Brain Grain · braingrain.in
Science — Practice Paper · Set 1
Class: 10Samacheer KalviMax Marks: 86
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.‘A’ is a cylindrical structure that begins from the lower end of medulla and extend downwards. It is enclosed in bony cage ‘B’ and covered by membranes ‘C’. As many as ‘D’ pairs of nerves arise from the structure ‘A’. (i) What is A? (ii) Name (a) bony cage ‘B’ and (b) membranes ‘C’ (iii) How much is D?[1]
2.An organic compound ‘A’ is widely used as a preservative and has the molecular formula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound ‘B’.[1]
3.Transpiration is a necessary evil in plants. Explain.[1]
4.The eyes of the nocturnal birds like owl are having a large cornea and a large pupil. How does it help them?[1]
5.The hydroxide ion concentration of a solution is 1 \times 10-11M. What is the pH of the solution?[1]
6.‘P’ is a gene required for the synthesis of vitamin A. It is integrated with genome of ‘Q’ to produce genetically modified plant ‘R’.[1]
7.Our body contains a large number of cells ‘L’ which are the longest cells in the body. L has long and short branch called as ‘M’ and ‘N’ respectively. There is a gap ‘O’ between two ‘L’ cells, through which nerve impulse transfer by release of chemical substance ‘P’. (i) Name the cells L (ii) What are M and N? (iii) What is the gap O? (iv) Name the chemical substance P[1]
8.Octopus, cockroach and frog all have eyes. Can we group these animals together to establish a common evolutionary origin. Justify your answer.[1]
9.Will the cool drinks give more fizz at top of the hills or at the foot? Explain[1]
10.How is the digestive system of rabbit suited for herbivorous mode of feeding?[1]
11.Cell phone towers should be placed far away from residential areas. Why?[1]
12.A piece of wire of resistance 10 ohm is drawn out so that its length is increased to three times its original length. Calculate the new resistance.[1]
13.a) Identify the bond between H and F in HF molecule.[1]
14.Under which conditions does the law of independent assortment hold good and why?[1]
15.Explain the experiment of measuring the real and apparent expansion of a liquid with a neat diagram.[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.Cross pollination[2]
17.Its unit is N (newton)[2]
18.Leeches do not have an elaborate secretion of digestive juices and enzymes -Why ?[2]
19.Cambium : Present (During secondary growth only)[2]
20.Secondary Growth : Present[2]
21.Cambium : Absent[2]
22.What are called thermolysis reactions?[2]
23.If one pollen grain produces two male gametes, how many pollen grains are needed to fertilize 10 ovules?[2]
24.A solution is prepared by dissolving 45 g of sugar in 180 g of water. Calculate the mass percentage of solute.[2]
25.Internal valves are absent : Internal valves are present[2]
26.Classify the types of force based on their application.[2]
27.Write the reaction for photosynthesis?[2]
28.What is the study of fossils called?[2]
29.A person who is sitting at a distance of 400 m from a source of sound is listening to a sound of 600 Hz. Find the time period between successive compressions from the source?[2]
30.The walls of the right ventricle are thicker than the right auricles.[2]
31.In symplastic movement, the water travels through the cells i.e. their cytoplasm; intercellular movement is through the plasmodesmata.[2]
32.Write the name of a synthetic auxin.[2]
33.State Rayleigh’s law of scattering[2]
Part III — Long Answer Questions 7 × 5 = 35
Answer in detail. (Answer all questions.)
34.Why are leucocytes classified as granulocytes and agranulocytes? Name each cell and mention its functions.[5]
35.Describe the structure and working of the human heart.[5]
36.Where are estrogens produced? What is the role of estrogens in the human body?[5]
37.When a number of resistors are connected in parallel, the reciprocal of the effective resistance is equal to the sum of the reciprocals of the individual resistances[5]
38.The electronic configuration of metal A is 2,8,18,1.[5]
39.Why is the Government imposing ban on the use of polythene bags and plastics? Suggest alternatives. How is this ban likely to improve the environment?[5]
40.What are the hormones secreted by posterior lobe of the pituitary gland? Mention the tissues on which they exert their effect.[5]
🔑 Show Answer Key — Set 1
- 1. (i) A – Spinal cord. (ii)(a) B – Vertebral column (b) C – Meninges. (iii) D – 31 pairs of spinal nerves.
- 2. (i) Compound A is ethanoic acid (acetic acid), CH3COOH. (ii) It reacts with ethanol in the presence of concentrated H2SO4 to form the sweet-smelling ester ethyl ethanoate, B: CH3COOH + C2H5OH --conc. H2SO4-> CH3COOC2H5 + H2O (iii) The process is esterification.
- 3. Transpiration, the process of water vapor loss from a plant's aerial parts, is often described as a 'necessary evil' because it is essential for plant survival and function, yet it also poses a risk of dehydration. It is necessary because it drives the ascent of sap, enabling the transport of water and dissolved mineral nutrients from the roots to the leaves, which is vital for photosynthesis and growth. Transpiration also plays a role in cooling the plant surface, preventing overheating, and helps maintain turgor pressure in cells, supporting leaf expansion and plant rigidity. However, it is considered an 'evil' because it leads to significant water loss. In conditions of water scarcity…
- 4. The eyes of nocturnal birds like owls are adapted to see in low light conditions. A large cornea, which is the transparent outer layer of the eye, allows a greater amount of light to enter. Similarly, a large pupil, the opening in the center of the iris, can expand significantly to let in even more light. This increased light gathering capacity ensures that more light reaches the retina, where photoreceptor cells convert it into neural signals. Consequently, the bird can form a brighter and clearer image of its surroundings, enabling it to hunt and navigate effectively in the dim light of night.
- 5. [OH-] = 1 x 10^-11 M pOH = -log10[OH-] = 11 pH + pOH = 14 pH = 14 - 11 = 3
- 6. P = gene(s) for provitamin A (beta‑carotene biosynthesis; e.g., psy and crtI). Q = the crop plant whose genome is modified (example: rice). R = the genetically modified plant (Golden Rice) that produces beta‑carotene (provitamin A) in edible tissues.
- 7. (i) The cells referred to as L, which are the longest cells in the body and are fundamental to the nervous system, are neurons. (ii) M represents the axon, which is the long branch extending from the neuron's cell body, responsible for transmitting nerve impulses away from the cell. N represents the dendrites, which are the shorter, branching extensions that receive nerve impulses from other neurons and transmit them towards the cell body. (iii) The gap O between two neurons, across which nerve impulses are transmitted, is called a synapse. (iv) The chemical substance P released at the synapse to transfer the nerve impulse is a neurotransmitter, specifically acetylcholine in many cases.
- 8. No. They cannot be grouped solely on presence of eyes. Correct classification: octopus — phylum Mollusca (Cephalopoda); cockroach — phylum Arthropoda (Insecta); frog — phylum Chordata (Amphibia).
- 9. Cool drinks will fizz more at the top of the hill. At higher altitude, pressure is lower, so the solubility of carbon dioxide in the drink decreases and more CO2 escapes as bubbles.
- 10. The digestive system of a rabbit is highly adapted for its herbivorous diet, which primarily consists of fibrous plant material. Key adaptations include specialized dentition and a significantly enlarged caecum. Rabbits possess heterodont dentition, meaning they have different types of teeth suited for their diet, although they lack canine teeth. Their incisors are prominent for gnawing, followed by a gap called the diastema, which facilitates chewing and manipulation of food. The large, well-developed caecum is a crucial component where microbial fermentation occurs. This fermentation process, carried out by bacteria and other microorganisms, breaks down cellulose, a complex carbohydrate…
- 11. Cell phone towers emit radio-frequency electromagnetic waves. To reduce continuous exposure and possible health concerns, they should be placed away from densely populated residential areas.
- 12. Given initial R = 10 Ω. Let initial length = L and area = A. R = ρL/A = 10 Ω. New length = 3L. With constant volume, new area = A/3. R' = ρ(3L)/(A/3) = 9 (ρL/A) = 9R = 9 x 10 Ω = 90 Ω.
- 13. a) The bond between H and F in the HF molecule is a polar covalent bond. b) This identification is based on the significant difference in electronegativity between hydrogen and fluorine. Fluorine is highly electronegative, while hydrogen is less electronegative. This unequal sharing of electrons creates a partial positive charge on the hydrogen atom and a partial negative charge on the fluorine atom, resulting in a polar bond. c) Electronegativity generally increases from left to right across a period in the periodic table due to an increasing nuclear charge and a decrease in atomic radius. Conversely, electronegativity decreases as one moves down a group because the atomic radius increas…
- 14. The law of independent assortment holds when the genes for the two traits are on different (non‑homologous) chromosomes or are far apart on the same chromosome (not linked), each trait is controlled by a pair of alleles that segregate during gamete formation, and there is no interaction or linkage between the genes.
- 15. Apparatus: small flask (or bulb) fitted with a narrow capillary tube, wooden or metal stand, scale/ruled glass behind the capillary (for marking heights), thermometer, burner. Procedure: 1. Fill the flask with the liquid up to a mark on the capillary and glass scale. Mark the initial level as L1 at room temperature and note the initial temperature T1. 2. Heat the flask gently. As the vessel (container) expands its internal volume increases and the liquid level in the capillary may fall slightly. When this fall is observed, mark this level as L2. 3. Continue heating so the liquid itself expands; the liquid level then rises and finally stabilises at L3 for a higher temperature T2. Observati…
- 16. Cross-pollination (xenogamy): Transfer of pollen grains from the anther of a flower on one plant to the stigma of a flower on a different plant of the same species. Example: Apple, maize, sunflower. <div
- 17. The quantity is weight, which is a force. Its SI unit is newton (N). Since W = mg, the unit of weight is kg m s^-2, which is equal to N.
- 18. Leech is sanguivorous, meaning it feeds on blood. It sucks blood and stores it in the crop, where it is digested very slowly. Hirudin prevents the stored blood from clotting. Since stored blood nourishes the leech for several months and is slowly processed, leech does not need elaborate secretion of digestive juices and enzymes.
- 19. The presence of cambium, which appears during secondary growth, is a key feature in certain plant tissues. This lateral meristem, known as vascular cambium, is responsible for producing secondary xylem towards the inside of the stem or root and secondary phloem towards the outside. This activity leads to an increase in the plant's girth, a process vital for woody plants.
- 20. Secondary growth, characterized by an increase in girth through the activity of lateral meristems like the vascular cambium and cork cambium, is a prominent feature in the stems and roots of dicotyledonous plants and gymnosperms. This process allows for the formation of wood and bark, providing structural support and enhancing water transport. In contrast, most monocotyledonous plants lack secondary growth, as they do not possess the necessary cambial tissues.
- 21. Cambium (vascular cambium) is absent in monocots, so secondary thickening does not occur.
- 22. Thermolysis reactions are decomposition reactions in which a reactant is decomposed by applying heat. Since the molecule dissociates by absorbing heat, the reaction is called thermolysis. 2HgO(s) --heat-> 2Hg(l) + O2(g)
- 23. 10 pollen grains.
- 24. $Mass percentage = ( Mass of the solute / Mass of the solution ) \times 100$ $= [ Mass of the solute / (Mass of the solute + Mass of the solvent)] \times 100$ $= [ 45 / (45+180)] \times 100 = 45 / 225 \times 100$ $Mass percentage = 20%$
- 25. Arteries, which carry blood away from the heart, do not have internal valves. This is because the blood pressure in arteries is high, and the heart's pumping action ensures unidirectional flow. In contrast, veins, which carry blood towards the heart, often have internal valves. These valves are crucial in veins, especially in the limbs, to prevent the backflow of blood due to gravity, ensuring that blood returns to the heart effectively against the force of gravity.
- 26. Forces can be classified into two main types based on whether they require physical contact between the interacting bodies or not. The first type is contact force, which is a force that acts only when two bodies are in direct physical contact. Examples of contact forces include frictional force, which opposes motion between surfaces in contact; normal force, which is perpendicular to the surface of contact; and muscular force, which is applied by the muscles of living beings. The second type is non-contact force, also known as action-at-a-distance force, which acts without any physical contact between the bodies. Examples of non-contact forces include gravitational force, the attractive f…
- 27. 6CO2 + 12 H2O -Light--chlorophyll\rightarrow C6H12O6 + 6H2O + 6O2 ↑ Carbon dioxide + Water \rightarrow Glucose + Water + Oxygen
- 28. Palaeontology.
- 29. Frequency f = 600 Hz. The time period between successive compressions is T = 1/f = 1/600 = 0.00167 s. The 400 m distance does not change the time period of the wave.
- 30. The walls of the right ventricle are thicker than those of the right auricle (atrium) because the right ventricle is responsible for pumping deoxygenated blood to the lungs, a task that requires generating higher pressure to push blood through the pulmonary circulation. The right auricle, on the other hand, primarily receives deoxygenated blood from the body via the vena cavae and simply delivers it to the right ventricle. This receiving function requires less muscular effort, hence its thinner walls compared to the ventricle.
- 31. Symplastic movement describes the transport of water through the living parts of plant cells, specifically moving from one cell's cytoplasm to another via plasmodesmata, which are small channels connecting adjacent cells. In contrast, apoplastic movement involves the transport of water through the non-living components of the plant, such as the cell walls and intercellular spaces, without passing through the plasma membrane or cytoplasm.
- 32. 2,4 D (2, 4 Dichlorophenoxy Acetic acid).
- 33. Rayleigh's law of scattering describes how light is scattered by particles that are much smaller than the wavelength of the light, such as molecules of gas in the atmosphere. The law states that the intensity of scattered light is inversely proportional to the fourth power of its wavelength. Mathematically, this can be expressed as: Intensity of scattering ∝ 1/λ⁴, where λ is the wavelength of the light. This relationship explains why shorter wavelength colours, such as blue and violet, are scattered much more effectively by atmospheric particles than longer wavelength colours, like red and orange. This is the reason why the sky appears blue during the day, as blue light is scattered in al…
- 34. Granulocytes (have cytoplasmic granules): - Neutrophils (≈60–65%): first responders; phagocytose bacteria and debris; numbers rise in acute bacterial infection. - Eosinophils (≈2–4%): combat parasitic infections and modulate allergic reactions. - Basophils (≈0.5–1%): release histamine and heparin during inflammation/allergic responses. Agranulocytes (lack visible granules): - Lymphocytes (≈20–25%): B lymphocytes produce antibodies (humoral immunity); T lymphocytes mediate cell‑mediated immunity. - Monocytes (≈3–8%): phagocytic; migrate to tissues and become macrophages.
- 35. The human heart is a four-chambered, muscular organ that functions as a pump to circulate blood throughout the body. It consists of two upper chambers, the right atrium and the left atrium, and two lower chambers, the right ventricle and the left ventricle. A muscular wall called the septum separates the right and left sides of the heart, preventing the mixing of oxygenated and deoxygenated blood. The heart is equipped with several valves: the tricuspid valve between the right atrium and right ventricle, the bicuspid (or mitral) valve between the left atrium and left ventricle, and the pulmonary and aortic semilunar valves at the exits of the ventricles. The working of the heart involves…
- 36. Estrogen is a female sex hormone and is produced by the Graafian follicles of the Ovary. Role of Estrogens in the human body : (i) It brings about the changes that occur during puberty. (ii) It initiates the process of oogenesis. (iii) It stimulates the maturation of ovarian follicles in the ovary. (iv) It promotes the development of secondary sexual characters (breast development, high pitched voice etc).
- 37. General derivation: For n resistors in parallel, voltage V is same across each. Total current I = sum of Ii = V(sum of 1/Ri). Define RP by I = V/RP so V/RP = V(sum of 1/Ri) => 1/RP = sum of 1/Ri. Identical resistors case: If R1 = R2 = ... = Rn = R, then 1/RP = n(1/R) => RP = R/n.
- 38. The metal A is copper (Cu). When copper is exposed to air and moisture, it forms a green layer of basic copper carbonate: 2Cu + O2 + CO2 + H2O -> CuCO3.Cu(OH)2 So, B is basic copper carbonate. With concentrated sulphuric acid, copper forms copper sulphate, sulphur dioxide and water: Cu + 2H2SO4 -> CuSO4 + SO2 + 2H2O So, C is copper sulphate (CuSO4) and D is sulphur dioxide (SO2).
- 39. (i) Polythene bags and plastics are non bio degradable materials. (ii) If they are used, they accumulate in the soil, water bodies etc., (iii) In the soil they get buried and alter the nature of the soil. It prevents aeration of the soil and affects microbes. Excessive accumulation of plastic can render the soil barren. (iv) In water bodies they cover the water surface and prevent oxygen from diffusing into the water thereby affecting aquatic flora and fauna. (v) Plastic covers also find their way into the stomach of animals during feeding and may even prove to be fatal. (vi) Burning of plastics produces dioxin which can cause developmental and reproductive problems, damage the immune sys…
- 40. The hormones secreted by the posterior lobe of the pituitary gland are (a) Vasopressin : In kidney tubules it increases reabsorption of water. It reduces loss of water through urine and hence the name antidiuretic hormone. (b) Oxytocin helps in the contraction of the smooth muscles of uterus at the time of child birth and milk ejection from the mammary gland after child birth.
Brain Grain · braingrain.in
Science — Practice Paper · Set 2
Class: 10Samacheer KalviMax Marks: 86
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.While doing an experiment for the determination of focal length of a convex lens, Raja Suddenly dropped the lens. It got broken into two halves along the axis. If he continues his experiment with the same lens, (a) can he get the image? (b) Is there any change in the focal length?[1]
2.What precautions can be taken for preventing heart diseases ?[1]
3.Susan’s father feels very tired and frequently urinates. After clinical diagnosis he was advised to take an injection daily to maintain his blood glucose level. What would be the possible cause for this? Suggest preventive measures.[1]
4.Calculate the % relative abundance of B -10 and B -11, if its average atomic mass is 10.804 amu.[1]
5.When sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound remain the same. Do you hear an echo sound on a hotter day? Justify your answer.[1]
6.“Wearing helmet and fastening the seat belt is highly recommended for safe journey” Justify your answer using Newton’s laws of motion.[1]
7.Where do the light dependent reaction and the Calvin cycle occur in the chloroplast?[1]
8.Read the following passage and answer the questions that follow[1]
9.List any three activities based on 3R approach to conserve natural resources.[1]
10.‘A’ is a cylindrical structure that begins from the lower end of medulla and extend downwards. It is enclosed in bony cage ‘B’ and covered by membranes ‘C’. As many as ‘D’ pairs of nerves arise from the structure ‘A’. (i) What is A? (ii) Name (a) bony cage ‘B’ and (b) membranes ‘C’ (iii) How much is D?[1]
11.An organic compound ‘A’ is widely used as a preservative and has the molecular formula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound ‘B’.[1]
12.Transpiration is a necessary evil in plants. Explain.[1]
13.The eyes of the nocturnal birds like owl are having a large cornea and a large pupil. How does it help them?[1]
14.The hydroxide ion concentration of a solution is 1 \times 10-11M. What is the pH of the solution?[1]
15.‘P’ is a gene required for the synthesis of vitamin A. It is integrated with genome of ‘Q’ to produce genetically modified plant ‘R’.[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.During light reaction, photosyntetic pigments absorb the light energy and convert it into chemical energy ATP and NADPH2.[2]
17.Name the parts of the hind brain.[2]
18.The inputs are water, solar energy, photosynthetic pigments. The end products are ATP and NADPH2.[2]
19.A human hand, a front leg of a cat, a front flipper of a whale and a bat’s wing look dissimilar and adapted for different functions. What is the name given to these organs?[2]
20.It is the breeding of unrelated animals. : 1. It refers to the mating of closely related animals within the same breed for about 4-6 generations.[2]
21.What are chemical messengers?[2]
22.What is bolting? How can it be induced artificially?[2]
23.Which acts as a link between the nervous system and endocrine system?[2]
24.Sonalika, Kalyan Sona : High yielding semi¬dwarf wheat variety.[2]
25.How are e-wastes generated?[2]
26.A plant hormone was first discovered in Japan when rice plants were suffering from Bakanae disease caused by Gibberella fujikoroi. Based on this information answer the following questions:[2]
27.Name any two devices, which are working on the heating effect of the electric current.[2]
28.The size of the nucleus is large. : 1. They have normal small sized nucleus.[2]
29.Explain smelting process.[2]
30.A breeder wishes to incorporate desirable characters into the crop plants. Prepare a list of characters he will incorporate[2]
31.Number of Xylem : Tetrarch[2]
32.What is the importance of rainwater harvesting?[2]
33.Which hazardous radiation is the cause for genetic disorders?[2]
Part III — Long Answer Questions 7 × 5 = 35
Answer in detail. (Answer all questions.)
34.A heavy truck and bike are moving with the same kinetic energy. If the mass of the truck is four times that of the bike, then calculate the ratio of their momenta. (Ratio of momenta = 2:1[5]
35.Arun was playing in the garden. Suddenly he saw a dragon fly sitting on a plant. He observed the wings of it. He thought it looked similar to a wing of a crow. Is he correct? Give reason for your answer.[5]
36.What is mean by reflection of sound? Explain: a) reflection at the boundary of a rarer medium b) reflection at the boundary of a denser medium c) Reflection at curved surfaces[5]
37.Why should the light dependent reaction occur before the light independent reaction?[5]
38.Arrange the following in the chronological order of discovery[5]
39.What are the types of inertia? Give an example for each type.[5]
40.A pure tall plant (TT) is crossed with pure dwarf plant (tt), what would be the F1 and F2 generations? Explain.[5]
🔑 Show Answer Key — Set 2
- 1. (a) Yes, he can still get the image using one half of the broken convex lens. (b) There is no change in the focal length because the curvature of the lens surfaces does not change. However, the intensity or brightness of the image will be reduced because less light passes through the broken lens.
- 2. Diet: reduce total calories if overweight; limit saturated fats and trans fats and dietary cholesterol; include moderate polyunsaturated and monounsaturated fats; reduce salt (sodium); eat more fruits, vegetables, whole grains and dietary fiber. Lifestyle: regular physical activity (daily exercise/walking), maintain healthy weight. Avoid smoking and excessive alcohol. Regular medical checkups to monitor blood pressure and blood cholesterol.
- 3. Susan's father is likely suffering from diabetes mellitus, a condition characterized by persistently high blood glucose levels. This can occur due to insufficient production or utilization of insulin, a hormone produced by the beta cells of the pancreas. The fact that he requires daily insulin injections suggests he has insulin-dependent diabetes, also known as Type 1 diabetes, where the pancreatic beta cells may have been destroyed or are not functioning properly. The symptoms of tiredness and frequent urination are classic signs of hyperglycemia (high blood sugar), as the body attempts to excrete excess glucose through urine, leading to dehydration and fatigue. While Type 1 diabetes can…
- 4. Let the percentage abundance of B-10 be x and B-11 be 100 - x. Average atomic mass = [10.01294x + 11.009305(100 - x)]/100 = 10.804. Solving, x = 20.636%. Therefore B-10 = 20.636% and B-11 = 79.364%.
- 5. On a hotter day, the speed of sound increases, so the echo returns in a shorter time: t = 2d/v. If the fixed distance is just enough for an echo on a cooler day, the return time may fall below 0.1 s and the echo will not be heard distinctly. If the reflecting surface is far enough that t remains at least 0.1 s, the echo can still be heard.
- 6. 1) State laws used: Newton's 1st law (inertia) and 2nd law (F = ma) plus impulse-momentum (Delta p = F_avg Delta t). 2) Describe the hazard: In a sudden stop or collision passenger's velocity v must change to zero (Delta v = -v); momentum change Delta p = mDelta v. 3) Use formula: average stopping force F_avg = mDelta v/Delta t. For fixed m and Delta v, larger Delta t -> smaller F_avg. 4) Apply to helmet: helmet cushions impact, increases Delta t and impact distance, so F_avg on skull decreases -> less injury. 5) Apply to seat belt: seat belt applies the unbalanced force to decelerate passenger, increases effective Delta t and spreads force across torso, preventing ejection and reducing l…
- 7. (i) The light dependent reaction refers to the light reaction of photosynthesis or Hill reaction and occurs in the grana of chloroplast. (ii) The Calvin cycle occurs in the stroma of chloroplast. ---
- 8. (a) Menarche — the first menstruation. Typical onset about 11–15 years (commonly 11–13 years but varies). (b) Napkin hygiene measures: use clean sanitary pads or tampons; change pads every 4–6 hours (or more often if needed); wash external genital area with mild soap and water and dry; wash hands before and after changing pads; wrap used pads in paper/plastic and dispose in bin or use napkin incinerator — do not flush; do not reuse disposable pads; store pads hygienically. (c) Yes. Rahini was correct — such advertisements raise awareness about menstrual hygiene and safe products.
- 9. (i) Reduce use of natural resources. E.g: coal. (ii) Reuse the waste whenever possible. Example water from kitchens can be used for growing plants. (iii) Recycle materials wherever possible. Example (a) Use of treated sewage water for gardening. (b) Bio wastes to be made into compost. ---
- 10. (i) A – Spinal cord. (ii)(a) B – Vertebral column (b) C – Meninges. (iii) D – 31 pairs of spinal nerves.
- 11. (i) Compound A is ethanoic acid (acetic acid), CH3COOH. (ii) It reacts with ethanol in the presence of concentrated H2SO4 to form the sweet-smelling ester ethyl ethanoate, B: CH3COOH + C2H5OH --conc. H2SO4-> CH3COOC2H5 + H2O (iii) The process is esterification.
- 12. Transpiration, the process of water vapor loss from a plant's aerial parts, is often described as a 'necessary evil' because it is essential for plant survival and function, yet it also poses a risk of dehydration. It is necessary because it drives the ascent of sap, enabling the transport of water and dissolved mineral nutrients from the roots to the leaves, which is vital for photosynthesis and growth. Transpiration also plays a role in cooling the plant surface, preventing overheating, and helps maintain turgor pressure in cells, supporting leaf expansion and plant rigidity. However, it is considered an 'evil' because it leads to significant water loss. In conditions of water scarcity…
- 13. The eyes of nocturnal birds like owls are adapted to see in low light conditions. A large cornea, which is the transparent outer layer of the eye, allows a greater amount of light to enter. Similarly, a large pupil, the opening in the center of the iris, can expand significantly to let in even more light. This increased light gathering capacity ensures that more light reaches the retina, where photoreceptor cells convert it into neural signals. Consequently, the bird can form a brighter and clearer image of its surroundings, enabling it to hunt and navigate effectively in the dim light of night.
- 14. [OH-] = 1 x 10^-11 M pOH = -log10[OH-] = 11 pH + pOH = 14 pH = 14 - 11 = 3
- 15. P = gene(s) for provitamin A (beta‑carotene biosynthesis; e.g., psy and crtI). Q = the crop plant whose genome is modified (example: rice). R = the genetically modified plant (Golden Rice) that produces beta‑carotene (provitamin A) in edible tissues.
- 16. During the light reaction, which occurs in the thylakoid membranes of the chloroplast, photosynthetic pigments such as chlorophyll absorb light energy. This absorbed energy is then utilized to convert light energy into chemical energy, stored in the molecules of ATP and NADPH. Concurrently, water molecules are split through a process called photolysis, releasing oxygen as a byproduct. Thus, the light reaction is essential for capturing solar energy and producing the energy carriers needed for the subsequent dark reaction.
- 17. It is formed of three parts cerebellum, pons and medulla oblongata.
- 18. The light-dependent reaction of photosynthesis has specific inputs and outputs. The essential inputs are water, which is split to release electrons and protons, and solar energy, which is captured by photosynthetic pigments like chlorophyll. The primary end products of the light reaction are ATP and NADPH, which are energy-carrying molecules. Additionally, oxygen is released as a byproduct from the photolysis of water. These products are then utilized in the subsequent dark reaction to synthesize glucose.
- 19. Homologous organs.
- 20. 1. Breeding of unrelated animals — Outbreeding. 2. Mating of closely related animals within the same breed for about 4–6 generations — Inbreeding.
- 21. The hormones produced by the endocrine glands are called chemical messengers. They diffuse into the blood stream and are carried to distant parts of the body. They act on specific organs called target organs.
- 22. Treatment of Rosette plants with Gibberellin induces sudden shoot elongation followed by flowering. This is called bolting.
- 23. Hypothalamus of the fore brain acts as a link between nervous and endocrine system.
- 24. Sonalika and Kalyan Sona — high‑yielding, semi‑dwarf wheat varieties.
- 25. E-wastes are generated when electrical and electronic devices (like mobiles, computers, TVs, refrigerators) become spoiled, outdated or non-repairable and are discarded by households, offices, industries, hospitals and institutions. Rapid technological change, short product life, lack of repair and mass disposal increase e-waste generation.
- 26. a. Gibberellin (GA) b. It causes excessive stem and internode elongation by stimulating cell elongation and cell division, producing the spindly plants seen in Bakanae disease. c. Two functions: (1) Promotes stem elongation (bolting) by increasing cell elongation and division. (2) Breaks dormancy and promotes seed/tuber germination (mobilises food reserves).
- 27. Two common household devices that operate based on the heating effect of electric current are the electric iron and the electric toaster. In both appliances, a high-resistance wire, typically made of a nichrome alloy (an alloy of nickel and chromium), is used. When an electric current passes through this nichrome coil, its high resistance causes it to heat up considerably due to the dissipation of electrical energy as heat (Joule heating). This generated heat is then utilized for the intended purpose: to press clothes in an electric iron or to toast bread in a toaster.
- 28. Cancer cells have a large nucleus, often with an increased nucleus-to-cytoplasm ratio. Normal cells have a comparatively small, regular nucleus.
- 29. Smelting is a pyrometallurgical process used to extract a metal from its ore by heating it strongly in the presence of a reducing agent, typically in a furnace. The primary objective of smelting is to reduce the metallic oxide ore to its molten metallic state. During this process, a flux, which is a chemical agent like limestone or silica, is often added. The flux reacts with the unwanted impurities in the ore (such as silica, alumina, or basic oxides) to form a molten slag. This slag has a lower melting point than the metal and is immiscible with it, allowing it to be easily separated from the molten metal by decantation or tapping. Smelting is a crucial step in the extraction of many im…
- 30. (i) Higher yield. (ii) Resistance to diseases. (iii) Resistance to insect pests. (iv) Short duration crop. (v) Tolerance to environmental conditions.
- 31. Tetrarch (four xylem arms) is typical of many dicot roots.
- 32. Rainwater harvesting collects and stores rainwater (e.g., from roofs) to recharge groundwater and store water for use. It helps conserve water, raise groundwater levels, reduce surface runoff and floods, decrease soil erosion, and provide a cleaner supplementary water source.
- 33. Radioactive radiations, particularly those with high penetrating power, are a significant cause of genetic disorders. Among these, highly penetrating gamma radiation poses a substantial risk. When these radiations interact with living cells, they can damage the DNA within the chromosomes. If this damage occurs in the germ cells (sperm or egg cells), it can lead to mutations that are passed on to future generations, resulting in heritable genetic disorders. Other forms of radioactivity can also contribute, but gamma rays are often highlighted due to their ability to penetrate deep into tissues and organs.
- 34. Let m_b = m, m_t = 4m. Equal kinetic energies: 1/2 m_t v_t^2 = 1/2 m_b v_b^2 => m_t v_t^2 = m_b v_b^2 => 4m v_t^2 = m v_b^2 => v_t^2 = (1/4) v_b^2 => v_t = v_b/2. Momentum: p_t = m_t v_t = 4m x (v_b/2) = 2 m v_b. p_b = m v_b. Therefore p_t : p_b = 2m v_b : 1m v_b = 2 : 1. (Units of momentum: kg m/s.)
- 35. (i) No. Wings of a dragon fly are different from the wings of crow. In the case of a crow, wings represent modified forelimbs. (ii) Wings of a dragon fly and crow have the same function. They serve to fly but their origin and developmental pattern are different. Such organs which look similar and perform similar function but have different origin and developmental pattern are called analogous organs.
- 36. Reflection of sound is the phenomenon where sound waves bounce back into the original medium upon striking the surface of another medium. This process is analogous to the reflection of light. a) When sound encounters the boundary of a rarer medium, which offers less resistance, a compression wave can be reflected back as a rarefaction. This occurs because the rarer medium cannot support the compression as effectively and essentially pushes back against it, inverting the wave. b) At the boundary of a denser or rigid medium, a compression wave is reflected back as a compression. This is due to the principle of equal and opposite reactions; the rigid surface exerts an equal and opposite forc…
- 37. (i) Light dependent reaction of photosynthesis refers to the light reaction / Hill reaction. This reaction occurs in the presence of light in the grana of chloroplast. (ii) During this process photosynthetic pigments absorb the light energy, and convert it into chemical energy ATP and NADPH2. (iii) The Light Independent reaction refers to the Dark reaction of photosynthesis or the biosynthetic pathway which occurs in stroma of chloroplast. (iv) During this reaction CO2, is reduced into carbohydrates with the help of light generated ATP and NADPH2. (v) Thus light dependent reaction occurs before the light independent reaction.
- 38. Chronological order: radioactivity (1896), discovery of radium (1898), artificial radioactivity (1934), nuclear reactor (1942).
- 39. (i) Inertia of rest: The resistance of a body to change its state of rest. Example: Leaves on a tree tend to remain at rest when the branch is shaken; they may get detached and fall. (ii) Inertia of motion: The resistance of a body to change its state of motion. Example: An athlete runs before jumping-the forward motion helps the athlete travel a longer distance in the jump. (iii) Inertia of direction: The resistance of a body to change its direction of motion. Example: When a car makes a sharp turn, passengers tend to be thrown outward or lean sideways because their bodies tend to continue in the original straight-line motion.
- 40. Crosses involving inheritance of only one pair of contrasting characters are called monohybrid cross. Cross between pure tall (TT) plant and Pure dwarf (tt) plant Parental Generation : Pure breeding Tall and dwarf plants are crossed (TT x tt). F1 Generation : Monohybrids are heterozygous tall. F2 Generation : Selfing of the F1 monohybrids takes place. Tall and dwarf plants are obtained in the ratio of 3:1 which is the phenotypic ratio. Genotypically plants are of three types as shown above and therefore genotypic ratio is 1:2:1.
Brain Grain · braingrain.in
Science — Practice Paper · Set 3
Class: 10Samacheer KalviMax Marks: 86
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.Our body contains a large number of cells ‘L’ which are the longest cells in the body. L has long and short branch called as ‘M’ and ‘N’ respectively. There is a gap ‘O’ between two ‘L’ cells, through which nerve impulse transfer by release of chemical substance ‘P’. (i) Name the cells L (ii) What are M and N? (iii) What is the gap O? (iv) Name the chemical substance P[1]
2.Octopus, cockroach and frog all have eyes. Can we group these animals together to establish a common evolutionary origin. Justify your answer.[1]
3.Will the cool drinks give more fizz at top of the hills or at the foot? Explain[1]
4.How is the digestive system of rabbit suited for herbivorous mode of feeding?[1]
5.Cell phone towers should be placed far away from residential areas. Why?[1]
6.A piece of wire of resistance 10 ohm is drawn out so that its length is increased to three times its original length. Calculate the new resistance.[1]
7.a) Identify the bond between H and F in HF molecule.[1]
8.Under which conditions does the law of independent assortment hold good and why?[1]
9.Explain the experiment of measuring the real and apparent expansion of a liquid with a neat diagram.[1]
10.While doing an experiment for the determination of focal length of a convex lens, Raja Suddenly dropped the lens. It got broken into two halves along the axis. If he continues his experiment with the same lens, (a) can he get the image? (b) Is there any change in the focal length?[1]
11.What precautions can be taken for preventing heart diseases ?[1]
12.Susan’s father feels very tired and frequently urinates. After clinical diagnosis he was advised to take an injection daily to maintain his blood glucose level. What would be the possible cause for this? Suggest preventive measures.[1]
13.Calculate the % relative abundance of B -10 and B -11, if its average atomic mass is 10.804 amu.[1]
14.When sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound remain the same. Do you hear an echo sound on a hotter day? Justify your answer.[1]
15.“Wearing helmet and fastening the seat belt is highly recommended for safe journey” Justify your answer using Newton’s laws of motion.[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.Actions performed without our control are called involuntary actions.[2]
17.Weight is a vector quantity[2]
18.Define the term: Solution[2]
19.Why are the rings of cartilages found in trachea of rabbit?[2]
20.Mention the artery which supplies blood to the heart muscle.[2]
21.Mature RBC in mammals do not have cell organelles.[2]
22.Define dispersion of light[2]
23.Define genetic engineering.[2]
24.It forms the grey matter of the brain[2]
25.Name two layered protective covering of human heart.[2]
26.Arrange in descending order, on the basis of their penetration power[2]
27.They remains less differentiated. : 5. They are well differentiated cells.[2]
28.Calculate the number of moles in $i) 27g of Al ii) 1.51 \times 1023 molecules of NH4Cl$[2]
29.Name the secondary sex organs in male[2]
30.Write a short note on editor and its main parts.[2]
31.What amount of radiation may cause death when a person is exposed to it?[2]
32.Arjun is studying in tenth standard. He was down with fever and went to meet the doctor. As he went to the clinic he saw a patient undergoing treatment for severe leech bite. Being curious, Arjun asked the doctor why leech bite was not felt as soon as it attaches to the skin ? What would have been the reply given by the doctor?[2]
33.When and where was the first nuclear reactor built?[2]
Part III — Long Answer Questions 7 × 5 = 35
Answer in detail. (Answer all questions.)
34.AIDS 5. CHD 6. NIDDM[5]
35.a) State Joule’s law of heating. b) An alloy of nickel and chromium is used as the heating element. Why? c) How does a fuse wire protect electrical appliances?[5]
36.Explain about domestic electric circuits. (circuit diagram not required)[5]
37.With a neat labelled diagram explain the structure of a neuron.[5]
38.How does developing embryo gets its nourishment inside the mother's body?[5]
39.How is the circulatory system designed in leech to compensate the heart structure ?[5]
40.While catching a cricket ball the fielder lowers his hands backwards. Why?[5]
🔑 Show Answer Key — Set 3
- 1. (i) The cells referred to as L, which are the longest cells in the body and are fundamental to the nervous system, are neurons. (ii) M represents the axon, which is the long branch extending from the neuron's cell body, responsible for transmitting nerve impulses away from the cell. N represents the dendrites, which are the shorter, branching extensions that receive nerve impulses from other neurons and transmit them towards the cell body. (iii) The gap O between two neurons, across which nerve impulses are transmitted, is called a synapse. (iv) The chemical substance P released at the synapse to transfer the nerve impulse is a neurotransmitter, specifically acetylcholine in many cases.
- 2. No. They cannot be grouped solely on presence of eyes. Correct classification: octopus — phylum Mollusca (Cephalopoda); cockroach — phylum Arthropoda (Insecta); frog — phylum Chordata (Amphibia).
- 3. Cool drinks will fizz more at the top of the hill. At higher altitude, pressure is lower, so the solubility of carbon dioxide in the drink decreases and more CO2 escapes as bubbles.
- 4. The digestive system of a rabbit is highly adapted for its herbivorous diet, which primarily consists of fibrous plant material. Key adaptations include specialized dentition and a significantly enlarged caecum. Rabbits possess heterodont dentition, meaning they have different types of teeth suited for their diet, although they lack canine teeth. Their incisors are prominent for gnawing, followed by a gap called the diastema, which facilitates chewing and manipulation of food. The large, well-developed caecum is a crucial component where microbial fermentation occurs. This fermentation process, carried out by bacteria and other microorganisms, breaks down cellulose, a complex carbohydrate…
- 5. Cell phone towers emit radio-frequency electromagnetic waves. To reduce continuous exposure and possible health concerns, they should be placed away from densely populated residential areas.
- 6. Given initial R = 10 Ω. Let initial length = L and area = A. R = ρL/A = 10 Ω. New length = 3L. With constant volume, new area = A/3. R' = ρ(3L)/(A/3) = 9 (ρL/A) = 9R = 9 x 10 Ω = 90 Ω.
- 7. a) The bond between H and F in the HF molecule is a polar covalent bond. b) This identification is based on the significant difference in electronegativity between hydrogen and fluorine. Fluorine is highly electronegative, while hydrogen is less electronegative. This unequal sharing of electrons creates a partial positive charge on the hydrogen atom and a partial negative charge on the fluorine atom, resulting in a polar bond. c) Electronegativity generally increases from left to right across a period in the periodic table due to an increasing nuclear charge and a decrease in atomic radius. Conversely, electronegativity decreases as one moves down a group because the atomic radius increas…
- 8. The law of independent assortment holds when the genes for the two traits are on different (non‑homologous) chromosomes or are far apart on the same chromosome (not linked), each trait is controlled by a pair of alleles that segregate during gamete formation, and there is no interaction or linkage between the genes.
- 9. Apparatus: small flask (or bulb) fitted with a narrow capillary tube, wooden or metal stand, scale/ruled glass behind the capillary (for marking heights), thermometer, burner. Procedure: 1. Fill the flask with the liquid up to a mark on the capillary and glass scale. Mark the initial level as L1 at room temperature and note the initial temperature T1. 2. Heat the flask gently. As the vessel (container) expands its internal volume increases and the liquid level in the capillary may fall slightly. When this fall is observed, mark this level as L2. 3. Continue heating so the liquid itself expands; the liquid level then rises and finally stabilises at L3 for a higher temperature T2. Observati…
- 10. (a) Yes, he can still get the image using one half of the broken convex lens. (b) There is no change in the focal length because the curvature of the lens surfaces does not change. However, the intensity or brightness of the image will be reduced because less light passes through the broken lens.
- 11. Diet: reduce total calories if overweight; limit saturated fats and trans fats and dietary cholesterol; include moderate polyunsaturated and monounsaturated fats; reduce salt (sodium); eat more fruits, vegetables, whole grains and dietary fiber. Lifestyle: regular physical activity (daily exercise/walking), maintain healthy weight. Avoid smoking and excessive alcohol. Regular medical checkups to monitor blood pressure and blood cholesterol.
- 12. Susan's father is likely suffering from diabetes mellitus, a condition characterized by persistently high blood glucose levels. This can occur due to insufficient production or utilization of insulin, a hormone produced by the beta cells of the pancreas. The fact that he requires daily insulin injections suggests he has insulin-dependent diabetes, also known as Type 1 diabetes, where the pancreatic beta cells may have been destroyed or are not functioning properly. The symptoms of tiredness and frequent urination are classic signs of hyperglycemia (high blood sugar), as the body attempts to excrete excess glucose through urine, leading to dehydration and fatigue. While Type 1 diabetes can…
- 13. Let the percentage abundance of B-10 be x and B-11 be 100 - x. Average atomic mass = [10.01294x + 11.009305(100 - x)]/100 = 10.804. Solving, x = 20.636%. Therefore B-10 = 20.636% and B-11 = 79.364%.
- 14. On a hotter day, the speed of sound increases, so the echo returns in a shorter time: t = 2d/v. If the fixed distance is just enough for an echo on a cooler day, the return time may fall below 0.1 s and the echo will not be heard distinctly. If the reflecting surface is far enough that t remains at least 0.1 s, the echo can still be heard.
- 15. 1) State laws used: Newton's 1st law (inertia) and 2nd law (F = ma) plus impulse-momentum (Delta p = F_avg Delta t). 2) Describe the hazard: In a sudden stop or collision passenger's velocity v must change to zero (Delta v = -v); momentum change Delta p = mDelta v. 3) Use formula: average stopping force F_avg = mDelta v/Delta t. For fixed m and Delta v, larger Delta t -> smaller F_avg. 4) Apply to helmet: helmet cushions impact, increases Delta t and impact distance, so F_avg on skull decreases -> less injury. 5) Apply to seat belt: seat belt applies the unbalanced force to decelerate passenger, increases effective Delta t and spreads force across torso, preventing ejection and reducing l…
- 16. Actions performed without our conscious control are called involuntary actions. Examples include heartbeat, breathing, digestion and reflex actions. <div
- 17. Yes. Weight is a vector quantity because it has both magnitude and direction. It acts vertically downward towards the centre of the Earth. Weight is given by W = mg and its SI unit is newton (N).
- 18. A solution is defined as a homogeneous mixture of two or more substances. In a homogeneous mixture, the composition and properties are uniform throughout the mixture. This means that the solute particles are completely dissolved in the solvent, and they cannot be distinguished by the naked eye or even under a microscope. Examples include salt dissolved in water or sugar dissolved in water.
- 19. The trachea, commonly known as the windpipe, in rabbits is reinforced with C-shaped rings of cartilage. These cartilaginous rings are crucial because they provide structural support to the tracheal walls, preventing them from collapsing inwards. This support ensures that the air passage remains open at all times, allowing for the unimpeded and free movement of air into and out of the lungs during respiration.
- 20. The artery that supplies oxygenated blood directly to the heart muscle itself is called the coronary artery. The heart, being a vital organ that works continuously, requires a constant and rich supply of oxygen and nutrients to function properly. The coronary arteries branch off from the aorta, the main artery carrying oxygenated blood from the left ventricle to the rest of the body, shortly after it leaves the heart. These arteries then spread across the surface of the heart, delivering blood to the cardiac muscle tissue. Blockage or narrowing of the coronary arteries can lead to serious conditions like angina or myocardial infarction (heart attack).
- 21. Mature red blood cells (RBCs) in mammals are anucleated, meaning they lack a nucleus, and also lack most other cell organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus. This unique adaptation maximizes the internal space available for hemoglobin, the protein responsible for oxygen transport, thereby increasing the oxygen-carrying capacity of the blood. Additionally, the absence of mitochondria prevents the RBCs from consuming the oxygen they are transporting through aerobic respiration; instead, they rely on anaerobic glycolysis for energy.
- 22. Dispersion of light is the phenomenon observed when a beam of white light passes through a transparent medium, such as a glass prism or water droplets, and splits into its constituent colours. This splitting occurs because each colour of light, corresponding to a different wavelength, travels at a slightly different speed within the medium. Consequently, each colour is refracted at a slightly different angle. Violet light, having the shortest wavelength, is deviated the most, while red light, with the longest wavelength, is deviated the least. This results in the formation of a spectrum of colours, typically observed as red, orange, yellow, green, blue, indigo, and violet (ROYGBIV).
- 23. Genetic engineering is the manipulation and transfer of genes from one organism into another to create a new DNA called as recombinant DNA (rDNA).
- 24. Grey matter is formed mainly by neuronal cell bodies (cytons), dendrites and unmyelinated nerve fibres (e.g., the cerebral cortex). Long VIII. Long Answer Questions 5 marks each <div
- 25. The human heart is enclosed within a protective double-layered sac known as the pericardium. The outer layer is the fibrous pericardium, a tough, inelastic sac that anchors the heart and prevents overfilling. Inside this lies the serous pericardium, which is further divided into two sub-layers. The parietal layer of the serous pericardium lines the inner surface of the fibrous pericardium, while the visceral layer, also called the epicardium, is directly adhered to the surface of the heart muscle. Between these two layers of the serous pericardium is the pericardial cavity, which contains a small amount of pericardial fluid. This fluid acts as a lubricant, reducing friction as the heart b…
- 26. The penetration power of different types of radiation refers to their ability to pass through matter. In descending order, meaning from highest penetration power to lowest, the arrangement is as follows: Cosmic rays possess the highest penetration power among these, capable of traversing significant distances through various materials. Gamma rays follow, being highly energetic electromagnetic radiation that can penetrate deeply into substances. Beta rays, which are fast-moving electrons or positrons, have moderate penetration power, less than gamma rays but more than alpha rays. Alpha rays, composed of helium nuclei, have the lowest penetration power and can be stopped by a thin sheet of…
- 27. Cancer cells — less differentiated (anaplastic); Normal cells — well differentiated.
- 28. (i) For 27 g of Al, number of moles = mass/atomic mass = 27/27 = 1 mole. (ii) For 1.51 x 10^23 molecules of NH4Cl, number of moles = number of molecules/Avogadro number = (1.51 x 10^23)/(6.023 x 10^23) = 0.25 mole approximately.
- 29. Secondary sex organs (male): epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral (Cowper's) glands, urethra and penis.
- 30. The Scratch editor has three main parts: Stage, Sprite and Script editor. The script editor contains the script area, block menu and block palette.
- 31. Exposure to approximately 600 Roentgens (R) of radiation can be lethal to humans. This level of radiation can cause severe damage to cells and organs, leading to acute radiation syndrome, which can be fatal if not treated promptly. The severity of the effects depends on the dose rate and the duration of exposure, as well as individual sensitivity.
- 32. The doctor would have explained that leeches possess a remarkable ability to make their bite painless initially. This is due to the secretion of an anaesthetic substance along with saliva when they attach to the skin, which numbs the area and prevents the host from feeling the bite immediately. Furthermore, the leech secretes hirudin, a powerful anticoagulant, which inhibits the clotting of blood. This ensures that the blood remains in a liquid state, allowing the leech to feed continuously and efficiently without interruption.
- 33. The world's first nuclear reactor was built in 1942 at the University of Chicago, USA. This groundbreaking achievement was part of the Manhattan Project and was led by physicist Enrico Fermi. The reactor, known as Chicago Pile-1 (CP-1), demonstrated the feasibility of achieving a self-sustaining nuclear chain reaction, a critical step towards harnessing nuclear energy.
- 34. Cancer cells have a large nucleus, often with an increased nucleus-to-cytoplasm ratio. Normal cells have a comparatively small, regular nucleus.
- 35. a) Derivation/use: H proportional to I^2, H proportional to R, H proportional to t => H = k I^2 R t; in SI units k = 1 so H = I^2 R t (J). b) Nichrome properties: high resistivity -> good heating for given length, high melting point -> doesn't melt during normal use, resists oxidation -> long life. c) Fuse operation: Fuse in series experiences full circuit current. If current > rated value, heat produced (I^2Rt) melts the fuse wire, opening the circuit and preventing damage.
- 36. - Supply from the local distribution transformer/service line is brought to the house and first passes through the energy meter (records consumption). - After the meter there is a main switch to disconnect the house supply when needed. - From the main switch the supply goes to the distribution board (main box) which contains fuses or MCBs to protect circuits. - Three conductors are used: Live (L) - carries the supply (colour: red or brown), Neutral (N) - return path (colour: black or blue), Earth (E) - safety/ground (colour: green or green-yellow). - Branch circuits are protected separately: typically lighting and low-power outlets on 5 A circuits, high-power appliances (iron, heater, air…
- 37. A neuron typically consists of three basic parts: Cyton, Dendrites and Axon. (i) Cyton: (a) Cyton is also called cell body or perikaryon. It has a central nucleus with abundant cytoplasm called neuroplasm. (b) The cytoplasm has large granular body called Nissl’s granules and the other cell organelles like mitochondria, ribosomes, lysosomes, and endoplasmic recticulum. (c) Neurons do not have the ability to divide. (ii) Dendrites : (a) These are the numerous branched cytoplasmic processes that project from the surface of the cell body. They conduct nerve impulses towards the cyton. (b) The branched projections increase the surface area for receiving the signals from other nerve cells. (iii…
- 38. (i) The placenta is a disc shaped structure attached to the uterine wall and is a temporary association between the developing embryo and maternal tissues. (ii) It allows the exchange of food materials, diffusion of oxygen, excretion of nitrogenous wastes and elimination of carbon dioxide. (iii) A cord containing blood vessels that connects the placenta with the foetus is called the umbilical cord.
- 39. In leeches, the circulatory system is primarily a haemocoelic system, meaning it is integrated with the coelomic cavity, and there isn't a distinct, highly developed heart as seen in many other animals. Circulation is managed by four longitudinal channels that are filled with a blood-like coelomic fluid containing haemoglobin. One of these channels is located dorsally, another ventrally, and two are situated laterally. The two lateral channels are particularly important as they are contractile and possess valves, functioning analogously to hearts. These contractile lateral channels rhythmically pump the coelomic fluid throughout the body, effectively circulating nutrients and oxygen, and…
- 40. 1) Initial momentum p = m v, final momentum approx. 0, so Delta p = -m v. 2) Impulse magnitude = |Delta p| = m v (units kg m/s or N s). 3) J = F_avg Delta t => F_avg = Delta p/Delta t. Increasing Delta t (by pulling hands back) decreases F_avg. Units: momentum (kg m/s), impulse (N s), force (N).