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In reverse bias Zener diode can be used as voltage regulator.

Tern Berners -Lee invented the World Wide Web.

It is an encyclopedia of knowledge accessible to every one round the clock through out the year.

Two sound waves of nearly same frequency are travelling in the same direction and interfere to produce a regular waxing (maximum) and waning (minimum) in the intensity of the resultant sound waves at regular intervals of time is called beats.

It two vibrating bodies have slightly difference in frequencies, beats can occur.

No. of beats can be heard ∆υ = υ₁ ∼ υ₂

Importance : 1. It Importance : can be used to tune musical Instruments

2. Beats are used to detect dangerous gases.

Explanation for tuning musical instruments with beats : Musicians use the beat phenomenon in tuning their musical instruments. If an instrument is sounded against a standard frequency and tuned until the beats disappear then the instrument is in tune with the standard frequency.

Animals in which the body cavity is formed from the mesodermal pouches of archenteron are called 'enterocoelomates'. 

Echinoderms, hemichordates and chordates are the enterocoelomates.

Exocrine glands are provided with ducts. Secrete mucus saliva, earwax, oil, milk, digestive enzymes and other cell products. 

Endocrine glands are ductless and their products are hormones which are not sent out via ducts, but are carried to the target organs by blood. 

Ex : pitutory gland.

Cephalisation : Concentration of nerve (Brain) and sensory cells at the anterior end of body is called as cephalisation. As a result of cephalisation, these animals can sense the new environment and move efficient than the other animals in seaking food, locating mater and in avoiding from predators.

Cnidarians and some flat warms are the first animals to exhibit a 'tube-within-a-tube' organisation. Body cavity is pseudo- coelom.

Exocrine glands are provided with ducts. Secrete mucus saliva, earwax, oil, milk, digestive enzymes and other cell products.

Endocrine glands are ductless and their products are hormones which are not sent out via ducts, but are carried to the target organs by blood. 

Ex : pitutory gland. 

Functions of canal system of sponge are gathering of food, respiratory exchange of gases and removal of wastes. 

Mast cells secrete heparin – an anticogulant – histamin, bradykinin – vasodilators and seroonina – vasocon strictor. Vasodilators cause inflammation in response to injury and infection. 

Male frog can be distinguished by the presence of sound ampliflying vocal sacs and a copulatory pad on the first digit of each forelimb.

The buccal cavity contains a file – like rasping organ called radula for feeding, except the bivalves and tusk of Molluscs.

Poisonous Snakes : 

(1) Naja naja (Cobra), 

(2) Bungarus (Krait) 

(3) Vipera russelli (Chain viper) 

Non – poisonous Snakes :

(1) Ptyas (rat snake) 

(2) Tropidonotus (Pond or grass snake)

In the ciliate protozoans a longitudinal row of kinetosomes together with kinetodesmata constitute a unit called kinety.

Upward movement of water through xylem aganist gravitational force is called accept of sap. The transpiration driven ascent of xylem sap depends on 

(a) cohesion mutual attraction between water molecules. 

(b) Adhesion - attraction of water molecules to palar surfaces. 

(c) Transpiration pull driving force for upward movement of water. These properties give water high tensile strength and high capillarity. In plants capillarity is aided by the small diameter of the tracheary elements. As water evaporates through the stomata. Since the thin film of water over the cells is continuous, it results in pulling of water, molecule by molecule, into the leaf from the xylem. Also, because of lower concentration of water vapour in the atmosphere, water diffuses into the surrounding air. This creates 'transpiration pull'. The forces generated by transpiration can creates pressures sufficient to lift a xylem sized column of water over 130 metres high.

Modern methods of Breeding plants :

(1) Plant breeding for disease resistance :- Several fungal, bacterial and viral pathogens affect the yield of cultivated crop species. In this situation, breeding and development of cultivars resistant to disease enhances food production. It also helps reduce the dependence on the use of fungicides and bacteriocides. Breeding is carried out by conventional breeding techniques or by mutation breeding. The method of breeding for disease resistance is that of hybridisation and selection. By this some crop varieties are produced which were disease resistance to bacteria and fungi. They are

Mutation breeding : It is the process by which genetic information is created through changes in the base sequence within genes resulting in the creation of new character of trait not found in the parental type.

Eg : Resistance to yellow mosaic virus in Bhendi (Abelmoschus esculentus) was transferred from a wild species and develop in a new variety called Parbhani Kranti.

(2) Plant breeding for developing resistance to insect pests : Large scale destruction of crop plants and crop produce is by insect and pest infestation. Insect resistance in Host crop plants may be due to morphological morphological, biochemical biochemical or physiological physiological characteristics. Hairy leaves in several plants are resistances to insect pests. 

Eg : Resistance to Jassids in cotton and cereal leaf beetle in wheat. Smooth leaved and nectar–less cotton do not attract bollworms. High aspartic acid, low nitrogen and sugar content in maize leads to resistance to maize stem borers.

Some released crop varieties bred by hybridisation and selection, for insect, pest resistance are

(3) Plant breeding for improved food quality : A far greater number–Three billion people-suffer from micro-nutrients, potein, and vitamin deficiencies or  'hidden hunger because they can not afford to buy enough nutritious food.  Biofortification aims at breeding crops with high vitamins and minerals or higher protein and healthier fats to improve public Health. Wheat, Atlas 66 having a high protein content has been developed by this method. β carotene containing rice variety 'Golden Rice',vitamin A enriched carrots, spinach, Vitamin C enriched bitter gourd mustard, tomato, iron and Calcium rich spinach, Protein rich garden peas are released IARI, New Delhi.

A parasite that parasitises another parasite is called Hyper parasite. 

Ex : Nosema notabilis (acnidosporan) is a parasite in Sphaerospora polymorpha (acnidosporan parasite in the urinary bladder of the toad fish).

(1) UV radiations kills the microorganisms present on the body surface of animals. 

(2) UV radiations helps in the conversion of sterols present in the skin into vitamin D in mammals.

Species : Species is the 'basic unit' of classification. Species is a Latin word meaning 'kind' or 'appearance'. John Ray in his book 'Historia Generalis Plantarum', used the term 'species' and described it on the basis of common descent (origin from common ancestors) as a group of morphologically similar organisms. Linnaeus considered species, in his book 'Systema Naturae', as the basic unit of classification. Buffon, in his book 'Natural History', proposed the idea of evolution of species which is the foundation for the biological concept of evolution. This biological concept of species (dynamic nature of species) became more popular with the publication of the book "The Origin of Species" by Charles Darwin.

Buffon's biological concept of species explains that species is an interbreeding group of similar individuals sharing the common 'gene pool' and producing fertile offspring. 

Species is considered as a group of individuals which are : 

(1) Reproductively isolated from the individuals of other species – a breeding unit. 

(2) Sharing the same ecological niche – an ecological unit. 

(3) Showing similarity in the karyotype – a genetic unit. 

(4) Having similar structure and functional chracteristics – an evolutionary unit.

The term Green House effect' has been derived from a phenomenon that occurs in a green house'. Green house is a small glass house and is used for growing plants especially during winter. In a green house the glass panel allows the passage of light into it, put does not allow heat to escape (as it is reflected back). Therefore, the greenhouse warms up, very much like inside a car that has been parked in the sun for a few hours.

The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of the Earth's surface and atmosphere. It would be surprising to know that without green house effect the average temperature of the Earth's surface would have been a chilly – 18°C rather than the present average of 15°C.

When sunlight reaches the outer most layer of the atmosphere, clouds and gases reflect about one – fourth of the incoming solar radiation and absorb some of it. Almost half of the incoming solar radiation falls on the Earth's surface and heats it up. While a small proportion is reflected back.

(1) Anthozoans are commonly referred to as sea anemones. 

(2) Anthozoa includes sea anemones, corals, sea pens. 

(3) All are marine forms. These are solitary or colonial. 

(4) They are sedentary and only polypoid inform. 

(5) Coelenteron is divided into several compartments by vertical septa called mesenteries. 

(6) Mesoglea contains connective tissue. 

(7) Cnidocytes occur both in the ectoderm and endoderm and is cellular as contains amoebocytes. 

(8) Germ cells are derived from the endoderm. 

Eg: Adamsia (sea anemone), Gorgonia(sea fan), Pennatual (sea pen).

Effect : Smoking increases the carbon monoxide (CO) level and reduces the oxygen level in the blood. Nicotine stimulates the adrenal gland to release adrenaline and nor – adrenaline into blood. These hormones raise the blood pressure and increase the heart rate. Smoking is associated with bronchitis, emphysema, coronary heart disease, gastric ulcer and increases in incidence of cancers of throat, lungs, urinary bladder etc. smoking also paves the way to hard drugs. Yet smoking is very prevalent in society, both among young and old. Tobacco chewing is associated risk of cancer of the oral cavity.