Science is Life

Monday 4 April 2016

NCERT questions on reflection and refraction

We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

Answer: When object is between principal focus and pole of a concave mirror, an erect, enlarged and virtual image is formed. So, we need to keep the object at a distance which is less than 15 cm (the given focal length).

Which one of the following materials cannot be used to make a lens?
- Water
- Glass
- Plastic
- Clay
  
  Answer: (d) Clay
The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
- Between the principal focus and the centre of curvature
- At the centre of curvature
- Beyond the centre of curvature
- Between the pole of the mirror and its principal focus.
  
  Answer: (d) Between the pole of the mirror and its principal focus
Where should an object be placed in front of a convex lens to get a real image of the size of the object?
- At the principal focus of the lens
- At twice the focal length
- At infinity
- Between the optical centre of the lens and its principal focus.
  
  Answer: (b) At twice of the focal length
A spherical mirror and a thin spherical lens have each a focal length of –15 cm. The mirror and the lens are likely to be
- both concave
- both convex
- the mirror is concave and the lens is convex
- the mirror is convex, but the lens is concave
  
  Answer: (a) both concave
No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
- plane
- concave
- convex
- either plane or convex
  
  Answer: (d) either plane or convex
Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
- A convex lens of focal length 50 cm
- A concave lens of focal length 50 cm
- A convex lens of focal length 5 cm
- A concave lens of focal length 5 cm
  
  Answer: (c) A convex lens of focal length 5 cm
Name the type of mirror used in the following situations.
- Headlights of a car.
  
  Answer: When a source of light is kept at focus of a concave mirror, the reflected rays form a parallel beam of light and go to infinity. Hence, concave mirror is used as reflector in the headlights. This helps in getting a parallel beam of light.
- Side/rear-view mirror of a vehicle.
  
  Answer: A convex mirror can show image of a wider area, because of its wide field of view. This enables the driver to see more of traffic coming from behind. Hence, convex mirror is used as rear-view mirror in vehicles.
- Solar furnace.
  
  Answer: The light rays coming from infinity converge at the focus after reflection from a concave mirror. Hence, a concave mirror is used in solar furnace because it helps in concentrating the solar energy at a point.
One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

Answer: Covering the half portion of a convex lens will not affect the image making ability of the lens. The following two figures illustrate this.
Condition 1: When upper half of the lens is covered:

Condition 2: When the lower half of the lens is covered
An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.

Answer: Given, height of object = 5cm
Position of object, u = - 25cm

Focal length of the lens, f = 10 cm

Hence, position of image, v =?

We know that;

Thus, distance of image is 16.66 cm on the opposite side of lens.

Now, magnification = v/u

The negative sign of height of image shows that an inverted image is formed.

Thus, position of image = At 16.66 cm on opposite side of lens

Size of image = - 3.3 cm at the opposite side of lens

Nature of image – Real and inverted.
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.

Answer: Given, focal length, f = - 15 cm
Distance of image, v = - 10 cm

Distance of object, v =?

Object distance can be calculated using the lens formula

Negative sign shows that object is at 30cm in front of the lens.

An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.

Answer: Given, distance of object, u = -10cm
Focal length, f = 15cm

Distance of image, v =?; which can be calculated as follows:

The positive sign of image shows that image is formed at the other side of lens at 6 cm

Magnification can be calculated as follows:

m = v/u

Or, m = -6 cm/-10 cm = 3/5 cm = 0.6 cm

The positive sign of magnification shows that image is erect. Image is erect and virtual and is formed 6 cm behind the mirror.
The magnification produced by a plane mirror is +1. What does this mean?

Answer: The magnification of +1 means that the image size is same as object size.
An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.

Answer: Given, distance of object, u = - 20 cm
Height of object = 5.0 cm

Radius of curvature, R = 30cm.

Hence, focal length = R/2 = 30/2 cm = 15 cm

Distance of image, v =?; which can be calculated as follows:

The positive sign of height of image is erect. Therefore, position of image 8.57 cm behind the mirror.

Nature of image – erect and virtual.

Size of image – 2.14 cm, this means image is smaller than object.
An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focussed image can be obtained? Find the size and the nature of the image.

Answer: Given, size of object, h = 7.0 cm
Distance of object, u = - 27 cm

Focal length, f = - 18 cm

Distance of image, v =?; which can be calculated as follows:

Height of image can be calculated as follows:

Negative sign of height of image shows, that image in inverted. Thus, screen should be placed at 54 cm in front of mirror.

The size of image = 14cm

Nature of image – real and inverted.
Find the focal length of a lens of power – 2.0 D. What type of lens is this?

Answer: Power P = -2.0D
Since, P = 1/f

Hence, -2.0 D = 1/f

Or, f = 1/(-2D) = -0.5 m

Since focal length is negative hence, it is a concave lens.
A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Answer: Given, power = +1.5 D
Since, P = 1/f

Hence, 1.5 D = 1/f

Or, f = 1/1.5 D = 0.66 m

The positive sign shows it is a converging lens.

questions on heredity and evolutions

Explain the importance of fossils in deciding evolutionary relationships.

Answer: There are certain animals which became extinct millions of years ago. Fossils of many of such animals give important clues about missing links in the evolutionary relationship. The fossil of archaeopteryx is a good example of missing link. The fossil of archaeopteryx shows characters of birds and reptiles; which suggests that birds have evolved from reptiles. This example shows the importance of fossils in deciding evolutionary relationships.

Explain the term analogous and homologous organs with examples.

Answer: Homologous Organs: Organs which have common design but serve different functions in different animals are called homologous organs. For example; the forelimbs of all tetrapods are composed of humerus, radio-ulna, tarsals and metatarsals. Yet, the forelimbs of frogs are adapted to a jumping movement, those of birds are used for flying and those of humans are used for handling tools. This shows that frogs, birds and humans have evolved from a common ancestor.

Analogous Organs: Organs which have different design but serve a common function in different animals are called analogous organs. Wings of birds and wings of bat are good examples of a pair of analogous organs. Wings of birds are composed of all the bones of forelimb and are covered with feathers. Wings of bats are mainly composed of the digital bones and a thin membrane covering the structure. Yet wings in both the organisms are used for flying.

A Mendelian experiment consisted of breeding tall pea plant bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic makeup of the tall parent can be depicted as?
- TTWW
- TTww
- TtWW
- TtWw
  
  Answer: (c) TtWW
An example of homologous organs is
- Our arm and a dog’s fore-leg
- Our teeth and an elephant’s tusks
- Potato and runners of a grass
- All of the above
  
  Answer: (d) All of the above
In evolutionary terms, we have more in common with
- A Chinese boy
- A chimpanzee
- A spider
- A bacterium
  
  Answer: (a) A Chinese boy
A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Answer: This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

How are the areas of study; evolution and classification interlinked?

Answer: The modern system of classification is also called phylogenetic classification; which means it is based on evolutionary relationships. Hence, evolution and classification are closely related.
Outline a project which aims to find the dominant coat colour in dogs.

Answer: For this, take a male dog with brown coat and bitch with white coat. Cross them to get the F1 generation. After that, allow the F2 generation to come into being. Tabulate data from two generations and find out the dominant coat colour.
What evidence do we have for the origin of life from inanimate matter?

Answer: The famous experiment by Miller and Urey could establish that life originated from inanimate matter. These scientists replicated the conditions which may have existed during the early years of origin of the earth. In that experiment, inorganic substances gave rise to amino acids. Amino acid; we know are the bases of various biomolecules.
Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Answer: During sexual reproduction, genotype of the progeny is contributed by two different individuals. This opens up scope for various permutations and combinations. Moreover, the crossing over during meiosis is another means for producing variations. Hence, there are more chances of variations during sexual reproduction than during asexual reproduction.
How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer: Gametogenesis involves meiosis which leads to haploidy in the gametes. A zygote thus gets 50% of genes from each parent. Thus, equal genetic contribution is ensured from male and female parents.
Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

Answer: This statement is true to some extent. There are many apparent variations which help an individual in survival. But there are certain variations which may not be beneficial, yet they are inherited through subsequent generations. The colourful plumage of peacock is a good example. The colourful plumage of a peacock helps it in finding a suitable mate but it also makes it conspicuous for its predators.

important questions of control and coordination

Which signals will get disrupted in case of a spinal cord injury?

Answer: The spinal nerves go to the organs which are below the head region. Moreover, the autonomous nervous system is also connected to the spinal cord. In case of spinal cord injury, communication between the spinal nerves and the brain would be disturbed. Similarly, the communication between the autonomous nervous system and brain would also be disturbed; in case of spinal cord injury.

What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer: Receptors provide information about the external environment so that the brain can instruct a related to organ to take necessary action. Receptors play an important role in our survival. Let us take the example of a person with hearing impairment. Certain ordinary task would be very difficult for that person. For example; while walking on the road, the person needs to hear the sound of vehicles moving near him. Without hearing those sounds, he would not be in a position to move safely on the road.

Which of the following is a plant hormone?
- Insulin
- Thyroxin
- Oestrogen
- Cytokinin
  Answer: (d) Ctyokinin
The gap between two neurons is called a
- Dendrite
- Synapse
- Axon
- Impulse
  Answer: (b) Synapse
The brain is responsible for
- Thinking
- Regulating the heart beat
- Balancing the body
- All of the above
  Answer: (d) All of the above
Draw the structure of a neuron and explain its function.
Answer: Function of Neuron: Neuron transmits the nerve impulses.

How does phototropism occur in plants?
Answer: Concentration of auxin changes in a particular plant part, in response to the direction of light. For example; in a stem, concentration of auxin increases in those parts which are away from light. This increases cell division in that part and thus the stem bends towards light. That is how phototropism occurs in plants.
How does chemical coordination occur in plants?
Answer: Plant hormones play their roles in chemical coordination. Most of the plant hormones promote growth in certain plant parts, e.g. auxin, gibberellins and cytokinin. Abscissic acid is a plant hormone which inhibits growth. Shedding of leaves or ripe fruits is facilitated by abscissic acid.
What is the need for a system of control and coordination in an organism?
Answer: A living being does not live in isolation. It has to constantly interact with its external environment and has to respond properly for its survival. For example; when a hungry lion spots a deer, the lion has to quickly make a move so that it can have its food. On the other hand, the deer needs to quickly make a move to run for its life.
How are involuntary actions and reflex actions different from each other?
Answer: Involuntary actions are part of routine activities, while reflex actions are in response to a sudden danger. Moreover, involuntary actions happen in involuntary organs, while reflex action happens in a voluntary organ.
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer: Nervous control is fast, while hormonal control is slow. Nervous control is facilitated by neurotransmitters, while hormonal control is facilitated by hormones.
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer: The movement in a sensitive plant is facilitated by chemical control, while the movement in our legs is facilitated by nervous control.
- Which of the following statements is correct about receptors?
  - Gustatory receptors detect taste while olfactory receptors detect smell
  - Both gustatory and olfactory receptors detect smell
  - Auditory receptors detect smell and olfactory receptors detect taste
  - Olfactory receptors detect taste and gustatory receptors smell
    Answer: (a) Gustatory receptors detect taste while olfactory receptors detect smell
- Electrical impulse travels in a neuron from
  - Dendrite ⇨ axon ⇨ axonal end ⇨ cell body
  - Cell body ⇨ dendrite ⇨ axon ⇨ axonal end
  - Dendrite ⇨ cell body ⇨ axon ⇨ axonal end
  - Axonal end ⇨ axon ⇨ cell body ⇨ dendrite
    Answer: (c) Dendrite ⇨ Cell body ⇨ Axon ⇨ Axonal end
- In a synapse, chemical signal is transmitted from
  - Dendritic end of one neuron to axonal end of another neuron
  - Axon to cell body of the same neuron
  - Cell body to axonal end of the same neuron
  - Axonal end of one neuron to dendritic end of another neuron
    Answer: (d) Axonal end of one neuron to dendritic end of another neuron
- In a neuron, conversion of electrical signal to a chemical signal occurs at/in
  - Cell body
  - Axonal end
  - Dendritic end
  - Axon
    Answer: (b) Axonal end
- Which is the correct sequence of the components of a reflex arc?
  - Receptors ⇨ Muscles ⇨ Sensory neuron ⇨ Motor neuron ⇨ Spinal cord
  - Receptors ⇨ Motor neuron ⇨ Spinal cord ⇨ Sensory neuron ⇨ Muscle
  - Receptors ⇨ Spinal cord ⇨ Sensory neuron ⇨ Motor neuron ⇨ Muscle
  - Receptors ⇨ Sensory neuron ⇨ Spinal cord ⇨ Motor neuron ⇨ Muscle
    Answer: (d) Receptors ⇨ Sensory neuron ⇨ Spinal cord ⇨ Motor neuron ⇨ Muscle
- Which of the following statements are true?
  - Sudden action in response to something in the environment is called reflex action
  - Sensory neurons carry signals from spinal cord to muscles
  - Motor neurons carry signals from receptors to spinal cord
  - The path through which signals are transmitted from a receptor to a muscle or a gland is called reflex arc
  - (i) and (ii)
  - (i) and (iii)
  - (i) and (iv)
  - (i), (ii) and (iii)
    Answer: (c) (i) and (iv)
- Which of the following statements are true about the brain?
  - The main thinking part of brain is hind brain
  - Centres of hearing, smell, memory, sight, etc. are located in forebrain.
  - Involuntary actions like salivation, vomiting, blood pressure are controlled by the medulla in the hind brain
  - Cerebellum does not control posture and balance of the body
  - (i) and (ii)
  - (i), (ii) and (iii)
  - (ii) and (iii)
  - (iii) and (iv)
    Answer: (c) (ii) and (iii)
- Posture and balance of the body is controlled by
  - Cerebrum
  - Cerebellum
  - Medulla
  - Pons
    Answer: (b) Cerebellum
- Spinal cord originates from
  - Cerebrum
  - Medulla
  - Pons
  - Cerebellum
    Answer: (b) Medulla
- The movement of shoot towards light is
  - Geotropism
  - Hydrotropism
  - Chemotropism
  - Phototropism
    Answer: (d) Phototropism
  - The main function of abscissic acid in plants is to
    
    Increase the length of cells
    
    Promote cell division
    
    Inhibit growth
    
    Promote growth of stem
    Answer: (c) Inhibit growth
    
    The growth of tendril in pea plants is due to
    
    Effect of light
    
    Effect of gravity
    
    Rapid cell divisions in tendrillar cells that are away from the support
    
    Rapid cell divisions in tendrillar cells in contact with the support
    Answer: (c) Rapid cell divisions in tendrillar cells that are away from the support
    The growth of pollen tubes towards ovules is due to
    
    Hydrotropism
    
    Chemotropism
    
    Geotropism
    
    Phototropism
    Answer: (b) Chemotropism
    
    The movement of sunflower in accordance with the path of sun is due to
    
    Phototropism
    
    Geotropism
    
    Chemotropism
    
    Hydrotropism
    Answer: (a) Phototropism
    
    The substance that triggers the fall of mature leaves and fruits from plants is due to
    
    Auxin
    
    Gibberellin
    
    Abscissic acid
    
    Cytokinin
    Answer: (c) Abscissic acid
    Which of the following is not associated with growth of plant?
    
    Auxin
    
    Gibberellins
    
    Cytokinins
    
    Abscissic acid
    Answer: (d) Abscissic acid
    
    Iodine is necessary for the synthesis of which hormone?
    
    Adrenaline
    
    Thyroxin
    
    Auxin
    
    Insulin
    Answer: (b) Thyroxine
    
    Choose the incorrect statement about insulin
    
    It is produced from pancreas
    
    It regulates growth and development of the body
    
    It regulates blood sugar level
    
    Insufficient secretion of insulin will cause diabetes
    Answer: (b) It regulates growth and development of the body
    
    Select the mis-matched pair
    
    Adrenaline: Pituitary gland
    
    Testosterone: Testes
    
    Estrogen: Ovary
    
    Thyroxin: Thyroid gland
    Answer: (a) Adrenaline: Pituitary gland
    
    The shape of guard cells changes due to change in the
    
    Protein composition of cells
    
    Temperature of cells
    
    Amount of water in cells
    
    Position of nucleus in the cells
    Answer: (c) Amount of water in cells
    
    Nerve impulse travels from dendritic end towards axonal end
    
    At the dendritic end electrical impulses bring about the release of some chemicals which generate an electrical impulse at the axonal end of another neuron
    
    The chemicals released from the axonal end of one neuron cross the synapse and generate a similar electrical impulse in a dendrite of another neuron
    
    A neuron transmits electrical impulses not only to another neuron but also to muscle and gland cells
    Answer: (c) The chemicals released from the axonal end of one neuron cross the synapse and generate a similar electrical impulse in a dendrite of another neuron
    
    Involuntary actions in the body are controlled by
    
    Medulla in forebrain
    
    Medulla in midbrain
    
    Medulla in hindbrain
    
    Medulla in spinal cord
    Answer: (c) Medulla in the hindbrain
    
    Which of the following is not an involuntary action?
    
    Vomiting
    
    Salivation
    
    Heart beat
    
    Chewing
    Answer: (d) Chewing
    
    When a person is suffering from severe cold, he or she cannot
    
    Differentiate the taste of an apple from that of an ice cream
    
    Differentiate the smell of a perfume from that of an agarbatti
    
    Differentiate red light from green light
    
    Differentiate a hot object from a cold object
    Answer: (b) Differentiate the smell of a perfume from that of an agarbatti
    
    What is the correct direction of flow of electrical impulses?
    
    Which statement is not true about thyroxin?
    
    Iron is essential for the synthesis of thyroxin
    
    It regulates carbohydrates, protein and fat metabolism in the body
    
    Thyroid gland requires iodine to synthesise thyroxin
    
    Thyroxin is also called thyroid hormone
    Answer: (a) Iron is essential for the synthesis of thyroxine
    
    Dwarfism results due to
    
    Excess secretion of thyroxin
    
    Less secretion of growth hormone
    
    Less secretion of adrenaline
    
    Excess secretion of growth hormone
    Answer: (b) Less secretion of growth hormone
    
    Dramatic changes of body features associated with puberty are mainly because of secretion of
    
    Oestrogen from testes and testosterone from ovary
    
    Oestrogen from adrenal gland and testosterone from pituitary gland
    
    Testosterone from testes and Oestrogen from ovary
    
    Testosterone from thyroid gland and Oestrogen from pituitary gland
    Answer: Testosterone from testes and Oestrogen from ovary
    
    A doctor advised a person to take an injection of insulin because
    
    His blood pressure was low
    
    His heart was beating slowly
    
    He was suffering from goiter
    
    His sugar level in blood was high
    Answer: (d) His sugar level in blood was high
    
    The hormone which increases the fertility in males is called
    
    Oestrogen
    
    Testosterone
    
    Insulin
    
    Growth hormone
    Answer: (b) Testosterone
    
    Which of the following endocrine glands is unpaired?
    
    Adrenal
    
    Testes
    
    Pituitary
    
    Ovary
    Answer: (c) Pituitary
    
    Junction between two neurons is called
    
    Cell junction
    
    Neuro muscular junction
    
    Neural joint
    
    Synapse
    Answer: (d) Synapse
    
    In humans, the life processes are controlled and regulated by
    
    Reproductive and endocrine systems
    
    Respiratory and nervous systems
    
    Endocrine and digestive systems
    
    Nervous and endocrine systems
    Answer: (d) Nervous and endocrine systems

notes of control and coordination

Importance of control and coordination

A living being does not live in isolation. It has to constantly interact with its external environment and has to respond properly for its survival. For example; when a hungry lion spots a deer, the lion has to quickly make a move so that it can have its food. On the other hand, the deer needs to quickly make a move to run for its life. The responses which a living being makes in relation to external stimuli are controlled and coordinated by a system; especially in complex animals.

Nervous System

The nervous system is composed of specialized tissues; called nervous tissue. The nerve cell or neuron is the functional unit of the nervous system. It is the nervous system which is mainly responsible for control and coordination in complex animals.

Neuron: Neuron is a highly specialized cell which is responsible for transmission of nerve impulses. The neuron consists of the following parts:

Cyton or cell body: The cell body or cyton is somewhat star-shaped; with many hair-like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.
Axon: This is the tail of the neuron. It ends in several hair-like structures; called axon terminals. The axon terminals relay nerve impulses.
Myelin Sheath: There is an insulator cover around the axon. This is called myelin sheath. The myelin sheath insulates the axon against nerve impulses from the surroundings.

Types of Neuron

Sensory neuron: These neurons receive signals from a sense organ.
Motor neuron: These neurons send signals to a muscle or a gland.
Association neuron: These neurons relay the signals between sensory neuron and motor neuron.

Nervous System in Humans

The nervous system in humans can be divided into two main parts, viz. the central nervous system and the peripheral nervous system. The peripheral nervous system can be further divided into the somatic nervous system and the autonomous nervous system.

Central Nervous System: The central nervous system is composed of the brain and the spinal cord. The brain controls all the functions in the human body. The spinal cord works as the relay channel for signals between the brain and the peripheral nervous system.
Peripheral Nervous System: The peripheral nervous system is composed of the cranial nerves and spinal nerves. There are 12 pairs of cranial nerves. The cranial nerves come out of the brain and go to the organs in the head region. There are 31 pairs of spinal nerves. The spinal nerves come out of the spinal cord and go to the organs which are below the head region.

Autonomous Nervous System: The autonomous nervous system is composed of a chain of nerve ganglion which runs along the spinal cord. It controls all the involuntary actions in the human body. The autonomous nervous system can be divided into two parts:

Sympathetic Nervous System: This part of the autonomous nervous system heightens the activity of an organ as per the need. For example; during running, there is an increased demand for oxygen by the body. This is fulfilled by an increased breathing rate and increased heart rate. The sympathetic nervous system works to increase the breathing rate and the heart rate; in this case.
Parasympathetic Nervous System: This part of the autonomous nervous system slows the down the activity of an organ and thus has a calming effect. During sleep, the breathing rate slows down and so does the heart rate. This is facilitated by the parasympathetic nervous system. It can be said that the parasympathetic nervous system helps in conservation of energy.

Human Brain

Human brain is a highly complex organ; which is mainly composed of the nervous tissue. The tissues are highly folded to accommodate a larger surface area in less space. The brain is covered by a three layered system of membranes; called meninges. Cerebrospinal fluid is filled between the meninges. The CSF provides cushion to the brain against mechanical shocks. Furthermore, the brain is housed inside the skull for optimum protection. The human brain can be divided into three regions, viz. forebrain, midbrain and hindbrain.

Parts of Human Brain

Forebrain: It is composed of the cerebrum.
Midbrain: It is composed of the hypothalamus.
Hindbrain: It is composed of the cerebellum, pons and medulla oblongata.

Some main structures of the human brain are explained below.

Cerebrum: The cerebrum is the largest part in the human brain. It is divided into two hemispheres; called cerebral hemispheres.

Functions of cerebrum:

The cerebrum controls the voluntary motor actions.
It is the site of sensory perceptions; like tactile and auditory perceptions.
It is the seat of learning and memory.

Hypothalamus: The hypothalamus lies at the base of the cerebrum. It controls sleep and wake cycle (circadian rhythm) of the body. It also controls the urges for eating and drinking.

Cerebellum: Cerebellum lies below the cerebrum and at the back of the whole structure. It coordinates the motor functions. When you are riding your bicycle; the perfect coordination between your pedaling and steering control is achieved by the cerebellum.

Medulla: Medulla forms the brain stem; along with the pons. It lies at the base of the brain and continues into the spinal cord. Medulla controls various involuntary functions; like hear beat, respiration, etc.

Reflex Action:

Reflex action is a special case of involuntary movement in voluntary organs. When a voluntary organ is in the vicinity of a sudden danger, it is immediately pulled away from the danger to save itself. For example; when your hand touches a very hot electric iron, you move away your hand in a jerk. All of this happens in flash and your hand is saved from the imminent injury. This is an example of reflex action.

Reflex Arc: The path through which nerves signals; involved in a reflex action; travel is called the reflex arc. The following flow chart shows the flow of signal in a reflex arc.

Receptor ⇨ Sensory Neuron ⇨ Relay neuron ⇨ Motor neuron ⇨ Effector (muscle)

The receptor is the organ which comes in the danger zone. The sensory neurons pick signals from the receptor and send them to the relay neuron. The relay neuron is present in the spinal cord. The spinal cord sends signals to the effector via the motor neuron. The effector comes in action moves the receptor away from the danger.

The reflex arc passes at the level of the spinal cord and the signals involved in reflex action do not travel up to the brain. This is important because sending signals to the brain would involve more time. Although every action is ultimately controlled by the brain, the reflex action is mainly controlled at the level of spinal cord.

Muscular Movements and Nervous Control: Muscle tissues have special filaments; called actin and myosin. When a muscle receives a nerve signal; a series of events is triggered in the muscle. Calcium ions enter the muscle cells. It results in actin and myosin filaments sliding towards each other and that is how a muscle contracts. Contraction in a muscle brings movement in the related organ.

Test Your Knowledge: control and coordination

Which part of the brain controls the movements of our hands?
Answer: Cerebrum
Memory is stored in which part of the brain?
Answer: Cerebrum
Which part of the neuron receives signals from an adjacent neuron?
Answer: Dendrites

Endocrine System

The endocrine system is composed of several endocrine glands. A ductless gland is called endocrine gland. Endocrine gland secretes its product directly into the bloodstream. Hormones are produced in the endocrine glands. Hormone is mainly composed of protein. Hormones assist the nervous system in control and coordination. Nerves do not reach to every nook and corner of the body and hence hormones are needed to affect control and coordination in those parts. Moreover, unlike nervous control; hormonal control is somewhat slower.

Endocrine gland	Location	Hormones Produced	Functions
Pituitary gland (Also known as the master gland)	At the base of brain	Growth hormone (GH), thyroid stimulating hormone (TSH), Follicle stimulating hormone (FSH)	GH stimulates growth, TSH stimulates functioning of thyroid gland, FSH stimulates the follicles during ovulation.
Thyroid Gland	Neck	Thyroxine	Controls general metabolism and growth in the body.
Adrenal gland	Above kidneys	Adrenalin	Prepares the body for emergency situations and hence is also called ‘Fight and flight’ hormone.
Pancreas	Near stomach	Insulin	Controls blood sugar level
Testis (male)	In scrotum	Testosterone	Sperm production, development of secondary sexual characters during puberty.
Ovary (female)	Near uterus	Oestrogen	Egg production, development of secondary sexual characters during puberty.

Coordination in Plants:

Unlike animals, plants do not have a nervous system. Plants use chemical means for control and coordination. Many plant hormones are responsible for various kinds of movements in plants.

Movements in plants can be divided into two main types, viz. tropic movement and nastic movement.

Tropic Movement:

The movements which are in a particular direction in relation to the stimulus are called tropic movements. Tropic movements happen as a result of growth of a plant part in a particular direction. There are four types of tropic movements, viz. geotropic, phototropic, hydrotropic and thigmotropic.

Geotropic Movement: The growth in a plant part in response to the gravity is called geotropic movement. Roots usually show positive geotropic movement, i.e. they grow in the direction of the gravity. Stems usually show negative geotropic movement.
Phototropic Movement: The growth in a plant part in response to light is called phototropic movement. Stems usually show positive phototropic movement, while roots usually show negative phototropic movement. If a plant is kept in a container in which no sunlight reaches and a hole in the container allows some sunlight; the stem finally grows in the direction of the sunlight. This happens because of a higher rate of cell division in the part of stem which is away from the sunlight. As a result, the stem bends towards the light. The heightened rate of cell division is attained by increased secretion of the plant hormone auxin in the part which is away from sunlight.
Hydrotropic Movement: When roots grow in the soil, they usually grow towards the nearest source of water. This shows a positive hydrotrophic movement.
Thigmotropic Movement: The growth in a plant part in response to touch is called thigmotropic movement. Such movements are seen in tendrils of climbers. The tendril grows in a way so as it can coil around a support. The differential rate of cell division in different parts of the tendril happens due to action of auxin.

Nastic Movement:

The movements which do not depend on the direction from the stimulus acts are called nastic movement. For example; when someone touches the leaves of mimosa, the leaves droop. The drooping is independent of the direction from which the leaves are touched. Such movements usually happen because of changing water balance in the cells. When leaves of mimosa are touched, the cells in the leaves lose water and become flaccid; resulting in drooping of leaves.

Some Plant Hormones: Auxin, gibberellins and cytokinin promote growth in plant parts. Abscissic acid inhibits growth in a particular plant part.

Test Your Knowledge

Which hormone prepares a lion when it is about to attack a deer?
Answer: Adrenaline
Which hormone plays an important role in ovulation?
Answer: Oestrogen

Periodic Classification ncert questions

Which element has

Two shells, both of which are completely filled with electrons?
Answer: Ne (Neon)
The electronic configuration 2, 8, 2?
Answer: Mg (Magnesium)
A total of three shells, with four electrons in its valence shell?
Answer: Si (Silicon) (14): 2, 8, 4
A total of two shells, with three electrons in its valence shell?
Answer: B (Boron) (5): 2, 3

Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.
- The elements become less metallic in nature.
- The number of valence electrons increases.
- The atoms lose their electrons more easily.
- The oxides become more acidic.
  Answer: (c) The atoms lose their electrons more easily
Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
- Na
- Mg
- Al
- Si
  Answer: (b) Mg
What property do all elements in the same column of the Periodic Table as boron have in common?
Answer: Boron is metalloid while all other elements in the same column of the Periodic Table are metals, thus metallic character is common in the same column of the periodic table as boron have.
What property do all elements in the same column of the Periodic Table as fluorine have in common?
Answer: All elements belong to same column as fluorine, are non-metals and are highly electronegative in character. All of them have valence electrons equal to seven, and thus can accept one electron to complete their octet.
An atom has electronic configuration 2, 8, 7.
- What is the atomic number of this element?
  Anwer: 17
- To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.) N(7) F(9) P(15) Ar(18)
  Anwer: F (9) Fluorine (As fluorine has valence electron equal to seven)

The position of three elements A, B and C in the Periodic Table are shown below

Group 16	Group 17

	A

B	C

State whether A is a metal or non-metal.
Answer: Non-metal
State whether C is more reactive or less reactive than A.
Answer: Less reactive than A
Will C be larger or smaller in size than B?
Answer: Smaller
Which type of ion, cation or anion, will be formed by element A?
Answer: Anion

Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Answer: Nitrogen (7): 2, 5
Phosphorus (15): 2, 8, 5

Since, electronegativity decreases with moving from top to bottom in a group, thus Nitrogen will be more electronegative.
How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer: Electronic configuration of an element gives the information of valence electrons and number of shell present in the element. We get the information of group number after knowing valence electrons. Number of shells present in an element is equal to period number. Thus, by knowing electronic configuration we know the group number and period number of an element, which is the position of element in periodic table.

In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?
Answer: Elements with atomic numbers 12 and 38 have the similar chemical and physical properties of calcium.
Compare and contrast the arrangement of elements in Mendeléev’s Periodic Table and the Modern Periodic Table.
Answer: Comparison of Mendeleev’s Periodic Table and Modern Periodic Table

Mendeleev's Periodic Table	Modern Periodic Table
Elements were arranged in increasing order of atomic masses.	Elements are arranged in increasing order of atomic numbers.
There are 8 groups.	There are 18 groups.
Each group is divided into sub groups a and b.	Groups are not divided into sub groups.
Group for noble gases was not present, as noble gases were not discovered at that time.	A separate group, i.e. group 18 is present for noble gases.
There was no place for isotopes.	This problem was rectified, as slots are determined on the basis of atomic number.

Upto which element, the Law of Octaves was found to be applicable

Oxygen
Calcium
Cobalt
Potassium
Answer: (b) Calcium

According to Mendeleev's Periodic Law, the elements were arranged in the periodic table in the order of
- Increasing atomic number
- Decreasing atomic number
- Increasing atomic masses
- Decreasing atomic masses
  Answer: (c) Increasing atomic masses
In Mendeleev’s Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later
- Germanium
- Chlorine
- Oxygen
- Silicon
  Answer: (a) Germanium
Which of the following statement (s) about the Modern Periodic Table are incorrect
- The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number
- The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses
- Isotopes are placed in adjoining group (s) in the Periodic Table
- The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number
- (i) only
- (i), (ii) and (iii)
- (i), (ii) and (iv)
- (iv) only
  Answer: (b) (i), (ii) and (iii)

Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period?
- A, B, C
- B, C, D
- A, D, E
- B, D, E
  Answer: (b) B, C, D
The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belongs to the same group?
- A and B
- B and D
- A and C
- D and E
  Answer: (a) A and B
Where would you locate the element with electronic configuration 2,8 in the Modern Periodic Table?
- Group 8
- Group 2
- Group 18
- Group 10
  Answer: (c) Group 18

An element which is an essential constituent of all organic compounds belongs to
- Group 1
- Group 14
- Group 15
- Group 16
  Answer: (b) Group 14
Which of the following statements about the Modern Periodic Table is correct:
- It has 18 horizontal rows known as Periods
- It has 7 vertical columns known as Periods
- It has 18 vertical columns known as Groups
- It has 7 horizontal rows known as Groups
  Answer: (c) It has 18 vertical columns known as Groups
- Which of the following is the outermost shell for elements of period 2?
  - K shell
  - L shell
  - M shell
  - N shell
    Answer: (b) L shell
  - Which one of the following elements exhibit maximum number of valence electrons?
    - Na
    - Al
    - Si
    - P
      Answer: (d) P
  - Which of the following gives the correct increasing order of the atomic radii of O, F and N?
    - O, F, N
    - N, F, O
    - O, N, F
    - F, O, N
      Answer: (d) F, O, N
  - Which among the following elements has the largest atomic radii?
    - Na
    - Mg
    - K
    - Ca
      Answer: (c) K
  - Which of the following elements would lose an electron easily?
    - Mg
    - Na
    - K
    - Ca
      Answer: (c) K
  - Which of the following elements does not lose an electron easily?
    - Na
    - F
    - Mg
    - Al
      Answer: (b) F
  - Which of the following are the characteristics of isotopes of an element?
    - Isotopes of an element have same atomic masses
    - Isotopes of an element have same atomic number
    - Isotopes of an element show same physical properties
    - Isotopes of an element show same chemical properties
    - (i), (iii) and (iv)
    - (ii), (iii) and (iv)
    - (ii) and (iii)
    - (ii) and (iv)
      Answer: (b) (ii), (iii) and (iv)
  - Arrange the following elements in the order of their decreasing metallic character: Na, Si, Cl, Mg, Al
    - Cl > Si >Al > Mg > Na
    - Na >Mg >Al >Si > Cl
    - Na > Al > Mg > Cl > Si
    - Al > Na> Si > Ca > Mg
      Answer: (b) Na > Mg > Al > Si > Cl
  - Arrange the following elements in the order of their increasing nonmetallic character: Li, O, C, Be, F
    - F < O < C < Be < Li
    - Li < Be < C < O< F
    - F < O < C < Be < Li
    - F < O < Be < C < Li
      Answer: (c) F < O < C < Be < Li
    - What type of oxide would Eka– aluminium form?
      
      EO3
      
      E3O2
      
      E2O3
      
      EO
      Answer: (c) E2O3
      
      Three elements B, Si and Ge are
      
      Metals
      
      Non-metals
      
      Metalloids
      
      Metal, non-metal and metalloid respectively
      Answer: (c) Metalloids
      
      Which of the following elements will form an acidic oxide?
      
      An element with atomic number 7
      
      An element with atomic number 3
      
      An element with atomic number 12
      
      An element with atomic number 19
      Answer: (a) An element with atomic number 7
      
      Which one of the following depicts the correct representation of atomic radius(r) of an atom?
      
      (i) and (ii)
      
      (ii) and (iii)
      
      (iii) and (iv)
      
      (i) and (iv)
      Answer: (b) (ii) and (iii)
      
      Which one of the following does not increase while moving down the group of the periodic table?
      
      Atomic radius
      
      Metallic character
      
      Valence
      
      Number of shells in an element
      Answer: (c) Valence
      
      On moving from left to right in a period in the periodic table, the size of the atom.
      
      Increases
      
      Decreases
      
      does not change appreciably
      
      first decreases and then increases
      Answer: (b) Decreases
      
      Which of the following set of elements is written in order of their increasing metallic character?
      
      Be Mg Ca
      
      Na Li K
      
      Mg Al Si
      
      C O N
      Answer: (a) Be Mg Ca
      
      The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?
      
      Metal
      
      Metalloid
      
      Non-metal
      
      Left-hand side element
      Answer: (b) Metalloid