CBSE Class 8 Science Microorganisms Friend and Foe Worksheet Set B

Question. It is found that many insecticides - used to kill insects - lose their effectiveness after some years. What could be the cause of this?
(a) The insecticides are equally effective - such myths are spread by manufacturers so that they can sell more.
(b) The species targeted by the insecticide are destroyed, but new insects which are unaffected, are born.
(c) The insects develop resistance to the insecticide, which is passed on to successive generations.
(d) The atmosphere contains so much of the insecticide that humans start being poisoned by it.

Answer : C

Question. Study this arrangement of an experiment. The type of seeds and other conditions are identical for all the three arrangements. What is the VARIABLE whose effect is being studied in this experiment?

(a) Number of seeds
(b) Amount of light
(c) Temperature
(d) Amount of water

Answer : D

Question. Some farmers found that corn plants grew better if decaying fish were buried nearby. What did the decaying fish probably supply to the plants to improve their growth?
(a) Energy
(b) Mineral
(c) Protein 
(d) Oxygen

Answer : B

Question. Corn is used as food and also as fodder for animals. In recent years, however, corn bushels are being used to produce Ethanol, an important fuel. Which of these correctly compares the use of corn as FUEL and FOOD?

(a) A
(b) B
(c) C
(d) D

Answer : A

Question. In which type of soil surface will rain water runoff be maximum after heavy rains?
(a) Sandy surface
(b) Grassy surface
(c) Impermeable surface
(d) Nearly flat surface

Answer : C

Question. Sarathy wishes to investigate the effect of the type of light on a plant growth. He takes three identical potted plants and places one in the lawn, one in a closed room containing a tube light; and a third in a closed room containing a bulb which gives yellow light. The bulb and tube light are always on. He waters the plants regularly and to the same extent. Which of these could introduce error into the experiment results?

(a) The fact that the tubelight and bulb are never switched off.
(b) The fact that the light intensities are different in the three cases.
(c) The fact that the three plants were watered similarly.
(d) All of the above

Answer : A

Question. Plants need light for photosynthesis. Which of these is true about the type of light they need?
(a) Plants need sunlight, no other type of light will do.
(b) Apart from sunlight, plants can grow only in green artificial light.
(c) Apart from sunlight, plants can grow in certain types of artificial light.
(d) Any type of natural or artificial light will do for plants

Answer : C

Question. Saket saw his papaya tree developing flowers. He was sure that fruits would form within a few days, but to his disappointment, this did not happen. He plucked a flower and found that pollen grains were being produced in the anthers. Which of these was definitely absent in the flowers?
(a) Sepal
(b) Ovule
(c) Filament
(d) Nectar

Answer : B

Question. Ashok has an aquarium at home. He wants to increase the oxygen available to his fish. What should Ashok do?
(a) Add some more fish to his aquarium.
(b) Add some aquatic plants to his aquarium.
(c) Reduce the light in the aquarium.
(d) Add some shells and stones to the aquarium.

Answer : B

Question. Which of the following process/processes help in INCREASING the oxygen content in air?
(a) respiration
(b) photosynthesis
(c) Burning of fuels
(d) All of them

Answer : B

Question. If the corn crop fails one year, how would the robin population be affected and why? Look at the food web given here and answer the question

(a) It would be unaffected since neither is a food for the other.
(b) It would increase because the snake population would decrease.
(c)  It would decrease as snakes and hawks will feed more on robins.
(d) It would increase since a change in one part of the web affects all animals.

Answer : C

Question. Charles Darwin, a British naturalist, and his son carried out the following experiment to find out the effect of light on the movement of a plant: When seedlings of a plant were exposed to light, the tip bent towards the light source (as shown in figure 1). If they placed an opaque cover over the tip (as shown in figure 2), it failed to bend even though the rest of the seedling was illuminated from one side. What can be concluded on the basis of this experiment?

(a) An opaque cover must be put on the tip of the seedling for bending to take place.
(b) The tip of the seedling needs to be exposed to light for bending to take place.
(c) The base of the seedling needs to be exposed to light for bending to take place.
(d) Bending of the seedling is not related to the direction of light.

Answer : B

Question. Which of the following organisms breaks down dead material and returns the substances to the environment?
(a) Lion
(b) Algae
(c) Bacteria
(d) Vulture

Answer : C

Question. Study the graphs given below. They show the rates of growth of four different bacteria. The bacteria corresponding to which graph could be called the fastest-growing?

Answer : C

Question. Into which of these boxes would the disease polio fit?

Answer : B
 

              Questions

              Very Short Answer

Q1)       What are polio drops?

Q2)       Who discovered the vaccine for small pox?

Q3)       Why we will give vaccination to children or infants?

Q4)       Who discovered fermentation and pasteurisation?

Q5)       Who discovered the bacterium which causes anthrax disease?

             Short Answer

Q6)       What do you mean by preservatives?

Q7)       What do you mean by the biological nitrogen fixers?

Q8)       What do you understand by the food poisoning?

Q9)       What do you mean by the food preservation?

Q10)     Why is biological nitrogen fixation important?

             Long Answer

 Q11)     Explain about nitrogen cycle?

Q12)     Explain the methods of the preservation?

Q13)     State the difference between pathogen and parasite?

Q14)     Write short note on harmful organisms?

Q15)     State the difference between antibiotics and vaccine?