Explanation

Thermal energy can be transferred through all three methods:

• Conduction: Direct transfer between particles in physical contact.
• Convection: Transfer through the movement of fluids.
• Radiation: Transfer through electromagnetic waves (e.g., light, radio waves).

Last verified on 13-03-2026

Explanation

• Tundra is a cold, treeless region found near the Arctic and Antarctic.
• Soil is often frozen (permafrost) throughout the year.
• Vegetation includes mosses, lichens, and low shrubs.
• Animals adapted: polar bears, arctic foxes, reindeer.

Last verified on 13-03-2026

Explanation

• Double Displacement Reaction: Two compounds exchange ions or radicals to form new compounds.
• General form: AB + CD → AD + CB.
• Example: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Additional information:

• Decomposition: Single compound breaks into two or more simpler substances.
• Combination (Synthesis): Two or more substances combine to form one compound.

Last verified on 13-03-2026

Explanation

• A molecule is the smallest particle of a substance that retains its chemical properties.
• It is made of two or more atoms chemically bonded together.
• Examples of molecules: H₂O, O₂, CO₂, NH₃, CH₄.

Additional information:

• An atom is the smallest unit of an element.
• A compound is a substance formed when different elements combine chemically.

Last verified on 13-03-2026

Explanation

• Humans have 20 primary teeth (also known as deciduous or baby teeth).
• 32 permanent teeth (also known as adult teeth).

Explanation

• According to the Kinetic Molecular Theory, faster gas particles hit container walls more often.
• More frequent and stronger collisions increase the pressure.
• Higher temperature → higher particle speed → higher pressure.
• Pressure depends on number of collisions of gas molecules with container walls.
• Unit of gas pressure: Pascal (Pa).

Last verified on 13-03-2026

Explanation

• Freezing is the process by which a liquid changes to a solid.
• It is the reverse of melting, which is the process by which a solid changes to a liquid.

Last verified on 13-03-2026

Explanation

• Respiration (breathing) is mainly controlled automatically by the brain’s respiratory center in the medulla oblongata.
• Normally, breathing occurs without conscious control, so it is an involuntary process.
• When a person cannot control breathing voluntarily (e.g., during sleep or unconsciousness), the body automatically continues respiration.

Last verified on 13-03-2026

Explanation

• Enamel is the hard, mineralized outer layer of teeth.
• It protects the inner parts of the tooth from damage and decay.
• Enamel is the hardest substance in the human body.
• It is mainly made of calcium phosphate.
  

Additional information:

• Incisors (8) – used for cutting food
• Canines (4) – used for tearing food
• Premolars (8) – help crush and grind food
• Molars (12) – grind food during chewing
• Total adult teeth = 32

Last verified on 13-03-2026

Explanation

• Digestion specifically means the mechanical and chemical breakdown of food into simpler substances.
• Mechanical digestion includes chewing and churning, while chemical digestion involves enzymes and acids.

Additional information:
Main 5 processes of the digestive system:

1. Ingestion – taking food into the body
2. Digestion – mechanical and chemical breakdown of food
3. Absorption – nutrients enter blood through the intestine
4. Assimilation – cells use absorbed nutrients
5. Egestion – removal of undigested waste

Last verified on 13-03-2026