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## Tricks to remember Trigonometric Angles : Notes For Class 10th NCERT

An Introduction to Trigonometry

Basic Definition – Trigonometry is a branch of mathematics which deals with the relationship between the sides and the angles of right-angled triangles. Here the term ‘Right-angled’ triangle is very important.

Let’s understand this with an example.

Consider a girl looking at the top of a tower which is few distances apart from her legs. Now, this will form a right-angled triangle whose height can be calculated without actually measuring it physically.

In this chapter, we will be learning about some standard trigonometric identities by using the relation between angles and the sides of the right-angled triangle.

### # Trigonometric Ratios-

• Consider a right triangle with sides AB, BC and AC with C as a right angle.
• Now, considering an acute angle let’s say Angle A, then side opposite to A i.e. a is called the hypotenuse. Also, side b is called the adjacent side.

The trigonometric ratios are defined as:

These ratios are generally represented in their short forms. These are sin A, cos A, tan A, cosec A, sec A and cot A respectively.

Notes:

1. cosec A, sec A and cot A are the inverse of sin A, cos A and tan A respectively.
2. sin A /cos A = tan A and therefore cos A/sin A = cot A

Example 1: Given sinA =4/5, Find all other trigonometric ratios of angle A.

Solution: Let’s draw a right triangle ∆ABC right angled at B.

Now, Given that sin A =4/5

∴BC/AC =4/5
∴ BC = 4k and AC= 5K, where K is a constant.

Now, In ∆ABC, applying Pythagoras Theorem,

(AC)2 = (AB)2 + (BC)2

∴ (5K)2 = (AB)2 + (4K)2

∴ AB = 3K

Similarly, cosec A = 1/ sin A = 5/4
And, sec A = 1/ cos A = 5/3
And, cot A = 1/ tan A = 4/3 Answer

## Trick To Remember All the Trigonometric Ratios

We will remember all the ratios using a mnemonics as

Here Look at the ratios and the words

• For Sin theta, we have Pandita/Hara which is P/H
• Similarly For Cos theta we have Badri/hara which is B/H
• Similarly for Tan theta, we have Prasad/Bola which P/B
• For other ratio take the reciprocal of the angles.
• Such as for Cosec theta it is H/P
• Sec Theta it is H/B and for Cot theta, it is B/P.

This note is Contributed by
Vishesh Meena
3rd Year, Electrical Engineering,
IIEST
[email protected]

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## NOMENCLATURE OF ORGANIC COMPOUNDS

• Organic compounds are the compounds mainly consisting of C and H atoms , along with some atoms like O,N, Halogens occasionally.
• An organic compound in general will have two names – common name and IUPAC name.
• IUPAC (International Unit of Pure and Applied Chemistry) nomenclature are the standard names.
• The common name is based on the source or some properties.
• For e.g. Citric acid is named so because it is found in citrus fruits and the acid found in red ant is named formic acid since the Latin word for ant is formica.

We will study IUPAC nomenclature in detail .

### IUPAC NOMENCLATURE OF ORGANIC COMPOUNDS

• A systematic name of an organic compound is generally derived by identifying the parent hydrocarbon and the functional group(s) attached to it.
• This name is called IUPAC name.
• It contains two parts – word root and suffix or prefix.
• The word root indicates the number of carbon atoms in the compound.
• The word roots for compounds containing 1 -12 carbon atoms are as follows:
 No. of C atoms Word root No. of C atoms Word root C1 Meth- C7 -Hept C2 Eth- C8 -Oct C3 Prop- C9 -Non C4 But- C10 -Dec C5 Pent- C11 -Undec C6 Hex- C12 -Dodec

There are two types of suffixes :

• primary suffix  and secondary suffix
• Primary suffix indicates saturation or unsaturation [for alkane the primary suffix is –ane, alkene –ene and for alkyne –yne].
• Secondary suffix indicates the type of functional group. Some functional groups are also indicated as prefixes.

## Nomenclature of branched chain alkanes

• A branch (side chain or substituent) is obtained by removing a hydrogen atom from an alkane. The resulting group is called an alkyl group [alkane]
• – H = alkyl (i.e. word root + yl)].

The names of some common branches are as follows:

 Branch Name -CH3 Methyl -CH2-CH3 Ethyl -CH2-CH2-CH3 n-propyl (normal propyl) (CH3)2CH- isopropyl -CH2-CH2-CH2-CH3 n-butyl CH3-CH-CH2-CH3 | sec-butyl (secondary butyl) (CH3)2CH-CH2– isobutyl

# Rules for naming branched chain alkanes:

IUPAC recommenced the following rules for naming a branched chain alkane.

1. Select the longest continuous chain of carbon atoms.
2. This chain is called parent chain or root chain.
3. If there is more than one such chain, the chain that contains maximum number of branches is selected as the parent chain.
4. Also identify all the branches or substituents.
5. Number the carbon atoms of the parent chain in such a way that the branched carbon atoms get the lowest possible numbers.
6. The names of alkyl groups attached as branches are then prefixed to the name of the parent alkane and position of the substituents is indicated by the appropriate numbers.
7. If different alkyl groups are present, they are listed in alphabetical order.
8. In alphabetical order, the prefixes iso- and neo- are considered to be the part of the fundamental name of alkyl group.
9. The prefixes sec- and tert- are not considered to be the part of the fundamental name.
10. If two or more identical substituent groups are present then their numbers are indicated by prefixes like di (for 2), tri (for 3), tetra (for 4), penta (for 5) etc. and the numbers are separated by commas.
11. The number and word are separated by a hyphen. (The IUPAC name is written as a single word).

For example:

• If the two substituents are found in equivalent positions, the lower number is given to the one coming first in the alphabetical listing. For example:
• The above compound is 3-ethyl-6-methyloctane and not 6-ethyl-3-methyloctane.
• While naming the branched alkyl groups, the carbon atom of the branch that attaches to the root alkane is numbered 1.

## IUPAC nomenclature of compounds containing functional groups

For naming organic compounds containing functional group, the following rules are used:

1. Select the longest continuous chain containing the functional group.
2. Number the carbon atoms in such a way that the carbon to which the functional group is attached should get the lowest possible number.
3. In the case of functional groups containing carbon atom like –CHO, -CN, – COOH, -CONH2, -COX. -COOR etc. the numbering should start from the carbon atom of the functional group.
4. (i.e. carbon atom of these groups should be numbered as 1).
5. (But for ketones, the functional group –CO- should get the lowest possible number).
6. The name of some of the functional group is indicated by the following suffix or prefix.
7. In the case of suffixes, the ending –e of the corresponding alkane is replaced.
8. E.g. IUPAC name of the alcohol CH3-OH is methanol (methane + ol).
9. But for nitriles, the –e of the corresponding alkane is retained.
10. E.g. IUPAC name of CH3-CH2-CN is propanenitrile.
11. In the case of alkenes and alkynes, the suffix –ane of the alkane is replaced by –ene and –yne respectively. (i.e. word root + ene or yne).
12. For naming alkenes or alkynes, the numbering is done in such a way that the double or triple bond should get the lowest possible number.
13. Some examples are:

CH3-CH2-CH=CH2 → 1-Butene

## Nomenclature of organic compounds containing more than one

functional groups (Poly functional compounds)

• Here one of the functional groups is chosen as the principal functional group and the compound is named on that basis.
• The remaining functional groups (called subordinate functional groups) are named as substituents using the appropriate prefixes.
• The choice of principal functional group is made on the basis of order of preference.
• The order of decreasing priority for some functional groups is: -COOH, –SO3H, -COOR (R=alkyl group), -COCl, -CONH2, -CN,-CHO, >CO, -OH, -NH2, >C=C<, -C≡CThe groups like alkyl (–R), phenyl (C6H5-), halogens (F, Cl, Br, I), nitro (–NO2), alkoxy (–OR) etc. are always prefix substituents.
• For example if a compound contains both alcoholic and aldehydic groups, it is named as hydroxyalkanal, since here aldehydic group is the principal functional group and –OH group is the subordinate functional group.
• The prefix names of some functional groups are as follows:

• If a compound contains more than one same functional group, their number is indicated by adding the numeral prefixes di, tri, etc. before the suffix.
• In such cases the full name of the parent alkane is written before the suffix.
• However, the ending – ne of the parent alkane is dropped in the case of compounds having more than one double or triple bonds.

## Nomenclature of Substituted Benzene Compounds

• For IUPAC nomenclature of substituted benzene compounds, the substituent is placed as prefix to the word benzene.
• But common names of some compounds are accepted by IUPAC.

Some examples are;

# Nomenclature of di or polysubstituted benzene

• If benzene ring is disubstituted, the position of substituents is indicated by numbering the carbon atoms of the ring such that the substituents get the lowest possible numbers.

Example – Dibromobenzene

• In the common system of nomenclature the terms ortho (o), meta (m) and para (p) are used as prefixes to indicate the relative positions 1,2- 1,3- and 1,4- respectively.
• So 1,2-dibromobenzene is named as ortho (or just o-) dibromobenzene, 1,3-dibromobenzene as meta (or just m-) dibromobenzene and 1,4-dibromobenzene as para (or just p-)-dibromobenzene.
• For tri – or higher substituted benzene derivatives, these prefixes cannot be used and the compounds are named by identifying substituent positions on the ring by following the lowest locant rule.
• In some cases, common name of benzene derivatives is taken as the base compound.
• Substituent of the base compound is assigned number1 and then the direction of numbering is chosen such that the next substituent gets the lowest number.
• The substituents are named in alphabetical order.

Eg:

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## Sex Determination In Human Beings Explained

### Sex Determination in Human Beings

• A person can have a male sex or a female sex.
• The process by which the sex of a person is determined is called sex determination.
• Genetics is involved in the determination of the sex of a person.
• The chromosomes which determine the sex of a person are called sex chromosomes.
• There are two types of sex chromosomes, one is called X chromosome and the other is called Y chromosome.
• Somatic cells in human beings contain 23 pairs of chromosomes.
• Out of them the 23rd pair is composed of different types of chromosomes which are named as X and Y chromosomes.

Heredity Evolution,Speciation Notes on Science For Class 10th

• The 23rd pair contains one X and one Y chromosome in a male.
• On the other hand, the 23rd pair in a female contains X chromosomes.
• This means that all the eggs would have X chromosome as the 23rd chromosome,
• While a sperm may have either X or Y chromosome as the 23rd chromosome.
• When a sperm with a chromosome fertilizes the egg.
• The resulting zygote would develop into a female child.
• When a sperm with Y chromosome fertilizes the egg, the resulting Zygote would develop into a male child

Heredity and Evolution NCERT Solutions For Class 10th SCIENCE

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## Interior of the Earth

• The internal structure of the earth is layered.
• The Earth is generally divided into four major layers: the crust, mantle, inner core, and outer core.
• Earth’s crust is the outermost layer composed of various types of rocks.
• Below the crust lies the Lithosphere
• These lithospheric plates appear to “float” and move around on the more ductile asthenosphere
• The boundary between the crust and mantle is generally called the Mohorovičić discontinuity
• The continental crust is thicker in comparison to oceanic crust.
• The lithosphere is the upper 80 Kilometers layer composed of both the crust and part of the upper mantle
• Earth’s mantle is a rocky shell about 2,890 Kms thick that constitutes about 84 percent of Earth’s volume.
• The outer core is in the liquid state.
• The inner core is in solid-state.

## Earth’s Crust-

• There are two types of earth’s crust
 Oceanic Crust Continental Crust The oceanic crust is thinner It is composed of basalt It has a high density The continental crust is thicker It is composed of Granite It has low density The low density helps it to flow over the oceanic crust

### Earth’s Mantle

• Earth’s mantle has olivine rock.
• The temperatures increase with depths.
• The temperature is lowest near the crust and increases with depth.
• The highest temperatures are found near the mantle material as it is in contact with the heat-producing core.
• This steady increase of temperature with depth is known as the geothermal gradient.
• This temperature difference responsible for different rock behaviors, and the different rock behaviors are used to divide the mantle into two different zones.
• Rocks in the upper mantle are cool and brittle, while rocks in the lower mantle are hot and soft (but not molten).
• Rocks in the upper mantle are brittle enough to break under stress and produce earthquakes.
• However, rocks in the lower mantle are soft and flow when subjected to forces instead of breaking.
• The lower limit of brittle behavior is the boundary between the upper and lower mantle.

Earth’s Core

• It is composed of alloys of iron and nickel
• the core gives heat to the inside of earth
• the radioactive material which is present inside it release heat as they break down into more stable substances.
• The core is divided into two different zones.
• The outer core is a liquid because the high temperatures melt the iron-nickel alloy.
• The inner core is a solid even though its temperature is higher than the outer core because of very high pressure from the weight of rocks lying above it .

Mineral and Energy Resources : NCERT Geography Lesson For class 10th

Resources

https://geology.com/nsta/earth-internal-structure.shtml

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## Heredity Evolution,Speciation Notes on Science For Class 10th

### Sex determination in human beings

• Human beings have 23 pairs of chromosomes in the nucleus of the cell.
• Out of this two chromosomes are sex chromosomes X and Y.
• The female has two X chromosomes (XX) and male has one X and one Y
chromosome (XY).
• The sperms and eggs have one set of sex chromosomes.
• Some sperms have X chromosome and some have Y chromosome.
• All eggs have X chromosome.
• If a sperm having X chromosome fuses with an egg having X chromosome the child will be a girl.
• If a sperm having Y chromosome fuses with an egg having X chromosome the child will be a boy.

### Variation and Evolution influence Survival Positively or Negatively

#### a) Some variations may help organisms to survive :-

• There are some beetles living in green bushes.
• They increase their numbers by reproduction.
• Crows can easily see the red beetles and they are eaten by the crows.
• During reproduction due to some variation some green beetles are produced instead of red beetles.
• The green beetles are not visible to crows and are not eaten by them.
• Then gradually the population of the red beetles decreases and the
population of the green beetles increases.
• This variation has helped the organisms to survive.

#### b) Some variations do not help organisms to survive :-

•  During sexual reproduction a colour variation occurs in red beetles and some blue beetles are produced instead of red beetles.
• Both the red and blue beetles are visible to crows and are eaten by them.
• Then the population of both red and blue beetles decreases.
• This variation has not helped the organisms to survive

### Aquired Traits and Inherited Traits

Distinguish between acquired and inherited traits giving one example of each

 Acquired traits Inherited traits A trait (or characteristic) of a organism which is not inherited‘ but develops in response to the environment is called an acquired trait. A trait (or characteristic) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait. The acquired traits of an organism can not be passed on to its future generations. he inherited traits of an organism are passed on to its future generations e.g. low weight‘ of beetle, cut tail of a mouse. e.g. red colour of beetles, fur coat of guinea pigs.

#### Aquired traits cannot be passed from one generation to the next :-

•  If the population of beetles increases and plants are affected by diseases, then the food available for the beetles decreases and their body weight also decreases.
• If after a few years the availability of food increases then the body weight of the beetles also increases.
• This acquired trait cannot be passed from one generation to the next because there is no change in their genetic composition.

### Speciation  and factors Influencing Speciation

• Formation of new species from existing species is called speciation
• The formation of new species from existing species is mainly due to one or more of the following factors.
• They are :- Accumulation of variations, Physical barriers, Genetic drift, Natural selection and migration.
1.  Accumulation of variations :- The differences between the individuals of the same species is called variations. The accumulation of variations over several generations produce new species.
2. Physical barriers :- Populations may get separated by physical barriers like mountains, rivers, lakes etc. These isolated groups produce variations which can produce new species.
3. Genetic drift :- Natural calamities or introduction of new members of the same species in an area can produce changes in the gene pool of the population and new variations are produced which can produce new species.
4. Natural selection :- Only those individuals of a species which have useful variations and can adapt to the changes in the environment survive and the others die. These organisms can produce variations and new species.
5. Migration :- Some individuals of a species may migrate to a new geographical area and adjust to the changes in the environment there and develop new variations and produce new species.

### Evolution

• The gradual changes taking place in living organisms giving rise to new organisms due to changes in their genetic composition is called evolution.

### Evidences of evolution

• There are a number of common features in different organisms which provide evidence to show evolutionary relationship.
• The main evidences of evolution are from the study of :- Homologous organs, Analogous organs and Fossils.

a) Homologous organs :- are organs which are similar in structure but different in functions.
Eg :- The fore limbs of amphibians, reptiles, birds, and mammals have similar structures but different functions.

Frog (amphibian) uses its fore limb to raise the front of the body. Lizard (reptile) uses its fore limb for walking and running. Birds fore limbs are modified as wings for flying.
Mammals use the fore limbs for grasping, walking, running, swimming,flying etc.

b) Analogous organs :- are organs which are different in structures but similar in functions.
Eg :- The wings of butterfly, bird and bat have different structures but similar functions. This shows evolutionary relationship.

### Evolution by stages :-

• Complex organisms and its organs developed from simpler organisms gradually over generations.
• Evolution of eyes :- The eyes of planaria are just eye spots to detect light. It developed gradually into a complex organ in higher animals.
• Evolution of feathers :- Feathers were first developed in dinosaurs and used for protection from cold. Later birds used them for flying.
• Evolution by artificial selection :- Humans cultivated wild cabbage for over 2000 years and produced different vegetables from it by artificial selection.
Eg :- Cabbage – by selecting short distance between the leaves.
Cauliflower – by selecting sterile flowers.
Kale – by selecting large leaves
Kholrabi – by selecting the swollen stem
Broccoli – by arresting flower growth

### Evolution should not be equated with progress :-

• Evolution has not resulted in progress.
• Evolution has resulted in the formation of several complex species from simpler species due to variations, genetic drift and natural selection.
• This does not mean that one species gets eliminated when new species are formed or that the new species are better than the older species.
• Species get eliminated only if they are not able to adapt to the changes in the environment.
• Several species which could adapt to the changes in the environment still continue to survive for example bacteria.
• Human beings have not evolved from chimpanzees.
• They had a common ancestor from which they evolved separately.
• Human beings are not the pinnacle of evolution but they are only one species among the several evolving species.

### Human evolution :- (Homo sapiens)

• There is a great diversity among human beings in their form and features around the world.
• Human beings evolved in Africa.
• Some of them stayed there and others migrated to different parts of the world.
• Then due to genetic variations and the environmental changes in different geographical regions they developed changes in their forms and features.

Heredity And Evolution : Class 10 Notes on NCERT

Heredity and Evolution NCERT Solutions For Class 10th SCIENCE

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## Heredity And Evolution : Class 10 Notes on NCERT

### ACCUMULATION OF VARIATION DURING REPRODUCTION

• Heredity :- The process of transfer of characters or traits from the parents to their offsprings is called heredity.
• Variations :- The differences between the characters or traits among the individuals of the same species are called variations.
• For example human height is a trait which shows different variations like tall, short, medium etc.

• Another example is earlobe, it shows two variations free earlobe and attached earlobe.
• The variation is necessary for evolution The great advantage of variation is that it increases the chance of survival in a changing environment

### Accumulation of variations during reproduction

• The reproduction produces variations in offsprings .
• The  minor variations are seen  due to inaccuracies in DNA copying.
• These variations are less in asexual reproduction and more in sexual reproduction.
• Some variations are useful variations and they help the organism to adjust to the changes in the environment.
• Some variations do not help the organism to adjust to the changes in the environment and they may die and become extinct

### Transfer of characters

• Characters are transferred through DNA molecules present in the gene on the chromosomes which are present in the nucleus of the cell.
• The inheritance of characters is due to the fact that both the father and mother contributes equal amount of genetic material to the child.
• So for each trait there are two factors one from the father and one from the mother

CHROMOSOME: A thread like structure in the nucleus of cell formed of DNA and protein
which carries the genes.
GENE: A unit of DNA or a segment of DNA which controls specific characteristic of an
organism.
ALLELES: They are various forms of a gene which occur at the same particular position or
locus over the chromosomes.
DOMINANT GENE: The gene which decide the expression of a character even in the presence of an alternative gene.
RECESSIVE GENE: The gene which decides the expression of an organism in the presence of another identical gene.

• The dominant gene is represented by a capital letter and the corresponding recessive gene is represented by the same letter in small.
• For example the dominant gene for tallness is represented by T and the recessive gene for dwarfness is represented by t.
• Genotype:-  The genotype is the description of genes present in an organism.
• Phenotype:- The characteristic or trait which is visible in an organism Is called phenotype. Ex- Tall or dwarf.

### Mono-Hybrid Crossing

• Gregor Johann Mendel conducted experiments with garden pea plants and determined the rules for the inheritance of traits
• Mendel selected pea plants having one pair of character – a tall pea plant and a
short pea plant.
• He selected pure tall (TT) and pure short (tt) pea plants and cross pollinated them.
• He obtained all tall plants (Tt) in the first generation (F1 )
• When the first generation plants were self pollinated, he obtained tall and dwarf
plants in the ratio 3:1 in the second generation. (F2)
• The ratio of pure tall (TT), hybrid tall (Tt) and pure dwarf (tt) was in the ratio 1:2:1
• The trait that is expressed in the F1 generation is called the dominant trait and the trait that is suppressed in the F1 is called the recessive trait.

### Dihybrid cross

• When plants having two pairs of characters (Eg:- shape and colour of seeds) were crossed (Dihybrid cross)
• Mendel selected pea plants having two pairs of characters – shape and colour
of seed.
• He selected plants having round yellow seeds (RRYY) and wrinkled green seeds (rryy) and cross pollinated them.
• He obtained all plants with round yellow seeds (RrYy) in the F1 generation.
• When these plants were self pollinated in the F2 generation out of 16 plants, 9 had round yellow (RrYy), 3 had round green (Rryy), 3 had wrinkled yellow (rrYy) and 1 had wrinkled green (rryy) seed  In the ratio 9:3:3:1.Heredity and Evolution NCERT Solutions For Class 10th SCIENCE
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## Sexual Reproduction in Human Beings : Study Notes for Class 10th Science

### Reproduction in human beings

• Puberty-it is the period during which adolescents reach sexual maturity and become capable of reproduction
• During early teenage whole new set of changes occurs, appearance of body and proportions change and new features develop.
• As the rate of general body growth slows down reproductive tissues begin to mature.
• If animals are to participate in the process of mating, their state of sexual maturity must be identifiable by other individuals.
 Pubertal changes in males Pubertal changes in females a) deepening of voice(low pitch) b) broadening of shoulders c) appearance of beard & moustaches d) Growth of axillary & pubic hairs a) high pitch voice b) widening of hips c) Growth of axillary & pubic hairs d) Initiation of menstruation e) Growth of mammary glands.

#### 1. Testis:

• Testis is a galndular organ made up of fine tubules.
• The formation of germ cells take place in testes, located outside the abdominal cavity in scrotum because sperm formation requires a lower body temperature.
• testis also produces certain hormones, like tetosterone which are responsible for secondary sexual characters in humans.
• These are deep male voice, hair growth in pubic area and under armpits, and facial hair.

2. Seminal Vesicle: Once sperm is produced it is stored in seminal vesicle.

#### 3. Vas Deferens:

• Vas deference is the tube through which semen containing sperm is transferred out.
• The sperms produced are transferred by vas deferens which unites with a tube coming from urinary bladder.
• Urethra forms a common passage for both sperm and urine.
• To make the transportation of sperms easier prostate and seminal vesicles add their seceretions along the path of vas deferens, that makes the sperms to be transported in fluid which provides nutrition.
• Cowper‘s gland – Produces white viscous & alkaline secretion
• Semen = sperm& secretion of accessory glands

### Female Reproductive system

#### 1. Ovary:

• Ovaries are situated on left and right side of the uterus.
• The female germ-cells are produced in ovary, which is also responsible for production of oestrogen.
• On reaching puberty some of the immature eggs present in the ovary of a girl start maturing.

#### 2. Fallopian Tubes:

• Fallopian tubes extends on both sides of the uterus in transverse direction.
• Fallopian tubes have finger like structures which catch the eggs to transfer them to the uterus.

#### 3. Uterus:

• Uterus is a bag like structure, with an opening in the vagina.
• Uterus opens into the vagina through cervix.

### Fertilization In Human Beings

• Sperms enter through the vaginal passage during sexual intercourse and encounters egg in fallopian tube.
• Once eggs reach uterus, a layer of soft tissues develops to support the embryo.
• This layer is called corpus luteum.
• If fertilization takes place, then the embryo develops into a foetus and ultimately to a fully developed child over a period of about 9 months
• The zygote gets implanted into the lining of the uterus and starts dividing.
• The uterus prepares itself every month to receive and nurture the the embryo, the lining thickens and is richly supplied with blood to nourish the growing embryo.
• The embryo gets nutrition from the mother’s blood with the help of a tissue called placenta, a disc embedded in uterine wall.
• The child is born as a result of rhythmic contractions of the muscles of uterus.
• Implantation : Attachment of embryo to the lining of uterus.
• Placenta : A connection between the mother & the foetus
• The foetus meets all its developmental needs such as nutrition, respiration and excretion through the placenta.
• Gestation period :The period between fertilisation & birth

### Menstrual Cycle in Females:

• If no fertilization takes place then after about two weeks the dead eggs and corpus luteum gets expelled out of the uterus through vagina.
• This process takes place over a period of about three to four days.
• This clears the way for new batch of eggs to come in the uterus.
• The whole cycle from egg production to the expulsion of eggs takes about four weeks.
• This cycle is known as Menstrual Cycle.
• Apart from humans, some primates like Chimpanzee and Gorilla also show same
phenomenon.
• Ovary secretes one of the important hormones estrogen, which is responsible for secondary sexual characters in female, like thin voice and breast enlargement.

Menarche – commencement of menstrual cycle at puberty which marks the beginning of reproductive life of the human female.

Menopause – cessation of menstrual cycle which marks the end of the  reproductive life of a human female.

### Reproductive Health and Birth Control Methods

• Creation of a mechanical barrier is a method of contraceptive so that the sperm does not reach the egg is called condoms.
• Oral pills change the hormonal balance of the body
• Loops and copper-T is placed in the uterus to prevent pregnancy
• Surgical method can be used to block vas deferens in male and fallopian tube in female.

Read Here on Sexual Reproduction In Plants(Second Part of the Lesson)

### Previously Asked Questions on Reproduction in Human beings

1. How does the male gamete reach the egg present in the ovary?
The pollen tube releases the male gametes in the embryo sac .
2. What are gonads?
Gonads are the primary sex organs which produce gametes & secrete sex
hormones.
3.  Define syngamy.
The process of fusion of male gamete with the female gamete is known as syngamy.
4.  At what age human males attain puberty?
At the age of 12-14 years
5.  At what age human females attain puberty?
At the age of 10-12 years.
6.  What are the functions of gonads?
i) production of gametes
ii) secretion of sex hormones.
7. Why are testes located outside the abdominal cavity ?
Sperm formation requires a temperature lower than that of the normal body temperature.
8.  Where are ovaries located in human females?
Ovaries are present in the abdominal cavity near the kidneys.
9. What is placenta?
A connection between the mother & the foetus.The foetus meets it all its developmental needs such as nutrition, respiration and excretion through the placenta.
10. What is menstruation?
If fertilization does not occur the uterine wall slowly breaks & comes out through vagina as blood and mucous.
11. What is ovulation?
It is the process of release of a mature ovum from the ovary.
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## Sexual Reproduction in Plants : Science Notes for Class 10 Biology

### SEXUAL REPRODUCTION

• In a population variations are useful for survival of a population.
• Sexual mode of reproduction allows individuals to have more variations to be generated.
• Generation of variations in DNA copying mechanism of asexual mode is fairly slow
• Each new variation is made in a DNA copy that already has variations accumulated from previous generations.
• Combining variations from two or more individuals would thus create new combinations of variants.
• Each combination would be novel, since it would involve two different individuals.
• For each new cell to not have twice the amount of DNA that previous generation have, special lineages of cells in specialised organs have only half the number of chromosomes and DNA as compared to other cells.
• Two individuals combining during sexual reproduction, result in re-establishment of the number of chromosomes and DNA content in new generation.
• Motile germ cell is called male gamete and germ-cell containing food is called female-gamete

### Sexual reproduction in flowers

• Flower can be termed as the sexual organ of a plant.
• All the parts of a flower are arranged around an axis.
1. Sepals: Green leaf like structure.
2. Petals: Colourful structures, which add attraction to a flower. This attraction is not only having ornamental value, but a more important role in facilitating reproduction. Insects and birds, attracted by the colour, help transfer pollen grains or male gametes from male flower to female flower. This helps in pollination.
3. Male Reproductive Organ of Plant: Androecium
• The flower of a plant contains tube like structures called stamen.
• At the top of stamen is a chambered structure called Androecium.
• Androecium is responsible for the production of male gamete also called pollen grains.
4. Female Reproductive Organ of Plant:
• GynoeciumUsually at the centre of a flower you can notice Gynoecium.
• Gynoecium is pitcher shaped structure with a long tube protruding out of it.
• The gynoecium produces female gamete also called eggs.

Difference between Unisexual and Bisexual Plants

 Unisexual Bisexual A flower containing either stamen or carpel is unisexual e.g.watermelon Flower containing both stamen and carpel are bisexual e.g hibiscus Stamen is the male-reproductive part producing pollen which is yellowish in color.

• Stamens and carpels are the reproductive parts of a flower.
• Carpel is present in the centre of the flower and is the female reproductive part.
• Carpel is made up of three parts , the swollen part is ovary , the middle elongated part is style and the terminal part is sticky and called stigma.
• The ovary contains ovule which has an egg cell, the male gamete fuses with the female gamete present in ovule.

### Pollination In flower

• Pollination is the transfer of pollen from a male part of a plant to a female part of a plant, later enabling fertilisation and the production of seeds.
• The pollen needs to be transferred from stamen to the stigma.
• If the transfer of pollen occurs in the same flower it is self-pollination, if the transfers occurs in a different flower it is called cross-pollination
•  Cross pollination can be facilitated by insects, birds, animals, air or water.
• A tube growing out of the pollen grain and travels through the style to reach the ovary helps the landed pollen grain to reach female-germ cell.

### Zygote Formation in Plant Reproduction

• Once pollen grains enter the androecium, one of them enters the egg to fertilize it to form a zygote.
• Seeds are the zygote or embryo of the plant.
• To survive and to germinate,  seeds need source of food.
• In all seeds there is abundance of food.
• That is why for our daily need we depend on so many seeds like rice, wheat, groundnut for food.
• During germination the food in the cotyledon is used to grow a new plant.
• Once green leaves come out, they take care of further food production
• After fertilization the zygote develops several times to form an embryo within the ovule.
• The ovule develops a tough coat and is gradually converted into a seed
• The seeds contain the embryo which develops into a seedling under proper conditions, this is known as germination

Appear the Quiz on Reproduction Topic

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## How do Organism Reproduce:Class 10th Science Notes on Biology

### Reproduction

• Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.
• Reproduction at its basic level involves creation of the copy of DNA
• DNA present in the chromosome of the cell is the information source for making proteins.
• If the information is changed, different proteins will be made, and would lead to altered body designs.
• The two DNA’s need to be separated, for the copy of DNA to have an organised cellular structure, DNA copying is accompanied by creation of additional cell apparatus.
• Since no bio-chemical reaction is absolutely reliable, therefore the copying of DNA will have some variations each time.
• DNA copies generated will be similar to each other and not identical.
• Some of the variations may even be drastic enough for the new DNA generated not would not be able to work with the cellular apparatus and would eventually lead to death of the new cell.
• The consistency of DNA copying during reproduction is important for maintenance of body design features that allow the organism to use a particular niche .
• Reproduction is linked to stability of population of species.

### IMPORTANCE OF VARIATION in Reproduction

• Population of organisms fill well-defined places or niches in the ecosystem, using their ability to reproduce.
• Variation in DNA copying can ensure the survival of some individuals among a population, in case of changes in a particular niche in which the population is suited to survive in.
• Variation is useful for survival of species over time.

### ASEXUAL REPRODUCTION

• Asexual reproduction:A sexual reproduction involves production of Offsprings by single parents.
• There is no involvement of specialized gamete cell .
• Offspring are genetically identical to their parents

### FISSION

• In unicellular organisms, fission is the mode of reproduction used to create new individuals.
• In simple unicellular organisms fission can take place in any plane, such as in amoeba.
• In organisms showing somewhat more organisation of body, it occurs in a definite orientation in relation to the structure, for example leishmania having a whip-like structure present in one end.
• Some single-celled organisms simply divide into many daughter cells simultaneously using multiple fission, for example plasmodium.
• Yeast can put out small buds that separate and grow further

### FRAGMENTATION

• Multicellular organisms with simpler body design use fragmentation as a method of reproduction, for example in spirogyra, which breaks up into smaller pieces upon maturation.
• These fragments grow into new individuals.
• Not all multicellular organisms can use cell by cell division for reproduction as they are not simply a random collection of cells, and have organised body designs and structures,
• In multicellular organisms reproduction via a single cell-type which is capable of growing, proliferating and making other cell types under right circumstances.

#### REGENERATION

• Many fully differentiated organisms have the ability to give rise to new individuals from their body parts.
• For example , if hydra or planaria is cut or broken into any number of pieces each piece grows into a complete organism this is known as regeneration
• It is not the same as reproduction, since organisms would not depend on being cut up to be able to reproduce.

Budding

• Organisms such as hydra use regenerative cells for reproduction in process of budding.
• In hydra a bud develops as an outgrowth due to repeated cell division at one specific site
• These buds develop into tiny individuals and detach themselves from parent body when fully mature.

#### Vegetative propagation

• There are many plants in which parts like roots, stems and leaves can develop into new plants in appropriate conditions, this property is used in vegetative propagation method such as layering or grafting
• Plants raised by vegetative propagation can bear fruits and flowers earlier than those reproduced by seeds.
• Plants raised by vegetative propagation are genetically similar enough to the parent plant to have all its characteristics.

#### Spore formation

• In rhizopus tiny blob-on-a-stick structures called sporangia containing spores that can develop into new rhizopus are involved in reproduction.
• The spores have thick walls that protect them until they come into contact of another moist surface and being to grow.

Read the NCERT Solution On Reproduction here

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## Airways

• The world’s first air-mail service was started in India at Allahabad; on 18th Feb 1911 on  the occasion of Kumbh mela
• Regular airmail services were started by Tata Sons Ltd, between Karachi and Madrasand.
• On 24th Jan 1920 Royal air force started regular airmail services
• Urmila K.Parikh became the first Indian woman to get a pilot’s license.
• in  1945 the Deccan Airways was founded – jointly owned by the Nizam of Hyderabad and Tata.Its first flight began in July 1946.
• All the airway companies were nationalized in 1953 and were put under two corporations namely – Indian Airlines and Air India.
• Air India provides international air services.
• Pawanhans Helicopters Ltd. provides helicopter services to Oil and Natural Gas Corporation in its offshore operations, to inaccessible areas and difficult terrains like the north-eastern states and the interior parts of Jammu and Kashmir, Himachal Pradesh and Uttarakhand

## Kalinga Airlines and Biju Pattanaik

• Kalinga Airlines was a private airline based in Calcutta, India.
• It was founded in 1947 by aviator and politician Biju Patnaik, who was also the airline’s chief pilot.
• The airline was nationalized and merged into Indian Airlines in 1953.
• It restarted operations as a non-scheduled charter operator in 1957 and flew passengers and cargo until 1972.

### Communication

• Communication is the act of transferring information from one place, person or group to another.
• The Indian postal network is one of the largest network in the world.
• It handles parcels ,personal written communications.
• Cards and envelopes are considered first–class mail and are airlifted between stations covering both land and air.
• The second–class mail includes book packets, registered newspapers and periodicals. They are carried by surface mail, covering land and water transport.

 James Augustus Hickey is considered as the “father of Indian press” He was the founder of the first Indian newspaper from Calcutta, the `Bengal Gazette` or the `Calcutta General Advertise` in January 1780.

#### Mass Communication

• Mass communication provides entertainment and creates awareness among people about various national programmes and policies.
• It includes radio, television, newspapers, magazines, books and films.
•  All India Radio (Akashwani) broadcasts a variety of programmes in national, regional and local languages for various categories of people.
• Doordarshan, the national television channel of India, is one of the largest terrestrial networks in the world.

• India is the largest producer of feature films in the world It produces short films; video feature films and video short films.
• The Central Board of Film Certification is the authority to certify both Indian and foreign films