Q.1 Draw the structure of a neuron and explain its function.
Ans. The neuron is a highly specialised cell responsible for the transmission of nerve impulses.
Soma or cell body is a star-shaped hair-like structure. Hair-like structures are called dendrites. Dendrites receive nerve impulses.
Axon is the tail of the nucleus it ends in hair-like structures which makes nerve endings. Nerve endings relay nerve impulses.
Myelin sheath acts as an insulator around the axon. It insulates axons from the electrical impulses from the surroundings.
The function of a neuron is to process and transmit information from the brain to all parts of the body.
Q.2 What are the major parts of the brain? Mention the functions of different parts.
Ans.
Functions of brain Parts
Forebrain: The forebrain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing, smell, sight and so on.
Midbrain and Hindbrain: Involuntary actions are controlled by the mid-brain and hind-brain.
Cerebellum: Responsible for voluntary actions and maintaining the posture and balance of the body.
Cerebrum: Cerebrum is responsible for sensory processing.
Medulla: Medulla controls involuntary functions.
Pons: Pons regulates respiration and controls involuntary action sensations such as touch and pain.
Hypothalamus: Hypothalamus control the sleep and wake cycle
Q.3 What constitutes the central and peripheral nervous systems? How are the components of central nervous system protected?
Ans. The central nervous system (CNS) consists of the brain and the spinal cord, while the peripheral nervous system (PNS) comprises all the nerves that branch out from the brain and spinal cord to the various parts of the body. The CNS is protected by three main features: the skull and vertebral column, which physically shield the brain and spinal cord; the meninges, which are three layers of protective tissues (dura mater, arachnoid mater, and pia mater) that enclose the CNS; and the cerebrospinal fluid, which circulates within the spaces in and around the CNS, cushioning it and providing a buffer against injury.
Q.4 Mention one function for each of these hormones :
(a) Thyroxin
(b) Insulin
(c) Adrenaline
(d) Growth hormone
(e) Testosterone.
Ans. Functions of hormones:
(a) Thyroxin: Regulates metabolism, growth, and development, and influences the metabolic rate.
(b) Insulin: Lowers blood glucose levels by facilitating the uptake of glucose by cells.
(c) Adrenaline: Increases heart rate, blood pressure, and energy supply in response to stress (‘fight or flight’ hormone).
(d) Growth hormone: Stimulates growth, cell reproduction, and regeneration in the body.
(e) Testosterone: Responsible for the development of male secondary sexual characteristics, such as increased muscle and bone mass, and the growth of body hair.
Q.5 Name various plant hormones. Also give their physiological effects on plant growth and development.
Ans. Various plant hormones and their physiological effects include:
- Auxins: Promote stem elongation, root initiation, and fruit growth; regulate phototropism and gravitropism.
- Gibberellins: Stimulate stem elongation, seed germination, and flowering; break seed dormancy.
- Cytokinins: Promote cell division, leaf expansion, and chloroplast formation; delay leaf senescence.
- Ethylene: Promotes fruit ripening, leaf abscission, and flower wilting; involved in response to stress.
- Abscisic acid (ABA): Inhibits growth, promotes seed dormancy, and helps close stomata during water stress.
Q.6 What are reflex actions? Give two examples. Explain a reflex arc.
Ans. Reflex actions are automatic, involuntary responses to stimuli that do not involve conscious thought. They are rapid and are meant to protect the body from harm. Examples include the blinking reflex in response to an object suddenly approaching the eyes and the knee-jerk reflex when the knee is tapped. A reflex arc is the neural pathway that mediates a reflex action. It involves a sensory neuron that detects the stimulus and sends a message to the spinal cord, where an interneuron relays the message to a motor neuron, which then triggers a response in the effector organ (muscle or gland).
Q.7 “Nervous and hormonal systems together perform the function of control and coordination in human beings.” Justify the statement.
Ans. The nervous and hormonal systems together perform the function of control and coordination in human beings by ensuring that internal processes run smoothly and can adapt to changes in the environment. The nervous system provides fast, short-term, and precise responses by transmitting electrical impulses along neurons. The hormonal system, through the release of hormones into the bloodstream, provides slower, more general, and longer-lasting effects to regulate growth, development, metabolism, and homeostasis. Both systems interact closely, as seen in the hypothalamus and pituitary gland, which link the nervous and endocrine systems, ensuring a cohesive and efficient response to internal and external stimuli.
Q.8 How does chemical coordination take place in animals?
Ans. Chemical coordination in animals occurs through the endocrine system, where hormones are released by glands directly into the bloodstream. These hormones then travel to target organs or tissues, where they bind to specific receptors and trigger responses that regulate various bodily functions. This system allows the body to maintain homeostasis, regulate growth and development, manage energy production and usage, and respond to environmental changes.
Q.9 Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse?
Ans. The flow of signals in a synapse from the axonal end of one neuron to the dendritic end of another neuron but not the reverse is due to the unidirectional nature of synapses. This directionality is because neurotransmitters are only released from the presynaptic neuron’s axon terminal and receptor sites are only located on the postsynaptic neuron’s dendrites or cell body. Additionally, the mechanisms for neurotransmitter release and receptor activation are designed to work in one direction. This ensures precise control over the transmission of nerve impulses, allowing for coordinated and appropriate responses to stimuli.
