Page 338 - Biology_F5

Regulation (Homeostasis)

Further excess Another example of positive feedback
mechanism is the release of volatile
Positive feedback
Excess plant hormone (ethylene) by the ripening
fruits that accelerates the ripening of
unripe fruits in its vicinity. The fruit
Set point ripening process involves changing the
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fruit texture, softening, and colour. As
Deficiency Positive feedback more fruits get ripe they produce more
hormones that further continue to ripen
Further deficiency more the surrounding fruits.

Figure 7.3: A positive feedback mechanism

Activity: Investigating the effect of positive feedback mechanism in ripening of fruits

Materials
One bunch of ten unripe green bananas, six containers, and dry banana leaves

Procedure
a) Label the six containers from A to F.

b) Isolate five bananas from the bunch and put one banana in each of the five
containers labelled B to F.

c) Put the remaining five undetached bananas in the container labelled A.

d) Cover all the containers with dry banana leaves and arrange them in a series;
starting with the one with five bananas. The distance from one container to another
should be not less than one meter (Figure 7.4).
e) Note the number of days it will take for all bananas in all containers to get ripe.

A B C D E F

Figure 7.4: Experimental set up for ripening of fruits

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