Life Processes – Case-based Questions with Answers
Biology — Chapter 5: Life Processes
15 Case-Based Questions with Model Answers — NCERT-aligned for CBSE Class 10
These case‑based questions are designed strictly as per the NCERT syllabus, making them ideal for CBSE Class 10 board exams standard.
Case 1 — Stressed Athlete
An athlete runs 400 m at high speed. Shortly after the race he feels muscle ache and breathlessness. Blood tests show elevated lactic acid in muscles.
Model Answer:
During intense exercise, oxygen supply to muscle cells may be insufficient for aerobic respiration. Hence muscles temporarily switch to anaerobic respiration (glycolysis followed by lactic acid formation) producing small amounts of ATP:
Glucose → lactic acid + small ATP. Accumulation of lactic acid causes muscle ache and breathlessness.
After exercise, increased breathing and circulation restore O₂ levels. Lactic acid is transported via blood to liver where it is oxidised back to pyruvate and then to CO₂ and H₂O (Cori cycle), or used to resynthesise glucose; this requires oxygen — the "oxygen debt" is repaid.
Case 2 — Wilting Houseplant
A houseplant left in a warm, sunny window begins to wilt during midday. The gardener waters it in the evening; by morning the leaves recover turgidity.
Model Answer:
During warm, sunny conditions, stomata open for photosynthesis and transpiration rate rises; excessive water loss can exceed water uptake, reducing cell turgor (wilting). Watering replenishes soil moisture, allowing roots to absorb water, restoring turgor and leaf erectness.
Factors that increase transpiration include high temperature, low humidity, strong wind, and bright light (which opens stomata).
Case 3 — Infant with Jaundice
A newborn shows yellowing of skin and sclera. Doctors explain that bilirubin, a breakdown product of haemoglobin, is accumulating.
Model Answer:
The liver normally conjugates bilirubin making it water-soluble for excretion in bile. In newborns, liver enzyme systems may be immature leading to accumulation of unconjugated bilirubin (jaundice).
Phototherapy uses light (blue) to convert bilirubin into water-soluble isomers that can be excreted without conjugation, thus reducing jaundice levels.
Case 4 — Farmer’s Field and Wilting Trees
A farmer notices many trees in a field show poor growth despite regular fertiliser application. Soil tests show poor oxygenation due to waterlogging.
Model Answer:
Waterlogging fills soil spaces with water, displacing air and reducing oxygen supply to roots. Aerobic respiration in root cells is impaired, reducing ATP production needed for active transport of mineral ions — so nutrient uptake declines causing poor growth.
Active transport mechanisms in root cells (e.g., ion pumps) require ATP from respiration — low O₂ limits ATP generation.
Case 5 — Patient with Frequent Urination
An adult reports frequent urination and increased thirst. Blood tests reveal elevated glucose levels.
Model Answer:
High blood glucose increases the filtered load of glucose at the glomerulus. Normally, renal tubules reabsorb all filtered glucose via carriers. When blood glucose exceeds renal threshold, carriers become saturated and excess glucose remains in filtrate — this increases osmotic pressure in tubule lumen, reducing water reabsorption and causing polyuria (glucosuria), leading to dehydration and thirst.
Thus, tubular reabsorption capacity (transport maximum, Tm) is exceeded at high glucose levels.
Case 6 — Seedling in Shade
A seedling grown under shade exhibits long, weak stems and small, pale leaves compared to those grown in light.
Model Answer:
In low light, plants elongate stems to reach light (shade avoidance) — mobilising resources for stem growth at expense of leaf development; chlorophyll synthesis and leaf expansion are reduced, producing pale, weak seedlings (etiolation).
Photosynthesis rates are lower in shaded plants due to reduced light intensity; sun-grown plants have higher photosynthetic capacity (more chlorophyll, thicker leaves) and higher rates under light.
Case 7 — Child with Recurrent Infections
A child has repeated bacterial infections. Blood tests show very low white blood cell counts.
Model Answer:
White blood cells (leukocytes) are central to immune defence — phagocytosis by neutrophils and macrophages and antibody-mediated responses by lymphocytes. Low WBC count (leukopenia) weakens these defences, making the child unable to clear infections effectively.
Major types: Neutrophils (phagocytose bacteria) and lymphocytes (B cells produce antibodies; T cells kill infected cells and regulate immune responses).
Case 8 — Farmer Notices Poor Fruit Set
A fruit farmer notices that despite healthy foliage, flowers are not setting fruit well. Soil tests and watering are normal; temperatures during flowering were unusually high.
Model Answer:
High temperatures can impair pollen viability, stigma receptivity, and pollinator activity — reducing successful pollination and fruit set. Heat can also disrupt meiosis during pollen formation leading to sterile pollen.
Measures: Provide shade during flowering (shade nets), irrigate to reduce canopy temperature (evaporative cooling), use heat-tolerant cultivars, or time planting to avoid peak heat during flowering.
Case 9 — Student Observes Bubbles from Yeast Mixture
A student mixes yeast with sugar solution and observes bubbling and slight warming over time.
Model Answer:
Yeast performs anaerobic respiration (fermentation) when metabolising sugar in low oxygen — producing ethanol and CO₂:
Glucose → ethanol + CO₂ + energy (small ATP). Bubbles are CO₂; slight warming is due to exothermic metabolism.
Applications: Bread making (CO₂ raises dough), brewing/alcohol production (ethanol), and bioethanol production.
Case 10 — Patient with Difficulty Breathing at High Altitude
A mountaineer who ascends rapidly to high altitude experiences breathlessness and headache.
Model Answer:
High altitude has lower partial pressure of oxygen; less O₂ diffuses into blood causing hypoxia — triggering hyperventilation (breathlessness) and cerebral vasodilation leading to headache. Acute mountain sickness results from hypoxia.
Acclimatisation: increased breathing rate and depth, increased red blood cell production (erythropoietin-mediated), raised haemoglobin, and increased capillary density over time improve O₂ delivery.
Case 11 — Overuse of Detergents in Water Bodies
Locals report algal blooms and fish deaths near a river outlet where detergents from laundry are discharged.
Model Answer:
Detergents add phosphates and organic compounds to water, which act as nutrients promoting excessive algal growth (algal blooms). Decomposition of algal biomass consumes dissolved oxygen causing hypoxic conditions and fish kills.
Mitigation: reduce phosphate-containing detergents, set up wastewater treatment, community awareness and regulation of effluent discharge.
Case 12 — Child with Dehydration after Diarrhoea
A child with persistent diarrhoea shows sunken eyes, dry mouth and low urine output.
Model Answer:
Diarrhoea causes excessive loss of water and electrolytes from the digestive tract leading to decreased blood volume. Kidneys conserve water by reducing urine output, causing oliguria. If fluid loss exceeds intake, hypovolaemia and shock can occur.
Immediate measure: Oral Rehydration Solution (ORS) — a balanced mix of salts and glucose to promote water and electrolyte absorption; continue breastfeeding and seek medical care if severe.
Case 13 — Garden with Yellowing Leaves
Several plants in a garden show interveinal chlorosis (yellowing between veins) while veins remain green. Soil tests show adequate water and light.
Model Answer:
Interveinal chlorosis is commonly due to iron or magnesium deficiency; iron deficiency typically causes new leaves to show chlorosis. Magnesium is central to chlorophyll; deficiency reduces chlorophyll synthesis.
Reduced chlorophyll lowers light absorption, decreasing photosynthetic rate and carbohydrate production, leading to stunted growth.
Case 14 — Farmer Observes Poor Growth after Excessive Fertiliser Use
A farmer applies high doses of nitrogenous fertiliser hoping for better yield but observes leaf burn and poor root development.
Model Answer:
Excess fertiliser increases soil osmotic concentration, causing water to move out of roots (physiological drought) and resulting in leaf burn and root damage. High salt levels can disrupt nutrient balance and harm beneficial soil microbes.
Safer practices: follow recommended dosages, use split applications, conduct soil testing, use organic manure to improve soil structure and prevent over-application.
Case 15 — Student Designs an Experiment on Stomata Density
A student hypothesises that sun-exposed leaves have lower stomatal density than shaded leaves due to adaptation to reduce water loss.
Model Answer:
Procedure: Collect equal-sized leaf samples from sun-exposed and shaded plants; prepare epidermal peels or clear nail-polish impressions of the lower surface; observe under microscope; count stomata per unit area (e.g., per mm²) in multiple fields; calculate mean stomatal density for each condition; apply simple statistics (mean ± SD) and compare.
Possible results: Sun-exposed leaves may show higher or lower stomatal density depending on species; often sun leaves have more stomata per unit area but may have smaller stomatal size — interpretation should consider trade-offs between CO₂ uptake and water conservation. Conclude based on observed difference and repeatability.