CBSE Class 9 Science Practical Skills – Life Cycle of Mosquito

EXPERIMENT

AIM
To study the life cycle of mosquito.

MATERIALS REQUIRED
A chart showing life cycle of a mosquito, permanent slides of mosquito eggs, larva, pupa, and compound microscope.

THEORY
CBSE Class 9 Science Practical Skills – Life Cycle of Mosquito 1
Like all insects, life cycle of mosquitoes begins from eggs and go through several stages before becoming adults. All mosquitoes need water to breed, the females lay their eggs in water, the larva and pupa stages live entirely in water. When the pupae changes into adults, they leave the water and become free-flying land insects. The life cycle of a mosquito can vary from one to several weeks depending upon the environmental temperature, but in all species, life cycle more or less show common features.

PROCEDURE
A.

  1. Observe the chart carefully.
  2. Note different stages present in the life cycle.
  3. Note the characteristics of each stage.
  4. Draw well labelled diagram of each stage.

B.

  1. Now, observe permanent slides of eggs, larva and pupa of mosquito under microscope.
  2. Note the characteristics of each stage.
  3. Draw well labelled diagram of each stage.

OBSERVATIONS
EGG

  1. The female mosquito lays eggs on the surface of stagnant water such as ponds, ditches, drains, lakes, marshy swamps, tree holes, gutters and open containers.
  2. About 40 to 200 tiny white eggs are laid at a time.
  3. The female pushes the laid eggs by its hind legs, as a result they stick together to make a floating raft.
  4. The bubbles of air trapped between the eggs keep the raft buoyant even if the water is disturbed.
  5. After one or two days, the eggs hatch and larvae come out.

LARVA

  1. The larvae float at the surface of the water.
  2. They have a distinct head, thorax and abdomen.
  3. Head contains a pair of compound eyes and two antenna.
  4. The larvae do not have legs but can propel themselves through the water by a vigorous flicking-wriggling movement.
  5. From the eighth segment of abdomen, a breathing tube or siphon projects which carry air from the atmosphere to all body parts.
  6. Many long bristles are present on its body which are protective in natpre.
  7. The tufts of bristles on the last abdominal segment help the larva to steer when swimming.
  8. The larvae filter organic material through their mouth parts and grow to about 1cm long.
  9. The growing larvae remove their skin several times. This is called moulting.

PUPA

  1. After the fourth change of the skin, the larva changes to a pupa.
  2. It is comma-shaped and able to swim vigorously by flicking its abdomen.
  3. In pupa, head and thorax fuse to form cephalothorax.
  4. The pupa breathes through a pair of breathing tubes.
  5. During the pupal stage, the insect does not feed. .
  6. At the end of the pupal stage, the pupa covers themselves with pupal case and transforms into adult mosquito.

ADULT

  1. Adult emerges from pupa.
  2. After emergence, it rests for a few days. During this period, the cuticle hardens and it becomes ready to fly.
  3. Its body is differentiated into head, thorax and abdomen.
  4. The adult mosquito has only one pair of wings.
  5. In female, the antennae are thread-like while in males many branched filaments arise from antennae providing them a bushy look.
  6. They have elongated tube like structure called proboscis which help them to suck fluids.
  7. Females are able to pierce the skin but males cannot do so and they only suck up plant juices such as nectar.
  8. Adult mosquitoes live for several weeks.

INTERACTIVE SESSION 

Examiner :
What is metamorphosis?
Examinee:
The physical transformation of an insect from one stage of its life cycle to another is called metamorphosis.

Examiner :
Which type of metamorphosis takes place in mosquito?
Examinee:
Complete metamorphosis.

Examiner :
Why it is called complete metamorphosis?
Examinee:
Each stage in the life cycle of mosquitoes is different from the adult.

Examiner :
Do you know any other organism in which phenomenon of metamorphosis takes place?
Examinee:
Butterfly, frog, lady bug, etc.

Examiner :
What are the various stages present in the life cycle of mosquito?
Examinee:
Four stages present in the life cycle are

  1. egg
  2. larva
  3. pupa
  4. adult.

Examiner :
What is moulting?
Examinee:
Shedding of the skin or exoskeleton during the growth is called moulting.

Examiner :
Give two examples which exhibit process of moulting.
Examinee:
Insects such as cockroaches, snakes, etc.

Examiner :
Where do the mosquitoes lay eggs?
Examinee:
In the stagnant water.

Examiner :
Name the stages present in the life cycle of mosquitoes which require water.
Examinee:
Egg, larva and pupa.

Examiner :
In the life cycle of mosquitoes which stage is comma shaped?
Examinee:
Pupa

Examiner :
What do we call to the mouth part of the mosquitoes which helps in sucking nectar?
Examinee:
Proboscis

Examiner :
What are the three types of mosquitoes?
Examinee:
Anopheles mosquitoes, Culex mosquitoes and Aedes mosquitoes.

Examiner :
Name three diseases transmitted by mosquitoes.
Examinee:
Malaria, dengue and yellow fever.

Examiner :
Which type of mosquitoes transmit malaria?
Examinee:
Anopheles mosquitoes.

Examiner :
Which type of mosquitoes transmit dengue?
Examinee:
Aedes mosquitoes.

Examiner :
How do mosquitoes transmit filariasis?
Examinee:
The adult worms of filariasis live in the lymphatic vessels of humans and the female worms produce microfilariae which at night circulate in the blood. The mosquitoes on biting the infected individuals carry the microfilariae which develop into adult worms. If the same mosquito bites a healthy person, the worms are transmitted to him and the infection is spread.

Examiner :
Why do female mosquitoes feed on blood?
Examinee:
The blood provides proteins and iron that the females need to lay eggs.

Examiner :
What is the food of male mosquitoes?
Examinee:
Nectar of flowers.

Examiner :
Do female mosquitoes also feed on nectar of flowers?
Examinee:
Yes, in addition to feeding on blood it also feeds on nectar of flowers.

Examiner :
Which stage in the life cycle of mosquito do not feed?
Examinee:
Pupa.

Examiner :
Can we distinguish the larvae of Anopheles from Culex mosquitoes?
Examinee:
Yes.

Examiner :
How?
Examinee:
Anopheles larvae lie parallel to the surface of the water, while Culex larvae extend down into the water.

NCERT LAB MANUAL QUESTIONS

Question 1:
Why is it important to study the life cycle of mosquito?
Answer:
Mosquitoes transmit various diseases. By studying the life cycle of mosquitoes we can control their breeding or in other terms we can control spread of diseases.

Question 2:
At which stage in the life cycle of a mosquito, moulting takes place?
Answer:
In the larval stage.

Question 3:
Why does only the female mosquito require a blood meal?
Answer:
The blood provides proteins and iron that the females need to lay eggs.

Question 4:
What are the conditions that are helpful for breeding of mosquitoes?
Answer:
Wet and warm weather are helpful for breeding of mosquitoes.

Question 5:
Suggest three measures to check the breeding of mosquitoes?
Answer:
Three measures to check the breeding of mosquitoes are:

  1. Water should not be allowed to collect around houses.
  2. Kerosene oil should be sprinkled in areas having standing water. Kerosene forms a thin layer on
    the surface of water and thus, it prevents the larvae from breathing. –
  3. Certain fishes such as cat fish, insectivorous plants and aquatic birds can be introduced to water bodies. These organisms will feed and eliminate the larvae and pupae of the mosquitoes.

PRACTICAL BASED QUESTIONS
Multiple Choice Questions/VSA (1 Mark)

Question 1:
The shape of pupa of mosquito is like a
(a) cylinder
(b) comma
(c) cup
(d) spiral

Question 2:
The female mosquito feeds on blood to get
(a) carbohydrate
(b) sugar
(c) protein
(d) fat

Question 3:
Which of the following shows moulting in mosquito?
(a) Egg
(b) Larva
(c) Pupa
(d) Adult

Question 4:
The physical transformation of an insect from one stage of its life cycle to another is called
(a) metamorphosis
(b) moulting
(c) fertilisation
(d) none of these

Question 5:
Mosquito larva breathes through
(a) gills
(b) lungs
(c) breathing tube
(d) all of these

Question 6:
How many stages are present in the life cycle of mosquito?
(a) Two
(b) Three
(c) Four
(d) Five

Question 7:
In the water, larva lives at, or near the
(a) surface
(b) bottom
(c) centre
(d) anywhere

Question 8:
Malaria is spread by
(a) Culex mosquito
(b) Anopheles mosquito
(c) Aedes mosquito
(d) none of these

Question 9:
The number of eggs laid by mosquito in one time are
(a) 10-20
(b) 2-3
(c) 40-200
(d) 500-1000

Question 10:
The part of body of mosquito which sucks blood is
(a) proboscis
(b) front legs
(c) teeth
(d) needle

Question 11:
Physical transformation of an insect is called
(a) moulting
(b) metamorphosis
(c) shedding
(d) none of these

Question 12:
Which of the following represents the first stage in the life cycle of a mosquito?
CBSE Class 9 Science Practical Skills – Life Cycle of Mosquito 2
(a) A
(b) B
(c) C
(d) D

Question 13:
Which is correct about the feeding habit of pupa of mosquito?
(a) It feeds on leaves.
(b) It feeds on organic waste.
(c) It feeds on blood.
(d) It does not feed at all.

Question 14:
The organism which shows metamorphosis is
(a) butterfly
(b) mosquito
(c) frog
(d) all of these

Question 15:
Which of the following can check the breeding of mosquitoes?
(a) Sprinkling of kerosene oil over standing water
(b) Use of net
(c) Use of repellents
(d) All of the above

ANSWER KEY
Multiple Choice Questions/VSA

  1. (b)
  2. (c)
  3. (b)
  4. (a)
  5. (c)
  6. (c)
  7. (a)
  8. (b)
  9. (c)
  10. (a)
  11. (b)
  12. (c)
  13. (d)
  14. (d)
  15. (a)

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