus entericus is the name given to
(i) a junction between ileum and large intestine
(ii) intestinal juice
(iii) swelling in the gut
(iv) appendix.
Solution: (a) (i) Pepsin, lipase and rennin
(b) (ii) Intestinal juice

2. Match column I with column II.
Column I                         Column II
(a) Bilirubin and           (i)Parotid biliverdin
(b) Hydrolysis of          (ii)Bile starch
(c) Digestion of fat       (iii)Lipases
(d) Salivary gland        (iv) Amylases
Solution: (a), – (ii),- (b) – (iv), (c) – (iii),- (d) – (i)

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3. Answer briefly:
(a) Why are villi present in the intestine and not in the stomach?
(b) How does pepsinogen change into its active form ?
(c) What are the basic layers of the wall of alimentary canal?
(d) How does bile help in the digestion of fats ?
Solution: (a) The absorptive surface area of small intestine is enormously increased by microvilli and as maximum absorption
of digested food takes place in small intestine as compared to other organs, therefore, villi are present in small intestine and not in stomach. Moreover, stomach is primarily associated with temporary storage of food.
(b) The proenzyme pepsinogen, on exposure to hydrochloric acid, secreted by oxyntic cells of gastric glands gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach.
(c) The wall of alimentary canal from oesophagus to rectum possesses four layers, namely serosa, muscularis, sub-mucosa and mucosa. Serosa is the outermost layer and is made up of a thin mesothelium with some connective tissues. Muscularis is formed by smooth muscles. The sub-mucosal layer is formed of loose connective tissues containing nerves, blood and lymph vessels. In duodenum, glands are also present in sub-mucosa. The innermost layer lining the lumen of the alimentary canal is the mucosa. This layer forms irregular folds (rugae) in the stomach and small finger¬like foldings called villi in the small intestine.
(d) Bile has no enzymes but contains bile salts, namely, sodium bicarbonate, sodium glycocholate and sodium taurocholate that reduce the surface tension of large fat droplets and break them into many small droplets by a process known as emulsification. These small fat droplets present large surface area for lipase (fat digesting enzyme) to act upon them. Moreover, bile also activates lipases.

4. State the role of pancreatic juice in digestion of proteins.
Solution: The pancreatic juice contains inactive enzymes – trypsinogen, chymotrypsinogen, procarboxypeptidases. Trypsinogen is acti¬vated by an enzyme enterokinase, (secreted by the intestinal mucosa) into active trypsin, which in turn activates the other enzymes of the pancreatic juice. Proteins, proteoses and peptones (partially hydrolysed proteins) in the chyme reaching the intestine are acted upon by these proteolytic enzymes of pancre¬atic juice.
NCERT Solutions For Class 11 Biology Digestion and Absorption Q4

5. Describe the process of digestion of protein in stomach.
Solution: The gastric glands of the stomach secrete gastric juice that contains HCl and proenzymes – pepsinogen and prorennin. The proenzyme pepsinogen, on exposure to HCl gets converted into the active enzyme pepsin, the proteolytic enzyme of stomach. The pepsin converts proteins into proteoses and peptones (peptides). Prorennin is found in gastric juice of infants and is activated by pepsin into active rennin. It helps in digestion of milk protein casein.
NCERT Solutions For Class 11 Biology Digestion and Absorption Q5

6. Give the dental formula of human beings.
Solution: The dental formula of human beings is
NCERT Solutions For Class 11 Biology Digestion and Absorption Q6
It shows arrangement of teeth in each half of
the upper and lower jaw.
NCERT Solutions For Class 11 Biology Digestion and Absorption Q6.1

7. Bile juice contains no digestive enzymes, yet it is important for digestion. Why ?
Solution: Bile has no enzymes but contains bile salts, namely, sodium bicarbonate, sodium glycocholate and sodium taurocholate that reduce the surface tension of large fat drop¬lets and break them into many small droplets by a process known as emulsification. These small fat droplets present large surface area for lipase (fat digesting enzyme) to act upon them. Moreover, bile also activates lipases.
NCERT Solutions For Class 11 Biology Digestion and Absorption Q7

8. Describe the digestive role of chymotrypsin. Which two other digestive enzymes of the same category are secreted by its source gland ?
Solution: Chymotrypsin is a proteolytic enzyme of pancreatic juice secreted by exocrine part of pancreas. It helps in digestion of proteins. It converts proteins, peptones and proteoses into oligopeptides and dipeptides. Two other proteolytic enzymes present in pancreatic juice are trypsinogen and procarboxypeptidase.

9. How are polysaccharides and disaccharides digested ?
Solution: Digestion of polysaccharides (starch and glycogen) starts from buccal cavity. In buccal cavity, polysaccharides are acted upon by salivary amylase or ptyalin which splits starch and glycogen into disaccharides and small dextrins called ‘a’ dextrin.
NCERT Solutions For Class 11 Biology Digestion and Absorption Q9
The digestion of carbohydrates does not occur in stomach because gastric juice itself has no carbohydrase.
In small intestine, the food mixes with two juices, pancreatic juice and intestinal juice. Pancreatic juice contains a carbohydrase named pancreatic amylase. This enzyme hydrolyses more starch and glycogen.
NCERT Solutions For Class 11 Biology Digestion and Absorption Q9.1
Intestinal juice contains carbohydrases; maltase, isomaltase, a-dextrinase, sucrase and lactase which act on disaccharides as follows:
NCERT Solutions For Class 11 Biology Digestion and Absorption Q9.2
fructose and galactose are monomers of carbohydrates. These are absorbed by intestinal mucosa.

10. What would happen if HCl were not secreted in the stomach?
Solution: HCl is secreted by parietal or oxyntic cells of gastric glands. It serves the following functions:

  1. It activates the pepsinogen and prorennin into their active form pepsin and rennin.
  2. It provides the acidic pH (pH 1.8) optimal for pepsin.
  3. It kills the harmful bacteria present in the food.
  4. It stops the action of saliva on food. Pepsin and rennin are the principle proteolytic enzymes of stomach. If these enzymes are not activated by HCl then digestion of protein will not take place in stomach, and also the harmful bacteria can cause various diseases.

11. How does butter in your food get digested and absorbed in the body ?
Solution: Butter is a saturated fat. Fats and oils of the ingested food are triglycerides.
They are digested by lipases. Small intestine is the principal organ for fat digestion.
In the small intestine food meets three secretions, bile, pancreatic juice and intestinal juice, all alkaline in nature.
Bile contains no enzyme but it contains bile salts which reduces the surface tension of large fat droplets and breaks them into smaller ones (emulsification).
NCERT Solutions For Class 11 Biology Digestion and Absorption Q11
Emulsified triglycerides Pancreatic juice contains pancreatic lipase, which is the principal fat digesting enzyme. It is activated by bile.
NCERT Solutions For Class 11 Biology Digestion and Absorption Q11.1
Fatty acid + Glycerol Intestinal lipase found in intestinal juice hydrolyses some triglycerides, diglycerides and monoglycerides to fatty acids and glycerol like pancreatic lipase.
Fatty acids, glycerol and monoglycerides are the end products of fat digestion and being insoluble in water cannot be directly absorbed from the intestinal contents. So they combine with the bile salts and phospholipids to form micelles (water soluble). From the micelles fatty acids, glycerides, sterols and fat soluble vitamins are absorbed into the intestinal cells by diffusion where they are resynthesised in the ER and are converted into very small protein coated fat molecules (droplets) called chylomicrons. The latter are released from the intestinal cells into the lymph present in the lymphatic capillaries, the lacteals. These lacteals ultimately release the absorbed substances into the blood stream.

12. Discuss the main steps in the digestion of proteins as the food passes through different parts of the alimentary canal.
Solution: Proteins of ingested food are broken down into amino acids by proteases (peptidases). Proteases are secreted in inactive forms called proenzymes which are converted into active forms at site of their action. Protein digestion starts in the stomach and is completed in the small intestine. Saliva contains no protease.
Digestion of proteins in stomach : Chief cells of gastric gland secrete pepsinogen and prorennin, which act as follows:
NCERT Solutions For Class 11 Biology Digestion and Absorption Q12

NCERT Solutions For Class 11 Biology Digestion and Absorption Q12.1
Digestion of proteins in small intestine: In small intestine, peptones and proteoses are acted upon by enzymes of pancreatic juice and intestinal juice.
Pancreatic juice contains 3 inactive proteases; trypsinogen, chymotrypsinogen and pro-carboxypeptidase. Their action is as follows:
NCERT Solutions For Class 11 Biology Digestion and Absorption Q12.2
Dipeptides + Amino acids Intestinal juice contains two digestive pro-teases; aminopeptidases and dipeptidases and a nondigestive enterokinase (enteropep- tidase).
NCERT Solutions For Class 11 Biology Digestion and Absorption Q12.3
Amino acids are the end products of protein digestion which are absorbed by intestinal cells.

13. Explain the term thecodont and diphyodont.
Solution: Thecodont: In human, each tooth is embedded in a socket of jaw bone. Such teeth are described as thecodont.
Diphyodont: Majority of mammals including human beings form two sets of teeth during their life, a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. This type of dentition is called diphyodont.

14. Name different types of teeth and their number in an adult human.
Solution: Adult human has 32 teeth with the
NCERT Solutions For Class 11 Biology Digestion and Absorption Q14
Human has heterodont dentition i.e., having four different types of teeth. The number of different types of teeth in human are as follows:incisors = 8, canines = 4, premolars = 8, molars = 12

15. What are the functions of liver?
Solution: Liver is the largest gland of the body and consists of hepatic cells. Besides being a digestive gland, the liver performs a number of functions for the welfare of body. Its varied functions are as follows

  1. Secretion of bile.
  2. Glycogenesis, gluconeogenesis and glycogenolysis.
  3. Storage of fat, glycogen, vitamins like A, D, E, K and B12, blood, water, etc.
  4. Deamination of amino acids.
  5. Synthesis of urea.
  6. Elimination of excretory substances.
  7. Detoxification of harmful substances.
  8. Formation and breakdown of blood
    corpuscles, i.e., in embryos, liver is haemopoietic (produces red blood corpuscles) and in adults its Kupffer cells phagocytise and destroy worn out and dead RBCs.
  9. Secretion of blood proteins, i.e., prothrombin and fibrinogen.
  10. Secretion of anticoagulant heparin.
  11. Production of heat.
  12. Secretion of enzymes.