NOTES PACK - President Girls' College · 2020. 6. 2. · 5 GRADE8 -SCIENCE NOTES MERVIN SIRIWARDANA...

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GRADE8 -SCIENCE NOTES MERVIN SIRIWARDANA PGC-KURUNEGALA

President Girls’ College

Kurunegala

NOTES PACK Grade 8 Science

Last two unit of 2nd Term

Unit- 09 -Human organ systems Unit- 10 -Electricity

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Unit – 09

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Human excretory system and excretory products

In different products that are useful to the body as well as useless to the body by

the biological processes that take place within the cells,

According to the above statement two types of products produced in the body.

i. useful products ii. useless products

Eg. Biological process - Respiration

i. useful products - energy

Energy is used for the biological processes in the body.

ii. useless products - carbon dioxide, water

Excretory products Useless products that are produced during chemical reactions within the cells.

• Fill the blanks of the following paragraph.

Carbon dioxide and water may become harmful to cells when there is an excess

amount. Therefore, they should be removed from the body.

Different excretory products of human

Fil the following table observing the above figure.

Excretory organ Form they are excreted Excretory products Lungs Exhaled air

Carbon dioxide, water

Skin

Sweat

Urea, uric acid, water, salt

Kidney

Urine

Urea, uric acid, water, salt

Exhaled air

(carbon dioxide,water) Sweat

(urea, uric acid,

water, salts) Urine

(urea, uric acid,

water, salts)

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Excretion Process that remove the excretory products from the body. Children do you why,

Faeces is not an excretory product.

What are faeces?

Waste matter remaining after food has been digested is known as

faeces.

Human excretory system What is following diagram shows? Human excretory system

• Label the parts of the following human excretory system.

Describe the location of the kidney Find the lower end of the kidney

1-Place your hands on your hips.

2-Then the tips of your thumb give an indicate the lower end

of the kidney.

Location

Against the back muscles.

• Right kidney is a bit lower than the other.

The reason for this is to accommodate the liver.

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Structure of the kidney

1-External appearance 13 cm long

6 cm wide

Bean shaped

2-Internal structure of the kidney

Two major parts of kidney.

1- Cortex 2- Medulla

• Colour of the cortex- Dark colour

• Reason for the dark colour - Consist of lot of blood capillaries.

• Two main blood vessels – 1-Renal artery 2-Renal vein

Functions of blood vessels.

• Renal artery – Supply blood to the kidney.

• Renal vein – Carries away the blood from kidneys.

Renal pyramids.

Triangular shaped structure can be seen in the internal structure of the kidney.

Renal pyramids are directed towards the pelvis of the kidney.

The process of urine production

Renal artery brings blood with excretory products to the kidney

Filtered Fluid with excretory products (urine)

Through ureter to the urine bladder

Temporarily stored in bladder

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Urination

When the bladder is full a person urinates through the urethra.

Urination also known as elimination.

Composition of the urine

Component Percentage

Water

Urea

Salt (More Salt chloride)

Uric acids

Diseases of urinary system

Disease Reason Disease situation

Not drinking enough water.

Taking salty diets regularly. Not

passing urine at proper time.

Calcium oxalate

deposited in the kidney

and form crystalline

structures

Entering of heavy metals and toxic

chemicals. Suffering from diabetes

for longtime. Using drugs for a

long time period. Smoking and

taking liquor.

Functioning of kidney

disorderd

Not practice good health habbit of

urinary system. Infecting of urethra by

microorganism

How maintain the healthy kidney

1-Drinking enough pure water daily.

2-Quit smoking and liquor.

3- Control the blood sugar levels.

4-If a person takes medications regularly over a prolonged period, he should take

them to the prescribed dosage.

5- One should concern about the cleanliness of the surrounding area.

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Nervous system

Sensory of the human body

Organs helps to obtain sense of the environment

Sense organ Sense

Vision

Tasty

Sound

Hotness, Coldness

Smell and odour

• Nerve system helps to coordination of the human

body.

Do you know what is known as coordination is?

Identify the receptor and effector

Receptor – Sensory organs

Effector - Organs responding the stimuli taken by receptors

Examples- Tissues and glands

Recepter Responce Effector

Tasty Salivation Salivary glands Ear Close ears by hands Muscles of the hands

Skin Sweating Salivary glands

Keep a good interaction between the receptors and

effectors to react for the changes occur within the

internal body of humans as well as in his surrounding

environment.

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Coordination What is known as coordination?

………………………………………………………………………

………………………………………………………………………

………………………………………………………………………

Types of coordination

1- Nervous coordination - Controlling various functions of

our body by the nervous system.

2- Endocrine coordination- Coordinating the body organs by

hormones.

Nervous coordination • This co-ordination is done by nervous system.

Major parts of the human nervous system given below.

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Parts of the brain

1- ……………………..

2- ……………………..

3- …………………….

Cerebrum

Cerebellum

Medulla oblangata

Central nerve system Two main organs of the central nerve system

1- Brain 2- Spinal cord

How protect the brain and spinal cord?

Brain - Skull

Spinal code - Vertebral column

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Meninges The tissues which protect the brain and the spinal cord.

Fluid in meninges - Cerebro-spinal fluid.

Functions of cerebrospinal fluid. 1- Absorb shocks.

2- Supply nutrients.

3- Prevents the central nerves system from microbial infections

Functions of central nervous system Part Function

Cerebrum/cortex 1-Controls higher brain functions such as

thought, intelligence.

2-Recognition of senses. 3-Controls

the movements of muscles with the intent

to perform a specific action (controlling the

voluntary actions)

Cerebellum Regulation and coordination of body

balance.

Medulla Controls the automatic functions

(nonvoluntary functions) such as heart

beat, breathing.

Spinal cord Relays messages from the brain to

different parts of the body.

Peripheral nervous system. All the nerves that lie outside the spinal cord and brain.

Peripheral nervous system

Spinal Nerves Cranial Nerves

31 pairs 12 pairs

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Cranial nerves

Spinal nerve

Functions of peripheral nervous system. 1- Transmitting impulses from receptors to the central nervous system.

2- Transmitting impulses from receptors to the effectors.

What is known as impulse? An electrical signal that travels along a nerve is called an impulse.

Activity 9.3

Study the difference of speed of impulses in human nerve.

Things need - 30 cm ruler

Method

1-Ruler was taken vertically in to the hand.

2-The ruler was made free from your hand and ask your friend to

catch it.

3-Touched reading of the ruler was recorded.

4-Activity was repeated with different students

Observation

Student Reading

1

2

3

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Conclusion

Each student gets different readings. Because, Speed of impulses differ

from each person.

The dropping of the ruler is recepted from the eyes. The message is

transmitted to the brain and is returned to the effector, the muscles of

the right hand. Then, the right-hand responses.

Most important part of the nerve system Brain Spinal cord

These organs are very fragile. Therefore, they should be protected.

Protective measures of brain and spinal cord.

1- Maintaining a balanced nutrition.

2- Prevent children facing accidents.

3- During pregnancy mother should get proper nourishment.

4- Be sure to get the correct posture during sports, exercises in daily

life and lifting a burden to force.

5- Control mental stress.

6- Avoid excessive keeping awake sleepless.

7- Engage in intelligence development activities.

8- Never move anyone who you think have a spinal injury unless it is

very necessary.

Attention

In an accident there is more possibility for spinal cord injuries. Never move

anyone who you think have a spinal injury unless it is very necessary. Keep the

person absolutely still and safe. Do not allow the body to bend or twist. Keep the

person on a wooden flat surface and rush to the nearest hospital.

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Human skin Skin is the largest organ in our body.

Important things about skin

• It weighs about 4.5 kg

• its thickness is about 1-2 mm in an adult.

Structure of the kidney

Layers of the kidney

• Skin mainly consists with two layers.

1. Epidermis 2. Dermis

3D structure of the kidney

Structure of the human skin

Two glands of the skin – 1- ……………………. 2-……………………

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Important things about skin

Information of epidermis.

Location – outermost layer.

Number of cell layers – several layers.

Heeding and replenishing – Thousands of dead cells

replenishing daily.

Colour gives by – melanin.

Function of pigments – To protect us from sun’s ultra violet

rays.

Information of dermis. Location – beneath the epidermis

Composition – hair, sweat glands, sebaceous glands

Thickness – thicker than the epidermis

Beneath layer – hypodermis Structure of the human skin

Functions of the human skin 1. Protective layer of the body 2. Regulation of body temperature 3. Acting as a sensory organ 4. Synthesis of vitamin D

Mention the functions of the followings.

1. The layers of the epidermis

Minimize water loss from the body and prevent from dehydration.

2. Melanin pigments

Protects the body from ultra violet rays.

3. Sebaceous gland

The secretion from sebaceous gland act as a barrier against

microorganism infections. This is a natural defense mechanism.

4.Sweat glands

Regulation of body temperature

When temperature increases - sweat glands secrete sweat to release

heat

When temperature decreases - blood supply to the surface of skin

prevented and secretion of sweat minimize.

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5.Nerve endings

Detect the pressure, touch and temperature.

6.Cells of the skin

Using the energy of sunlight, vitamin D is synthesized

Maintain a healthy skin.

Some tips that help to maintain a healthy skin.

Important practices to maintain a healthy skin.

1- Eat nutritious diet

2- Be gentle to your skin o Protection from sun

3- Avoid smoking and smokers

Skin disorders.

1-Pityriasis 2-Removal of skin 3-Warts

4-Eczema 5- Heel getting dry Acne

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Unit – 10

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Electricity

Electric current The flow of electric charges through a circuit.

Electric circuit The path of an electric current is called an electric circuit.

Necessary condition to flow current through a circuit Conductors.

Closed circuit.

Electric sources

The things which produce electricity are called sources of

electricity.

Example- Battery,Dry cell,Solar panel

Components of the electric circuit.

Bulb, Battery,Conneting wires,Switch

Various methods of connecting cells and bulbs

There are two methods of connecting cells and bulbs.

1- Series connection. 2- Parallel connection.

Series connection of batteries/cells

1-Two or more cells connect one after the other

2- Positive and negative terminals of cells are connected

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Activity

Find out methods of lighting a bulb, using several 1.5 V dry

cells

First connect one dry cell with the bulb and the switch

Circuit Circuit diagram V Brightness

1.5V Less

Next connect two dry cells with the bulb and the switch


3.0V Bit more

Next connect three dry cells with the bulb and the switch


4.5V High

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Parallel connection of dry cells. Another method of connecting the cells in a cell system

(battery)

Two dry cells parallel Three dry cells parallel

In this connection, positive terminals of all the cells are

connected to one point and the negative terminals of them are

connected to another point.

First connect one dry cell with the bulb and the switch

Circuit Circuit

diagram

Brightness

Same

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Circuit Circuit diagram Brightness

Same


Circuit Circuit diagram Brightness

Same

• The current flowing through the bulbs is equal, in a

parallel connection of the batteries.

• When cells are connected in this manner, each cell

supplies less current.

• The collection of current supplied by cells is equal to

current supplied by one cell.

• When cells are connected parallelly bulb can light for a

longer time thus cells can last a longer time.

Therefore,

When current should be supplied for a long time to an electrical

equipment parallel cell system are used.

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Systems of bulbs

Two simple methods of connecting several bulbs to circuits. 1-Series bulb connection.

2-Parallel bulb connection

Series bulb system First connect one bulb with a switch and a cell


1.5V Less



1.5V Bit more



1.5V High

Conclusion- The brightness of the bulbs decreases, with the

increase of bulbs connected in series across a voltage supply

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Parallel bulb system

First, connect one bulb to a cell and a switch


Same

Connect two parallelly connected bulbs to a switch and a cell


Same

Connect three parallelly connected bulbs to a switch and a cell


Same

• The brightness will not significantly change even though

the number of bulbs, connected in parallel are increased.

They all will light with almost the same brightness.

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Simple electric circuits

Electric torch

Name diagram of an electric circuit of an electric torch

• There are electric torches with only one dry cell or

with several dry cells connected in series.

How bulb is lighted up of a torch?

When the switch is pushed forward, the gap between the

conducting connectors is closed and the bulb is lit

Function of the reflector

• To make the non-parallel light rays emit by the torch bulb

as parallel.

• To have more parallel light rays.

Circuit diagram for an electric torch

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Light decoration

Make a light decorating circuit. Things needed - Power supply 6V Six color LEDs Connecting

wires Copper strips

Method

Circuit was made and switches were connected as in the figure.

Essential

• Make the circuit on a board.

• Take all switches to one place of the board. Supply power to the

circuit.

current controlling components of the electric circuits.

1- Switches 2- Tap keys 9- Plug key Reason of using copper wires to connect circuits.

Because their resistance is very low.

The suitable metals to make resistors.

Wires made of nichrome, manganin.

(b). Reason. - Resistance is very high.

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Switches Switches or keys are used to turn on or turn off an electric current

flow through a circuit when necessary.

Various types of keys

Tap key

This switch is used to let the current to flow one direction.

This is called one-way direction

switch.

Plug key There is a gap between the metal

blocks made by brass.

How does switch is works?

When the plug rod is inserted into

the hole between the gap, the circuit

is closed.

When the plug rod is removed, circuit is disconnected.

Resistors Resistors are used to make a resistance for the circuit.

What are known as resistance?

Obstacle to flow an electric current through a conductor.

Resistance

Components that have the property of resistance

Types of resistance

1-Fixed resistance

2-The resistors, value can be changed?

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i. Variable resistance.

ii. Rheostat

iii. Light dependent resistor

Functions of resistance

1.Fixed resistance -

The resistance which having an exact resistance value.

Therefore, they also can be considered as permanent resistors.

Function-Reduce the electric current of a circuit.

An activity to study the relationship between resistance and the

flow of current.

Activity 10.6

Make following two circuits.

Circuit diagram

Circuit diagram

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Observation

Instance Observation

Bulb Ammeter

Without permanent resistor Brightness

high

With permanent resistor of 2 Ω Brightness

few

With permanent resistor of 5 Ω Brightness

less

Conclusion

• When the resistance of the circuit increased further current

flowing decreases.

• Therefore, it is clear that the current flowing through a circuit

can be reduced by connecting fixed resistors to increase the

resistance.

2-The resistors, value can be changed.

iv. Variable resistance.

v. Rheostat

vi. Light dependent resistor

Variable resistance

An activity to observe the relationship between current flow

and resistance of a circuit using variable resistor.

Activity 10.7

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Observation

current flowing through the circuit decreases when the

resistance is increased.

The disadvantage of variable resistor.

Electric current cannot be changed to a definite value

Rheostat

The advantage of rheostat than variable resistor.

Electric current can be changed to a definite value

• Slider move backward-

Resistance decreased

• Slider move forward-

Resistance increased

An activity to demonstrate

the use of rheostat.

Activity 10.8

Observation

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Light dependent resistors.

o Resistors that change their resistance when light falls on them

Activity 10.9

Explain an activity to demonstrate the action of light

dependent resistor.

1.When light falls on a light dependent resistor its resistance decreases.

Therefore, current flowing through the circuit increases.

2.When the intensity of light falling increases, the resistance decreases.

Therefore, current flowing through the circuit increases further.

Soldering tools The use of soldering tools is connected the component to the

circuit.

How this soldering is done? Use Electric bouth.

How does it work?

• When electricity is supplied to the tool the tip

of this tool gets heated. So, the melted soldering

lead is applied to the joints of the circuit.

• Then joints are firmly connected by soldering lead and are not

disconnected.

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House hold electric appliance

The electrically powered appliances used in house.

Tabulate appliances according to their use.

Important facts that should be considered when using electrical

appliances.

1. Selection of an appliance to suit the need.

2. Selection of an efficient appliances

3. Safe use of appliances, so that user and the others are out of

danger.

4. Usage of household electric circuit and the appliances without

getting damaged.

Effects of current

1.Heating effect

2. Light effect

3. Magnetic effect

4 Chemical effect.

Heating effect

When an electric current is flowing through a wire, electric

energy is transformed to heat.

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Some electrical appliances in which the heating effect of electricity

is effectively used.

Name of the appliance Purpose

Electric iron

Rice cooker

Heater

Hot plate

Oven

Hair dryer

……………………………………………….

……………………………………………….

……………………………………………….

……………………………………………….

……………………………………………….

……………………………………………….

Activities and observation and reason for the observation.

The bulb has heated after the flow

of electricity for some time

same electric current flows

through both wires. But nichrome

wire is heated more than the

copper wire.

Factors effecting on heating effect of electric current.

o Resistance. o Flow of electricity.

Heating effect of electricity is a disadvantage in some electrical

appliances.

Some methods are used to avoid this.

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Lightning effect of electric current This emission of part of the electric energy as light energy is known as

the light effect of electric current.

Light emitting diodes (LED) The diodes that emit light are known as Light emitting diodes

(LED)

When electricity flows through junction diode.

a) Some electricity is emitted as heat.

b) Some electricity is emitted as light.

Light emitting diodes.

a) It emits various colors of light.

b) Emitting color depend on compound used to make the

junction of LED.

c) Some emits several colors.

Uses of LEDs.

Emit various colors.

Indicators.

Light decorative purposes.

Symbol Internal strucutre

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Magnetic effect of electric current

Generation of a magnetic field around current carrying

conductors.

Activity 10.13

Place the compass under the stretched copper wire.

Close the switch. The bulb will light and a deflection of the compass

needle can be observed.

Observation

Compass needle deflects.

Making electro-magnet.

Observation

pins are attracted.

The strength of an electromagnet depends on,

1-The type of core in the coil

2-The electric current flowing through the coil

3-The number of turns of the coil.

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Uses of electromagnets.

In some electrical appliances, electro magnets are used.

Electric fans electric bells electric grinders,

electric water pumps, washing machines,

some automatic switches

Assignment 10.5

Electric bell

Chemical effect of electric current

When electricity is supplied to two electrodes dipped in

electrolyte, electrical energy is converted to chemical energy.

An activity to demonstrate chemical effect of electricity

Observation Bubbling of gas can be observed near

the carbon rod, when the dry cells

were removed no bubbling can be

observed.

Electroplating

Electroplating is an instance where

the chemical effect of electric

current is used.

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Plating of one metal on another metal using chemical effect of

current.

The uses of electroplating.

1.Plating gold silver on jewelry.

2.Plating metals on iron to prevent iron from rusting.

Eg – chromium Nickel

3.Plating tin inside iron containers, used for canning food

Observation Spoon dipped in copper sulphate solution has turned copper

colour.

Conclusion One element can plate on other element using electricity.

NOTES PACK - President Girls' College · 2020. 6. 2. · 5 GRADE8 -SCIENCE NOTES MERVIN SIRIWARDANA...

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Transcript of NOTES PACK - President Girls' College · 2020. 6. 2. · 5 GRADE8 -SCIENCE NOTES MERVIN SIRIWARDANA...