Structure And Functions Of Human Body Organ Systems

All other except embryonic nervous tissue have bipolar and multipolar neurons. Only embryonic nervous tissue has unipolar neurons in which development of nervous system is under process.

All sensory organs contain bipolar neurons in which they have one axon at one end and one dendrite at other end. They don’t have unipolar and multipolar neurons.

They have bipolar neurons because they are the suitable one for the conduction of impulses in sensory organs.

Hypothalamus is the part of brain which controls emotional reactions. All other parts given in the options like Cerebellum controls voluntary movements, Cerebrum controls intelligence, memory, reasoning etc and thalamus controls conduction of sensory and motor signals. None of the given options except hypothalamus controls emotional reactions.

Brain stem is an extension of brain to the spinal cord. This brain stem is extended from midbrain, pons and medulla which are parts of hind brain to the spinal cord.

Therefore Midbrain and Hindbrain are parts of brain stem.

It can be better understood by following picture.

Mixed nerves are those which contain both sensory nerve fibers and motor nerve fibers. Spinal nerve contain both sensory neurons i.e. can receive information from central nervous system and can give response using motor nerve fibers.

The location of all other endocrine glands i.e. adrenal gland, pituitary gland and pancreas are Abdomen, brain and abdomen respectively.

Thyroid gland out of the given options is the only gland present in the neck.

From following picture the locations of various glands can be seen:

Pancreas secrete both hormone from endocrine part of pancreas i.e. islets of Langerhans and enzymes from exocrine part of pancreas i.e. acinar cells. All other glands secrete only hormones and thus exhibit only endocrine nature.

Therefore, pancreas is both exocrine and endocrine.

This value represents the normal blood glucose level in 1 dl of blood maintained by the insulin and glucagon hormones of pancreas.

All other options represent values which are somewhat low or high than the normal blood glucose level. 80-120 mg/dl represents the correct range of blood glucose level maintained by insulin and glucagon.

“T” lymphocytes for their differentiation require the thymosin hormone which is secreted only by the thymus gland.

Other mentioned glands do not secrete thymosin hormone. Therefore, differentiation of “T” lymphocytes takes place only in the thymus gland.

During Zygotene process of meiosis I homologous chromosomes exhibit pairing with each other. In other steps like Leptotene- condensation of chromosome take place, Pachytene- crossing over of homologous chromosomes take place and in diplotene- terminalization take place.

Therefore, correct option is Zygotene.

It can be better understood with the following picture:

Nervous and endocrine systems are the two systems which controls and coordinates the metabolic processes. Nervous system does so by electrochemical coordination and endocrine system done so by chemical coordination.

All other processes given help to carry out different essential life processes but do not help in control and coordination.

Synaptic knobs for the transmission of impulse from one neuron to the other secrete the neurotransmitter. While the other parts like dendrites receive the stimulus, organelles play their respective roles in cell body and myelin sheath prevents leakage of impulse.

So, correct option is Synaptic knobs.

Since thymus gland regulates the differentiation of the T- lymphocytes which play role in adaptive immune system.

Therefore, thymus gland is the endocrine gland related to the immune system.

Relaxin is the hormone administered by doctors to a pregnant woman to help in childbirth during the time of natural delivery because relaxin hormone helps in the expulsion of the baby from the uterus and it does so by causing relaxation of the pelvic muscles as its name suggests.

Other hormones oestrogen and progesterone are for maintaining pregnancy and insulin is for maintaining for blood glucose level.

Therefore relaxin is the correct option.

During pachytene process of meiosis crossing over between homologous chromosomes takes place. In this they homologous chromosomes exchanges their segments.

In other steps like Leptotene- condensation of chromosome take place, Diplotene- - terminalization take place and in Zygotene- pairing of homologous chromosomes takes place.

Therefore, correct option is Pachytene.

It can be better understood with the following picture:

Reduction division takes place in germinal epithelial cells because these are part of germ cells i.e. gametes. All other cells mentioned are type of somatic cells which do not require reduction.

Therefore correct option is germinal epithelial cells.

It is because amoeba is a unicellular organism which divides by the process Amitosis. In this process there is nothing like chromosome synthesis and no changes in the chromosome takes place prior to the division as take place during mitotic and meiotic divisions.

Therefore, in amoeba cell division take place without involving change in chromatin reticulum.

This is the sequence which is followed during the prophase I step of Meiosis I. For the division firstly condensation of chromosomes take place, then pairing of homologous chromosomes take place, after that crossing over, then terminalisation take place and finally disappearance of nuclear membrane and nucleolus takes place.

Since, above mentioned steps are followed by sequence (iii).

Therefore, correct answer is (iii).

It can be better understood with the following picture:

Nervous system is the system which controls and coordinates the various body activities and movement of limbs is one of them. The polio virus causes physical disability because upon infection it causes destruction of the motor neurons which help in movement. As, motor neurons get destructed there is physical disability.

All other systems do not get affected to that much high level as nervous system gets affected.

Therefore, correct option is Nervous system.

Reflex action is a process in which immediately message is sent to brain and an immediate response is also given.

It can happen only when neurons can transmit signals to the brain and from the brain. Also, it is an involuntary action which does not involve thinking process in which time is consumed. So, brain is not the centre for reflex actions.

In spinal cord we have mixed neurons and therefore an immediate action can take place. So, this process can take place only there.

Therefore, spinal cord is the correct answer. All other options do not play any role in the reflex actions.

Following picture explains the same:

Firstly the stimulus is received with the help of dendrites, after that they are transmitted to cyton, and then they travel through the axon and at the end reaches to the terminal branches from where they are transmitted to another neuron.

Therefore correct sequence is : ii) dcab. It is also shown in following picture:

Because synapse is the site from where the transmission of the impulse takes place. When the impulse of transmission is arrested the signal does not reach the brain and we do not feel any pain and sensation. Therefore anesthesia acts on synapses.

Mixed nerves are those nerves which contain both the sensory and motor neurons. Spinal nerves are one of them which can receive stimuli through sensory neurons and show effector functions using motor neurons.

Since both ‘A’ and ‘R’ are true and ‘R’ explains ‘A’. Therefore correct option is (i).

Nervous system and Endocrine systems help in control and coordination of metabolic activities.

● Medullated neurons are present in the neurons of central nervous systems and a somatic nervous system where neurons are of larger length, present in the white matter of the brain.

● Nonmedullated neurons are present in the neurons of an autonomic nervous system where neurons are of smaller length, present in the grey matter of the brain.

● In general, neurons which are long are medullated and which are short are non- medullated.

Figure: Medullated and non medullated nerve fibers

Medulla oblongata part of the Hind Brain regulates heart beat and respiration.

Location of Medulla oblongata- It is a part of the hind brain which is located in between the Pons part of the hind brain and spinal cord.

Location can be better understood by looking at the following figure:

Corpora quadrigemina are a part of mid-brain. It consists of four bodies therefore known as quadrigemina where quad stands for four. It is located at the distal portion of the midbrain. It is divided into two parts where upper two calculi (spherical structures) are called superior calculi and lower calculi are called inferior calculi. It can be better understood with the following diagram showing its location and parts.

Functions associated with the corpora quadrigemina- They are involved in the regulation of reflexes associated with the vision, hearing.

Endocrine glands- These are the glands which help in chemical coordination. Endocrine glands are a group of cells which secrete certain chemicals and they secrete them directly into the blood as endocrine glands lack ducts.

The chemicals secreted from endocrine glands are called hormones.

The following table depicts different endocrine glands and their secretions in the human body:

All the endocrine glands are ductless and release their secretions into the blood. So, these secretions reach their target organs with the help of blood only.

As blood flows into complete body and hormones being secreted into it flow with it but what happens is each hormone has an affinity with its target organs. Target organs of all hormones have some specific receptors associated with them, so due to this specific receptors hormone only reach and react with their target organs and don’t reach to some other organ.

i) The master of the endocrine orchestra- Pituitary gland is known as the Master of the endocrine orchestra.

It is so called because it regulates the secretion of all other endocrine glands present in the body.

ii) The dual gland- Pancreas is the dual gland. It is so called because it exhibits nature of both glands i.e. exocrine and endocrine. It secretes hormone insulin from its endocrine part i.e. Islets of Langerhans and enzymes chymotrypsin and pancreatic lipase from its exocrine part i.e. acinar cells. So, pancreas s the dual gland.

i) Personality hormone- Thyroxine

Reason- Thyroxine is called Personality hormone as it controls the growth and metabolic rate. Over secretion of thyroxine can increase the metabolic rate more than normal level and deficiency in secretion lead to decrease in metabolic rate due to which growth of body gets affected. Therefore it is called Personality hormone.

ii) fight, flight and fright hormones- Adrenaline and Noradrenaline hormones.

Reason- They are called so because these hormones are released into the stress conditions which supply more oxygen to the body, increases the breathing rate, beating of heart faster, the fast supply of blood. All this lead to the preparation of the body in order to deal the situation by fighting, fighting and frighting.

Male sex hormone- Testosterone is the male sex hormone secreted by the leydig cells of the testis.

The functionof testosterone-

● It is responsible for the masculine characteristics.

● It stimulates the growth of male reproductive organs- There is enlargement of penis, scrotum, and testis.

● It also regulates the formation of sperms.

● It is also responsible for the excessive body hair growth in the men.

● The characteristic thick skin that men have lacking softness is due to this hormone only.

● The low pitch voice that males have is also due to this hormone.

Female sex hormones- Oestrogen and progesterone are two female sex hormones secreted by the ovary.

Functions of oestrogen-

● It causes the growth of the female reproductive organs- There is growth in the size of the uterus, vagina, and fallopian tubes. etc.

● It is also responsible for the growth of the breasts.

● It is responsible for the feminine characteristics.

● It is responsible for the pubic and axillary hair growth in females and does not cause dense hair growth as males have.

● It is responsible for the soft skin of women.

● It is also responsible for the high pitch voice in females.

Functions of Progesterone-

● It also regulates the growth of the breasts in females.

● It helps in regulation of the menstrual cycle in females.

● It also helps in maintaining pregnancy in females.

i) Pairing of homologous chromosomes – Zygotene

In zygotene step of prophase, I of meiosis I pairing of homologous chromosomes takes place and this process is called synapsis. In this homologous chromosomes come near each other and start pairing.

ii) Terminalisation- Diplotene

In this separation of the paired homologous chromosomes takes place except for the region where crossing over had taken place. Formation of X- shaped structures take place which is called chiasmata and they move towards terminals. Therefore, this process is called terminalisation.

iii) Crossing over- Pachytene

Crossing over refers to the process in which segments are exchanged between non sister chromatids of homologous chromosomes. In meiosis, I pachytene is the step in which crossing over takes place.

In this tetrads are clearly visible.

iv) formation of spindle apparatus- Diakinesis

This is the last step of prophase I in meiosis I. During this step there is complete dissolution of nuclear membrane and nucleolous and they become disappear. In this step we left with spindle apparatus.

The following figure explains all the concepts:

(i) False because pituitary gland is an endocrine gland and secretes hormone only.

(ii) The given statement is false as thyroxine is the only hormone secreted by thyroid gland. Insulin is not secreted by thyroid gland, it is secreted by the pancreas.

(iii) The given statement is true because leydig cells of the testis are responsible for the secretion of male sex hormone i.e. testosterone. Testosterone is secreted by Leydig cells.

(iv) Yes, the given statement is true as pancreas exhibit dual nature being exocrine and endocrine gland both. The islets of Langerhans is the endocrine part which secretes hormone insulin and glucagon. While acinar cells secrets various enzymes like chymotrypsin, lipases which help in digestion of foods.

Therefore, pancreas produces both enzymes and hormones.

(i) Given statement is wrong. The correct sentence is as follows:

Alpha cells produce glucagon and beta cells produce insulin.

(ii) Given statement is true.

(iii) Given statement is true.

(iv) Given statement is wrong. The correct statement is as follows:

Ovary produces eggs and oestrogen, progesterone and relaxin.

(i) Given statement is true because endocrine system is responsible for chemical coordination and through this chemical coordination, they controls and co-ordinates the physical process of growth, reproduction, and sustenance of life.

(ii) Given statement is false as endocrine glands are ductless glands. They do not bear ducts and secrete their secretion into the blood. So, the correct statement is as follows:

Endocrine glands are ductless glands which secrete chemical substances called hormones.

(iii) Given statement is true as pancreas exhibits both exocrine and endocrine nature. It exhibits exocrine nature by secreting enzymes chymotrypsin, lipase from acinar cells (exocrine part) and secrete hormone insulin and glucagon from Islets of Langerhans (endocrine part).

(iv) Given statement is false, as thymus is in no way related to the goitre. Goitre is caused due to deficiency of iodine due to which swelling of thyroid glands take place. So, correct statement is as follows:

Malfunctioning of the thyroid gland causes goitre.

i) It is otherwise called supra-renal gland.

ii) It secretes two hormones, namely aldosterone, and cortisone.

a) It is otherwise called supra renal gland – Adrenal gland

b) It secretes two hormones, namely aldosterone, and cortisone -

First one is unipolar neuron as it has a single extension from its cyton.

The second one is bipolar neuron as it has two extensions at the opposite poles. One extension acts as dendrite and the longer extension as the axon.

The third one is multipolar as it has multiple extensions which are dendrites through its cyton and a single extension in opposite direction which is axon.

(i) Given statement is false because meiosis is a reduction kind of division which take place only in germinal cells for formation of gametes. It never takes place in somatic cells.

(ii) Given statement is true because in meiosis the number of chromosomes after the meiotic division exactly becomes half of the original number. As the reduction in a number of chromosomes takes place meiosis is also called reduction division.

(iii) Given statement is false. The pairing of chromosomes is not called crossing over because both are different processes. In pairing homologous chromosomes comes near each other and pair with each other. This process is called synapsis.

Whereas in crossing over the exchange of non sister chromatids in homologous chromosomes takes place.

(iv) Given statement is true because in meiosis crossing over takes place between the non sister chromatids of homologous chromosomes due to which exchange of information takes place. Due to this exchange in information variations occur and as it takes place in the germinal cells these variations are further inherited by the future generation, so variations arising due to crossing over in meiosis lead the basis of evolution.

Explanation: As the above-mentioned processes take place in these particular steps, the correct matches would be as shown above.

For better understanding following diagram can be referred:

The damage had taken place in a Hind part of the brain. And, in hind part, this damage had taken place mainly in the Medulla oblongata part.

Justification: As it is given in question that person had died due to breathlessness and heart failure and medulla oblongata is the part of the hind brain which controls and coordinates both these processes. So, might be damage had taken place in medulla oblongata part of the hind brain.

Explanation: A. Vasopressin: As vasopressin hormone regulates the reabsorption of water and urine formation. If in some way the secretion of this hormone is affected, regulation of water reabsorption and urine formation will get affected and the person will suffer from Diabetes insipidus.

B. Insulin: Insulin hormone regulates the blood glucose level. If the secretion of insulin is affected in some way the blood glucose level will also get affected and the person will suffer from Diabetes mellitus.

C. Oxytocin: This hormone is released during the childbirth as it causes contraction and relaxation of the uterus and thus helps in the delivery of the baby as contraction and relaxation helps in expelling the baby out.

D. Thymosin: This hormone helps in the differentiation of T- lymphocytes which are a part of adaptive immune system and thus help in resisting infections.

The transmission will be faster in the pathway P.

Reason- The thickness and structure of the neurons in pathway p and pathway Q are same. But the length of neurons and number of synapses are different in both the pathways.

As the lengths of the axons are greater in pathway P due to which the nerve impulse will travel a longer distance in shorter time and as there are less number of synapse here the leakage in impulse and time in the transmission will be less.

On the other hand in pathway Q the length of neurons are smaller due to which more neurons will be required and there will be leakage of impulses and more time consumption as there are more number of synapses due to which in order to transmit impulse to the next neuron at each synapse, time will be consumed. So, transmission of impulse will be slower.

Therefore, due to above-mentioned reasons, nerve impulse will travel faster in pathway P.

Pancreas is called the Dual gland. It is called so because it exhibits both exocrine and endocrine nature.

Exocrine nature of pancreas-

Pancreas exhibit exocrine nature because it secretes some enzymes through its acinar cells which also have ducts.

It secretes chymotrypsin, pancreatic lipases through pancreatic duct and thus exhibits exocrine nature.

Endocrine nature of pancreas-

Pancreas exhibit endocrine nature due to its Islets of Langerhens. This islet of langerhens secrets hormones insulin and glucagon and are ductless. Glucagon is secreted by alpha cells and insulin is secreted by beta cells of islets of langerhens. So, in this way pancreas exhibits endocrine nature.

The glands that are not functioning properly in the boy are testis and the hormone lacking in the body is testosterone.

Reason- It is because testis is responsible for the secretion of testosterone and this testosterone is the only hormone responsible for the all the masculine characteristics i.e. moustache, beard, gruff voice, broadening of shoulders, muscular body etc.

Since the boy is lacking all the masculine characteristics he is definitely lacking the testosterone hormone responsible for these characteristics due to non- functioning of his testis gland.

The neuron is the functional unit of the nervous system and it consists of the following parts:

● CELL BODY- It is also known as cyton and is irregular in shape. Its extensions give rise to dendrites and axon as shown in the above diagram. It also contains a nucleus and granular substance called Nissel’s granules within it.

● DENDRITES- These are extensions of the cell body which are branched in nature. The function of these dendrites is to receive a stimulus and then transfer this stimulus to the cell body which further transfers the stimulus to complete nerve fibre.

● AXON- It is also an extension of nerve fibre which is very long and the nerve impulse transmits through this axon only. Ion channels are present in axon only which help in impulse transmission.

● AXON TERMINALS- This are branched endings of the axon which are also known as synaptic knobs because they are responsible for synapse and this knobs by secreting neurotransmitter helps in transmission of impulse through synapse from one neuron to the other.

● SCHWANN CELLS- Schwann cells are present over the axon and helps in formation of myelin sheath which prevents of leakage of current through the axon.

● NODES OF RANVIER- These are the sites where myelin sheath is absent and impulse transmission takes place through ion channels present over this nodes of ranvier.

Human brain is divided into three parts- Forebrain, Midbrain and Hindbrain. And all these are further classified into their subparts.

This picture represents the different parts of brain.

Parts of brain along their functions are written below sequentially –

A. FOREBRAIN- It consists of three sub parts- Cerebrum, Thalamus and Hypothalamus.

● Cerebrum- It forms the major part of the human brain as represented in the diagram. Cerebrum is divided into two parts termed as Left and Right cerebral hemispheres. Corpus collosum establishes a connection between two hemispheres.

Cerebral cortex exhibits grey colour due to the presence of non medullated neurons and white matter of cerebrum is white due to the presence of medullated neurons.

Functions associated with cerebrum-

● The cerebrum is the conscious mind which controls our thinking, imagination processes.

● It controls all voluntary actions.

● Cerebrum contains different centers for all our senses. There are different centers in cerebrum for taste, smell, hearing, vision.

● Thalamus- It is also a part of forebrain around which the cerebrum remains present.

Functionof thalamus-

It controls and coordinates the signal and impulse transmission in sensory and motor neurons.

● Hypothalamus- It is present beneath the thalamus region.

Functions of the hypothalamus-

It controls all our emotions and feelings like love, anger, sadness.

It is also responsible for regulation of sexual behaviour.

Our body temperature, thirst, hunger all are regulated by the hypothalamus.

B. MIDBRAIN- As the name suggests it is located between the middle of forebrain and hindbrain. Therefore, it is called midbrain. Midbrain along with the Hindbrain forms the brain stem which is an extension from midbrain which through hind brain joins to the spinal cord and is called Brain stem.

Midbrain consists of Corpora quadrigemina.

● Corpora quadrigemina- It consists of four bodies therefore known as quadrigemina where quad stands for four. It is located at the distal portion of the midbrain. It is divided into two parts where upper two calculi (spherical structures) are called superior calculi and lower calculi are called inferior calculi.

Functions of corpora quadrigemina-

They are involved in the regulation of reflexes associated with the vision, hearing.

C. HINDBRAIN- It consists of three subparts – Pons, Cerebellum and Medulla oblongata.

● Pons- It acts as a connection. It along with connecting different portions of cerebellum also connects cerebrum and cerebellum.

Functions of pons-

It regulates our sleep.

Due to the formation of a connection between forebrain and cerebellum helps in sharing of information received by the parts of the brain.

● Cerebellum- It is just present in the cerebrum part of the forebrain.

Functions of the cerebellum-

It regulates the movement of our limbs.

● Medulla oblongata- This part joins with the spinal cord and forms the brain stem. It is located between the pons and brain stem.

Functions of Medulla oblongata-

It controls various involuntary activities like breathing, heart beating etc.

Location of various endocrine glands can be better understood by the following diagram:

Ovary- This endocrine gland is present only in females and secretes female sex hormones Oestrogen and progesterone.

These are two in number and are present in the abdominal cavity. They also produce eggs.

Functions of oestrogen-

● It causes the growth of the female reproductive organs- There is growth in the size of the uterus, vagina, and fallopian tubes.etc.

● It is also responsible for the growth of the breasts.

● It is responsible for the feminine characteristics.

● It is responsible for the pubic and axillary hair growth in females and does not cause dense hair growth as males have.

● It is responsible for the soft skin of women.

● It is also responsible for the high pitch voice in females.

Functions of Progesterone-

● It also regulates the growth of the breasts in females.

● It helps in regulation of the menstrual cycle in females.

● It also helps in maintaining pregnancy in females.

Pancreas- This is a dual gland which exhibits both endocrine and exocrine nature. It is present in the abdomen. The endocrine part of the pancreas is islets of langerhens. There are two hormones secreted by pancreas called insulin and glucagon. Insulin is secreted by the beta cells and glucagon is secreted by the alpha cells of the islets of langerhens. Both insulin and glucagon regulate the blood glucose level.

Functions of Insulin-

● It maintains the blood sugar level by converting extra glucose into the glycogen which is stored in liver cells.

● Whenever there is enough amount of glucose present in the body insulin prevents more synthesis of glucose by preventing the breakdown of carbohydrates and thus maintains blood glucose level.

Functions of glucagon-

● It maintains blood sugar level by converting glycogen into the glucose whenever there is a deficiency of glucose.

● It prevents synthesis of glycogen and promotes breakdown of carbohydrates whenever there is deficiency of glucose in blood level.

So, according to the level of glucose in the blood secretion of insulin and glucagon regulates the normal blood glucose level i.e. 80-120 mg/dl of blood.

Deficiency of insulin leads to excess blood glucose level and causes disease Diabetes Mellitus.

Meiosis is the division which takes place for the formation of gametes or germ cells in which the number of chromosomes is exactly half the number of chromosomes present in the somatic cell.

As due to the meiotic division the number of chromosomes becomes exactly half of the original number, meiosis is known as reduction division because the number of chromosomes is getting reduced into it.

Meiosis takes place into two broad steps mainly- Meiosis I and Meiosis II.

A. Meiosis I- In meiosis I the reduction of chromosomes takes place. It comprises of four steps- Prophase I, Metaphase I, Anaphase I and Telophase I. Each step of meiosis I am discussed below with its diagram-

I. Prophase I- It is longer than all other phases. During this step unwinding of the chromatin, material takes place and processes like the pairing, crossing over of homologous chromosomes take place. All this take place in five different step which is as follows:

a) Leptotene- During this step condensation of chromosomes takes place.

b) Zygotene- During this step homologous chromosome comes near each other and they start pairing with each other. This process is called synapsis.

c) During pairing, homologous

chromosomes get attached to each other and then those paired chromosomes are called bivalents.

d) Pachytene- In this four chromatids calling tetrad start appearing. During this step crossing over takes place in which there is exchange of segments between non sister chromatids of homologous chromosomes. The point of contact between homologous chromosomes is termed as chiasmata.

e) Diplotene- During this step separation and terminalisation takes place. The homologous chromosomes get separated from each other and they start moving to the terminals.

f) Diakinesis- In this there is dissolution of the nucleolus and the nuclear membrane and spindle apparatus is there.

II. Metaphase I- In this step formation of an equatorial plate takes place which is also known as metaphasic plate. All the bivalents get arranged on that plate and centromere remains attached to the spindle fibers.

III. Anaphase I- In this separation of homologous chromosomes take place and they start moving to the opposite poles. Here reduction of the chromosomes takes place.

IV. Telophase I- In this division of cytoplasm takes place and this process is called cytokinesis. Nuclear membrane and nucleolus start appearing and result in two cells in which chromosome number are exactly half to the original number.

B. Meiosis II- This process is exactly like mitosis in which equational division take place. In this chromosome number remains same and there is no reduction in chromosome number. It consist of four steps- Prophase II, Metaphase II, Anaphase II and Telophase II. Each step is discussed below:

I. Prophase II- In this step nuclear membrane and nucleolus again start disappearing. The chromosomes again get shortened.

II. Metaphase II- In this step formation of an equatorial plate takes place which is also known as metaphasic plate. And the chromatids get arranged on that plate and centromere remains attached to the spindle fibers.

III. Anaphase II- In this step, there is a splitting of the centromere and new chromosomes are formed which move towards the opposite poles.

IV. Telophase II- In this again the formation of nuclear membrane and nucleolus take place. Haploid chromosomes are there at each pole and again cytokinesis take place which divides the cell into two.

And as we have two cells here, so at the end we get four cells having haploid chromosome.

In this way the complete process of meiosis takes place including all the steps mentioned above and at end we get four daughter cells, each having haploid chromosome.

Significanceof meiosis-

1. Meiosis helps in maintaining the chromosome number with each generation because if there won’t be reduction division and gametes were also having the same number of chromosomes as somatic cells do, with each fertilisation there would be increment in the ploidy number and there will be nothing like maintenance of chromosome number with generations.

2. It also helps in evolution as it helps in generating variations. During meiosis crossing over take place in which there is exchange of non sister chromatids which ultimately lead to variations. As these variations pass from generation to generation they help in evolution.

3. And as discussed above meiosis helps in formation of gametes.

Figure: Flow chart of Meiosis I and Meiosis II

The central nervous system is covered by three protective coverings collectively called Meninges. The outermost cover lying below the skull and vertebral column is double thick and is called Duramater. The middle covering is thin and vascularised and is called Arachnoid membrane. The innermost cover is a very thin delicate membrane and is closely stretched over the outer surface of Brain and Spinal cord and is called Piamater.

a) Sleep centre and respiratory centre – Pons

b) Several reflexes involved in the regulation of heart beat, blood vessel contraction, breathing etc - Medulla oblongata

c) Consists of the cerebrum, thalamus, and hypothalamus- Forebrain

d) Motor and sensory areas - Thalamus

e) A major conducting center for sensory and motor signaling- Cerebral cortex

f) Regulation of sexual behaviour - Hypothalamus

g) Consists of pons, cerebellum and medulla oblongata – Hind Brain

h) Co-ordinates the group movements of voluntary muscles, as in walking or running- Cerebellum

i) The area responsible for consciousness, intelligence, memory, imagination and reasoning – Cerebrum

ii) The area responsible for regulation and co-ordination of group movements of voluntary muscles. – Cerebellum

iii) The area responsible for sleeping and respiration – Pons

iv) The area responsible for reflexes involved in the regulation of heart beat, blood vessel contraction, breathing etc – Medulla oblongata