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Chemistry 5 Marks Questions

Biomolecules · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 16 questions.

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Question 15 Marks
  1. What are essential and non-essential amino acids? Give two examples of each.
  2. What are the two types of photosynthesis in green plants? Give the basic equations of photosynthesis.
  3. Mention the two products of glycolysis.
Answer
  1. The amino acids that can be made by our body and therefore, we do not require them in our diet are called non-essential amino acids.
The amino acids which are not synthesized in our body and are to be supplied to our diet are called essential amino acids.
  1. Basic equation: $\text{6CO}_{2}+\text{6H}_{2}\text{O}\xrightarrow[Chlorophyll]{hv}\text{C}_{6}\text{H}_{12}\text{O}_{6}+\text{6O}_{2}.$
  2. Pyruvate and ATP molecules.
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Question 25 Marks
  1. Define the following terms:
  1. Co-enzymes.
  2. Mutation in biomolecules.
  3. Nucleotides.
  1. List four main functions of carbohydrates in organisms.
Answer
  1.  
  1. Co-enzymes: The non proteinous components which increase the activity of enzymes are called co- enzymes.
  2. Mutation in biomolecules: It is a chemical change in DNA molecule that could lead to synthesis of proteins with altered amino acid sequence e.g sickel cell anaemia is caused by mutation.
  3. Nucleotide: is a species which contains a phosphate unit, a sugar unit, and any one of the pyrimdine nitrogen bases or purines. e.g Ribonucleotide, deoxy -ribonucleotides.
  1.  
  1. They support plant structure, e.g cellulose.
  2. They produce energy necessary for functioning of living body and doing work.
  3. They are used to store chemical energy in the form of glycogen in liver. Starch is main storage polysaccharide of plants.
  4. Cellulose present in grass and plants acts as a food for various grazing animals.
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Question 35 Marks
  1. Answer the following questions briefly:
  1. What are any two good sources of vitamin A?
  2. What are nucleotides?
  3. Give an example of simple lipids.
  1. How are carbohydrates classified?
Answer
    1. Green vegetables, fish oil, rice polishing, liver, kidney.
    2. Nucleotides: A nucleotide is a phosphate ester of nucleoside.
    3. Neutral fats/waxes/tripalmitin/tristearate/trioleate.
  1. Carbohydrates are classified into three categories: monosaccharides, oligosaccharides/disaccharides, polysaccharides.
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Question 45 Marks
  1. Answer the following questions briefly:
  1. What are reducing sugars?
  2. What is meant by denaturation of a protein?
  3. How is oxygen replenished in our atmosphere?
  1. Define enzymes.
Answer
    1. Reducing sugars: Reducing sugars are the sugars which contains free aldehydic or ketonic group and reduce Fehling’s solution and Tollen’s reagent.
    2. Denatured protein: If a native protein is subjected to physical or chemical treatment which may disrupt its higher structures withoutout affecting its primary structure, the protein is said to be denatured and it loses its biological activity.
    3. By photosynthesis.
  1. Enzymes: Are the biological catalysts which increase the rate of metabolism a and they are highly specific in nature.
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Question 55 Marks
After watching a programme on TV about the presence of carcinogens (cancer causing agents) Potassium bromate and Potassium iodate in bread and other bakery products, Veena, a class XII student, decided to make others aware about the adverse effects of these carcinogens in foods. She consulted the school principal and requested him to instruct the canteen contractor to stop selling sandwiches, pizzas, burgers and other bakery products to the students. The principal took an immediate action and instructed the canteen contractor to replace the bakery products with some proteins and vitamins-rich food like fruits, salads, sprouts, etc. The decision was welcomed by the parents and students.
After reading the above passage, answer the following questions:
  1. What are the values (at least two) displayed by Veena?
  2. Which polysaccharide component of carbohydrates is commonly present in bread?
  3. Write the two types of secondary structures of proteins.
  4. Give two examples of water soluble vitamins.
Answer
  1. Concerned, caring, socially alert, leadership.
  2. Starch.
  3. $\alpha$ -Helix and β-pleated sheets.
  4. Vitamin $B / B_1 / B_2 / B_6 / C$.
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Question 65 Marks
  1. How are lipids classified? Give an example of each class.
  2. Explain the following terms:
  1. Mutarotation.
  2. Avitaminosis.
Answer
  1.  
  1. Simple lipids (Homolipids): e.g, Natural fats/waxes.
  2. Compound Lipids (Hetrolipids): e.g, Phospholopids/Glycolipids.
  3. Derived Lipids: fatty acids/fatty alcohols/steroids/terpenes, etc.
  1.  
  1. Mutarotation: The spontaneous change in specific rotation of an optically active compound is called mutarotation.
  2. Avitaminosis: The deficiency of multiple vitamins leads to characteristic deficiency symptoms in humans. This condition of vitamin deficiency is known as avitaminosis.
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Question 75 Marks
  1. Name the three major classes of carbohydrates and give an example of each of these classes.
  2. Answer the following:
  1. What type of linkage is responsible for the primary structure of proteins?
  2. Name the location where protein synthesis occurs in our bod.
Answer
  1.  
  1. Monosaccharides: eg., glucose, fructose.
  2. Oligosaccharides/Disaccharides: eg., sucrose, lactose, mannose.
  3. Polysaccharides: eg., starch, cellulose.
  1.  
  1. Peptide linkage or – CO - NH - linkage.
  2. Ribosome/In the cytoplasm of the cell.
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Question 85 Marks
  1. State two main differences between globular proteins and fibrous proteins.
  2. Based on their chemical composition, state how are lipids classified Give one example of each class.
Answer
  1. Sr. No.
    Globular Proteins
    Fiberous Proteins
    I.
    II.
    They are cross linked condensation products .
    Three dimensional spherical shape.
    They are linear condensation products.
    Rod like rigid shape.
  2. Lipids are naturally occuring compounds related to fatty acids which include fats, oils, waxes, etc.
  1. Simple lipids (Homolipids): e.g, neutral fats/waxes.
  2. Compound Lipids (Hetrolipids): e.g, Phospholopids/Glycolipids.
  3. Derived Lipids: fatty acids/fatty alcohols/steroids/terpenes, etc.
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Question 95 Marks
  1. ‘Hormones are chemical messengers.’ Explain.
  2. Name the main disease caused due to lack of the vitamin and its source in each of the following: A, $B_6$ and E.
Answer
  1. Hormones transfer information from one group of cells to distant tissue or organ. Because of their action as communication among cells, they are called Chemical messangers.
  2.  
Sr. no.
Name of Vitamins
Source
Deficiency disease
01
02
03
Vitamins A
Vitamins $B_6$
Vitamin E
Fish oil, Liver of fresh water fish, rice polishing.
Cereal, grains, egg yolk, yeast, molasses and meat.
Wheat germ oil, cotton seed oil and soybean Oil.
Xerophthalmia, nightblindness.
Severe dermatitis, convulsions.
Sterility.
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Question 105 Marks
Describe the mechanism of replication of DNA.
Answer
The process by which a DNA molecule produces two identical copies of itself is called replication of DNA. In the DNA double helix, the sequence of bases in one chain is complementary to the sequence in the other chain, therefore, one controls the other. During cell division (mitosis), the two strands of the DNA double helix partly unwind and each serves as the template for the synthesis of a new DNA molecule. DNA replication follows the base pairing rules by which A pairs with T and G pairs with C. Therefore, each daughter molecule is an exact replication of the parent molecule. DNA replication is semiconservative, i.e., only half of the parental DNA is conserved and only one strand is synthesised. DNA replication takes place only in the 5′ → 3′ direction.
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Question 115 Marks
Answer the following questions.
Comment on the specificity of enzyme action. What is the most important reason for their specificity?
Answer
In case of enzymatic reaction, the enzyme is so built that it binds to the substrate in a specific manner. Enzymatic reaction involves the following steps:
Step I: Binding of substrate (S) to enzyme (E) to form a complex.
E + S → [ES] (Enzyme-Substrate complex)
Step II: Product formation in the complex.
[ES] → (Enzyme-product complex)
Step III: The dissociation of the enzyme product complex, leaving the enzyme unchanged.
EP → E + P
The specificity of the enzymes is due to the presence of some specific regions, called the active site, on their surface. The shape of active site is such that only a specific substrate can fit into it in the same way as one key can open a particular lock. This specific binding leads to the formation of an enzyme–substrate complex which accounts for the high specificity of enzyme catalysed reactions. This most accepted model is popularly known as Lock and Key model. For example, urease catalyses only the hydrolysis of urea and none of the several thousand other enzymes present in the cell catalyses that reaction.
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Question 125 Marks
Which forces are responsible for the stability of $\alpha-\text{helix}?$ Why is it named as $3.6_{13}$ helix?
Answer
Hydrogen bonds between $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{||}\\-\text{N}-\text{H}\text{ and }-\text{C}-$ groups of peptide bonds give stability to the structure. Thus, a structure having maximum hydrogen bonds shall be favoured. a-Helix is one of the most common ways in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right-handed screw (helix) with the -NH group of each amino acid residue hydrogen bonded to the -C ═ O of an adjacent turn of the helix. The a-helix is also known as $3.6_{13}$ helix, since each turn of the helix has approximately 3.6 amino acid residue and a 13-member ring is formed by hydrogen bonding.
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Question 135 Marks
Answer the following questions.
Write chemical reaction to show that glucose contains aldehyde as carbonyl group.
Answer
$\text{CHO}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{COO}\\\ \ \ \ \text{|}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|}\$\text{CH}-\text{OH})_4+2[\text{Ag}(\text{NH}_3)_2]^++3\text{OH})\xrightarrow{\ \ \ \ \ \ \ \ \ \ }(\text{CHOH})_4+2\text{Ag}\downarrow+2\text{H}_2\text{O}\\\ \ \ \ \text{|}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|}\\\text{CH}_2\text{OH}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_2-\text{OH}\\\text{D}-(+)-\text{Glucose}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Glucose acid}$
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Question 145 Marks
Define enzymes. How do enzymes differ from ordinary chemical catalysts?
Answer
Ans. Enzymes are naturally occurring simple or conjugate proteins acting as specific catalysts in cell processes. The enzyme facilitates a biochemical reaction by providing alternative lower activation energy pathways thereby increasing the rate of reaction.Enzymes are different from ordinary chemical catalysts in following ways:
  1. They are highly specific in their action, i.e., each enzyme can catalyse only a specific type of reaction.
  2. Enzymes can speed up reactions to the extent of about ten million times.
  3. Enzymes function at a moderate temperature (about 310K) and moderate pH (6-8).
  4. Even a small quantity of an enzyme can catalyse the reaction of a large quantity of the substrate. This is because in chemical reactions the catalyst (enzyme) is regenerated after the reaction.
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Question 155 Marks
Explain the terms primary and secondary structure of proteins. What is the difference between α-helix and β-pleated sheet structure of proteins?
Answer

Primary structure: Proteins may have one or more polypeptide chains. Each polypeptide chain has a large number of a-amino acids linked to one another in a specific sequence. The specific sequence in which the various α-amino acids present in a protein are linked to one another is called its primary structure. Any change in this primary structure, i.e., sequence of amino acids creates a different protein.

The primary structure of a protein is usually determined by its successive hydrolysis with either enzymes or mineral acids into various products having decreasing molecular mass as shown below:

Secondary structure: The secondary structure gives the manner in which the polypeptide chains are folded or arranged. Therefore, it gives the shape or conformation of the protein molecule.
This arises from the plane geometry, of the peptide bond and hydrogen bond between the >C = O and N – H groups of different peptide bonds.
$\alpha-$Helix structure: A helix form is the most common form in which a polypeptide chain forms all possible types of hydrogen bonds by twisting into a right handed screw (helix) with the -NH group of each amino acid residue hydrogen bonded to -C = O group of the adjacent turn of the helix. The a-helix structure is also known as 3.613 helix. This represents that each turn of the helix contains approximately 3.6 amino acids and a 13-member ring is formed by hydrogen bonding. The helix is held in its shape primarily by hydrogen bonds between one amide group and carbonyl group which is 3.6 amino acids units away.

$\beta-$pleated sheet structure: In this conformation, the polypeptide chains lie side by side in a zigzag manner with alternate R groups on the same side situated at fixed distances apart. The two such neighbouring polypeptide chains are held together by intermolecular H-bonds. A number of such chains can be interbounded to form a sheet. These sheets are then stacked one above the other like the pages of this book to form a three-dimensional structure. This structure resembles pleated folds of drapery and hence is also called β-pleated sheet structure.
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Question 165 Marks
Give reasons for the following:
On electrolysis in acidic solution amino acids migrate towards cathode, while in alkaline solution these migrate towards anode.
Answer
In acidic solution, the carboxylate anion accepts a proton and gets converted into carboxylic group resulting in the formation of a positive ion.
$\text{H}_3\stackrel{{+}}{\hbox{N}}-\text{CH}-\text{COO}^-\xrightarrow[\text{(acid)}]{\text{H}^+}\text{H}_3\stackrel{{+}}{\hbox{N}}-\text{CH}-\text{COOH}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{R}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{R}\\ \ \ \ \ \ \text{Zwitter ion}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(Positive ion)}$
In presence of a base, the $\mathrm{NH}_3{ }^{+}$ion changes to $-\mathrm{NH}_2$ group by losing a proton and this gives a negative ion.
$\text{H}_3\stackrel{{+}}{\hbox{N}}-\text{CH}-\text{COO}^-\xrightarrow[\text{(base)}]{\text{H}^+}\text{H}_2\text{N}-\text{CH}-\text{COO}^-+\text{H}_2\text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{R}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{R}\\ \ \ \ \ \ \text{Zwitter ion}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(Negative ion)}$
This means that in acidic medium, the amino acid migrates towards the cathode while in alkaline solution, it migrates towards anode on electrolysis.
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