Express Notes Science Form 2

All Rights Reserved ©2012 Ng Chee Kin

Written By Ng Chee Kin

B.Sc.(Hons.), MBA [email protected]

[email protected]

EXPRESSEXPRESSEXpresS��

CHAPTER 1The World through Our Senses

1.1 Sensory Organs

1 Humans have five senses. Table 1 shows the senses, sensory organs and stimulus detected.

Sense Sensory organ Stimulus

Touch SkinTouch, pressure, cold, heat, pain

Smell NoseChemical

substances in air

Taste TongueChemical

substances in food

Hearing Ear Sound

Sight Eye Light

Table 1

2 Each sensory organ has receptors to detect stimuli.

3 Pathway from stimulus to responses:

Stimuli sensory organ nerves brain

responses effectors nerves

4 Nerve impulses are electrical messages produced by receptors.

5 Effectors are organs which carry out responses. 6 Responses are reactions which occur after

receiving a stimulus.

1.2 Sense of Touch

1 The skin has five receptors.

Epidermis

Dermis

Fatty layer

Fine hair

Pain receptor

Heat receptor

Pressure receptor

Cold receptor

Touch receptor

2 The sensitivity of skin depends on:(a) the closeness of receptors(b) the depth of receptors

1.3 Sense of Smell

1 The roof of the nasal cavity has many sensory cells to detect smells.

To the brain

Nasal cavity

Nostril

Into the lungs

Impulses are sent to the brain

Nerve sends nerve impulse to the brain to be interpreted

Receptor cell detects smell and generates nerve impulse

Cilium contains mucus to dissolve inhaled particles

Nerve impulse

4

3

2

1

1.4 Sense of Taste

1 The surface of the tongue has many taste buds to detect chemical substances.

2 The tongue:

Bitter

Sour

Salty

Sweet

Taste bud

Chemical particles dissolve in saliva on the surface of the tongue

Taste projections receive stimulus and send it to the taste receptors

Taste receptor sets off impulse

Impulse is sent to the brain to be interpreted as taste

21

3

4

1.5 Sense of Hearing

1 The human ear:

Pinna

Ear canal

Ossicles

Semicircular canal

Auditory nerve

Cochlea

Oval windowEustachian tube

Eardrum

2 The mechanism of hearing:

Pinna ear canal eardrum ossicles

auditory cochlea oval window

nerve brain

WB Science F2 (Exp Note) 1st.indd 1 4/2/2009 5:48:16 PM

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CHAPTER 2Nutrition

1.6 Sense of Sight

1 The human eye:

Iris

Supportive ligament

Lens

Cornea

PupilAqueous humour

Ciliary muscle Conjunctiva Blind spot

Yellow spot

Retina

Sclera

ChoroidVitreous humour

Optic nerve

2 The retina has photoreceptors to detect light. 3 Mechanism of sight:

Cornea aqueous humour lens

optic nerve retina vitreous humour

brain optic effectors nerves

1.7 Light and Sight

1 Reflection of light happens when it bounces off the surface on which it falls.

2 Refraction is the bending of light due to speed change as it travels through transparent medium of different densities.

3 Defects of vision:

Defects of vision Symptoms Possible

causesWays of

correction

Short-sightedness

• Can see near objects clearly

• Cannot focus on distant objects

• Lens is too thick

• Eyeball is too long

Concave lenses

Long-sightedness

• Can see distant objects clearly

• Cannot focus on near objects

• Lens is too thin

• Eyeball is too short

Convex lenses

Astigmatism • See distorted images

• Irregular surface of the cornea

Cylindrical lenses or through surgery

4 Devices to overcome the limitations of sight: Microscope, telescope, magnifying glass, periscope, x-ray, binoculars and ultrasound scanning device

5 Stereoscopic vision helps predators to detect the location of their preys accurately.

6 Monocular vision helps prey to detect their enemies from all directions.

1.8 Sound and Hearing

1 Properties of sounds:(a) they are produced by vibrations of objects.(b) they need a medium to travel, such as solids,

liquids or gases.(c) they cannot travel through a vacuum.(d) they can be absorbed by soft and rough

surfaces.(e) they can be reflected by hard and smooth

surfaces as echoes. 2 Stereophonic hearing helps to detect the location

of the source of sound.

1.9 Stimuli and Responses in Plants

1 Tropism is a growth response to external stimuli.

Tropism Stimuli Example

Hydrotropism WaterThe roots grow towards a water

source

Geotropism GravityThe roots grow in the direction of

gravity

Phototropism LightThe shoots grow towards sunlight

ThigmotropismTouch

(contact)

The tendrils wrap around a solid

structure

2 Nastic movements are responses of plants to external stimuli which may come from any direction.

2.1 Classes of Food

1 Seven classes of food (nutrients):

Nutrient Sources Function Deficiency disease

Carbohydrates Sugar, starch, glucose • Supply energy to the body Body lacks energy, marasmus

Proteins Milk, fish, eggs, chicken • For growth • Repair of body tissues

Stunted growth, kwashiorkor

Fats Oil, ghee, margarine, butter • Keep the body warm • Transport vitamins A, D, E and K • Supply a lot of energy

Body lacks energy

Fibre (roughage) Fruits, vegetables, cereals • Helps peristalsis and removal of undigested food from the body

Constipation

Water Fruits, vegetables, drinking water

• Dissolves chemicals in the body• Controls body temperature

Dehydration


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Nutrient Sources Function Deficiency disease

Vitamins Vitamin A Carrot, fish liver oil, green vegetables

• For night vision• Healthy skin

• Night blindness• Skin infections

Vitamin B Milk, eggs, meat, cereals • Healthy nervous system• Formation of red blood cells

• Beriberi• Anaemia

Vitamin C Citrus fruit, vegetables • Healing of wounds• Resistance to diseases

• Scurvy

Vitamin D Made by our body in sunlight, also found in eggs, milk

• Strong bones and teeth • Rickets

Vitamin E Nuts, vegetable oil, whole grains • For healthy reproduction system• Fights against diseases

• Sterility

Vitamin K Made in the human intestine, also found in green vegetables

• Helps blood clotting and stops bleeding

• Prolonged bleeding

Minerals Calcium Milk, cheese, green vegetables • Strong bones and teeth• Healthy muscles and nerve

• Rickets• Osteoporosis• Muscle cramps

Sodium Table salt, cheese, meat • Controls body fluid• Proper functioning of nerves

• Muscular cramps

Iron Meat, green vegetables, eggs • For the formation of haemoglobin in the red blood cells

• Anaemia

Iodine Seafood, iodised salt • For making hormones in the thyroid glands

• Goitre

Phosphorus Meat, eggs, cheese, milk, vegetables

• Strong bones and teeth• Stores energy

• Rickets• Fatigue

Potassium Bananas, meat, nuts • Proper functioning of nerves • Paralysis

2 The energy requirement depends on the age, body size, sex, occupation, physical activity, climate and state of health of an individual.

3 Calorific value (or energy value) is the amount of energy released from one gram of a particular type of food.

Class of food Energy value (kJ/g)

Carbohydrates 17

Proteins 18

Fats 39

2 Food tests:

Nutrient Test Result

Starch (a type of carbohydrate)

Iodine testBlue-black

colour

Glucose (a type of carbohydrate)

Benedict’s test

Brick-red precipitate

Protein Millon’s test Red precipitate

Fat Emulsion test Milky solution

2.2 The Importance of a Balanced Diet

1 A balanced diet contains seven classes of food in the right amount.

2.3 Human Digestive System

1 Digestion is the breakdown of large food molecules into smaller molecules that can be easily absorbed by the body.

2 Digestion occurs in the alimentary canal (or gut):

Mouth oesophagus stomach

optic nerve small intestine duodenum

large intestine anus

3 Peristalsis is the contraction and relaxation of the muscles along the gut wall.

4 Enzymes are substances which generally act as catalysts to speed up the chemical reactions in our body.

Mouth– Physical digestion

occurs– Starch is broken

down into maltose

Oesophagus– Produces a wave-like action called peristalsis– Peristalsis helps to push bolus into the stomach

Lower part of small intestine– Secretes intestinal juice– Maltose is broken down

into glucose– Polypeptides are broken

down into amino acids– Fats are broken down into

fatty acids and glycerol

Liver

Gall bladder produces bile

Rectum

Anus

Duodenum– Receives bile from the gall

blader and pancreatic juice– Starch is broken down into

maltose– Proteins are broken down into

polypeptides– Fats are broken down into

fatty acids and glycerol

Pancreas produces pancreatic juice

Stomach– Produces gastric juices– Gastric juice contains

hydrochloric acid and protease

– Proteins are broken down into polypeptides or peptones

Large intestine


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5 Plant kingdom can be divided into:(a) flowering plants(b) non-flowering plants

6 Classification of flowering plants:

Flowering plants

Monocotyledons Dicotyledons

One cotyledon

A maize grain cut in half

Two cotyledon

A green bean (split into two)

Parallel-veined leaf

Stem

Fibrous root

Example: Maize plant

• Fibrous root system• Parallel-veined

leaves• Non-woody and

soft stems• Other examples:

Grass, orchid plant, sugar cane, paddy

Stem

Flower

Tap root

Network-veined leaf

Example: Balsam plant

• Tap root system• Network-veined

leaves• Woody and hard

stems• Other examples:

rubber tree, rose shrub, bougainvillea, sunflower plant

7 Classification of non-flowering plants:

Non-flowering plants

Conifers Mosses Ferns Algae

Examples: • Pine tree• Casuarina

tree

Examples: • Stag’s

horn fern

Examples: • Cup

moss

Examples: • Seeweed• Phytoplankton

CHAPTER 3Biodiversity

3.1 Organisms and Their Classification

1 Biodiversity (or biological diversity) refers to the wide variety of organisms on earth.

2 Organisms are classified into groups called kingdoms, such as animal and plant kingdoms.(a) vertebrates (animals with backbones)(b) invertebrates (animals without backbones)

4 Vertebrates are divided into five groups:

Vertebrate Characteristic

Fish Slimy scales and fins

Amphibians Exposed and moist skin

Reptiles Hard dry scales

Birds Feathers and wings

Mammals Hair or fur

2.4 Absorption of Digested Food

1 Absorption is the diffusion of digested food from the gut into the bloodstream.

2 Absorption mainly happens in the small intestine. 3 Villi on the inner wall of small intestine help to

speed up the absorption.

2.5 Reabsorption of Water and Defecation

1 Reabsorption happens in the large intestine. 2 Water, with dissolved minerals and vitamins are

reabsorbed into our body. 3 Defecation is the process of removing faeces

from the body through the anus. 4 Difficulty in defecation is called constipation,

which is caused by the lack of water and roughage in the diet.

2.6 Healthy Eating Habits

1 We should practice healthy eating habits to prevent diet-related diseases.

2 We should eat a wide variety of foods according to the recommended amounts in the food pyramid.

CHAPTER 4Interdependence among Living Organisms and the Environment

4.1 Interdependence among Living Organisms

Key terms Description

Species Organisms with common characteristics which can breed among themselves to produce fertile offspring

Population A group of organisms of the same species which live in the same place

Community Many types of populations living in the same place, interacting with one another

Habitat The place or area where an organisms live and reproduce

Ecosystem The community of organisms living in the same habitat, together with the non-living environment

Ecology The study of relationship between living things and the environment

1 A balanced ecosystem is created when there is interdependence among living organisms and the environment.


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4.2 Interaction between Living Organisms

Type of interaction Description Examples

Prey-predator • A predator is an animal that hunts other animals for food

• A prey is an animal hunted and killed by predators for food

• Goat (prey) and tiger (predator)

• Frog (prey) and snake (predator)

• Rat (prey) and owl (predator)

Competition Intra-specific competition

• Competition between the same species of organisms

• Wolves compete with each other for food and mate

Inter-specific competition

• Competition between organisms of different species

• Crows and fox compete with each other for food

Symbiosis Commensalism • Interaction between two organisms

• The commensal receives benefits from the host

• The host is not harmed nor received any benefit

• Remora fish (commensal) and shark (host)

Mutualism • An interaction which benefits both organisms

• Fungi (provide shelter to algae) and algae (produce food for fungi and itself)

Parasitism • A parasite benefits by living in or on the host

• The host is harmed by the parasites

• Tapeworm (parasite) living in the human intestine (host)

1 Biological control uses the prey-predator relationship to control pests.

4.3 Food Web

Key terms Description

Producer Green plants which can produce food through photosynthesis.

Consumer Animals which eat plants and other animals

Decomposer Organisms that break down dead animal and plant materials into simpler substances which can be used again by the producers.

1 A pyramid of numbers shows the number of organisms at each stage of a food chain.

Number of organisms decreases,

Size of organisms increases

Amount of energy decreases

Level 4 (tertiary consumer)

Level 3 (secondary consumer)

Level 2 (primary consumer)

Level 1 (producer)

4.4 Photosynthesis

1 Photosynthesis is a process of making food by green plants.

2 Requirements for photosynthesis:(a) Water(b) Carbon dioxide(c) Chlorophyll(d) Sunlight

3 Products of photosynthesis:(a) Oxygen(b) Glucose

Chlorophyll Water + Carbon dioxide Oxygen + Glucose

Sunlight

4.5 Conservation and Preservation of Living Organisms

1 Conservation is the wise use of natural resources with the least disturbance to the ecosystem.

2 Preservation refers to the actions taken to maintain ecosystem in its balanced state.

3 Some steps to conserve and preserve ecosystem:

Steps Purpose

Controlling pollution

To minimise destruction of habitats of animals and plants

Managing natural resources

To protect animals and plants by the establishment of sanctuaries, forest and wetland reserves

Renewing natural resources

To restore destroyed habitats due to logging, mining and overfishing

Managing forest To minimise deforestation and illegal logging, and prevent forest fires

Passing of legislation of wildlife protection

To monitor commercial hunting, overfishing, and protect endangered species

Educating the public

To increase public awareness on the importance of conservation and preservation of ecosystem

4 Technology which can help in the conservation and preservation of living organisms:

Technology Importance

Tissue culture (cloning technology)

To increase the population of endangered species

Artificial insemination

To prevent the extinction of the endangered species

Satellite imaging To detect fires in the ecosystem and prevent the destruction of natural habitats


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4.6 Role of Humans in Maintaining the Balance of Nature

1 Examples of human activities:(a) Deforestation(b) Land overuse due to intensive farming(c) Overfishing and overhunting(d) Industrialisation(e) Poor solid waste management

2 The effects of human activities:(a) Global warming(b) Destruction of habitats(c) Extinction of species(d) Soil erosion(e) Pollution of air, water and soil

CHAPTER 5Water and Solution

5.1 Physical Characteristics of Water

1 Impurities can change the physical characteristics of water.

Physical characteristics of pure water

Boiling point = 100°C

Odourless, tasteless, colourless

Poor electrical conductor

Poor thermal conductor

Density = 1 g/cm3 at 4°C

Expands upon freezing

Freezing point = 0°

5.2 Composition of Water

1 Water is made up of hydrogen and oxygen elements.

2 A water molecule contains two atoms of hydrogen and one atom of oxygen.

3 Electrolysis is a method of breaking down water using electricity.

4 During electrolysis, oxygen gas is released at the anode and hydrogen gas is released at the cathode.

5.3 Evaporation of Water

1 Evaporation is the process by which a liquid changes into water vapour.

2 Factors affecting the rate of evaporation of water:

Factors Explanation

Temperature of the surrounding

The higher the temperature of the surrounding, the higher the rate of evaporation of water

Surface area of water

The larger the surface area of water, the higher the rate of its evaporation

Humidity The lower the humidity, the higher the rate of evaporation of water

Movement of air

Air movement increases the rate of evaporation

3 Differences between evaporation and boiling:

Evaporation Boiling

A slow process A fast process

Occurs at the surface of liquid

Occurs throughout liquid

Occurs at all temperatures (below the boiling point of liquid)

Occurs at the boiling point of liquid

Nothing visible observed Air bubbles observed

Affected by humidity, temperature of surrounding, surface area of water and air movement

Affected by air pressure, presence of impurities, rate of heating and volume of liquid

4 Similarities between evaporation and boiling:(a) both involve the change of state from liquid

to gas (steam)(b) both processes absorb heat

5.4 Solution and Solubility

Key terms Definition

Solution A product formed when a solute dissolves in a solvent

Solute A substance which dissolved in a liquid

Solvent A liquid which dissolves a substance

Dilute solution A solution which has very little solute in it

Concentrated solution

A solution which has a lot of solute in it

Saturated solution

A solution which has maximum amount of solute in it

Suspension Mixtures which contains insoluble substances

1 Differences between a solution and a suspension:

Solution Suspension

Contains dissolved substances

Contains insoluble substances

Homogeneous (uniform in colour and transparent

appearance)

Non-homogeneous (opaque or cloudy

appearance)

Light can pass through it

Light cannot pass through it

No residue is formed when filtered

Residue is collected when filtered

2 Solubility is the maximum amount of a solute in grams that will dissolve in 100 g of solvent at a certain temperature.


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3 Factors affecting the solubility of a solute:

Factors Explanation

Nature of solute

Different solutes have different solubility in the same solvent

Temperature The solubility of a solute varies with temperature

4 The rate of dissolving means the time taken by a solute to dissolve completely in a liquid.

5 Factors affecting the rate of dissolving:

Factors Explanation

Temperature The higher the temperature of the solvent, the higher the rate of dissolving

Rate of stirring The higher the rate of stirring, the higher the rate of dissolving

Size of solute particles

The smaller the size of solute particles, the higher the rate of dissolving

6 Water is known as the universal solvent. It can dissolve most substances.

7 Organic solvents can also be used to dissolve some solutes.

8 Characteristics of organic solvents:(a) volatile (evaporate easily)(b) carcinogenic (likely to cause cancer)(c) toxic (poisonous to the living cells)(d) flammable (easy to catch on fire)

5.5 Acid and Alkali

1 Properties of acid and alkali:

Acid Alkali

• Corrosive• Turns moist blue litmus

paper red• Has a pH less than 7• Tastes sour• Reacts with most metals

to product hydrogen gas

• Corrosive• Turns moist red litmus paper

blue• Has pH greater than 7• Tastes bitter and feels soapy

2 Both acid and alkali need water to show their properties.

3 In neutralisation, an acid reacts with an alkali to produce to produce a salt solution.

Acid + Alkali Salt + Water

5.6 Water Purification

Water purification method

Purpose

Filtration To separate solid particles such as clay, sand and other insoluble particles

Boiling To kill micro-organisms with heat energy

Chlorination To kill micro-organisms with chlorine

Distillation To remove dissolved substances, insoluble particles and to kill micro-organisms

Ultraviolet (UV) treatment

To kill micro-organisms with ultraviolet rays

5.7 Water Supply System

1 Process of water treatment in a water treatment plant:

Screening Aeration Coagulation

Filtration Sedimentation

Chlorination and fluoridation

Process of water treatment Purpose

Screening To remove large objects (fish, branches and rubbish)

Aeration To dissolve oxygen and to remove unpleasant smell and taste

Coagulation • Alum – To make small particles stick together to form larger and heavier lumps

• Lime – To reduce the acidity of water

Sedimentation To settle out and remove large lumps

Filtration To remove the remaining solid particles

Chlorination and fluoridation

• Chlorine – To kill harmful micro-organisms• Fluoride – To prevent dental decay

5.8 Preservation of Water Quality

1 Causes and effects of water pollution:

Causes Effects

Silt (mud and sand) Water becomes muddy and rivers become shallower

Domestic waste (garbage and untreated sewage from homes)

Contains harmful micro-organisms which can cause cholera and typhoid

Agricultural waste (pesticides and fertilisers)

Causes rapid growth of algae and therefore reduces oxygen level in the water

Oil spillage (from tankers in the sea)

Kills aquatic life and seabirds

Industrial waste (chemical and radioactive wastes from factories)

Poisons aquatic life and cause skin cancer

2 Ways to control water pollution:

Ways of controlling water pollution

Explanation

Prevention • Planning of proper sewage system in the new residential areas

• Treating wastewater before discharging into the public sewage system

• Avoid dumping rubbish or waste into the water

Enforcement • Imposing fines and punishment for those who dump untreated water, garbage and chemical wastes into rivers

Monitoring • Raw sewage should be treated and turned into safe effluent before discharging into the sewage system


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Device Explanation

Drinking straw

Atmospheric pressure pushes the water up the straw

Water

Drinking straw

(a) Air sucked from straw causes low pressure in the straw.

(b) Air pressure pushes liquid into the straw and the mouth.

Gas Under High Pressure

1 Gases can be compressed into liquid under high pressure, and stored in gas tanks.

2 Safety measures when using gas under high pressure:(a) Keep aerosol cans away from the sources

of heat, such as open flames, sunlight and heaters. High temperature may cause an explosion.

(b) Do not dispose aerosol cans into incinerators as they may explode.

(c) Do not dent or puncture aerosol cans as they may explode.

(d) Gas tanks must be kept in an open, cool and good ventilated place.

(e) Always place the gas tank upright to prevent gas from leaking.

(f) Turn off the valve each time after use.(g) Perform regular gas leakage checks to ensure

there are no leakages.

CHAPTER 6Air Pressure

6.1 Air Pressure

1 Air pressure exists when the air around us presses on the surfaces of the objects.

2 Activities to show that air exerts pressure:(a)

Water

Cardboard

When the hand is released, the water in the glass does not flow out because air pressure presses on the under surface of the cardboard.

(b)

Steam

Steam

Hot water

Heat

Cold water

CoverSteam condensed

Atmospheric presure

When cold water is poured over a heated tin, the tin is crushed and collapses.

3 The kinetic theory of gases can be used to explain the existence of air pressure.

4 According to the kinetic theory of gases,(a) a gas has many particles which are far apart

from each other(b) these gas particles move freely and randomly,

in all directions(c) these gas particles continuously collide with

the walls of the container and bounce back(d) a force is exerted by the gas particles on the

walls of the container(e) the force produces a pressure on the walls of

the container 5 Factors affecting air pressure:

Factor Relationship

Volume Air pressure increases when volume decreases

Temperature Air pressure increases when temperature increases

6.2 Application of the Principle of Air Pressure

Device Explanation

Syringe

Pistonpulledupwards

Atmosphericpressure forces the liquid into the barrel

Nozzle

Liquid

(a) When the piston is pulled up, a lower pressure is created inside the barrel of the syringe.

(b) The air pressure outside forces liquid

into the barrel of the syringe.

Siphon

Atmospheric pressure pushes water into tube

Reduced pressure when water flows out of tube

Tube filled with water

(a) A lower pressure is developed in the tube.

(b) The air pressure outside pushes water into the tube.

Spraying pump

Air is compressed and pressure increases when piston is pushedPiston

Reduced presure when air comes out at high speed

Fine droplets

Atmospheric pressure pushes liquid up the tube

PushLiquid

(a) When the piston is pushed, the air inside the barrel is compressed, pressure increases and pushes air out of nozzle at high speed.

(b) The pressure reduces when air comes out at high speed.

(c) Air pressure pushes liquid up and out as fine droplets.

CHAPTER 7Dynamics

7.1 Force

1 A force is a push or a pull acting upon an object. 2 Effects of forces:

(a) Can change shape(b) Can change position(c) Can change direction(d) Can change speed (increases or reduces speed)


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3 Different types of forces:

Type Description

Gravitational force

The force that causes objects to fall to the ground

Magnetic force The force that acts on magnetic materials at a distance

Electrostatic force

The force that is caused by charged materials

Frictional force The force that is caused by surfaces in contact

Electromagnetic force

The force that is produced by running electricity through a magnetic material

7.2 Measurement of Force

1 The SI unit for force is Newton (Symbol: N). 2 Spring balance (or Newton balance) can be used

to measure force.

7.3 Application of Frictional Force

1 Frictional force has a magnitude and a direction. 2 The direction of the frictional force is parallel

to the surface and in the opposite direction of motion.

3 Factors affecting magnitude of frictional force:

Factor Description

Type of surface The rougher the two surfaces are, the greater the frictional force between them

Weight of object The heavier the object, the greater the frictional force

4 Advantages and disadvantages of friction:

Advantages Disadvantages

• Provides a good grip and prevents objects from slipping

• Provides resistance to motion, so that moving objects can stop

• Produces heat, for example striking a matchstick

• Wears off surfaces in contact, such as shoe soles and tyres

• Produces unwanted heat that can damage surfaces

• Produces noise and causes noise pollution

• Wastes energy as more energy is needed to overcome friction

5 Methods to reduce friction:

Method Application

Roller or ball bearings In automobiles and machines

Layer of air cushion Hovercrafts

Lubricants (grease, oil) Moving gears, engine pistons, door hinges

Wheels Roller blades, trolleys, sofas, pianos, wheelchairs

7.4 Application of Work

1 Work is done when a force is exerted to move an object in the same direction as the application of the force.

Work (J) = Force (N) × Distance (m)

2 The unit for work is joule (J). 3 1 joule of work is done when 1 newton of force

moves a distance of 1 metre, in the direction of the force.

7.5 Application of Power

1 Power is the rate of doing work.

Work done (J)Power (W) = ––––––––––––––– Time taken (s)

2 The unit for power is watt (W) or joule per second (J s–1).

7.6 Importance of Force in Life

1 Our daily activities cannot function without force.

2 Importance of force:(a) frictional force enables us to hold all objects(b) magnetic force and electrical force make the

machines work(c) gravitational force allows objects to stay on

the ground

CHAPTER 8Support and Movement

8.1 Support Systems in Animals

Support System Description Examples of animals

Exoskeleton(in invertebrates)

An outer skeleton which is made of hard materials (such as chitin)

Grasshoppers, cockroaches, prawns, crabs

Endoskeleton(in vertebrates)

An internal skeleton which is made of bones and muscle attachments

Humans, elephants, horses, whales

Hydrostatic skeleton (in invertebrates)

Liquid (mainly water) which supports and maintains body shape and turgidity

Earthworms, sea anemones, starfish

1 Aquatic vertebrates have smaller endoskeletons compared to land vertebrates.

2 Aquatic vertebrates gain support from buoyancy.

3 Buoyancy is the force from water that enables objects to float.

8.2 Support Systems in Plants

Support system Description Examples of plants

Buttress roots Large roots which form the base of the stem to provide extra support

Rain tree, flame of the forest

Prop roots Roots which grow from the branches or the nodes of the stem

Banyan tree, maize

Clasping roots Roots which enable the plant to climb by growing around and gripping its support

Orchids, money plant, pepper plant


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Support system Description Examples of plants

Tendrils Coiled structures that develop from the stem or leaf. They wrap around the support and help the plants to climb

Cucumber, garden pea, pumpkin

Thorns Modified braches that cannot be removed easily from the stem

Bougainvillea

Prickles The outgrowth of the epidermis which can be easily removed from the stem

Roses

Air sacs Provide buoyancy and help plants to stay afloat in water

Brown alga

Stilt roots Roots which develop from the main stem of the trees

Mangrove tree

8.3 Appreciating the Support System in Living Organisms

1 Physically disabled persons, aged people, injured persons use various ambulatory aids for additional support.

2 Examples of ambulatory aids are:(a) Cane (walking stick)(b) Crutches(c) Walking frame

3 Beached and stranded whales will die because their internal organs will be crushed by their own weight.

CHAPTER 9Stability

9.1 Stability

1 The stability of an object refers to its ability to maintain its original position.

2 A stable object does not topple easily. 3 The centre of gravity of an object is the point at

which the whole weight of the object seems to concentrate at.

4 The centre of gravity of an object is also the point of equilibrium of the object.

5 The centre of gravity of objects can be determined using a plumb line.

6 Factors that affect the stability of an object:

Factor Description

Position of the centre of gravity

The lower the centre of gravity of an object, the more stable is the object

Base area The larger the base area of an object, the more stable is the object

9.2 Importance of Stability

1 Stability is important to ensure that an object does not topple over.

2 Stability of an object can be increased by:(a) lowering its centre of gravity(b) increasing its base area

CHAPTER 10Simple Machine

10.1 Levers

1 Levers are simple machines. 2 A lever consists of a rigid bar that turns freely

about a fixed point (called fulcrum, F), when a force (called effort, E) is applied to overcome the resistance force (called load, L).

3 There are three classes of levers.

Type of lever Feature Use Examples

First-class lever

F between E and L

EF

L

To produce a large force from a small force

• Pliers• Scissors• Crowbar• Claw hammer

Type of lever Feature Use Examples

Second-class lever

L between F and E

EF

L

To produce a large force from a small force

• Nutcracker• Paper cutter• Wheelbarrow• Bottle opener

Third-class lever

E between F and L

EF

L

To produce a large movement from a small movement

• Broom• Ice tongs• Fishing rod• Human arm

4 The moment of a force refers to the turning effect of a force.

Moment of a force (N m)= Force (N) × Perpendicular distance from the

pivot to the force (m)

5 Moments in a lever describe the opposing moments produced by the effort and the load in a lever.

6 When two opposing moments are balanced:

Load (N) × Distance of load from the fulcrum (m)= Effort (m) × Distance of the effort from the

fulcrum (m)

10.2 Appreciating the Innovative Efforts in the Design of Machines to Simplify Work

1 Levers can be used to design machines that help to simplify our work.


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Express Notes Science Form 2

Education

Transcript of Express Notes Science Form 2