Grade 10 biology – Chemicals of Life Quiz
1. Which property of water makes it a good solvent for many biological reactions in cells?
Water's polarity (oxygen end slightly negative, hydrogen ends slightly positive) allows it to surround and dissolve many charged and polar substances, making it an excellent solvent for cellular reactions.
2. What is the basic building block (monomer) of proteins?
Proteins are polymers made from amino acid monomers joined by peptide bonds; the sequence of amino acids determines protein structure and function.
3. Which type of biomolecule stores genetic information in cells?
Nucleic acids (DNA and RNA) store and transmit genetic information; DNA holds the hereditary instructions for building proteins and organisms.
4. Which test would you use to detect the presence of starch in a food sample?
Iodine reacts with starch to give a blue-black colour; Benedict's tests reducing sugars, Biuret tests proteins, and Sudan III tests lipids.
5. Which substance is the main structural component of plant cell walls?
Cellulose is a polysaccharide made of glucose units and provides structural strength to plant cell walls; glycogen is animal storage, starch is plant storage, cholesterol is a lipid.
6. What type of bond links nucleotides together in a DNA strand?
Phosphodiester bonds join the sugar of one nucleotide to the phosphate of the next, forming the sugar-phosphate backbone of DNA and RNA.
7. Which element is present in proteins but not in carbohydrates?
Proteins contain nitrogen (in amino groups) in addition to C, H and O; carbohydrates are composed mainly of carbon, hydrogen and oxygen and generally lack nitrogen.
8. What is the main role of enzymes in biological systems?
Enzymes are biological catalysts that lower activation energy and increase reaction rates; they are not consumed and can be reused.
9. Which of the following describes the effect of high temperature on most enzymes?
High temperatures can disrupt an enzyme's three-dimensional structure (denaturation), preventing substrate binding and reducing or abolishing activity.
10. Which molecule is known as the 'energy currency' of the cell?
ATP stores and transfers energy for many cellular processes; when ATP is hydrolysed to ADP and inorganic phosphate, energy is released for cellular work.
11. Which category of biomolecules are fats and oils classified under?
Fats and oils are lipids, hydrophobic molecules that store energy, form membranes and provide insulation.
12. What is the result of a dehydration synthesis reaction between two monosaccharides?
Dehydration synthesis (condensation) joins two monosaccharides to form a disaccharide and releases a water molecule.
13. Which of the following is a function of vitamins in living organisms?
Many vitamins function as coenzymes or precursors to cofactors that assist enzymes in metabolic reactions; they are not structural backbones or major energy stores.
14. Which macromolecule is primarily used by cells for short-term energy and quick release?
Carbohydrates (like glucose) are readily broken down to release energy quickly for immediate cellular needs; lipids store energy long-term.
15. What is glycogen?
Glycogen is a branched polymer of glucose used by animals (including humans) to store carbohydrate energy, mainly in liver and muscle.
16. Which test indicates the presence of reducing sugars like glucose?
Benedict's reagent reacts with reducing sugars, producing a colour change (usually from blue to orange/red) when heated; iodine is for starch, Biuret for protein, emulsion for lipids.
17. Which atom is the backbone element of all organic molecules of life?
Carbon's ability to form four covalent bonds allows it to build diverse organic molecules (carbohydrates, proteins, lipids, nucleic acids) essential for life.
18. Which of these is a structural difference between DNA and RNA?
DNA includes the base thymine while RNA has uracil; additionally DNA has deoxyribose sugar and is usually double-stranded, whereas RNA has ribose and is usually single-stranded.
19. Which of the following best explains why lipids do not mix with water?
Lipids are largely nonpolar molecules that do not form favourable interactions with polar water molecules, so they separate from water (are hydrophobic).
20. What type of bond holds two amino acids together in a protein chain?
A peptide bond (an amide linkage) forms between the amino group of one amino acid and the carboxyl group of another during protein synthesis.
21. Which molecule contains instructions for making proteins and is found in the cell nucleus?
DNA in the nucleus carries the genetic code that directs the synthesis of proteins via transcription and translation.
22. Which mineral is most important for strong bones and teeth in humans?
Calcium is essential for bone and tooth mineralisation; iron is important for blood, sodium for fluid balance; fluoride can help tooth enamel but calcium is primary for bones.
23. What is meant by an enzyme's 'active site'?
The active site is a specific region on the enzyme with a shape and chemical environment that fits the substrate, allowing the catalytic reaction to proceed.
24. Which of the following describes the primary structure of a protein?
Primary structure refers to the linear order of amino acids in a polypeptide; higher levels (secondary, tertiary, quaternary) refer to folding and interactions.
25. How do buffer systems (like bicarbonate in blood) help maintain homeostasis?
Buffers absorb excess H+ or OH- ions, minimising pH fluctuations and helping maintain stable conditions required for enzyme activity and cell function.
26. Which of the following elements is essential for the formation of ATP and nucleic acids and is part of the chemicals of life?
Phosphorus is a key component of ATP (in phosphate groups) and the phosphate backbone of nucleic acids; it is essential in many biological molecules.
27. Which property of water helps lakes and rivers remain at a stable temperature, protecting aquatic life in Kenya?
Water's high specific heat capacity means it absorbs or releases large amounts of heat with little change in temperature, helping aquatic environments stay stable for organisms.
28. Which test would you use to detect the presence of reducing sugars (like glucose) in a leaf extract during a school practical?
Benedict's reagent reacts with reducing sugars to give a colour change (blue to green/yellow/orange/red) depending on concentration; Biuret is for proteins, iodine for starch, Sudan III for lipids.
29. Which biomolecule is the main component of cell membranes and forms a bilayer that controls entry and exit of substances?
Phospholipids have hydrophilic heads and hydrophobic tails that arrange into a bilayer, forming the basic structure of cell membranes.
30. Which of the following is a polymer made of amino acid monomers and performs many structural and functional roles in cells?
Proteins are polymers of amino acids and serve as enzymes, structural materials, transporters and more; glucose is a monosaccharide, fatty acids form lipids, nucleotides form nucleic acids.
31. Which nutrient deficiency is commonly associated with iron deficiency anaemia among adolescents and can be tested by checking haemoglobin levels?
Iron is required for haemoglobin synthesis; lack of iron leads to reduced haemoglobin and iron-deficiency anaemia, common in growing adolescents.
32. Which biomolecule stores genetic information and is made of nucleotides containing deoxyribose, phosphate and four bases?
DNA (deoxyribonucleic acid) is composed of nucleotide monomers with deoxyribose sugar, phosphate groups and four bases (A, T, C, G) and stores genetic information.
33. Which of the following is a function of carbohydrates in plants and human diets?
Carbohydrates (e.g., glucose) are primary energy sources; enzymes are proteins, genetic information is stored in nucleic acids, phospholipid bilayers are lipids.
34. Which molecule is described as the 'energy currency' of the cell used in metabolic reactions?
Adenosine triphosphate (ATP) stores and transfers energy for cellular processes; cholesterol is a lipid, cellulose is structural carbohydrate, amino acids form proteins.
35. Which class of lipid is the main storage form of energy in animal tissues?
Triglycerides store large amounts of energy in their fatty acid chains and are stored in adipose tissue; phospholipids form membranes, steroids have hormonal roles, waxes are protective.
36. Which molecule is a structural polysaccharide found in plant cell walls that provides rigidity and is not digestible by human gut enzymes?
Cellulose is a long polymer of glucose with β-glycosidic bonds forming fibrous cell walls; humans lack the enzyme to break these bonds, so it acts as fibre.
37. Which vitamin is important for vision and can be obtained from foods like carrots and green leafy vegetables common in Kenya?
Vitamin A (as retinol or provitamin A carotenoids) is essential for normal vision and eye health; carrots and leafy greens are good sources.
38. What effect does increasing temperature beyond the optimum generally have on an enzyme's activity?
High temperatures can change an enzyme's shape (denaturation), destroying the active site and decreasing activity; they do not convert enzymes to other macromolecules.
39. Which ion is essential for muscle contraction and also important for strong bones and teeth?
Calcium ions are required for muscle contraction, neurotransmission and are a major component of bone and tooth mineral matrix.
40. Which substance acts as a biological catalyst in cells and speeds up reactions without being consumed?
Enzymes are proteins (or RNA in some cases) that lower activation energy and increase reaction rates while remaining unchanged.
41. Which of the following is NOT a component of a nucleotide (the building block of DNA and RNA)?
Nucleotides are made of a pentose sugar, a phosphate group and a nitrogenous base; amino acids are the monomers of proteins.
42. Which of these is an example of a disaccharide formed from two monosaccharides?
Sucrose is composed of glucose + fructose (a disaccharide); cellulose and glycogen are polysaccharides, fructose is a monosaccharide.
43. Which test gives a purple colour in the presence of proteins during a school experiment?
The Biuret reagent reacts with peptide bonds in proteins to give a violet/purple colour; Benedict's is for reducing sugars, iodine for starch, Sudan III for lipids.
44. Which substance helps maintain pH in blood and other body fluids by acting as a buffer?
Bicarbonate ions form part of the carbonic acid–bicarbonate buffer system which resists pH changes in blood.
45. Which fatty acid type has no double bonds between carbon atoms and is usually solid at room temperature?
Saturated fatty acids have single bonds only, pack closely and are often solid at room temperature; unsaturated fats have one or more double bonds.
46. Which molecule produced by green plants during photosynthesis is used directly as a source of chemical energy by many organisms?
Photosynthesis produces glucose (C6H12O6) which organisms metabolise for energy; oxygen is a by-product, nitrogen gas is not produced by photosynthesis, cellulose is structural.
47. Which mineral deficiency causes goitre due to insufficient thyroid hormone production and can affect people in regions with low iodine in soil?
Iodine is required for thyroid hormone synthesis; lack of iodine causes thyroid enlargement (goitre) and impaired metabolism.
48. Which statement best describes an enzyme's active site?
The active site is the specific region of an enzyme that binds substrate(s) and catalyses the chemical reaction.
49. Which molecule forms the primary structural material of fungal cell walls rather than cellulose?
Fungal cell walls are made of chitin, a polymer of N-acetylglucosamine; glycogen and starch are storage polysaccharides, peptidoglycan is found in bacterial walls.
50. Which process breaks down large biological molecules into smaller ones using water and is important in digestion?
Hydrolysis uses water to split bonds in macromolecules (e.g., proteins to amino acids) during digestion; dehydration synthesis builds polymers by removing water.
51. Which organic compound contains long chains of carbon and hydrogen and is insoluble in water, making it important for waterproofing and energy storage?
Lipids are hydrophobic molecules made of long hydrocarbon chains, used for energy storage, insulation and waterproofing (e.g., waxes, fats).