 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 grows towards sunlight.
Conclusion: By the above experiment it is proved that roots grow towards gravity (earth) away from sun light.
Give an example to show how hormones can influence visible changes in your body.
What are the effects of hormones on human beings?
- Endocrine glands secrete chemical substances called Hormones directly into blood.
- Hormones act on the cells of other organs and increase or decrease the metabolism of carbohydrates, proteins and fats.
- The external features by which the males and females can be distinguished are called secondary sexual characters.
- Testosterone in males and estrogen in females promotes the development of secondary sexual characteristics.
- For example, if a dog chases us, our nervous system stimulate the adrenal glands to secrete more adrenaline hormone into our body.
- When we are afraid, the rate of heart beat increases, the breath rate will be faster, blood pressure increases, the hair on the body becomes errect.
- All these changes occur due to the production of Adrenaline hormone.
How does a neuron differ from an ordinary cell in structure? Write notes.
|Neuron (Nerve cell)||Ordinary cell|
|1. It is the longest cell in our body.||1. Generally cells are round or oval shaped.|
|2. It belongs to only nervous system.||2. These are the structural units of body.|
|3. Nerve cell has three parts: 1. Cyton 2. Axon 3. Dendrites||3. Commonly divided as 1. Cytoplasm and 2. Nucleoplasm|
|4. These cells carry impulses to brain and spinal cord.||4. Involve in metabolic activities.|
|5. These are not regenerated.||5. The cells have cell division and replace the death cells.|
|6. Nerve cells end with dendrites.||6. These cells do not have end points.|
|7. Some nerve cells are covered with lipid coat.||7. Generally these are covered with plasma membrane.|
|8. Nissl granules are special character of nerve cells.||8. These cells do not have Nissl granules.|
Is the structure of neuron suitable for transmission of impulses? Analyse.
- Yes. The structure of neuron is suitable for 