CBSE Class 10 Board Exam Science Syllabus

Define nutrition and distinguish autotrophic from heterotrophic nutrition.

Nutrition is the process of obtaining and using food for energy and growth. Autotrophic organisms make their own food (e.g. green plants by photosynthesis); heterotrophic organisms depend on others for food (e.g. animals, fungi).

Write the balanced equation for photosynthesis and name the site where it occurs.

6CO2 + 6H2O --(sunlight, chlorophyll)--> C6H12O6 + 6O2. It occurs in the chloroplasts (containing chlorophyll) of green plant cells.

What is the role of stomata in plants?

Stomata are tiny pores (mainly on leaves) that allow exchange of gases (CO2 and O2) and release of water vapour during transpiration. They are opened and closed by guard cells.

Differentiate aerobic and anaerobic respiration, including end products in muscle cells.

Aerobic uses oxygen, breaking glucose fully into CO2 + water + much energy. Anaerobic occurs without oxygen, giving less energy: in yeast → ethanol + CO2; in human muscles → lactic acid (causing cramps).

Name the two transport pathways in plants and what each carries.

Xylem carries water and dissolved minerals upward from roots to leaves. Phloem carries (translocates) food (sucrose) from leaves to other parts; this requires energy (ATP).

What is the functional unit of the kidney, and what is excretion?

The nephron is the functional/filtering unit of the kidney. Excretion is the removal of harmful metabolic wastes (like urea) from the body.

Describe the human double circulation of blood.

Blood passes through the heart twice per cycle: pulmonary circulation (heart→lungs→heart) for oxygenation, and systemic circulation (heart→body→heart). This keeps oxygenated and deoxygenated blood separate.

What is a neuron, and name its three main parts.

A neuron (nerve cell) is the structural/functional unit of the nervous system that conducts impulses. Parts: dendrites (receive impulses), cell body/cyton, and axon (transmit impulses).

Define a reflex action and a reflex arc.

A reflex action is a sudden, automatic, involuntary response to a stimulus. The reflex arc is the pathway of nerves it travels: receptor → sensory neuron → spinal cord → motor neuron → effector (muscle).

Name the plant hormones and the role of auxin and abscisic acid.

Auxins, gibberellins, cytokinins, abscisic acid, ethylene. Auxin promotes cell elongation and phototropism (growth toward light). Abscisic acid is a growth inhibitor causing wilting and dormancy.

Name the hormone secreted by the thyroid, pancreas, and adrenal gland and its function.

Thyroid → thyroxine (regulates metabolism, needs iodine). Pancreas → insulin (regulates blood sugar). Adrenal gland → adrenaline (prepares body for emergency/'fight or flight').

Differentiate between asexual and sexual reproduction.

Asexual involves a single parent and produces genetically identical offspring (no gametes). Sexual involves two parents and fusion of gametes, producing genetically varied offspring.

Name and describe three modes of asexual reproduction with an example each.

Binary fission (Amoeba splits in two), budding (Hydra/yeast grows an outgrowth that detaches), and fragmentation/regeneration (Spirogyra/Planaria broken pieces grow into new organisms).

What are the parts of a flower and which are the reproductive whorls?

Sepals, petals, stamens, and carpel(s)/pistil. Stamen (anther + filament) is the male reproductive whorl; carpel (stigma, style, ovary) is the female reproductive whorl.

Differentiate between pollination and fertilisation in flowering plants.

Pollination is the transfer of pollen from anther to stigma. Fertilisation is the fusion of the male gamete (from pollen) with the female gamete (egg) in the ovule to form a zygote.

Name the male and female reproductive organs in humans that produce gametes and the hormones they make.

Testes produce sperm and the hormone testosterone. Ovaries produce eggs (ova) and the hormones oestrogen and progesterone.

What is variation, and why is it important for a species?

Variation is the differences in characteristics among individuals of a species. It is important because it helps the species survive environmental changes and is the basis of evolution by natural selection.

State Mendel's findings on dominant and recessive traits using the F1 and F2 generations.

In a cross of pure tall × pure short pea plants, all F1 were tall (dominant trait expressed). In F2 (self-cross of F1) the ratio was 3 tall : 1 short, showing the recessive trait reappears in a 3:1 phenotypic ratio.

What is the genotypic ratio of a monohybrid F2 cross (Tt × Tt)?

1 TT : 2 Tt : 1 tt (i.e. 1:2:1), giving a phenotypic ratio of 3 dominant : 1 recessive.

How is sex determined in humans?

By sex chromosomes. Females are XX, males are XY. The egg always carries X; if a sperm carrying X fertilises it → girl (XX), if a sperm carrying Y → boy (XY). The father determines the child's sex.

State the laws of reflection of light.

1) The angle of incidence equals the angle of reflection (∠i = ∠r). 2) The incident ray, reflected ray, and the normal at the point of incidence all lie in the same plane.

What is the nature, position, and size of the image formed by a plane mirror?

Virtual and erect, of the same size as the object, laterally inverted, and formed as far behind the mirror as the object is in front of it.

Give the mirror formula and the magnification formula for spherical mirrors.

Mirror formula: 1/v + 1/u = 1/f. Magnification: m = h'/h = -v/u, where v=image distance, u=object distance, f=focal length, h'=image height, h=object height.

State the relationship between focal length and radius of curvature, and the sign convention for a concave vs convex mirror's focal length.

f = R/2. By the New Cartesian Sign Convention, focal length is negative for a concave mirror and positive for a convex mirror.

Define refraction of light and state Snell's law.

Refraction is the bending of light when it passes from one transparent medium to another due to a change in speed. Snell's law: sin i / sin r = constant (the refractive index of the second medium with respect to the first).

Give the lens formula and the power-of-a-lens formula, with units.

Lens formula: 1/v − 1/u = 1/f. Power P = 1/f (with f in metres); unit of power is the dioptre (D). Convex lens has +ve power, concave lens has −ve power.

What is the power of accommodation of the human eye, and which part performs it?

The ability of the eye to adjust its focal length to focus on objects at different distances. The ciliary muscles change the curvature (thickness) of the eye lens to do this.

Name the defects of vision myopia and hypermetropia and the lens used to correct each.

Myopia (short-sightedness): distant objects blurred; corrected by a concave (diverging) lens. Hypermetropia (long-sightedness): near objects blurred; corrected by a convex (converging) lens.

Why is the sky blue and the sun reddish at sunrise/sunset?

Due to scattering of light. Blue light (shorter wavelength) scatters more, making the sky blue. At sunrise/sunset light travels through more atmosphere, so blue is scattered away and mostly red (longer wavelength) reaches us.

State Ohm's law and give the formula relating V, I, and R.

At constant temperature, the current through a conductor is directly proportional to the potential difference across it. V = IR, where V=voltage (volts), I=current (amperes), R=resistance (ohms).

Give the formula for electric power and the unit of electrical energy used for billing.

P = VI = I²R = V²/R, measured in watts. Electrical energy is measured in kilowatt-hours (kWh), where 1 kWh = 1 'unit' = 3.6×10⁶ joules.

State the rules for total resistance in series and in parallel combinations.

Series: R = R1 + R2 + R3 + ... (resistances add). Parallel: 1/R = 1/R1 + 1/R2 + 1/R3 + ... (total resistance is less than the smallest individual resistance).

What does the magnetic field around a current-carrying straight conductor look like, and which rule gives its direction?

Concentric circles around the conductor, whose direction is given by the Right-Hand Thumb Rule: point the thumb in the direction of current; the curled fingers show the direction of the magnetic field.

State Fleming's Left-Hand Rule and where it is applied.

Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular: forefinger = magnetic field, middle finger = current, thumb = force/motion of the conductor. It gives the direction of force on a current-carrying conductor in a magnetic field (used in electric motors).

State Fleming's Right-Hand Rule and where it is applied.

Stretch the thumb, forefinger, and middle finger of the right hand mutually perpendicular: thumb = motion of conductor, forefinger = magnetic field, middle finger = induced current. It gives the direction of induced current (used in generators / electromagnetic induction).

What is a solenoid, and what is special about its magnetic field?

A solenoid is a coil of many circular turns of insulated wire. A current-carrying solenoid produces a uniform magnetic field inside it (like a bar magnet), with one end acting as the north pole and the other as the south pole.

What is an ecosystem and what are its two components?

An ecosystem is a self-sustaining unit of living organisms interacting with their physical environment. Its two components are biotic (living: producers, consumers, decomposers) and abiotic (non-living: light, temperature, water, soil, air).

Define producers, consumers, and decomposers with an example of each.

Producers make their own food (green plants). Consumers depend on others for food (herbivores, carnivores). Decomposers break down dead matter and recycle nutrients (bacteria, fungi).

What is a food chain, and how does it differ from a food web?

A food chain is a single linear sequence showing 'who eats whom' with energy flow (e.g. grass→deer→tiger). A food web is a network of many interconnected food chains in an ecosystem.

What are trophic levels, and state the 10% law of energy transfer.

Trophic levels are the steps/feeding positions in a food chain (producers = 1st level, etc.). The 10% law: only about 10% of energy at one trophic level is passed to the next; the rest is lost as heat, limiting food chains to 3–4 levels.

What is biological magnification (biomagnification)?

The progressive increase in the concentration of harmful, non-biodegradable chemicals (like pesticides) at each successive trophic level of a food chain, with top consumers accumulating the highest amounts.

What is the ozone layer, where is it located, and what is its function?

A layer of ozone (O3) in the upper atmosphere (stratosphere) that absorbs harmful ultraviolet (UV) radiation from the sun, protecting living organisms from its damaging effects.

What causes ozone depletion, and what is one harmful effect?

Mainly chlorofluorocarbons (CFCs) released from refrigerants, aerosols, etc., which break down ozone molecules. Effects include increased UV reaching Earth, causing skin cancer, cataracts, and damage to crops and the immune system.

Differentiate between biodegradable and non-biodegradable wastes with examples.

Biodegradable wastes are broken down by microorganisms (e.g. paper, food scraps, leaves). Non-biodegradable wastes are not decomposed by microbes and persist/pollute (e.g. plastics, glass, metals, DDT).