PSLE Science — Complete Study Guide

An experiment was conducted using the same type of plants and an equal volume of water. Each beaker was placed in the same location. The volume of water left in the beaker was measured after 10 hours.

e.g. What is the purpose of Set-up C?
➡ Set-up C acts as a control to compare and confirm that any difference in the volume of water left in the beaker is solely due to the plants absorbing water through their roots.

e.g. How using the same type of plant ensures a fair test.
➡ This ensures that the type of plant is kept the same, so there is only one changed variable which is the amount of roots.

• The accuracy of the results is how close the experimental result is to the actual result.
• It depends on the instruments used for measurement.

e.g. Explain how using measuring cylinders instead of beakers to measure the volume of water can help to improve the experiment.
➡ It allows the volume of water left in the beaker to be measured more accurately.

Other factors which may have an effect on the measured variable must be considered in the design of the experiment.

e.g. Why was coloured water used in the experiment?
➡ It was to allow the water level to be seen more clearly when measuring the volume of water left in the beaker.

Keep these key words ready for experiment questions — aim, conclusion, changed variable, measured variable, controlled variable, control set-up, fair test, reliability, accuracy.

These are the key features that help you identify each group:

The life cycle of a plant goes through three main stages, to ensure the continuity of their own kind:

1. Seed
2. Young plant / seedling
3. Adult plant

• H: Habitat — life cycle takes place entirely on land / partly in water
• A: Appearance — young resembles / do not resemble the adult
• S: Stages — three / four stages

• Larva vs larval stage; pupa vs pupal stage
• Many eggs are laid at one time to increase the chances of eggs hatching into young, to ensure the continuity of their own kind.
• Egg and pupa — does not feed / move.
• Nymph and larva:

• Moulting — sheds hard outer covering to grow bigger.
• No wings, cannot fly.
• Larva feeds the most.

• Bar magnet
• U-shaped magnet
• Ring magnet

• Poles of a magnet have the greatest magnetic strength.
• Only magnets can repel another magnet when their like poles face each other.
• The size of a magnet does not affect its magnetic strength.
• A freely-floating magnet always comes to rest in the North–South direction.
• Magnetic force can pass through non-magnetic materials.

• Heating over a strong flame
• Dropping repeatedly
• Hammering repeatedly

• Refrigerator door
• Compass
• Scrapyard
• Doorbell
• Microphone
• Loudspeaker
• Maglev train
• Hard disk
• Magnetic strip (credit/debit cards)

• Systems depend on each other; e.g. circulatory system carries oxygen from respiratory system and digested food from digestive system to all body parts.
• Muscles use oxygen to release energy.

• Flower
• Leaf
• Fruit
• Stem
• Root

Leaves trap light to make food by photosynthesis.

• Holds the plant upright.
• Elevates the leaves so that the leaves can trap more light to make more food by photosynthesis.
• Food-carrying tubes: transports food from the leaves to all parts of the plant.
• Water-carrying tubes: transports water and mineral salts from the roots to all parts of the plant.

So that its leaves can trap more light to make more food through photosynthesis.

• Hold or anchor the plant firmly to the ground.
• Absorb water and mineral salts from the soil.

• Has mass — Mass: amount of matter in an object.
• Occupies space — Volume: amount of space an object occupies.

The glass jar has a capacity of 400 cm³.

A 100 cm³ flask containing 10 cm³ of water was connected to a pump. Peter first added 20 cm³ of air using the pump, then added another 40 cm³ of air.

• Air has mass.
• Air can be compressed.

Justin placed two identical empty bottles, A and B, each with a capacity of 1 000 cm³, on a beam balance.

• Travels in a straight line.
• Can be reflected.
• Can be blocked.

• Use a ruler to draw straight lines.
• Direction: light source → object → eye.
• Draw a single arrow in the middle of each line.

• Shadow formation: light travelling in straight lines is blocked by an object that allows some or no light to pass through.
• Darkness of shadow: opaque object → dark shadow; translucent object → light shadow; transparent object → no shadow.

Identify 3 things:

1. Conductor of heat (“messenger”)
2. Heat source / region of higher temperature
3. Region of lower temperature

• The greater the surface area in contact, the greater the rate of heat gain / heat loss.
• E.g. crushed ice cubes vs whole ice cube.

• Depends on mass/volume and temperature.
• Temperature: how hot or cold an object is.
• Heat: is a form of energy.

The balloon will burst after some time.

• Air in the flask gained heat, expanded and occupied more space.
• This pushed the needle outwards and towards the balloon.

• Melting point: temperature at which a substance gains heat to undergo a change in state from a solid to a liquid.
• Boiling point: temperature at which a substance gains heat to undergo a change in state from a liquid to a gas.
• Freezing: process by which a liquid loses heat to the surroundings and becomes a solid at a fixed temperature called its freezing point.
• Condensation: process by which a gas loses heat to the surroundings and becomes a liquid.

Warmer water vapour comes into contact with a cooler surface → loses heat to the surface → condenses into water droplets.

Depends on:

• Wind speed / presence of wind
• Exposed surface area
• Temperature

Liquid gains heat from <> to evaporate, causing <> to lose heat and cool down.

Depends on the temperature difference between water vapour and surface for condensation.

• Conservation: reduce, reuse, recycle.
• Pollution causes: oil spills; dumping of untreated sewage; destruction of aquatic life.

Substance P, a solid, was heated for about 16 mins.

• During a change in state (e.g. melting, boiling): there is a mixture of 2 states.
• During melting (PQ) — solid + liquid.
• During boiling (RS) — liquid + gas.

<> is a conductor / non-conductor of electricity.

• Too much electric current flows through.
• Filament melts → bulb fuses.

• Bulb: connect to metal casing and metal tip.
• Batteries: positive terminal of a battery is connected to the negative terminal of another battery.

• When one bulb fuses, the other bulbs remain lit.
• Bulbs can be controlled individually using switches.

• Magnetic material is magnetised into an electromagnet — only when electric current is flowing through.
• Magnetic strength depends on:

• Number of coils of wire
• Number of batteries connected in series

• To ensure the continuity of their own kind.
• Males release a large number of sperm to increase the chances of sperm reaching the egg for fertilisation to occur.

The nucleus of sperm fuses with the nucleus of egg.

• Transports nutrients and oxygen in the blood from mother to foetus.
• Transports carbon dioxide and waste materials in the blood from foetus to mother.

• During fertilisation, genetic material from the nucleus of sperm and nucleus of egg fuse together.
• The offspring that develops from the fertilised egg has traits from both parents.
• Length of nails, hair are non-hereditary traits.

• Many pollen grains are released by anthers each time to increase the chances of pollination.
• Stigma removed: pollination cannot occur.
• Ovary removed: fertilisation cannot occur.

Transfer of pollen grains from the anther to the stigma.

• Large, brightly-coloured petals.
• Scented.
• Nectar.
• Sticky stigma.

When animal pollinators (bees) collect nectar from a flower, pollen grains will be stuck on the bee. When the bee collects nectar from another flower, pollen grains will be transferred to the stigma of the flower — pollinating the flower.

• Small, dull-coloured petals.
• Scentless.
• Feathery stigma (to receive pollen grains carried by the wind more easily).
• Anthers hang out of flower (for pollen grains to be carried away by the wind more easily).

• Ovary develops into fruit.
• Ovule develops into seed.
• If flower has many ovules → fruit has many seeds. If flower has one ovule → fruit has one seed.
• Petals, anther, filament, stigma, style wither and fall off.

To avoid overcrowding and reduce competition between young and parent plants — for nutrients/mineral salts, space, light, water.

• Food-carrying tubes: food made by leaves to all parts of plant.
• Water-carrying tubes: water absorbed by roots to all parts of the plant.

Stomata allow gaseous exchange between plant and surrounding air, and water loss.

Transports food made by the leaves to other parts of the plant.

Transports water and mineral salts absorbed by the roots to other parts of the plant.

• Air sacs increase exposed surface area of lungs.
• Allowing gaseous exchange between air in the lungs and bloodstream to take place faster.

• Oxygen is absorbed into bloodstream.
• Carbon dioxide is released.
• Blood entering will contain less oxygen and more carbon dioxide.
• Blood exiting will contain more oxygen and less carbon dioxide.

Body requires more Energy → we Breathed faster to take in more Oxxygen to undergo a greater rate of Respiration to release more Energy.

• This also allows carbon dioxide given out during respiration to be removed faster.

Body needs more Energy → our heart Pumps faster to transport more Oxxygen and digested food in the blood to other parts of our body faster, to undergo a greater rate of Respiration to release more Energy.

• This also allows carbon dioxide given out during respiration to be removed faster.

• Gill filaments in the gills increase exposed surface area of gills.
• Allowing gaseous exchange between gills and surrounding water to take place faster.
• Same function as air sacs in lungs.

1. Move a stationary object.
2. Stop a moving object.
3. Speed up or slow down a moving object.
4. Change the direction of a moving object.
5. Change the shape (and size) of an object.

• Opposes motion.
• Depends on roughness of surface and weight of object.
• Not affected by surface area in contact.
• Rough/smooth surface; lubricant (reduces friction).
• Causes wear and tear.
• Streamlined body shape: reduce air/water resistance.

• Length vs extension.
• Extension, compression, stretched, compressed.
• Elastic limit.
• Extension = final length − original length.
• Compression = original length − final length.

• Depends on mass.
• Weight: amount of gravitational force acting on an object.
• Mass vs weight (they are different!)
• Gravitational force is always constant!

• Attraction (pull).
• Repulsion (push).

• Gravitational potential energy (GPE): depends on mass and height. As height increases, amount of GPE increases. (Note the difference between GPE and GF graphs!)
• Elastic potential energy: depends on extension/compression. To increase amount of EPE: use thicker springs / more springs.
• Chemical potential energy: stored in fuels, batteries, food.
• Kinetic energy: depends on mass and speed.
• Electrical energy.
• Sound and heat energy (due to friction).

Energy can be converted from one form to another, or transferred from one object to another.

1. Light intensity — move lamp closer/further from plant.
2. Amount of carbon dioxide — baking soda increases amount of carbon dioxide.
3. Colour of light — blue light gives greatest ROP, green light gives lowest ROP.
4. Temperature.

Increasing the amount of a certain factor will increase ROP until a certain point — the limiting factor (maximum ROP).

• Transfer of energy through an ecosystem.
• All food chains and food webs begin with a food producer.
• All animals are consumers.
• Animals that hunt and consume other animals are predators.
• Animals that are hunted are prey. Plants are not prey.
• Herbivores only feed on plants; carnivores only feed on animals; omnivores feed on both plants and animals.

• When the population size of a predator decreases, there will be fewer predators to consume/feed on its prey, causing the population size of its prey to increase.
• When the population size of a prey decreases, there will be less food for its predators, causing the population size of the predators to decrease.

• Breaking down animal waste and dead matter into simpler substances.
• Decomposers are fungi and bacteria.
• Conditions: warmth, oxygen, water.
• Simpler substances released during decomposition are returned as nutrients to the soil, enabling plants to grow more healthily.
• Decomposition helps to prevent animal waste and dead matter from piling up on the surface of the earth.

• The sun is the main source of energy for life on Earth.
• The amount of energy transferred to the next organism decreases along the food chain as energy is lost in heat, as waste, or used to sustain the organisms’ life processes.
• Only 10% of energy is transferred.

• Caused by the use of insecticides and pesticides.
• What was meant to kill organisms lower in the food chain may end up killing predators at the top of the food chain.

• E.g. termites, woodlice, vultures.
• They help to increase decomposition by breaking up animal waste and dead matter into smaller pieces, increasing the surface area of the animal waste and dead matter exposed to decomposers.

• The act of removing large sections of forest by cutting down trees or burning.
• Soil erosion: increased risk of landslides; may result in water pollution when soil is washed into water bodies; submerged plants trap less light and make less food.
• Other effects: loss of habitats and food sources for forest wildlife.

• Releases harmful chemicals into the air.
• Increase in greenhouse gases — increase in the amount of greenhouse gases in the atmosphere, trapping more heat from the Sun on Earth’s surface.
• Increase in the greenhouse effect → global warming.

• Rise in global temperatures.
• Melting of polar ice caps.
• Expansion of ocean waters → rising of sea levels.

• Destabilisation of climates and extreme weather changes.
• Death of temperature-sensitive wildlife.
• Habitat loss for Arctic wildlife.
• Flooding in low-lying coastal areas.