Gastric acid activates digestive enzymes, particularly pepsinogen to pepsin, and helps in protein digestion.

Gastric juice contains hydrochloric acid and pepsin, which are essential for the digestion of proteins.

The immune system's primary function is to protect the body against pathogens and diseases.

Stomata are small openings on the leaf surface that facilitate gas exchange, allowing carbon dioxide in and oxygen out.

The nephron is the functional unit of the kidney responsible for the filtration of blood and the formation of urine.

The nucleus stores the cell's genetic information and coordinates activities such as growth, metabolism, and reproduction.

The nucleus stores genetic information and controls cellular activities by regulating gene expression.

The pancreas produces digestive enzymes that help in the digestion of carbohydrates, proteins, and fats.

The renal pelvis collects urine from the collecting ducts and transports it to the ureter.

The main function of the respiratory system is gas exchange, specifically the intake of oxygen and the removal of carbon dioxide.

The root system primarily anchors the plant and absorbs water and nutrients from the soil.

The main function of the seminal vesicles is the production of seminal fluid, which nourishes and helps transport sperm.

Sepals protect the flower bud before it opens and can also support the petals.

Oxygen is the main gas that is taken in during respiration and is essential for cellular metabolism.

Bioremediation aims to clean up contaminated environments using microorganisms, making option 'To clean up contaminated environments' the correct answer.

The main goal of conservation biology is to protect endangered species and their habitats.

Family planning allows couples to make informed decisions about the number and spacing of their children, promoting reproductive health.

Sustainable development aims to meet the needs of the present without compromising the ability of future generations to meet their own needs, balancing economic growth with environmental protection.

Quantization in atomic physics means that energy levels in an atom are discrete, not continuous.

Plastic pollution leads to ingestion and entanglement of marine animals, causing injury and death.

The Rutherford model fails to explain why electrons do not spiral into the nucleus, thus not accounting for atomic stability.

The main method of hydrogen production in the industry is steam reforming of natural gas.

In the laboratory, hydrogen is commonly produced by the reaction of metals (like zinc) with acids.

HIV is primarily transmitted through sexual contact.

Polystyrene is produced from the polymerization of styrene monomers.

Birds and reptiles primarily excrete uric acid, which is less toxic and conserves water compared to urea.

Reptiles and birds primarily excrete uric acid, which is less toxic and conserves water.

When aluminum reacts with hydrochloric acid, hydrogen gas (H2) is produced along with aluminum chloride (AlCl3).

When hydrogen reacts with oxygen, the main product formed is water (H2O).

The main products of the combustion of hydrocarbons are water (H2O) and carbon dioxide (CO2).