▶️ Answer/Explanation
All living things share certain life processes, commonly summarized by the acronym MRS GREN (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition). Reproduction is essential for the survival of a species. Other options are specific to certain groups: breathing is a physical mechanism used by some animals but not plants or single-celled organisms; photosynthesis is unique to autotrophs like plants; and transpiration is a process specifically related to water movement in plants.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
The system used to name organisms is called binomial nomenclature, developed by Carl Linnaeus. This system uses two Latin words to uniquely identify every species. The first part of the name represents the genus, which is always capitalized, and the second part represents the species (or specific epithet), which is written in lowercase. Together, these two levels of classification provide a precise “first and last name” for an organism, ensuring scientists worldwide use the same terminology regardless of local common names. For example, in Homo sapiens, Homo is the genus and sapiens is the species.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
To solve this, we must distinguish between plant and animal cell structures. A palisade cell is a specialized plant cell found in leaves, whereas a neurone (nerve cell) is an animal cell. Both cells are eukaryotic, meaning they both possess a cell membrane, cytoplasm, and a nucleus (Options A, C, and D). However, plant cells are characterized by a rigid cell wall made of cellulose for structural support, a feature entirely absent in animal cells like the neurone.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
To find the diameter of the lumen, we must subtract the thickness of the vessel wall from both sides of the total diameter. Since the wall exists on all sides of the vessel, the lumen diameter is calculated as:
$$\text{Lumen Diameter} = \text{Total Diameter} – (2 \times \text{Wall Thickness})$$
$$\text{Lumen Diameter} = 36\text{ mm} – (2 \times 9\text{ mm}) = 36\text{ mm} – 18\text{ mm} = 18\text{ mm}$$
To match the answer choices, convert millimeters to micrometers ($\mu\text{m}$) by multiplying by $1000$:
$$18\text{ mm} \times 1000 = 18\,000\text{ μm}$$
✅ Answer: (C)
$$\text{Lumen Diameter} = \text{Total Diameter} – (2 \times \text{Wall Thickness})$$
$$\text{Lumen Diameter} = 36\text{ mm} – (2 \times 9\text{ mm}) = 36\text{ mm} – 18\text{ mm} = 18\text{ mm}$$
To match the answer choices, convert millimeters to micrometers ($\mu\text{m}$) by multiplying by $1000$:
$$18\text{ mm} \times 1000 = 18\,000\text{ μm}$$
✅ Answer: (C)
▶️ Answer/Explanation
Diffusion is a passive process where particles move from an area where they are more crowded to an area where they are less crowded. This means they move from a higher concentration ($1$) to a lower concentration ($2$). Since the particles are following the natural slope of concentration, the movement is described as going down ($3$) the concentration gradient. This process does not require energy input because it relies on the random kinetic energy of the particles. Therefore, the sequence that correctly fills the gaps is higher, lower, and down.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
To determine where the potato cells gained water, we look at the ratio of final length to initial length. If the ratio is greater than $1.0$, it means the final length is longer than the initial length, indicating the cells took in water via osmosis and became turgid. Looking at the graph, the ratio is above $1.0$ at concentrations $0.1 \text{ moles per dm}^3$ (ratio $\approx 1.2$) and $0.2 \text{ moles per dm}^3$ (ratio $\approx 1.05$). At $0.3 \text{ moles per dm}^3$, the ratio is exactly $1.0$, meaning no net movement of water (isotonic). Beyond that point, the ratio drops below $1.0$, indicating water loss. Therefore, the cells gained water at both $0.1$ and $0.2$ concentrations.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
To solve this, we must consider enzyme specificity and surface area. First, lipase is the specific enzyme required to digest lipids (oils), whereas trypsin is a protease that digests proteins. Second, chemical digestion occurs at the surface of the droplets. By breaking the same mass of oil into many smaller drops (as seen in option C), the total surface area to volume ratio is significantly increased. This provides more active sites for the lipase molecules to bind and catalyze the reaction simultaneously. Therefore, the combination of the correct enzyme and the smallest droplet size results in the fastest rate of digestion.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Chlorophyll is the green pigment in plants responsible for absorbing light energy for photosynthesis. At the center of its porphyrin ring structure sits a single magnesium ion ($Mg^{2+}$), which is essential for its function. Without sufficient magnesium, plants cannot synthesize chlorophyll and develop a condition called chlorosis. In contrast, cellulose, glucose, and glycerol are organic compounds composed strictly of carbon, hydrogen, and oxygen ($C$, $H$, and $O$).
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
In a vascular bundle of a leaf, the xylem is typically located on the upper side (closer to the adaxial surface), while the phloem is located on the lower side. Looking at the labels: A points to the palisade mesophyll cells, B points to the xylem vessels within the bundle, C points to the phloem, and D points to the lower epidermis/guard cells. The xylem vessels are characterized by their larger, often thicker-walled appearance and their position above the phloem in the vein structure.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
In this setup, the black cover prevents light from reaching the leaf, meaning photosynthesis cannot occur. Consequently, the leaf only undergoes aerobic respiration, taking in oxygen ($O_2$) and releasing carbon dioxide ($CO_2$). The substance in the tube absorbs any $CO_2$ produced, meaning there is a net decrease in the volume of gas inside the sealed tube as $O_2$ is consumed. This drop in internal pressure pulls the ink drop towards the leaf to equalize the pressure. Therefore, the movement is caused by the depletion of gas during respiration.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Chemical digestion involves the use of enzymes to break the chemical bonds of large, insoluble food molecules into small, soluble ones. In option (A), enzymes like amylase chemically transform starch into simpler reducing sugars. Options (B) and (C) represent mechanical digestion, where food is physically broken into smaller pieces to increase surface area. Option (D) describes emulsification by bile, which is a physical process that aids lipid digestion but does not involve breaking chemical bonds. Therefore, only the conversion of starch to sugar qualifies as a chemical change.
✅ Answer: (A)
▶️ Answer/Explanation
The part labelled $X$ is the lacteal, which is a central lymphatic vessel located inside each villus of the small intestine. While the surrounding blood capillaries are responsible for absorbing water-soluble nutrients like glucose and amino acids, the lacteal specializes in the transport of lipid-soluble molecules. Specifically, products of fat digestion, such as fatty acids and glycerol, are reassembled into chylomicroons and absorbed into the lacteal. This makes row $D$ the correct identification of both the structure’s name and its physiological role in the digestive system.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Transpiration is the process of water vapor loss from the leaves, driven by a concentration gradient. High humidity decreases this gradient by making the air outside the leaf saturated, so the highest rate requires low humidity (“no” to high air humidity). Windy conditions increase the rate by blowing away the “boundary layer” of water vapor, maintaining a steep gradient (“yes” to very windy). Finally, higher temperatures increase the kinetic energy of water molecules and the evaporation rate, so the rate is highest when air temperature is not low (“no” to low air temperature). Combining these factors, option B represents the ideal conditions for maximum water loss.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
In plants, a source is an organ that produces or releases sugars (like leaves), while a sink is an organ that consumes or stores them (like roots or developing fruits). Statement $1$ is incorrect because palisade cells photosynthesize and primary act as sources. Statement $2$ is correct as roots store energy. Statement $3$ is false because phloem transports sucrose, not glucose, and sinks can receive other nutrients. Statement $4$ is correct because spongy mesophyll cells also photosynthesize and can export sugars. Therefore, only statements $2$ and $4$ are accurate.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Veins are blood vessels that carry blood back toward the heart under relatively low pressure. To ensure that blood flows in the correct direction and does not flow backward due to gravity, veins contain valves. Unlike arteries, which have thick muscular walls and a narrow lumen to handle high pressure, veins have thinner walls and a much wider lumen. The “one-cell-thick wall” mentioned in option A is actually a characteristic of capillaries, which allows for efficient diffusion. Therefore, the presence of valves is the distinguishing structural feature of veins among the choices provided.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
To identify the correct structure, we must first orient the heart: the left side of the diagram represents the right side of the heart. Atrioventricular (AV) valves are located between the atria and the ventricles. Structure D represents the tricuspid valve, which is the AV valve on the right side. In contrast, C is the bicuspid (mitral) valve on the left side, while A and B represent the semilunar valves (pulmonary and aortic respectively) that lead out of the ventricles into the major arteries.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Active immunity occurs when the body’s own immune system is stimulated to produce antibodies and memory cells in response to an antigen. In option (A), the body “actively” reacts to a pathogen during an infection to create a long-term defense. In contrast, options (B), (C), and (D) describe passive immunity, where pre-formed antibodies are transferred from an external source. These external antibodies provide immediate but temporary protection because the recipient’s immune system does not learn to produce them independently. Therefore, only the production of antibodies by the individual’s own lymphocytes qualifies as active immunity.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Expiration (breathing out) is a passive process that occurs when the muscles involved in inhalation relax. During expiration, the external intercostal muscles relax, causing the ribcage to move downwards and inwards. Simultaneously, the diaphragm relaxes and returns to its original dome-like shape, which means it moves up. These movements decrease the volume of the thoracic cavity and increase the air pressure inside the lungs relative to the atmosphere, forcing air out. Therefore, option D correctly describes both muscle actions.
✅ Answer: (D)
▶️ Answer/Explanation
Urea is produced in the liver through the deamination of excess amino acids. It leaves the liver via the hepatic vein to enter the general circulation. The blood travels to the heart, is pumped to the lungs for oxygenation, and returns to the heart. From there, the urea-rich blood is pumped into the aorta and enters the renal artery, which carries it specifically to the kidney for filtration and subsequent excretion as urine. Options A and B are incorrect because production starts in the liver, not the kidney. Option C is incorrect because the hepatic artery carries blood to the liver, not away from it.
✅ Answer: (D)
▶️ Answer/Explanation
To focus on a near object, the eye must increase the refractive power of the lens to bend light rays more sharply. This process is called accommodation. During this, the ciliary muscles contract, which reduces the diameter of the ciliary ring. This inward movement releases the tension on the suspensory ligaments, making them slack. Consequently, the elastic lens is allowed to bulge and become more spherical (convex), increasing its focal power. This specific combination is represented in row A.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The process begins when an electrical impulse reaches the presynaptic terminal, triggering the release of neurotransmitters from vesicles ($2$). These chemical messengers then travel by diffusion across the narrow synaptic gap ($4$). Once they reach the postsynaptic membrane, the molecules bind to specific receptor proteins ($3$). This binding causes a change in the membrane potential, which ultimately stimulates a new electrical impulse in the next neurone ($1$). Following this logical flow, the correct sequence is $2 \rightarrow 4 \rightarrow 3 \rightarrow 1$.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
To prevent hypothermia, mammals use negative feedback mechanisms to conserve and generate heat. Shivering involves rapid, involuntary muscle contractions that convert chemical energy into thermal energy, raising the core temperature. Vasoconstriction occurs when the smooth muscles in the walls of arterioles near the skin surface contract, narrowing the lumen. This reduces blood flow to the skin’s surface, minimizing heat loss to the environment via radiation. In contrast, sweating and vasodilation are cooling mechanisms used when the body is too warm. Therefore, only the combination of shivering and vasoconstriction effectively combats falling temperatures.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The label $X$ points to the pancreas, a leaf-shaped gland located behind the stomach. The pancreas plays a vital role in regulating blood glucose levels by secreting the hormone insulin from its beta cells. While the diagram also shows the adrenal glands (above the kidneys) which secrete adrenaline, and the ovaries which secrete oestrogen, $X$ specifically identifies the pancreatic structure. Therefore, among the given options, insulin is the correct hormone produced by this specific gland.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Hormonal control involves chemicals (hormones) traveling through the bloodstream to target organs, making the speed of action slow compared to electrical impulses. However, these effects often last for a long duration because the chemicals remain in the blood until broken down. In contrast, nervous control is characterized by rapid electrical signals (fast) that have immediate, localized, and fleeting effects (short). Therefore, row B correctly identifies the characteristics of hormonal control.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Statement $1$ is correct because gravity causes auxin to accumulate on the lower side of a horizontal stem (gravitropism). Statement $3$ is also correct as auxin is synthesized in the apical meristem of the shoot tip. Statement $2$ is false; auxin actually moves away from light to the shaded side. Statement $4$ is incorrect because auxin stimulates cell elongation in shoots, though it inhibits it in roots. Therefore, only statements $1$ and $3$ are accurate descriptions of auxin’s role in shoot growth.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Antibiotics are medications specifically designed to kill or inhibit the growth of bacteria. Cholera is caused by the bacterium Vibrio cholerae, making it treatable with antibiotics. In contrast, HIV is a viral infection, and antibiotics have no effect on viruses. Rickets is a deficiency disease (usually lack of Vitamin D or calcium), not an infection. While pathogens include bacteria, viruses, and fungi, antibiotics do not treat “all” pathogens, only bacterial ones.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Method $V$ is self-pollination, which still involves meiosis and the fusion of gametes; therefore, the offspring are not genetically identical (clones), making conclusion $1$ incorrect. Method $W$ is cross-pollination between two different plants, which significantly increases genetic variation by combining alleles from two distinct parents. This increased genetic diversity ensures that offspring are genetically different (conclusion $2$) and provides a larger gene pool for natural selection to act upon. Consequently, the species has a better chance of adapting to environmental changes (conclusion $3$). Since only statements $2$ and $3$ are valid, the correct option is $D$.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
The umbilical artery carries deoxygenated blood and metabolic waste products, such as urea and carbon dioxide, from the fetus to the placenta for removal. Consequently, blood in the umbilical artery has a low oxygen concentration. In contrast, the umbilical vein carries oxygenated and nutrient-rich blood from the placenta back to the fetus. Since the placenta filters out waste from the fetal blood into the mother’s system, the blood returning via the umbilical vein has a low urea concentration.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
During pregnancy, the placenta acts as a temporary endocrine organ. While the corpus luteum initially produces hormones to maintain the uterine lining, the placenta eventually takes over the production of progesterone and estrogen. Progesterone is vital because it maintains the endometrium, prevents uterine contractions, and supports the developing fetus throughout the pregnancy. In contrast, FSH and LH are secreted by the anterior pituitary gland, and testosterone is primarily produced in the testes.
✅ Answer: (D)
▶️ Answer/Explanation
An allele is a specific variation of a gene. While a gene determines a general characteristic, such as eye color, the alleles are the specific instructions for that trait, like blue or brown. In diploid organisms, individuals inherit two alleles for every gene—one from each parent. These alleles are located at the same position, or locus, on homologous chromosomes. If the two alleles are identical, the organism is homozygous; if they differ, it is heterozygous. Therefore, alleles represent the different “versions” of genetic information that contribute to an organism’s unique phenotype.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
To solve this, let $P$ represent the dominant allele for polydactyly and $p$ represent the recessive allele for normal toes. Since both parents are heterozygous, their genotypes are both $Pp$. A Punnett square for this cross ($Pp \times Pp$) results in the following offspring genotypes: $PP$, $Pp$, $Pp$, and $pp$. Because polydactyly is a dominant trait, cats with genotypes $PP$ and $Pp$ will have extra toes. Only the homozygous recessive genotype ($pp$) results in a cat with no extra toes. This occurs in $1$ out of $4$ possible combinations. Therefore, the probability is $1/4$, which equals $0.25$.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Red-green colour blindness is a sex-linked trait caused by a recessive allele found specifically on the $X$ chromosome. Since males have only one $X$ chromosome ($XY$), a single recessive allele will cause the condition. In contrast, females ($XX$) require two copies of the recessive allele to be colour blind, making the condition far more common in males than females. Option (A) is incorrect as it follows a recessive-dominant pattern, not codominance. Options (B) and (C) are incorrect because while it is rare in females, it certainly does occur.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Meiosis is a specialized form of cell division that occurs in sexually reproducing organisms. It is known as a reduction division because it halves the chromosome number from diploid ($2n$) to haploid ($n$). Unlike mitosis, meiosis involves processes like crossing over and independent assortment, which ensure that the resulting daughter cells exhibit genetic variation. Feature $2$ is incorrect for meiosis because the daughter cells are genetically unique, not identical. Therefore, features $1$, $3$, and $4$ are the correct descriptors.
✅ Answer: (C)
▶️ Answer/Explanation
An adaptive feature is an inherited functional, structural, or behavioral trait that increases an organism’s fitness within its specific habitat. These traits are the result of natural selection, ensuring that individuals better suited to their surroundings are more likely to reach reproductive age. While a phenotype describes any observable trait, not all phenotypes are necessarily helpful for survival. Competition is a process between organisms, and an observable feature is a general term that lacks the specific context of evolutionary advantage. Therefore, “adaptive feature” is the most precise biological term for a trait that actively aids survival and reproduction.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Photosynthesis is the only biological process listed that acts as a carbon “sink.” During this process, green plants and algae capture light energy to convert $CO_{2}$ and water into glucose and oxygen. In contrast, respiration and decomposition release $CO_{2}$ back into the atmosphere as organic matter is broken down. Combustion, the burning of fossil fuels or biomass, also adds significant amounts of $CO_{2}$ to the air. Therefore, photosynthesis is essential for regulating atmospheric carbon levels and mitigating the greenhouse effect.
✅ Answer: (C)
▶️ Answer/Explanation
Process $X$ represents the conversion of ammonia into nitrate ions in the soil, which is known as nitrification; this is carried out by nitrifying bacteria. Process $Y$ shows the conversion of nitrate ions back into nitrogen gas in the atmosphere, a process called denitrification performed by denitrifying bacteria in anaerobic conditions. Other processes in the diagram include nitrogen fixation (atmosphere to ammonia/nitrates) and decomposition (waste to ammonia). Therefore, row $D$ correctly identifies both specific biological transformations.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
A typical sigmoid (S-shaped) growth curve consists of four main phases: the lag phase, the exponential (log) phase, the stationary phase, and the death phase. Looking at the provided graph, the period from $1650$ to $1850$ represents the lag phase, where growth is slow. From $1900$ onwards, the curve shoots upward steeply, representing the exponential (log) phase. However, the curve does not level off at a carrying capacity, nor does it decline. Therefore, the stationary phase (where birth rates equal death rates) and the death phase (where population declines) are missing from this specific representation of human history.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
In an ecological pyramid, trophic levels represent the feeding positions of organisms. The first level consists of producers (plants), which create their own energy. Herbivores are organisms that eat these producers directly, making them the first group of consumers in the chain. Therefore, they are classified as primary consumers. Higher levels like secondary or tertiary consumers consist of carnivores or omnivores that eat other animals.
✅ Answer: (A)
▶️ Answer/Explanation
When fertiliser enters a river, it causes an immediate increase in nutrient levels, leading to rapid growth of algae and subsequent death of plants. Bacteria then decompose this organic matter, and their population increases significantly. Because these bacteria are aerobic, they consume large amounts of dissolved oxygen for respiration, causing oxygen levels to plummet.
Looking at the graph, the point where the bacteria curve starts its sharp ascent and the oxygen curve begins its steep decline is at position A. At positions $B$ and $C$, the impact is already in progress or at its peak, while $D$ shows the recovery phase. Therefore, the point of entry must be the earliest point where these changes are triggered.
✅ Answer: (A)
▶️ Answer/Explanation
The process begins by identifying and isolating the human insulin gene using restriction enzymes (Step 2). This gene is then inserted into a bacterial plasmid to create recombinant DNA (Step 3). Once the bacteria are transformed with this plasmid, they are grown in fermenters where they multiply rapidly (Step 4), expressing the human gene to produce insulin protein. Finally, the produced insulin is extracted and purified from the bacterial culture (Step 1). Following this logical sequence of genetic engineering leads to the order $2 \rightarrow 3 \rightarrow 4 \rightarrow 1$.
✅ Answer: (B)
✅ Answer: (B)