Class 10 Science Chapter 6 Previous Year Questions - Control and Coordination

Ans: (c)
This is the place where the electrical impulse traveling along a nerve cell is converted into a chemical signal to communicate with a muscle cell. At this junction, neurotransmitters are released, allowing the nerve cell to signal the muscle to contract.

Ans: (A) 
OR
(B)

• Thyroxine 
• Thyroid gland  
• Iodine is necessary for thyroid gland to make thyroxine hormone. Deficiency of iodine in our diet causes goitre.

Ans: Reflex action is a sudden/spontaneous/immediate action in response to the environment/stimulus e.g. sneezing.

Ans: (a)
The pituitary gland is a single gland located at the base of the brain and is often referred to as the "master gland" because it controls many other hormone glands in the body. In contrast, the ovaries, testis, and adrenal glands occur in pairs (one on each side of the body).

Ans: (i)

(ii) (1) Cerebrum/forebrain,
(2) cerebellum/hindbrain
(3) medulla/ hindbrain
(4) hypothalamus/forebrain.
(iii) Brain – Bony box/skull/cranium/fluid filled balloon in skull, Spinal cord – Backbone/Vertebral column.
OR
(b) (i) Plant growth movements in response to stimuli in a particular direction/directional movements due to light, gravity etc.
(1) Plant growth inhibitor: Abscisic Acid
(2) Promotes cell division: Cytokinins
(ii)  When the tendrils come in contact with any support, auxins move away from the point of contact of the support. More growth occurs on the side away from the support. As a result, unequal growth occurs on its two sides and thus tendrils coil/ circle around the support.
Auxins

Ans: (d)
Cytokinins are a type of plant hormone that promote cell division and growth in plants. They help stimulate the growth of shoots and leaves and play a crucial role in various processes, such as fruit development and delaying aging in plant tissues.

Ans: (c)
Abscisic acid is a plant hormone that acts as a growth inhibitor and helps plants respond to stress, such as drought. It causes the stomata to close, reducing water loss and leading to wilting of leaves when the plant is under stress.

Ans: (i) Synthesized at shoot tip/root tip
(ii) When light falls on one side of the plant, auxin diffuses towards the shady side of shoot. The concentration of auxin stimulates the cells to grow longer on the side of shoot which is away from light. Thus plant appears bent towards light/phototropism.

Ans: (a) (i) 

• The pathway in which impulses travel during the reflex action is called a reflex arc. 
• Because the thinking part of the brain is not fast enough/for quick response to avoid injury. 
• Reflex arc:
  
  

(ii) Peripheral Nervous System Components : Cranial Nerves; Spinal Nerves
OR
(b)  (i) 

• Touch 
• The shape of the leaves changes by changing the amount of water in  them. 
• No 

(ii)  Growth of a part of plant in response to the pull of earth or gravity is called geotropism.

• Positive geotropism − Movement of plant part towards the earth gravity. Example − Roots grow downwards
• Negative geotropism − Movement of plant part away from the force of gravity. Example − Shoots grow upwards.

Ans: (c)
Receptors in skin → Sensory neuron → Relay neuron → Motor neuron → Effector muscle in arm. 
When you touch something hot, the receptors in your skin detect the heat and send a signal through sensory neurons to the relay neurons in the spinal cord. Then, relay neurons send the signal to motor neurons, which activate the effector muscles in your arm to pull away quickly, helping you avoid injury.

Ans: (a)
Olfactory receptors, which are responsible for the sense of smell, are located in the nasal cavity of the nose. When you inhale, these receptors detect different scents and send signals to the brain, allowing you to identify various smells.

Ans: (i) 

• Growth hormone.
• Secreted by pituitary gland. 
• It stimulates growth in all organs. 

(ii) 

• Thyroxin.
• Secreted by thyroid gland. 
• It regulates carbohydrate, protein and fat metabolism for body growth. 

Ans: (a)
Sol: Reflex arc is pathway taken by nerve impulses and responses in a reflex action, i.e., from receptor organs like skin to spinal cord and from spinal cord to effector organs like muscles.

Ans: (i) Cerebellum
(ii) Medulla oblongata
(iii) Cerebrum
(iv) Medulla oblongata

Ans: (a) Brain and spinal cord are protected by skeleton- brain by the cranium and spinal cord by vertebral column,
(b) (i) Medulla - It controls involuntary actions like heart beat, respiration, etc.
(ii) Cerebellum - It maintains posture and balance of body

Ans: Auxin is synthesised at tip of the stem apices or shoots.
(i) Shoots
(ii) Shoots
(iii) Roots (bend towards water)

Ans: Auxin is responsible for bending of a shoot of a plant when it is exposed to unidirectional light. In the presence of sunlight, the auxin present in the stem starts accumulating in the region away from sunlight, due to which the concentration of auxin in the region of the stem increases, resulting in bending of a shoot of a plant when it is exposed to unidirectional light. Thus, auxin promote phototropism that is the regulation of physiology or development in response to day length.

Ans: (d)
Tropic movements in plants are growth-related movements that occur in response to specific directional stimuli, such as light, gravity, water, or chemicals.
These movements are typically slow and involve growth in a particular direction, either towards (positive tropism) or away from (negative tropism) the stimulus.
Therefore, the correct answer is (d) It is a growth-related movement.

Ans: (A) Glucose enters the blood stream as soon as meals containing carbohydrates is digested by the body. As a result, the body's blood glucose levels rise. In order to direct all of the body's cells to take in the glucose, the pancreas releases chemical signals in the form of insulin. The majority of this glucose is consumed by the cells as energy. The liver and muscle cells take the extra glucose in the bloodstream and convert it to glycogen for later usage. In the end, insulin secretion reduces blood sugar levels. Diabetes is either caused due to the insufficient production of insulin by the pancreas or it may occur if the cells of the body are not effectively responding to the insulin produced. 
(B) Hormones are chemicals that our body secretes in a precise quantity and at a certain time. The release of hormones and the timing of their release are controlled by particular regulatory centres in our bodies. For instance: Regulation of insulin release - the pancreas secretes insulin, which regulates blood glucose levels. The higher blood glucose concentration affects how much insulin is produced. When blood glucose levels are really high, the pancreas releases more insulin.

Ans: Geotropism refers to the upward and downward growth of shoots and roots respectively in response to the pull of earth or gravity. If the plant part moves in the direction of gravity, it is called positive geotropism. Likewise, if the plant part moves against the direction of gravity, it is termed as negative geotropism. A well labelled diagram of plant showing geotropism is:

Ans: When squirrel is in a scary situation then its nervous system stimulates the adrenal glands to secrete more adrenaline hormone into blood. This adrenaline hormone increases heartbeat, breathing rate, blood flow into muscles and causes liver to put more stored glucose into its blood. All these actions of adrenaline hormone produces a lot of energy in squirrel’s body. In this way, squirrel prepares itself for fighting or running away action.

Ans: In animals, the message communicated in the form of nerve impulses, from receptors to central nervous system and from letter to effectors is very quick. But nerve impulses can reach only those animal cells which are connected by the nervous tissue.
These cells after generation and transmission of nerve impulses, take some time to reset their mechanism before a new impulse is generated and transmitted. It means, cells cannot continuously generate and transmit electrical impulses. This is the reason most multicellular organisms use another means of communication called chemical communication. In chemical communication, information spreads out throughout the body by blood and its effects lasts longer. Chemical communication is however slow, but it can reach all the cells of body regardless of nervous connections.

Ans: The cheetah senses its prey by photoreceptors and the information is sent to the central nervous system. The response is then carried by neurons. Along with nervous system, the hormonal system also plays a role. Adrenaline hormone produced by the adrenal glands triggers the flight or fight action. On seeing a prey, these hormones are released into the cheetah's bloodstream. It speeds up heartbeat, breathing increases blood flow into leg muscles and causes liver to put more stored glucose into cheetah's blood. All these actions of adrenaline hormone produces a lot of energy which helps cheetah to run fast.

Ans: Central nervous system consists of brain and spinal cord. It contains centres for controlling various activities of the body. Peripheral nervous system consists of cranial nerves and spinal nerves. Components of the central nervous system are protected by:
(i) Brain is contained within the skull while the spinal cord is encircled by a series of vertebrae.
(ii) Meninges are a succession of tissue layers that reside within these bony structures.
(iii) Cerebrospinal fluid (CSF) is a clear, colourless, slightly alkaline fluid that surrounds the brain and spinal cord that protects from infections.
The following signals will get disrupted in case of a spinal cord injury:

• Reflex action 
• Impulses from various body parts will not be conducted to brain. 
• Message from brain will not be conducted to various organs of the body.

Ans: (a) (i) Pituitary secretes hormones GH, TSH, ACTH, FSH, LH, PRL, MSH, oxytocin and vasopressin. Growth hormone (GH) or somatotropic hormone controls the overall development of body, muscles, bones and tissues. Disorder related to thyroid gland: Goitre (enlarged thyroid gland) can occur due to inadequate dietary intake of iodine which result in low level of thyroid hormones (since iodine is essential to make thyroid hormones). Low levels of thyroid hormones stimulates pituitary gland to secrete more TSH, which causes thyroid gland enlargement. Hyposecretion of growth hormone (GH) during growth year results into dwarfism. This could happen due to the hyperactivity of the pituitary gland.
(ii) Thyroid gland secrete three hormones thyroxine (T₄), triiodothyronine (T₃) and calcitonin. Thyroxine and triiodothyronine maintain the basal metabolic rate (BMR) of the body by regulating the rate of oxidation of carbohydrates, fats and proteins and production of energy in our body. They promote growth of body tissues and development of mental faculties.
(b) Both the timing and amount of hormone released are regulated by feedback mechanism. For example, the pancreas involved in the secretion and release of hormone insulin when the positive feedback is signalled by the increased blood glucose level, the insulin sequester the glucose in adipose tissue and liver cells as glucose and fats respectively. When the blood glucose level decreases, the negative feedback will signal the pancreas to stop the secretion of insulin.

Ans: (a) In humans, growth hormone is synthesized in the pituitary gland. In plants, growth hormone is synthesized in the apical meristem.
(b) When a plant is exposed to unidirectional light, the following sequence of events occur leading to bending of a growing shoot:
1. Photoreceptors in the shoot tip detect the direction and intensity of light.
2. Auxin, a plant hormone, is produced in higher concentrations on the shaded side of the shoot tip.
3. The higher concentration of auxin promotes cell elongation on the shaded side, causing the shoot to bend towards the light source.
4. The bending of the shoot towards the light is known as phototropism.
5. The bending helps the plant optimize its exposure to light, allowing for efficient photosynthesis.

Ans: A nerve impulse is a gradual physicochemical change in a nerve fibre's membrane that occurs after stimulation. This impulse travels from the dendrite to the cell body and then along the axon to its end.

Ans: Diagrammatic representation of a neuron is as follows:

Ans: At the synapse (functional junction between neurons), axon terminal comes in close proximity to the dendron terminal of next neuron. Axon terminal is expanded to form pre-synaptic knob and the other dendrite terminal forms post-synaptic depression. In between the two, lies a narrow fluid filled space called synaptic cleft. As the nerve impulse reaches the pre-synaptic knob, the synaptic vesicles get stimulated to release neurotransmitter in the synaptic cleft. The neurotransmitter molecules diffuse across the gap to come in contact with post-synaptic membrane. In this way, nerve impulse passes across the minute gap to stimulate dendron of another neuron. The synapse acts as a one-way valve to conduct impulse in one direction only. This is so because chemical substance called neurotransmitter is secreted only on one side of the gap, i.s., on axons side. It carries impulse across the synapse and passes it to the dendron of the other neuron. In this way, impulses travel across the neurons only in one direction, i.e., from axon of one neuron to dendron of other neuron through a synapse.

Ans: Distinguishing features between cerebrum and cerebellum:

Ans: When tendrils come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This is caused by the action of auxin hormone. Less auxin occurs on the side of contact as compared to the free side. As a result, auxin promotes growth on the free side and the tendrils coil around the support.

Ans: (a) In genetically dwarf plants, the length of internode is very much reduced but the number of nodes remains the same. Gibberellins overcome the phenotypic expression of dwarfism in certain plants. Besides general increase in stem length, gibberellins specifically induce internodal growth in some genetically dwarf varieties of plants like pea and maize. Gibberellins, however, have little or no effect when they are applied to the normal plant.
(b) Auxin is the plant hormone which promote cell enlargement and cell differentiation in plants. It also plays a role in apical dominance (i.e., the phenomenon in which presence of apical bud does not allow the nearby lateral buds to grow). When the apical bud is removed, the lateral buds sprout. This produces dense bushy growth. The phenomenon is widely used in tea plucking. Apical bud inhibits the growth of lateral buds by release auxin.
(c) Abscisic acid or ABA is a plant hormone or phytohormone which acts as growth inhibitor. It promotes dormancy in seeds and buds, abscission (falling of leaves) and senescence in leaves and thus inhibits growth of plant.

Ans: Plant hormones or phytohormones are chemical substances produced naturally in plants and capable of translocation and regulating one or more physiological processes when present in low concentration. These are also known as plant growth substances or plant growth regulators.
The plant hormones responsible for different functions are as follows:
(i) Growth of stem: Gibberellins (Gibberellic acid) promote growth in stems.
(ii) Promotion of cell division: Cytokinins promote cell division in plants.
(iii) Inhibition of growth: ABA (Abscisic acid) promotes dormancy in seeds as well as in buds and thus inhibits growth.
(iv) Elongation of cells: Auxin and cytokinin both cause cell elongation.

Ans: (a) Two types of neurons are:
(i) Sensory neurons - They transmit information from the receptors to the central nervous system.
(ii) Motor neurons - They transmit information from the brain to the effector organs.
(b) 

(i) Forebrain (a centre for hunger)
(ii) Hindbrain (medulla)

Ans: (a) (i) Voluntary actions are controlled by the cerebrum (the forebrain).
(ii) Involuntary actions are controlled by mid-brain (the medulla oblongata).
(b) Peripheral nervous system facilitates the communication between central nervous system and other body parts.
Components of peripheral nervous system are:
(i) Cranial Nerves: Originating from brain.
(ii) Spinal Nerves: Originating from spinal cord.

Ans: (a) Gland that secretes:
(i) Insulin - Pancreas
(ii) Thyroxine - Thyroid gland
(b) The timing and amount of hormone secreted are regulated by the “Feedback mechanisms”. For example:
(i) High glucose level in blood induces the pancreatic cells to produce more insulin which converts glucose to glycogen.
(ii) Low glucose level in the blood does not induce the pancreatic cells to produce insulin so that less conversion of glucose to glycogen occurs.

Ans: (a) Role of plant hormones:
Chemical control in the plants is performed through plant hormones. They help to coordinate growth, development and responses to the environment.
Plant hormones auxin and cytokinin help in cell division.
(b) When growing plants detect light, a hormone called auxin, synthesised at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light.

Ans: The downward growth of roots due to attraction by earth’s gravity and upward growth of shoots against it, is geotropism.

Ans: Feedback system is a regulatory mechanism in which the presence of a certain level of hormone promotes or inhibits its further formation.
Regulation of thyroxine production by its concentration in blood is an example of hormonal feedback system. If the level of thyroxine is more in the blood, this is detected by hypothalamus, which stops producing thyroid-stimulating hormone (TSH). Non-availability of TSH results in failure of thyroid to produce thyroxine. This automatically results in reduction of thyroxine in blood.
But if concentration of thyroxine is low in the blood, hypothalamus produces TSH which then passes into circulatoray system and reaches thyroid gland. Thyroid now begins to secrete more thyroxine.

Ans: 

Ans: Each step/level of the food chain where energy transfer takes place is called a trophic level.
Example: (i) Plants → Grasshopper Frog → Snake
(ii) Plants Deer → Hyena Tiger

Ans: (a) Cerebrum - Forebrain
(b) Medulla - Hind brain
(c) Cerebellum - Hind brain
(d) Cerebellum - Hind brain

Ans: (a) Phytohormones are chemical substances that regulate various physiological processes in plants. They are produced naturally by plants and control growth, development, and responses to environmental stimuli. 
Four types of phytohormones are:

• Auxins: These hormones regulate cell elongation, apical dominance, and phototropism. They are mainly synthesized in the apical meristem, young leaves, and developing seeds.
• Gibberellins: These hormones promote stem elongation, seed germination, and fruit development. They are primarily synthesized in the apical meristem, young leaves, and developing seeds.
• Cytokinins: These hormones promote cell division and differentiation, delay senescence, and regulate apical dominance. They are synthesized in actively growing tissues such as roots, embryos, and fruits.
• Abscisic Acid: This hormone controls seed dormancy, stomatal closure, and stress responses. It is synthesized in mature leaves, fruits, and seeds.

(b) When a growing plant detects light, it triggers a series of responses known as photomorphogenesis. The plant's photoreceptors, specifically phytochrome and cryptochrome, detect the light signal and initiate various physiological changes. These changes include:

• Phototropism: The plant bends towards the light source, which is controlled by auxin distribution in the stem.
• Chloroplast movement: Chloroplasts within the plant cells move to optimize light absorption for photosynthesis.
• Stomatal opening: Light stimulates the opening of stomata, allowing for gas exchange and transpiration.
• Flowering: Light is crucial for triggering the flowering process in many plants.

Overall, the detection of light by plants is essential for their growth, development, and ability to respond to their environment. 

Ans: (a) Cerebrum 
(b) Medulla
(c) Cerebrum
(d) Cerebrospinal fluid
(e) Meninges or three membranes covering the brain.

Ans: Brain and spinal cord are the two components of central nervous system.
Human brain is protected by a bony skull, also called as cranium. Internal to the skull it is covered from outside by three membranes called meninges. In between the meninges there is a fluid called as cerebrospinal fluid. Beneath the membranes brain is subdivided into three major parts namely fore-brain, midbrain and hind brain.
Brain is considered as highest coordinating centre of the body.
Its three regions are given below:

• Fore-brain is the main thinking part of the brain. It has different regions or areas such as:
  (i) Sensory area - It receives sensory impulses from various receptors.
  (ii) Auditory area - It is concerned with hearing.
  (iii) Olfactory area - It is concerned with smell.
  (iv) Gustatory area - It is concerned with taste.
  (v) Optic area - It is concerned with sight.
  (vi) Association area - This area interprets various sensory informations and makes decision how to respond.
  (vii) Motor area - Decisions made by association area are passed on to this area which control the movement of voluntary muscles.
• Midbrain comprises of four lobes. So it is also known as copra quadrigemina. Actions of involuntary muscles are controlled by the mid-brain and hind-brain.
• Hind-brain comprises of cerebellum, pons varolii and medulla oblongata. Cerebellum is the second largest part of brain that coordinates muscular activity of the body as well as maintains body equilibrium or posture. Pons connects cerebellum and medulla oblongata and functions as a relay centre among different parts of brain. It possesses pneumotaxic area of respiratory centre. Medulla oblongata lies below the cerebellum and continues behind the spinal cord. Involuntary actions like blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain.

Ans: The stimulus oriented movement of plant or plant part is called tropism. The direction of movement is related to the direction of stimulus. These movements are always growth oriented movements. They are of different types namely phototropism (growth movement in response to light), hydrotropism (water), geotropism (force of gravity), thigmotropism (contact) and chemotropism (chemicals).

• Phototropism is a directional growth movement which occurs in response to unidirectional exposure to light. The region of photoreception is shoot apex where auxin is produced. Auxin moves from the illuminated region to the shaded region. This causes more growth on the dark side of the stem causing it to bend towards the source of light. Movement of shoot towards light is called phototropism.
• Roots are positively geotropic and negatively phototropic. Shoots are positively phototropic and negatively geotropic.
• Growth of pollen tube inside the style, ovary and ovule in response to the chemicals produced by them is an example of chemotropism.

Ans: (a) Hormones are chemical informational molecules that are required in minute quantities and are directly poured in the blood stream by the glands. They act on a specific organ called target organ. So their site of production varies from site of action.
Their characteristics are:

• They are poured into blood stream.
• Are generally proteinaceous or steroid.
• Their secretion is regulated by feedback mechanism.
• Their site of action and secretion is different.

(b) 
(i) Dwarfism
(ii) Gigantism
(iii) Diabetes
(iv) Goitre.

Ans: When blood sugar level rises in blood, a hormone named ‘insulin" is produced by β-cells of islet of Langerhans in the organ Pancreas. Pancreas also produces pancreatic juice which contains pancreatic enzymes such as trypsin, pancreatic amylase and pancreatic lipase.
Insulin promotes glucose absorption by individual cells and absorption and formation of glycogen in liver and muscles. This reduces glucose level in blood. As soon as the blood sugar comes to normal the pancreatic cells stops secretion of insulin.
Pancreas secretes slightly alkaline pancreatic juice which contains three major following enzymes:

• Trypsin which digests proteins.
• Lipase which digests fats.
• Amylase which digests carbohydrates.

Ans: Plants possess chemical coordination. They respond to stimuli by secreting chemical substances called as plant growth regulators. They either stimulate or retard growth. Five major types of plant growth hormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene.
These plant growth regulators are also known as phytohormones.
These are synthesised at shoot apices, leaves, developing embryos, root tips etc.

Ans: (i) Auxin is a phytohormone which is synthesized at shoot tip.
(ii) When a plant is exposed to light coming from one side of the plant then auxin located at the shoot tip diffuses towards the shaded side of the shoot. High concentration of  auxin in the shaded region stimulates the cells  to grow longer in comparison to the region  exposed to light. So the shoot tends to bend towards the light.

Ans: Thyroxine regulates carbohydrates, protein and fat metaboslism in our body.
Thyroxine is secreted from thyroid gland. Deficiency of iodine in our food causes (goitre) where the thyroid gland to enlarges as it needs to absorbs more amount of iodine. Iodine is required to make thyroxine. Therefore, iodine is added to salt to supplement iodine requirement.

Ans: The two components of the Central Nervous System in humans are the brain and spinal cord.

Ans: Plants do not have nervous system and muscles. Even then they exhibit well coordinated and controlled movements. Plants possess chemical coordination. They respond to stimuli by secreting chemical substances called plant growth regulators. They either stimulate or retard growth. Five major types of plant growth hormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene.
Certain changes in the orientation of plant parts in relation to other parts caused by intrinsic or external stimuli are non-directional, growth independent movements. They are referred to as nastic movements. Thus, plants show movements due to growth or change in turgor pressure.

Ans: (a) Differences between enzymes and hormones:

(b) Pancreas performs dual function. It produces enzymes like Trypsin, Lipase etc., which aid in digestion. It also produces insulin hormone which regulates blood-sugar level.

Ans: Peripheral nervous system.

Ans: Synapse is the junction between two adjustment neuron or nerve cells, i.e. between axon ending of one and the dendrite of the next.
Transmission of Nerve Impulse. The information acquired at the end of the dendritic tip of a neuron sets off a chemical reaction which creates an electrical impulse. This impulse travels from the dendrite to the cyton along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals, which cross the synapse and start a similar electrical impulse in a dendrite of the next neuron. In this way nerve impulses travel in the body.
Synapse helps in transmitting impulses from one neuron to another.

Ans: Insulin is a hormone that regulates our blood sugar level by converting it into glycogen which can be stored.
Hence, if there is more levels of sugar in blood then more insulin is produced and if the sugar level is less then insulin production is also reduced.
This is because of feedback mechanism where the blood sugar itself acts as a feedback for more or reduced insulin synthesis.

Ans: Roles of ovary:

• Ovaries produce female gametes, ova.
• It also produces a female sex hormone called estrogen. Estrogen is essential for development of secondary sex organs in female as well as secondary sexual characters like high pitch voice, development of mammary glands.

Ans: Reflex action is defined as an unconscious, automatic and involuntary response of effector, i.e. muscle and gland to a stimulus which is monitored through the spinal cord.

Sequence of events when we touch a hot object are:

• Receptor organ skin receives the stimulus and activates a sensory nerve impulse.
• Sensory neuron carries the message in the form of sensory impulse to the spinal cord.
• The spinal cord acts as a modulator. The neurons of the spinal cord transmit the sensory nerve impulses to the motor neuron.
• Motor nerve conducts these impulses to the effector organ hand which responds by pulling back the hand away from the hot object.

Ans: