HSC Biology Feb 2026 solve question paper
BIOLOGY (56)
Time : 3 Hrs. Max.
Marks : 70
General
Instructions :
The question paper is divided into
four sections.
(1) Section A : Q. 1 contains Ten
multiple choice type of questions carrying one mark each. Evaluation will be
done for the first attempt only.
Q. No. 2 Contains Eight very short answer type of questions
carrying one mark each.
(2) Section B: Q. No. 3 to 14 are short answer type of questions
carrying two marks
each. (Attempt any Eight)
(3) Section C: Q. No. 15 to 26 are short answer type of questions
carrying three marks
each. (Attempt any Eight)
(4) Section D : Q. No. 27 to 31 are long answer type of questions
carrying four marks
each. (Attempt any Three)
(5) Begin the answer of
each section on a new page.
SECTION – A
Q.1. Select
and write the correct answer for the following multiple-choice type of questions: [10]
|
(i) |
A cell divides mitotically into two. Daughter cells divide and
redivide repeatedly. Such growth is called………………. |
|
(a) |
Arithmetic growth |
|
(b) |
Geometric growth |
|
(c) |
Growth ratio |
|
(d) |
Qualitative growth |
|
Ans |
Geometric growth |
|
(ii) |
The transgenic plant Tomato contains transgene…………… for the
production of flavonoids. |
|
(a) |
Phytoene synthase |
|
(b) |
Ferritin |
|
(c) |
Chalone isomerase |
|
(d) |
Phytase |
|
Ans |
Ferritin |
|
(iii) |
The cranial capacity of Neanderthal -man was………………C.C. |
|
(a) |
650 |
|
(b) |
900 |
|
(c) |
1400 |
|
(d) |
1450 |
|
Ans |
1400 |
|
(iv) |
Identify the organism which meet their energy and nutrient
requirements by degrading the detritus: |
|
(a) |
Omnivores |
|
(b) |
Carnivores |
|
(c) |
Autotrophs |
|
(d) |
Saprotrophs |
|
Ans |
Autotrophs |
|
(v) |
Identify the algae among the following: |
|
(a) |
Spirulina spp. |
|
(b) |
Aspergillus niger |
|
(c) |
Candida utilis |
|
(d) |
Trichoderma viridi |
|
Ans |
Aspergillus niger |
|
(vi) |
In plants, soluble food is always translocated in the from of
………….. |
|
(a) |
Glucose |
|
(b) |
Starch |
|
(c) |
Sucrose |
|
(d) |
Fructose |
|
Ans |
Glucose |
|
(vii) |
Identify invasive plant species from the following : |
|
(a) |
Gloriosa |
|
(b) |
Michelia |
|
(c) |
Sansvieria |
|
(d) |
Parthenium |
|
Ans |
Parthenium |
|
(viii) |
The mature plasma cell produces antibodies at the rate of
…………….molecules per second. |
|
(a) |
2000 |
|
(b) |
1000 |
|
(c) |
900 |
|
(d) |
300 |
|
Ans |
2000 |
|
(ix) |
Which is the largest WBC among the following? |
|
(a) |
Eosinophil |
|
(b) |
Monocyte |
|
(c) |
Basophil |
|
(d) |
Lymphocyte |
|
Ans |
Monocyte |
|
(x) |
The number of deaths when environmental pressures come into play
is known as ………….. |
|
(a) |
Absolute mortality |
|
(b) |
Absolute natality |
|
(c) |
Realized mortality |
|
(d) |
Realized natality |
|
Ans |
Absolute mortality |
Q . 2.Answer the following questions: [8]
(i)
Give the function of Leydig’s cells.
Ans: Leydig cells, located in the interstitial spaces of the
testes, are the primary source of testosterone in males. Under the regulation of pituitary luteinzing
hormone (LH), they produce this androgen to stimulate spermatogenesis (sperm
production), drive sexual differentiation in embryos, and maintain male
secondary sexual characteristics.
(ii)
Define endangered species.
Ans: An endangered species is a plant or animal population at high
risk of extinction due to a sudden, rapid population decrease or loss of critical
habit. Listed by organizations like the LUCN red list, these species face a
very high risk of vanishing in the near future, largely driven by human
activities like habitat destruction, poaching, and pollution.
(iii)
Name the gene which is inherited directly from father to son.
Ans: Y-linked genes (also
known as holandric genes) are inherited directly from father to son. Because
fathers have an XY sex chromosome pair, they pass their single Y chromosome
exclusively to their male offspring.
(iv)
The producers receive 5000 Joules of light energy, then how much
energy will be transferred to the carnivores (secondary consumers)?
Ans: If the producers receive 5000J of energy, then 50J of energy
will be transferred to the carnivores (secondary consumers) This calculation is
based on Lindeman’s 10% Law, which states that only approximately 10% of the
energy from one trophic level is transferred to the next.
(v)
Define the term chlorosis.
Ans: Chlorosis is a condition in plants where leaves turn yellow,
white, or pale green due to a lack of chlorophyll, often caused by nutrient
deficiencies (iron, magnesium). Poor soil, or disease.
(vi)
Give the name of key factor in DNA profiling.
Ans: The key factor in DNA profiling is variable Number Tandem
Repeats (VN TRs) These are specific non-coding regions of DNA where short
sequences are repeated, With the number of repeats varying significantly
between individuals, allowing for unique identification.
(vii)
Define combined water.
Ans: Combined water is water chemically bound within the crystal
structure of minerals, soil, or compounds, rather than existing as free
moisture.
(viii)
Give the role of tapetum.
Ans: The tapetum is the innermost nutritive layer of the anther
wall, crucial for pollen development. It provides essential nutrients to
developing microspores, secretes enzymes (like cells) for microspore
separation, produces sporopollenin for the protective exine layer, and
contributes pollen kit to assist in insect pollination.
SECTION – B
Attempt any EIGHT of the following questions : [16]
Q.3. Give the features of
respiratory surface for gaseous exchange.
Ans: Efficient respiratory surfaces for gaseous exchange, such as
alveoli in lungs or gills in fish, must have a large surface area, thin
(single-cell thick) membranes to minimize diffusion distance, a moist surface
to dissolve gases, and a rich blood supply (high vascularity) to maintain
concentration gradients.
Q. 4. Differentiate between
complete sex-linkage and incomplete sex-linkage with reference to location of
the gene and inheritance.
Ans: Complete sex linkage involves genes on the non-homologous
regions of sex chromosomes inheriting together without recombination.
Incomplete sex linkage involves genes located on the homologous (pairing)
regions of X and Y chromosomes, allowing for crossing over and recombination
during meiosis.
Q. 5. Explain the properties
of nerve fibers with reference to :
(a) Irritability
(b) Conductivity
Ans: Nerve fibers are specialized structures possessing key
properties, primary irritability (excitability) – the capacity to detect
stimuli and generate an action potential – and conductivity – the ability to
transmit that electrical impulse along the axon. Irritability, or excitability
involves responding to physical, chemical, or electrical stimuli by converting
resting potential to an action potential. Conductivity, or action potential
propagation, allows the single to travel, often at high speeds and in some
cases, bidirectionally.
(a)
Irritability
(Excitability)
Definition / Synonyms:
Also known as Excitability, this is the ability of a nerve fiber to respond to
a stimulus (e.g. electrical, chemical, mechanical) by generating a nerve
impulse or action potential.
(b)
Conductivity.
Definition / synonyms:
Also known as transmission or propagation, this is the capacity to move a
generated nerve impulse or action potential down the axon from the site of
stimulation.
Q. 6. Draw a neat diagram of a nucleosome and label
the following:
(i)
(ii) DNA
(iii) Octamer
Ans: A
nucleosome is the fundamental repeating unit of eukaryotic chromatin, composed
of roughly 146-200 base pairs of DNA wrapped around a histone octamer, secured
histone.
Here is a
diagram resenting the structure :
Text
Key components
Labeled :
·
[label
: DNA] : Represents the double helix DNA wrapping roughly 1.65 times around the
core.
·
[label
: H1 Histone] : known as the “ linker” or “clamping” histone that secures the
DNA in place.
·
Core
Octamer : The central protein spool (H2A, H2B, H3, H4X2).
Q. 7. Give any four advantages of micropropagation.
Ans:
Micropropagation allows rapid, year-round production of thousands of uniform,
pathogen – free plants from a small amount of parent tissue, regardless of the
season.
Four key
Advantages of Micropropagation:
- Rapid
Multiplication: large numbers of genetically identical plants (clones) are
produced within a short period and a limited space.
- Disease-free
plants: The tech ique is conducted in sterile conditions, allowing the
production and plants, such as virus-free stock.
- Year-Round
production: production is independent of season, allowing plants to be cultured
throughout the year.
- Propagation
of difficult the year. It allows for the rapid multiplication of rare,
endangered, or slow-propagating plant special.
Q. 8. Name the organism and
their role in conversion of rock into soil.
Ans: Organisms contribute to soil formation (pedogenesis) through
biological weathering breaking down rock via chemical secretions and physical
pressure. Key organisms include lichens (pioneer species releasing acid) mosses
(widening cracks), bacteria/ fungi (decomposing material), and
earthworms/animals (tunneling and organic mixing), transforming bare rock into
fertile soil.
Q. 9. Explain various
harmful effects of noise pollution on human being.
Ans: Harmful Effects of Noise pollution on Humans:
Cardiovascular Diseases : chronic noise triggers stress hormones
(like cortisol), leading to high blood pressure (hyper tension) which increases
the risk of heart disease and strokes.
Sleep
Disturbances and insomnia: Environmental noise from traffic or neighbors
disrupts sleep cycles, leading to insomnia, fatigue, and lower work efficiency.
Q. 10. Explain
skeletal features of Homo erectus.
Ans: Homo
erectus skeletons exhibit a maxiture of primitive and primitive and modern
traits, characterized by a long, low, and thick-boned skull, a prominent brow
ridge, a smaller chinless jaw, and a cranial capacity of 900-1100 cc. They were
fully bipedal with shorter arms and longer legs for walking, and possessed
robust, thick-walled leg bones. Suited for endurance walking.
Q. 11. Enlist
the main objectives for improved animal breeding programs using gene transfer
technology.
Ans: The main objectives for improved animal breeding programs
using gene transfer technology (genetic engineering) are to enhance production
efficiency, quality, and animal heath, key goals include accelerating growth
rates, increasing milk, meat, egg, and wool yield, introducing disease
resistance, and creating novel, high-value traits (e.g, lower fat, better
nutrient profiles), Key objectives of Gene Transfer
Technology in Animal Breeding:
Enhanced production Efficiency: increasing growth rates and
improving feed conversion efficiency in livestock.
Q. 12. Mention any four factors affecting water absorption.
Ans: Water absorption, particularly in plants, is crucial for
survival and is influenced by several external and internal factors, The key
factor include the amount of available soil water, the temperature of the soil,
the degree of soil aeration, and the concentration of the soil solution.
Four key factors affecting water absorption
Available soil water: The rate of absorption is directly
proportional to the amount of water available in the soil. A higher
concentration of available, capillary water in the soil increases the rate of
water absorption.
Soil Temperature: Water absorption is most efficient at soil
temperatures between 20
Soil
Aeration: Proper soil aeration is necessary. Well-aerated soil contains
oxygen, which is necessary for metabolic activity (respiration) of the roots.
Poorly aerated soil, which is deficient in oxygen, causes poor absorption
rates.
Soil solution Concentration: The concentration
of solutes (salts) in the soil affects absorption. High concentrations of salt
in the soil increase the osmotic pressure, making it harder for plants to
absorb water, thus reducing the rate of absorption.
Q. 13. Write briefly on Alzheimer’s disease.
Ans: Alzheimer’s disease is a progressive
neurodegenerative disorder that acts as the most common cause of dementia,
accounting for 60% to 80% of case. It is characterized by the slow destruction
of memory, thinking skills, and eventually, the ability to perform simple daily
tasks. Alzheimer’s is not a normal part of aging, though the risk increases
significantly after age 65.
Key Aspects of
Alzheimer’s Disease:
Brain Changes:
It is marked by the abnormal buildup of proteins in the brain, forming amyloid
plaques between cells and tau tangles within neurons. These structures block
communication between nerve cells (neurons) and cause them to die, leading to
brain shrinkage (atrophy).
Symptoms: Early
signs typically include short-term memory loss (e.g., forgetting recent
conversations, repeating questions). As the disease progresses, it causes
significant confusion, personality changes, difficulty with language, and
inability to recognize family members.
Q. 14.
Calculate the amount of ATP required by nitrogen fixer for the formation of
1000 molecules of ammonia Name the specialized cell of cyanobacteria where
nitrogen is fixed.
Ans: The
formation of 1000 molecules of ammonia (
Key Details:
ATP Calculation
: The biological nitrogen fixation reaction (
Specialized
Cells: Heterocysts are thick- walled
specialized cells that provide an anaerobic (oxygen-free) environment necessary
for the oxygen-sensitive function.
SECTION-C
Attempt any
EIGHT of the following questions : [24]
Q. 15. Match
the respiratory surface to the organism in which it is found :
|
Organisms |
Respiratory surface / organs |
|
a)
Limulus b)
Protists c)
Tadpoles
of frog d)
Fishes e)
Reptiles f)
Spiders |
a)
Lungs
b)
Internal
gills c)
Book
lungs d)
External
gills e)
Plasma
membrane f)
Book
gill g)
Cloaca |
Ans:
|
Organisms |
Respiratory
surface / organs |
|
a)
Limulus
b)
Protists
c)
Tadpoles
of frog d)
Fishes e)
Reptiles f)
Spiders |
Book gills Plasma membrane External gills Internal gills Lungs Book lungs |
Q. 16. Explain Criss-cross
inheritance with reference to bleeder’s disease by suitable charts.
Ans: Criss-cross inheritance (or sex-linked inheritance) is the
transmission of a gene from a father to his daughter (F1 carrier and then to
her sons (F2 affected). In bleeder’s disease (hemophilia, an X-linked recessive
disorder), the gene passes from often skipping a generation in females.
Key concepts of Criss-cross
inheritance in Hemophilia:
· Carrier Female:
· Bleeder Male:
·
Pattern:
Father to Daughter (Carrier), then Daughter to son (Affected).
2.Example 2: Carrier Female (
The carrier female passes the defective gene to
50% of her sons (
Synonyms and key Features
Synonyms: sex-linked inheritance, X-linked
inheritance (specifically related to the X-chromosome).
Bleeder’s Disease: A hereditary disease,
officially hemophilia A or B, where blood fails to clot property due to
deficient clotting factors (VIII or IX).
Q. 17. (a)
Distinguish between hibernation and aestivation.
(b)
Give two behavioral adaptations of desert animals.
Ans: Hibernation is a state of dormancy, or
“winter sleep,” where animals conserve energy to survive freezing temperatures
and food scarcity. Aestivation is “summer sleep,” a dormant state designed to
survive extreme heat and drought by reducing metabolic activity to prevent
water loss.
Behavioral Adaptations of Desert Animals
1.
Nocturnal
Activity: Many desert animals, such as the kangaroo rat, are activity only at
night, hiding in cool burrows during the day to avoid extreme heat and reduce
water loss.
2.
Burrowing
Behavior: Desert reptiles and small mammals burrow deep into the sand during
the afternoon to escape the heat, managing their body temperature by moving
between sun and shade.
Q. 18. Define :
(a) Siphonogamy
(b) Parthenocarpy
(c ) polyembryony
Ans: (a) siphonogamy: The process of sexual
reproduction in seed-bearing plants (spermatophytes) where non-motile male
gametes are transported to the female ovule via a hollow pollen tube.
Usage/Synonyms: Often referred to as “pollen
tube fertilization”. It ensures that non-motile sperm can reach the egg cell.
(b)
Parthenocarphy: The production of fruit without fertilization of ovules,
resulting in seedless (parthenocarpic) fruit.
(c)
Polyembryony:
The phenomenon of having more than one embryo in a single seed, which results
in the development of multiple seedings from one seed.
Q. 19. What is
transpiration? Explain stomatal opening and closing mechanism with reference to
starch-sugar interconversion theory.
Ans:
Transpiration is the evaporative loss of water from aerial plant parts,
primarily through stomata, facilitating nutrient transport and cooling.
Stomatal movement is regulated by turgor changes in guard cells via the
starch-sugar interconversion theory: daytime photosynthesis increases sugar
levels, driving endosmosis and opening stomata, while night-time starch
synthesis increases flaccidity, closing them.
Q. 20. Enlist
any six characteristics of genetic code.
Ans: Here are
six key characteristics of the genetic code.
1.
Triplet
Nature: The code is composed of three consecutive nucleotide bases (codon) that
specify a particular amino acid.
2.
Degeneracy
(Redundancy): some amino acids are encoded by more than one codon, allowing61
codons to code for only 20 amino acid.
3.
Universality:
The genetic code is generally the same across all organisms, from bacteria to
humans, with few exceptions.
4.
Non-Overlapping:
The code is read sequentially, three bases at a time, and a single base cannot
be part of two adjacent codons.
5.
Non-Ambiguous
(specific): Each codon codes for one specific amino acid only.
6.
Commas
less and polar: There are no commas or spaces between codons in the sequence,
and the information is read in a specific 5’
Q. 21. (a) Mention the name of germ layer from
which adrenal cortex and pancreas are developed.
(b) Explain the role of alpha (
Ans: The adrenal cortex is derived from the
mesoderm, while the pancreas is derive from the endoderm.
Role of lets of Langerhans cells:
Alpha (
Delta (
Q. 22. Define addiction. Give the physiological
effects of:
(a) Cocaine
(b) Cannabinoids
Ans: Addiction is defined as a chronic,
relapsing brain disease characterized by compulsive drug seeking and use
despite harmful, often devastating consequences. It involves functional changes
to brain circuits involved in reward, stress, and self-control, leading to an
inability to stop using a substance or engaging in a behavior, often
accompanied by physical dependence and withdrawal symptoms.
(a)
Cocaine
: Cardiovascular system : Acute use increases heart rate and blood pressure,
causes constriction of blood vessels, and can lead to arrhythmias, heart
attacks, and sudden death.
Behavioral and
Mental: It induces euphoria, extreme energy, mental alertness, and with high
doses, paranoia, anxiety, and psychosis.
(b)
Cannabinoids
: Heart and vascular system: Acute use commonly causes tachycardia (rapid heart
rate) and increased blood pressure, which may increase the risk of stroke or
heart disease.
Neurological
and psychological: Causes relaxation, euphoria (“high”), and altered sensory
perception, but can also lead to anxiety, paranoia, and panic attacks.
Q. 23. What is
infertility? Describe in brief ZIFT and GIFT.
Ans:
Infertility is a disease defined as the inability to conceive after one year or
more of unprotected intercourse. It affects both men and women due to factors
like low sperm count, ovulation issues, or blocked fallopian tubes. ZIFT and
GIFT are assisted reproductive technologies (ART) uses to treat infertility,
often as alternatives to IVF for patients with at least one functioning
fallopian tube, involving the transfer of fertilized eggs (ZIFT) or gametes
(GLFT) into the fallopian tube, rather than the uterus.
Q. 24. Draw
Urey and Miller’s experimental setup and Label it.
Ans: The Urey
and Miller experiment (1952) demonstrated that organic molecules, specifically
amino acids, could from inorganic constituents under simulated primitive Earth
conditions. The apparatus was a closed, sterile glass system combining boiling
water, a mixture of methane (
Label Diagram
of Miller and Urey Experiment.
·
Spark
Discharge : Electrodes providing a 60,000 – 100,000 volt electric are to
simulate lightning, providing energy for chemical reactions.
· Gases chamber : Contains the “reducing atmosphere” of methane (
Q. 25. (a) What
is grand period of growth?
(b) Give two examples each of :
(1) Growth promoters
(2) Growth inhibitors
Ans: The grand period of growth refers to the specific phase in a
plant’s life cycle where rate of growth is at its maximum. It is the period of
most rapid growth (exponential / log phase) following the initial slow lag
phase and before the growth rate slows down during maturity or senescence.
1)
Growth
promoters (stimulate growth cell division, and flowering)
·
Auxins
(e.g., IAA – indole – 3- acetic acid) Responsible for cell enlargement and
apical dominance.
·
Gibberllins
(e.g., GA3 – Gibberellic acid) : Promote stem elongations and seed germination.
·
Other
examples: Cytokinins (promote cell division).
2)
Growth
inhibitors (inhibit growth, promote dormancy and senescence)
·
Abscisic
acid (ABA) : Acts as a stress hormone, inducing stomatal closure and seed
dormancy.
·
Ethylene:
Promotes senescence and fruit ripening, often acting as a stress- related
inhibitor.
·
Other
examples : Phenolic inhibitors (e.g., coumarin).
Q. 26. (a) What is biofertilizer?
(b) Draw and Label
the T.S. of root nodules.
Ans: Biofertillizers are substance containing living
microorganisms-----such as bacteria, fungi, or blue-green algae-that, when
applied to seeds, plant surfaces, or soil, promote growth by increasing the
supply or availability of essential nutrients enhancers that reduce dependency
on chemical fertilizers.
Key Aspects of Biofertillizers:
· Mechanism: They work by nitrogen fixation (converting atmospheric
·
Examples:
Rhizobium (symbiotic whit legume roots), Azotobacter (free-living),
Azospirillum, and Mycorrhizal fungi (VAM)
( b) T.S. of Root Nodule Labeled Diagram
SECTION - D
Attempt any
THREE of the following questions: [12]
Q. 27. With the
help of labelled diagram describe the structure of human sperm.
Ans: A human sperm is a microscopic, elongated haploid male gamete.
It consists of four main parts:
1.
Head:
Contains an elongated haploid nucleus. The anterior portion is covered by a
cap-like structure called the acrosome, which contains enzymes (hyaluronidase)
that help in fertilizing the ovum.
2.
Neck:
A very short region containing two centrioles.
3.
Middle
piece: Contains numerous mitochondria coiled around the axial filament. These
provide energy (ATP) for sperm motility.
4.
Tail:
The longest part, which performs lashing movements to propel the sperm forward.
Q. 28. What is
cardia cycle? Draw a normal ECG and label it. What do p-wave and QRS complex
represent?
Ans: Cardiac
cycle: It is the sequence of events (electrical and mechanical) that occurs
from the beginning of one heartbeat to the beginning of the next.
It typically
lasts about 0.8 seconds and includes atrial systole, ventricular systole, and
joint diastole.
ECG
Representation:
·
P-wave:
Represents the electrical excitation or depolarization of the atria, which
leads to atrial contraction.
·
QRS
complex: Represents the depolarization of the ventricles, which initiates
ventricular contraction.
Q. 29. Write the name of disorders caused due to hypo and hyper
secretion of adrenal corticoids. Mention any 3 symptoms of each of these
disorders.
Ans: 1. Hyposecretion: Addison’s Disease symptoms:
·
Extreme
fatigue and muscle weakness.
·
Hyperpigmentation
(darkening) of the skin.
·
Low
blood pressure and salt craving.
2.
Hypersecretion:
Cushing’s syndrome symptoms:
·
Development
of a “moon-shaped” face due fat redistribution.
·
Obesity
in the upper body and thin arms/legs.
·
High
blood sugar (hyperglycemia) and high blood pressure.
Q. 30. Explain nuclear and helobial type of endosperm with suitable
examples.
Ans: 1. Nuclear Endosperm: This is the most common type of
endosperm development. The primary endosperm nucleus undergoes successive free
nuclear divisions without immediate wall formation. This creates a large number
of free nuclei distributes in the periphery of the cell around a large central
vacuole. Walls are formed much later, starting from the periphery
Example: Coconut water (which is free nuclear endosperm) and Maize.
3.
Helobia
Endosperm: This is an intermediate type between nuclear and cellular endosperm.
The first division of the primary endosperm nucleus is followed by a wall,
dividing the cell into a large micropylar chamber and a small chalazal chamber.
In the micropylar chamber, further division are free-nuclear (like nuclear
type), while the chalazal chamber may or may not divide further.
Example: Found
commonly in the order Helobiales, such as Asphodelus.
Q. 31. Describe
in brief :
(a) What is
germ line gene therapy? Why is it not encouraged?
(b) Explain
somatic gene therapy. Mention any two acquired disorders for which it is used.
Ans: (a)
Definition: This involves inserting functional genes into germ cells (sperm or
eggs) or early embryos. These changes are heritable and passed on to future
generations.
Why it is not
encouraged: It faces major ethical and social concerns because the genetic
changes are permanent and affect individuals who cannot give consent (future
offspring). There are also risks of unpredictable long-term side effects on the
human gene pool.
(b) Definition:
This involves the insertion of a therapeutic gene into the somatic (body) cells
of a patient to treat a disease. These genetic changes are restricted to the
individual patient and are not passed on
·
Acquired
disorders it is used for:
1.
Cancer
2.
AIDS
(HIV)
v