Punjab Board Nots

Notes of Science for Class 8th

CHAPTER # 1

HUMAN ORGAN SYSTEM

 1) Define nervous system

The organ system in our body that carries messages from one part of the body to another part and coordinates body functions is called nervous system.

2) What is CNS?

 CNS means central nervous system that includes brain and spinal cord.

3) What is PNS?

 PNS means peripheral nervous system that includes a network of nerves connecting the central system to whole body.

4) Define Neuron or Nerve Cell.

Neuron or nerve cell is the basic structure and functional unit of the nervous system. All parts of the nervous system are made up of neurons.

5) Define Nerve impulses.

Neurons carry messages in the form of electro-chemical waves called nerve impulses.

6) Define cell body.

The part of neuron containing nucleus and most of the cytoplasm is called cell body.

 7) Define Dendrites.

A fine projection of the cell body that receives messages is called dendrites.

8) What is Axon?

A long projection of the cell body that conducts messages away from the cell body is called axon.

9) Define Nerve.

It is an enclosed, cable like bundle of axons present side by side in a common sheath. Nerve conveys messages carried by the individual neurons from one body part to another.

 10) How many types of neurons are there?

There are three types of neurons on the basis of functions

1. Sensory neurons

2. Motor neurons

3.Inter neurons

1. Sensory neurons

It carries nerve impulses from sense organs (ears, eyes, skin, tongue, nose etc) to the central nervous system (CNS). which respond.

2. Inter neurons

These are present in CNS. They form a link between sensory and motor neurons.

11) Write the names of main parts of the followings

1. Forebrain

It consists of three main parts

i.Cerebrum

ii.Thalamus

iii.Hypothalamus

2. Hindbrain

It consists of three main parts

i. Cerebellum

ii. Pons

iii. Medulla oblongata

3. Neuron

It consists of three main parts

i. Cell body

ii.Dendrites

iii. Axon

4. Nephron

It consists of two main parts

i. Renal corpuscle

ii. Renal tubule

12) Write the function of the followings

1. Forebrain

It is the largest part of the brain. It consists of three main  parts

i. Cerebrum

ii. Thalamus

iii. Hypothalamus

Cerebrum is the topmost and the largest part of the brain. It controls many actions like thinking, feelings, emotions, seeing, hearing, perceptions, memory, speech, decision making, etc.

Inside cerebrum there is a small structure called thalamus. It controls many sensory functions. Hypothalamus lies at the base of thalamus. It controls body temperature, hunger and thirst.

2. Hindbrain

It consists of three main parts

i. Cerebellum

ii.Pons

iii. Medulla oblongata

Cerebellum lies under the back part of cerebrum. It acts as a controller for maintaining balance and accurate movements. Pons is oval structure and present beneath the midbrain. It controls many function like sleeping, swallowing,

2. Motor Neurons

It carries nerve impulses from central nervous system (CNS) to effectors (muscles and glands), i.e. the parts Medulla oblongata is connected with the spinal cord. It controls heartbeat, breathing and digestion etc. it also keeps working when rest of brain goes to sleep.

3. Neuron or Nerve Cell

Neuron or nerve cell is the basic structure and functional unit of the nervous system. All parts of the nervous system are made up of neurons. It consists of three main parts

i. Cell body II. Dendrites III. Axon

i. Cell body

The part of neuron containing nucleus and most of the cytoplasm is called cell body.

ii. Dendrites

A fine projection of the cell body that receives messages is called dendrites.

iii.Axon

A long projection of the cell body that conducts messages away from the cell body is called axon. Terminal ends of the axons transmit the messages to the next cells.

Axon

4. Nephron

It is the functional unit of kidneys. It consists of two main parts

  1. Renal corpuscle
  2. Renal tubule

These are the tubules where urine is formed. There are over one million nephrons in each kidney.

13) Skin is considered as excretory organ. Why?

Because some extra salts are also removed through skin during perspiration.

14) Differentiate between  

Receptors

Effectors

The special organ tissue which detect any change in environment is called receptors

The parts respond after receiving nerve impulses through motor neurons is called effectors

Neuron

Nerve

Neuron or nerve cell is the basic structure and functional unit of the nervous system. All parts of the nervous system are made up of neurons.

It is an enclosed cable like bundle of axons present side by side in a common sheath. Nerve conveys messages carried by the individual neurons from one body part to another

Voluntary actions

Involuntary actions

The body actions which are performed under conscious control. These actions are done after thinking. e.g. speaking, eating, reading, walking, running, etc

The body actions which are performed without thinking over them under conscious control are called involuntary actions. e.g. Heartbeat, blood circulation, blinking of eyes etc

Kidneys

Lungs

Human body has two dark brown, bean shaped kidneys in the abdominal region. The main function is removing waste material from the body in the form of urine

Lungs are present in the thorax cavity in pair form. Lungs make oxygenated blood and remove carbon dioxide from the blood.

Lithotripsy

Dialysis

It is the bombardment of shock waves on the stones from outsides. Shock waves break the stones into small pieces which are passed out of the body in the form of urine

Clearing of blood by artificial methods is called dialysis. It is done by dialyzer.

15) Explain central nervous system.

CNS acts as a control Centre of the whole nervous system. It contains brain and spinal cord.

Brain

Human brain is enclosed in a bony skull called cranium. It divided into following parts.

1. Forebrain

It is the largest part of the brain. It consists of three main parts

  1. Cerebrum
  2. Thalamus
  3. III. Hypothalamus

Cerebrum is the topmost and the largest part of the brain. It controls many actions like thinking, feelings, emotions, seeing, hearing, perceptions, memory, speech, decision making, etc.

Inside cerebrum there is a small structure called thalamus. It controls many sensory functions.

Hypothalamus lies at the base of thalamus. It controls body temperature, hunger and thirst.

2. Midbrain

It is a small part of the brain that is present below cerebrum. It receives information from sense organs and sends messages to concerned part.

3. Hindbrain

It consists of three main parts

  1. Cerebellum
  2. Pons
  3. Medulla oblongata

Cerebellum lies under the back part of cerebrum. It acts as a controller for maintaining balance and accurate movements.

 Pons is oval structure and present beneath the midbrain. It controls many function like sleeping, swallowing, equilibrium and taste etc.

 Medulla oblongata is connected with the spinal cord. It controls heartbeat, breathing and digestion etc. it also keeps working when rest of brain goes to sleep.

 4. Spinal Cord

 It is an extension of medulla oblongata. It runs backwards inside the backbone up to its lower end.

 It creates a link between brain and different body parts. It also controls some reflex actions and some other involuntary actions.

 16) Describe peripheral nervous system (PNS).

 PNS includes a network of nerves connecting the central system to whole body.

 The nerves which arise from brain are called cranial nerves. The nerves which arise from spinal cord are called spinal nerves. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves in human body.

 Describe the main parts of excretory system in man. It consists of one pair of kidneys and associated structure. i.e. two ureter, a urinary bladder and urethra.

 1. Kidneys

 Human body has two dark brown bean shaped kidneys in the abdominal region. The main function is removing waste material from the body in the form of urine. The outer surface of kidney is convex while the inner surface is concave.

 2. Ureter

 A tube which arises from each kidney and enters in urinary bladder is called ureter.

 3. Urinary bladder

 Ureter transports urine from kidneys to urinary bladder. Urinary bladder is a muscular sac which collects urine from both ureters.

 4. Urethra

 A fine tube through which urine is released from urinary bladder to the outside is called urethra.

 Write a note on internal structure of kidneys Each kidney is divided into three regions

 1. Renal cortex

It is the outer most region of kidney

 2. Renal medulla and renal pyramids

 Renal medulla is the middle regions which is divided into conical masses called renal pyramids.

 3. Renal pelvis

 It is the inner area where urine is drained. The urine from renal pelvis moves into ureter.

 19) Describe structure of nephron

 It is the functional unit of kidneys. It consists of two main parts

 i. Renal corpuscle

ii. Renal tubule

 These are the tubules where urine is formed. There are over one million nephrons in each kidney.

Axon

Renal corpuscle

It is the first part of nephron. It consists of two structures, i.e. glomerulus and Bowman’s capsule. Glomerulus is a tuft of blood capillaries formed by the division of small arteries.

Bowman’s capsules is a cup shaped structure enclosing glomerulus.

Renal tubule

It is start after bowman’s capsules. The first coiled part of renal tubule is called proximal tubule. The next part is U-shaped and is called Loop of Henle. The last part of the renal tubule is again coiled called distal tubule.

20) Define reflex action.

An immediate and involuntary response to a stimulus is called reflex action.

Quick pulling of hand just after touching the hot object is a common example of reflex action.

Explanation

When we touch hot object a nerve impulse is created in skin. It is carried by the sensory neuron to the spinal cord. The inter neuron transmit the impulse to motor neuron. They carried the impulse to muscles. The pathway of nerve impulse that complete a reflex action is called reflex arc. It consists of receptor, a sensory neuron, an inter neuron, a motor neuron and effectors.

21) Define Reflex arc.

The inter neuron transmit the impulse to motor neuron. They carried the impulse to muscles. The pathway of nerve impulse that complete a reflex action is called reflex arc. It consists of receptor, a sensory neuron, an inter neuron, a motor neuron and effectors.

22) What is renal failure?

It is a complete or partial failure of kidneys to work. The main cause of renal failure are

i. long term infection ii. Diabetes mellitus iii. Hypertension

Define diabetes

Diabetes mellitus is disease in which sugar level increases in the blood.

24) What is Hypertension?

It is a state of high blood pressure in the body.

25) What is dialyzer?

Clearing of blood by artificial methods is called dialysis. It is done by a machine called dialyzer.

26) What is kidney transplant?

In this method a kidney donated by some healthy person is grafted in the body of the patient. The donar of kidney may be blood relative or any other close relative.

27) Name any two waste materials produced by the human body

1: Urine 2: Feces

How stones are formed in the kidney and how can these be removed?

Sometimes kidneys cannot work properly to remove salt from blood. In such situation, the salts gather in kidneys and form stones.

Stones can be removed in three ways\

i. By drinking water II. Lithotripsy  iii. shockwaves

 

CHAPTER # 2

CELL DIVISION

Name two inheritable characters.

1.Eye colour

2.Skin colour

 Name two non-inheritable characters.

 1.Loss of any part of body does not transferred to children.

2. Some diseases like malaria, kidney-stone etc does not transferred to children

3) What is gene?

The basic physical and functional unit of heredity is called gene. Genes act as instructions to make molecules called proteins. Gene occur in pairs. Every hereditary character in an organism (tallness, eye colour) is controlled by a pair of genes. Genes are the sections of DNA molecule and are located on chromosomes

4) Define heredity

During reproduction, living things pass on their characteristics to their offspring. This process is called heredity e.g. colour of eye, skin colour, hair colour etc

5) What are haploid cells?

When an organism forms gametes (sperms or eggs) by meiosis, the number of chromosomes is reduced to half in the gametes, is called haploid cell.

6) Define cell division

It is a process by which a cell divides into two daughter cells.

7) What are parent cell and daughter cell?

During cell division the cell which divides is called Parent Cell and the cell which is produced as a result of cell division is called Daughter Cell.

8) What are chromatids?

A typical chromosome consists of two arms called chromatids, which are attached to the same part called centromere.

Axon

9)   Difference between Mitosis and Meiosis

     

Mitosis

Meiosis

During mitosis,            two

daughter         cells     are

produced from the parent

cell.                            

During meiosis,           four

daughter         cells     are

produced from parent           

                                   

The                  number           of

chromosomes   in       the

daughter cells remains the

same as in parent cell

The      number           of

chromosomes in         the

daughter         cells     is reduced

to  half  as  compared  to

parent cell                  

Mitosis occurs in general

body cells       

Meiosis occurs to produce

gametes          in         animal  or

spores in plants

Only     one      division

place in mitosis

Two division take place in

meiosis.

 

 

10) Name the cells produced by meiosis in plants and animals 

Plant:  Spores             Animals:                      Gametes

11) Define heredity and describe its importance in transferring characteristics from parents to offspring.

During reproduction, living things pass on their characteristics to their offspring. This process is called heredity for examples

i. Colour of eye ii.Skin colour iii. Hair colour

1. Free or attached earlobes

 i. Height ii) Intelligence

 12) Write a note on DNA

 DNA means Deoxyribonucleic acid. As different sections of DNA are a set of information for the development of different characters in an organism. So, DNA is called hereditary material.

13) What is Watson and crick Model of DNA?

Each DNA molecule is made of thousands of small units called nucleotides. There are four types of nucleotides in DNA.

i). Adenine (A) nucleotides   ii).Thymine (T) nucleotides  

iii). Cytosine (C) nucleotides    iv). Guanine (G) nucleotides

According to them, DNA molecule consists of two stands formed of nucleotides. These two are linked with each other by cross bands like a ladder.

14) Write a note on Chromosomes.

The nucleus of the cell contains thread like structures called chromosomes. Chromosomes are composed of DNA and proteins. They appear as distinct structures found in the nucleus of a cell. They appear as distinct structures only during cell division.

A typical chromosome consists of two arms called chromatids, which are attached to the same part called centromere.

CHAPTER # 3 

BIOTECHNOLOGY

 

 1)   What is biotechnology?

The technology in which living things are used in different ways to help and benefit human beings is called biotechnology.

2)   What is genetic testing?

It is one of the latest biotechnological techniques used for genetic diagnosis of inherited diseases. It involves the direct examination of DNA molecule. It is also used to determine a child’s paternity or a person’s ancestry.

3)   Briefly describe gene therapy

 It is an advanced biotechnological technique which is used to cure genetic and acquired diseases like cancer and AIDS. In the process, defective genes are supplemented or replaced by normal genes.

4)   Name two life saving products of biotechnology.

Insuline:          it is used for diabetes

Vaccines:         it is used against many infection disease.

5)   What is DNA replication?

The process by which DNA makes its copy is called DNA replication.

6)   What is genetic engineering?

It is an advanced technique of biotechnology in which scientist select and isolate the useful gene from one organism (donor organism) and insert it into another organism usually bacterium.

7)   What is transgenic organism?

The organism that contains a foreign gene in its cells is called transgenic organism.

8)   Why do scientists use bacteria in genetic engineering?

Bacterial cell is very simple and easy to handle for the scientists. It is easy for the scientists to isolate plasmid from a bacterial cell and attach a gene with it. Another reason is its fast rate of reproduction.

9)   What is genetic modification?

The change in the genes of organism using biotechnology techniques is called genetic modification.

10) What is GMO?

The organism whose genes are modified called genetically modified organism (GMO). GMO are also used to prepare useful and life saving products such as insulin and vaccines etc.

11) What is insulin?

Insulin is a human protein. In human body it is produced by pancreas. It controls the glucose level in blood.

12) What is vaccine?

Vaccine is a material which contains weakened or killed pathogens (disease causing germs) and is used to produce immunity against a disease.

13) How vaccine works?

When a vaccine is given to human body, the blood cells in the body take the dead or weak pathogens as real ones and prepare antibodies against them. These antibodies remain in blood when any real pathogens enters the body, the already present antibodies kill it immediately and the body becomes protected from disease.

14) What is diabetes mellitus?

If pancreas does not produce the required amount of insulin, the level of glucose in blood rises. This condition is known as diabetes mellitus.

Differentiate between herbicides and pesticides?

Herbicides are weed killing chemicals and pesticides are insect killing chemicals which are used to eliminate the crop enemies (weed and insects) such chemicals also cause damage to the crop plants.\

Which major crops have been modified?

Maize (corn), wheat, rice, conola, potato, soybean, cotton, etc

17) What are trying to produce Pakistani scientist?

They are trying to produce wheat higher production of iron in the flour. This may help to overcome iron deficiency in food.

18) Which insects damage the wheat crop? How can solve this problem?

Insects called aphids damage the wheat crop.

This problem can solved by producing aphid resistant varieties using genetic engineering techniques.

19) Describe the use of vitamin B12.

Vitamin B12 widely used as food addictive and in some medicines. It is produced in high yielding cultures of bacteria.

Name some biotechnology products and tell about their uses.

  1. Insulin:Useful for diabetes.
  2. Vaccine: Used against many infections disease.
  3. Beta Endorphin: A pain killer drug
  4. Interferon: Anti-viral proteins.

21) Define cloning.

 It is also amongst the latest biotechnological techniques used for treating various diseases. It can also be used for the production of animal organs.

 

CHAPTER # 4

POLLUTANTS & THEIR EFFECTIS ON ENVIRONMENT

 

 What are the main air pollutants?

 i) Carbon monoxide (CO) ii) Sulphur dioxide (SO2)

iii)  Oxides of nitrogen (NO & NO2)   iv) Chlorofluoro carbons (CFCs)

 

1.Name greenhouse gases.

i) Carbon dioxide ii). Methane

iii) Oxides of nitrogen iv). Water vapours

 

2.Name the acids which are present in acid rain.

i) Sulphuric acid ii) . Nitric acid

3. Why ozone layer is important?

Ozone layer prevents to enter ultraviolet (UV) rays to the earth. These rays are harmful for life.

 

4)   3R strategies stand for what?

3R stands for “Reduce-Reuse-Recycle”

 5) Write down the names of products which are recycled?

 i) Glass piece  

ii) Aluminum

iii). Steels cans

 v).Copper wires

 vi) Paper

 

6) Name common method used for solid waste management.

 i) Landfill

ii) Incineration III. Recycling

 

6) How does ozone depletion contribute towards global warming?

 UV rays can enter into the earth so the temperature of the earth is increasing and earth globe is getting warmer. This is called global warming.

 7) Sulphur dioxide is an important. From where does it enter the atmosphere?

 Sulphur dioxide is produced by burning of coal or oil in factories. Smoke released from thermal power stations usually contain Sulphur dioxide.

 8) Describe the adverse effect of carbon monoxide on human organ system.

 i) It causes headache.

 ii) It causes brain damage and respiratory problems.

 iii) When CO reaches our blood, it gets bonded with hemoglobin and reduced its oxygen carrying capacity.

 9) What is greenhouse effect?

 When sunlight falls on the earth, a small part of it is absorbed by the earth and is converted to heat energy. A part of this heat energy is reflected back to the atmosphere by the earth. Some gases present in the atmosphere e.g,

 i) Carbon monoxide (CO)

 ii) Sulphur dioxide (SO2)

 iii)  Oxides of nitrogen (NO & NO2)

These gases trap a part of the heat reflected by the earth causing increase in the atmospheric temperature. These gases are called greenhouse gases and the phenomenon is called greenhouse effect.

 

10) What is global warming? Write its effect on earth.

Due to greenhouse effect, the earth’s globe is getting warmer. This is called global warming Effects.

i) Ice in the Polar Regions and at the mountains melts, sea level rise and results in flood.

 ii) Climate of the World is changing.

 

11) What is ozone depletion?

 A layer in the upper atmosphere is called ozone (O3) layer.

 It prevents to enter ultraviolet (UV) rays to the earth.

 These rays are harmful for life.

 Chlorofluorocarbons (CFCs) react with ozone layer and cause thinning of ozone layer when leaked form air conditioners etc. Hence depletion is takes place and called ozone depletion.

Effects

 i) UV rays can enter into the earth and causes serious diseases like skin cancer, eye problems.

 ii) The temperature is increasing.

 

14) What is acid rain?

 Oxides of Sulphur and nitrogen (SO2 , NO, NO2) react with water vapours in the air and forms acids which make the rain water acidic.

 

Effects

i) Acid rain kills the aquatic life in rivers and ponds.

 ii) Acid rain destroys the leaves of trees.

 iii) Acid rain destroys the metals and stones in buildings IV. Crops do not grow in acidic soil.

 

15) Point out the sources of air pollutants you find in your locality and suggest ways to reduce the pollution.

 

Sources of pollutants

 i) Vehicle’s smoke II. Industrial smoke III. CFC in aerosol spray IV. Rotting vegetation

 Methods to reduce pollution

 i) Public transport should be used instead of personal cars.

 ii) Sulphur and lead free fuel should be used in vehicles III. Factories should be shifted away from urban areas.

 iii) CFC free products should be used.

 iv) Deforestation should be avoided.

 

16)Suggest what can following communities do to reduce air pollution.

 i) Students

By keeping the environment clean

They can make awareness among people to reduce harmful human activities.

By planting new plants.

ii) Farmers

By planting more and more trees

By keeping fields greens throughout the years.

By making artificial forests to reduce pollution.

iii) Factory owners

Factory wastes must be treated before disposing them.

Waste should be neutralizes before entering in the air.

 Factories should be shifted far from urban areas.

 iv) cientists

Scientist must recycle chemicals and solids

Less use of resources must be done.

Wastage of resources must be stopped and checked.

What is deforestation? Explain its effect on wild life.

Destruction of forests due to human activities is called deforestation.

Effects

It destroys habitats of wild life.

Extinction rate of wild life is increased.

 

What types of climatic changes can appear by deforestation?

Due to deforestation, the rate of evaporation is reduced which results in less rain.

Greenhouse effect  is increased  which results  in global warming.

 

19) What is recycling?

In this method, plastic items, glass pieces, aluminum, steels cans, copper wires, etc are collected separately cleaned, melted and moulded into new products. In this way, they are used again and again to reduce pollution.

 
What should we do to adopt 3R strategies for conservation of resources?

Reduce

By reducing the use of non-biodegradable objects and the resources that are used in their manufacture should be conserved.

Reuse

Secondly, reuse of non-biodegradable objects again and again instead of throwing them after first use.

Recycle

Thirdly, plastic items, glass pieces, aluminum, steels cans, copper wires, etc are collected separately cleaned, melted and moulded into new products