Life Processes

  • Question 97

    Observe fish in an aquarium. They open and close their mouths and the gill-slits (or the operculum which covers the gill-slits) behind their eyes also open and close. Are the timings of the opening and closing of the mouth and gill-slits coordinated in some manner?

    (ii) Whether the number of times the fish opens and closes its mouth in a minute is faster than to the number of times you breathe in and out in a minute?


    The timing of the opening and closing of the mouth and gill-slits in a fish are coordinated.
    Reason: The water engulfed from the mouth is immediately pushed to gills for absorbing oxygen dissolved in water, into blood. It is then removed by gill-slites.
    (ii) The number of times the fish opens and closes its mouth in a minute is much faster than the number of times we breathe.
    Reason: The amount of dissolved oxygen in water is very low. The fish opens and closes its mouth (to push water over the gills) more number times  so that more and more water passes over the gills. So that sufficient oxygen can be absorbed by the blood in the gills to meet the body's requirement.

    Question 98

    How do exchange gases take place in aquatic animals?

    Most of the aquatic animals like prawns, fish, tadpoles use gills as the respiratory organs. Respiration through gills is known as branchial respiration. The blood flowing in the capillaries of gills absorb oxygen and gives carbon-dioxide to the water passing over them by diffusion through thin epithelium.

    Respiration in fish


    Question 99

    What three features all respiratory organs have in common whether gills, lungs or skin?


    Common features of respiratory organs (gills, lungs and skin).
    (i) A large surface area to absorb sufficient oxygen.
    (ii) Thin walls for easy exchange of respiratory gases by diffusion.
    (iii) Rich blood supply for transport of gases.

    Question 100

    How does nasal cavity help in respiration?


    Functions of Nasal Cavity

    (i) Nasal cavity has external nostrils through which air is drawn into nasal cavity.
    (ii) The nasal cavity is separated from oral cavity by a bony palate. So that air can breathe in even while we eat.
    (iii) In nasal cavity the air is warmed to match the body temperature, moistened to avoid friction, and dust particles are removed by mucous secreted by mucous glands.
    (iv) The hairs present in the nasal cavity filters the air .
    (v) It provides passage to air from external nostrils to pharynx through internal nostrils.

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