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8th Std Science English Medium 2nd Assignment July 2021(With Answers)

8th Std Science English Medium 2nd Assignment July 2021(With Answers) :- This is the full answerkey for 8th standard july month second assignment. students Can download this answerkey via google drive.The direct link to download 8th tamil 2nd assignment for july month is shared in the bottom section.

8th Std Science English Medium 2nd Assignment July 2021(With Answers)

8th Science EM 2nd Assignment July 2021(With Answers)

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ASSIGNMENT

Class: 8 Subject: Science(Physics)

Part A

UNIT-2 Force and Pressure


I.One Mark Questions.

1.Atmospheric pressure ————-with altitude from the surface of the
earth.


a) Increases

b) decreases

c) first decreases then increases

d) does not change

Answer: a) Increases


2.Pascal’s law is used in


a) hydraulic lift

b) brake system

c) pressing heavy bundles

d) all the above

Answer: d) all the above


3.Why more number of wheels are set on heavy vehicles?


a) to increase the pressure
b) to increase the area of contact on the road
c) to increase the speed
d) to control the speed

Answer: b) to increase the area of contact on the road


4.The SI unit of atmospheric pressure is ———-


a) Newton/metre2

b) Newton/metre

c) Newton

d) Joule

Answer:


5.The factor that determines whether a substance floats or sinks in a liquid


a) upward force

b) downward force

c) gravitational force

d) frictional force

Answer: a) upward force


Part B

II. Short Answer.

1.State Pascal’s law.

Pascal’s law : The pressure applied at any point of a liquid at rest, in a closed system, will be distributed equally through all regions of the liquid.


2.Camels can walk easily on the sand. Why?

Camels can walk easily on it because they have large padded feet,which increase the area of contact with the sandy ground


Water spider insect slides on the water surface easily. Give reason.

Water strider insect slides on the water surface easily due to the surface tension of water



Part C


III. Answer in detail.

a) What is friction? Write their types.

Friction : Friction is a force that shows down moving objects or prevents stationary objects from moving.

Static Friction

Kinetic Friction



b)Write advantages and disadvantages of friction.

Advantages of friction : Friction is a necessity in most of our day to day activities. It is desirable in most situations of our daily life.

  1. We can hold any object in our hand due to friction.
  2. We can walk on the road because of friction. The footwear and the ground help us to walk without slipping.
  3. Writing easily with a pen on paper is due to friction.
  4. Automobiles can move safely due to friction between the tyres and the road. Brakes can be applied due to frictional resistance on brake shoes.
  5. We are able to light a matchstick, sew clothes, tie a knot or fix a nail in the wall because of friction. Though it is giving a negative effect, in most of our day to day life friction helps us to make our life easy. So, it is called as “necessary evil”.

Disadvantages of friction:

  1. Friction wears out the surfaces rubbing with each other, like screws and gears in machines or soles of shoes.
  2. To overcome the friction an excess amount of effort has to be given to operate a machine. This leads to wastage of energy.
  3. Friction produces heat, which causes physical damage to the machines.

ASSIGNMENT

Class: 8 Subject: Science(Chemistry)

Part A

UNIT- 10 Changes around us

I. Choose the correct answer.

1.What kind of changes take place in the following?


i) sugar dissolved in water
ii) strong heating of sugar


a) i) and ii) – Physical change

b) i) and ii) – Chemical change

c) i) – Physical change, ii) – Chemical change

d) i) – Chemical change, ii) – Physical change

Answer: c) i) – Physical change, ii) – Chemical change


2.In which of the following, new products are formed?


a) Physical change

b) Chemical change

c) Reversible change

d) None of the above

Answer: b) Chemical change


3.The chemicals in the head of a matchstick


a) Red phosphorous

b) White phosphorous

c) Potassium chlorate and antimony trisulphide

d) Sliver nitrate

Answer: c) Potassium chlorate and antimony trisulphide


4.In which state, sodium chloride and silver nitrate undergo chemical changes


a) solid – liquid

b) liquid- solid

c) solid-liquid

d) liquid-liquid

Answer: d) liquid-liquid


The chemical reactions proceed only by the passage of electricity in


a) Electrolysis

b) Conductors

c) Electroplating

d) Electricity

Answer: a) Electrolysis


Part B

II. Short Answer.

1.What happens when quick lime comes into contact with water?

When quick lime comes into contact with water. It forms slaked lime


2.What is Exothermic and Endothermic Reaction?

Chemical reactions accompanying evaluation of heat are called exothermic reactions


3.When a small amount of lead nitrate taken in a dry test tube and heated gently over a flame, what changes would occur?

Hear cracking sound and evolution of reddish brown coloured gas


Part-C

III. Answer in detail.

a) Explain the electrochemical reaction and thermo chemical reaction.

Electrochemical Reactions:

Some chemical reactions proceed only by the passage of electricity, Hence,such reactions are called as electrochemical reactions

Thermo Chemical Reactions:

Some chemical reactions can be achieved by the supply of heat only, These reactions are called thermo chemical reactions.



b) Write down the chemical changes in the following:


i) Spoilage of food and vegetables

Spoilage of food and vegetables:
Food spoilage may be defined as any change that causes food unfit for human consumption. The chemical reactions catalyzed by the enzymes result in the degradation of food quality such as development of bad taste and odour, deterioration and loss of nutrients.

Example 1 : Rotten eggs develop a bad smell due to formation of hydrogen sulphide gas.
Example 2 : Decaying of vegetables and fruits due to microbes.


ii) Rancidity of fishes and meat

Rancidity of fishes and meat:
Fishes and meat containing high levels of polyunsaturated fatty acids that undergo oxidation causes bad odour when exposed to air or light. This process is called rancidity.


iii) Apples and fruits turn brown when we cut.

  • Apples and some fruits turn brown due to chemical reaction with oxygen in air. This chemical reaction is called browning.
  • The cells of apples, fruits and other vegetables contain an enzyme called polyphenol oxidase or tyrosinase, when come in contact with oxygen catalyses a biochemical reaction of plants, phenolic compounds to brown pigments known as melanins

Part-D

IV. Activity


Categorize the given chemical substances and write their effects in the given
table.


Methane, detergents, carbon dioxide, plastics, oil spillage, oxides of sulphur, solid wastes, dyes, herbicides, carbon monoxide, oxides of nitrogen, pesticides, chlorofluorocarbons.

Types of PollutionChemical Substances Effects
Air PollutionCarbon dioxide, Carbon monoxide, Oxides of sulfur,oxides of nitrogen, Chlorofluorocarbons, Methane EtcAcid rain, global warming, respiratory problems, etc.
Water PollutionWastewater containing chemical substances, Eg., Dyeing industries, Detergents, Oil Spillage, etcDecrease in the quality of water, Skin disease, etc
Land PollutionFertilizers like urea, various pesticides, herbicides, solid wastes, plastics, etcSpoilage of land, cancer, respiratory diseases, etc



ASSIGNMENT

Class: 8 Subject: Science(Biology)

Part- A
UNIT- 17 Plant Kingdom


I. Choose the correct answer.

In how many ways does algae reproduce?


a) 1

b) 2

c) 3

d) 4

Answer: c) 3


The meaning of sperma is


a) Seed

b) Fruit

c) Flower

d) Sperm

Answer: d) Sperm


The antibiotic penicillin is obtained from


a) Algae

b) Fungi

c) Pteridophytes

d) Bryophytes

Answer: b) Fungi


The plants which are called as naked seed plants


a) Angiosperms

b) Gymnosperms

c) Thalophyta

d) Pteridophyta

Answer: b) Gymnosperms


An organism gets food from another living organism is


a) Carnivore

b) Decomposer

c) Parasite

d) Saprophyte

Answer: c) Parasite


Part- B

II. Short Answer.

1.What do you mean by Lichens?

A organism that arise from the algae and this is in a symbiotic relationship. lichens formed by the 2 other plants

Algae living with fungi and both are mutually benefitted like lichens


2.Bryophytes are called as amphibians. Why?

Water is essential for bryophytes to complete their life cycle. So they are called as amphibians of the plant kingdom.


3.What is meant by Herbarium?

Herbarium is the collection of pressed dried plants pasted on a sheet and arranged according to any one of the accepted systems of classification


Part- C

III . Answer in detail.


1.Write the Economic importance of fungi.

Antibiotic :
Penicillin (Penicillium notatum), Neomycin, Gentamycin, Erythromycin are some antibiotics obtained from fungi, which cure variable diseases.

2. Food:
Mushroom contains rich protein and minerals. The most common edible mushroom is Agaricus. (Button mushroom)

3. Vitamins :
Fungus like Ashbya gospii and Erymothecium ashbyii are used to produce vitamin B? (riboflavin).

4. Alcohol:
Fungus like yeast contain enzymes invertase and zymase, which ferment the sugar molasses into alcohol


Part- D

IV. Activity
With the help of your parents, collect the medicinal plants found around your house and complete the following table.

S.NoVernacular
name
Binomial
name
Part used
asmedicine
(leaf/stem/root/flower/fruit)
Uses
1KuppaimeniAcalypha indicaPast obtained from LeaveCure burns on skin,cure ringworm
2VilvamAegle marmelosunripe fruit treat indigestion,chronic, diarrhoea and dysentery
3.ThoothuvalaiSolanum trilobatumleaves and fruitscough,cold,for tuberculosis and bronchial asthma
4.KeezhanelliPhyllanthus amarusentire plant jaundice,liver disorders
5.Sothu katrazhaiAloe veraLeaves cure piles and inflammation, cures peptic ulcer