ARTICLESBAZAR

Sunday, 13 September 2020

Describe the Composition and Structure of Earth's Atmosphere.

Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. There is no definite boundary between the atmosphere and outer space. It slowly becomes thinner and fades into space.

Three quarters of the atmosphere's mass is within 11 km of the planetary surface. The atmosphere is one of the most important components of the environment on the earth. In the absence of atmosphere life would not have been possible on the earth.

What are the two mode of reproduction ? Organs of Reproductive System.

“Nothing survives forever, still life continues in this universe." It is because of reproduction which is the most fundamental feature of all the living functions. The living organisms reproduce at the molecular, cellular and organismie levels.

What are the Characteristics and Functions of Harmones ?

Endocrine(ductless) glands that control, communicate, coordinate and integrate various functions of all the body organs, by the secretion of chemical messengers called hormones collectively constitute endocrine system.

Working alone or in concert as a single neuroendocrine system, they perform the same general functions. The endocrine glands secrete very minute quantities of chemical messengers called hormones (Gk. hormoein : to excite).

The hormones are released directly into the bloodstream. There are no ducts in endocrine glands, hence, called ductless glands.

Most their widespread despite distribution by the blood, are highly specific in their action. Cells that respond to a particular hormone are called target organ cells.

The science concerned with the structure and functions of endocrine glands, diagnosis and treatment of disorders of endocrine glands is known as endocrinology.

CHEMICAL NATURE OF HORMONES

Hormones are organic compounds of diverse chemical nature. Chemically, hormones may be proteinaceous (FSH, LH, TSH, etc.), peptides (ACTH, oxytocin, vasopressin, etc), steroids (sex hormones) or amino acid derivatives (thyroxine, epinephrine, etc.).

CHARACTERISTICS OF HORMONES

These are listed below:

Hormones are the secretions of endocrine glands. They are transported by way of blood.
They always act away from the site of their secretion. Their action is always at distant place called target organ.
They are secreted and required in very small quantities.
They are organic compounds of diverse nature and are soluble in water.
They may accelerate or inhibit specific physiological processes.
They are usually used up in their regulatory actions.
Specific action : Hormones are very specific in their action and they do not initiate chemical reactions.
Slow in action : The hormones are generally slow in action.
Feedback inhibition : Hormones usually work on the principle of feedback inhibition i.e. the secretion of a hormone is stimulated or inhibited by the end-product of its activity.
Prepare the body to cope with emergency: Hormones prepare the body to cope with the emergency conditions, such as, infections, trauma, fear, emotional stress, sexual desire, etc.
They are harmful both when secreted in excess (hypersecretion) or deficiency (hyposecretion)
The hormones are not stored in the body. They are destroyed and excreted immediately after their action.

Functions of hormones

Control and regulate metabolic activities.
Maintain homoeostasis.
Control and regulate morphogenic activities, e.g., growth, development, differentiation.
Regulate mental activities.
Control growth, maturation and regeneration.
Produce secondary sexual characters and regulate reproductive activities.
Control the activities of other endocrine glands.
Cause adaptations to external stimuli.

ENDOCRINE GLANDS IN HUMANS

In human, several endocrine glands are present. Some of them are purely endocrine in function and others are partly endocrine glands.

The purely endocrine glands (Holocrine) are pituitary, thyroid, parathyroid, adrenal, pineal and thymus. Their sole function is to produce hormones.

Whereas partly endocrine glands (Heterocrine) in addition to secretion of hormones also perform some other functions. These include pancreas, gonads (testes and ovaries), lining of alimentary canal, kidneys, placenta, etc.

Various endocrine glands and their location in man. These endocrine glands are given below. The syllabus includes only the first four ones (given in bold). Hence, the other four are not discussed.

Pituitary
Thyroid
Adrenal
Pancreas
Parathyroid
Placenta
Gonads
Thymus

PITUITARY GLAND [Associated with Brain]

The pituitary is a small, red-grey, pea- shaped gland. It hangs from the base of the midbrain below hypothalamus. The pituitary consists of 3 parts :
(a) Anterior pituitary
(b) Intermediate lobe
(c) Posterior pituitary

(a) Anterior pituitary

It constitutes about 75% of the total weight of the gland. Anterior pituitary secretes 6 hormones- GH, LTH, TSH, ACTH, FSH, LH or ICSH, out of which except GH all others are tropic hormones. Tropic hormones are those which stimulate certain other endocrine glands to secrete their secretions.

Growth hormone or Somatotrophic hormone (GH or STH) : It stimulates the growth of bones and soft tissues of the body.
Prolactin (LTH) or Luteotrophic hormone : It stimulates the mammary glands to secrete milk immediately after the birth of a baby. Moreover, it also helps to maintain corpus luteum of ovary after ovulation, hence, called luteotrophic hormone.
Thyroid Stimulating hormone (TSH) : It stimulates thyroid gland to secrete hormone thyroxine.
Adreno Cortico Trophic hormone (ACTH) : It promotes and maintains growth and development of adrenal cortex and stimulates it to secrete its hormones.
Follicle Stimulating hormone (FSH) : It stimulates ovarian follicles to start growth and to continue till the point It also stimulates the of ovulation. follicle cells to secrete hormone estrogen. In males FSH helps in the development of seminiferous tubules and spermatogenesis.
Luteinizing hormone (LH) : LH helps in the process of ovulation from the Graafian follicle and formation of corpus luteum in the ruptured follicle. It also stimulates corpus luteum to secrete hormone progesterone and estrogen. In males, it is called ICSH (interstitial cell stimulating hormone). It stimulates interstitial cells in the testes to develop and secrete testosterone (male hormone).

(b) Intermediate lobe

It is a small middle part of pituitary gland. It secretes hormone MSH (melanocyte stimulating hormone). This hormone controls the distribution of pigments in the skin.

(c) Posterior pituitary

Posterior lobe of pituitary serves as a storage area for the two hormones - ADH or antidiuretic hormone or vasopressin and oxytocin. These two hormones are secreted by the hypothalamus but released by the posterior pituitary.

Antidiuretic hormone (ADH) : It prevents the formation of large amount of urine and thus decreases the water loss from the body (conservation of body water). It can also raise the blood pressure by bringing about constriction of the blood vessels (vasoconstriction) in several tissues.

Deficiency of ADH causes diabetes insipidus (water diabetes). In this urination is frequent, resulting in loss of water from the body making a person become thirsty.

Oxytocin : It has two actions. It stimulates powerful contractions by the pregnant uterus during childbirth. The term oxytocin itself means swift childbirth. (Greek oxys-swift, tokos-childbirth).

It also causes milk ejection from lactating breast. Under its influence, alveoli release the milk into the ducts of breast.

THYROID GLAND [Associated with Pharynx (neck)]

It is the largest endocrine gland (5 x 3 cm) weighing about 25 g. It lies on the ventral and lateral sides of trachea just below the larynx in the neck.

It is brownish-red, butterfly shaped, bilobed gland, one lobe present on either side of the trachea. The two lobes are interconnected by a transverse glandular band called isthmus.

Histologically, it consists of about 3 million small oval or rounded thyroid follicles.

ADRENAL GLANDS [Associated with Kidneys]

Adrenal glands are located above the kidneys, fitting like a cap over these organs. The outer portion of the gland is called cortex, the inner substance, the medulla. These two parts function as separate endocrine glands and secrete different hormones.

Hormones of adrenal cortex

Adrenal cortex secretes many hormones, all of them are steroid in nature. They can be placed into 3 broad classes as follows :

(a) Mineralocorticoids : As the name indicates, these hormones regulate mineral metabolism; mainly sodium and potassium. Aldosterone is the hormone of this group and it increases reabsorption of sodium in the renal tubules. It helps in raising the sodium chloride content of blood.

(b) Glucocorticoids : They are concerned with carbohydrate, protein and fat metabolism. They are under the control of ACTH from adrenohypophysis. The main hormones of this group are cortisol and corticosterone. They have following biological action:

Effect on carbohydrate metabolism: Glucocorticoids raise the blood sugar level. The liver cells form glucose from non-carbohydrate source i.e. proteins and fats. This process is known as gluconeogenesis.
Effect on protein and fat metabolism: Glucocorticoids decrease the rate of protein synthesis. They also stimulate the formation of fat droplets from fats.
Effect on lymph and blood : Glucocorticoids cause the decrease in the number of eosinophils and lymphocytes, thereby reducing the antibody formation.
They prepare the body to cope with stress situation, thus they are anti-stress hormones.

(c) Sex corticoids : They stimulate the development of external sex characters in males. Adrenal androgen is the hormone of this group.

Hormones of adrenal medulla

The adrenal medulla secretes catechola- mines or emergency hormones. Adrenalin (epinephrine) and noradrenalin (norepine- phrine) are the two hormones of this group. Both adrenalin and noradrenalin act on organs and tissues supplied by sympathetic nerve fibres of the autonomic nervous system.

They produce most of the effects like those of sympathetic stimulation. They mainly control the contraction of involuntary muscles including the muscles of heart and arteries.

In man, adrenalin is secreted much more than noradrenalin. At rest adrenal medulla secretes a very small amount of hormones. But, a sharp increase in the rate of release of these hormones occurs during emergencies (fight or flight reactions).

For example, if there is a danger for life of an organism, it can react to this by running away (flight) for safety or by giving a tough fight to the enemy (fight reaction).

In general adrenal medulla and sympathetic nervous system function as closely integrated system called sympatheticoadrenal system. It shows a close co-ordination between nerves and hormones.

Adrenalin is also known as emergency hormone. It is secreted in large amount at the time of emergency. It helps to face physical stress like fall in blood pressure or blood sugar, muscular exertions (like dance and running), pain, cold, injury and emotional stress like anger, fear and grief.

PANCREAS [Associated with Liver]

Pancreas is both an exocrine as well as an endocrine gland. It is located just below the stomach in the loop of duodenum of small intestine. It is a flattened, almost triangular structure.

It contains two types of secretory structures i.e. acini (exocrine part) and islet of Langerhans (endocrine part). The islet of Langerhans are present in the connective tissue of the pancreas. Three types of cells are differentiated in the islet of Langerhans :

(a) Alpha cells (a-cells) : These cells secrete hormone glucagon. Glucagon converts glycogen to glucose whenever glucose level of the blood decreases. Low glucose level in the blood, exercise and protein-rich diet stimulates its formation.

(b) Beta cells (B-cells) : These cells secrete hormone insulin that converts glucose to glycogen (glycogenesis) in the liver and muscle cells. It helps to maintain the blood glucose level constant.

(c) Delta cells (8-cells) : These secrete hormone somatostatin which is a growth hormone-inhibiting hormone (GH-IH). It inhibits the secretion of both glucagon and insulin.

Also Read -

Friday, 7 August 2020

What are the different parts and functions of Ear ?

A pair of ears present on the lateral sides of head, one on either side are the organs for perceiving the sound waves. The ears convey these sound waves to the brain.We are going to discuss about different parts and functions of ears in sense organs.

It helps in analysing the pitch, quality, timbre, intensity, and direction of the sound waves. Moreover, the ears are related with totally unrelated function of maintaining balance and body equilibrium. Parts of ear : Human ear is divided into three parts:

External ear,
Middle ear, and
Internal ear.

What are the Functions and Structure of Eyeball ?

The body has millions of sense organs in the form of sensory neurons which are the receptors for general sensation . These receptors are almost evenly distributed throughout the body .

Can you imagine what your mental condition would be if you would have no knowledge about things outside your body ? Survival will become almost impossible .

Describe the Mechanism and the Factors affecting Photosynthesis.

All metabolism begins with the chemical raw materials that are collectively referred to as food . Some organisms are capable of synthesising organic materials from inert inorganic substances . Such organisms are known as autotrophs . Whereas , others depend upon autotrophs directly or indirectly for the purpose of food and known heterotrophs . The autotrophic organisms are further categorized as

a) photoautotrophs and

b) chemoautotrophs .

PHOTOSYNTHESIS ICSE Class 10th Biology Chapter 5

Photoautotrophs are the green coloured plants and some algae . They synthesise living matter ( organic compounds ) from the inert inorganic materials in the presence of chlorophyll and solar energy . Whereas , chemoautotrophs utilize energy released by their chemical processes , for the purpose of synthesising their food , e.g. sulphur bacteria .

On the other hand , heterotrophs depend upon the autotrophs directly or indirectly for the purpose of their food . facile Photosynthesis is a physiological process by which green plants in the presence of sunlight and chlorophyll prepare food in the form of carbohydrates using carbon dioxide and water .

RAW MATERIALS REQUIRED FOR PHOTOSYNTHESIS

Four important materials are required for the process of photosynthesis . These are :

Carbon dioxide ( CO2 ) ,
Water ( H20 ) ,
Radiant ( Solar ) energy , and
Chloroplasts .

(1) Carbon dioxide ( CO ) :

It is the raw material for the formation of glucose . Plants obtain CO2 from the atmosphere through the stomata . The stomata open or close depending upon the need of CO2 by the plants .

(2) Water ( H20 ) :

It is the second raw material for the process of photosynthesis . Plants get water from the soil by absorption.

(3) Radiant energy ( Solar energy ) :

The Tradiant energy is trapped from the solar energy ( sun ) by the green coloured pigment chlorophyll - present in the chloroplast .

(4) Chloroplasts :

These are green coloured plastids found in the green coloured part of plants . They are very abundant in the leaves ( normally 40-50 in each cell ) . In the leaves they are present mainly in mesophyll cells located between upper and lower epidermis ( i.e. , in palisade cells and spongy cells ) . There may be 50,00,000 chloroplasts per square mm of leaf surface . Chloroplasts are minute , microscopic cell organelles of plant cells . Each chloroplast can be differentiated into three parts i.e.
a) membranes
b) stroma and
c) thylakoids.

( a ) Membranes : The chloroplast is covered by a double membraned envelope . Each membrane is lipo proteinaceous in chemical nature and selectively permeable . In - between the two membranes is present a narrow space called periplastidial space .

( b ) Stroma : The chloroplast is filled with a colourless ground substance or living matrix called stroma .

( c ) Thylakoids : In the stroma are present flattened membranous sac - like structures called thylakoids . The thylakoids are present like the piles of coins . These piles of thylakoids are called grana . The grana are connected by stromatal or fret lamellae .

Chlorophyll :

The vital pigment , is found in walls of thylakoids . The chlorophyll is a highly complex organic substance . It is made of carbon , hydrogen , oxygen , nitrogen and magnesium . There are five types of chlorophyll molecules out of which commonly occurring and most abundant are chlorophyll - a and chlorophyll - b .

The chlorophyll molecules are associated with the membranes of thylakoids . About 250 molecules of chlorophyll form one quantasome . It is capable of trapping one quantum of energy and converting into chemical energy . This process is called photochemical act .

In addition to chlorophyll molecules , the chloroplasts also contain accessory pigments carotenes and xanthophylls . These pigments help in the transference of light energy to chlorophyll - a . Chlorophyll is highly sensitive to light . Too much light may destroy it .

Mechanism of opening and closing of Stoma :

The opening and closing of stoma is regulated by turgidity of guard cells . The stoma is open when guard cells are turgid . On losing turgidity in guard cells the stoma gets closed .

According to sugar concentration theory ( Old one ) :

During daytime the guard cells start photosynthesis . The sugar produced during this process increases the osmotic pressure . Due to increased osmotic pressure water enters in the guard cells because of endosmosis , from the adjoining cells . Hence , the guard cells become turgid and bulge outwards due to their thin outer wall thus widening the stomatal opening lying between them .

According to potassium ion concentration theory ( New one ) :

The opening and closing of stoma depend on the generation of potassium ion gradient . During day , photosynthesis occurs in chloroplast of guard cell which leads to the production of ATP in the light reaction phase . ATP pumps the potassium ions of adjoining cells into guard cells .

Increased potassium ion concentration in guard cells makes them hypertonic , hence , water from adjoining cells rushes inside and the cells become turgid . The guard cells move outwards to open out the stomatal pore . At night , potassium ions leak out thus reducing the turgor of the guard cells and the stomatal pore closes .

MECHANISM OF PHOTOSYNTHESIS

Mesophyll cells ( palisade and spongy cells ) in the leaves are the main centre of photosynthesis . During daytime the chlorophyll molecules trap solar energy . This trapped energy is utilized for the synthesis of organic compounds ( glucose ) using CO2 and H20 as inorganic ingredients .

Oxygen gas is evolved as a by - product of this process . The overall reaction that takes place in photosynthesis can be expressed as follows :
6CO2 + 12H20 → C6H12O6 + 602 + 6H20

The 6 molecules of water liberated in the equation above are those that are reformec during a chain of reactions and not out of the original ones .

FORMATION OF STARCH AND OTHER ORGANIC COMPOUNDS

The process by which several molecules of glucose are transformed to produce one molecule of starch is called polymerisation . The starch is insoluble in water . It is used for the storage of food in the plant cells . In some plants glucose is converted into sucrose or other sugars .

FATE OF END - PRODUCTS OF PHOTOSYNTHESIS

Photosynthesis results in the formation of three types of end - products :

Glucose ( C6H1206 ) - a simple sugar
Water
Oxygen .

Some of the glucose produced during photosynthesis is oxidized immediately for the release of energy , required for the metabolism of cells . The rest of the glucose is converted into insoluble starch . It is stored in the cells as reserve food material . It is also transported to non - photosynthetic cells in the form of sucrose .

Water produced during photosynthesis is reutilized for the continuity of this process .Oxygen produced during photosynthesis is partially utilized by the plant cells for oxidation . Rest of the O2 is released into the atmosphere through the leaf surfaces , specially through stomata . The oxygen released helps to maintain the air composition constant .

This 02 is used by the animals and plants for the purpose of oxidation of glucose during respiration . The process of respiration releases CO2 which is utilized by the plants in photosynthesis . It means respiration and photosynthesis are antagonistic to each other and help to maintain O2 and CO2 concentration in the air constant .

PRICE OF PHOTOSYNTHESIS

Stomata are primarily meant for the diffusion of CO2 which is to be used for photosynthesis . But when CO2 diffuses in at the same time , a large amount of H2O is lost due to transpiration . So , we say that the plants have to pay the price of photosynthesis in the form of transpiration .

Fate of carbohydrates formed in photosynthesis

Carbohydrates formed in photosynthesis are used up in three main ways :

Respiration : Most cells receive sugar through phloem . This is broken down during respiration to liberate energy the cells require .
Food storage : Some of the sugar may be stored for future use either in organs , such as bulbs , tubers , corms or rhizomes or for the next generation in seeds or fruits . Usually the sugar is converted into starch for storage but quite often it is stored as sucrose as in sugarcane . In fact , many of our vegetables are really plant food storage organs . For example , potato tubers are storage stems , carrot , turnip and beetroots are storage roots . In many cases , carbohydrates are converted to oils for storage e.g. , mustard oil and groundnut oil .
Growth : Sugar is also transported to actively growing parts of the plant where these provide energy and are used in the formation of cellulose , fats and proteins .

TRANSPORTATION ( TRANSLOCATION ) OF ORGANIC COMPOUNDS IN THE PLANTS

Primarily , the process of photosynthesis i.e. , formation of glucose and other organic compounds takes place in the cells of leaves . But these organic compounds are needed by all the cells of a plant . Formation of glucose in the leaf cells is continuous and very rapid . It cannot be transported to other cells with the same rapidity .

That is why , most of the glucose is converted into insoluble starch for the purpose of temporary storage. At night the stored starch is reconverted into soluble sucrose . The soluble sucrose in the form of solution is transported ( translocated ) to all the cells of the plant .

Sucrose passes through the veins of leaves down through the phloem of the stem and roots . The sucrose is converted into glucose in different cells . It is partially oxidized in respiration to release energy . Rest of glucose is reconverted into starch for the purpose of storage .

ADAPTATIONS IN LEAF FOR PHOTOSYNTHESIS

Large surface area : The surface area of the leaves is very large . It helps in the absorption of maximum light energy from the sunlight .
Leaf arrangement : The leaves are arranged on the stem in such a way ( right angle to light source ) so that maximum surface area of leaves is exposed to sunlight .
Chloroplasts containing chlorophylls are concentrated in the upper layers of the leaf cells , near the cell walls . It helps in trapping maximum radiant energy from the sunlight quickly .
Numerous stomata in the leaves allow quick exchange of O , and CO2 through them .
Thinness of leaves further enhances the rapid transport of materials between adjoining cells .
Network of veins in the leaves helps in the rapid transport to and from the mesophyll cells of leaves .

FACTORS AFFECTING PHOTOSYNTHESIS

I. External Factors :

Light : Radiant energy of light is an important factor in three aspects i.e. , intensity , quality and duration . About 0.2-1 % of the total solar radiations is utilized in photosynthesis . Within limits , increase in light intensity increases the rate of photosynthesis . At very high light intensity , the photosynthetic apparatus may get damaged . This phenomenon is called solarization .Photosynthesis is greatly influenced by light quality . Blue and red regions of the visible spectrum are most effective and green the least .The process of photosynthesis is also directly proportional to the duration of light .
Carbon dioxide : If light intensity is good and the temperature is optimum , then increase in CO2 concentration increases the rate of photosynthesis .
Temperature : Temperature at which the rate of photosynthesis is maximum is called optimum temperature . It is 35 ° C . The rate of photosynthesis goes on increasing from lower temperature to 35 ° C . It again starts decreasing above 35 ° C and stops above 40 ° C . A rise of 10 ° C below the optimum temperature doubles the rate photosynthesis , provided the light intensity is high . It is called Q10 law .
Water : Under normal conditions water has no direct bearing on the rate of photosynthesis . But , if the water supply is poor , then a decrease in photosynthesis has been observed .

II . Internal Factors :

Chlorophyll : Deficiency of magnesium causes loss of chlorophyll , hence , leaves are not able to absorb sunlight ( Solar energy ) .
Leaf structure : The size of leaf , distribution of stomata and thickness of cuticle influences the amount of CO2 and light entering the leaf , hence , affects the rate of photosynthesis .

SIGNIFICANCE OF PHOTOSYNTHESIS

Photosynthesis is the most important and basic process which sustains life on this earth . It has manifold significance , such as :

It synthesises food from inorganic substances . This food becomes the ultimate source of energy and life for all the living organisms . This helps in maintaining food chain amongst the producers , herbivores and carnivores . The food chain may have a number of stages but the starting point is always a plant ( producer ) . The non - green plants like fungi and bacteria obtain their food from decaying organic matter in their environment . Hence , it is very rightly said that " All flesh is grass " .
It is the only known method which releases oxygen in the atmosphere . It keeps the O2 concentration constant . The consumption of O2 by living organisms during respiration is compensated by photosynthesis .
It also helps to keep the CO2 concentration in the atmosphere constant . The CO2 being released due to the respiration of living organisms is being incorporated in glucose during photosynthesis .
Coal , petroleum and natural gas are fossil fuels . These have been produced by the application of heat and compression on the past plants .
All useful plant products , such as , timber , rubber , resins , drugs , oils , fibres , etc. are derived from the process of photosynthesis .

CARBON CYCLE

Carbon is the building material of all the organic compounds found in the living cells , e.g. carbohydrates , lipids , proteins and nucleic acids . In the biosphere , there are 4 sources of carbon :

Carbon dioxide present in the air .
Carbon dioxide present in air gets dissolved in water easily .
Carbonates of the earth's crust derived from rocks . These give rise to carbon dioxide by the chemical changes .
The fuels , such as , coal and petroleum products , produce carbon dioxide after burning.

The carbon cycle can be defined as a series of chemical reactions in which carbon as an element from carbon dioxide is removed from the atmosphere , used up by living organisms in their body processes and is again returned to the atmosphere .

Also Read -

Saturday, 25 July 2020

How does the Absorption of Water & Minerals by Roots take place ?

Plant physiology is the branch of Biology that deals with the study of functions of a plant. It includes functioning of cells, tissues, organs, organ systems and the organisms as a whole. Here in this chapter, you are going to study about, the most fundamental processes occurring in plants which have tremendous importance in their life. These are - absorption of water and minerals by the roots, ascent of sap, transpiration, photosynthesis and respiration.

Describe briefly about Pollution and its types.

What is Pollution ?

Pollution is an undesirable change in the physical, chemical and biological characteristics of environment. It is harmful to human life and other organisms. Agents causing pollution are known as pollutants.