Explanation

• Chemotropism is the directional growth of a plant or its parts in response to a chemical stimulus.
• The growth of a pollen tube towards the ovule due to chemical signals is an example of positive chemotropism.

Additional information:

• Thigmotropism is a response to touch, hydrotropism to water and phototropism to light.
• Chemotropism helps in plant reproduction, especially during fertilization.

Last verified on 02-11-2026

Explanation

• The axial skeleton forms the central supporting axis of the human body.
• It includes the skull, vertebral column, ribs and sternum.
• The adult human axial skeleton consists of 80 bones.
• The appendicular skeleton consists of the limbs and the shoulder and pelvic girdles, containing 126 bones.

Last verified on 02-11-2026

Explanation

• Nephridiopore is the external opening of the nephridium in an earthworm.
• Nephridia are the excretory organs that remove metabolic waste and help regulate water balance.
• Nephrostome is the funnel-shaped internal opening of a nephridium.
• Earthworms use nephridia to eliminate nitrogenous waste from their bodies.

Last verified on 02-11-2026

Explanation

• Vitamin K is essential for the production of blood-clotting proteins.
• Its deficiency reduces the blood's ability to clot, causing prolonged bleeding.
• It may lead to easy bruising, nosebleeds and excessive bleeding from wounds.
• Vitamin K is found in green leafy vegetables such as spinach, kale and broccoli.

Last verified on 02-11-2026

Explanation

• Vitamin C deficiency → Scurvy
• Causes bleeding gums and poor wound healing.
• Vitamin C is important for collagen formation.
• Main sources: Citrus fruits, guava, tomatoes, and vegetables.

Last verified on 02-11-2026

Explanation

• Malaria is caused by Plasmodium, a protozoan parasite transmitted through the bite of an infected female Anopheles mosquito.
• African sleeping sickness (African trypanosomiasis) is caused by Trypanosoma brucei.
• It is transmitted to humans through the bite of an infected tsetse fly.
• Both diseases are caused by protozoan parasites.

Last verified on 02-11-2026

Explanation

• Sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) react with water and oxygen in the atmosphere to form sulfuric acid and nitric acid.
• These acids mix with rainwater and fall to the Earth as acid rain.
• Carbon dioxide (CO₂) can form weak carbonic acid in rainwater, but it is not considered a major cause of acid rain.

Last verified on 02-11-2026

Explanation

• Water pollution occurs when harmful substances contaminate water bodies.
• Common pollutants include industrial waste, sewage, pesticides, plastics and chemicals.
• It makes water unsafe for drinking and harms aquatic organisms.
• Major sources include factories, agricultural runoff and untreated domestic wastewater.

Last verified on 02-11-2026

Explanation

• Cholera is an infectious disease caused by the bacterium Vibrio cholerae.
• Symptoms include severe diarrhea, dehydration, and vomiting.
• Cholera can be prevented by clean drinking water and proper sanitation.

• It mainly spreads through contaminated water and food.
  It is most common in areas with poor hygiene and overcrowding.

Last verified on 3-03-2026

Explanation

• Chlorine atoms destroy ozone molecules (O₃) through chemical reactions in the stratosphere.
• Chlorine is mainly released from chlorofluorocarbons (CFCs) when ultraviolet radiation breaks them down.
• One chlorine atom can destroy thousands of ozone molecules before being removed from the stratosphere.
• The Montreal Protocol (1987) was adopted to phase out ozone-depleting substances such as CFCs.

Last verified on 02-11-2026