TAMIL NADU STATE BOARD CLASS 10 SCIENCE 2026

(i) The rings of cartilage in the trachea of rabbit prevent the windpipe from collapsing and keep the air passage open for free movement of air during breathing. (ii) Any two parasitic adaptations in leech are: 1. It has suckers at both ends to attach firmly to the host. 2. It has sharp jaws/proboscis to pierce the skin and suck blood. Other adaptations include a flattened body and anticoagulant in saliva.

Neurons can be classified based on structure into three types: 1. Unipolar neurons – have only one process arising from the cell body. 2. Bipolar neurons – have two processes, one axon and one dendrite. 3. Multipolar neurons – have one axon and many dendrites.

Importance of forests: 1. Forests produce oxygen and absorb carbon dioxide. 2. They help maintain the water cycle and bring rainfall. 3. Forests prevent soil erosion and conserve soil fertility. 4. They provide habitat for many animals and plants. 5. They supply timber, fuel, fruits, medicines, rubber, and other useful products. 6. Forests help regulate climate and maintain ecological balance.

Initial volume of liquid = $50\,\text{mL}$ After initial heating, the level falls to $48.5\,\text{mL}$. So the real volume expansion of the liquid at this stage is $$50 - 48.5 = 1.5\,\text{mL}$$ This is due to the expansion of the container and is called the apparent decrease before the liquid begins to rise. When heated further, the level rises to $51.2\,\text{mL}$. So the apparent expansion is $$51.2 - 50 = 1.2\,\text{mL}$$ The expansion of the container between the two readings is $$50 - 48.5 = 1.5\,\text{mL}$$ But the apparent rise after further heating is $1.2\,\text{mL}$. Hence, the real expansion of the liquid is $$1.2 + 1.5 = 2.7\,\text{mL}$$ Therefore: - Apparent expansion = $1.2\,\text{mL}$ - Real expansion = $2.7\,\text{mL}$

(a) (i) Types of inertia: 1. Inertia of rest – the tendency of a body to remain at rest. Example: A passenger falls backward when a bus starts suddenly. 2. Inertia of motion – the tendency of a moving body to continue in motion. Example: A passenger falls forward when a moving bus stops suddenly. 3. Inertia of direction – the tendency of a body to resist change in direction. Example: Passengers are thrown sideways when a car takes a sharp turn. (ii) While catching a cricket ball, the fielder lowers his hands backward to increase the time of stopping the ball. This reduces the force exerted on the hands, since force is inversely proportional to time. OR (b) (i) In a parallel circuit, potential difference across each resistor is the same. For the $1\,\Omega$ resistor, current $I=1\,\text{A}$, so voltage is $$V = IR = 1\times1 = 1\,\text{V}$$ Thus current through $2\,\Omega$ resistor: $$I = \frac{V}{R} = \frac{1}{2} = 0.5\,\text{A}$$ Current through $4\,\Omega$ resistor: $$I = \frac{V}{R} = \frac{1}{4} = 0.25\,\text{A}$$ (ii) Ohm’s Law: At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends. Mathematically, $$V \propto I$$ or $$V = IR$$

(a) (i) A binary solution is a solution containing only two components: a solute and a solvent. (ii) Examples: 1. Gas in liquid – carbon dioxide in water 2. Solid in liquid – sugar in water 3. Solid in solid – brass (zinc in copper) 4. Gas in gas – air (iii) Aqueous solution: a solution in which water is the solvent. Example: salt in water. Non-aqueous solution: a solution in which a liquid other than water is the solvent. Example: iodine in alcohol. OR (b) (i) Double displacement reactions are reactions in which two compounds exchange ions to form two new compounds. Types: 1. Precipitation reaction – formation of an insoluble solid (precipitate). Example: $$\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl}\downarrow + \text{NaNO}_3$$ 2. Neutralization reaction – acid reacts with base to form salt and water. Example: $$\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$$ (ii) For $1.0\times10^{-4}$ M HNO$_3$, since HNO$_3$ is a strong acid, it dissociates completely. So, $$[H^+] = 1.0\times10^{-4}$$ $$\text{pH} = -\log[H^+] = -\log(10^{-4}) = 4$$ Therefore, pH = 4.

(a) (i) The three basic tissue systems in flowering plants are: 1. Epidermal tissue system 2. Ground tissue system 3. Vascular tissue system (ii) Photosynthesis is the process by which green plants use sunlight, chlorophyll, carbon dioxide, and water to prepare food and release oxygen. It occurs in the chloroplasts of plant cells. (iii) Respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration. $$\text{RQ} = \frac{\text{Volume of }CO_2\text{ evolved}}{\text{Volume of }O_2\text{ consumed}}$$ OR (b) (i) Mendel selected pea plant because: - It has many clear contrasting characters. - It has a short life cycle. - It is easy to grow and maintain. - It produces a large number of seeds. - It is naturally self-pollinating but can also be cross-pollinated. (ii) Okazaki fragments are short segments of newly synthesized DNA formed on the lagging strand during DNA replication. (iii) DNA consists of two antiparallel chains.