N-Level Science 2 — Questions and Answers
Question 1: What is the difference between a chemical change and a physical change?
- There is no difference
- A chemical change produces new substances and is usually irreversible, while a physical change does not produce new substances and is usually reversible (Correct answer)
- Physical changes are always permanent
- Chemical changes only occur in labs
Correct answer: A chemical change produces new substances and is usually irreversible, while a physical change does not produce new substances and is usually reversible
Chemical changes involve the formation of new substances (e.g., burning, rusting). Physical changes alter the form but not the chemical composition (e.g., melting ice, dissolving sugar).
Question 2: What is the function of the kidneys in the human body?
- To pump blood
- To filter blood, remove waste products (urea), regulate water balance, and produce urine (Correct answer)
- To digest food
- To produce hormones only
Correct answer: To filter blood, remove waste products (urea), regulate water balance, and produce urine
The kidneys filter blood to remove metabolic waste (especially urea from protein breakdown), regulate water and salt balance, maintain blood pH, and produce urine for excretion.
Question 3: What is the law of conservation of energy?
- Energy can be created from nothing
- Energy cannot be created or destroyed, only converted from one form to another; the total energy in a closed system remains constant (Correct answer)
- Energy always decreases over time
- Energy can be destroyed but not created
Correct answer: Energy cannot be created or destroyed, only converted from one form to another; the total energy in a closed system remains constant
This fundamental law states that the total energy in a closed system is constant. Energy can change form (e.g., electrical to heat, kinetic to potential) but the total amount never changes.
Question 4: What causes the seasons in Singapore and other parts of the world?
- The distance between Earth and the Sun changes
- The tilt of Earth's axis (23.5°) relative to its orbital plane around the Sun causes different regions to receive varying amounts of sunlight (Correct answer)
- The Sun gets hotter and cooler
- The Moon's gravity affects the seasons
Correct answer: The tilt of Earth's axis (23.5°) relative to its orbital plane around the Sun causes different regions to receive varying amounts of sunlight
Earth's axis is tilted at approximately 23.5°. As Earth orbits the Sun, this tilt causes different hemispheres to receive more direct sunlight at different times, creating seasons. Singapore, being near the equator, has minimal seasonal variation.
Question 5: What is an ecosystem?
- A type of plant
- A community of living organisms interacting with each other and their non-living environment (e.g., air, water, soil) in a specific area (Correct answer)
- A single species of animal
- A type of rock formation
Correct answer: A community of living organisms interacting with each other and their non-living environment (e.g., air, water, soil) in a specific area
An ecosystem includes all living organisms (biotic factors) and non-living components (abiotic factors like temperature, water, light) in a particular area, and the interactions between them.
Question 6: What is the pH scale used to measure?
- Temperature
- The acidity or alkalinity of a substance, ranging from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral (Correct answer)
- Weight
- Electrical resistance
Correct answer: The acidity or alkalinity of a substance, ranging from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral
The pH scale ranges from 0 to 14. Values below 7 are acidic, 7 is neutral, and above 7 is alkaline (basic). Common examples: lemon juice (pH 2), water (pH 7), soap (pH 10).
N-Level Science 2
What is the difference between a chemical change and a physical change?