Sec 2 Science Study Notes

How to use these notes

Each section maps to one Sec 2 theme. Read through once, then use the key terms as flashcard prompts. The common traps and exam tips are drawn from typical Singapore school assessment patterns.

Alignment note: Independently written and mapped to public MOE/SEAB Lower Secondary Science syllabus structures. Not affiliated with MOE, SEAB or Cambridge.

Key terms

Hypothesis Variable Anomaly Precision Reliability Validity Correlation Inference

Observation vs inference

An observation is what you directly detect with your senses or instruments. An inference is a conclusion drawn from observations. Examiners deduct marks when students state an inference as if it were an observation.

Handling anomalies

Identify the outlier, state that it is anomalous, and give a plausible reason (e.g. misreading, parallax, contamination). Calculate the mean from the remaining consistent readings. Do not silently delete data.

Precision vs reliability vs validity

• Precision — how small the scale divisions are; affects how exactly you can read an instrument.
• Reliability — improved by repeating measurements; reduces the effect of random error.
• Validity — the experiment actually tests what it claims; requires fair-test conditions.

Describing graph trends

State the overall pattern, quote specific values with units, and then comment on any anomalous points. Use language such as "as X increases, Y increases at a decreasing rate" rather than "X goes up so Y goes up."

Key terms

Water cycle Carbon cycle Evaporation Condensation Photosynthesis Respiration Decomposition Fossil fuels

The water cycle

• Evaporation — liquid water gains energy and becomes water vapour; occurs from oceans, lakes and soil.
• Condensation — water vapour loses energy; forms clouds and droplets.
• Precipitation — water falls as rain, sleet or snow.
• Transpiration — water vapour released by plants through leaves.

The carbon cycle

• Carbon enters organisms through photosynthesis (CO₂ → glucose).
• Carbon is released through respiration, combustion and decomposition.
• Fossil fuels return carbon stored millions of years ago; burning them adds extra CO₂ to the atmosphere.

Materials and their uses

Link material properties to function: metals conduct heat and electricity; polymers are flexible and insulating; ceramics are hard and heat-resistant. For exam questions, always justify your choice using at least one specific property.

Key terms

Organ system Homeostasis Nervous system Hormones Stimulus Response Digestion Enzyme

Organ systems overview

• Digestive system — breaks food into absorbable molecules; enzymes are produced in the mouth, stomach and small intestine.
• Circulatory system — transports oxygen, nutrients and hormones; removes waste.
• Nervous system — rapid electrical signals via neurons; brain, spinal cord and nerves.
• Endocrine system — slower chemical signals (hormones) via blood; e.g. insulin controls blood glucose.

Enzymes

Enzymes are biological catalysts made of protein. They are specific (one enzyme, one substrate type), work fastest at an optimum temperature (~37 °C in humans), and are denatured by high temperatures or extreme pH. At low temperatures they slow but are not destroyed.

Homeostasis

The body maintains a stable internal environment. Key examples: blood glucose regulation (insulin and glucagon), body temperature (sweating, shivering), and water balance (kidneys). All involve a stimulus → receptor → coordinator → effector → response pathway.

Key terms

Current Voltage Resistance Series circuit Parallel circuit Force Pressure Wave

Circuits — series vs parallel

• Series: same current throughout; voltage is shared; one break stops all components.
• Parallel: voltage is the same across each branch; current splits; one branch can fail without affecting others.

Ohm's Law: V = I × R (Voltage = Current × Resistance).

Pressure

Pressure = Force ÷ Area. Same force over a smaller area gives higher pressure (e.g. a knife blade). In fluids, pressure increases with depth and acts equally in all directions at a given depth.

Introduction to waves

• Transverse waves — vibration perpendicular to direction of travel (e.g. light, water waves).
• Longitudinal waves — vibration parallel to direction of travel (e.g. sound).
• Key quantities: amplitude, wavelength, frequency, wave speed. Relationship: wave speed = frequency × wavelength.

Key terms

Biodiversity Food web Ecosystem Pollution Renewable energy Sustainability Carbon footprint Deforestation

Food webs and energy flow

Energy flows from producers (plants) through primary consumers, secondary consumers and so on. At each level, most energy is lost as heat — only about 10% is transferred to the next level. This is why food chains rarely exceed 5 links.

Human impact and sustainability

• Deforestation — reduces carbon sinks, destroys habitats, increases soil erosion.
• Pollution — eutrophication from fertiliser run-off depletes oxygen in water; air pollutants cause acid rain.
• Biodiversity loss — reduces ecosystem resilience; once extinct, species cannot be recovered.

Sustainable choices

For exam questions on trade-offs, weigh economic benefits against environmental costs. Use evidence: state a specific impact, explain the mechanism, then assess the significance. Avoid vague phrases like "bad for the environment" — say which aspect and why.

Must-know checklist — Sec 2

• Can distinguish observation from inference and identify anomalies.
• Can describe the water cycle and carbon cycle with correct terminology.
• Can explain enzyme action and the effect of temperature and pH.
• Can calculate pressure (P = F/A) and apply Ohm's Law (V = IR).
• Can compare series and parallel circuits.
• Can evaluate a human impact question using evidence and trade-offs.
• Can describe energy flow in a food web and explain why chains are short.