Pick a topic or study all at once!
Primary 4 Science is a significant step up from P3. Students begin to encounter more complex biological systems, physical phenomena, and scientific processes. The P4 Science syllabus under MOE 2026 covers 8 main topics that build directly towards PSLE Science preparation in P5 and P6.
ScienceStar's free P4 Science section covers all 8 MOE topics with interactive quizzes, digital flashcards and complete study notes. Every question includes an instant explanation so students learn from every answer โ right or wrong.
The following 8 topics make up the P4 Science syllabus for 2026:
Use ScienceStar's free P4 quizzes, flashcards and study notes to revise all 8 topics. Everything is aligned to the MOE 2026 P4 Science syllabus and completely free for all Singapore students.
Primary 4 is the year when Singapore Science shifts from naming and classifying to explaining and connecting. In P3, students learn what things are โ what the parts of a plant are called, which animals have backbones, what magnets attract. In P4, students must begin to explain why and how. Why does the small intestine absorb food instead of the stomach? How does adding a bulb to a circuit make the other bulbs dimmer? What causes friction, and why is it sometimes helpful and sometimes harmful?
This shift from naming to explaining is the single biggest adjustment P4 students face. Students who struggle in P4 Science are usually not lacking knowledge โ they are answering "what" when the question is asking "why" or "how." This guide covers every P4 topic in the depth needed to make that shift successfully.
Plant reproduction is the most frequently tested P4 topic in both school exams and PSLE. It has three distinct phases that students must understand in sequence: pollination, fertilisation, and seed dispersal. Treating these as separate unrelated facts instead of a connected process is the most common mistake P4 students make.
Pollination is the transfer of pollen from the anther (male part) to the stigma (female part). It can happen within the same flower (self-pollination) or between two flowers of the same species (cross-pollination). The two main pollination agents are insects and wind. Insect-pollinated flowers have bright petals, sweet scent, and sticky or large pollen โ all features designed to attract and trap insects. Wind-pollinated flowers are small, dull, and produce enormous amounts of light, smooth pollen that can float through the air. Exam questions often show students a photograph of a flower and ask them to predict whether it is insect- or wind-pollinated. The answer always comes from the flower's features.
Fertilisation happens when pollen reaches the stigma and travels down to the ovary, where it fuses with the ovule to form a seed. After fertilisation, the ovary wall becomes the fruit (the flesh or shell surrounding the seed), and the ovule becomes the seed. This is why all seeds are found inside fruits โ the fruit is the matured ovary. Students are frequently confused when told that peas, tomatoes, and mangoes are all "fruits" in scientific terms. In science, a fruit is anything that develops from the ovary of a flower, regardless of taste.
Seed dispersal is the spreading of seeds away from the parent plant. This prevents overcrowding, reduces competition for light, water and minerals, and allows the species to colonise new areas. There are four main dispersal methods. Wind dispersal: seeds are light with wing-like structures (e.g. maple) or feathery parachutes (e.g. dandelion). Water dispersal: seeds are waterproof and buoyant (e.g. coconut, mangrove). Animal dispersal: seeds either have hooks that attach to fur (e.g. burdock), or are contained in sweet, edible fruit and excreted elsewhere (e.g. mango). Self-dispersal: the fruit dries and bursts open explosively, throwing seeds outward (e.g. balsam, Pong Pong). For each method, students must be able to link the feature of the seed to the dispersal mechanism.
Many P4 students can list the organs of the digestive system in order but cannot explain what each one does or why it matters. PSLE questions always go one level deeper than the list โ they ask about function. Here is what each part does and why:
The mouth starts both mechanical digestion (teeth breaking food into smaller pieces) and chemical digestion (saliva begins breaking down starch). Smaller pieces have more surface area, which allows digestive juices to work more efficiently โ this is why chewing thoroughly matters scientifically, not just for manners. The oesophagus is a muscular tube that pushes food from the mouth to the stomach using waves of muscle contraction called peristalsis. It does not digest food โ it only transports it. The stomach churns food and mixes it with acid and digestive juices that break down protein. The acid also kills most bacteria in food. The small intestine is where most digestion is completed and where all nutrients are absorbed into the bloodstream. It is very long (6โ7 metres in adults) to maximise the surface area for absorption. The large intestine absorbs water from the remaining undigested material. The rectum stores solid waste temporarily. The anus is where waste is expelled from the body.
The liver produces bile, which helps break down fats. The pancreas produces digestive juices that flow into the small intestine to help digest all three types of nutrients: carbohydrates, proteins and fats. A common exam question asks students to name an organ that is not part of the digestive tube but still plays an important role โ the answer is the liver or pancreas.
P4 students learn simple (series) circuits. The most important concept โ and the one most frequently tested โ is what happens when you change the number of cells or the number of bulbs in a series circuit.
Adding more cells to a circuit increases the electrical push (voltage), which means more current flows, which makes all the bulbs brighter. Adding more bulbs to a series circuit splits the available electrical energy among more bulbs, so each bulb receives less energy and shines dimmer. This is why Christmas lights in old series circuits would all go out if one bulb broke โ removing one bulb broke the entire circuit. Modern lights use parallel circuits to avoid this problem (introduced in P5).
Conductors allow electricity to flow through them. All metals conduct electricity, but not all conductors are metals โ the human body, water and graphite (pencil lead) also conduct electricity. Insulators do not allow electricity to flow. Common insulators include rubber, plastic, wood, glass and dry air. A switch works by creating or closing a gap in a circuit โ when open, the gap acts as an insulator and stops current flow; when closed, the circuit is complete and current flows.
A force is a push or a pull. Forces have two effects on objects: they can change the speed of an object (make it faster or slower, start it moving or stop it) and they can change the shape of an object. P4 students study two main forces: gravity and friction.
Gravity is the force that pulls all objects towards the centre of the Earth. It acts on all objects regardless of their mass. The weight of an object is the gravitational force acting on it โ weight is a force measured in Newtons (N), while mass is the amount of matter in an object measured in kilograms (kg). This distinction โ weight vs mass โ is a very commonly tested concept. On the Moon, where gravity is weaker, your mass stays the same but your weight decreases.
Friction is the force that opposes the motion of one surface sliding over another. It acts in the direction opposite to movement. Friction is increased by rough surfaces and reduced by smooth surfaces or lubrication. Friction can be useful (it allows us to walk without slipping, allows brakes to stop vehicles, allows us to write with a pen) and harmful (it causes wear and tear in moving parts of machines, generates unwanted heat). Exam questions often ask students to identify situations where friction should be increased (add grip to shoe soles) or reduced (oil a bicycle chain).
Most P4 students know that the water cycle involves evaporation and condensation, but they often cannot explain the energy source that drives each process or why the cycle matters for life on Earth.
The sun provides the energy that drives evaporation โ it heats surface water in oceans, lakes, rivers and wet soil, converting liquid water into water vapour. Plants also release water vapour through their leaves in a process called transpiration. Together, evaporation and transpiration move water from the land and water bodies into the atmosphere. As water vapour rises and cools, it condenses around tiny dust particles to form water droplets, creating clouds. When water droplets in clouds combine and become heavy enough, they fall as precipitation โ rain, hail, sleet or snow. The water collects in rivers, lakes and the sea, and the cycle begins again.
P4 questions sometimes ask students about factors that affect the rate of evaporation. Evaporation is faster when: the temperature is higher, the surface area of water is larger, air movement (wind) is greater, and air humidity is lower. Students who understand these factors can answer application questions about everyday situations โ why clothes dry faster on a sunny windy day, or why a wide shallow dish of water evaporates faster than a narrow deep one.
A food chain shows the flow of energy from one organism to another through feeding. Arrows in a food chain point in the direction energy flows โ from the organism being eaten to the organism that eats it. The first organism in a food chain is always a producer (a plant or algae that makes its own food through photosynthesis). All other organisms are consumers โ animals that get energy by eating other organisms. Primary consumers eat producers. Secondary consumers eat primary consumers. Tertiary consumers eat secondary consumers.
A food web is multiple food chains linked together, showing all the feeding relationships in an ecosystem. Real ecosystems always have food webs, not simple chains, because most animals eat more than one type of food. P4 exam questions frequently ask what would happen to other organisms if one population increased or decreased. The key skill is to trace the effect through the web: if a predator's numbers decrease, its prey's numbers increase; if the prey's numbers increase, the organisms eaten by the prey decrease.
Decomposers โ bacteria and fungi โ break down dead organisms and return nutrients to the soil. They do not usually appear in food chains but are crucial to the ecosystem because they recycle matter. A P4 question that asks "what would happen if all decomposers disappeared" expects students to understand that nutrients would not be returned to the soil, plants would not have the minerals they need to grow, and the entire food chain would eventually collapse.
Q: Which P4 topics are most likely to appear in the PSLE?
All P4 topics can appear in the PSLE, but Electrical Systems, Plant Reproduction, Forces (Gravity and Friction), Photosynthesis and Food Chains are the most consistently tested. These topics have appeared in every PSLE paper from 2015 to 2024. Matter (States of Change) and the Water Cycle appear frequently and are often used as contexts for data interpretation and fair test questions.
Q: My child understands the content in P4 but makes careless mistakes. What helps?
Most "careless mistakes" in Science are actually misreading mistakes โ students answering the question they expected rather than the question that was asked. The fix is to train the habit of underlining key words in the question before answering: words like "not," "except," "always," "most likely," and "which of the following is correct." For open-ended questions, the habit of checking whether the answer contains the required scientific keyword before moving on eliminates most lost marks.
Q: How is P4 Science assessed in Singapore schools?
P4 Science is assessed through school-based assessments (continuous assessment tasks and end-of-year examinations). The format mirrors PSLE style โ multiple choice questions and open-ended written questions. P4 is also the first year students encounter structured science experiment questions, where they are asked to design or evaluate a simple experiment. Practising these from P4 onwards builds the fair test skills needed for the PSLE Booklet B.