Ans. (d) Cytokinin

 

Ans. (b) Synapse

 

class 10 science ch 7 important question

Ans. (d) All  of the above

 

Ans.(i)Receptors or sense organs are groups of highly specialized cells which receive the stimuli. Each  receptors is specialized to receive a specific stimulus and change it into appropriate nerve impulse.

        (ii) When receptors fail to work properly, the body functions will be disturbed and may be health- hazard or fatal.

 

Ans. (i) Figure 7.1 Structure of neuron (page no.115) 

        

 

(ii) (a)Dendrites receive the stimuli and conduct the nerve impulses towards the cyton.

      (b) Axon conducts the nerve impulse away from the cyton towards dendrite of another neuron                      or target muscle or glandular cell.

 

Ans. Spinal cord control reflex actions of the body  because the reflex arcs are formed in it.So in case of injury to spinal cord, the signals of reflex actions will be disrupted and the body will not be able to give quick and automatic mechanical responses to harmful stimuli. this increases the chances of damage to the body by such stimuli.

Ans. In phototropic movements,  shoots respond by bending towards light, while roots respond by blending  away from it. when growing plants receive light, plant hormone,auxin formed at shoot tip, helps the cells to elongate.in case light comes from one direction, auxins move towards shade side of shoot. They thus stimulate the cells to grow longer on the side of shade. Thus plant bends towards light.

 

Ans. Due  to stimulation, cells release chemicals which are able to diffuse all over the original cell. Cells lying nearby can detect this chemical using special molecules on their surface. They can identify information and are able to transmit  it. It is potentially able to reach all the cells of the body, without having nervous connections. It can be carried out continuously and persistently , Different plant hormones  help in coordination to growth, development and responses to the environment. Their point of formation and action differs but are able to become the region of action.

 

Ans. (i) So that various organs of body operate harmoniously to ensure their smooth functioning.

        (ii) To maintain a constant internal environment, called homeostasis, inside the body.

        (iii) To adjust themselves according to the change in environment.

 

Ans. Involuntary  actions are those muscular movements which are not under will or any thinking             control, e.g., heart movements, blood pressure , salivation, vomiting, etc., and are controlled               by specific centres located in the mid brain and hind brain. 

        Reflex actions are spontaneous automatic mechanical responses in which will is not involved               like the  involuntary actions but are controlled by the spinal cord e.g., withdrawal of hand when           pricked with a needle, secretion of saliva on sight of delicious food, etc.  

Ans.

 

cbse website

Characters	Nervous  coordination	Chemical   coordination
1. Speed of action	Always quick acting.	May be quick or slow acting.
2. Mode of transmission of      information	As electrical nerve impulse.	As chemical messengers(hormones).
3. Path of transmission	Through nerve fibers.	Through blood.
4. Durability	Short-term effect.	long lasting.

Ans. Quick folding of leaflets of mimosa pudica( sensitive plant touch-me-not) and drooping of whole leaf occur due to changes in the amount of water in its motat cells. No nervous and muscular tissue are involved. But the movements in our legs are due to contraction and relaxation of muscle proteins regulated by nervous  tissue. Muscle cells bring about movements by changing their shape. 

NCERT Solutions for Class 10 Science Chapter 7: Control and Coordination