Ontogeny refers to the development of an organism while phylogeny refers to how the organisms have evolved. Phylogeny is the study of the evolutionary development of groups of organisms. The relationships are hypothesized based on the idea that all life is derived from a common ancestor. Relationships among organisms are determined by shared characteristics, as indicated through genetic and anatomical comparisons. Ontogeny refers to the development of an organism while phylogeny refers to how the organisms have evolved. Let us take an example of a chicken, the ontogeny will explain the entire development cycle of the chicken right from the single cell.

A wavefront is an imaginary surface over which an optical wave has a constant phase. The shape of a wavefront is usually determined by the geometry of the source. 

Huygen's principle: 

(i) Every point on a given wavefront acts as a fresh source of secondary wavelets which travel in all directions with the speed of light.
(ii) The forward envelope of these secondary wavelets gives the new wavefront at any instant. 

Laws of reflection by Huygen's principle: 
Let, PQ be reflecting surface and a plane wavefront AB is moving through the medium (air) towards the surface PQ to meet at the point B. 
 

Let, c be the velocity of light and t be the time taken by the wave to reach A' from A. 
Then,  AA' = ct.
 

Using Huygen's principle, secondary wavelets starts from B and cover a distance ct in time t and reaches B'.

To obtain new wavefront, draw a circle with point B as centre and ct (AA' = BB') as radius. Draw a tangent A'B' from the point A'. 

Then, A'B' represents the reflected wavelets travelling at right angle. Therefore, incident wavefront AB, reflected wavefront A'B' and normal lies in the same plane. 

Consider ∆ABA' and B'BA'
AA' = BB' = ct       [∵ AA' = BB' = BD = radii of same circle]
BA' = BA'              [common]
∠BAA' = ∆BB'A'     [each 90°]
∴ ∆ABA' ≅ ∠DBA'    [by R.H.S]
∠ABA' = ∠B'A'B    [corresponding parts of congruent triangles] 

∴ incident angle i = reflected angle r
i.e.,                 ∠i = ∠r

1. IAEA:- International Atomic and Energy Agency
2. SARA:- State Adoption Resource Agency
3. FDI:-  Foreign direct investment

Osteoporosis refers to the decreased bone material contents. It is a skeletal disorder. In fact, low oestrogen levels and poor nutrition specially low calcium intake can lead to osteoporosis which is one of the significant triad of female athlete. Osteoporosis is weakening of the bones due to the loss of bone density and improper bone formation.

Such factors are stated below;
1.Insufficient calcium in diet:The main cause of oesteoporosis is intake of insufficient amount of calcium in diet. In fact, 100mg calcium should be taken in daily diet by a woman athlete. In addition to calcium, vitamin 'D' should also taken because it is essential for absorbing calcium in our boby.
2.Eating disorders:eating disorders like anorexia and bulimia etc. In fact, not getting sufficient amount of calcium can also have a lasting effect on how strong a woman's bones are in later part of life. So eating disorders may also lead to oesteoporosis among women athletes.
3. Bad eating habits: various research studies indicate that intake of caffeine,alcohol,tabacco or smoking etc. may also lead to oesteoporosis. Indeed these products have a negative effect on the bone density.

Lemons are full of vitamins, minerals, phytonutrients and antioxidants. They are especially good sources of vitamin C and folate. Lemons are one of the most popular acid citrus fruits, according to the Purdue University Horticultural Department.

A transport network is a realisation of a spatial network, describing a structure which permits either vehicular movement or flow of some commodity. 

The Trans-Alaska Pipeline System (TAPS) includes the trans-Alaska crude-oil pipeline, 11 pump stations, several hundred miles of feeder pipelines, and the Valdez Marine Terminal. TAPS is one of the world's largest pipeline systems. It is commonly called the Alaska pipeline, trans-Alaska pipeline, or Alyeska pipeline, (or the pipeline as referred to in Alaska), but those terms technically apply only to the 800 miles (1,287 km) of the pipeline with the diameter of 48 inches (1.22 m) that conveys oil from Prudhoe Bay to Valdez, Alaska. The crude oil pipeline is privately owned by the Alyeska Pipeline Service Company.

1. ट्रांस-साइबेरियाई रेलमार्ग एक प्रसिद्ध रेलमार्ग है जो रूस की राजधानी मास्को को रूस के साइबेरिया क्षेत्र से गुज़रते हुए सूदूर-पूर्वी शहर व्लादिवोस्तोक से जोड़ता है।
2. इसकी शाखाएँ मंगोलिया से गुज़रती हुई चीन भी जाती हैं।
3. यह एक 9,289 किमी लम्बा रेलमार्ग है और इसपर एक छोर से दुसरे छोर तक पूरा सफ़र करने में आठ दिन लग जाते हैं।
4. इसे रूस के शाही ज़माने में सन् 1891-1916 के काल में बनाया गया था।
5. साइबेरिया की आबादी बढ़ाने में और वहाँ के आर्थिक विकास में इस रेलमार्ग का बहुत बड़ा हाथ रहा है। हज़ारों सैलानी भी इसके द्वारा हर वर्ष साइबेरिया की सैर करते हैं और इस पर यात्रा करना विश्व के अनूठे अनुभवों में से एक माना जाता है।

Darwin proposed the theory of natural selection to understand the process of evolution. According to this theory, nature itself selects various traits or characteristics that will suit the members of a species. And thus the individuals who have those traits will be able to survive and reproduce to maintain the continuity of their species while others who are not able to survive perish over time.

A capacitor blocks DC as once it gets charged up to the input voltage with the same polarity then no further transfer of electrons can happen accept to replenish the slow discharge due to leakage if any. hence the flow of electrons which represents electric current is stopped.