Counting down to the end of PSLE and Science Notes

Dear all,

Thank you to all who came for Saturday's morning lesson. Hope it was fruitful for you in what we have gone through for the PSLE booklet. We have almost come to the end of the physical science section. We will finish up some of the last few and the specimen paper on Monday's extra lesson from about 12.45pm - 2.30pm.

I will be uploading the answers for mcq and open-ended for physical science so that you can go through, make notes and revise. I will also finish up with the remaining notes, part 5 of your Science.

Part 5 Science Revision Notes

Primary 6
The Environment

• Organisms (living things such as insects, animals, plants, bacterias)
• Habitat (place that the organisms live in) (such as garden, seashore, rotting log, field, tree, pong, mangrove swamp)
• Community (when two or more organisms live together)
• Population (size of a particular organism)
• Organisms are affected by temperature of a place, amount of light, amount and quality of air, amount of water, type of soil and other types of organisms present.
• Watter lettuce have hairy leaves. Water hyacinth has waxy leaves. 
• These leaves enable the water plants to stay afloat by prevent water from staying onto the leaves. The water runs off the leaves. 
• Water Hyacinth has swollen leaf stalks filled with air spaces. Air is lighter than water, enabling the plant to stay afloat.
• Organisms migrate to other habitats if their own habitats are unfavourable to live in.
• Earthworms like dark and damp place. 
• Organisms are interdependent on one another for survival. 
• Plants help to produce oxygen during photosynthesis for animals to breathe. Animals give out carbon dioxide which is essential for plants to make food.
• Plants also help to provide shelter and a habitat for some animals to live in and to lay their eggs. 
• Plants provide food for animals. They become a source of food for animals. 
• Animals also provide nutrients as fertilizers from their wastes for plants. These wastes enrich the soil and allow plants to grow more healthily. 
• Decomposition is the process of breaking down dead matter and animal wastes into simpler substances such as mineral salts and carbon dioxide. Decomposition takes in oxygen and gives out carbon dioxide. 
• Earthworms helps to loosen the soil by burrowing through the soils, opening up more spaces and spreading out the soil. This helps to improve the growth of grass and plants in the soil. 
• Plants like hydrilla are completely submerged in the water. If there are many floating plants at the top, it would block off sunlight from reaching these plants and they will eventually die off. 
• Fully submerged water plants - Hydrilla, elodea
• Partially submerged water plants - Cattail, Lotus, Arrowhead
• Floating plants - Duckweed, water lettuce, water hyacinth
• A seed can germinate on a wet cotton wool but when it grows into a plant, it will eventually die if it remains on the cotton wool as the cotton wool has no nutrients unlike the soil which the plant needs. 

Interactions - Food chains and webs

• Food producers (plants) which trap sunlight from the sun to photosynthesize and make food. Are a source of food for other organisms. 
• Consumers are any organisms that consumes (eats) any other organisms.
• Decomposers (fungi and bacteria)
• Predators (Organisms that eat other ANIMALS only)
• Preys (ANIMALS that are eaten by other ANIMALS only)
• Food chain shows one path.
• Food web shows multiple or more paths. 
• Always check for the food producer in a food web or chain. There can be more than 1 producer.
• In a food pyramid, the bottom (base of the pyramid) is the largest and that represents the food producer (plants). The top is the smallest and represents the predators.

Adaptations 

• Can be structural or behavioural
• Structural adaptations (physical features found on the body that helps an organisms to survive)
• Behavioural adaptations (how an organism behaves that helps it to survive)
• Adaptations help an organisms to find food, hide from predators and catch preys, protect from predators, reproduce by finding a mate or dispersing and cope with physical factors of the environment such as extreme temperatures and amount of water.
• Birds have feathers to keep them warm and to help them fly. They also have light, hollow bones that enable them to fly.
• Penguins cannot fly but they have a layer of fats under their skin to keep them warm in the extreme cold temperatures. Their back is also black and its back faces the sun to absorb the warmth from the sun as darker colours are good absorbers of heat compared to lighter colours. 
• Penguins have fins to help them swim easily in the water and reduce water resistance.
• Ducks, Pelicans, Swans all have webbed feet which help them to move/swim easily in the water. 
• Ostrich has long, powerful feet to help them move quickly and overcome friction on land. Longer legs help them to take bigger steps and cover a larger distance on land. Powerful legs help them to run quickly and further. 
• Eagles have strong, powerful and sharp claws on their feet to help them catch and wrap their preys tightly. Only the legs are responsible for catching prey. The beaks are not responsible. They are responsible for tearing the flesh and eating the prey. 
• Crocodiles, lions, tigers are some of the animals that have strong powerful jaws and teeth to tear apart the flesh.
• The male peacock has beautiful feathers which it opens up to attract a mate for mating and reproduction. 
• Fireflies light up in the dark in order to attract mates.
• Climbers - plants that climb upwards around a support to reach for sunlight through tendrils (have curls at the end) (passion fruit, grapes), hooks and thorns (rose plants), twinning (morning glory, pole beans) and clasping roots (pepper plant, ivy plant). 
• Creepers - plants that creep along the ground to spread its roots and shoots as wide as possible to gain sunlight and water. example: grass.
• Mangrove trees have aerial roots which hang above the water to gain moisture and air. The mangrove swamp can be too muddy at times and there might not be enough nutrients, water and sunlight if the roots grow inside. 
• Some animals who live in the water have streamlined body shape (broad the middle and narrow at the ends) to help overcome water resistance to move quickly in the water. 
• Fishes have fins to help balance them and propel them forward in the water.
• A crab has gill chambers that help store water with dissolved water in them to help them breathe on land but a fish does not and cannot survive on land. 
• Breathing tubes - water stick insect, wrigglers, water scorpion
• Air bubbles - Great diving beetle, water spider
• Blowholes - Dugong, whales
• Lungs - Mammals and humans
• Skin (moist) - Frogs, mudskippers 
• Some animals have stripes on their body coverings to blend in with the environment to camouflage and hide from predators or to catch their preys unaware.
• Plants have different ways of seed dispersal to help reproduce their own kind.
• Water - Fibruous husks which are light and trap air to float and move on water such as the coconut. Seeds dispersed by water flow in one direction downstream or down a river. 
• Animals - Hooks and thorns to stick onto the fur of animals to help carry them away. Can be scattered anywhere. Not dependent on direction of wind. Fruits can be edible, juicy and fleshy to attract animals to eat them. Can contain seeds that are big and inedible and are thrown out or spit out by the animals. Can also contain small seeds that are edible and passed out through wastes of animals for dispersal. 
• Wind - Light, wing-like structure and be float in the air for a long time to disperse as far as possible. Can be dispersed anywhere by dependent on direction of wind. 
• Explosion - Light pods in the fruit which opens up and explodes when ripe. Only scattered around the parent plant. 
• In a hot and dry desert, plants like the cactus have small, needle-like leaves to reduce the surface area that prevents too much transpiration that loses water. Also, it has a thick juicy stem that helps store lots of water for the plant. The cactus also spreads out its root over a wide surface area to reach out for as much water as possible. 
• The amount of water loss increases when the surface area of leaves increases too.
• Camels have large padded feet which help them to move easily on the sand as it increases the amount of exposed surface area of the feet to the sand, increasing the amount of friction between the feet and the sand and enable the camel to move without sinking into the sand. 
• Camel's humps store fats, not water. 
• They have thick and long eye lashes to prevent sand dust from blowing into their eyes.
• They can drink up alot of water at one go to prevent dehydration. 
• Polar bear has thick layer of fats underneath their fur to help keep them warm against the cold temperatures. 
• When we cut the middle of the swollen air stalk of a water hyacinth, we can see air bubbles escaping from the cut portion if we immerse the air stalk into the water. 

People and the Environment

• We can have a positive or negative impact on the environment. 
• Positive impact such as reforestation, recyling, reducing and reusing helps conserve the environment. 
• Negative impact such as increasing burning of fuels, deforestation and using of CFC products can harm the environment. 
• Deforestation leads to global warming, NOT THINNING OF OZONE LAYER. Deforestation is the cutting down of trees. Trees provide oxygen and reduces carbon dioxide in the air through photosynthesis. Thus, when we cut down trees, the amount of carbon dioxide increases. Carbon dioxide is a greenhouse effect and it traps heat, causing the world to get hotter. When the world gets hotter, the temperatures at the arctic increases. Ice caps will melt and there will be flooding. Animals, humans and houses will be affected. Burning of fuels also uses up oxygen and produce more carbon dioxide, leading to global warming.
• Using of CFC products will harm the environment as these chemicals will cause the ozone layer to be thinner and the harmful UV rays will shine onto the earth, causing skin cancer. 
• Deforestation also causes soil erosion. Without trees and roots to hold the soil in place, soil will be washed away during rainfall and these soil can flow down into rivers and pollute the rivers. 

Forces and energy 

• Forces can be a push or pull.
• Forces can move a stationary object.
• Forces can speed up or slow down or change direction of a moving object.
• Forces can cause a moving object to stop.
• Forces can change shape of objects. 
• Frictional force is a force that slows down a moving object and acts in the opposite direction to the moving object. Friction can be useful and not useful in our lives. Friction enables us to move about without slipping but it also causes wear and tear of objects. 
• Friction can be reduced by applying oil, powder, lubricants onto the surface in which an object is travelling. 
• Friction is important for tyres as without friction, the tyres will wear out and cars will crash and skid. 
• Elastic Spring Force is the force that measures the elasticity of a spring. The more elastic spring force there is, the more kinetic energy there is. 
• Remember that a rubber band DOES NOT HAVE ELASTIC POTENTIAL ENERGY. Only a STRETCHED rubber band has elastic potential energy.
• Gravitational force is a pulling force that acts between any two objects. 
• The amount of gravity force that acts on an object depends on its weight.
• Example: If I place a pencil 10m above the ground and the same identical pencil 20m above the ground, the amount of gravity force that acts on them is the same BUT THE PENCIL AT 10m above the ground will HAVE LESS GRAVITATIONAL POTENTIAL ENERGY than the pencil at 20m above the ground.
• Example: If I place an elephant at 5m above ground and a feather at 5m above ground, the amount of force acting on the elephant will be greater than the feather because it weighs heavier but both have the SAME amount of gravitational potential energy. 
• Magnetic force is the force exerted by magnets (refer back to the topic of magnets for precise information)
• Kinetic energy - found in moving objects. 
• Gravitational potential energy - Stored when an object is above ground level. 
• Chemical potential energy - Stored in dry cells and fuels before use
• Electrical energy -  Electricity flow through circuits in objects. 
• Heat energy - Measures heat for different purposes
• Light energy - Measures light for different purposes
• Sound energy - Measures sound for different purposes. 
• The more gravitational potential energy, the more kinetic energy there is.
• The more elastic potential energy, the more kinetic energy there is. 
• Energy is converted into many different forms. Energy loss occurs when energy is converted into other forms. 
• The higher an object moves, the more gravitational potential energy it has and lesser kinetic energy it has.
• When an objects moves downwards, it has more kinetic energy and less gravitational potential energy. 

That's it for your revision. Study hard for your Chinese tomorrow and for your Science on Monday. :)

Answers for PSLE Physical Science Section

MCQ 

Open-ended

12a (i) South pole

       (ii) North pole

12b. A magnet cannot have the same poles at each end.

13a. Vary amount of water in the bottle / Have specific amounts of water (50ml vs 100ml) / Roll an empty bottle vs one with water 

13b. There is more gravitational force at a greater height (or) Only one variable can be changed at any one time.

14a (i) Different metal bars expand to different lengths (or at different rates) after heating.

14a (ii) Less than 210mm. A thicker rod will take a longer time to heat up than a thinner one so it will expand less. 

14b. The bridge will buckle/ bend/ crack/ break if there were no gaps to allow for expansion on hot days.

15a. Circuit P - 3        Circuit Q - 2 

15b (i) Smallest number of bulbs remaining lit --> 0

            If bulbs 1 of 4 blows, there would not be a complete path for electricity to flow. (must identify 

            the bulbs)

15b (ii) Largest number of bulbs remaining it --> 3

            If bulbs 2 or 3 blows, there would still be a complete path for electricity to flow.

16a. More water adds weight (or gravitational force) and causes the test tube to sink. 

16b. Empty/remove water from the water tanks

17a. The plastic bottle occupies space / has volume so that less water is needed to fill the tank back to water level L.

17b. Matter occupies space / has volume. 

18a. There was still kinetic energy in the car.

18b. Use 2 or more balloons. / Pump more air into the balloons. / Use bigger balloons / Apply lubrican on wheels or floor / Give toy car a push at the starting position.

19a. The ends/poles of the magnet are stronger.

19b. Rod P. The ends of rod P have a stronger force of attraction than the middle of the rod.

20a. Reason 1: Larger exposed surface area results in higher rate of evaporation.

        Reason 2: Water can drip/flow down as plates are placed vertically. 

20b. Put the plates in the sun / windy place / dish dryer / switch on the fan.

21a. Pin Q moved towards the iron rod W (1 mark) when iron rod W becomes magnetised or an electromagnet (1 mark).

21b. The circuit is open / incomplete. / There is a break or gap in the circuit.

21c. To save or conserve electricity.

22a. The large sand particles have more/larger air spaces/gaps. OR The fine sand particles have smaller/lesser air spaces.

22b. Fine sand can trap more dirt/impurities OR Find sand can filter water BETTER.

22c. No. There may be poison / harmful substances / bacteria / germs / pollutants. / Water is polluted.

23a. Spring P. The increase in length for P is more for the same mass hung on the spring.

23b. 4cm. (No units of measurement --> no marks is given for the question) It has reached its elastic limit. OR The spring has lost some of its elasticity. 

24a. The temperature of the water decreases as time increases. 

24b. The temperature of A decreases at a slower rate compared to B. 

24c. Air is a poor conductor of heat. 

25a. B. It is able to stay the longest in the air. 

25b. Weight / Mass / Size of the paper aeroplane. Wind-free environment. 

26a. It is a good conductor of heat. 

26b (i) The wire will melt.

26b (ii) Circuit is incomplete / broken. 

27a. Place the magnets at the same height / distance from the pins.

27b. Observation 1: It will attract more pins.

        Observation 2: Magnets A, B and C may be attracted or repelled by Magnet X.

28a. Evaporation of water (1mark) removes heat (1mark) from the surrounding. 

28b. The fans add wind OR The fans blow the mist over a larger area. 

29a. Q can be seen at the furthest / longest distance. OR Light is reflected from the furthest distance. 

29b. Light sensor is more accurate / more reliable. 

30a. (Gravitational) Potential energy --> Kinetic energy --> Electrical energy

30b. Advantage: More electrical energy can be produced. 

        Explanation: there is more gravitational potential energy.

***** Remember to use comparison words such as 'GREATER' 'MORE THAN' 'LESS THAN' LEAST' 'MOST' GREATEST' 'LONGEST' 'SLOWER' 'SLOWEST' 'HOTTER' 'HOTTEST' 'COLDER' 'COLDEST' when you see more than 2 items. You are always comparing and these words are important!!!!!!!!

Sincerely,

Mr Nelson Ong