49 short questions of 9th Class Biology Chapter 6, Biomolecules, with exam-ready answers in the book's words: the textbook exercise questions plus SLO-based questions asked in board papers. Punjab Board new syllabus.
Exam-ready answers. Learn the meaning, then write them in your own words.
The short questions at the end of the chapter in your book.
Monosaccharides have sweet taste; disaccharides are less sweet; polysaccharides are tasteless.
Monosaccharides: glucose and fructose (also galactose, ribose). Disaccharides: sucrose and maltose (also lactose).
Sucrose (table sugar) is made of two monosaccharides, i.e. glucose and fructose.
Starch is a storage polysaccharide found in plants. It is composed of straight as well as branched chains of glucose units (e.g. in wheat, rice, maize, potato).
An amino acid is an organic molecule made of an amino group (NH₂), a carboxyl group (COOH), a hydrogen (H) and a side group (R) which are attached to a central carbon atom. Amino acids join in specific number and sequence to make proteins.
Lipids are composed of glycerol and fatty acids. Glycerol is an alcohol having 3 carbon atoms, each with a hydroxyl group. Fatty acids are long hydrocarbon chains with a carboxyl group (COOH) at the end.
| Type | Function |
|---|---|
| mRNA (messenger) | carries the genetic information from DNA to the ribosomes during protein synthesis |
| tRNA (transfer) | transfers specific amino acids to the ribosomes, ensuring the correct sequence |
| rRNA (ribosomal) | makes the structural and functional components of ribosomes |
DNA contains the hereditary information in the form of a sequence of nucleotides. This sequence determines the order of amino acids during protein synthesis. A segment of DNA that codes for a protein is a gene. During reproduction DNA is passed to the next generation, so it carries hereditary information.
The book's in-text exercises first, then short questions on every topic of the chapter (SLO-based), as asked in board papers.
All the chemical reactions that occur in an organism are collectively called metabolism. Anabolism: simpler substances combine to form complex substances; energy is used. Catabolism: complex molecules are broken down into simpler ones; energy is released.
Essential: the 9 amino acids which cannot be synthesized by our body and are supplied by foods. Non-essential: the 11 amino acids that can be synthesised in our bodies.
James Watson and Francis Crick, in 1962 (shared with Maurice Wilkins). They proposed the model in 1953.
Polysaccharides; cellulose is the most abundant carbohydrate.
Biochemistry is the study of the chemical processes that occur within living organisms. Molecular biology is the study of the structure and function of the biomolecules.
The molecules produced by organisms are called biomolecules: carbohydrates, lipids, proteins and nucleic acids. They are mostly large in size, so they are called macromolecules.
Proteins 50 %, nucleic acids 18 %, carbohydrates 15 %, lipids 10 % (total 93 %); the remaining 7 % is vitamins and inorganic substances.
DNA: nucleus (eukaryotes), nucleoid region (prokaryotes), mitochondria and chloroplasts. RNA: nucleus, ribosomes and cytoplasm.
Because in them the ratio of H and O is 2 : 1, the same as in water; general formula Cₙ(H₂O)ₙ.
Ribose C₅H₁₀O₅, deoxyribose C₅H₁₀O₄, glucose (also fructose, galactose) C₆H₁₂O₆.
Pentoses are monosaccharides with 5 carbon atoms (ribose, deoxyribose); hexoses have 6 carbon atoms (glucose, fructose, galactose).
Maltose is made of two glucose molecules. It is found in cereals.
| Starch | Glycogen |
|---|---|
| storage polysaccharide of plants | animal starch |
| straight and branched chains of glucose | highly branched chains of glucose |
| in cereals, potatoes | in liver and muscles |
Chitin is a modified form of cellulose. It is found in the exoskeletons of crabs, lobsters and insects, and makes the cell wall of fungi.
Dietary fibre contains undigestible carbohydrates, e.g. cellulose. It helps for proper bowel movements.
Plants convert their monosaccharides to disaccharides like sucrose to transport them between body parts.
Sucrose: sugar beet, sugar cane and fruits. Lactose: milk and dairy products. Maltose: cereals.
Proteins are the polymers of amino acids. They are the most abundant biomolecules in cell.
Insulin has 51 amino acids and haemoglobin has 574 amino acids.
They differ only in the side group (R): in glycine it is H, in alanine it is CH₃.
Meat (mutton, beef, chicken), fish, eggs, milk, pulses and beans.
Collagen and keratin make almost whole structures of cartilage, hair and nails.
Actin and myosin are the main components of muscle cells and are responsible for muscular movements. Fibrin forms a blood clot to prevent the loss of blood after an injury.
Enzymes catalyse all biochemical reactions in organisms; antibodies (immune system) defend the body against harmful pathogens.
Lipids are organic compounds that are insoluble in water but are soluble in organic solvents (alcohol, ether, benzene). They are composed of glycerol and fatty acids.
| Saturated | Unsaturated |
|---|---|
| carbons bonded with maximum hydrogen | fewer hydrogen atoms |
| no double bond | one or more C=C double bonds |
| solid at room temperature | liquid at room temperature |
Fats contain saturated fatty acids and so are solid; oils contain unsaturated fatty acids and so are liquid at room temperature.
A phospholipid consists of one glycerol, two fatty acids and a phosphate group. Phospholipids make the core of all membranes.
Animals: meat and dairy products. Plants: nuts, seeds, olive oil; oils stored in seeds such as sunflower, coconut, groundnut and corn.
Adipose tissue around organs provides cushioning and insulation. Lipids help in the absorption of vitamins A, D, E and K in the digestive system.
They serve as a long-term energy reserve in the form of fats in adipose tissues; when the body needs energy, they are broken down to fatty acids and glycerol, which are used as fuel. A gram of fat gives about twice the energy of a gram of carbohydrate.
The unit of nucleic acids. It is made of a pentose sugar (ribose or deoxyribose), a nitrogenous base and a phosphate group (PO₄).
DNA: adenine, thymine, cytosine, guanine. RNA: adenine, uracil, cytosine, guanine.
In 1953, US biologist James Watson and British biologist Francis Crick.
The pairing of nitrogenous bases is specific: adenine pairs with thymine (two hydrogen bonds) and cytosine pairs with guanine (three hydrogen bonds).
T A C G G T, because A pairs with T and C pairs with G.
The segment of DNA in which the sequence of nucleotides determines the synthesis of a protein (polypeptide chain) is called a gene.
| DNA | RNA |
|---|---|
| double-stranded | single-stranded |
| deoxyribose sugar | ribose sugar |
| thymine | uracil instead of thymine |
Transcription: the process of making an mRNA copy of DNA. Translation: the ribosome reads the nucleotide sequence of mRNA and joins specific amino acids to form a protein.
The flow of genetic information: DNA → mRNA (transcription) → protein (translation). The book calls the working of DNA the central dogma.
