CBSE Class 10 Science Control and Coordination Worksheet Set 11

Answer: Chemical coordination is carried out by hormones. Hormones are secreted by endocrine glands and carried by the blood to the target organs.

Teacher's Note:
1. Hormones act as chemical messengers.
2. Their action is slower than nerve impulses but lasts longer.

Answer: It is the mechanism that regulates the amount of hormone released. For example, when blood sugar rises, the pancreas releases more insulin, and when the sugar level falls, insulin release is reduced.

Teacher's Note:
1. The level of a substance in the blood controls the gland that regulates it.
2. This keeps the hormone level neither too high nor too low.

Answer: The medulla, which is part of the hind brain.

Teacher's Note:
1. Medulla controls actions that we do not think about.
2. It lies at the base of the brain and joins the spinal cord.

Answer: Growth of the pollen tube towards the ovule is chemotropism. The tube grows in response to chemicals released by the ovule.

Teacher's Note:
1. Tropism is directional growth in response to a stimulus.
2. In chemotropism the stimulus is a chemical.

Answer: The axon.

Teacher's Note:
1. Dendrites receive the information and the axon carries it away.
2. The axon ends in nerve endings that pass the signal to the next cell.

Answer: The brain is enclosed in the bony box called the cranium and is also surrounded by cerebrospinal fluid. The spinal cord is enclosed in the vertebral column (backbone).

Teacher's Note:
1. Both organs are delicate and need strong protection.
2. The fluid works as a shock absorber.

Answer: 1. Maintaining posture and balance of the body.
2. Precision of voluntary actions such as walking in a straight line or picking up a pencil.

Teacher's Note:
1. The cerebellum is part of the hind brain.
2. A damaged cerebellum makes movements jerky and unsteady.

Answer: (i) Cerebellum (hind brain).
(ii) Medulla (hind brain).
(iii) Hypothalamus (fore brain).
(iv) Cerebrum (fore brain).

Teacher's Note:
1. The brain has three main regions: fore brain, mid brain and hind brain.
2. Each region handles specific functions.

Answer: A reflex arc is the pathway of the nerve impulse in a reflex action: receptor, sensory neuron, spinal cord, motor neuron, effector. Reflex arcs have evolved because the brain takes too long to think and decide, while quick reactions protect the body from harm.

Teacher's Note:
1. In a reflex the spinal cord, not the brain, takes the decision.
2. The signal still reaches the brain afterwards.

Answer: The cerebrum is the largest part of the fore brain and is the seat of thinking, memory, learning and voluntary action. The spinal cord carries messages between the body and the brain and controls reflex actions.

Teacher's Note:
1. The cerebrum is in the skull and the spinal cord is in the backbone.
2. Only the cerebrum handles conscious thought.

Answer: The body needs growth hormone in the right amount. Too little in childhood causes dwarfism, while too much causes gigantism.

Teacher's Note:
1. Growth hormone is secreted by the pituitary gland.
2. Hormones must be in balance for normal growth.

Answer: Signals travelling between the body and the brain through the spinal cord will be disrupted, so sensations from below the injury will not reach the brain and commands from the brain will not reach the muscles. Reflex actions controlled at the level of the injury may also be affected because the spinal cord is their control centre.

Teacher's Note:
1. The spinal cord is the main nerve pathway to the brain.
2. A helmet protects the head, and the backbone needs care too.

Answer: A reflex action is a quick automatic response to a stimulus, usually through the spinal cord (example: pulling the hand away from a hot object). An involuntary action is not under our will but is controlled mostly by the medulla and works continuously inside the body (example: heartbeat or digestion).

Teacher's Note:
1. Both happen without conscious thinking.
2. Reflex actions are fast responses to outside stimuli.

Answer: 1. Nervous control uses electrical impulses along nerves, hormonal control uses chemicals carried by the blood.
2. Nervous response is very fast, hormonal response is slow.
3. Nervous effects are short lived, hormonal effects last longer.
4. Nerve impulses reach only specific cells, hormones spread through the body and act on target cells.

Teacher's Note:
1. Both systems work together to coordinate the body.
2. Nerves suit quick actions and hormones suit slow processes such as growth.

Answer: In the sensitive plant, leaves fold on touch because cells lose water and change shape, with no nerves involved. In the leg, muscles move under signals sent by nerves and the brain.

Teacher's Note:
1. Plants have no nervous tissue.
2. They use electrical-chemical signals and hormones to pass information.

Answer: (a) Pituitary gland.
(b) Pancreas.
(c) Adrenal gland.
(d) Testes.

Teacher's Note:
1. Endocrine glands release hormones directly into the blood.
2. The pancreas is both an exocrine and an endocrine gland.

Answer: Nervous tissue and muscular tissue.

Teacher's Note:
1. Nervous tissue receives and sends information.
2. Muscular tissue carries out the response by changing shape.

Answer: A tropic movement is directional growth of a plant part towards or away from the stimulus (example: roots growing down due to gravity). A nastic movement does not depend on the direction of the stimulus (example: leaves of touch-me-not drooping on touch).

Teacher's Note:
1. Tropic movements involve growth, nastic movements usually do not.
2. Directional growth is the key difference.

Answer: (i) Phototropism.
(ii) Geotropism.
(iii) Chemotropism.

Teacher's Note:
1. The prefix tells the stimulus: photo (light), geo (earth), chemo (chemical).
2. The suffix tropism means directional growth.

Answer: Goitre (swollen neck). Iodine is needed by the thyroid gland to make thyroxine, so iodised salt prevents deficiency.

Teacher's Note:
1. Thyroxine controls the metabolism of carbohydrates, fats and proteins.
2. Goitre is common in regions where soil and water lack iodine.

Answer: Endocrine glands have no ducts and release hormones directly into the blood. Exocrine glands have ducts that carry their secretions, such as enzymes, to the site of action.

Teacher's Note:
1. The pancreas has both kinds of cells.
2. Salivary glands are exocrine glands.

Answer: (a) Sensory neuron carries information from receptors to the brain or spinal cord.
(b) Vertebral column protects the spinal cord and supports the body.
(c) Motor neuron carries instructions from the brain or spinal cord to the effector (muscle or gland).

Teacher's Note:
1. Sensory neurons bring messages in and motor neurons carry them out.
2. Remember the direction: receptor to centre to effector.