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Balbharati, solutions, for, Biology, 11th, Standard, Maharashtra, State Board, Chapter 6, Biomolecules, Exercise, [Pages 74 – 75, Answer the following question,

Exercise | Q 3. (A) | Page 74

Answer the following question.

What are building blocks of life?


Life is composed of four main building blocks: Carbohydrates, proteins, lipids, and nucleic acids.

Explain the peptide bond.


1. The covalent bond that links the two amino acids is called a peptide bond.

2. Peptide bond is formed by condensation reaction.

How many types of polysaccharides you know?.


There are two types of polysaccharides:

1. Homopolysaccharides: It contains same type of monosaccharides. E.g. Starch, glycogen, cellulose.

2. Heteropolysaccharides: It contains two or more different monosaccharides. E.g. Hyaluronic acid, heparin, hemicellulose.

Enlist the significance of carbohydrates.


Significances of carbohydrates are as follows:

1. Carbohydrates provide energy for metabolism.

2. Glucose is the main substrate for ATP synthesis.

3. Lactose, a disaccharide present in the milk provides energy to babies.

4. Polysaccharide serves as a structural component of cell membrane, cell wall and reserved food as starch and glycogen.

What is reducing sugar?


1. A sugar that serves as a reducing agent due to the presence of free aldehyde or ketone group is called a reducing sugar.

2. These sugars reduce Benedict’s reagent (Cu 2+ to Cu + ) since they are capable of transferring hydrogens (electrons) to other compounds, a process called reduction.

3. All monosaccharides are reducing sugars.

What is the basic difference between saturated and unsaturated fatty acid?


Enlist the examples of simple protein and add their significance.


Examples of simple proteins are: E.g.: Albumins and histones.


1. Albumin:

a. It is the main protein in the blood.

b. It maintains the pressure in the blood vessels.

c. It helps in the transportation of substances like hormone and drugs in the body.

2. Histones:

a. It is the chief protein of chromatin.

b. They are involved in the packaging of DNA into structural units called nucleosomes.

Explain the secondary structure of a protein with examples.


1. There are two types of the secondary structures of protein: α-helix and β-pleated sheets.

2. The polypeptide chain is arranged in a spiral helix. These spiral helices are of two types: α-helix (right-handed) and β-helix (left-handed).

3. This spiral configuration is held together by hydrogen bonds.

4. The sequence of amino acids in the polypeptide chain determines the location of its bend or fold and the position of formation of hydrogen bonds between different portions of the chain or between different chains. Thus, peptide chains form an α-helix structure.

5. Example of α-helix structure is keratin.

6. In some proteins two or more peptide chains are linked together by intermolecular hydrogen bonds. Such structures are called β-pleated sheets.

7. Example of a β-pleated sheet is silk fibres.

8. Due to the formation of hydrogen bonds peptide chains assume a secondary structure.

Explain the induced fit model for the mode of enzyme action.


The induced fit model shows that enzymes are flexible structures in which the active site continually reshapes by its interactions with the substrate until the time the substrate is completely bound to it. It is also the point at which the final form and shape of the enzyme are determined

What is RNA? Enlist types of RNA.


1. RNA stands for Ribonucleic Acid. It is a long single-stranded polynucleotide chain that helps in protein synthesis, functions as a messenger and translates messages coded in DNA into protein.

2. There are three types of RNA:

mRNA (messenger RNA), rRNA (ribosomal RNA) and tRNA (transfer RNA).

Describe the concept of metabolic pool.


1. Metabolic pool is the reservoir of biomolecules in the cell on which enzymes can act to produce useful products as per the need of the cell.

2. The concept of metabolic pool is significant in cell biology because it allows one type of molecule to change into another type E.g. Carbohydrates can be converted to fats and vice-versa.

How do secondary metabolites useful for mankind?


1. Drugs developed from secondary metabolites have been used to treat infectious diseases, cancer, hypertension, and inflammation.

2. Morphine, the first alkaloid isolated from Papaver somniferum is used as a pain reliver and cough suppressant.

3. Secondary metabolites like alkaloids, nicotine, cocaine and the terpenes, cannabinol are widely used for recreation and stimulation.

4. Flavours of secondary metabolites improve our food preferences.

5. Tannins are added to wines and chocolate for improving astringency.

6. Since most secondary metabolites have antibiotic property, they are also used as food preservatives.

7. Glucosinolates is a secondary metabolite which is naturally present in cabbage imparts a characteristic flavour and aroma because of nitrogen and sulphur–containing chemicals. It also offers protection to these plants from many pests.

Balbharati, solutions, for, Biology, 11th, Standard, Maharashtra State Board, Chapter 5, Cell Structure and Organization, Exercise, [Pages 57], Answer the following question,

Exercise | Q 2. (A) | Page 57

Answer the following question.

Plants have no circulatory system? Then how cells manage intercellular transport?


1. Plant cells show the presence of plasmodesmata which are cytoplasmic bridges between neighboring cells.

2. This open channel through the cell wall connects the cytoplasm of adjacent plant cells and allows water, small solutes, and some larger molecules to pass between the cells.

In this way, though plants have no circulatory system, plant cells manage intercellular transport.

Is nucleolus covered by membrane?


A nucleolus is a specialized structure present in the nucleus which is not covered by the membrane.

Fluid mosaic model proposed by Singer and Nicolson replaced Sandwich model proposed by Danielli and Davson? Why?


1. The Davson–Danielli model of the plasma membrane of a cell, was proposed in 1935 by Hugh Davson and James Danielli.

2. The model describes a phospholipid bilayer that lies between two layers of globular proteins.

3. This model was also known as a ‘lipo-protein sandwich’, as the lipid layer was sandwiched between two protein layers.

4. But through experimental studies membrane proteins were discovered to be insoluble in water (representing hydrophobic surfaces) and varied in size. Such type of proteins would not be able to form an even and continuous layer around the outer surface of a cell membrane.

5. In case of Fluid-mosaic model, the experimental evidence from research supports every major hypothesis proposed by Singer and Nicolson. This hypothesis stated that membrane lipids are arranged in a bilayer; the lipid bilayer is fluid; proteins are suspended individually in the bilayer; and the arrangement of both membrane lipids and proteins is asymmetric.

Therefore, Fluid mosaic model proposed by Singer and Nicolson replaced Sandwich model proposed by Danielli and Davson.

The RBC surface normally shows glycoprotein molecules. When determining blood group do they play any role?


1. Glycoproteins are protein molecules modified within the Golgi complex by having a short sugar chain (polysaccharide) attached to them.

2. The polysaccharide part of glycoproteins located on the surfaces of red blood cells acts as the antigen responsible for determining the blood group of an individual.

3. Different polysaccharide part of glycoproteins act as different type of antigens that determine the blood groups.

4. Four types of blood groups A, B, AB, and O are recognized on the basis of presence or absence of these antigens.

How cytoplasm differs from nucleoplasm in chemical composition?


Smooth endoplasmic reticulum (SER):

1. Depending on cell type, it helps in the synthesis of lipids for e.g. Steroid secreting cells of the cortical region of the adrenal gland, testes and ovaries.

2. Smooth endoplasmic reticulum plays a role in detoxification in the liver and storage of calcium ions (muscle cells).

Rough Endoplasmic Reticulum (RER):

1. Rough ER is primarily involved in protein synthesis. For e.g. Pancreatic cells synthesize the protein insulin in the ER.

2. These proteins are secreted by ribosomes attached to rough ER and are called secretory proteins. These proteins get wrapped in a membrane that buds off from the transitional region of ER. Such membrane-bound proteins depart from ER as transport vesicles.

3. Rough ER is also involved in the formation of membrane for the cell. The ER membrane grows in place by the addition of membrane proteins and phospholipids to its own membrane. Portions of this expanded membrane are transferred to other components of the endomembrane system

1. A thick liquid enclosed by a cell membrane which surrounds the central nucleus in eukaryotes or nucleoid region in prokaryotes is known as cytoplasm.

2. The cytoplasm shows the presence of minerals, sugars, amino acids, t-RNA, nucleotides, vitamins, proteins, and enzymes.

3. The liquid or semiliquid substance within the nucleus is called the nucleoplasm.

4. Nucleoplasm shows the presence of various substances like nucleic acid, protein molecules, minerals, and salts.


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