NCERT Solutions for Class 11 Biology in PDF

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NCERT Solutions for Class 11 Biology




Class:11
Subject:Biology
Contents:NCERT Solutions

Table of Contents

NCERT Solutions for Class 11 Biology

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Basic Branches of Biology
  • Taxonomy
    Man has always tried to name and classify the things present in the surrounding according to their utility. This led to extensive collection of knowledge about plants and animals. At present about 1200000 species of animals and about 7 to 8 lakh species of plants are known to us. The branch of biology which deals with the identification and classification of organisms is called Taxonomy.



  • Morphology
    It is the study of external features of organisms. It essentially includes the understanding and interpretation of structure both external and internal.
  • Anatomy
    It is the study of gross internal structure of organs and different parts. It ascertains the identification and similarities of one organism with other organism in the course of studies. Some organism have considerable similarities in external and internal features, where as in some organisms, there is close resemblance in external features but they differ in internal structure. For example – Man, Monkey and Dog have analogy in internal organ system but externally all of them differ from one another.
  • Histology
    The body of various plants and animals are composed of different kinds of organs and organ systems. These organs are formed by special structures called tissues. The tissues are the groups of such cells which are similar in structure, function and origin. Thus the tissues are microscopic structures and can be studied only with the help of microscope. Substantially the microscopic study of internal structure of living organism is called as Histology.
  • Cell Biology
    The body of living beings is composed of one or many cells. The structure, function and division of the cell directly determines the life activities of living beings. All researches or studies related to cell are included under the branch known as Cell Biology. It involves the studies of all kinds of cells and their behaviour.
  • Molecular Biology
    The cell consists of large number of micro and macro molecules such as nucleic acids, proteins, lipids etc. The interaction between these bio-chemical molecules results into life and all these studies of cells at molecular level are included under the branch known as Molecular Biology. It involves the studies of composition and mechanism of synthesis of the biomolecules of cells.
  • Physiology
    Plants and animals perform life processes in a similar fashion. For example digestion, respiration, excretion etc. In addition, plants also perform photosynthesis. All these life activities are the consequences of bio-chemical reactions that occur inside the cell. The detailed study of these reactions is known as Physiology. The study of life processes and functions of plants is called Plant-Physiology. Whereas study related to animals is defined as Animal Physiology. [Read More…]

Table of Contents

Define a taxon. Give some examples of taxa at different hierarchical levels.

Each unit or category of classification is termed as a taxon. It represents a rank. For example, the basic level of classification is species, followed by genus, family, order, class, phylum or division, in ascending order. The highest level of classification is known as kingdom.

Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Viruses are sub-microscopic infectious agents that can infect all living organisms. A virus consists of genetic material surrounded by a protein coat. The genetic material may be present in the form of DNA or RNA.
Most of the viruses, infecting plants, have single stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double stranded RNA or double stranded DNA.
Bacteriophages or viruses infecting bacteria mostly have double stranded DNA. Their protein coat called capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms.
A.I.D.S, small pox, mumps, and influenza are some common examples of viral diseases.

Describe the important characteristics of gymnosperms.

Important features of gymnosperms:
(a) The term gymnosperm refers to plants with naked seeds (gymnos – naked, sperma – seeds), i.e., the seeds of these plants are not enclosed in fruits.
(b) The plant-body ranges from medium to tall trees and shrubs. The giant redwood tree Sequoia is one of the tallest trees in the world.
(c) The root system consists of tap roots. The coralloid roots present in Cycas are associated with nitrogen-fixing cyanobacteria.
(d) The stem can be branched (as in Pinus and Cedrus) or un-branched (as in Cycas).
(e) The leaves can be simple (as in Pinus) or compound (pinnate in Cycas). The leaves are needle-like, with a thick cuticle and sunken stomata. These help in preventing water loss.
(f) Gymnosperms are heterosporous. They bear two kinds of spores – microspores and megaspores.
(g) Flowers are absent. The microsporophylls and megasporophylls are arranged to form compact male and female cones.
(h) Pollination occurs mostly through wind and pollen grains reach the pollen chamber of the ovule through the micropyle.
(i) The male and female gametophytes are dependent on the sporophyte.
(j) The seeds contain haploid endosperms and remain uncovered.

What are the reasons that you can think of for the arthropods to constitute the largest group of the animal kingdom?

The phylum, Arthropoda, consists of more than two-thirds of the animal species on earth. The reasons for the success of arthropods are as follows.
Jointed legs that allow more mobility on land
Hard exoskeleton made of chitin that protects the body
The hard exoskeleton also reduces water loss from the body of arthropods making them more adapted to terrestrial conditions.

Describe the arrangement of floral members in relation to their insertion on thalamus?

Based on the position of the calyx, corolla, and androecium (with respect to the ovary on the thalamus), the flowers are described as hypognous, perigynous, and epigynous.
In hypogynous flowers, the ovary occupies the highest position on the thalamus while other floral parts are situated below it. In such flowers, the ovary is superior
e.g., China rose, mustard etc.
In perigynous flowers, the ovary is situated at the centre and other floral parts are arranged on the rim of the thalamus. The ovary here is said to be half inferior e.g., plum, rose, peach
In epigynous flowers, the thalamus grows around the ovary fusing with its wall. The other floral parts are present above the ovary. Hence, the ovary is said to be inferior
e.g., flowers of guava and cucumber.

What is periderm? How does periderm formation take place in dicot stem?

Periderm is composed of the phellogen, phellem, and phelloderm.
During secondary growth, the outer epidermal layer and the cortical layer are broken because of the cambium. To replace them, the cells of the cortex turn meristematic, giving rise to cork cambium or phellogen. It is composed of thin-walled, narrow and rectangular cells.
Phellogen cuts off cells on its either side. The cells cut off toward the outside give rise to the phellem or cork. The suberin deposits in its cell wall make it impervious to water. The inner cells give rise to the secondary cortex or phelloderm. The secondary cortex is parenchymatous.

Mention briefly about the circulatory system of earthworm.

Earthworms (Pheretima) have closed blood vascular systems, which consists of the heart, blood vessels, and capillaries. The heart pumps blood for circulating it in one direction. Blood is supplied by smaller blood cells to the gut nerve cord and the body wall. Blood glands are present in the 4th, 5th, and 6th segments, which produce blood cells and haemoglobin dissolved in blood plasma. Blood cells in earthworms are phagocytic in nature.

Cell is the basic unit of life. Discuss in brief.

Cells are the basic units of life capable of doing all the required biochemical processes that a normal cell has to do in order to live. The basic needs for the survival of all living organisms are the same. All living organisms need to respire, digest food for obtaining energy, and get rid of metabolic wastes.
Cells are capable of performing all the metabolic functions of the body. Hence, cells are called the functional units of life.

What are gums made of? Is Fevicol different?

Gums are hetero-polysaccharides. They are made from two or more different types of monosaccharides. On the other hand, fevicol is polyvinyl alcohol (PVA) glue. It is not a polysaccharide.

Can there be DNA replication without cell division?

There can be DNA replication without cell division. During cell division, the parent cell gets divided into two daughter cells. However, if there is a repeated replication of DNA without any cell division, then this DNA will keep accumulating inside the cell. This would increase the volume of the cell nucleus, thereby causing cell expansion. An example of DNA duplication without cell division is commonly observed in the salivary glands of Drosophila. The chromosome undergoing repeated DNA duplication is known as polytene chromosome.

Explain pressure flow hypothesis of translocation of sugars in plants.

According to the pressure flow hypothesis, food is prepared in the plant leaves in the form of glucose. Before moving into the source cells present in the phloem, the prepared food is converted into sucrose. Water moves from the xylem vessels into the adjacent phloem, thereby increasing the hydrostatic pressure in the phloem. Consequently, the sucrose moves through the sieve cells of the phloem. The sucrose already present in the sink region is converted into starch or cellulose, thereby reducing the hydrostatic pressure in the sink cells. Hence, the pressure difference created between the source and the sink cells allows sugars to be translocated from the former to the latter. This starch or cellulose is finally removed from the sink cells through active transport.

How are the minerals absorbed by the plants?

The absorption of soil nutrients by the roots of plants occurs in two main phases – apoplast and symplast.
During the initial phase or apoplast, there is a rapid uptake of nutrients from the soil into the free spaces of plant cells. This process is passive and it usually occurs through trans-membrane proteins and ion-channels.
In the second phase or symplast, the ions are taken slowly into the inner spaces of the cells. This pathway generally involves the expenditure of energy in the form of ATP.

Suppose there were plants that had a high concentration of Chlorophyll-b, but lacked chlorophyll-a, would it carry out photosynthesis? Then why do plants have chlorophyll-b and other accessory pigments?

Chlorophyll-a molecules act as antenna molecules. They get excited by absorbing light and emit electrons during cyclic and non-cyclic photophosphorylations. They form the reaction centres for both photosystems I and II. Chlorophyll-b and other photosynthetic pigments such as carotenoids and xanthophylls act as accessory pigments. Their role is to absorb energy and transfer it to chlorophyll-a. Carotenoids and xanthophylls also protect the chlorophyll molecule from photo-oxidation.
Therefore, chlorophyll-a is essential for photosynthesis.
If any plant were to lack chlorophyll-a and contain a high concentration of chlorophyll-b, then this plant would not undergo photosynthesis.

Define RQ. What is its value for fats?

Respiratory quotient (RQ) or respiratory ratio can be defined as the ratio of the volume of CO2 evolved to the volume of O2 consumed during respiration. The value of respiratory quotient depends on the type of respiratory substrate. Its value is one for carbohydrates. However, it is always less than one for fats as fats consume more oxygen for respiration than carbohydrates.
It can be illustrated through the example of tripalmitin fatty acid, which consumes 145 molecules of O2 for respiration while 102 molecules of CO2 are evolved. The RQ value for tripalmitin is 0.7.

Would a defoliated plant respond to photoperiodic cycle? Why?

A defoliated plant will not respond to the photoperiodic cycle.
It is hypothesised that the hormonal substance responsible for flowering is formed in the leaves, subsequently migrating to the shoot apices and modifying them into flowering apices. Therefore, in the absence of leaves, light perception would not occur, i.e., the plant would not respond to light.

Name different types of teeth and their number in an adult human.

There are four different types of teeth in an adult human. They are as follows:
Incisors
The eight teeth in the front are incisors. There are four incisors each in the upper jaw and the lower jaw. They are meant for cutting.
Canines
The pointy teeth on either side of the incisors are canines. They are four in number, two each placed in the upper jaw and the lower jaw. They are meant for tearing.
Premolars
They are present next to the canines. They are eight in number, four each placed in the upper jaw and the lower jaw. They are meant for grinding.
Molars
They are present at the end of the jaw, next to the premolars. There are twelve molars, six each placed in the upper jaw and the lower jaw.
Hence,the dental formula in humans=2123/2123×2=32
This means each half of the upper jaw and the lower jaw has 2 incisors, 1 canine, 2 premolars, and 3 molars. Hence, an adult human has 32 permanent teeth.

Have you heard about hypoxia? Try to gather information about it, and discuss with your friends.

Hypoxia is a condition characterised by an inadequate or decreased supply of oxygen to the lungs. It is caused by several extrinsic factors such as reduction in pO2, inadequate oxygen, etc. The different types of hypoxia are discussed below.
Hypoxemic hypoxia
In this condition, there is a reduction in the oxygen content of blood as a result of the low partial pressure of oxygen in the arterial blood.

Anaemic hypoxia
In this condition, there is a reduction in the concentration of haemoglobin.

Stagnant or ischemic hypoxia
In this condition, there is a deficiency in the oxygen content of blood because of poor blood circulation. It occurs when a person is exposed to cold temperature for a prolonged period of time.

Histotoxic hypoxia
In this condition, tissues are unable to use oxygen. This occurs during carbon monoxide or cyanide poisoning.

Explain heart sounds.

Heart sounds are noises generated by the closing and opening of the heart valves. In a healthy individual, there are two normal heart sounds called lub and dub. Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of systole. The second heart sound dub is associated with the closure of the semilunar valves at the beginning of diastole.
These sounds provide important information about the condition and working of the heart.

What is the significance of juxtaglomerular apparatus (JGA) in kidney function?

Juxtaglomerular apparatus (JGA) is a complex structure made up of a few cells of glomerulus, distal tubule, and afferent and efferent arterioles. It is located in a specialised region of a nephron, wherein the afferent arteriole and the distal convoluted tubule (DLT) come in direct contact with each other.
The juxtaglomerular apparatus contains specialised cells of the afferent arteriole known as juxtaglomerular cells. These cells contain the enzyme renin that can sense blood pressure. When glomerular blood flow (or glomerular blood pressure or glomerular filtration rate) decreases, it activates juxtaglomerular cells to release renin.
Renin converts the angiotensinogen in blood into angiotensin I and further into angiotensin II. Angiotensin II is a powerful vasoconstrictor that increases the glomerular blood pressure and filtration rate. Angiotensin II also stimulates the adrenal cortex of the adrenal gland to produce aldosterone. Aldosterone increases the rate of absorption of sodium ions and water from the distal convoluted tubule and the collecting duct. This also leads to an increase in blood pressure and glomerular filtration rate. This mechanism, known as renin-angiotensin mechanism, ultimately leads to an increased blood pressure.

Which part of our central neural system acts as a master clock?

Hypothalamus acts as a master clock of the human body.

10 thoughts on “NCERT Solutions for Class 11 Biology in PDF”

  1. GOOD EVENING RESPECTED MADAM/SIR

    SO I WAS GOING THROUGH THE NCERT PDF OF BIOLOGY OF CHAPTER 9 OF CLASS 11. TO MY UTTER SURPRISE I FOUND THAT THE PDF HERE IS NOT THE LATEST ONE SINCE I FOUND AN ERROR WHICH HAS BEEN CORRECTED IN THE LATEST EDITION .

    NCERT CLASS X1
    CHAPTER 9 : STRUCTURAL ORGANISATION IN ANIMALS
    PAGE 108
    LINE/STATEMENT : The characteristic feature of
    the intestine between 26-35 segments is the
    presence of internal median fold of dorsal wall
    called typhlosole.

    THE SAME STATEMENT IN THE LATEST VERSION IS : THE CHARACTERISTIC FEATURE OF THE INTESTINE AFTER 26TH SEGMENT EXCEPT THE LAST 23RD-25TH SEGMENT IS THE PRESENCE OF INTERNAL MEDIAN FOLD OF DORSAL WALL CALLED TYPHLOSOLE.

    RESPECTED MADAM/SIR
    IT IS AN EARNEST REQUEST TO YOU THAT YOU UPDATE THE LATEST PDFs OF THE NCERT FOR CLASS 11 AND 12 .
    I AM A PRE-MED AND YOUR WEBSITE IS REALLY HELPFUL . (PREVIOUSLY I WAS COMPARING THE CHAPTERS WHILE STUDYING FROM THE WEBSITE BUT TODAY WHEN I FOUND THIS ERROR I REALLY FELT THE NEED TO UPDATE YOU .)
    I GOT MY NCERT IN 2015 .
    THERE HAVE BEEN CORRECTIONS IN NCERT AFTER THAT TOO.
    I’LL BE HIGHLY OBLIGED IF YOU LOOK INTO THE MATTER AND UPDATE THE NEW PDF OF ALL THE CHAPTERS 🙂

    1. Thanks for your feedback. We will make the needful changes within 15 days so that students take the benefits of the proper courses.

  2. Sir,
    Kindly upload Biology Class XI NCERT solutions to Chapter 21 and Chapter 22 viz. CHAPTER 21: NEURAL CONTROL AND COORDINATION and CHAPTER 22: CHEMICAL COORDINATION AND INTEGRATION. I am fully depended on Tiwari.com study materials. Please do the same for the interest of the students.

  3. its really a very nice experience using this site.. answers here are easy and quick to understand.. thankyou so much for creating such a platform..

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