NCERT Solutions for Class 11 Biology

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NCERT Solutions for Class 11 Biology

Class:11
Subject:Biology
Contents:NCERT Solutions

NCERT Solutions for Class 11 Biology in English




NCERT Solutions for Class 11 Biology in English Medium updated for new academic session 2020-21 in PDF format free. NCERT books and answers, study material for final exams and other online study books for revision are available to free download. NCERT Solutions 2020-21 based on latest CBSE Syllabus are available to free download. Join the discussion forum to ask your doubts and reply to other’s questions.

What is meant by 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.

What is 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.

What do you know about 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.

What is Morphology?

It is the study of external features of organisms. It essentially includes the understanding and interpretation of structure both external and internal.



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.

Branches of Biology – 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.




Branches of Biology – 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.



Important Questions on Class 11 Biology

What different criteria would you choose to classify people that you meet often?
To classify a class of forty students, let us start the classification on the basis of sexes of the students. This classification will result in the formation of two major groups- boys and girls.
Each of these two groups can be further classified on the basis of the names of the students falling in these groups.
Since it is possible that more than one student can have a particular name, these names can be further divided based on the surnames.
Since there is still some chance that more than one student can have the same surname, the final level of classification will be based on the roll numbers of each student.
Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.
Algal bloom
Algal bloom refers to an increase in the population of algae or blue-green algae in water, resulting in discoloration of the water body. This causes an increase in the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals.
Red-tides
Red tides are caused by red dinoflagellates (Gonyaulax) that multiply rapidly. Due to their large numbers, the sea appears red in colour. They release large amounts of toxins in water that can cause death of a large number of fishes.
What are the characteristic features of Euglenoids?
Some characteristic features of Euglenoids are as follows.
Euglenoids (such as Euglena) are unicellular protists commonly found in fresh water.
Instead of cell wall, a protein-rich cell membrane known as pellicle is present.
They bear two flagella on the anterior end of the body.
A small light sensitive eye spot is present.
They contain photosynthetic pigments such as chlorophyll and can thus prepare their own food. However, in absence of light, they behave similar to heterotrophs by capturing other small aquatic organisms.
They have both plant and animal-like features, which makes them difficult to classify.
Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a fern; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.
(a) Protonemal cell of a moss – Haploid
(b) Primary endosperm nucleus in a dicot – Triploid
(c) Leaf cell of a moss – Haploid
(d) Prothallus of a fern – Haploid
(e) Gemma cell in Marchantia – Haploid
(f) Meristem cell of a monocot – Diploid
(g) Ovum of a liverwort – Haploid
(h) Zygote of a fern – Diploid
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.
Explain with suitable examples the different types of phyllotaxy?
Phyllotaxy refers to the pattern or arrangement of leaves on the stem or branch of a plant. It is of three types, alternate, opposite, and whorled phyllotaxy.
In alternate phyllotaxy, a single leaf arises from the node of a branch. This type of phyllotaxy is observed in the sunflower, mustard, and peepal. Plants with opposite phyllotaxy have two leaves arising from the node in opposite directions. It is found in guava and jamun plants. Plants with whorled phyllotaxy have three or more leaves arising from the node. It is found in Alstonia.
Explain the process of secondary growth in stems of woody angiosperm. What is the significance?
In woody dicots, the strip of cambium present between the primary xylem and phloem is called the interfascicular cambium. The interfascicular cambium is formed from the cells of the medullary rays adjoining the interfascicular cambium. This results in the formation of a continuous cambium ring. The cambium cuts off new cells toward its either sides. The cells present toward the outside differentiate into the secondary phloem, while the cells cut off toward the pith give rise to the secondary xylem. The amount of the secondary xylem produced is more than that of the secondary phloem.
The secondary growth in plants increases the girth of plants, increases the amount of water and nutrients to support the growing number of leaves, and also provides support to plants.
How many segments are present in the abdomen of cockroach?
In both sexes, the abdomen of a cockroach consists of ten segments.
What are the characteristics of prokaryotic cells?
Prokaryotic cell is a unicellular organism lacking membrane-bound organelles.
The characteristics of prokaryotic cells are as follows:
Most of them are unicellular.
They are generally small in size. The size of a prokaryotic cell varies from 0.5 – 5 µm.
The nuclear region of a prokaryotic cell is poorly-defined because of the absence of a nuclear membrane. Hence, a prokaryotic cell lacks a true nucleus.
The genetic materials of prokaryotic cells are naked. They contain single, circular chromosomes. In addition to the genomic DNA, they have a small, circular plasmid DNA.
They have specialised membranous structures called mesosomes. Mesosomes are formed by the invagination of the cell membrane. These extensions help in the synthesis of the cell wall, replication of DNA. They also help in the equal distribution of chromosomes into the daughter cells.
Membrane-bound cell organelles such as mitochondria, plastids, and endoplasmic reticulum are absent from a prokaryotic cell.
Most prokaryotic cells contain a three-layered structure – outermost glycocalyx, middle cell wall, and the innermost plasma membrane. This structure acts as a protective unit.
Examples of prokaryotic cells include blue green algae, bacteria, etc.
Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (e.g., cosmetics, etc.)
Proteins used as therapeutic agents are as follows:
Thrombin and fibrinogen – They help in blood clotting.
Antigen (antibody) – It helps in blood transfusion.
Insulin – It helps in maintaining blood glucose level in the body.
Renin – It helps in osmoregulation.
Proteins are also commonly used in the manufacture of cosmetics, toxins, and as biological buffers.
Why is mitosis called equational division?
Mitosis is the process of cell division wherein the chromosomes replicate and get equally distributed into two daughter cells. The chromosome number in each daughter cell is equal to that in the parent cell, i.e., diploid. Hence, mitosis is known as equational division.
Briefly describe water potential. What are the factors affecting it?
Water potential quantifies the tendency of water to move from one part to the other during various cellular processes such as diffusion, osmosis, etc. It is denoted by the Greek letter Psi or Ψ and is expressed in Pascals (Pa). The water potential of pure water is always taken as zero at standard temperature and pressure.
Water potential (Ψw) is expressed as the sum of solute potential (Ψs) and pressure potential (Ψp).
Ψw = Ψs + Ψp
When some solute is dissolved in water, the water potential of pure water decreases. This is termed as solute potential (Ψs), which is always negative. For a solution at atmospheric pressure, Ψw = Ψs.
The water potential of pure water or a solution increases on the application of pressure values more than atmospheric pressure. It is termed as pressure potential. It is denoted by Ψp and has a positive value, although a negative pressure potential is present in the xylem. This pressure potential plays a major role in the ascent of water through the stem.
Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.
Macronutrients: They are the nutrients required by plants in large amounts. They are present in plant tissues in amounts more than 10 m mole kg–1 of dry matter. Examples include hydrogen, oxygen, and nitrogen.
Micronutrients: They are also called trace elements and are present in plant bodies in very small amounts, i.e., amounts less than 10 m mole kg– 1 of dry matter. Examples include cobalt, manganese, zinc, etc.
Beneficial nutrients: They are plant nutrients that may not be essential, but are beneficial to plants. Sodium, silicon, cobalt and selenium are beneficial to higher plants.
Toxic elements: Micronutrients are required by plants in small quantities. An excess of these nutrients may induce toxicity in plants. For example, when manganese is present in large amounts, it induces deficiencies of iron, magnesium, and calcium by interfering with their metabolism.
Essential elements: These elements are absolutely necessary for plant growth and reproduction. The requirement of these elements is specific and non-replaceable.
They are further classified as macro and micro-nutrients.
Even though a very few cells in a C4 plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?
The productivity of a plant is measured by the rate at which it photosynthesises. The amount of carbon dioxide present in a plant is directly proportional to the rate of photosynthesis. C4 plants have a mechanism for increasing the concentration of carbon dioxide. In C4 plants, the Calvin cycle occurs in the bundle-sheath cells. The C4 compound (malic acid) from the mesophyll cells is broken down in the bundlesheath cells. As a result, CO2 is released. The increase in CO2 ensures that the enzyme RuBisCo does not act as an oxygenase, but as a carboxylase. This prevents photorespiration and increases the rate of photosynthesis. Thus, C4 plants are highly productive.
Discuss “The respiratory pathway is an amphibolic pathway.”
Respiration is generally assumed to be a catabolic process because during respiration, various substrates are broken down for deriving energy. Carbohydrates are broken down to glucose before entering respiratory pathways. Fats get converted into fatty acids and glycerol whereas fatty acids get converted into acetyl CoA before entering the respiration. In a similar manner, proteins are converted into amino acids, which enter respiration after deamination.
During synthesis of fatty acids, acetyl CoA is withdrawn from respiratory pathway. Also, in the synthesis of proteins, respiratory substrates get withdrawn. Thus, respiration is also involved in anabolism. Therefore, respiration can be termed as amphibolic pathway as it involves both anabolism and catabolism.
List five main groups of natural plant growth regulators.
Plant growth regulators are the chemical molecules secreted by plants affecting the physiological attributes of a plant. There are five main plant growth regulators. These are:
(i) Auxins
(ii) Gibberellic acid
(iii) Cytokinins
(iv) Ethylene
(v) Abscisic acid
How does bile help in the digestion of fats?
Bile is a digestive juice secreted by the liver and stored in the gall bladder. Bile juice has bile salts such as bilirubin and biliverdin. These break down large fat globules into smaller globules so that the pancreatic enzymes can easily act on them. This process is known as emulsification of fats. Bile juice also makes the medium alkaline and activates lipase.
How is respiration regulated?
The respiratory rhythm centre present in the medulla region of the brain is primarily responsible for the regulation of respiration. The pneumotaxic centre can alter the function performed by the respiratory rhythm centre by signalling to reduce the inspiration rate.
The chemosensitive region present near the respiratory centre is sensitive to carbon dioxide and hydrogen ions. This region then signals to change the rate of expiration for eliminating the compounds.
The receptors present in the carotid artery and aorta detect the levels of carbon dioxide and hydrogen ions in blood. As the level of carbon dioxide increases, the respiratory centre sends nerve impulses for the necessary changes.
Why do we consider blood as a connective tissue?
Connective tissues have cells scattered throughout an extra-cellular matrix. They connect different body systems. Blood is considered as a type of connective tissue because of two reasons.
Like the other connective tissues, blood is mesodermal in origin.
It connects the body systems, transports oxygen and nutrients to all the parts of the body, and removes the waste products. Blood has an extra-cellular matrix called plasma, with red blood cells, white blood cells, and platelets floating in it.
Explain micturition.
Micturition is the process by which the urine from the urinary bladder is excreted. As the urine accumulates, the muscular walls of the bladder expand. The walls stimulate the sensory nerves in the bladder, setting up a reflex action. This reflex stimulates the urge to pass out urine. To discharge urine, the urethral sphincter relaxes and the smooth muscles of the bladder contract. This forces the urine out from the bladder.
An adult human excretes about 1 – 1.5 litres of urine per day.
Explain the mechanism of generation of light-induced impulse in the retina.
Retina is the innermost layer of the eye. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. Photoreceptor cells are composed of a protein called opsin and an aldehyde of vitamin A called retinal. When light rays are focused on the retina through the cornea, retinal gets dissociated from opsin. As a result, the structure of opsin gets changed. This in turn causes the permeability of the membrane to change, thereby generating a potential difference in the cells. Consequently, an action potential is generated in the ganglion cells and is transmitted to the visual cortex of the brain via the optic nerves. In the cortex region of the brain, the impulses are analysed and the image is formed on the retina.
What are Endocrine glands?
Endocrine Glands
Glands that do not discharge their secretions into ducts are known as endocrine glands. Instead, these glands discharge their secretions directly into the blood. Pituitary gland, thyroid gland, adrenal gland, etc. are examples of endocrine glands.

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