Living Science Solutions for Class 8 Science Chapter 20 Summative Assessment Sa I are provided here with simple step-by-step explanations. These solutions for Summative Assessment Sa I are extremely popular among Class 8 students for Science Summative Assessment Sa I Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science Book of Class 8 Science Chapter 20 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science Solutions. All Living Science Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

Page No 133:

Question 1:

Name three plant diseases caused by microorganisms. Name the microorganism each is caused by and how each disease spreads.

Answer:

The three plant diseases caused by microorganisms are:
(a) Citrus canker: It is a bacterial disease that affects trees of citrus fruits and is spread by air.
(b) Yellow vein mosaic: It is a viral disease that affects vegetables such as bhindi. It is spread by insects.
(c) Rust of wheat: It is a fungal disease that spreads by air and seeds.

Page No 133:

Question 2:

Discuss the properties of nylon that make it such a useful fibre.

Answer:

Following properties make nylon a useful fibre: 
(a) Nylon is very strong and elastic. Its thread is stronger than a steel wire.
(b) It is light and wrinkle resistant.
(c) Nylon is also wear resistant. This is the reason why nylon garments last for a long time.
(d) It is easy to wash and absorbs very little water. Therefore clothes made from nylon dry quickly.  

Page No 133:

Question 3:

What are fossil fuels? Discuss why they are an important source of energy for us today.

Answer:

Coal, petroleum and natural gas are called fossil fuels, as they are naturally formed from the remains of organisms. Fossil fuels are concentrated stores of energy and give off heat and light on burning. The heat can be used to cook food or run engines (such as automobile engines). They can also be used to generate electricity in powerhouses (the most common fuel in many powerhouses is coal). Thus, fossil fuels are an important source of energy for us today.

Page No 133:

Question 4:

Explain with the help of a diagram, how binary fission takes place in Amoeba.

Answer:

Binary fission is the simplest type of asexual reproduction and is seen in single-celled organisms such as Amoeba. First, its nucleus divides into two equal halves. Then the cytoplasm also divides into two parts, each part receiving a nucleus. The two daughter cells thus formed grow and attain full size before they split again. 

Page No 133:

Question 1:

Which is the best method of irrigation when there is scarcity of water?

Answer:

Drip irrigation is the best method of irrigation when there is scarcity of water.

Page No 133:

Question 2:

When a vaccine is injected into the body, what does the body produces to fight the germs in the vaccine?

Answer:

The body produces antibodies to fight the germs in the vaccine.

Page No 133:

Question 3:

Can bakelite be repeatedly softened by heating?

Answer:

Bakelite is a thermosetting plastic which can be softened by heating only once.

Page No 133:

Question 4:

Metals can be drawn into thin wires. What is this property known as?

Answer:

The property of metals by which they can be drawn into thin wires is known as ductility.

Page No 133:

Question 5:

An animal cell does not have a cell wall. What protects the animal cell?

Answer:

An animal cell does not have a cell wall. But the animal cell is protected by the cell membrane.

Page No 133:

Question 1:

How is transplanting useful to a farmer?

Answer:

Transplanting allows a farmer to select only the healthy seedlings and also space them properly while planting.

Page No 133:

Question 2:

State the rule that governs the displacement of a metal from its salt solution by another metal.

Answer:

The rule of 'metal displacement reaction' governs the displacement of a metal from its salt solution by another metal. By this rule, the more reactive metal displaces the less reactive one from its solution. 

Page No 133:

Question 3:

What is the main purpose of petroleum refining?

Answer:

Petroleum is obtained from oil wells in the form of crude oil which is a mixture of many useful hydrocarbons such as, kerosene, petrol, wax etc. Refining by fractional distillation is done in order to obtain these various hydrocarbons which have different boiling points.

Page No 133:

Question 4:

Why is the calorific value of a fuel important?

Answer:

Calorific value of a fuel is defined as the amount of heat released when a unit of a fuel is burnt completely in air or oxygen. It gives useful information about the heating efficiency of a fuel.

Page No 133:

Question 5:

Algae are considered to be closer to plants than to animals. Why?

Answer:

Algae contain cell wall and chlorophyll within their cells like plants. They too manufacture their own food with the process of photosynthesis. Therefore, algae are considered to be closer to plants than to animals.

Page No 133:

Question 6:

What are polymers?

Answer:

Polymers are large molecules, consisting of long chains made from thousands of similar small molecules called monomers. Some examples of polymers are polyester, rayon and nylon.

Page No 133:

Question 7:

What is an endemic species?

Answer:

Endemic species are those species of plants and animals that are found exclusively in a particular area, and are not naturally found anywhere else. For example, the Asiatic lion is endemic to Gir National Park in Gujarat.

Page No 133:

Question 8:

What is the main function of the nucleus of a cell?

Answer:

A nucleus is the control centre of a cell. It directs the growth of the cell and controls all the activities that take place within it.

Page No 133:

Question 9:

How is a zygote formed?

Answer:

Zygote is formed by the fusion of a sperm and an ovum in the oviduct of a female. This process is known as fertilization. A single sperm fuses with an ovum to produce a zygote.

Page No 133:

Question 10:

What is the function of hormones in the body?

Answer:

Hormones regulate many processes in the body such as growth, development, behaviour and reproduction. A body possesses more than 30 hormones.

Page No 133:

Question 1:

what is pasteurization of milk? How is it useful?

Answer:

Pasteurization of milk is the heating of milk to a high temperature (70 degree Celsius) for about 30 seconds, and then cooling it down quickly. By this process, most of the bacteria present in milk get killed without affecting its flavour. 

Page No 133:

Question 2:

Silver is more likely to be tarnished near a petroleum refinery that releases hydrogen sulphide into the atmosphere than in a place with unpolluted air. Explain why.

Answer:

Silver combines with hydrogen sulphide released from petroleum refineries to form silver sulphide that leads to tarnishing of silver. Unpolluted air does not contain hydrogen sulphide and so, it does not tarnish silver.

Page No 133:

Question 3:

Differentiate between renewable and non-renewable resources, giving one example of each.

Answer:

 

RENEWABLE RESOURCES NON-RENEWABLE RESOURCES
Renewable resources are those resources which will either never run out or those which are renewed within a reasonable period of time through natural processes.   Non-renewable resources are those which once used up cannot be replaced or renewed within a reasonable period of time.
Examples: sunlight, oxygen. Examples: coal, petroleum.

Page No 133:

Question 4:

Explain with examples the difference between endangered and extinct species.

Answer:

 

ENDANGERED SPECIES EXTINCT SPECIES
Endangered species are those species which are facing a high risk of extinction in the world in the near future. Extinct species are those which have been completely eliminated and do not exist anymore.
Examples: Red Panda, Asiatic Wild Ass. Examples: Dodo, Dinosaurs.

Page No 133:

Question 5:

Why do adolescents commonly suffer from body odour, pimples and acne?

Answer:

In adolescents, at the onset of puberty there is an increase in the activity of sweat and sebaceous glands. This leads to increased sweating which results in body odour. The skin becomes oilier which often leads to the occurrence of acne and pimples on the face.



Page No 134:

Question 1:

Which of the following nutrients does compost lack?
(a) potassium
(b) nitrogen
(c) phosphorous
(d) all of these

Answer:

(d) all of these

Compost is a manure obtained by the decomposition of dead plants and animal waste. It is rich in organic nutrients but lacks some important nutrients such as nitrogen, phosphorus and potassium.

Page No 134:

Question 2:

Pick the odd one out.
(a) virus
(b) mammal
(c) bacterium
(d) fungus

Answer:

(b) mammal

All the other options are examples of microorganisms. Mammal is the odd one out.

Page No 134:

Question 3:

Which of these synthetic fibres can substitute wool?
(a) acrylic
(b) rayon
(c) nylon
(d) polyester

Answer:

(a) acrylic

Acrylic is a synthetic fibre that resembles wool in terms of its properties. It is lightweight with a wool-like feel. Clothes made from acrylic are cheaper than wool.

Page No 134:

Question 4:

An iron pipe coated with which of the following metals is called a galvanized pipe?
(a) silver
(b) copper
(c) chromium
(d) zinc

Answer:

(d) zinc

Galvanization is the process of deposition of a layer zinc on iron. This prevents corrosion of iron.

Page No 134:

Question 5:

Which of these is not obtained by refining petroleum?
(a) LPG
(b) CNG
(c) Diesel
(d) Petrol

Answer:

(b) CNG

The various products obtained by refining petroleum are LPG, petrol, kerosene, diesel, lubricating oil and asphalt.

Page No 134:

Question 6:

Which zone in a candle flame gives out the maximum light?
(a) dark zone
(b) non-luminous zone
(c) blue zone
(d) luminous zone

Answer:

(d) luminous zone

The luminous zone of a candle flame is the zone of incomplete combustion. The wax vapours do not burn completely, since the supply of oxygen is inadequate in this zone. When an object is placed over this zone, it releases black soot and other residues. The carbon particles in it, glow, emitting a yellow light.

Page No 134:

Question 7:

The animals found in a particular region are known as
(a) endemic species.
(b) endangered species.
(c) flora.
(d) fauna.

Answer:

(d) fauna
Animals found in a particular region are called as fauna of that region.
 

Page No 134:

Question 8:

Organelles are
(a) small organs in the body of multicellular organisms.
(b) small unicellular living organisms.
(c) small multicellular organisms.
(d) small living structures present inside a cell.

Answer:

(d) small living structures present inside a cell

Organelles are small living structures present inside a cell that function independently. For example, chloroplast, mitochondria and ribosomes.

Page No 134:

Question 9:

After fertilization, the zygote gets implanted in
(a) the vagina.
(b) an ovary.
(c) the oviduct.
(d) the wall of the uterus.

Answer:

(d) the wall of the uterus

After fertilization, the zygote divides several times to form an embryo. The embryo then gets implanted in the wall of the uterus, where further development occurs.

Page No 134:

Question 10:

A woman is no longer reproductive after the occurrence of
(a) menstrual cycle
(b) menarche
(c) menopause
(d) ovulation

Answer:

(c) menopause
At around 4550 years of age, a woman is no longer reproductive, as the menstrual cycle stops. This condition is called menopause.



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