Question 1(i)
1(i)PopulationEasy1 Mark
The number of live births per thousand people per year is called:
Answer
(d) Natality
Explanation: Natality refers to the birth rate, or the number of live births per thousand people per year.
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ICSE Class 10 Biology Solved Paper 2025
Complete ICSE Class X Biology 2025 question paper with accurate, step-by-step solutions.
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Section A (40 Marks)
(Attempt all questions from this section)
Question 1(ii)
1(ii)Sense OrgansEasy1 Mark
The structure that lies at the junction of the choroid and the iris and is itself a part of the choroid is called:
Answer
(a) Ciliary body
Explanation: The ciliary body is a part of the choroid, located at the junction between the choroid and the iris. It produces aqueous humour and controls the shape of the lens.
Question 1(iii)
1(iii)The Reproductive SystemModerate1 Mark
Assertion (A): Seminal vesicles pour an alkaline secretion into the semen as it passes through the ureter.
Reason (R): The female vagina is acidic and needs to be neutralized for sperm survival.
Answer
(b) A is False and R is True
Explanation: Seminal vesicles secrete an alkaline fluid, but semen passes through the ejaculatory duct and urethra, not the ureter. The vagina is acidic and must be neutralized for sperm survival.
Question 1(iv)
1(iv)The Endocrine SystemEasy1 Mark
The hormone that induces vigorous contractions of the uterus in a pregnant mother is:
Answer
(c) Oxytocin
Explanation: Oxytocin stimulates strong uterine contractions during labour and childbirth.
Question 1(v)
1(v)Human EvolutionModerate1 Mark
A scientist wanted to conduct a genetic experiment on mice. He cut the tails of all the mice and made them reproduce. What will be the phenotype of the offsprings?
Answer
(c) All the offsprings will have tails.
Explanation: Cutting a mouse’s tail is an acquired change and does not alter the DNA in germ cells. Therefore, it cannot be inherited by the offspring.
Question 1(vi)
1(vi)Absorption by RootsModerate1 Mark
Assertion (A): A turgid plant cell is in a balanced state.
Reason (R): In a turgid cell, turgor pressure and wall pressure are equal and in the same direction.
Answer
(a) A is True and R is False
Explanation: Turgor pressure pushes outward while wall pressure pushes inward. They are equal in magnitude but act in opposite directions, balancing each other.
Question 1(vii)
1(vii)PhotosynthesisEasy1 Mark
The optimum temperature for photosynthesis is:
Answer
(d) 25 – 35°C
Explanation: Photosynthesis is most efficient at moderate warm temperatures, when its enzymes work effectively.
Question 1(viii)
1(viii)GeneticsModerate1 Mark
Ajay and Vijay are siblings. Ajay can roll his tongue while Vijay cannot. What is the genotype of their parents?
Answer
(d) Both the parents are heterozygous dominant.
Explanation: Tongue rolling is dominant (R). Vijay is rr, so each parent must contribute r. Since both parents can roll their tongues, each must be Rr.
Question 1(ix)
1(ix)The Endocrine SystemModerate1 Mark
Assertion (A): Deficiency of Antidiuretic hormone causes an increase in urination.
Reason (R): Antidiuretic hormone acts on the kidney to reabsorb water from the kidney tubules.
Answer
(c) Both A and R are True
Explanation: ADH helps the kidneys reabsorb water. When ADH is deficient, less water is reabsorbed and more urine is produced.
Question 1(x)
1(x)Structure of Chromosomes, Cell Cycle and Cell DivisionEasy1 Mark
A phase of cell division where the spindle fibres disappear is:
Answer
(a) Telophase
Explanation: During telophase, chromosomes reach opposite poles, spindle fibres disappear and nuclear envelopes re-form.
Question 1(xi)
1(xi)Nervous SystemModerate1 Mark
Assertion (A): Arachnoid layer helps in speeding up the transmission of nerve impulses along the axons.
Reason (R): Axon endings at the synapse secrete acetylene.
Answer
(d) Both A and R are False
Explanation: The arachnoid is a meningeal membrane and does not speed impulse conduction; the myelin sheath performs that function. Axon terminals release acetylcholine, not acetylene.
Question 1(xii)
1(xii)PollutionModerate1 Mark
Many nuclear power plants are constructed near water sources. They use water for cooling their machinery and release it back into the water stream. Identify the kind of pollution caused.
Answer
(d) Thermal pollution
Explanation: Heated cooling water raises the temperature of rivers or lakes, reduces dissolved oxygen and harms aquatic life. This is thermal pollution.
Question 1(xiii)
1(xiii)Sense OrgansEasy1 Mark
Owls are nocturnal animals. They are active at night and hunt small animals for food. Owls have large eyes and can see well at night. This is due to:
Answer
(c) Rods and Rhodopsin
Explanation: Owls have many rods that work in dim light. Rods contain rhodopsin, which helps detect light in darkness.
Question 1(xiv)
1(xiv)Chemical Coordination in PlantsModerate1 Mark
Sunil tried to match the tropic movements in plants with the stimulus they respond to.
| Tropism | Stimulus | |
|---|---|---|
| P | Thigmotropism | Touch |
| Q | Geotropism | Water |
| R | Chemotropism | Chemicals |
| S | Phototropism | Gravity |
Identify the correct pair:
Answer
(a) P and R
Explanation: Thigmotropism is a response to touch and chemotropism is a response to chemicals. Geotropism responds to gravity, while phototropism responds to light.
Question 1(xv)
1(xv)The Endocrine SystemModerate1 Mark
Observe the following picture, identify the defect and the cause of the defect.
Answer
(b) Ex-ophthalmic goitre, over secretion of thyroxine.
Explanation: Ex-ophthalmic goitre is caused by over-secretion of thyroxine and produces symptoms such as protruding eyes, increased metabolism and swelling of the neck.
Question 2(i)
2(i)The Reproductive SystemModerate5 Marks
Name the following:
(a) The fully developed part of the ovary containing a mature ovum.
(b) A waxy layer on the upper epidermis of leaves meant to reduce Transpiration.
(c) The ear ossicle which opens into the oval window of Cochlea.
(d) The physiological process which is the starting point of all food chains.
(e) An insect which is a classic example of natural selection due to industrial melanism.
Answer
(a) Graafian follicle
(b) Cuticle
(c) Stapes
(d) Photosynthesis
(e) Peppered moth (Biston betularia)
Question 2(ii)
2(ii)The Circulatory SystemModerate5 Marks
Given below is the diagram of a human heart. Read the information below the diagram and fill in the blanks:
The human heart pumps blood throughout the body. It is the size of a large fist. The heart is located between the lungs in the thoracic cavity. It has four chambers. The heart functions all through the lifespan of a person and is responsible for the survival of the person.
The heart is enclosed by a membrane called (a) …………… . The ventricles give rise to two large blood vessels called (b) …………… and (c) …………… . The flaps of the cuspid valves are kept in position by (d) …………… . (e) …………… arteries supply oxygenated blood to the walls of the heart.
Answer
(a) Pericardium
(b) Pulmonary artery
(c) Aorta
(d) Chordae tendineae
(e) Coronary
Question 2(iii)
2(iii)TranspirationModerate5 Marks
Arrange the terms in each group in the correct order. Write them in a logical sequence beginning with the term that is underlined.
(a) Palisade cells, Cuticle, Upper epidermis, Spongy cells.
(b) Hepatic portal vein, Stomach, Hepatic vein, Liver.
(c) Cyton, Dendrites, Synaptic cleft, Axon endings.
(d) Insulin release, High blood sugar, Lowers blood sugar, Stimulates glucose uptake from blood.
(e) Sperm duct, Seminiferous tubule, Epididymis, Efferent ducts.
Answer
(a) Cuticle → Upper epidermis → Palisade cells → Spongy cells
(b) Stomach → Hepatic portal vein → Liver → Hepatic vein
(c) Dendrites → Cyton → Axon endings → Synaptic cleft
(d) High blood sugar → Insulin release → Stimulates glucose uptake from blood → Lowers blood sugar
(e) Seminiferous tubule → Efferent ducts → Epididymis → Sperm duct
Question 2(iv)
2(iv)The Reproductive SystemModerate5 Marks
Read the explanations given below and name the structures:
(a) The canal through which the testes descend down into the scrotum just before the birth of a male baby.
(b) The part of the brain that regulates the peristaltic movement of the alimentary canal.
(c) A structure that collects the soundwaves and conducts them through the external auditory canal.
(d) The point of attachment of two chromatids of a chromosome.
(e) Regulation of the opening and closing of stomata.
Answer
(a) Inguinal canal
(b) Medulla oblongata
(c) Pinna
(d) Centromere
(e) Guard cells
Question 2(v)
2(v)The Endocrine SystemModerate5 Marks
Given below is an outline of the human body showing the important endocrine glands. Match the glands marked (a) to (e) with their correct functions:
Example: (f) – 6. Secretes Testosterone.
| Endocrine Gland | Functions |
 |
(1) Prepares the body to face stress.
(2) Secretes tropic hormones (3) Secretes Oestrogens (4) Maintains blood sugar level (5) Regulates basal metabolism (6) Secretes Testosterone. |
Answer
(a) → (2) Pituitary gland — Secretes tropic hormones.
(b) → (5) Thyroid gland — Regulates basal metabolism.
(c) → (1) Adrenal gland — Prepares the body to face stress.
(d) → (4) Pancreas — Maintains blood sugar level.
(e) → (3) Ovaries — Secretes Oestrogens.
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Section B (40 Marks)
(Attempt any four questions)
Question 3(i)
3(i)PhotosynthesisEasy1 Mark
Write the overall chemical equation for photosynthesis.
Answer
\mathrm{6CO_2 + 12H_2O \xrightarrow[chlorophyll]{light\ energy} C_6H_{12}O_6 + 6H_2O + 6O_2 \uparrow}
Question 3(ii)
3(ii)Chemical Coordination in PlantsEasy2 Marks
Ramesh is a farmer who has a vineyard and cultivates grapes. To improve the shape of the grapes and make them elongated he sprays a particular phytohormone at the time of fruiting.
(a) Name the phytohormone that Ramesh sprays on the plant at the time of fruiting.
(b) These grapes are said to be seedless. What is the technical term for the formation of such fruits?
Answer
(a) Gibberellins
(b) Parthenocarpy
Question 3(iii)
3(iii)Structure of Chromosomes, Cell Cycle and Cell DivisionEasy2 Marks
Mention the two pairs of nitrogenous bases that are present in a DNA strand and pair with each other by hydrogen bonds.
Answer
1. Adenine (A) pairs with Thymine (T) through two hydrogen bonds.
2. Guanine (G) pairs with Cytosine (C) through three hydrogen bonds.
Question 3(iv)
3(iv)PollutionEasy2 Marks
State any two disadvantages of living close to an airport.
Answer
- Noise Pollution — Constant sound from airplanes taking off and landing can disturb sleep, lower efficiency of work and disturb peace of mind.
- Air Pollution — Emissions from aircraft and airport traffic can lead to poor air quality, affecting respiratory health over time.
Question 3(v)
3(v)Structure of Chromosomes, Cell Cycle and Cell DivisionEasy3 Marks
Draw a neat, labelled diagram of an animal cell showing Metaphase with four chromosomes.
Answer
A neat, labelled diagram of an animal cell in metaphase should show four chromosomes arranged at the equatorial plane, spindle fibres attached to their centromeres, centrioles at opposite poles and the cell membrane.
Question 4(i)
4(i)Structure of Chromosomes, Cell Cycle and Cell DivisionEasy1 Mark
What is the structure of DNA as proposed by Watson and Crick?
Answer
Watson and Crick proposed the double helical model of DNA composed of two complementary strands wound around each other in a double helix. Each strand has a sugar-phosphate backbone with nitrogenous bases in the center.
Question 4(ii)
4(ii)The Circulatory SystemEasy2 Marks
Name the white blood cells that:
(a) Show phagocytosis
(b) Produce antibodies
Answer
(a) Neutrophils
(b) Lymphocytes
Question 4(iii)
4(iii)PollutionEasy2 Marks
Complete the food chain by mentioning the names of the organisms in (c) and (d):
Answer
(c) Snake
(d) Hawk
Question 4(iv)
4(iv)PollutionEasy2 Marks
State any two harmful effects of acid rain.
Answer
1. Damage to plants and crops: Acid rain injures leaves, reduces photosynthesis and removes essential nutrients from the soil.
2. Damage to aquatic life: It makes lakes and rivers acidic, which can kill fish and other aquatic organisms.
Question 4(v)
4(v)Absorption by RootsEasy3 Marks
Given below is a picture of a tree. Mention the scientific phenomena occurring in the parts labelled (a), (b) and (c).
Answer
(a) Absorption of water
(b) Transportation of water
(c) Transpiration
Question 5(i)
5(i)The Excretory SystemEasy1 Mark
What is Micturition? Explain.
Answer
Micturition is the process by which urine is expelled from the urinary bladder out of the body through the urethra. It occurs when the bladder muscles contract and the sphincter muscles relax.
Question 5(ii)
5(ii)PollutionEasy2 Marks
What are biomedical wastes? Give an example.
Answer
Biomedical wastes are the wastes generated from hospitals, clinics, laboratories, and other healthcare facilities during diagnosis, treatment, or immunization of humans or animals.
Example: Used syringes and needles.
Question 5(iii)
5(iii)The Excretory SystemEasy2 Marks
Differentiate between the functions of Urethra and Uterus.
Answer
| Urethra | Uterus |
|---|---|
| Carries urine from the urinary bladder to the outside of the body. | Receives the embryo and supports its development during pregnancy. |
| In males, it also carries semen during ejaculation. | Its muscular walls contract during childbirth to expel the baby. |
| It belongs mainly to the urinary system. | It is a part of the female reproductive system. |
Question 5(iv)
5(iv)Sense OrgansEasy2 Marks
Rachna is an expert gymnast on the balance beam. She has been vigorously practising for the Olympic Games. Lately, she has been experiencing dizziness and losing her balance during the practice sessions.
(a) Which part of the membranous labyrinth is responsible for maintaining the body balance on the beam?
(b) Which type of balance is maintained by the structure mentioned in (a)?
[Space for diagram]
Answer
(a) The semicircular canals.
(b) Dynamic balance.
Question 5(v)
5(v)PhotosynthesisEasy3 Marks
Draw a neat, labelled diagram to show that oxygen is released during photosynthesis.
Answer
The labelled setup should show an aquatic plant under an inverted funnel in a beaker of water, with an inverted water-filled test tube placed over the funnel stem to collect the gas released in sunlight.
Question 6(i)
6(i)TranspirationEasy1 Mark
Where are Hydathodes located?
Answer
Hydathodes are located at the tips or margins of leaves, usually at the ends of veins.
Question 6(ii)
6(ii)Human EvolutionEasy2 Marks
What are Vestigial organs? Give one example of a vestigial structure in the human mouth.
Answer
Vestigial organs are reduced structures that have lost most or all of their original function but continue to persist through generations.
Example in the human mouth: Wisdom teeth.
Question 6(iii)
6(iii)Sense OrgansEasy2 Marks
Ahmed had a severe throat infection. After a few days he developed an earache too. What could be the reason for the pain in his ears? Explain.
Answer
The infection probably spread from the throat to the middle ear through the Eustachian tube.
Explanation: The Eustachian tube connects the pharynx with the middle ear. Microorganisms from a throat infection can travel through it, causing inflammation and fluid accumulation in the middle ear, which produces pain.
Question 6(iv)
6(iv)Sense OrgansEasy2 Marks
Mr. Sharma is a 76 year old man. His vision was gradually becoming blurred. He consulted an eye doctor and it was diagnosed as cataract.
(a) Which part of the eye does cataract affect?
(b) Why does the vision become blurred?
Answer
(a) The lens of the eye.
(b) Vision becomes blurred because the lens becomes cloudy or opaque and prevents light from passing clearly to the retina.
Explanation: A cataract reduces the transparency of the lens, so a sharp image cannot be formed on the retina.
Question 6(v)
6(v)Absorption by RootsEasy3 Marks
Given below is the diagram of a plasmolysed cortical cell of a root.
Copy the diagram and label the following parts:
(a) Cytoplasm
(b) Hypertonic solution
(c) Plasma membrane
Answer
The labelled diagram is shown below:
Question 7(i)
7(i)GeneticsEasy1 Mark
Define the term Allele.
Answer
Alleles are alternative forms of the same gene that occupy the same locus on homologous chromosomes and control different expressions of the same character.
Question 7(ii)
7(ii)PopulationEasy2 Marks
In the last century, the human population has increased tremendously. Death rate has reduced and life expectancy has increased. This rapid growth has placed significant pressure on resources. Global cooperation is needed for environmental preservation.
(a) Mention any one reason for reduction in the death rate.
(b) Name any one resource that is under pressure due to population explosion.
Answer
(a) Improved healthcare and medical facilities.
(b) Freshwater.
Question 7(iii)
7(iii)The Reproductive SystemEasy2 Marks
Mention any two functions of amniotic fluid.
Answer
The two functions of amniotic fluid are
- It cushions the foetus and protects it from jerks and mechanical shocks.
- It maintains uniform pressure around the embryo and permits free movement.
Question 7(iv)
7(iv)PollutionEasy2 Marks
Expand the following abbreviations:
(a) CFC
(b) CNG
Answer
(a) CFC — Chlorofluorocarbon
(b) CNG — Compressed Natural Gas
Question 7(v)
7(v)Nervous SystemEasy3 Marks
Vineet’s day begins with a cup of piping hot coffee. Caffeine is a stimulant present in coffee which increases the circulation of Adrenaline in the body. Vineet feels refreshed, alert and focussed.
(a) Name the organ that is stimulated by caffeine which makes Vineet alert and focussed.
(b) Give the collective term for the protective membranes of the organ mentioned in (a).
(c) Which part of the autonomic nervous system increases the secretion of Adrenaline?
Answer
(a) Brain
(b) Meninges
(c) Sympathetic nervous system
Question 8(i)
8(i)The Excretory SystemEasy1 Mark
Explain the term Excretion.
Answer
Excretion is the biological process by which harmful and unwanted metabolic waste products, especially nitrogenous wastes, are removed from the body.
Question 8(ii)
8(ii)The Excretory SystemEasy2 Marks
State the difference between Nephron and Neuron.
Answer
| Nephron | Neuron |
|---|---|
| It is the structural and functional unit of the kidney. | It is the structural and functional unit of the nervous system. |
| It filters blood and forms urine. | It receives and transmits nerve impulses. |
| It consists of a renal corpuscle, PCT, loop of Henle and DCT. | It consists of a cell body, dendrites and an axon. |
Question 8(iii)
8(iii)PollutionEasy2 Marks
Mention any two objectives of Swachh Bharat Abhiyan.
Answer
The two objectives of Swachh Bharat Abhiyan are
- To eliminate open defecation by constructing individual, community and public toilets.
- To improve cleanliness, sanitation and hygiene in urban and rural areas.
Question 8(iv)
8(iv)Human EvolutionEasy2 Marks
Give any two characteristic features of a Cro-Magnon man.
Answer
The two characteristic features of a Cro-Magnon man are:
- Cranial capacity of approximately 1450–1600 cm³.
- A large skull with a broad face, rounded forehead and prominent chin.
Question 8(v)
8(v)GeneticsEasy3 Marks
A farmer cultivates a unique species of tomato plants. The two traits selected for breeding were: Colour of the fruits and height of the plants. The farmer initially crosses a homozygous tall plant bearing red fruits (TTRR) with a dwarf plant bearing yellow fruits (ttrr) and the genotype of all the offsprings of the F1 generation was TtRr. Next, he crosses two F1 generation plants (TtRr).
(a) Explain the phenotype of the offsprings of the F1 generation obtained from the initial cross.
(b) Mention the phenotypic ratio of the F2 generation offsprings.
(c) State Mendel’s Law of Independent Assortment.
Answer
Initial cross: TTRR × ttrr
Gametes: TR and tr
F1 genotype: All TtRr
(a) All F1 plants are tall and bear red fruits because T (tallness) is dominant over t (dwarfness), and R (red fruit colour) is dominant over r (yellow fruit colour).
F1 cross: TtRr × TtRr
Each parent produces four kinds of gametes: TR, Tr, tR and tr.
| Gametes | TR | Tr | tR | tr |
|---|---|---|---|---|
| TR | TTRR | TTRr | TtRR | TtRr |
| Tr | TTRr | TTrr | TtRr | Ttrr |
| tR | TtRR | TtRr | ttRR | ttRr |
| tr | TtRr | Ttrr | ttRr | ttrr |
(b) The F2 phenotypic ratio is 9 tall red : 3 tall yellow : 3 dwarf red : 1 dwarf yellow.
(c) Mendel’s Law of Independent Assortment states that during gamete formation, the alleles of one pair of contrasting characters assort independently of the alleles of another pair.
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