Page 107 - Biology - XII

Note: 1. There is a ratio between the size of pulley and the needle/pointer.

2. If the pulley size is 4 inches and needle is 20 inches from the centre of the pulley, then the
growth depicted/shown on the scale is 10 times.
For example, in 8 hours if the needle moves by 4 cm. (i.e. 10 times the actual growth.) Then
the actual growth is —

Growth in 8 hours = 4 cm = 0.4 cm or 4 mm
10
4
Growth in 1 hour· = = 0.5 mm/hour
8
Make your own observations and calculate the rate of growth accordingly.

Conclusion
1. ___________________________________________________________________________________

_________________________________________________________________________________

Precautions
1. Tie the string carefully to the growing point/tip.
2. Note your observations carefully.

VIVA VOCE

Q1. Which type of growth curve is obtained if a graph is made?
Ans. S-shaped curve

Q2. What is growth?
Ans. Growth is a permanent and irreversible change of an organism/organ.
Q3. What is the actual cause of growth?
Ans. The addition of new cells continuously by the pre-existing cells.

Q4. What is the growing points/tissues called?
Ans. Meristems
Q5. Why did you use this instrument instead of a scale?
Ans. Measurement by a scale would not give the correct results, whereas this instrument gives more
correct results than a scale.

COMPETENCY BASED QUESTIONS

Multiple Choice Questions

Q1. The period during which there is increase in growth is called
(a) sigmoid curve (b) maturity stage (c) senescence phase (d) none of these

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