Q&A: practice questions with answers

Concept: Fermentation is anaerobic respiration by yeast, which breaks down sugars in the absence of oxygen.

1. Glucose → ethanol + carbon dioxide + energy.
2. ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\to 2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{O}\mathrm{H}+2\mathrm{C}{\mathrm{O}}_2$.
3. This is how alcohol is made and why dough rises ($\mathrm{C}{\mathrm{O}}_2$).

Yaad rakhein: Yeast → ethanol + $\mathrm{C}{\mathrm{O}}_2$; muscles (lack of ${\mathrm{O}}_2$) → lactic acid.

Answer: (D) Ethanol

Concept: Some plants move quickly in response to touch (e.g. 'touch-me-not', Mimosa) without any growth.

1. Touch acts as a stimulus; electrical-chemical signals pass from cell to cell.
2. Cells lose or gain water, so they shrink or swell and change shape.
3. The leaves fold immediately – it is a response to a stimulus, not a growth movement.

Yaad rakhein: Mimosa leaf folding = immediate, non-growth movement by change in water content (turgor).

Answer: (A) In immediate response to some stimulus

Concept: Metallic oxides are basic; they react with acids to give salt and water (neutralisation).

1. $\mathrm{C}\mathrm{u}\mathrm{O}+\mathrm{H}\mathrm{C}\mathrm{l}\to \mathrm{C}\mathrm{u}\mathrm{C}{\mathrm{l}}_2+{\mathrm{H}}_2\mathrm{O}$.
2. Cl: 2 needed on right, so take $2\mathrm{H}\mathrm{C}\mathrm{l}$; then H = 2 and O = 1 on both sides.
3. $\mathrm{C}\mathrm{u}\mathrm{O}+2\mathrm{H}\mathrm{C}\mathrm{l}\to \mathrm{C}\mathrm{u}\mathrm{C}{\mathrm{l}}_2+{\mathrm{H}}_2\mathrm{O}$ (blue-green solution).

Yaad rakhein: Metal oxide + acid → salt + water; no ${\mathrm{H}}_2$ or ${\mathrm{O}}_2$ is released.

Answer: (C) $\mathrm{C}\mathrm{u}\mathrm{O}+2\mathrm{H}\mathrm{C}\mathrm{l}\to \mathrm{C}\mathrm{u}\mathrm{C}{\mathrm{l}}_2+{\mathrm{H}}_2\mathrm{O}$

Concept: Hot concentrated sulphuric acid is a dehydrating agent; it removes water from ethanol.

1. At $443K$ with excess conc. ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$, one ${\mathrm{H}}_2\mathrm{O}$ is removed from each ethanol molecule.
2. $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{O}\mathrm{H}\stackrel{\text{conc. }{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4,443K}{\to }\mathrm{C}{\mathrm{H}}_2=\mathrm{C}{\mathrm{H}}_2+{\mathrm{H}}_2\mathrm{O}$.
3. The product is ethene (an alkene).

Yaad rakhein: $443K$ + excess acid → ethene; lower temperature (about $413K$) with excess ethanol → ether.

Answer: (D) Ethene

Concept: Ligaments and tendons are both connective tissues found at joints, but they join different structures.

1. Ligament: joins bone to bone; it is very elastic and strong.
2. Tendon: joins muscle to bone; strong but with limited flexibility.
3. Cartilage smoothens bone surfaces at joints; adipose tissue stores fat.

Trick: Ligament = Links bone–bone; Tendon = Ties muscle to bone.

Answer: (D) Ligament

Concept: Some metals like zinc and aluminium react with strong bases (NaOH) to form a salt and hydrogen gas.

1. $\mathrm{Z}\mathrm{n}+2\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}\to \mathrm{N}{\mathrm{a}}_2\mathrm{Z}\mathrm{n}{\mathrm{O}}_2+{\mathrm{H}}_2$.
2. $\mathrm{N}{\mathrm{a}}_2\mathrm{Z}\mathrm{n}{\mathrm{O}}_2$ is sodium zincate.
3. Hydrogen gas is also released (burns with a pop sound).

Yaad rakhein: Zn + NaOH → sodium zincate + ${\mathrm{H}}_2$; Al + NaOH → sodium aluminate + ${\mathrm{H}}_2$.

Answer: (D) sodium zincate

Concept: A homogeneous mixture has uniform composition throughout (solutions); a heterogeneous mixture has visibly different parts.

1. Sugar in water, salt in water and copper sulphate solution are true solutions – homogeneous.
2. Iron filings stay as separate solid particles that can be seen and separated (e.g. by a magnet).
3. So the iron chloride + iron filings mixture is heterogeneous.

Yaad rakhein: Every true solution is homogeneous; mixtures with visible separate particles (sand + water, iron filings + salt) are heterogeneous.

Answer: (B) Mixture of iron chloride and iron fillings

Concept: Momentum is the quantity of motion of a body, defined as the product of its mass and velocity.

1. $p=m\times v$.
2. It is a vector, in the direction of velocity.
3. SI unit: $\mathrm{k}\mathrm{g}\mathrm{m}{\mathrm{s}}^{-1}$.

Yaad rakhein: Force = rate of change of momentum: $F=\frac{\Delta p}{t}=ma$.

Answer: (C) $P=mv$

Concept: Plaster of Paris is calcium sulphate hemihydrate, made by heating gypsum at $373K$.

1. Gypsum: $\mathrm{C}\mathrm{a}\mathrm{S}{\mathrm{O}}_4·2{\mathrm{H}}_2\mathrm{O}$.
2. On heating: $\mathrm{C}\mathrm{a}\mathrm{S}{\mathrm{O}}_4·2{\mathrm{H}}_2\mathrm{O}\to \mathrm{C}\mathrm{a}\mathrm{S}{\mathrm{O}}_4·\frac{1}{2}{\mathrm{H}}_2\mathrm{O}+1\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$.
3. So one formula unit of POP has half a molecule of water (two units share one water molecule).

Yaad rakhein: Gypsum – 2 water; POP – ½ water ('hemi' = half); adding water to POP gives gypsum again (sets hard).

Answer: (A) Half molecules of water

Concept: After pollination, the pollen grain on the stigma grows a pollen tube to carry male germ cells to the ovule in the ovary.

1. Pistil = stigma (top) + style (long middle part) + ovary (base).
2. The pollen tube grows from the stigma down through the style.
3. It reaches the ovary and the ovule, where fertilisation occurs.

Yaad rakhein: Path of pollen tube: stigma → style → ovary → ovule. Filament and anther belong to the stamen (male part).

Answer: (A) style

Concept: Mitochondria carry out aerobic respiration and release energy as ATP, the energy currency of the cell.

1. Energy needed for cell activities is stored as ATP made in mitochondria.
2. Golgi apparatus packages and dispatches materials; ER transports materials.
3. Plastids (chloroplasts) make food in plant cells.

Yaad rakhein: Mitochondria – powerhouse; lysosome – suicide bag; ribosome – protein factory; chloroplast – kitchen of the cell.

Answer: (C) Mitochondria

Concept: Pressure is the force acting perpendicularly on unit area: $P=\frac{F}{A}$.

1. Unit of force = $N$, unit of area = ${\mathrm{m}}^2$.
2. So unit of pressure = $\frac{N}{{\mathrm{m}}^2}=\mathrm{N}{\mathrm{m}}^{-2}$.
3. This is called the pascal ($\mathrm{P}\mathrm{a}$).

Yaad rakhein: $1\mathrm{P}\mathrm{a}=1\mathrm{N}{\mathrm{m}}^{-2}$; $\mathrm{N}\mathrm{m}$ is the unit of work/torque.

Answer: (D) $\text{N}{m}^{-2}$

Concept: Regeneration is the ability of a fully differentiated organism to give rise to new individuals from its body parts, using specialised cells.

1. Hydra and Planaria, when cut into pieces, regenerate whole organisms – correct.
2. Specialised cells multiply rapidly and form many cells, which then organise into tissues – correct.
3. Amoeba is unicellular; it reproduces by binary fission, not regeneration – so statement (A) is incorrect.

Yaad rakhein: Regeneration: Hydra, Planaria; binary fission: Amoeba, Paramecium; multiple fission: Plasmodium.

Answer: (A) Amoeba exhibit regeneration.

Concept: Rhizopus (bread mould) reproduces asexually by spore formation.

1. Thin thread-like hyphae grow on bread.
2. Tiny blob-on-a-stick structures form at their tips; these blobs are sporangia.
3. Sporangia contain spores that develop into new Rhizopus under suitable conditions.

Yaad rakhein: Sporangium = spore case; spores have thick walls that protect them until they find moist surfaces.

Answer: (C) sporangia

Concept: Check each statement against the correct definition.

1. (i) Translocation is the transport of soluble products of photosynthesis (through phloem) – statement says insoluble, so incorrect.
2. (ii) Evaporative loss of water through stomata is transpiration, not respiration – incorrect.
3. (iii) Photosynthesis converts substances into stored energy in the presence of sunlight – incorrect.
4. All three are incorrect.

Yaad rakhein: Translocation – soluble food via phloem; transpiration – water loss via stomata; photosynthesis needs sunlight + chlorophyll.

Answer: (A) (i), (ii) and (iii)

Concept: For uniformly accelerated motion, $v=u+at$; in free fall $a=g$.

1. Starts from rest: $u=0$; $g=10\mathrm{m}{\mathrm{s}}^{-2}$; $t=2s$.
2. $v=0+10\times 2=20\mathrm{m}{\mathrm{s}}^{-1}$.
3. (Height of building $=\frac{1}{2}g{t}^2=20m$.)

Trick: Dropped from rest: speed after $t$ seconds $=10t$ (with $g=10$).

Answer: (B) 20 m/s

Concept: Adrenaline is secreted by the adrenal glands into the blood during emergencies; it prepares the body for 'fight or flight'.

1. (i) Heart beats faster to supply more oxygen to muscles – correct.
2. (ii) Breathing rate increases due to contraction of diaphragm and rib muscles – correct.
3. (iii) Blood to digestive system and skin is reduced, so blood pressure rises, not falls – incorrect.

Yaad rakhein: Adrenaline = emergency hormone: heart rate ↑, breathing ↑, blood pressure ↑, blood diverted to skeletal muscles.

Answer: (C) Only (i) and (ii)

Concept: A nerve cell (neuron) is the structural and functional unit of the nervous system.

1. Dendrites receive information (impulses) and pass it to the cell body.
2. The axon carries the impulse away from the cell body to the axon ending.
3. Blood cells and fibres do not have dendrites or axons.

Yaad rakhein: Impulse path: dendrite → cell body → axon → axon ending → synapse.

Answer: (C) Nerve cells

Concept: Fleming's left-hand rule gives the direction of force on a current-carrying conductor placed in a magnetic field.

1. Forefinger → magnetic field, middle finger → current, thumb → force (motion).
2. An electric motor works because its current-carrying coil experiences such a force in a magnetic field and rotates.
3. Iron, geyser and bulb work on the heating effect of current.

Trick: Left hand → Motor; Right hand → generatoR (induced current).

Answer: (B) Electric motor

Concept: By Newton's law of gravitation, $F=G\frac{m_1{m}_2}{d^2}$, where $G$ is the universal gravitational constant.

1. $G=\frac{F{d}^2}{m_1{m}_2}$, so its unit is $\mathrm{N}{\mathrm{m}}^2\mathrm{k}{\mathrm{g}}^{-2}$.
2. Its value (found by Henry Cavendish) is $6.673\times {10}^{-11}\mathrm{N}{\mathrm{m}}^2\mathrm{k}{\mathrm{g}}^{-2}$.
3. Rounded: $6.7\times {10}^{-11}\mathrm{N}{\mathrm{m}}^2\mathrm{k}{\mathrm{g}}^{-2}$.

Yaad rakhein: $G$ is very small (power $-11$) and the same everywhere; $g=9.8\mathrm{m}{\mathrm{s}}^{-2}$ changes from place to place.

Answer: (C) $6.7\times {10}^{-11}{\text{N m}}^2{\text{kg}}^{-2}$