ays controlled especially external stimuli.||2. It could be controlled.|
|3. Stimulus could be of any magnitude.||3. The response could never go beyond the highest capability of an organism.|
|4. Response can not determines the stimulus.||4. Stimulus determines the response.|
b) Afferent and Efferent nerves
|Afferent nerves||Efferent nerves|
|1. Nerves coming from receptors or sense organs are called afferent nerves.||1. Nerves that carry impulses from brain or spinal cord are called efferent nerves.|
|2. These are also called sensory nerves.||2. These are also called motor nerves.|
|3. Sensory nerves carry information from sensory organs like ears, eyes, from brain or spinal cord.||3. The motor nerves carry impulses to effector nose, tongue and skin to brain and organs (muscles) and are responsible for the movement of hands and legs.|
|4. These are incoming nerves.||4. These are outgoing nerves.|
c) Central nervous system and peripheral nervous system :
|Central nervous system||Peripheral nervous system|
|1. It consists of Brain and spinal cord.||1. It consists of nerves that arise from brain and spinal nerves.|
|2. Both of them have nerve cells and glial cells.||2. It has 43 pairs of nerves. Among them 12 pairs are cranial nerves and 31 pairs are spinal nerves.|
|3. Brain and spinal cord are continuous with each other.||3. Cranial nerves take their origin from brain and spinal nerves take their origin from spinal cord.|
|4. Brain and spinal cord receive information.||4. The cranial nerves carry information to the sense organs and spinal nerves from organs to spinal cord.|
|5. Central nervous system coordinates all neural functions.||5. These supply information required for the movement of the muscles.|
d) Receptor and effector:
|1. The sense organs which are made up of cells called receptors.||1. Muscles or tissues which are linked with nerves are called an effector.|
|2. Receptors respond to stimulus.||2. Effectors are the organs that produce response.|
|3. These send information to central nervous system.||3. They follow the commands of central nervous system.|
|4. These are connected to sensory organs.||4. These follow the motor nerves.|
|5. Nervous system sense the changes inside and outside the body through receptors.||5. Effectors receive messages from brain or spinal cord through motor nerves.|
How does phototropism occur in plants?
- Bending of plants towards light is called phototropism. (Photo = light) (tropism = movement)
- For example a creeper which is growing near the window bend towards sunlight.
- Auxins are the phyto hormones which are present at the tip of the shoot respond the plant to bend towards sunlight.
Give an example and explain how plants may immediately respond to a stimulus.
- The plant responding to stimulus is mimosa pudica is the example.
- Mimosa pudica leaves have pad like sweelings at the base are called PULVINI.
- Here cells contain water and large intercellular spaces. Due to water pressure pulvini hold the leaf errect.
- When we touch the leaves, an electrical impulse is generated due to plant hormone.
- Because of this hormone water in the pulvini cells which are closer to the leaf vein migrate to other side’of the cells.
- Then pulvini loss its fitness hence leaves become fold. After 20 to 30 minutes water comes back leaves become errect.
Suggest an experiment to show how roots grow away from light in most plants.
Aim: To prove that roots grow away from light in most plants.
Material required: Glass jar, Bean seed.
- A plant jar is taken and filled with mud.
- A bean seed is sown just adjacent in the inner wall of the jar.
- So that it is easy to observe the growth of root and shoot.
- After 4-5 days the germination of the seed is observed.
- Keep the jar in the sunlight. We observe the growth of roots and shoot.
- Finally the jar is tilted to keep the growing plant horizontally.
- After the growth of 4-5 days, tilt the glass jar and keep the plant horizontally.
Observation: It is observed that the roots extends downwards to the earth that is away from the sun light and the shoot