CBSE class 11 Biology Solutions – Page 5

NCERT Solutions for Class 11 Biology Chapter 1 The Living World

January 5, 2022June 18, 2021 by Raju

NCERT Solutions for Class 11 Biology Chapter 1 The Living World

These Solutions are part of NCERT Solutions for Class 11 Biology. Here we have given NCERT Solutions for Class 11 Biology Chapter 1 The Living World.

Question 1.
Why are living organisms classified?
Solution:
Classification of living organisms grouped them in special categories, which is based on observable characters. It makes their study easy and convenient. For example, Mammals are those who possess mammary glands, the hair on the body, external pinnae, etc.

Question 2.
Why are classification systems changing every now and then?
Solution:
The classification system changes when more information becomes available about the organisms. Additional information are updated from time to time about different organisms at this stage there is a need arises to make changes in the classification system.

Question 3.
What different criteria would you choose to classify people that you meet often?
Solution:
Classification means the arrangement of organisms into groups on the basis of their affinities or relationships. The branch of biology that deals with the study of principles and procedures of biological classification are called taxonomy. Some fundamental elements of taxonomy are discussed below.

Nomenclature: It is the science of providing distinct and proper names to organisms. It is the determination of the correct name as per established universal practices and rules.

Classification: It deals with the mode of arranging organisms or group^ of organisms into categories according to a systematic plan or ah order. The categories used in the classification of animals are Class, Order, Family, Genus, and Species. Each category is a unit and is also called a taxon (PI. Taxa).

Identification: It is the determination of the correct name and place of an organism in a system of classification. It determines that the particular organism is similar to some other organism of known identity. This implies assigning an organism to a particular taxonomic group. Suppose there are three plants say x, y, z. AH represent different species. Another plant w resembles y. The recognition of the plant was identical to the already known plant y is its identification.
One of the important features of systematics is the naming of living organisms. The organisms have been given two types of names i.e

common or vernacular names
Scientific names.

Question 4.
What do we learn from the identification of individuals and populations?
Solution:
Identification of individuals and populations determines their exact place or position in the set plan of classification.

Question 5.
Given below is the scientific name of mango. Identify the correctly written name.
(a) Mangifera Indica
(b) Mangifera indica
Solution:
(b) Mangifera indica

Question 6.
Define a taxon. Give some examples of taxa at different hierarchical levels.
Solution:
“Taxon is a unit of classification or a rank or a level of hierarchy in system of classification. The following chart gives taxonomical categories showing a hierarchical arrangement in ascending order.

Kingdom
↑
phylum or Division
Class
↑
Order
↑
Family
↑
Genus
↑
Species

Question 7.
Can you identify the correct sequence of taxonomical categories?
(a) Species → Order → Phylum → Kingdom
(b) Genus → Species → Order → Kingdom
(c) Species → Genus → Order → Phylum
Solution:
(c) Species → Genus → Order → Phylum

Question 8.
Try to collect all the currently accepted meanings for the word ‘species’. Discuss with your teacher the meaning of species in the case of higher plants and animals on one hand and bacteria on the other hand.
Solution:

Species is one of the basic units of biological classification. A species is often defined as a
group of organisms capable of interbreeding aid in producing fertile offspring.
Sometimes more precise or differing measures such as similarity of DNA, morphology o,^ecological niche are used to define the basis of species.
In case of animals, the name of species is defined by the specific name or the specific epithet. For example, gray wolves belong to the species Canis lupus, golden Jackals to Cam’s aureus etc.
Both of them belong to same genus Canis, but species name varies. But species name of plant is only called species epithet.
The ‘specific name’ in botany is always the combination of genus name and species epithet such as saccharum in Acer saccharum (Sugar maple).
But bacteria are grouped under four categories based on their shape – spherical, rod-shaped, comma and spiral shaped and species of bacteria is according to their shapes. Thus the meaning of species in higher organism and bacteria are different.

Question 9.
Define and understand the following terms:
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Solution:
(i) Phylum: A phylum is a group of related classes having some common features, e.g., protozoa.
(ii) Class: A class is a group of related orders, for e.g., order Rodentia, Lagomorpha and Carnivora all having hair and milk glands are placed in class Mammalia.
(iii) Family: A family is a group of related genera. The genus Felis of cats and the genus Panthera of lion, tiger and leopard are placed in the family Felidal.
(iv) Order: An order is a group of related families. The family Felidae of cats and the »family Coridal of dogs are assigned to the order Carnivora. Cats and dogs have large canine teeth and are flesh-eaters.
(v) Genus: A genus is a group of species alike in the broad features of their organization but different in detail. As per the rules of binomial nomenclatures, a species can not be named without assigning it to a genus.
NCERT Solutions for Class 11 Biology Chapter 1 The Living World 1

Question 10.
How is key helpful in the identification and classification of organisms?
Solution:
Keys are contrasting pairs of characters (couplet), it represents the choice made between two opposite options. This results in acceptance of only one and rejection of the other. Each statement in the key is called a lead. Separate taxonomic keys are required for each taxonomic category such as family, genus, and species for identification purposes.

Question 11.
Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Solution:
NCERT Solutions for Class 11 Biology Chapter 1 The Living World 2

VERY SHORT ANSWER QUESTIONS

Question 1.
Name the basic Unit of classification.
Solution:
Species.

Question 2.
Who introduced the hierarchy in taxonomy?
Solution:
Linnaeus

Question 3.
Who is the father of taxonomy?
Solution:
Carolus Linnaeus.

Question 4.
What is meant by cytotaxonomy?
Solution:
Classification based on chromosome number.

Question 5.
Who devised the binomial nomenclature?
Solution:
Carolus Linnaeus

Question 6.
What is a type specimen?
Solution:
Establishment of the name of the new species on the basis of the original specimen is called type specimen

Question 7.
In which language binomial nomenclature is written?
Solution:
Latin

Question 8.
What term is used to describe organisms without a well-developed nucleus?
Solution:
Prokaryote

Question 9.
Is inter-specific breeding possible?
Solution:
Yes, both.

Question 10.
What are DNA viruses / RNA viruses?
Solution:
Viruses that possess DNA as the genetic material are called DNA viruses.

Question 11.
What is speciation?
Solution:
Formation of a new species from an existing one by the appearance of mutation.

Question 12.
What are correlated characters?
Solution:
The common features the species have to qualify for inclusion in a genus are called correlated characters

Question 13.
Why classification of plants and animals is necessary?
Solution:
Classification divides millions of plant and animal species into convenient groups that make their study easier

Question 14.
What is cohort or order?
Solution:
The cohort is a unit of classification higher than the 6. family

Question 15.
Give an example of symbiotic bacteria.
Solution:
Rhizobium leguminosarum

Question 16.
Give botanical and zoological names of the following:
(1) Pea
(2) Wheat
(3) Man
(4) Potato
Solution:
(1) Pea → Pisumsatinum
(2) Wheat → Triticumaextivum
(3) Man → Homo sapiens
(4) Potato → Solanum tuberosum

SHORT ANSWER QUESTIONS

Question 1.
Write a note on bacteriophages. (Dharwar. 2004, Belgaum. 04,2005)
Solution:
The viruses that infect bacteria are called bacteriophages. They were discovered by Twort. They are Tadpole shaped. They have DNA as their genetic material. They are distinguished into T – odd phages as well as T – even phages.

Question 2.
What is a taxonomic aid?
Solution:
A taxonomic aid is storage of record of either live or dead specimens of flora or fauna, which helps scientists in taking reference to study classification

Question 3.
Give the classification of man.
Solution:
Common Name – Human
Scientific Name – Homo sapiens
Genera – Homo
Families – Hominidae
Orders – Primata
Classes – Mammalia
Phyla/Division – Chordate

Question 4.
What is a museum? How many kinds of museums are found?
Solution:
Museum in an institution where artistic and educational materials are exhibited to the public. The material available for observation and study is called a collection.
Kinds of Museums:

Art Museum
History Museum
Applied Science Museum
Natural Science Museum

Question 5.
Give a reason for the following.
Bacteria are the Natural Scavengers ‘ (D.Kannada 2006)
Solution:
because they bring about the decomposition of organic debris and clean the earth’s surface.

Question 6.
What is the role of characteristics of living beings in classification?
Solution:
A group of common features of living beings are placed under a common category of classification and when uncommon under a different category. It means more systematic a process for further study, research, protection and recording.

Question 7.
What is the significance of a HERBARIUM?
Solution:
HERBARIUM:- A book, case, or room containing an orderly collection of dried plants is called Herbarium. It develops interest in Nature for the activists in it. It can be used to gain knowledge and be updated about plants and their scientific names and even compare various samples. It is a small scale it can be proactive to do. One can make projects too from it for schools, colleges and research institutions.

Question 8.
Explain the role of blue-green algae in soil fertility.
Solution:
Blue-green algae like Nostoc, Anabaena fix atmospheric nitrogen. Heterocyst contains nitrogens enzyme that helps in nitrogen fixation. Nitrogen-fixing blue-green algae are inoculated in the rice field to increase soil fertility.

LONG ANSWER QUESTIONS

Question 1.
Write a short note on Binomial Nomencia? ture and guidelines for Binomial nomenclature.
Solution:
Binomial Nomenclature was introduced by Carolus Linnaeus. In this method every organism is given a scientific name, which has two parts, the first is the name of the genus (generic name) and the second is the name of the species (specific epithet) e.g.: Homo sapiens In the above examples, Homo is a generic name, while sapiens is the name of the species belonging to Homo.

Guidelines:

scientific names are generally in Latin or derived from Latin irrespective of their origin
The scientific names are written in italics or underlined (when handwritten)
The first word denotes the name of the genus and the second word denotes the specific epithet
The generic name starts with a capital letter, while the specific name starts with a small letter (If a specific name starts with a capital letter it denotes the name of a person or place)
The name of the author is written in an abbreviated form after the specific name. e.g.: Homo sapiens Linn.

Question 2.
What is the difference between living and nonliving?
Solution:
Question 3.
Explain the binomial system of nomenclature.
Solution:
Binomial nomenclature system was developed by Linnaeus. Binomial nomenclature is the system of providing organisms with appropriate and distinct names consisting of two words, first generic and second specific. The first or 4.

generic word is also called genus. It is like a noun and its first letter is written in capital form.The second word or specific epithet represents the species.
It is like an adjective. Its first letter is written in small form except occasionally when it denotes a person or place. The two word name is appended with the name of the taxonomist who discovered the organism and provided with its scientific name, e.g., Ficus bengalensis L., Mangifera indica Linn, The name of taxonomist can be written in full or in abbreviated form.
There are several technical names which have three words, e.g., Homo sapien sapiens, Acacia nilotica indica, Gerilla gorilla. Here the first word is generic, the second specific while the third word represents variety (mostly in botanical literature) or subspecies (mostly in zoological literature).
If the same scientific name is to be written time and again, the name of the genus can be abbreviated, e.g., F. bengalensis.

Question 4.
What is the role of zoological parks in wildlife conservation?
Solution:

In the early stages, the zoological parks were considered as places of relaxation and enjoyment for public, however, there has been a change in the objective of the purposefulness of these parks.
The establishment of zoological parks help in providing knowledge about different native and exotic wild mammals, birds, reptiles, fish and flora to the public in general and school children in particular.
Since the key to wildlife conservation lies in the education of the masses and the involvement of voluntary organisations, zoological parks are very useful in spreading knowledge on the wildlife wealth of the country.
These are also important centres for organising seminars, training and researches on the management of wildlife species and for study of their social behaviour, breeding and ecological species.

We hope the NCERT Solutions for Class 11 Biology at Work Chapter 1 The Living World, help you. If you have any query regarding NCERT Solutions for Class 11 Biology at Work Chapter 1 The Living World, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration

January 5, 2022June 18, 2021 by Raju

NCERT Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration

These Solutions are part of NCERT Solutions for Class 11 Biology. Here we have given NCERT Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration.

Question 1.
Define the following:
(a) Exocrine glands
(b) Endocrine glands Hormones
Solution:
(a) Glands with duct is known as an exocrine gland. They secrete their secretions through ducts. Eg: Pancreas.
(b) Gland without duct is known as an endocrine gland. They directly secrete their secretions. Eg: Pituitary gland.
(c) Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts. Eg: thyroxine.

Question 2.
Diagrammatically indicate the location of the various endocrine glands in our body.
Solution:

Question 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-ITract
Solution:
(a) Hypothalamus: Gonadotrophic releasing hormone (GnRH), somatostatin.
(b) Pituitary: Growth hormone, prolactin, thyroid-stimulating hormone, luteinizing hormone and follicle stimulating hormone, oxytocin, vasopressin.
(c) Thyroid: triiodothyronine (T₃) and tetraiodothyronine (T₄).
(d) Parathyroid: Parathyroid hormone.
(e) Adrenal: Adrenaline or epinephrine and noradrenaline or norepinephrine.
(f) Pancreas: Insulin and glucagon.
(g) Testis: A group of androgens mainly testosterone.
(h) Ovary: Estrogens and progesterone.
(i) Thymus: Thymosins.
(j) Atrium: Atrial Natriuretic factor (ANF)
(k) Kidney: Erythropoietin.
(l) G-I tract: Gastrin, secretin, cholecystokinin (CCK).

Question 4.
Fill in the blanks:
Hormones Target gland
(a) Hypothalamic hormones ……………….
(b) Thyrotrophin (TSH) ………………
(c) Corticotrophin (ACTH) ………………
(d) GonadobTjpfains(LH,FSH) ……………….
(e) MeIanotrophin(MSH) ………………..
Solution:
(a) Anterior pituitary and posterior pituitaiy.
(b) Thyroid glands
(c) Adrenal cortex
(d) Gonads (testis and ovary)
(e) Pituitary

Question 5.
Write short notes on the functions of the following hormones:
(a) Parathyroid hormone (PTH)
(b) Thyroid hormones
(c) Thymosins
(d) Androgens
(e) Estrogens
(f) Insulin and Glucagon
Solution:
(a) The secretion of PTH is regulated by the circulating levels of calcium ions. Parathyroid hormone (PTH) increases the Ca²⁺ levels in the blood. PTH acts on bones and stimulates the process of bone resorption. PTH also stimulates reabsorption of Ca²⁺ by the renal tubules and increases Ca²⁺ absorption from the digested food. PTH is a hypercalcemic hormone, i.e., it increases the blood Ca²⁺ levels. Along with TCT, it plays a significant role in calcium balance in the body.

(b) Thyroid hormones play an important role in the regulation of the basal metabolic rate. These hormones also support the process of red blood cell formation. Thyroid hormones control the metabolism of carbohydrates, proteins, and fats. Maintenance of water and electrolyte balance is also influenced by thyroid hormones. The thyroid gland also secretes the protein hormone thyrocalcitonin (TCH) which regulates blood calcium levels.

(c) Thymosins play a major role in the differentiation of T – lymphocytes, which provide cell-mediated immunity. In addition, thymosins also promote the production of antibodies to provide humoral immunity.

(d) Androgens regulate the development, maturation and functions of the male accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland, urethra etc. These hormones stimulate muscular growth, growth of facial and axillary hair, aggressiveness, low pitch of voice etc. Androgens play a major stimulatory role in the process of spermatogenesis and act on the central neural system and influence male sexual behaviour. These hormones produce anabolic effects on protein and carbohydrate metabolism.

(e) Estrogens produce wide-ranging actions such as stimulation of growth and activities of female secondary sex organs, development of growing ovarian follicles, appearance of female secondary sex characters, mammary gland development. Estrogen also regulate female sexual behaviour.

(f) Glucagon is a peptide hormone, and plays an important role in maintaining normal blood glucose levels. Glucagon acts mainly on the liver cells and stimulates glycogenolysis resulting in increased blood sugar. In addition, this hormone stimulates the process of gluconeogenesis which also contributes to hyperglycemia. Glucagon reduces cellular glucose uptake and utilisation. Thus, glucagon is a hyperglycemic hormone.

Insulin is a peptide hormone, which plays a major role in the regulation of glucose homeostasis. Insulin acts mainly on hepatocytes and adipocytes and enhances cellular glucose uptake and utilisation. As a result, there is a rapid movement of glucose from blood to hepatocytes and adipocytes resulting in decreased blood glucose levels (hypoglycemia). Insulin also stimulates conversion of glucose to glycogen in the target cells. The glucose homeostasis in the blood is thus maintained jointly by the two insulin and glucagons.

Question 6.
Give example(s) of:
(a Hyperglycemic hormone and hypoglycemic hormone
(b Hypercalcemic hormone
(c) Gonadotrophic hormones
(d Progestational hormone
(e) Blood pressure lowering hormone
(f) Androgens and estrogens
Solution:
(a) Glucagon and insulin
(b) Parathyroid hormone
(c) LH and FSH
(d) Progesterone
(e) Atrial Natriuretic Factor (ANF)
(f) Testosterone and estradiol

Question 7.
Which hormonal deficiency is responsible for the following:
(a) Diabetes mellitus
(b) Goitre
(c) Cretinism
Solution:
Diabetes mellitus: Insulin deficiency.
Goiter: Deficiency of thyroid hormones due to deficiency of iodine.
Cretinism: Deficiency of thyroid hormones during childhood.

Question 8.
Briefly mention the mechanism of action of FSH.
Solution:
Follicle-stimulating hormone (FSH) and LH Stimulate gonadal activity. In males, FSH and androgens regulate spermatogenesis. In females, FSH is responsible for the growth and development of the ovarian follicles, maturation of egg, and secretion of estrogens

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

VERY SHORT ANSWER QUESTIONS

Question 1.
Give two examples of endocrine glands.
Solution:
Examples of endocrine glands are
(i) pituitary gland
(ii) pineal gland.

Question 2.
Which gland secretes glucagon?
Solution:
Pancreas secretes glucagon.

Question 3.
What is the location of the pituitary gland?
Solution:
The pituitary gland is located in a bony cavity called Sella tursica and is attached to the hypothalamus by a stalk.

Question 4.
Which hormone is secreted by pars intermedia?
Solution:
Pars intermedia secretes melanocyte-stimulating hormone (MSH).

Question 5.
Which hormone is secreted by the pineal gland?
Solution:
Pineal gland secretes melatonin hormone.

Question 6.
Name one disorder caused by hyperfunctioning of the pituitary.
Solution:
Gigantism caused by hyperfunctioning of the pituitary.

Question 7.
How many lobes does the thyroid gland have?
Solution:
The thyroid gland is composed of two lobes which are located on either side of the trachea.

Question 8.
Which gland produces the hormone called thyrocalcitonin (TCT) which regulates the blood calcium levels?
Solution:
Thyroid gland secretes a protein hormone called thyrocalcitonin (TCT) which regulates the blood calcium levels.

Question 9.
Name the organ which secretes progesterone.
Solution:
Ovary secretes progesterone.

Question 10.
Name two hormones of pancreas.
Solution:
Glucagon and insulin are two hormones of pancreas.

Question 11.
Which gland secretes somatostatin?
Solution:
Hypothalamus secretes somatostatin.

Question 12.
Which complex is formed during the binding of hormone to a receptor ?
Solution:
Hormone-receptor complex is formed during the binding of a hormone to a receptor.

Question 13.
Name one hormone secreted by gastro-intestinal tract.
Solution:
Gastrin is secreted by gastro-intestinal tract.

Question 14.
Which hormone is secreted by testes and write the function of hormone also.
Solution:
Testosterone is secreted by testes. It controls growth and development of male secondary
v-sexual characters.

Question 15.
What are membrane bound receptors?
Solution:
Hormone receptors that are present on the cell membrane of the target cells are called membrane bound receptors.

Question 16.
How many types of cells are present in Islets of Langerhans?
Solution:
There are two types of cells present in Islets of Langerhans which are a-cells and P-cells.

Question 17.
Why is oxytocin called as birth hormone ?
Solution:
Oxytocin stimulates the contraction of smooth muscles of uterus and facilitates the child birth.

Question 18.
Why is vasopressin known as antidiuretic hormone?
Solution:
Vasopressin stimulates the reabsorption of water and electrolytes and reduces the loss of water through urine, known as diuresis. Hence it is called as anti-diuretic hormone.

Question 19.
What is cretinism ?
Solution:
Cretinism is reduction in body growth as well as underdevelopment of brain resulting in various structural and functional defects mainly due to deficiency of thyroxine (hypothyroidism) in infants and children.

Question 20.
Which hormone interacts with membrane bound receptor and does not normally enter the target cell?
Solution:
Follicle stimulating hormone interacts with membrane bound receptor and does not normally enter the target cell.

Question 21.
Which hormone opposes parathormone?
Solution:
Thyrocalcitonin opposes parathormone.

Question 22
Which hormone is known as anti-aging hormone?
Solution:
Melatonin, secreted by pineal gland is known as anti-ageing hormone.

SHORT ANSWER QUESTIONS

Question 1.
Discuss the location and function of parathyroid hormone.
Solution:
There are four parathyroid glands present on the back side of thyroid glands, two on each of the lobes of the thyroid gland.
The parathyroid glands secrete parathyroid hormone (PTH), a peptide hormone. Parathyroid hormone (PTH) increases the Ca2+ levels in the blood. PTH acts on bones and stimulates the process of bone resorption (dissolution/ demineralization. PTH also stimulates reabsorption of Ca2+ by the renal tubules and increases Ca2+ absorption from the digested food.

Question 2.
What is progesterone? Name two important functions of progesterone.
Solution:
Progesterone is a steroid hormone secreted by ovary.
Functions of progesterone are as follows:
• It supports pregnancy.
• It acts on mammary glands and stimulates the formation of alveoli (sac-like structures which store milk) and milk secretion.

Question 3.
Name the principal mineralocorticoid secreted by adrenal cortex. Give its any two functions
Solution:
Aldosterone is main mineralocorticoid secreted by adrenal cortex.
Functions of aldosterone are :
• It stimulates reabsorption of Na⁺ and water.
• It stimulates excretion of K⁺ and phosphate ions.

Question 4.
What are hormone receptors? What are the modes of their action ?
Solution:
Receptors are specific proteins present on the surface of target cell which bind with hormones and produce physiological changes in cell. Their are two types of hormone receptors which are discussed below:
NCERT Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration 2

Question 5.
Name the gland that functions as a biological clock in our body. Where is this gland located ? Name its one secretion.
Solution:
Pineal gland functions as a biological clock in our body.

It is located on the dorsal side of the forebrain.
It secretes melatonin.

Question 6.
Where is thymus gland located in the human body ? Describe its role.
Solution:
The thymus gland is a lobular structure located on the dorsal side of the heart and the aorta.
– It secretes hormone thymosin, which has a stimulating effect on the immune system.
– Thymosin promotes proliferation and maturation of T-lymphocytes.

Question 7.
How does insulin act on high glucose content in the blood in a normal human body ?
Solution:
• Insulin is a peptide hormone, which plays a major role in the regulation of glucose homeostasis. Insulin acts mainly on hepatocytes and adipocytes (cells of adipose tissue), and enhances cellular glucose uptake and utilisation. As a result, there is a rapid movement of glucose from blood to hepatocytes and adipocytes resulting in decreased blood glucose levels (hypoglycemia)
• Insulin also stimulates conversion of glucose to glycogen (glycogenesis) in the target cells.
• The glucose homeostatasis in blood is thus maintained jointly by the two enzyme insulin and glucagon.

Question 8.
What is corpus luteum ? Name its one secretion.
Solution:
Corpus luteum is the structure formed by the ruptured ovarian follicles after ovulation.
– It mainly secretes the hormone progesterone.

Long ANSWER QUESTIONS

Question 1.
Explain briefly the structure and functions of middle ear.
Solution:
Calcitonin (from thyroid) : Essential for maintaining bone strength as it does not allow calcium mobilisation from bones. It also lowers plasma level of calcium ifthe same is high. Parathormone: Low level of parathormone secretion decreases blood plasma level of calcium, prevents reabsorption from bones and causes tetany. Higher levels of parathormone (PTH) increase plasma level of Ca²⁺ by withdrawal from bones resulting in (i) Inflammation and tenderness in bones due to dissolution of calcium from bones, formation of cavities which get plugged with fibrous nodes and cysts (osteitis fibrosa cystica) making bones soft deformed and prone to fracture, (ii) Excess plasma calcium gets deposited in various parts of body which often leads of obstruction and death.

Question 2.
Draw a well labelled diagram showing the location of parathyroid gland. Discuss the function/(s) of parathormone and hyperparathyroidism.
Solution:
NCERT Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration 3
Function : Parathormone (Collip’s hormone) regulates the metabolism of calcium and phosphate between blood and other tissue.
(i) Hyperparathyroidism : It leads to demineralisation resulting in softing and bending of bones. An excess of parathormone cause osteoporosis and kidney stones.

Question 3.
What are the causes for following disorders?
(a) Acromegaly
(b) Cretinism
(c) Gigantism
(d) Myxoedema
Solution:
Disorders and their causes.
(a) Acromegaly (Acro-extremity, megaly – large) – It is caused by excess secretion of growth hormone after adulthood is reached.
(b) Cretinism : It is caused by deficiency of thyroid hormone in infant.
(c) Gigantism : It is caused by excess of growth hormone from early age.
(d) Myxoedema: It is caused by deficiency of thyroid hormone in adults.

We hope the NCERT Solutions for Class 11 Biology at Work Chapter 22 Chemical Coordination and Integration, help you. If you have any query regarding NCERT Solutions for Class 11 Biology at Work Chapter 22 Chemical Coordination and Integration, drop a comment below and we will get back to you at the earliest.

NCERT Exemplar Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration

January 5, 2022September 10, 2018 by Raju

NCERT Exemplar Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration

These Solutions are part of NCERT Solutions for Class 11 Biology. Here we have given NCERT Exemplar Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration.

VERY SHORT ANSWER QUESTIONS

Question 1.
Which of the two adrenocortial layers, zona glomerulosa and zona reticularis lies outside enveloping the other?
Solution:
Zona glomerulosa envelops zona reticularis from the outside.

Question 2.
What is erythropoiesis? Which hormone stimulates it?
Solution:
The process of formation of RBC is Erythropoiesis. Erythropoietin, a Peptide hormone secreted from the juxtaglomerular cells of kidney stimulates erythropoiesis.

Question 3.
Name the only hormone secreted by pars intermedia of the pituitary gland.
Solution:
The only hormone secreted by Pars intermedia ^ of pituitary gland is Melanocyte Stimulating hormone (MSH). This hormone causes dispersal of pigment granules in the pigment cells, which darken the colour in certain animals like fishes and amphibians.

Question 4.
Name the endocrine gland that produces calcitonin and mention the role played by this ‘ hormone.
Solution:
Calcitonin/thyrocalcitonin linear polypeptide hormone comprising of 32 amino acids that is produced in humans primarily by the parafollicular cells of the thyroid gland. It checks excess Ca2+ and phosphate in plasma by • decreasing mobilization from bones.

Question 5.
Name the hormone that helps in cell-mediated immunity.
Solution:
The hormone thymosin plays a maj or role in the development and differentiation of T-lymphocytes, which provide cell-mediated immunity.

Question 6.
A patient complains of constant thirst, excessive 3. passing of urine and low blood pressure. When the doctor checked the patients’ blood glucose and blood insulin level, the level were normal or 4. slightly low. The doctor diagnosed the condition a diabetes insipid us. But he decided to measure one more hormone in patients blood. Which hormones does the doctor intend to measure?
Solution:
The doctor intends to measure the hyperglycaemia hormone, and its action is opposite to that of insulin Excess of glucose in blood suppresses the secretion of glucose, whereas fall in glucose level enhance glucose production.

Question 7.
Correct the following statements by replacing the term underlined.
(a) Insulin is a steroid hormone.
(b) TSH is secreted from the corpus leteum.
(c) Tetraiodothyronine is an emergency hormone.
(d) the pineal gland is located on the anterior part of the kidney.
Solution:
(a) Insulin is a peptide hormone
(b) TSH is secreted from the pars distalis region ofpitutary.
(c) Adrenaline is an emergency hormone.
(d) The adrenal gland is located on the anterior part of the kidney.

Question 8.
Match the following columns.
Column I Column II
A. Oxytocin 1. Amino acid derivative
B. Epinephrine 2. Steroid
C. Progesterone 3. Protein
D. Growth hormone 4. Peptide
Solution:
The correct matching is
Column I Column II
A. Oxytocin – Peptide
B. Epinephrine – Amino acid derivative
C. Progesterone – Steroid
D. Growth hormone – Protein

SHORT ANSWER QUESTIONS

Question 1.
What is the role-played by luteinising hormones in males and females respectively.
Solution:

LH and FSH stimulate activity of gonads and hence are called gonadotropins.
Luteinising hormone (LH) in males stimulates the synthesis and secretion of hormones called androgens from testis. Androgens along with FSH (Follicle Stimulating Hormone) regulate spermatogenesis.
LH induces ovulation of fully mature follicles in females and maintains the corpus luteum, formed from the remnants of the graafian follicles after ovulation. This secretes progesterone.

Question 2.
George comes on a vacation to India from US. The long journey disturbs his biological system and he suffers from jet lag. What is the cause of his discomfort?
Solution:

The melatonin hormone secreted by the pineal gland is also called as ‘sleep hormone’ as it promotes sleep-wake cycle.
The disruption of the body clock as it is out of synchronisation because of the unfamiliar time zone of the destination causes Jet lag. The body experiences different patterns of light and dark conditions than it is normally used to, this disrupts the natural sleep-wake cycle.
A hormone that plays a key role in body rhythms and causes jet lag is melatonin. Eyes perceive darkness after the sun sets and alert the hypothalamus to begin releasing melatonin, which promotes sleep. Conversely, when the eyes perceive sunlight, they induce the hypothalamus to with hold melatonin prodtiction.
The hypothalamus however cannot readjust its schedule instantly and it may take several days, to overcome this problem.

Question 3.
Inflammatory responses can be controlled by a certain steroid. Name the steroid, its source and also its other important functions.
Solution:

Glucocorticoids cortisol in particular, produce anti-inflammatory reactions and suppress the immune response.
The middle zone, in adrenal cortex which is the widest of three zones called zona fasciculata is the source for glucocorticoids.
The glucocorticoids as the name suggests affect carbohydrate metabolism and metabolism of proteins and fats.
They stimulate gluconeogenesis, lipolysis and proteolysis. They also inhibit utilization of amino acid and cellular uptake. Cortisol is also called stress hormone as it copes with stress.

Question 4.
Old people have weak immune system. What could be the reasons?
Solution:

A major role in the development of the immune system is played by thymus.
The thymus gland is a lobular structure located on the dorsal side of the heart and the aorta. It is derived from the endoderm of the embryo. Thymus secretes a hormone named thymosin which stimulates the development of white blood cells (WBCs), involved in producing immunity.
In old individuals, thymus is degenerated which results in decreased production of thymosin. The immune system as a result becomes weak, in old people.

LONG ANSWER QUESTIONS

Question 1.
Calcium plays a very important role in the formation of bones. Write on the role of endocrine glands and hormones responsible for maintaining calcium homeostasis.
Solution:
The hormones and endocrine glands that are responsible for maintaining calcium
homeostasis, are thyroid and parathyroid glands j and their associated hormones are calcitonin and Parathyroid Hormone (PTH).
(i) Parathyroid glands – These glands developed from the endoderm of the embryo. The cells of parathyroid glands are
of two types – chief cells and oxyphil cells. The chief cells of the parathyroid glands secrete parathyroid hormone (PTH).
This hormone (PTH) is involved in regulation of calcium and phosphate balance between the blood and other tissue. It mobilises the release of calcium into the blood from bones. PTH increases reabsorption of calcium by the body organs like intestine and kidneys.
(ii) Thyroid gland – It is the largest endocrine gland located anterior to the thyroid cartilage of the larynx in the neck.

This gland plays a major role in maintaining calcium homeostasis. It releases thyrocalcitonin hormone produced by the parafollicular cells, also called, ‘C’ cells. This hormone is secreted when the calcium level in blood gets high.

It is a 32 amino acid peptide hormone that lowers the calcium level by suppressing release of calcium ions from the bones. Calcitonin thus has an action opposite to that of the parathyroid hormone in calcium homeostasis.
NCERT Exemplar Solutions for Class 11 Biology Chapter 22 Chemical Coordination and Integration 1

Question 2.
Hypothalamus is a supper master endocrine gland. Elaborate.
Solution:
Hypothalamus is a minor but extremely important part of the diencephalon that is involved in the mediation of endocrine, autonomic and behavioural fiinction.

It consists of several groups of neuro secretory cells called nuclei which produce hormones. Hypothalamus provides anatomical connection between the nervous and endocrine system. It controls the release of major hormones by

hypophysis which include :
(i) Growth Hormone Releasing Hormone stimulates the anterior lobe of the pituitary gland to release growth hormone or somatostatin.
(ii) MSH Releasing Hormone stimulates the intermediate lobe of the pituitary gland to secrete Melanocyte Stimulating Hormone (MSH)
The hormones released from hypothalamus are involved in the processes like temperature regulation, control of water balance in body, sexual behaviour and reproduction, control of daily cycles in physiological state, behaviour and mediation’ of emotional response hypothalamus is thus called as super master endocrine gland of body.
(iii) Prolactin Releasing Hormone (PRH) stimulates the anterior lobe of the pituitary gland to secret prolactin.
(iv) Gonadotropin Releasing Hormone stimulates the anterior lobe of the pituitary gland to release gonadotropic hormones (FSHandlH).
(v) Thyrotropm Releasing Hormone (TRH) stimulates the anterior lobe of pituitary gland to release Thyroid Stimulating Hormone (TSH).
(vi) Adrenocorticotrophic releasing Hormone (ARH) stimulates the anterior lobe of pituitary gland to secrete Adrenocorticotropic Hormone (ACTH). ACTH stimulates the synthesis and secretion of steroid hormones called glucocorticoids by adrenal glands.
The hormones released from hypothalamus are involved in the processes like temperature regulation, control of water balance in body, sexual behaviour and reproduction, control of daily cycles in physiological state, behaviour and mediation of emotional responses. Hypothalamus is thus called as super master endocrine gland of body.

We hope the NCERT Exemplar Solutions for Class 11 Biology at Work Chapter 22 Chemical Coordination and Integration, help you. If you have any query regarding NCERT Exemplar Solutions for Class 11 Biology at Work Chapter 22 Chemical Coordination and Integration, drop a comment below and we will get back to you at the earliest.

NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination

January 5, 2022September 10, 2018 by Raju

NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination

These Solutions are part of NCERT Exemplar Solutions for Class 11 Biology. Here we have given NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination.

VERY SHORT ANSWER QUESTIONS

Question 1.
Rearrange the following in the correct order of involvement in electrical impulse movement.
Solution:
The correct order of involvement in electrical impulse movement is as follows:
(i) Dendrites
(ii) Cell body
(iii) Axon
(iv) Axon terminal (vi) Synaptic knob
NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination 1.1

Question 2.
Which cells of the retina enable us to see coloured objects around us?
Solution:
Cone cells present in unable us to see the colours. There are three types of cones which possess their own characteristic photopigments that respond to red, green and blue light.

Question 3.
Arrange the following in the order of reception and transmission of sound wave from the ear drum. Cochlear nerve, external auditory canal, ear drum, stapes, incus, malleus, cochlea.
Solution:
The reception and transmission of sound waves occurs in following order – External Auditory canal —» Eardrum —» Malleus —> Incus —> Stapes —>• Cochlea —> Cochlear nerve

Question 4.
During resting potential, the axonal membrane is polarized, indicate the movement of H-ve and -ve ions leading to polarisation diagrammatically.
Solution:
NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination 4.1

Question 5.
Our reaction like aggressive behaviour, use of abusive words, restlessness etc. are regulated by brain, name the parts involved.
Solution:
Functions as aggressive behaviour, use or abusive words, restlessness, etc. The inner part of cerebral hemispheres and a group of associated deep structures called limbic lobe or limbic system along with hypothalamus are involved.

Question 6.
What do grey and white matter in the brain represent?
Solution:
A major component of CNS is Grey matter consisting of neutronal cell bodies, dendrite, unmyelinated axons, glial cells and capillaries. White matter is also a component of CNS and consists mostly of gilal cell and myelinated axons.

Question 7.
Where is the hunger centre located in human brain?
Solution:
Hypothalamus in human brain contains many centres which control urge for eating and drinking.

Question 8.
Complete the statement by choosing appropriate match among the following.
NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination 8.1

Solution:
A. -> (3), B. -> (4), C. -> (2), D. -> (1)
NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination 8.2

SHORT ANSWER QUESTIONS

Question 1.
The major parts of the human neural system is depicted below. Fill in the empty boxes with appropriate
words.
NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination s1.1

Solution:
The major parts of the human neural system is filled in the boxes with appropriate words
NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination s1.2

Question 2.
Neuron system and computers share certain common features. Comment in five lines.
Solution:
In various organs the sensory neurons is present to sense the environment and extend the message to the brain. So, it is equivalent to input device of computers.
Brain acts as the CPU, or Central Processing Unit. The information gathered by sensory neurons is processed by brain and it gives command to the concerned organ to act accordingly. This message is taken or conveyed by motor neurons which act as output devices.

Question 3.
What is the function described to Eustachian tube?
Solution:
The eustachian tube forms connection between the middle ear cavity with the pharynx. It helps in equalising the pressure on either sides of the ear drum. At the pharyngeal opening of the eustachian tube there is a valve which normally remains closed.
The valve opens during yawning, swallowing and during an abrupt change in altitude, when air enters or leaves the tympanic cavity to v equalise the pressure of air on the two sides of the tympanic membrane.

LONG ANSWER QUESTIONS

Question 1.
Explain the process of the transport and release of neurotransmitter with the help of a labelled diagram showing a complete neuron, axon terminal and synapse.
Solution:
The three main parts of a neuron include the
(i) Cell body
(ii) Axon
(iii) Dendrites
Stimulus or nerve impulse of any kind passes from one neuron to another via axon. This nerve impulse is wave of bioelectric/electrochemical disturbance that passes along the neuron during conduction of an excitation.
NCERT Exemplar Solutions for Class 11 Biology Chapter 21 Neural control and co-ordination l1.1

Within a synapse transport and release of a neuro transmiter occurs.
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.
Upon arrival of an impulse (action potential) at the axon terminal, it stimulates the movement of the synaptic vesciles towards the membrane, where they fuse with the plasma membrane and 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, that can generate a new action potential in the

Question 2.
Explain the structure of middle and internal ear with the help of diagram.
Solution:
Ears are a part of statoacoustic organ meant for balancing and hearing the external ear in most mammals is a heap of tissue also called pinna. It is a part of auditory system.

The human ear consists of three main parts external ear, middle, ear and internal ear.

Structure of Middle Ear

The middle ear consists of three bones or ossicles-the malleus (hammer), incus (anvil and stapes (stir-up).
These bones are attached to one another in a chain-like manner.
The malleus is attached to the tympanic membrane and the stapes is attached to the oval window (a membrane beneath the stapes) of cochlea.
These three ossicles increase the efficiency of transmission of sound waves to the inner ear.
The middle ear also opens into the eustachian tube, which connects with the pharynx and maintains the pressure between the middle ear and the outside atmosphere.

Structure of Internal Ear

Thd inner ear consists of a labyrinth of chambers filled with fluid within temporal bone of the skull. The labyrinth consists of two parts the bony and membranous labyrinth. The bony labyrinth is a series of channels.
Membranous labyrinth lies inside these channels which is surrounded by a fluid called perilymph. The membranous labyrinth is filled with a fluid called endolymph. The coiled portion of the labyrinth is called cochlea.
The cochlea has two large canal separated by a small cochlear duct (scala media). An upper vestibular canal (scala vestibuli) and a lower tympanic canal (scala tympani). The vestibular and tympanic canals contain perilymph and the cochlear duct is filled with endolymph.
The wall of membranous labyrinth comes in contact with the fenestra ovalis at the base of scale vestibuli while the fenestra rotunda.

We hope the NCERT Exemplar Solutions for Class 11 Biology at Work Chapter 21 Neural control and co-ordination, help you. If you have any query regarding NCERT Exemplar Solutions for Class 11 Biology at Work Chapter 21 Neural control and co-ordination, drop a comment below and we will get back to you at the earliest.

NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement

January 5, 2022September 10, 2018 by Raju

NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement

These Solutions are part of NCERT Exemplar Solutions for Class 11 Biology. Here we have given NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement.

VERY SHORT ANSWER QUESTIONS

Question 1.
Name the cells/ tissues in human body which
(a) exhibit amoeboid movement
(b) exhibit ciliary movement
Solution:
(a) Macrophages and leucocytes in blood exhibit amoeboid movement. Cytoskeletal elements like microfilaments are also involved in amoeboid movement.
(b) Ciliary Movement occurs mostly in the internal organs, lined by the ciliated epithelium, e.g., cilia in trachea helps in removing dust particle and foreign substances inhaled along with atmospheric air.
Passage of ova through the female reproductive tract is also facilitated by the ciliary movement. This is due to the presence of ciliated epithelium in the Fallopian tube.

Question 2.
Locomotion requires a perfect coordinated activity of muscular …… systems.
Solution:
Locomotion requires a prefect coordinated activity of muscular, skeletal and neural systems.

Question 3.
Sarcolemma, sarcoplasm and sarcoplasmic reticulum refer to particular type of cell in our body. Which is this cell and to what parts of that cell do these names refer to?
Solution:
Muscle fibre is lined by the plasma membrane called sarcolemma. Muscle fibre is a syncitium because sarcoplasm (the cytoplasm) of muscle fibre contains number of nuclei and sarcoplasmic reticulum is the endoplasmic reticulum of the muscle fibre and is the store house of calcium ions.

Question 4.
Label the different components of actin filament in the diagram given below
NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement 4.1v
Solution:
Each actin filament is made of two ‘F (filamentous) actins helically wound to each other and each ‘F’ actin is a polymer of monomeric ‘G’ (globular) actins.
The different components of action filament can be represented as
NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement 4.2v

Question 5.
What is the difference between the matrix of bones and cartilage?
Solution:
Difference between the matrix of ones and cartilage
NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement 5.1v

Question 6.
Which tissue is affected by mysthenia gravis? What is the underlying cause.
Solution:
Myasthenia gravis is autoimmune disorder of skeletal muscle, which affects neuromuscular junction, that leads to fatigue, weakening and paralysis of the skeletal muscle.

Question 7.
How do our bone joints function without grinding noise and pain?
Solution:
The presence of synovial fluid, between articulating surface of the two bones enclosed within synovial cavity of synovial joints to enables out joints to function without grinding noise and pain.

Question 8.
Give the location of a ball and socket joint in a human body.
Solution:
In human body Ball and socket joint are present between humerus and pectoral girdle. These joints allows free movement of bone in all direction. E.g., shoulder joints (humerus bone in socket of pectoral girdle) and

SHORT ANSWER QUESTIONS

Question 1.
With respect to rib cage, explain the following
(a) bicephalic ribs
(b) true ribs
(c) floating ribs
Solution:
There are 12 pairs of ribs. Each rib consist of a thin flat bone dorsally connected to the vertebral column and ventrally to the sternum.
(a) Bicephalic ribs each rib has two articulating surfaces on its dorsal end hence, are called as bicephatic ribs.
(b) The first seven pairs of ribs are true ribs. These ribs are dorsally attached to the thoracic vertebrae and ventrally connected to the sternum with the help of hyaline cartilage.
(c) The last two pair (11th and 12th) of ribs are not connected ventrally to the sternum therefore, called as floating ribs.
NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement 1.1s

Question 2.
Exchange of calcium between bone and ^extracellular fluid takes place under the
influence of certain hormones
(a) What will happen if of Ca²⁺ is in extracellular fluid?
(b) What will happen if very less amount of Ca²⁺ is in the extracellular fluid?
Solution:
Parathyroid and thyroid glands, function under the feed back control of blood calcium
(a) More Ca²⁺ concentration in extracellular fluid is associated with hyperparathyroidism. It causes demineralisation, resulting in softening and bending of the bones. This condition leads to osteoprosis.
(b) Very less amount of Ca²⁺ in extracellular fluid is associated with hypoparathyroidism. This increases the excitability or nerves and muscles, causing cramps, sustained contraction of the muscles of larynx, face, hands and feet. This disorder called parathyroid tetany or hypercalcemic tetany.

Question 3.
Rahul exercises regularly by visiting a gymnasium. Of late he is gaining weight. What could be the reasons? Choose the correct answer and elaborate.
(a) Rahul has gained weight due to accumulation of fats in body
(b) Rahul has gained weight due to increased muscle and less of fat
(c) Rahul has gained weight because his muscle shape has improved
(d) Rahul has gained weight because he is accumulating water in the body
Solution:
(b) Rahul has gained weight because the shape of his muscle has changed. Regular exercise increases the body muscle. There is an enlargement of muscles due to increase in the amount of sarcoplasm and mitochondria and the strength he to developed led him to gain the mass and size of body muscle and reduction in fat content.

Question 4.
Radha was running on a treadmill at a great speed for 15 minutes continuously. She stopped the treadmill and abruptly came out. For the next few minutes, she was breathing heavily/fast. Answer the following questions.
(a) What happened to her muscles when she did strenuously exercised?
(b) How did her breathing rate change?
Solution:
(a) Her muscles got fatigues due to continuous exercise because of the accumulation of lactic acid within skeletal muscles. Pain is also often experienced in the fatigued muscles.
(b) Her breathing rate changes from normal to
high as during as her body muscles require thus oxygen for the ATP production, than the normal value, her breathing thus enhances, to take most oxygen from the atmosphere.

Question 5.
Write a few lines about gout.
Solution:
Gout is a disease caused due to improper purine metabolism. It causes accumulation of uric acid and its crystals in the joints. The level of uric acid and crystals of its salts get raised in blood causing their accumulation in the joint to which causes gouty arthritis. The excess of urates in blood can also lead to the formation stones in the kidneys.

Question 6.
What are the points for articulation of pelvic and pectoral girdles?
Solution:

Each half of the pectoral girdle consist of a clavicle and a scapula.
The dorsal flat, triangular body of scapula has a slightly elevated ridge called the spine that, projects flat expanded process called the acromion and the clavicle articulating with it.
There a depression below the acromion is called the glenoid cavity which articulates with the head of the humerous to form the shoulder joint.
Pelvic girdle consist of two coxal bones, each formed by the fusioin of three bones, ilium, ischium and pubis. It articulates with femur through a cavity called acetabulum forming thigh joint.

LONG ANSWER QUESTIONS

Question 1.
How does a muscle shorten during its contracting and return to its original form during relaxation?
Solution:
Muscles contract due to formation of cross-bridge between the actin and myosin filament
(i) An ATP molecule j oins the active site on the head of myosin myofilament. These heads contains an enzyme, myosin ATPase along with Ca²⁺ and Mg²⁺ ions that catalyses the break down of ATP.

(ii) The energy is transferred to myosin head which straightens to join an active site on actin myofilament, forming a across-
NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement 1.1l
(iii) The energised cross-bridges move, causing the attached actin filaments to move towards the centre of A-band. The Z-line is also pulled inwards causing shortening of sarcomere, contraction. During contraction A-bands retain the length, while I-bands get reduced.
(iv) The myosin head releases ADP and Pi where relaxes to its low energy state. The head detaches from actin myofilaments when new ATP molecule joins it and cross-bridge are broken.
(v) In the next cycle, the free head cleaves the new ATP. The cycles of cross-bridge formation and breakage is repeated causing further sliding.
NCERT Exemplar Solutions for Class 11 Biology Chapter 20 Locomotion and Movement 1.2l
(vi) After contraction muscle relaxation occurs when the calcium ions are pumped back to the sarcoplasmic cistemae, thus, blocking the sites on actin myofilaments. The Z-line returns to original positions or relaxation.

We hope the NCERT Exemplar Solutions for Class 11 Biology at Work Chapter 20 Locomotion and Movement, help you. If you have any query regarding NCERT Exemplar Solutions for Class 11 Biology at Work Chapter 20 Locomotion and Movement, drop a comment below and we will get back to you at the earliest.