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DNA is a very large molecule (a polymer) made up of repeating smaller units called nucleotides. Each nucleotide in a DNA molecule consists of three components: - A phosphate group. - A deoxyribose sugar (a pentose sugar). - One of four nitrogenous bases (adenine, guanine, cytosine, or thymine).

Carbon monoxide (CO) is a highly toxic gas that binds to haemoglobin in the blood with an affinity much greater than oxygen. This forms carboxyhaemoglobin, which effectively reduces the amount of oxygen that the blood can transport to the body's organs and tissues, leading to tissue hypoxia (oxygen deprivation). A. Major cause of respiratory tract infections: Carbon monoxide does not cause infections; it is a chemical asphyxiant. C. Preventing clotting of blood: Carbon monoxide does not interfere with the blood clotting process (coagulation); it primarily affects oxygen transport. D. Causing gene mutation: While some chemicals can cause gene mutations (are carcinogenic or mutagenic), this is not the primary or immediate effect of carbon monoxide poisoning. Its main harm is through oxygen deprivation. The correct answer is reducing oxygen carrying capacity of the blood - option B.

Apical meristems are specialized regions of undifferentiated cells located specifically at the growing tips (apices) of stems and roots. They undergo continuous cell division (mitosis) to produce new cells, allowing the plant to grow in length (primary growth). A. Intercalary meristems are found at the base of leaves and nodes, particularly in monocots like grasses. They also contribute to an increase in length (e.g., leaf regrowth after mowing), but they are located in the middle of the plant, not the apex. C. Meristematic is the general term for any plant tissue composed of actively dividing cells. Apical, intercalary, and lateral are all types of meristematic tissue. The question asks for the specific type found at the apex. D. Lateral meristems are found along the sides of stems and roots. They are responsible for secondary growth, which increases the plant's girth or width, not its length at the apex.

Macronutrients are needed in large amounts (e.g., Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulphur, Carbon, Hydrogen, Oxygen), while micronutrients are needed in small amounts (e.g., Iron, Zinc, Manganese, Copper, Boron, Molybdenum, Chlorine) for plant growth, with macros forming biomass and micros acting as cofactors for enzymes, supporting essential functions like photosynthesis and metabolism.

Seaweeds primarily live in saltwater environments, including oceans and seas, where they form the base of many food chains and provide habitat. While some green seaweeds can be found in freshwater or estuarine environments, the majority of brown and red seaweeds are strictly marine. Barnacles are exclusively marine crustaceans, related to crabs and lobsters. They are commonly found attached to hard surfaces like rocks, piers, and boat hulls in shallow and tidal (intertidal) waters within marine habitats. Both organisms are characteristic of rocky shores within marine ecosystems.

Interspecific competition occurs between individuals of different species competing for the same limited resources. In this scenario, cows and goats are two different species both requiring the scarce grasses for survival during the dry season. A. Intraspecific refers to competition between individuals of the same species, for example, between two cows, or two goats. B. Predation is an interaction where one animal (predator) hunts and kills another animal (prey) for food, which is not what is happening as both are herbivores eating grass. D. Commensalism is a relationship where one species benefits and the other is neither significantly harmed nor benefited. This is not the case as both species are negatively affected by the scarcity of grass.

The oxygen transported in the blood is used by the body's cells for cellular respiration (aerobic respiration), a process that breaks down food molecules (like glucose) to generate the chemical energy (ATP) needed for all bodily functions. A. removal of waste products: Oxygen is not directly used for the removal of waste products. Instead, waste products like carbon dioxide are generated from the process that uses oxygen and are then removed by the blood. B. growth and development of cells: While oxygen is essential for the energy required for cell growth and development, it is the energy-releasing process itself (cellular respiration) that is the direct use of the oxygen, not the growth process in isolation. C. formation of carboxyl haemoglobin: This option is incorrect because carboxyhemoglobin is formed when carbon monoxide (a poison) binds to hemoglobin, not oxygen. This binding prevents the normal transport of oxygen.

The tiny, non-functional hind leg bones (and pelvic bones) found in the bodies of modern whales are considered vestigial structures. These are remnants of anatomical features that were functional in an organism's ancestors but have lost their original purpose over time due to evolution and adaptation to a different environment (in this case, a fully aquatic one). Their presence provides strong evidence that whales descended from four-legged, land-dwelling mammals that walked on land around 50 million years ago. A. are not related to land animals. This is incorrect because the presence of these structures is key evidence of a shared evolutionary history and common ancestry with terrestrial mammals, such as even-toed ungulates like hippos, cows, and deer. C. have never had legs in their evolutionary history. This is incorrect because fossil records show a clear transitional series of whale ancestors with progressively smaller, but functional, hind limbs. D. bones serve a major function in swimming. This is incorrect due to the fact that, the bones are tiny, internal, and not connected to the rest of the skeleton or used for locomotion. Whales use their powerful tail flukes for swimming, not these vestigial bones. (Note: some recent research suggests they may play a minor, secondary role as an anchor for reproductive organs in some male whales, but their major ancestral function was for walking, and they are non-functional in the context of movement).

The genotype is the complete genetic make up of an organism, specifically the set of genes or alleles (variant forms of a gene) it carries. It is the hereditary material passed from parents to offspring, coded in the DNA. A. nucleotide is the basic building block (monomer) of the nucleic acids DNA and RNA, not the entire genetic makeup itself. B. karyotype refers to the number and visual appearance of the chromosomes in the cell nucleus of an organism or species, often represented in an organized image, but not the specific genetic information or gene variants within them. C. phenotype refers to the observable physical characteristics or traits of an organism (e.g., eye color, height), which are a result of the interaction between the genotype and environmental factors, not the genetic makeup itself.

The longest bone in the human body is the femur, also known as the thigh bone, located in the upper leg between the hip and knee; it's also one of the strongest bones, supporting body weight and enabling movement like walking and running.

Bats are mammals and, by definition, females possess mammary glands which produce milk to nourish their young. Also, birds do not have mammary glands and feed their young in other ways (e.g., with chewed food or regurgitated food). A. possess four chambered heart: Both bats (mammals) and birds have a four-chambered heart, so this characteristic does not differentiate them. B. are active at night: While many bat species are nocturnal (active at night), this is a behavioral trait, not a defining physical characteristic that differentiates all bats from all birds, as some bird species are also nocturnal. C. are warm blooded: Both bats and birds are warm-blooded (endothermic), meaning they can regulate their own body temperature, so this characteristic is shared, not a differentiator.

The above diagram represents the female reproductive system. The various labelled parts are: I - Ovary : Two oval-shaped glands that produce eggs (ova) and hormones like estrogen and progesterone. II - Uterus : A hollow, pear-shaped muscular organ where a foetus develops. It is also called the womb. III - Cervix : The lower part of the uterus that opens into the vagina. It acts as a gateway for sperm and a passage for menstrual blood. IV - Vagina: A muscular canal that connects the cervix to the outside of the body, serving as the birth canal and the site for sexual intercourse. The part labelled II is the uterus

Symbiosis is a general term for any close and long-term biological interaction between two different species. The relationship in the rumen is a form of symbiosis known as mutualism. The bacteria and protozoa get a stable, warm environment and a constant supply of food (plant material). The cattle get the ability to break down tough plant material, like cellulose, which they cannot digest on their own because they lack the necessary enzymes. The microbes ferment the cellulose into usable energy sources (volatile fatty acids) and are also a source of protein and vitamins for the cow. B. In commensalism, one organism benefits, while the other is neither significantly harmed nor helped. This is incorrect because the cattle receive essential nutrients from the interaction and would not survive on a cellulose-rich diet without the microbes. C. In parasitism, one organism (the parasite) benefits at the expense of the other (the host), causing harm. This is incorrect because the cattle are not harmed; in fact, the relationship is vital for their survival and health. D. Predation is an interaction where one organism kills and eats another organism. This is incorrect as the primary relationship is a sustained, mutually beneficial living arrangement, not a predator-prey dynamic.

In Tilapia, studies have shown that intraspecific variation, particularly size-dependent trophic niche overlap, demonstrates how different individuals within the same species utilize different resources. Smaller individuals may overlap in their feeding niche with a different set of species or resources compared to larger individuals, effectively partitioning resources and reducing direct intraspecific competition. A. Deer: While intraspecific competition occurs in deer (e.g., males competing for mates), they do not exhibit the same pronounced, size-dependent niche differentiation in feeding as observed in the Tilapia examples, where different life stages or sizes consistently use distinct food sources to avoid competition. B. Pigeon: Studies involving rock pigeons suggest that exposure to competition can lead to increased selectivity and niche contraction (becoming more specialized on a particular resource), rather than expanding their niche to avoid intraspecific competition. D. Toad: There is less evidence to suggest that toads widely use niche differentiation among individuals within a single population as a primary means of consistently reducing intraspecific competition in the same manner as the well-documented examples in Tilapia or certain birds/lizards.

Chameleons use their colour-changing ability for camouflage, which is a key part of their defense mechanism to avoid predators such as birds and snakes. Blending into their environment makes them less visible to threats, increasing their chances of survival.