Express Notes Science Form 2

Written By
Ng Chee Kin
B.Sc.(Hons.), MBA
ngcheekin@gmail.com
mrcheekin@blogspot.com.au

All Rights Reserved ©2012 Ng Chee Kin

PREsSS
E X p r e��

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2 The tongue:
CHAPTER 1

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Fine hair
The World through Our Senses Bitter
Epidermis Pain receptor
1.1 Sensory Organs Sour
Heat

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receptor
1 Humans have five senses. Table 1 shows the Dermis Salty
Pressure
senses, sensory organs and stimulus detected. receptor
Cold Sweet
Sense Sensory organ Stimulus receptor

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Fatty layer
Touch
Touch, pressure, 1 Chemical particles 2 Taste projections receive
receptor
Touch Skin dissolve in saliva stimulus and send it to
cold, heat, pain on the surface of the taste receptors
the tongue
Chemical

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Smell Nose 2 The sensitivity of skin depends on:
substances in air 3 Taste receptor
(a) the closeness of receptors
Chemical sets off impulse
Taste Tongue (b) the depth of receptors
substances in food 4 Impulse is sent to

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Taste bud the brain to be
Hearing Ear Sound 1.3 Sense of Smell interpreted as taste

Sight Eye Light .b
1 The roof of the nasal cavity has many sensory
cells to detect smells. 1.5 Sense of Hearing
Table 1
4 Impulses are sent to the brain 1 The human ear:
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2 Each sensory organ has receptors to detect 3 Nerve sends nerve impulse to
stimuli. Pinna Ossicles
the brain to be interpreted
3 Pathway from stimulus to responses: Nerve impulse Semicircular
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canal
2 Receptor cell detects smell and
Stimuli sensory organ nerves brain generates nerve impulse Ear Auditory
canal nerve
responses effectors nerves Nasal 1 Cilium contains mucus to
cavity dissolve inhaled particles Cochlea
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4 Nerve impulses are electrical messages produced To the brain Eardrum Eustachian
Nostril Oval window
by receptors. tube
5 Effectors are organs which carry out responses. Into the lungs
6 Responses are reactions which occur after 2 The mechanism of hearing:
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receiving a stimulus. Pinna ear canal eardrum ossicles
1.4 Sense of Taste
1.2 Sense of Touch auditory cochlea oval window
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1 The surface of the tongue has many taste buds to
detect chemical substances. nerve brain
1 The skin has five receptors.

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

1.6 Sense of Sight 4 Devices to overcome the limitations of sight: 1.9 Stimuli and Responses in Plants
Microscope, telescope, magnifying glass,
1 The human eye: 1 Tropism is a growth response to external stimuli.

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periscope, x-ray, binoculars and ultrasound
Vitreous humour scanning device
Choroid Tropism Stimuli Example

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Supportive ligament 5 Stereoscopic vision helps predators to detect the
Retina
Iris
location of their preys accurately. The roots grow
Sclera
Lens 6 Monocular vision helps prey to detect their Hydrotropism Water towards a water
Yellow spot

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Cornea enemies from all directions. source
Optic nerve
Pupil The roots grow in
Aqueous humour 1.8 Sound and Hearing
Geotropism Gravity the direction of
1 Properties of sounds: gravity
Ciliary muscle Conjunctiva Blind spot

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(a) they are produced by vibrations of objects.
2 The retina has photoreceptors to detect light. The shoots grow
(b) they need a medium to travel, such as solids, Phototropism Light
3 Mechanism of sight: towards sunlight
liquids or gases.
(c) they cannot travel through a vacuum. The tendrils wrap
Cornea aqueous humour lens Touch

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(d) they can be absorbed by soft and rough Thigmotropism around a solid
optic nerve retina vitreous humour (contact)
surfaces. structure
(e) they can be reflected by hard and smooth
brain optic effectors nerves
surfaces as echoes. 2 Nastic movements are responses of plants to

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2 Stereophonic hearing helps to detect the location external stimuli which may come from any
1.7 Light and Sight of the source of sound. direction.
1 Reflection of light happens when it bounces off

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the surface on which it falls.
2 Refraction is the bending of light due to speed
CHAPTER 2
change as it travels through transparent medium Nutrition
of different densities.
3 Defects of vision: 2.1
.bClasses of Food
in
Defects of Possible Ways of 1 Seven classes of food (nutrients):
Symptoms
vision causes correction
Nutrient Sources Function Deficiency disease
Short- • Can see near • Lens is too Concave
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sightedness objects clearly thick lenses Carbohydrates Sugar, starch, glucose • Supply energy to the body Body lacks energy, marasmus
• Cannot focus on • Eyeball is
Proteins Milk, fish, eggs, chicken • For growth Stunted growth, kwashiorkor
distant objects too long
• Repair of body tissues
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Long- • Can see distant • Lens is too Convex
Fats Oil, ghee, margarine, butter • Keep the body warm Body lacks energy
sightedness objects clearly thin lenses
• Transport vitamins A, D, E and K
• Cannot focus on • Eyeball is • Supply a lot of energy
near objects too short
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Fibre (roughage) Fruits, vegetables, cereals • Helps peristalsis and removal of Constipation
Astigmatism • See distorted • Irregular Cylindrical undigested food from the body
images surface of lenses or
the cornea through
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Water Fruits, vegetables, drinking • Dissolves chemicals in the body Dehydration
surgery water • Controls body temperature


Nutrient Sources Function Deficiency disease 2.3 Human Digestive System

Vitamins Vitamin A Carrot, fish liver oil, green • For night vision • Night blindness 1 Digestion is the breakdown of large food

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vegetables • Healthy skin • Skin infections molecules into smaller molecules that can be
easily absorbed by the body.

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Vitamin B Milk, eggs, meat, cereals • Healthy nervous system • Beriberi
2 Digestion occurs in the alimentary canal (or
• Formation of red blood cells • Anaemia
gut):
Vitamin C Citrus fruit, vegetables • Healing of wounds • Scurvy

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• Resistance to diseases Mouth oesophagus stomach

Vitamin D Made by our body in sunlight, • Strong bones and teeth • Rickets optic nerve small intestine duodenum
also found in eggs, milk large intestine anus
Vitamin E Nuts, vegetable oil, whole grains • For healthy reproduction system • Sterility

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• Fights against diseases 3 Peristalsis is the contraction and relaxation of the
muscles along the gut wall.
Vitamin K Made in the human intestine, • Helps blood clotting and stops • Prolonged bleeding 4 Enzymes are substances which generally act as
also found in green vegetables bleeding catalysts to speed up the chemical reactions in

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Minerals Calcium Milk, cheese, green vegetables • Strong bones and teeth • Rickets our body.
• Healthy muscles and nerve • Osteoporosis
• Muscle cramps Oesophagus
– Produces a wave-like action called peristalsis

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Sodium Table salt, cheese, meat • Controls body fluid • Muscular cramps – Peristalsis helps to push bolus into the stomach
• Proper functioning of nerves
Iron Meat, green vegetables, eggs • For the formation of haemoglobin • Anaemia Mouth Stomach
– Physical digestion – Produces gastric juices
in the red blood cells

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occurs – Gastric juice contains
Iodine Seafood, iodised salt • For making hormones in the • Goitre – Starch is broken hydrochloric acid and
down into maltose protease
thyroid glands
– Proteins are broken
Phosphorus Meat, eggs,
vegetables
cheese,
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milk, • Strong bones and teeth
• Stores energy
• Rickets
• Fatigue Liver
down into polypeptides
or peptones
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Potassium Bananas, meat, nuts • Proper functioning of nerves • Paralysis Gall bladder Pancreas produces
produces bile pancreatic juice
2 Food tests: 2 The energy requirement depends on the age,
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Nutrient Test Result body size, sex, occupation, physical activity, Large intestine
Starch (a type of Blue-black climate and state of health of an individual.
Iodine test 3 Calorific value (or energy value) is the amount of Rectum
carbohydrate) colour
energy released from one gram of a particular Anus
Glucose (a type Benedict’s Brick-red
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type of food.
of carbohydrate) test precipitate
Duodenum Lower part of small intestine
Protein Millon’s test Red precipitate Class of food Energy value (kJ/g) – Receives bile from the gall – Secretes intestinal juice
blader and pancreatic juice – Maltose is broken down
Fat Emulsion test Milky solution
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Carbohydrates 17 – Starch is broken down into into glucose
maltose – Polypeptides are broken
2.2 The Importance of a Balanced Diet Proteins 18 – Proteins are broken down into down into amino acids
polypeptides – Fats are broken down into
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1 A balanced diet contains seven classes of food in Fats 39
– Fats are broken down into fatty acids and glycerol
the right amount. fatty acids and glycerol


2.4 Absorption of Digested Food 5 Plant kingdom can be divided into: 7 Classification of non-flowering plants:
(a) flowering plants
1 Absorption is the diffusion of digested food from (b) non-flowering plants Non-flowering plants

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the gut into the bloodstream. 6 Classification of flowering plants:
2 Absorption mainly happens in the small intestine.

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3 Villi on the inner wall of small intestine help to Flowering plants Conifers Mosses Ferns Algae
speed up the absorption.

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2.5 Reabsorption of Water and Defecation Monocotyledons Dicotyledons Examples: Examples: Examples: Examples:
• Pine tree • Stag’s • Cup • Seeweed
1 Reabsorption happens in the large intestine.
• Casuarina horn moss • Phytoplankton
2 Water, with dissolved minerals and vitamins are
tree fern
reabsorbed into our body.

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3 Defecation is the process of removing faeces
from the body through the anus.
Two CHAPTER 4
4 Difficulty in defecation is called constipation, One cotyledon
which is caused by the lack of water and cotyledon Interdependence among Living

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roughage in the diet. Organisms and the Environment
A maize grain cut in A green bean (split
2.6 Healthy Eating Habits half into two)
4.1 Interdependence among Living Organisms
1 We should practice healthy eating habits to

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prevent diet-related diseases.
Network- Key terms Description
2 We should eat a wide variety of foods according to
the recommended amounts in the food pyramid. veined leaf
Species Organisms with common characteristics

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which can breed among themselves to
CHAPTER 3 Parallel-veined produce fertile offspring
leaf Flower
Biodiversity
3.1 Organisms and Their Classification
.b Stem Stem

Tap root
Population

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

Many types of populations living in
Fibrous root
in
1 Biodiversity (or biological diversity) refers to the the same place, interacting with one
wide variety of organisms on earth. Example: Maize plant Example: Balsam another
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2 Organisms are classified into groups called plant
Habitat The place or area where an organisms
kingdoms, such as animal and plant kingdoms. • Fibrous root system
live and reproduce
(a) vertebrates (animals with backbones) • Parallel-veined • Tap root system
(b) invertebrates (animals without backbones) leaves • Network-veined Ecosystem The community of organisms living in
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4 Vertebrates are divided into five groups: • Non-woody and leaves the same habitat, together with the
soft stems • Woody and hard non-living environment
Vertebrate Characteristic • Other examples: stems
Fish Slimy scales and fins Grass, orchid plant, • Other examples: Ecology The study of relationship between living
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Amphibians Exposed and moist skin sugar cane, paddy rubber tree, things and the environment
Reptiles Hard dry scales rose shrub,
bougainvillea, 1 A balanced ecosystem is created when there is
Birds Feathers and wings
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sunflower plant interdependence among living organisms and
Mammals Hair or fur the environment.


4.2 Interaction between Living Organisms 1 Biological control uses the prey-predator 4.5 Conservation and Preservation of Living
relationship to control pests. Organisms

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Type of interaction Description Examples
4.3 Food Web 1 Conservation is the wise use of natural resources
Prey-predator • A predator is • Goat (prey) with the least disturbance to the ecosystem.

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an animal that and tiger Key terms Description 2 Preservation refers to the actions taken to
hunts other (predator) maintain ecosystem in its balanced state.
animals for food • Frog (prey) Producer Green plants which can produce 3 Some steps to conserve and preserve ecosystem:

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• A prey is an and snake food through photosynthesis.
animal hunted (predator)
and killed by • Rat (prey) and Steps Purpose
Consumer Animals which eat plants and other
predators for owl (predator) animals Controlling To minimise destruction of habitats
food
Decomposer Organisms that break down dead pollution of animals and plants

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Competition Intra-specific • Competition • Wolves
animal and plant materials into Managing natural To protect animals and plants by
competition between the compete with
same species of each other simpler substances which can be resources the establishment of sanctuaries,
organisms for food and used again by the producers. forest and wetland reserves

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mate
1 A pyramid of numbers shows the number of Renewing natural To restore destroyed habitats
Inter-specific • Competition • Crows and fox organisms at each stage of a food chain. resources due to logging, mining and
competition between compete with overfishing
organisms of each other for Number of

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Level 4 Managing forest To minimise deforestation and
different species food organisms (tertiary consumer)
decreases, illegal logging, and prevent forest
Symbiosis Commensalism • Interaction • Remora fish Level 3 (secondary fires
between two (commensal) Size of consumer)
Passing of To monitor commercial hunting,

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organisms and shark organisms
• The commensal (host) increases Level 2 (primary legislation of overfishing, and protect
receives benefits consumer) wildlife protection endangered species
Amount
from the host
• The host is not
harmed nor
received any
.b
of energy
decreases
Level 1
(producer)
Educating the
public
To increase public awareness on
the importance of conservation
and preservation of ecosystem
in
benefit
4.4 Photosynthesis 4 Technology which can help in the conservation
Mutualism • An interaction • Fungi (provide
and preservation of living organisms:
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which benefits shelter 1 Photosynthesis is a process of making food by
both organisms to algae) green plants.
and algae Technology Importance
2 Requirements for photosynthesis:
(produce food (a) Water Tissue culture To increase the population of
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for fungi and
(b) Carbon dioxide (cloning endangered species
itself)
(c) Chlorophyll technology)
Parasitism • A parasite • Tapeworm (d) Sunlight
benefits by (parasite) Artificial To prevent the extinction of
3 Products of photosynthesis:
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living in or on living in insemination the endangered species
(a) Oxygen
the host the human
(b) Glucose Satellite imaging To detect fires in the ecosystem
• The host is intestine
Chlorophyll and prevent the destruction
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harmed by the (host)
Water + Carbon dioxide Oxygen + Glucose of natural habitats
parasites Sunlight


4.6 Role of Humans in Maintaining the Balance of 2 A water molecule contains two atoms of 4 Similarities between evaporation and boiling:
Nature hydrogen and one atom of oxygen. (a) both involve the change of state from liquid
3 Electrolysis is a method of breaking down water to gas (steam)

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1 Examples of human activities: using electricity. (b) both processes absorb heat
(a) Deforestation 4 During electrolysis, oxygen gas is released at

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(b) Land overuse due to intensive farming the anode and hydrogen gas is released at the 5.4 Solution and Solubility
(c) Overfishing and overhunting cathode.
(d) Industrialisation

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Key terms Definition
(e) Poor solid waste management 5.3 Evaporation of Water
2 The effects of human activities: Solution A product formed when a solute
(a) Global warming 1 Evaporation is the process by which a liquid dissolves in a solvent
(b) Destruction of habitats changes into water vapour.
2 Factors affecting the rate of evaporation of Solute A substance which dissolved in a
(c) Extinction of species

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water: liquid
(d) Soil erosion
(e) Pollution of air, water and soil Solvent A liquid which dissolves a substance
Factors Explanation
Dilute solution A solution which has very little solute

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Temperature The higher the temperature of the in it
CHAPTER 5 of the surrounding, the higher the rate of
Concentrated A solution which has a lot of solute
Water and Solution surrounding evaporation of water
solution in it

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Surface area The larger the surface area of water, the Saturated A solution which has maximum
of water higher the rate of its evaporation solution amount of solute in it
5.1 Physical Characteristics of Water
Humidity The lower the humidity, the higher the Suspension Mixtures which contains insoluble
1 Impurities can change the physical characteristics
rate of evaporation of water

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of water. substances
Movement Air movement increases the rate of 1 Differences between a solution and a
of air evaporation suspension:

Freezing
point = 0°
Boiling point
= 100°C
Expands upon
freezing
.b
3 Differences between evaporation and boiling:
Solution Suspension
Evaporation Boiling
in
Contains dissolved Contains insoluble
A slow process A fast process substances substances
Physical
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Odourless, Occurs at the surface of Occurs throughout liquid Homogeneous (uniform Non-homogeneous
characteristics Density
tasteless, liquid in colour and transparent (opaque or cloudy
of pure water = 1 g/cm3 at 4°C
colourless appearance) appearance)
Occurs at all temperatures Occurs at the boiling point
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(below the boiling point of liquid Light can pass Light cannot pass
of liquid) through it through it
Poor electrical Poor thermal
conductor conductor Nothing visible observed Air bubbles observed No residue is formed Residue is collected
when filtered when filtered
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Affected by humidity, Affected by air pressure,
temperature of presence of impurities, rate
5.2 Composition of Water
surrounding, surface of heating and volume of 2 Solubility is the maximum amount of a solute in
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1 Water is made up of hydrogen and oxygen area of water and air liquid grams that will dissolve in 100 g of solvent at a
elements. movement certain temperature.


3 Factors affecting the solubility of a solute: 3 In neutralisation, an acid reacts with an alkali to 5.8 Preservation of Water Quality
produce to produce a salt solution.
Factors Explanation 1 Causes and effects of water pollution:

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Acid + Alkali Salt + Water
Nature of Different solutes have different solubility in Causes Effects

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solute the same solvent
5.6 Water Purification Silt (mud and sand) Water becomes muddy and
The solubility of a solute varies with
Temperature rivers become shallower
temperature Water purification

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Purpose
method
4 The rate of dissolving means the time taken by a Domestic waste (garbage Contains harmful micro-
solute to dissolve completely in a liquid. Filtration To separate solid particles such as clay, and untreated sewage from organisms which can cause
5 Factors affecting the rate of dissolving: sand and other insoluble particles homes) cholera and typhoid
Factors Explanation Boiling To kill micro-organisms with heat energy

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Agricultural waste (pesticides Causes rapid growth of algae
Temperature The higher the temperature of the solvent, Chlorination To kill micro-organisms with chlorine and fertilisers) and therefore reduces oxygen
the higher the rate of dissolving level in the water
Distillation To remove dissolved substances, insoluble
particles and to kill micro-organisms

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Rate of stirring The higher the rate of stirring, the higher
the rate of dissolving Oil spillage (from tankers in Kills aquatic life and seabirds
Ultraviolet (UV) To kill micro-organisms with ultraviolet the sea)
Size of solute The smaller the size of solute particles, the treatment rays
particles higher the rate of dissolving
Industrial waste (chemical Poisons aquatic life and cause

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6 Water is known as the universal solvent. It can 5.7 Water Supply System and radioactive wastes from skin cancer
dissolve most substances. factories)
7 Organic solvents can also be used to dissolve 1 Process of water treatment in a water treatment

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some solutes. plant: 2 Ways to control water pollution:
8 Characteristics of organic solvents: Screening Aeration Coagulation Ways of controlling
(a) volatile (evaporate easily) Explanation
(b) carcinogenic (likely to cause cancer)
(c) toxic (poisonous to the living cells)
(d) flammable (easy to catch on fire)
.b Filtration Sedimentation
Chlorination and fluoridation
water pollution

Prevention • Planning of proper sewage system in
in
the new residential areas
Process of water • Treating wastewater before
Purpose
5.5 Acid and Alkali treatment discharging into the public sewage
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Screening To remove large objects (fish, branches and system
1 Properties of acid and alkali: rubbish) • Avoid dumping rubbish or waste into
Acid Alkali Aeration To dissolve oxygen and to remove unpleasant the water
smell and taste
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• Corrosive • Corrosive
Coagulation • Alum – To make small particles stick Enforcement • Imposing fines and punishment for
• Turns moist blue litmus • Turns moist red litmus paper
paper red blue together to form larger and heavier lumps those who dump untreated water,
• Has a pH less than 7 • Has pH greater than 7 • Lime – To reduce the acidity of water garbage and chemical wastes into
• Tastes sour • Tastes bitter and feels soapy rivers
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Sedimentation To settle out and remove large lumps
• Reacts with most metals
to product hydrogen gas Filtration To remove the remaining solid particles Monitoring • Raw sewage should be treated and
turned into safe effluent before
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2 Both acid and alkali need water to show their Chlorination and • Chlorine – To kill harmful micro-organisms
fluoridation • Fluoride – To prevent dental decay discharging into the sewage system
properties.


CHAPTER 6 Factor Relationship Device Explanation

Air Pressure Volume Air pressure increases when volume Drinking straw (a) Air sucked from

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decreases straw causes low
pressure in the

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6.1 Air Pressure Temperature Air pressure increases when Atmospheric pressure
pushes the water straw.
temperature increases
1 Air pressure exists when the air around us presses up the straw (b) Air pressure pushes
liquid into the straw

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on the surfaces of the objects. Water
2 Activities to show that air exerts pressure: 6.2 Application of the Principle of Air Pressure Drinking straw and the mouth.
(a)
Device Explanation
Gas Under High Pressure
Water Syringe (a) When the piston is

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pulled up, a lower 1 Gases can be compressed into liquid under high
Cardboard
Piston
pressure is created pressure, and stored in gas tanks.
pulled 2 Safety measures when using gas under high
upwards inside the barrel of
the syringe. pressure:
When the hand is released, the water in

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(b) The air pressure (a) Keep aerosol cans away from the sources
the glass does not flow out because air of heat, such as open flames, sunlight and
Atmospheric outside forces liquid
pressure presses on the under surface of the Nozzle pressure heaters. High temperature may cause an
cardboard. forces the into the barrel of
Liquid liquid into the syringe. explosion.

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(b) (b) Do not dispose aerosol cans into incinerators
the barrel
Steam as they may explode.
Steam Cover condensed Siphon (a) A lower pressure is
Cold (c) Do not dent or puncture aerosol cans as they
Steam water Reduced pressure developed in the may explode.

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Atmospheric Atmospheric when water
presure tube. (d) Gas tanks must be kept in an open, cool and
Hot pressure pushes flows out of tube
water water into tube (b) The air pressure good ventilated place.
outside pushes (e) Always place the gas tank upright to prevent
Heat
When cold water is poured over a heated tin,
the tin is crushed and collapses.
.b
Tube filled
with water
water into the tube. gas from leaking.
(f) Turn off the valve each time after use.
(g) Perform regular gas leakage checks to ensure
in
3 The kinetic theory of gases can be used to explain there are no leakages.
the existence of air pressure. Spraying pump (a) When the piston
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4 According to the kinetic theory of gases, Reduced is pushed, the air
(a) a gas has many particles which are far apart
Air is compressed presure
inside the barrel is CHAPTER 7
and pressure when air
from each other increases when comes out at compressed, pressure Dynamics
(b) these gas particles move freely and randomly, Piston piston is pushed high speed increases and pushes
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in all directions Fine droplets
air out of nozzle at
(c) these gas particles continuously collide with high speed. 7.1 Force
the walls of the container and bounce back Push (b) The pressure reduces
Liquid 1 A force is a push or a pull acting upon an object.
(d) a force is exerted by the gas particles on the when air comes out
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Atmospheric pressure pushes 2 Effects of forces:
walls of the container liquid up the tube at high speed. (a) Can change shape
(e) the force produces a pressure on the walls of (c) Air pressure pushes (b) Can change position
the container liquid up and out as
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(c) Can change direction
5 Factors affecting air pressure: fine droplets. (d) Can change speed (increases or reduces speed)


3 Different types of forces: 5 Methods to reduce friction:
CHAPTER 8
Type Description Method Application
Support and Movement

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Gravitational The force that causes objects to fall to the Roller or ball bearings In automobiles and machines
force ground

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Magnetic force The force that acts on magnetic materials at Layer of air cushion Hovercrafts 8.1 Support Systems in Animals
a distance Lubricants (grease, oil) Moving gears, engine pistons,
Electrostatic The force that is caused by charged door hinges Support System Description Examples of animals

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force materials
Wheels Roller blades, trolleys, sofas, Exoskeleton An outer skeleton Grasshoppers,
Frictional force The force that is caused by surfaces in (in invertebrates) which is made of cockroaches,
pianos, wheelchairs
contact hard materials prawns, crabs
Electromagnetic The force that is produced by running (such as chitin)
force electricity through a magnetic material

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7.4 Application of Work Endoskeleton An internal Humans, elephants,
(in vertebrates) skeleton which is horses, whales
7.2 Measurement of Force 1 Work is done when a force is exerted to move an
made of bones and
object in the same direction as the application of muscle attachments
1 The SI unit for force is Newton (Symbol: N).

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the force.
2 Spring balance (or Newton balance) can be used
Hydrostatic Liquid (mainly Earthworms, sea
to measure force. Work (J) = Force (N) × Distance (m) skeleton (in water) which anemones, starfish
invertebrates) supports and
7.3 Application of Frictional Force maintains body
2 The unit for work is joule (J).

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1 Frictional force has a magnitude and a direction. 3 1 joule of work is done when 1 newton of force shape and turgidity
2 The direction of the frictional force is parallel moves a distance of 1 metre, in the direction of
to the surface and in the opposite direction of the force. 1 Aquatic vertebrates have smaller endoskeletons

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motion. compared to land vertebrates.
3 Factors affecting magnitude of frictional force: 7.5 Application of Power 2 Aquatic vertebrates gain support from
Factor Description buoyancy.
Type of surface The rougher the two surfaces are, the
greater the frictional force between them
.b
1 Power is the rate of doing work.

Work done (J)
3 Buoyancy is the force from water that enables
objects to float.
Power (W) = –––––––––––––––
in
Weight of object The heavier the object, the greater the 8.2 Support Systems in Plants
Time taken (s)
frictional force

4 Advantages and disadvantages of friction: Support system Description Examples of plants
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2 The unit for power is watt (W) or joule per second
Advantages Disadvantages (J s–1). Buttress roots Large roots which Rain tree, flame of
form the base of the the forest
• Provides a good grip and • Wears off surfaces in stem to provide extra
prevents objects from contact, such as shoe soles 7.6 Importance of Force in Life
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support
slipping and tyres 1 Our daily activities cannot function without
• Provides resistance to • Produces unwanted heat Prop roots Roots which grow Banyan tree, maize
force. from the branches or
motion, so that moving that can damage surfaces 2 Importance of force: the nodes of the stem
• Produces noise and causes
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objects can stop (a) frictional force enables us to hold all objects
• Produces heat, for example noise pollution (b) magnetic force and electrical force make the Clasping roots Roots which enable Orchids, money
striking a matchstick • Wastes energy as more machines work the plant to climb by plant, pepper
growing around and plant
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energy is needed to (c) gravitational force allows objects to stay on
overcome friction gripping its support
the ground


2 A stable object does not topple easily.
Support system Description Examples of plants Type of
3 The centre of gravity of an object is the point at Feature Use Examples
lever
Tendrils Coiled structures that Cucumber, garden which the whole weight of the object seems to

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develop from the stem pea, pumpkin concentrate at.
or leaf. They wrap 4 The centre of gravity of an object is also the Second- L between F and E To produce • Nutcracker

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around the support point of equilibrium of the object. class a large • Paper cutter
E
and help the plants to lever force from a • Wheelbarrow
5 The centre of gravity of objects can be determined F
climb small force • Bottle opener
using a plumb line.

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Thorns Modified braches that Bougainvillea 6 Factors that affect the stability of an object: L
cannot be removed
easily from the stem Factor Description

Prickles The outgrowth of the Roses Position of the The lower the centre of gravity of an object, Third- E between F and L To produce • Broom

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epidermis which can centre of gravity the more stable is the object class a large • Ice tongs
be easily removed E
Base area The larger the base area of an object, the lever movement • Fishing rod
from the stem F
more stable is the object from a small • Human arm
Air sacs Provide buoyancy and Brown alga movement
L

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help plants to stay 9.2 Importance of Stability
afloat in water
1 Stability is important to ensure that an object
Stilt roots Roots which develop Mangrove tree does not topple over.
from the main stem of 4 The moment of a force refers to the turning

gs
2 Stability of an object can be increased by:
the trees effect of a force.
(a) lowering its centre of gravity
(b) increasing its base area
8.3 Appreciating the Support System in Living
Moment of a force (N m)

lo
Organisms
= Force (N) × Perpendicular distance from the
1 Physically disabled persons, aged people, CHAPTER 10 pivot to the force (m)
injured persons use various ambulatory aids for .b
additional support. Simple Machine
5 Moments in a lever describe the opposing
2 Examples of ambulatory aids are:
10.1 Levers moments produced by the effort and the load in
(a) Cane (walking stick)
in
a lever.
(b) Crutches 1 Levers are simple machines. 6 When two opposing moments are balanced:
(c) Walking frame 2 A lever consists of a rigid bar that turns freely
ek

3 Beached and stranded whales will die because about a fixed point (called fulcrum, F), when a
their internal organs will be crushed by their force (called effort, E) is applied to overcome the Load (N) × Distance of load from the fulcrum (m)
own weight. resistance force (called load, L). = Effort (m) × Distance of the effort from the
3 There are three classes of levers. fulcrum (m)
he

Type of
CHAPTER 9 lever
Feature Use Examples
Stability First- F between E and L To produce • Pliers
rc

class a large • Scissors 10.2 Appreciating the Innovative Efforts in the
E Design of Machines to Simplify Work
9.1 Stability lever F force from a • Crowbar
small force • Claw hammer
1 Levers can be used to design machines that help
m

1 The stability of an object refers to its ability to L to simplify our work.
maintain its original position.


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