Spontaneous process. A process which has a natural tendency to take place either by itself or after initiation under a given set of conditions is known as a spontaneous process. For example,

(i) Sugar dissolve in water and forms a solution.

Sugar + water   →Solution of sugar in water

CELL THEORY

• Schleiden and Schwann together formulated the cell theory.
• Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells.
• Cell theory states that
• All living organisms are composed of cells and products of cells.
• All cells arise from pre-existing cells.

The body composition means the amount of the fat-free body weight. It is well known that a high percentage of body fat in relation to the total body weight is harmful and may lead to obesity from the health point of view, the normal percentage of body fat for young men and women should not exceed 15 and 25 percentage. It means that for health-related fitness an individual should have ideal body weight and fat percentage.

Flight adaptations found in birds
(i) Body is streamlined to reduce air resistance during flight.
(ii) Four limbs are modified into wings.
(iii) Wings have long quill feathers to increase the efficiency of heating of wings,
(iv) Pneumatic bones are present to reduce the body weight.
(v) High metabolic rate to provide energy.
(vi) Air sacs present in lungs help in double respiration.

Flight adaptations in birds
(i) Boat-shaped body helps to propel through the air easily.
(ii) Feathery covering of body to reduce the friction of air.
(iii) Holding the twigs automatically by hindlimbs.
(iv) Extremely powerful muscles that enables the wings to work during flight.
(v) Bones are light, hollow and provide more space for muscle attachment. Presence of pneumatic bones which reduce the weight of body and help in flight.

(vi) The first four thoracic vertebrae are fused to form a furculum for walking of the wings.

(vii) Lungs are solid and elastic and have associated air sacs.

(viii) The power of accommodation of eyes is well developed due to the presence of comb-like structure pecten. (ix) A single left ovary and oviduct to reduce the body weight.

Mycoplasma are the smallest living cells known till date. They lack proper cell wall and can survive without oxygen.

The law of variable proportion states that as we increase the quantity of only one input, keeping other inputs fixed, the total product increases at an increasing rate (convex shape) in the beginning, then increases at diminishing rate (concave shape) and after a level of output ultimately falls.

2. Assumptions of Law of Variable Proportions
(a) Only one input is variable, the other is held constant or fixed.
(b) It is possible to change the proportion in which the factor units are combined.
(c) It assumes a short run.
(d) The state of technology is given and remains unchanged.
(e) Price of factors of production do not change.
3. It can be explained with the help of schedule and diagram:

The Body Mass Index is also known as Qetelet Index because it was invented by Adolphe Quetelet. In fact, it is a statistical measurement which compares an individual’s weight and height. Although/ it does not actually measure the percentage of body fat, yet is very useful tool to estimate a healthy body weight based on how tall an individual is. Indeed it is the most widely used tool to indentify the weight problem. BMI is very easy to measure and evaluate. With the help of BMI one can come to know whether one is under weight, normal weight, over weight or in classes of obesity. BMI can be defined as the individual’s body weight divided by the square of his height i.e.,

BMI can be determined using BMI chart. It’s value is measured in Kg/m2.
Now with the help of WHO (World Health Organization) criteria for under weight and obesity, an individual may come to know that he belongs to category of under weight, normal weight, over weight in the categories of obesity. The categories are:

When a particle is thrown obliquely near the earth’s surface, it moves along a curved path under constant acceleration that is directed towards the center of the earth (we assume that the particle remains close to the surface of the earth). The path of such a particle is called a projectile and the motion is called projectile motion. Air resistance to the motion of the body is to be assumed absent in projectile motion.

In a Projectile Motion, there are two simultaneous independent rectilinear motions:

1. Along the x-axis: uniform velocity, responsible for the horizontal (forward) motion of the particle.
2. Along y-axis: uniform acceleration, responsible for the vertical (downwards) motion of the particle.

Molecular mass of an element is defined as the sum of the masses of the elements present in the molecule. Molecular mass is obtained by multiplying the atomic mass of an element with the number of atoms in the molecule and then adding the masses of all the elements in the molecule. Let us see an example: carbon dioxide.
The molecular mass of carbon dioxide CO2 = atomic mass of carbon + 2 × (atomic mass of oxygen)
= 12.011 u + 2 × (16.00 u)
= 44.011 u

REGULATION OF RESPIRATION

• A specialised centre present in the medulla region of the brain called respiratory rhythm centre is primarily responsible for this regulation.
• Another centre present in the pons region of the brain called pneumotaxic centre can moderate the functions of the respiratory rhythm centre.
• Neural signal from this centre can reduce the duration of inspiration and thereby alter the respiratory rate.
• A chemosensitive area is situated adjacent to the rhythm centre which is highly sensitive to CO₂ and hydrogen ions.
• Receptors associated with aortic arch and carotid artery also can recognise changes in CO₂ and H⁺ concentration and send necessary signals to the rhythm centre for remedial actions.

Blood transports CO₂ from the tissue cells to the lungs in three ways:

1. Dissolved in plasma : About 7 – 10% of CO₂ is transported in a dissolved form in the plasma.

2. Bound to haemoglobin : About 20 – 25% of dissolved CO is bound and carried in the RBCs as carbaminohaemoglobin (Hb CO₂ ) CO₂ + Hb → Hb CO₂ .

3. As bicarbonate ions in plasma about 70% of CO₂ is transported as bicarbonate ions. This is influenced by pC0₂ and the degree of haemoglobin oxygenation. RBCs contain a high concentration of the enzyme, carbonic anhydrase, whereas small amounts of carbonic anhydrase is present in the plasma.

→ At the tissues the pCO₂ is high due to catabolism and diffuses into the blood to form HCO₂ and H ions. When CO₂ diffuses into the RBCs, it combines with water forming carbonic acid (H₂ CO₂ ) catalyzed by carbonic anhydrase. Carbonic acid is unstable and dissociates into hydrogen and bicarbonate ions.

Carbonic anhydrase facilitates the reaction in both directions.

The HCO₃^- moves quickly from the RBCs into the plasma, where it is carried to the lungs. At the alveolar site where pCO₂ is low, the reaction is reversed leading to the formation of CO₂ and water. Thus CO₂ trapped as HCO₃^- at the tissue level is transported to the alveoli and released out as CO₂ . Every 100 mL of deoxygenated blood delivers 4 mL of CO₂ to the alveoli for elimination.

Transport of oxygen

• Haemoglobin is a red coloured iron containing pigment present in the RBCs.
• O₂ can bind with haemoglobin in a reversible manner to form oxyhaemoglobin.
• Binding of oxygen with haemoglobin is primarily related to partial pressure of O₂ and partial pressure of CO2, hydrogen ion concentration and temperature are the other factors which can interfere with this binding.
• A sigmoid curve is obtained when percentage saturation of haemoglobin with O₂ is plotted against the pO₂ and the curve is called the oxygen dissociation curve.
• pCO2, H⁺ concentration have effect on binding of O₂ with haemoglobin.
• In the alveoli, where there is high pO₂, low pCO₂, lesser H⁺ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, and where low pO₂, high pCO₂, high H⁺ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin.
• Every 100 ml of oxygenated blood can deliver around 5 ml of O₂ and each haemoglobin molecule can carry a maximum of four molecules of O₂.

1. The exchange of gases between air and blood takes place across the walls of the alveoli.
2. The human respiratory system:

• Tidal Volume (TV): Volume of air inspired or expired during a normal respiration, which is approx. 500 mL.
• Inspiratory Reserve Volume (IRV): Additional volume of air, a person can inspire by a forcible inspiration, which averages 2500 mL to 3000 mL.
• Expiratory Reserve Volume (ERV ): Additional volume of air, a person can expire by a forcible expiration, which averages 1000 mL to 1100 mL.
• Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration, which averages 1100 mL to 1200 mL.
• Inspiratory Capacity (IC): Total volume of air a person can inspire after a normal expiration, which includes tidal volume and inspiratory reserve volume ( TV+IRV).
• Expiratory Capacity (EC): Total volume of air a person can expire after a normal inspiration, which includes tidal volume and expiratory reserve volume (TV+ERV).
• Functional Residual Capacity (FRC): Volume of air that will remain in the lungs after a normal expiration, which includes ERV+RV.
• Vital Capacity (VC): The maximum volume of air a person can breathe in after a forced expiration, which includes ERV, TV and IRV.
• Total Lung Capacity: Total volume of air accommodated in the lungs at the end of a forced inspiration, which includes RV, ERV, TV and IRV.

MECHANISM OF BREATHING

• Breathing involves two stages :
• Inspiration- during which atmospheric air is drawn in.
• Expiration- during which the alveolar air is released out.
• Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure.
• Expiration takes place when the intra-pulmonary pressure is higher than the atmospheric pressure.
• The diaphragm and a specialised set of muscles – external and internal intercostals between the ribs.
• The contraction of external inter-costal muscles lifts up the ribs and the sternum causes an increase in the volume of the thoracic chamber in the dorso-ventral axis.
• An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs.
• Relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum to their normal positions and reduce the thoracic volume and thereby the pulmonary volume, which leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs.
• A healthy human breathes 12-16 times/minute.
• The volume of air involved in breathing movements can be estimated by using a spirometer.

Larynx – “Adam‟s apple” 

Glottis – Aperture in laryngopharynx which opens into trachea. 

Epiglottis – A cartilaginous flap present at the anterior margin of glottis. It projects into the pharynx opposite the uvula. During swallowing, larynx moves upward to close the glottis to check the entry of food into it. 

Trachea/ Windpipe – thin walled tube extends downward through the neck. 

Bronchi – Trachea divides into two tubes called bronchi in the middle of the thorax. 

Bronchioles – Bronchi divide and re-divide into tertiary bronchi which divide into alveolar ducts which enter into alveolar sacs. 

Lungs – Human respiratory organ, located in the thoracic cavity.  

Alveolar sac – In the lung, each alveolar duct opens into a blind chamber, the alveolar sac which appears like a small bunch of grapes. 

Alveoli / Air sacs – The central passage of each alveolar sac gives off several small pouches on all sides, the alveoli or air sacs. 

Alveolar wall – is very thin (0.0001 mm) wall composed of simple moist, non-ciliated, squamous epithelium which easily recoil and expand during breathing.

जैव विविधता के ह्रास के निम्नलिखित कारण हैं
(i) कृषि भूमि को बढ़ाने के लिए वनों का तेजी से ह्रास किया जा रहा है। वन-भूमि के हास के कारण वन्य-जीवों के निवास स्थल का भी ह्रास होता जा रटा है।
(ii) कई क्षेत्रों में मनुष्य ने जंगली जानवरों का काफी मात्रा में शिकार किया है, जिससे इन क्षेत्रों में इन जंगली जानवरों की संख्या काफी कम हो गई है।
(iii) वर्तमान औद्योगिक युग में उद्योगों से निकलने वाला रसायनयुक्त प्रदूषित जल जब जलाशयों में मिल जाता है तो उन जलाशयों के जीव-जंतु या तो खत्म हो जाते हैं या उनका जीवन खतरे में रहता है। इसे रोकने के निम्नलिखित उपाय हैं
(क) विश्व की बंजर भूमि में वनों को लगाना चाहिए।
(ख) जहरीली गैसों से युक्त उद्योगों पर प्रतिबंध लगा देना चाहिए या जनसंख्या विहीन क्षेत्रों में उनकी स्थापना की जानी चाहिए।
(ग) जैविक विविधता के संरक्षण से संबंधित एक रूपरेखा तैयार करनी चाहिए, जिसको अमल में लाने के लिए सभी देशों को बाध्य करना चाहिए।

खाद्य श्रृंखला में एक स्तर से दूसरे स्तर पर ऊर्जा प्रवाह ही खाद्य श्रृंखला (Food Chain) कहलाती है।
चराई खाद्य श्रृंखला (Grazing Food-chain) पौधों से आरम्भ होकर मांसाहारी तृतीयक उपभोक्ता तक जाती है। इसमें शाकाहारी मध्यम स्तर पर होता है। उदाहरण के लिए-पौधा/पादप → गाय/खरगोश → शेर या घास → टिड्डे → मेंढक → सर्प → बाज। चराई खाद्य श्रृंखला लघु आकारीय तथा वृहत् आकारीय दोनों होती है। जिस श्रृंखला में तीन स्तर होते हैं, उसे लघु चराई खाद्य शृंखला तथा जिसमें पाँच या इससे अधिक स्तर होते हैं उसे वृहत् चराई श्रृंखला कहा जाता है।