P4 Science: A Complete Guide to All Topics

Primary 4 Science is a significant step up from P3. Where P3 introduces fundamental concepts, P4 goes deeper — you study complete body systems rather than individual organs, explore how plants reproduce, understand the behaviour of matter in different states, and learn about electrical circuits for the first time. Everything you learn in P4 is directly tested at PSLE, often in more complex questions that require you to apply concepts rather than just recall them.

This guide covers every major P4 Science topic with the depth and vocabulary you need to do well in both school exams and as preparation for PSLE.

1. Plant Parts and Their Functions

In P3, you learned the basic parts of a plant. In P4, you study their functions in much more detail, particularly the transport of water and nutrients:

• Roots — anchor the plant in the soil; absorb water and dissolved minerals through root hair cells (which have a large surface area). Water enters by osmosis through the semi-permeable root hair cell membrane.
• Stem — supports the plant; contains xylem vessels (transport water and minerals UP from roots to leaves) and phloem vessels (transport glucose made in leaves DOWN to all other parts)
• Leaves — main site of photosynthesis; contain chloroplasts with chlorophyll; stomata allow gas exchange (CO₂ in, O₂ out) and water loss (transpiration); waxy cuticle reduces water loss
• Flowers — reproductive organs; contain stamens (male, produce pollen) and pistils/carpels (female, contain ovules). Petals attract pollinators (insects, birds).

2. Plant Reproduction

P4 introduces the complete process of sexual reproduction in flowering plants:

• Pollination — transfer of pollen from the anther (male part of stamen) to the stigma (top of the pistil). Can be by insects, wind, water, or birds.
• Fertilisation — pollen tube grows from the pollen grain down through the style to the ovule. The male nucleus fuses with the female nucleus (fertilisation) inside the ovule.
• Seed and fruit development — after fertilisation, the ovule develops into a seed and the ovary develops into a fruit. The fruit contains and protects the seed(s).
• Seed dispersal — seeds must be dispersed away from the parent plant to reduce competition for resources. Methods: wind (maple, dandelion), water (coconut), animals eating fruit (mango, berries), animals carrying (hooked seeds like burdock), explosion (rubber tree, touch-me-not)
• Germination — a seed sprouts when it receives water, warmth, and air (oxygen). The seed coat softens, the embryo absorbs water, and the root (radicle) emerges first, followed by the shoot (plumule).

3. Human Digestive System

The digestive system is a core P4 topic covered in detail in the digestive system article on this site. Key concepts:

• Order: mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus
• Digestion is both mechanical (teeth, churning) and chemical (enzymes)
• Amylase (mouth/pancreas) digests starch; pepsin (stomach) and protease (pancreas) digest protein; lipase (pancreas) digests fat; bile (liver) emulsifies fat
• Absorption occurs mainly in the small intestine through villi
• Large intestine absorbs water; forms and stores faeces

4. Matter and Its Changes

P4 introduces the particle model of matter and changes of state:

• Three states of matter — solid (fixed shape and volume), liquid (fixed volume, takes shape of container), gas (no fixed shape or volume; fills its container)
• Changes of state — melting (solid → liquid at melting point), freezing (liquid → solid), evaporation (liquid → gas at any temperature), condensation (gas → liquid), boiling (liquid → gas at boiling point), sublimation (solid → gas)
• Water's special points — melts/freezes at 0°C; boils/condenses at 100°C
• Expansion and contraction — most materials expand when heated and contract when cooled; gases expand most, solids least; applications include railway track gaps, thermometers, bridges

5. Electrical Systems and Circuits

P4 is the first year students learn about electrical circuits in detail. Key concepts:

• A complete circuit requires a power source, conducting path, and component(s)
• Conductors (metals, especially copper) vs insulators (rubber, plastic, wood)
• Series circuits: one path, all share current, one break = all stop, more bulbs = dimmer
• Parallel circuits: multiple paths, each branch independent, more reliable
• Factors affecting bulb brightness: number of batteries, number of bulbs, type of circuit

6. Forces

Forces cause objects to change their speed, direction, or shape. In P4, you study:

• Types of forces — gravitational force (pulls objects toward Earth), magnetic force (attracts iron, steel, nickel, cobalt), elastic force (spring force), frictional force (opposes motion between surfaces), air resistance
• Contact vs non-contact forces — friction and elastic force require contact; gravity and magnetism act at a distance (non-contact)
• Effects of forces — can start or stop movement, change speed, change direction, change shape of an object
• Measuring force — using a spring balance (force meter); unit is the Newton (N)
• Friction — rough surfaces create more friction; smooth surfaces less. Friction can be useful (brakes, shoes gripping ground) or a nuisance (engine wear, slowing machines)

How P4 Connects to PSLE

Every P4 topic directly feeds into PSLE questions, often in combination with P5 material. Here is how each P4 topic typically appears at PSLE:

P4 Science Exam Tips

P4 Science exams in Singapore schools typically follow a similar format to PSLE — multiple choice questions and open-ended questions. The topics that most commonly appear as high-mark OEQ items in P4 school exams are:

• Digestive system — naming organs, explaining their functions, explaining what happens if an organ is damaged or removed
• Plant reproduction — explaining the steps from pollination to fruit formation; identifying seed dispersal method from a diagram and justifying your answer
• Electrical circuits — predicting whether bulbs light up and their relative brightness in given circuit configurations; explaining why a circuit does or does not work
• Forces — explaining what happens when forces are balanced or unbalanced; explaining the effect of friction in a scenario; calculating net force

For P4 OEQ answers, the same principles apply as for PSLE: always use scientific keywords, always explain the mechanism (not just describe the observation), and always answer every part of the question. A common P4 mistake is to describe what an organ does without explaining why — for example, "the small intestine absorbs nutrients" is worth 1 mark, but "the small intestine has thousands of tiny villi which greatly increase the surface area for the absorption of digested nutrients into the bloodstream" is worth 2 marks because it includes the mechanism.