Science — Plants, Animals, Human Body, Matter, Force & Environment — Practice

Question 1

A student plants two seeds. Seed A is kept in a warm, moist pot with good air. Seed B is kept in a dry, airtight jar at room temperature. Which seed will germinate? Why won't the other one germinate?

Accepted Answer

Seed A will germinate because it has all THREE conditions: warmth (warm pot), water (moist soil), and air/oxygen (good air circulation).

Seed B will NOT germinate because it lacks TWO conditions:
(1) It is DRY — no water to soften the seed coat and activate enzymes.
(2) It is AIRTIGHT — no oxygen for cellular respiration to power the embryo's growth.

✦ Answer: Seed A germinates. Seed B fails because it has no water and no air/oxygen.

Question 2

What type of metamorphosis does a butterfly undergo? Name the stages in order. How does a frog's development differ?

Accepted Answer

BUTTERFLY — COMPLETE METAMORPHOSIS (4 stages):
  (1) Egg (laid on a leaf)
  (2) Larva/Caterpillar (eats leaves, grows rapidly)
  (3) Pupa/Chrysalis (enclosed, complete transformation occurs)
  (4) Adult Butterfly (emerges)

FROG — INCOMPLETE METAMORPHOSIS (no pupa stage):
  (1) Egg (laid in water)
  (2) Tadpole (aquatic, breathes through gills, no legs)
  (3) Froglet (legs develop, tail shrinks)
  (4) Adult Frog (lungs + skin breathing, amphibious)

Key difference: Butterfly has a PUPA stage (complete transformation). Frog undergoes GRADUAL change with no pupal resting stage.

✦ Answer: Butterfly = complete, 4 stages (egg→caterpillar→pupa→adult). Frog = incomplete, no pupa.

Question 3

Name the change of state in each case: (a) Ice cream melts (b) Wet clothes dry in the sun (c) Dew forms on glass (d) Water in a freezer becomes ice.

Accepted Answer

(a) Ice cream melts → MELTING (solid → liquid, heat gained)
(b) Wet clothes dry → EVAPORATION (liquid → gas, heat gained from sun)
(c) Dew on glass → CONDENSATION (water vapour/gas → liquid, heat lost; warm moist air meets cold glass surface)
(d) Water in freezer → FREEZING (liquid → solid, heat lost)

✦ Answer: (a) Melting (b) Evaporation (c) Condensation (d) Freezing.

Question 4

Trace the journey of a chapati from mouth to absorption of nutrients. Name each organ and what happens there.

Accepted Answer

1. MOUTH: Teeth chew chapati (mechanical digestion). Saliva mixes in; salivary amylase begins breaking STARCH → MALTOSE (a simple sugar). A soft ball called BOLUS is formed.

2. OESOPHAGUS (food pipe): Bolus is swallowed. Muscular waves (PERISTALSIS) push it downward. No digestion here.

3. STOMACH: Bolus enters stomach. GASTRIC JUICE (hydrochloric acid + pepsin) breaks PROTEINS → PEPTIDES. Churning action mixes food. Acidic environment kills most bacteria. Food becomes semi-liquid CHYME.

4. SMALL INTESTINE: Most important step!
   - BILE from liver emulsifies fats (breaks fat globules into tiny droplets)
   - PANCREATIC JUICE digests starch, proteins, and fats further
   - INTESTINAL ENZYMES complete digestion
   - VILLI (tiny finger-like projections on the wall) ABSORB glucose, amino acids, fatty acids into blood

5. LARGE INTESTINE: Water and minerals are absorbed from the remaining material. Waste becomes more solid (FAECES).

6. RECTUM and ANUS: Waste is stored in rectum and expelled.

✦ Answer: Nutrients from the chapati are fully absorbed in the SMALL INTESTINE through villi.

Question 5

Explain three adaptations of a polar bear for survival in the Arctic. How are these adaptations different from a camel's desert adaptations?

Accepted Answer

POLAR BEAR — ARCTIC ADAPTATIONS:
1. THICK FUR (double layer): Dense underfur for insulation + longer guard hairs that are actually hollow for extra warmth. Keeps body heat in at −40°C temperatures.
2. LAYER OF BLUBBER (fat under skin): Up to 10 cm thick. Provides insulation when fur alone isn't enough and acts as an energy reserve when food is scarce.
3. WHITE COAT: Camouflage against white snow and ice for hunting seals. (Fun fact: polar bear fur is actually transparent/colourless — it just looks white because of light scattering.)

CAMEL — DESERT ADAPTATIONS (for contrast):
1. Hump (fat store for energy), not insulation
2. Wide feet to walk on sand without sinking
3. Long eyelashes and closeable nostrils to block sand
4. Concentrated urine and minimal sweating to conserve water

KEY DIFFERENCE: Polar bear adaptations TRAP and GENERATE heat. Camel adaptations CONSERVE water and tolerate heat.

✦ Answer: Polar bear = thick fur + blubber + white colour (for insulation and camouflage). Camel = hump + water conservation (opposite challenge: managing heat, not cold).

Question 6

Write a food chain: Sun → grass → grasshopper → frog → snake. What would happen if grasshoppers were wiped out by pesticides?

Accepted Answer

FOOD CHAIN:
Sun → Grass (producer) → Grasshopper (primary consumer/herbivore) → Frog (secondary consumer/carnivore) → Snake (tertiary consumer/carnivore)

IF GRASSHOPPERS WERE WIPED OUT:
1. FROGS: Their food source disappears. Frog population would CRASH (starvation).
2. SNAKES: Fewer frogs means snakes also starve. Snake population would CRASH.
3. GRASS: With no grasshoppers eating it, grass would OVERGROW. The ecosystem would be unbalanced.
4. OTHER EFFECTS: Birds and other animals that eat frogs/snakes would also be affected.

KEY PRINCIPLE: In a food chain, removing any ONE organism affects ALL organisms above and below it.

✦ Answer: Frog and snake populations crash; grass overgrows. Every link matters in a food chain.

Question 7

Classify the following and explain WHY: iron nail, wooden stick, glass window, frosted glass, copper wire, rubber glove, salt dissolved in water, sand in water.

Accepted Answer

ELECTRICAL CONDUCTOR vs INSULATOR:
  Iron nail → CONDUCTOR (metal; free electrons carry charge easily)
  Copper wire → CONDUCTOR (best common conductor; free electrons)
  Salt dissolved in water → CONDUCTOR (ions in solution carry charge)
  Wooden stick → INSULATOR (no free charges; wood blocks electricity)
  Rubber glove → INSULATOR (rubber has no free charges; used to protect electricians)

TRANSPARENT vs TRANSLUCENT vs OPAQUE:
  Glass window → TRANSPARENT (all light passes; you can see through clearly)
  Frosted glass → TRANSLUCENT (some light passes; you see light but not clear images)
  Wooden stick → OPAQUE (no light passes; casts a full shadow)

SOLUBLE vs INSOLUBLE IN WATER:
  Salt dissolved in water → SOLUBLE (salt dissolves completely; forms a solution)
  Sand in water → INSOLUBLE (sand does not dissolve; settles at the bottom)

✦ Answer: Conductors: iron nail, copper wire, salt water. Insulators: wood, rubber. Transparent: glass. Translucent: frosted glass. Opaque: wood. Soluble: salt. Insoluble: sand.

Practice — Science — Plants, Animals, Human Body, Matter, Force & Environment

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