The Biology Of Movement
Class 9th Biology Kerala Board Solution
Let Us Assess
Question 1.The basic contractile unit of a muscle cell
A. Fascicle
B. Muscle fiber
C. Sarcomere
D. Myofibril
Answer:
Muscle is a soft tissue found in most animals. They are responsible for maintaining and changing posture, locomotion. Skeletal muscles are enclosed by a tough layer known as epimysium. Within the epimysium are numerous bundles called fascicles, each of which contains many muscle fibers collectively enclosed by the layer perimysium. These muscle fibres contain muscle cells which are further divided into myofibrils. Myofibrils are complex strands of protein filaments organized together into repeating units called sarcomeres. Hence, a sarcomere is the basic contractile unit of a muscle.
Question 2.
Observe the figure and answer the following questions.
a. What changes do you observe in the growth of root and stem in a plant, if it is kept
stationary as shown in the figure for a few days. Why?
b. If the system is rotated continuously and slowly, what change would you observe in its root and stem?
Answer:
a) If the given setup is kept stationary for a few days then we would observe the growth in the roots downwards.
Because of positive geotropic movement in the roots whereas the stem grows away from the gravity, i.e. shows negative geotropism.
b) If the setup is rotated continuously then there will be no net change in the position of root and stem.
When the system is placed at one position, the roots will start growing downwards. But if the system is rotated, suppose by 180o, the roots just after rotation will face opposite to the ground. They will again start growing downwards, but after sometime they will again be rotated. Thus, there will be no net change in the position of root and stem, and they will remain parallel to the ground.
Question 3.
3 Identify the odd one giving reason.
• Coconut trees near a river bend towards the river.
• Root of trees near a well grows towards the well.
• Leaves of touch-me-not fold when we touch it.
• Roots of plants grow towards gravity.
Answer:
• Leaves of touch-me-not fold when we touch it.
i.e. leaves of touch me not fold when we touch it. Leaves of Mimosa pudica fold because of the chemicals released.
Following options are not correct and the reason is as follows :
a) Coconut trees near a river bend towards the river so that there seeds can easily float in water and the coconuts can also travel a long distance.
b) Root of trees near a well grows towards the well as roots grow in the direction of water i.e. show positive hydrotropism.
c) Roots of plants grow towards gravity. Roots being positive hydrotropic are also positive geotropic which means that they grow freely in the direction of gravity.
* All these options lie in the same category because they are influenced by the physical factors whereas in case of touch me not plant chemical factors are involved.