Biology — Mixed Practice — Part 4: 24 MCQs with Explanations

Platelets (thrombocytes) form plugs at injury sites and release clotting factors for coagulation cascade.

Convergent evolution produces analogous structures (e.g., wings of bats and insects) with similar function but different evolutionary origins and developmental pathways.

Oxygen does not absorb significant infrared radiation and therefore does not contribute to the greenhouse effect.

CSF is produced by choroid plexuses, circulates in ventricles and subarachnoid space, providing buoyancy, protection, nutrient delivery, and waste removal.

Urinary bladder stores urine before excretion; nephron consists of renal corpuscle (glomerulus + Bowman's capsule) and renal tubule.

Menstruation (days 1-5 of menstrual cycle) involves breakdown and expulsion of endometrial lining due to declining progesterone and estrogen levels.

Cerebellum compares intended movement (from motor cortex) with actual movement (via proprioceptive feedback) and makes corrective adjustments for smooth, coordinated motion.

Nitrogen constitutes 78% of atmosphere but is transparent to infrared radiation and does not trap heat; CO₂, CH₄, N₂O, and H₂O vapor are greenhouse gases.

Sigmoid shape results from cooperative binding: binding of first O₂ molecule increases affinity for subsequent O₂ molecules (positive cooperativity).

Hypothalamus contains thermoregulatory center that triggers sweating/vasodilation when hot and shivering/vasoconstriction when cold.

Countercurrent multiplier system in loop of Henle creates hyperosmotic medulla essential for water conservation in collecting duct under ADH influence.

Metabolism (sum of all chemical reactions) is a defining characteristic of life; crystallization, radioactivity, and magnetism occur in non-living matter.

Cerebral cortex has sensory areas (receiving input) and motor areas (initiating movement); association areas integrate information for complex functions.

Cornea provides about two-thirds of eye's focusing power; lens provides adjustable focus (accommodation) for near/far vision.

CFCs release chlorine atoms in stratosphere that catalyze ozone destruction; one Cl atom can destroy thousands of ozone molecules.

Follicular phase (days 1-13): developing follicles secrete estrogen causing proliferation of endometrial lining.

Pressure flow: sugars loaded into sieve tubes at source create osmotic gradient drawing in water, generating turgor pressure that pushes sap to sink where sugars unloaded.

O₂ accepts electrons and H⁺ at end of electron transport chain to form water: ½O₂ + 2H⁺ + 2e⁻ → H₂O.

Medulla contains reflex centers for vomiting, coughing, sneezing, and swallowing in addition to vital autonomic centers.

Cerebellum fine-tunes motor commands from cerebral cortex, ensuring smooth, coordinated movements and maintaining balance/posture.

Liver continuously produces bile; gallbladder stores and concentrates bile between meals, releasing it into duodenum when needed for fat digestion.

Oxygen (O₂) and nitrogen (N₂) are transparent to infrared radiation; greenhouse gases (H₂O, CO₂, CH₄, N₂O, O₃) absorb and re-emit IR radiation.

Cerebellum compares intended movement (from motor cortex) with actual movement (via proprioceptive feedback) and makes real-time corrections.

Upper respiratory tract: nose, nasal cavity, pharynx, and larynx; lower respiratory tract: trachea, bronchi, bronchioles, and lungs.

In Urea cycle 2 ammonia molecules combine with 1 CO2 molecule to form 1 molecule of urea.

Homeostatic mechanisms keep the internal environment fixed despite of wide changes in external environment is the correct answer to “Which of the following statement about Homeostasis is incorrect”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Bony fishes is the correct answer to “Which of the following fish drink large amount of sea water and excrete concentrated urine resulting in maximum salt excretion and minimal water loss”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

The characteristic which enable animals to tolerate dehydration is called Anhydrobiosis .

Fresh water fishes is the correct answer to “Which of the following fishes excrete large volume of diluted urine”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Rose is an example of Mesophytes .

In a hot summer after noon, if your bodys Homeostatic machinery keep your internal temperature quite lower than that of external than this is an example of Negative feed back .

Trimethylamine oxide is the correct answer to “Marine fish can keep their internal environment hypertonic with respect to the surrounding salty water by retaining.”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Terrestrial animals like kangaroo rat survive even without drinking water since They are anhydrobiotic organisms .

Aquatic animals excrete nitrogenous waste commonly in the form of Ammonia .

Protonephridia are present in Flateworm .

Nitrogenous waste is the correct answer to “Which of the following constituent is/are maximum in the filtrate that leaves proximal convoluted tubules”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Production of pyrogens is a Protective phenomenon.

Animals that produce metabolic heat at low level and also absorb heat from the surroundings are called Heterotherms .

Blubber a thick layer of fat is present in Marine Mammals .

Metanephridium is the correct answer to “Which of the following is a sentimentally arranged excretory system”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Excessive lactic acid is converted into Glycogen by liver.

Excrete some of the waste materials directly into soil, occasionally using them as a chemical weapon against other competing plants. is the correct answer to “Which of the following statement about conifers is correct”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Purine and pyrimidine metabolism results in production of Xanthine .

Amount of water required to excrete 1gN of Urea is 50 ml .

Each ach nephridium of earthworm opens to the exterior by Nephridiopore .

The main nitrogenous waste formed in the body of earthworm is/are Urea .

Malpighian tubules is the correct answer to “Which of the following excretory structure is associated with gut of the organism”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Juxtramedullary is the correct answer to “Which of the following nephrons play important role in production of concentrated urine”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Hemodialysis is the correct answer to “Which of the following treatment will be administered first in a newly diagnosed renal failure patient”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

In animals excess of nitrogen is excreted primarily in form of Ammonia .

The whole body cells are in contact with water is the correct answer to “Hydra has no specialized excretory system because:”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

The distal blind end of the malpighian tubules bathes freely in Haemocoel .

Evaporative cooling. is the correct answer to “Panting is a representative of which mechanism”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Fishes, most of the invertebrates and amphibians are examples of Ectotherms animals.

The mechanism of regulation, generally between organism and its environment, of solutes and the gain and the loss of water is called Osmoregualtion .

Increases transpiration by increasing the surface area of the leav is the correct answer to “Which of the following represents osmoregulatory steps taken by hydrophytes”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Most of the marine invertebrates are Osmoconformers .

Bony fishes is the correct answer to “Which of the following marine fishes are considered direct descendents of fresh water ancestors”. Items of this type are drawn from the Biology — Mixed Practice — Part 4 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Open circulatory system can contain White Blood Cells .

Pressure flow theory was proposed by Earnst Munch .

Guard cells function as multisensory hydraulic valve.

Monocyte give rise to macrophages, which destroy larger particles by phagocytosis.

Tricuspid valve is present Between right atrium and right ventricle .

Cooleys anemia is another name used for Thalassaemia .