Science [2 Mark Questions]

Iodine is necessary for the thyroid gland to make thyroxine hormone which regulates the metabolism of carbohydrates, fats and proteins so as to produce the best balance for the growth. Iodised salt is advisable as it contains appropriate amounts of iodine compounds needed by the thyroid gland to make sufficient thyroxine hormone for the body and hence goitre disease can be prevented.

The folding of leaves of a sensitive plant is not a case of tropism (like thigmotropism) because in this case the direction of movement of leaves does not depend on the direction of stimulus (touch).

The movement of a plant part in response to an external stimulus in which the direction of response is not determined by the direction of stimulus is called nastic movement. Example: The folding up of the leaves of a sensitive plant on touching is an example of thigmonasty.

A receptor is a cell (or a group of cells) in a sense organ which is sensitive to a particular type of stimulus (or a particular type of change in the environment). Example: Photoreceptors and Phonoreceptors.An effecter is the part of the body which can respond to the stimulus according to the instructions sent from the nervous system (spinal cord and brain). Example: Muscles and glands.

Tendrils are the thin, thread-like growths on the stems or leaves of climbing plants. The two types of tendrils are stem tendrils and leaf tendrils. The tendrils grow towards the things they happen to touch. This phenomenon is known as thigmotropism.

Photonasty	Thigmonasty
The non-directional movement of a plant part (usually petals of flowers) in response to light is called photonasty. Example: The opening and closing of petals of dandelion flowers in response to the intensity of light.	The non-directional movement of a plant part in response to the touch of an object is called thigmonasty. Example: In Mimosa pudica plant, the leaves fold up in response to touch.

1. Bending of stem towards light.
2. Folding up of leaves of a sensitive plant on touching.

The function of insulin hormone is to lower the blood sugar level (or blood glucose level). People having severe diabetes are treated by giving injections of insulin.

The endocrine glands do not have ducts to secrete their hormones. They release hormones directly into the blood of a person and reach the concerned body part through the blood and act on it.

1. A dandelion flower opens up in the morning in bright light. This phenomenon is known is positive photonasty.
2. At night, the dandelion flower closes and this phenomenon is known as negative photonasty.

Reflex Action	Involuntary Action
It is a rapid, automatic response to a stimulus which is not under the voluntary control of the brain. Example: Sneezing, coughing.	Those actions which do not need thinking and are not performed by us knowingiy are called involuntary action. Example: Digestion, respiration.

Autonomic nervous system means self governing nervous system. Its function is to control and regulate the functions of the internal organs of our body involuntarily.

1. Both the processes are similar as the response is not determined by the direction of the stimulus. They are nastic movement.
2. The first process of folding up of leaf is thigmonastic and the stimulus is touch. The second process of closing of petals is photonastic and the stimulus is light.

When a piece of thread is tightly tied around an animal’s pancreatic duct, the pancreatic juice containing digestive enzymes will not be able to reach the small intestine. The pancreatic juice contains enzymes which help in the digestion of food. In its absence (due to the blockage of the pancreatic duct), the animal would have difficulty in digesting certain food substances.
However, the pancreas being an endocrine gland releases insulin directly into the blood. Since, the main function of insulin is to maintain the blood sugar level in the body; the animal will not suffer from diabetes.

Receptors are sensory structures (organs/ tissues/ cells) that detect changes in the environment, which are called stimuli, and turn them into electrical impulses to be transferred to the brain. The tongue has taste buds which can detect chemicals in food and identify taste. Hence, it is considered as receptor. Effector is an organ that responds to stimulus. The tongue is a muscular organ that can respond to a stimulus. Hence, it is also considered as an effector organ.

The directional growth movement of a plant part in response to the touch of an object is called thigmotropism. Example: Tendrils grow towards any support which they happen to touch and wind around it.

Tropic movements:

1. These movements are always in the direction of the stimulus.
2. These movements are slow.
3. These movements are exhibited by all parts of a plant. For example, movement of shoot towards the light and not towards gravity.

Nastic movements:

1. These movements are neither away nor towards the stimulus.
2. These movements are fast.
3. These movements are exhibited by the flat organs (like leaves and petals of flowers) of a plant. For example, the bending and drooping of leaves in ‘Touch-me-not’ plant.

1. The phenomenon exhibited by the positions of plant parts A and B is geotropism.
2. The stimulus which causes plant part A to grow and bend upwards and part B to bend downwards is gravity.

1. During the daytime the petals of moon flower close when there is bright light.
2. At night, when it is dark the petals of moon flower opens up. This phenomenon is known as photonasty.

There are 5 sense organs: Eyes, ears, nose, tongue and skin.

Phototropism – The movement of a plant part in response to light is called phototropism.
Example - Stem bends towards the light is positive phototropism.

A growth movement ofa plant part in response to an external stimulus in which the direction of stimulus determines the direction of response is called tropism. Example – The bending of plant stem towards light is an example of positive phototropism.

CNS – Central nervous system.

1. Cerebrum.
2. Spinal cord.

The five types of tropisms are: Phototropism, Geotropism, Chemotropism, Hydrotropism and Thigmotropism. The various types of tropic movements help the plants to survive. Example even if a seed is planted upside down, its root will grow downwards into earth because it is positively geotropic.

The movement of plant part in response to gravity is called geotropism. Example – Roots grow towards gravity.

1. The function of the nervous system is to coordinate the activities of our body.
2. It helps all other systems of our body to work together.
3. It receives information from the surroundings, processes it, interprets it and then responds accordingly.

The growth of a plant part due to chemical stimulus is known as chemotropism. For example the growth of pollen tube towards the ovule induced by a sugary substance as stimulus. This is an example of positive chemotropism.

1. Testosterone.
2. Progesterone and oestrogen.

The function of testosterone hormone is to control the development of male sex organs and male features such as deeper voice, moustache, body hairs etc. The function of oestrogen is to control the development of female sex organs and female features such as feminine voice, soft skin and mammary glands.

Hindbrain has 3 regions:

1. Pons:

It takes part in regulating respiration.

2. Cerebellum:

​​​​​​​It helps in maintaining posture and balance of the body. It enables us to make precise and accurate movements.

3. Medulla:

​​​​​​​The medulla controls various involuntary actions such as heart beat, breathing, blood pressure and peristaltic movements of the elementary canal. It is also the controlling centre for reflexes such a swallowing, coughing, sneezing, secretion of saliva and vomiting.

Function of cerebrum: It is the main thinking part of the brain. It is the site of our faculties such as learning, reasoning, intelligence, personality and memory. All our thoughts, sensation, actions and movements are controlled by cerebrum.

The medulla controls various involuntary actions such as heart beat, breathing, blood pressure and peristaltic movements of the elementary canal. It is also the controlling centre for reflexes such a swallowing, coughing, sneezing, secretion of saliva and vomiting.

Spinal cord is a cylindrical structure which begins in continuation with medulla and extends downwards. Its function is the conduction of nerve impulses to and from the brain and it is concerned with spinal reflex actions.

Receptors are the special cells present in our sense organs which detect all the information from our environment and feed it to the nervous system. An effector responds to electrical impulses sent from the nervous system through motor nerves.

The classification of nervous into various parts is given in the following chart:

When the sense organ in our body is affected, it sends the message to the brain in the form of electrical impulses through the sensory neurons. The brain analyses this message and decides the action to be taken. The brain then sends out instructions to the muscles of the concerned body parts through motor nerves and the concerned body part acts accordingly.

1. Figure(ii)

2. Geotropism.

The closing of a dandelion flower at dusk (when it gets dark) is not a tropism because the direction of movement of petals of dandelion flower does not depend on the direction of stimulus (light).