Tuesday, 2 May 2017
Wednesday, 1 March 2017
DAV Public
School
Sec.6,
Dwarka, New Delhi-75
HEREDITY AND
EVOLUTION
Biology Class-10
Heredity is
the transmission of characters or traits from parents to their offspring.
Genetics is
the science of heredity, i.e., the study of inheritance of characteristics in
offspring from their parents.
Variations –
The difference in the character among the individuals of a species is called
variation.
1.
Variations necessary for organic evolutions.
2.
It increases the chances of its survival in
changing environment.
The free earlobes and attached earlobes are the two
variation found in human population.
Accumulation of variations-
The significance of variations shows up only if its continues to be inherited
by the offspring for several generations.
Some important terms:-
1.
Genotype-the genetic make of an organisms
2.
Phenotype- the physical appearance of an
organisms
3.
Genes- unit of heredity which transfer traits
from parents to their offspring
4.
Diploid- two sets of chromosomes
5.
Haploid- one set of chromosomes
6.
Dominant genes- the gene which decides the
appearance of organisms even in presence of alternative genes is known as
dominant. Dominant gene represented by a capital letter.
7.
Recessive genes- the gene which decides the
appearance of organisms only in presence of another identical gene is called
recessive genes. Recessive genes represented by a small letter.
8.
F1 generation- when two parents cross
to produces to progeny then their progeny is called first filial generation.
9.
F2 generation- when first filial
progeny cross among themselves to produce second generation progeny, then this
progeny is called second filial generation.
10.
Hybrid- a new form of plants resulting from a
cross of different varieties of a plant is known as hybrid
11.
Monohybrid cross- crosses between one pair
contrasting characteristics.
12.
Dihybrid cross- crosses between two pair of
contrasting characteristics.
Rules of
inheritance of traits given by GREGOR JOHANN MENDEL
Gregor Johann
Mendel was an Austrian monk who grew garden peas (PISUM SATIVUM) in the church
garden. He identified the number of characteristics showing contrasting traits
follows-
1.
Pea plants are easy to cultivate and have large
flowers which help in cross pollination under controlled conditions.
2.
These plants are self pollinated in nature.
3.
These plants show discrete variations in
characters or traits.
4.
There are no intermediate forms produced.
1.
Mendel first crossed pure-bred tall pea plants
with pure-bred dwarf pea plants and found that only tall plants were produces
in the first generation or F1 generation. No dwarf pea plant (or
short pea plants) was obtained in the first generation of progeny. From this Mendel
concluded that the first generation showed the traits of only one of the parent
plants: tallness. The trait of other parent plant, dwarfness, did not show up
in the progeny of first generation.
2.
Mendel then crossed the tall pea plants of the
first generation and found that tall plants and dwarf plants were obtained in
the second generation in the ratio of 3:1. In other words in the F2
generation, three-fourth plants were tall and one- fourth were dwarf. Mendel
noted that the dwarf trait of the parent pea plant which had seemingly
disappeared in the first generation progeny reappeared in the second
generation. Mendel said that the trait of dwarfness of one of the parent pea
plant had not been lost; it was merely conceals or suppressed in the first
generation to remerge in the second generation. Mendel also noted that all the
pea plants produces from the hybrid tall parents of F2 generation,
were either tall or dwarf. There were no plants with intermediate height (or
medium height) in between the tall and dwarf plants. In this way, Mendel’s
experiment showed that the traits (like tallness and dwarfness) are inherited
independently.
Tall
plants: Dwarf plants=3:1
Dihybrid
inheritance involve the inheritance of two pairs of contrasting characteristics
( or contrasting traits)at the same time. The two pairs of contrasting
characteristics chosen by Mendel were shape and color of seeds: round-yellow
seeds, and wrinkled- green seeds.
Mendel
first crossed pure-bred pea plants having round- yellow seeds with pure- bred
pea plants having wrinkled green seeds and found that only round-yellow seeds
were produces in the first generation. No wrinkled – green seeds were obtains
in the F1 generation from this it was concluded that round shape and
yellow color of the seed were dominant traits over the wrinkled shape and green
color of the seeds.
When
the F1 generation pea plants having round yellow seeds were
cross-bred by self pollination, then four types of seeds having different
combinations of shape and color were obtained in second generation. These were
round-yellow, round- green, wrinkled- yellow and wrinkled- green seed. Mendel
collected a total of 556 F2 seeds and counted them shape wise and color
wise. He got the following result:
Round-
Yellow seeds-315
Round-green
seeds- 108
Wrinkled-
yellow seeds-101
Wrinkled-green
seeds-32
The
phenotypic ratio of different types of seed can be written as:
Round Round Wrinkled Wrinkled
Yellow: Green: Yellow : Green = 315 :108 :101 :32
Seeds Seeds Seeds Seeds
=
9 :3 :3 :1
Thus,
the ratio of each phenotype (or appearance) of the seeds in the F2
generation is 9:3:3:1. This known as the dihybrid ratio.
According
to Mendel’s second law of inheritance: in the inheritance of more than one pair
of traits in a cross simultaneously, the factors responsible for each pair of
traits are distributed independently to the gametes.
How
do traits get expressed?
Cellular
DNA has the blueprint(information) to make cellular proteins. A fragment of DNA
that gives information for synthesis of one protein is called a gene for that
protein.
All
biochemical reactions in the cell are controlled by protein/ enzyme. An enzyme
is necessary for protein production.
The
tallness or characteristics of the pea plant is controlled by hormone that
triggers the growth. The height/ tallness will depend upon the amount of the
particular hormone in the plant. The amount of the growth hormone will depend
on the efficiency of the enzymes making it.
If
the enzymes is working efficiently than the amount of growth hormone will be
more, resulting in tall plant. And if the enzyme is less efficient then the
amount will be less, resulting in short height plant. The gene controls the
efficiency of the enzyme. Thus, genes control the characteristics or traits.
SEX DETERMINATION
The process by which the sex of a
child is determined is called sex determination.
Genetic factors - genetics is
involved in the determination of sex of a person. This can be explained as
follows.
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.
A. male( man or
father) has one X chromosome and one Y chromosome. This means that half the male gametes or half the
sperms will have X chromosome and the other half will have Y chromosome.
A female (women or mother) has two
X chromosome (but no Y chromosome). This means that all the female gametes
called ova (or eggs) will have only X chromosome.
The sex of a child depends on what happens
at fertilization:
(a)
if a sperm carrying one chromosome fertilizes an
ovum (or egg) which carries X chromosome, then the child born will be a girl
(or female). This is because the child will have XX combination of sex
chromosome.
(b)
If a sperm carrying Y chromosome fertilizes an
ovum (or egg) which carries X chromosome, then the child born will be a boy (or
male). This is because the child will have XY combination of sex chromosomes.
Please
note that it is the sperm which
determines the sex of a child. This is because half of the sperms have X
chromosomes and the other half have Y chromosomes. Thus, there is 50% chance of
a boy and 50% chance of a girl being born to the parents. This is why the human
population is roughly half males and half females
Environmental factors –Environmental factors play an important role in sex determination.
1.In turtles Chrysema picta High
incubation temperature -- Results in
development of female.
2. In lizard Agama agama high
incubation temperature – Results in development of female.
Organic
Evolution
It is the gradual changes in the
structure and function of organism which may
Result in change in existing body
design of the organism or result in formation of new species.
Microevolution- Structure and
functions at small scale. Result in change in existing body design.
Macroevolution- Structure and function changes at a large scale
involving long period of time result in
formation of new species.
Factors/sources of evolution
1. Variations during sexual reproduction
2. Mutations
3. Natural selection
4. Genetic drift
Natural selection-the process by which nature selects organism with best
possible variations to survive is called as natural selection .it occurs
gradually and continuously in any population at any time.
Genetic drift- chance elimination of certain genes from a population due
to an accident or natural calamity is called genetic drift .it occurs in a
small population only .
Inherited trait
Acquired trait
1. The trait which a person inherit 1.The trait
which a person acquire
from his parents. from
environment.
2.Inherited traits involve DNA of a 2. They are not
incorporated
Person. in
the DNA of a person
Eg. Eye colour etc eg.
The son of the wrestler
not be a wrestler
Specition- A process of formation of new species from already existing one is called Speciation.
1. Existence of sub – populations which
are separated by a geographical barrier.
Hence restriction to genus flow.
2. Action of different forces of natural selection and gemetic dirift on sub-population ,in their separate ways.
3.
Accumulation of variations in the
sub-population over a period of time making incompatable and unable to interbreed
and therefore they form two different species.
Geographical
isolation:
Two sub-population of the same species which are separated by
some physical barrier like river ,mountain range etc. are unable to interbreed
,tough in the absence of physical barrier, interbreeding is possible. The
sub-populations are said to be geographical.
Evidence of
evolution
1.
Homologus organs (similar organs)- the organs of different organism
having similar origin but they perform different functions are called homologus
organs .these organs have same arrangement of bones ,similar blood vessels and
nerves . Eg. hands of man ,floppres of whale ,, forelimbs of frog
2.
Analogous organs- The organs that
differ in their origin and structural details but perform `the same
function are called analogous organs.
e.g. the wings of birds
and wings of insects are analogous organs.
3. Evidences from fossils- Fossils
Fossils are impressions/preserved traces of organisms that once lived on
earth. These impressions can be on different materials such as rocks
,gums/resins.
Organisms that die ,get buried in moist soil ,clay or any other material.
When the material hardens in due course of time ,the soft body parts decay. But
impressions of hard body parts such as bones ,are left on material. It gets
converted to fossil. Formation of fossils is called Fossilisation.
How Old is a Fossil?
The age of fossil is determined by:
1.The depth at which fossil is
found. The fossils found close to the earth surface are of recent origin
and the ones in deeper layers old.
2.Dating of the fossils. It is
done by the detection of different isotopes of the same element found in the
fossil material.
Evolution by Stages
Evolution is not all of by sudden. It takes through stages. For example
,from primitive to intermediate then to developed and then advanced stage. Like
development and adaptation of wings in animals to fly ,eyes also developed.
1.Eyes. Eyes ,the sense organs were
developed to’identify’. Some animals have rudimentary eyes just to detect
light. Some have identification of objects ,in insects and image formation in
vertebrates like man.
You know that flatworm has rudimentary eyes insects have compound eyes
,octopus has eyes ,structure of eye is different in each case. They have
separate evolutionary origins.
2.Feathers on body. Feathers o body appeared for
different purposes but later were used for other function also.
Initially ,it might have started for providing insulation in cold weather
,such as in some dinosaurs. But later ,it was used for flight by birds.
Dinosaurs did not use it for flying. This means that bird are closely related
to reptiles. Since dinosaurs were reptiles.
3.Descendants of wild cabbage. Over two thousand years farmers have
cultivated wild cabbage as a source of food plant. They produced different
vegetables from it by selection as we see today, six varieties of vegetables
were produced by this artificial selection.
Some farmers selected for swollen stem and formed kohlrabi.
Some selected for sterile flowers and formed cauliflower.
Some selected for arrested flowers and formed broccoli.
Some farmers cultivated for short distance between the leaves cabbage.
Some preferred for colored red leaves for forming red cabbage.
While some others grew it for large leafy type called kale.
We can also trace the evolutionary relationship by studying the changes
in DNA during the reproduction. Comparing the DNA of different species gives us
a direct estimate of how much the DNA has changed from its original form during
formation of new species. This method is now extensively used to define
evolutionary relationships.
Evolution should not be equated with
progress
Evolution as said is still in progress. The organisms observed today are
the descendants of past and due accumulation of past changes. It does not mean
that past organisms/ancestors were not good or the present ones are better. It
all depends on environmental selection for survival. Still today we have very
simple organisms like bacteria surviving in all habitats and inhospitable
habitats. Neither the human beings are pinnacle of evolution. They are just one
species of evolutionary life.
Human Evolution
Study of human evolution has been done by use of same tools for study of
evolutionary relationships.
1.
Excavation-digging
the soil.
2.
Time
dating.
3.
Study
of fossils.
4.
Study
of DNA sequences.
There is a great diversity of human beings and features across the world.
People used to talk about ‘races’. These races were identified on the basis of
skin color as – white, black, brown and yellow. Actually all are one species.
Regardless the places where humans lived for past thousand years they all
originated from Africa. Homo sapiens, the earliest human species lived there.
From here our ancestors spread in all directions. Though they kept going there
for mixing with each other. Some stayed there only and spread across Africa.
The other people migrated from Africa to West Asia, Central Asia, Eurasia,
South Asia and East Asia. They also travelled to Indonesia and Philippines to
Australia and America. Like all other species, the humans also evolved accidently
and were tried to live their lives the best as they could.
Thursday, 9 February 2017
Thursday, 17 November 2016
HOW DO ORGANISMS REPRODUCE
Reproduction is a process by which all living organisms give rise to
new organisms similar to themselves (parents).
It is essential for the survival of the species since all living
organisms have a limited life span.
Since the genetic material from one generation is passed in to the
next, it not only maintains the continuity of species but also the continuity
of the parental generation.
It enables a species to increase the total number of individuals.
Types of reproduction:
There are two main forms of reproduction. These are:
1.
Asexual
reproduction
2.
Sexual
reproduction
Asexual reproduction means formation of organisms without the fusion of
gametes. The important features of asexual reproduction are:
i.
It involves only
a single organisms or parent.
ii.
It gives rise to
two or more individuals of the same kind. The individuals formed ate
genetically identical to the parent.
iii.
The cell
divisions are mitotic in nature.
iv.
It is a most
common mode of reproduction in unicellular organism, some plants and lower
multlicellular organisms like sponges and hydra. It is absent in higher
invertebrates and all vertebrates.
Types of Asexual reproduction:
i.
Fission (binary
fission, multiple fission)
ii. Budding
iii. Spore formation iv. Regeneration
v. Vegetative propagation vi. Tissue culture
1. Fission :
Fission means splitting. It occurs in unicellular
organisms. The parent organisms split into two or more equal parts. Each part
then develops as a separate individual. Depending on the number of individuals
formed after splitting of the parent organism, fission is or two types.
a) Binary
fission: The terms binary fissions “splitting of a
single cell into two”.
·
In this method,
first the nucleus elongates and divides into two.
·
Then a
constriction appears in the cell membrane which deepens further, dividing cytoplasm
into two parts.
·
This way the
parent cell divides into two daughter cells.
·
Each part then
grows into an adult organism, similar to the parent.
·
Paramecium also
reproduces by binary fission in the same number as explained in Amoeba in
transverse plane but Euglena and Leishmania (the protozoan causing Kalaazar)
reproduce by binary fission in longitudinal plane.
b) Multiple
fission: Multiple fission means
division of the parent body into a number of daughter organisms.
·
In this the
parent nucleus divides repeatedly.
·
The nuclei move
towards the periphery and each one is surrounded by a small amount of cytoplasm
and cell membranes.
·
Finally each one
of these structure gives rise to a new individual. The multinucleate body gives
give to as many number of daughter individuals as the number of nuclei formed.
·
It is a common
mode of reproduction in malarial parasite (plasmodium), when it invades the RBC
of man.
2. Budding:
In budding the new individual arises as an outgrowth
(bud) from the parent. In can be seen in lower organisms like hydra and yeast.
a) Hydra: In multicellular organisms like hydra, a bulge like
projection as a result of repeated mitotic division grows in the parent body.
·
This bulge is
called the bud.
·
This bud grows
and develops organs like mouth and tentacles around it.
·
It grows to a
full size and develops into a new hydra attached to the parent body.
·
Finally a
constriction at the base separates the new hydra from the parent body.
b)
Yeast: In unicellular organisms like yeast (a fungus)
a bud starts as a small outgrowth from the surface of an adult cell.
As it enlarges the nucleus of the adult cell divides
and then the bud gets pinched off but still remains attached to the parent
cell.
This in turn produces another bud at its tip and the
process continue 3-4 times resulting in a chain of yeast cells.
3. Spore
formation: It is the most common type
of asexual reproduction in majority of fungi and bacteria. The spores develop
in a structure called sporangium. Sporangium develops on slender, erect fungal
nuclei. Each nucleus with a bit of cytoplasm develops into a spore. A spore is
a small microscopic structure with a thick wall.
·
The wall of
sporangium breaks releasing the spores in the air.
·
Sooner or later
under favorable conditions in ground or substratum, each spore germinated into
a hypha and grows into new plants.
E.g.
Rhizopus, mucor, penicillium.
4. Regeneration: The process of getting back a full organism from is
body parts are called regeneration. The simple animals like Hydra and Planaria
show regeneration. This means that in these organisms, whole new organisms can
be reproduced from their cut body parts. In other words or Hydra or planaria
somehow get cut into a number of pieces, then each body piece can grow into a
complete organisms.
Planaria is a flatworm which is found in freshwater ponds and
slow-moving streams. Planaria possesses great power of regeneration. If the
body of planaria somehow gets cut into a number of pieces, then each body piece
can regenerate into a complete Planaria
by growing all the missing parts.
The regeneration of organisms from its cut body parts occurs by the
process of growth and development. This happens as follows: the cell of cut
body part of the organisms divide rapidly to make a ‘ball of cell’. The cell
present in the ‘ball of cell’ move to their proper places within the ball where
they have to inform various organs and body parts of the organisms. The cells
then change their shape (or become specialized) to form different types of
tissues. These different tissues form various organs and body parts of the
organism. In this way a complete organisms is regenerated.
The complex multicellular organisms (like mammals) cannot give rise to
complete individuals from their cut body parts through the process of
regeneration.
Regeneration can be used to reproduce only those organisms which have
relatively simple body organization consisting of only a few specialized cells
(or tissues). In complex multicellular organisms, specialized cells make up
tissues; tissues make up organs; organs make up organ system; and finally organ
systems make up organisms. Since complex multicellular organisms have a very
high degree of organization in their body, they cannot be reproduced from their
cut body parts by the process of regeneration.
5. Fragmentation-
The breaking up of the body of a simple multicellular into two or more pieces on maturing , each of which subsequently grows to form a complete organisms is called fragmentation.
The organisms likes spirogyra and sea anemone can reproduces by these methods.
The main difference between fission and fragmentation is that in fission , a unicellular organism break up to form two daughter organisms whereas in fragmentation , a multicellular organisms breaks up to form two daughter organisms.
6. Vegetative propagation:
I.
It is the
simplest and a rapid way of producing new plants in number of higher plants.
II.
It is development
of a new plant from a vegetative part of plant like stem, root or leaf.
III.
Plants produced
are identical to the parent plant. Same variety of fruit or flower can be
produced year after year.
Vegetative
propagation can be natural or artificial. A number of ornamental plants,
orchids, plants of economical or medicinal value are grown by artificial
vegetative propagation. A number of flowering plants show natural vegetative
propagation. Some of the common ways the plants propagate naturally are by 1. Stem 2. Root 3. Leaves
1. By stem: Underground stems of potato, onion, banana and garlic
etc.
2. By roots: Roots of certain plants like guava, carrot , sweet
potato and
Dahlias have adventitious buds (adventitious buds are
buds
which are present at points
other than the shoot tip and axil of leaves) on the roots which give out shoots
that develop into new plants.
3. By leaves: In Bryophyllum, the adventitious buds ate present
along the
Notches of the leaves. During favorable conditions
young plantlets develop from these buds. These plantlets fall off; grow roots
into the soil and from independent plants.
Artificial
vegetative propagation:
Artificial vegetative propagation is tried by gardeners and
horticulturists for large scale commercial purposes. Some or the common modes
used are:
1. Cutting 2.Layering and 3. Grafting
1. Cutting: Cutting are short pieces of the plant which could be
a stem, root, leaf or a bulb scale. When these are placed in moist soil with
suitable conditions, they develop roots and shoot and grow into a new plant.
Generally the cutting selected has some buds on them. At times stem cuttings
are dipped into a hormone rooting powder to stimulate rooting.
2. Layering: In this method leaves from one of the branches are
removed from a small portion. This small portion of the branch without leaves called
layer is given a small cut and covered with soil. After two days the layer
develops roots and it can be separated from the parent plant and planted
separately.
3. Grafting: Grafting is used to reproduce fruit tree and roses. In
this method a twig (called the scion) is cut from the plant to be increased. It
is then joined to the stem (called the stock) of a rooted plant. The cut
surfaces are taped together. The graft heals on the rooted plant to give a new
plant. Grafting is useful if plants are difficult to grow from seeds.
Advantages
of vegetative propagation:
1.
It is an easier,
less expensive and rapid way of producing new plants under favorable
conditions.
2.
The plants that
cannot produce viable seeds such as banana, pineapple, orange, grape and
produced by seeds.
3.
Plants produced
by vegetative propagation bear flowers and fruits much earlier than those
produced by seeds.
4.
Vegetative
propagation takes much less time and so is highly suitable for plants that have
small number of seeds, poor seed viability or ling periods of seed dormancy.
5.
Superior quality
fruits or flowers can be produced by method of grafting.
6.
Since vegetative
propagation gives rise to plants that are identical to plants, it can be used
to preserve a stock of preserved varieties.
Sexual
Reproduction in Flowering Plants:
The important features of sexual reproduction are:
1.
It involves two
parents a different sex, like male and female.
2.
Each parent
produces special sex cells called gametes. Male gamete is often referred as
sperm and female gamete as ovum.
3.
The gametes are
haploid and are produced as a result of meiotic division.
4.
The fusion of
male and female gamete results in the formation of a single celled diploid
zygote.
5.
The zygote
undergoes repeated mitotic division and grows into an embryo that gives to
multicellular organisms by cell differentiation.
6.
The organism
formed is genetically different from both the parents and resembles both the
parents in certain features only.
Some
important terms:
Unisexual: It refers to
organisms being either male or female.
Bisexual or
hermaphrodite: It refers to an
individual that has both male and female sex organs.
Gonads: gonads are the reproductive or sex organs that produce
gametes.
Male gonad is called
testis and produced sperms.
Female gonad
is called ovary and it produced eggs or ova.
Gametes: These are specialized cells produced from gonads as a
result of meiotic (reduction division) .These is of two types: sperms and ova
Fertilization:
Fertilization can be defined as the
fusion of a sperm and an egg to give rise to a fertilized egg or zygote.
Zygote: zygote is a singled celled structure formed by the
fusion of a sperm with an egg ovum.
Types of
fertilization:
I.
External fertilization: when the fertilization takes place outside the body of
organism, it is called external fertilization.
In animals like fishes and frogs (amphibians), male
and female come together and discharge their gametes in the surrounding water.
The sperm fertilize the ova in water. This type of fertilization is called
external fertilization.
II.
Internal fertilization: when fertilization takes place inside the body of
female, it is called internal fertilization.
In animals like insects, reptile, birds and mammals
including human beings, the made discharges the sperms inside the body of
female during mating or copulation. The sperm fertilizes the ovum in the
oviduct of female. This type of fertilization is called internal fertilization.
The structure associated with mating is called
accessory sex organs.
Significance
of sexual reproduction:
1.
It promotes
diversity of characters in the offspring since offspring have the genetic
material of both the parents.
2.
There is
increased opportunity for new combination of character to appear in the
offspring. It plays a vital role in the origin of species. At times characters
hidden in the parents get expressed in the offspring.
3.
It results in
variations. The individuals formed are genetically different from both the
parents. Variation is necessary for evolution.
Sexual
reproduction in plants:
Flowers are the reproductive organs in flowering
plants.
Structure of
a flower
A flower is a reproductive part of a plant. Though
flowers differ in color, size and arrangement, their basic plan remains the
same.
Part of a
typical flower:
A typical flower has four whorls arranged around the
receptacle or thalamus – the expanded portion of the stalk.
Whorls: Starting from outside,
the whorl are arranged
Sepals: They are outermost whorl generally green and leaf
like.
They protect the flower bud before it opens.
Petals: They form the second whorl, inner to sepals.
They
are generally large, colored and showy.
They help in
pollination by attracting insects.
Stamens: Stamens are the male reproductive parts. Each stamen has two
Parts, filament and anther.
a)
Filaments are
a long slender stalk.
b)
Anther is a
bilobed flattened structure present at the tip of filament. Each anther has
four pollen sacs which contain pollen grains.
Each pollen grain produces two male gametes.
Carpel or pistil: They form the fourth and the inner most whorl
containing
Female parts. Each carpel has three parts.
a)
Stigma: It
is attached to the style and receives the pollen grains.
b)
Style: it
forms the neck of carpel to which stigma is attached.
c)
Ovary: it is
swollen basal part. It contains ovules. Each ovule contains an egg, the female
gamete.
At maturity,
the pollen grains develop into anthers and egg cell into the ovules.
Pollination:
Pollination is the transfer if pollen grains from an
anther to the stigma. After the pollen grains are shed from the anthers, they
can reach stigma of a flower by a number of means. The flowers could be self
pollinated or cross pollinated.
Types of
pollination
A. Self pollination:
It refers to the transfer of the pollens forms the
anther of a flower, to the stigma of the same flower or to the stigma of
another flower of the same plants.
e.g- china rose, maize
B. Cross
pollination:
It refers to the transfer or the pollens from the anther
of a flower to the stigma of another flower of a different plant of the same
species.
It involves two separates plants and outside agencies
like wind, water, air or insects.
e.g- papaya, mulberry
Agencies of scientific
terms cross pollination
Winds –
Anemophily
Water –
Hydrophily
Insects –
Entomophily
Birds – Orinthiophily
Bats -
Chiropterophily
Fertilization
in plants
After pollination, occurs fertilization in plant. The
main events that lead t fertilization are as given below:
1.
Immediately
after pollination, as pollen grains land in stigma, they give rise to pollen
tubes.
2.
One
pollen tube grows through the style and reaches the ovary where ovules are
located.
3.
Each
pollen tube has two male gametes.
4. Pollen tube enters the ovule through
a small opening called the micropyle.
On
reaching the ovary, the pollen tube releases two male gametes into the embryo sac of ovule.
One male gamete fuses with other male gamete with the
the egg
cell of the ovule. two polar
nuclei in the ovule 
It is known as fertilization or since it is
fusion of 3 nuclei,
Syngamy and produces a it is
known as triple fusion.
fertilized egg or zygote. (Triple fusion produces a (zygote is diploid
in nature 2n). triploid nucleus and
this 3n in nature.
It is called double
Fertilization
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Double fertilization: Since the process of fertilization occurs twice in the
embryo sac, it is called double fertilization. It is unique to flowering
plants.
Double fertilization includes two fusions – syngamy
and triple fusion
i) Male gametes+ egg
cell = Zygote ( syngamy)
ii) Male gamete + 2
polar nuclei =Triploid nucleus ( triplet fusion)
Double
fertilization = Syngamy + Triple Fusion
Results of double fertilization are:
i. Zygote (2n)
divides mitotically and forms the embryo plant.
ii.
Triploid nucleus
(3n) gives rise to a mass of tissues called endosperm of seed. It provides
nourishment to the growing embryo at the time of seed germination.
Summary of changes after
fertilization
1. The ovary develops into the fruit.
2.The ovules
develop into seeds.The seed contain the
embryo or the potential plant. During the formation of fruit, rest of the
flower withers away.
Germination:
If a seed lands where conditions are appropriate, i.e.
water, oxygen and warmth are available, it will start to grow. Germination is
when the embryo begins to grow. The beginning of the growth of seed is called
germination of seeds. Germination begins when the seed absorbs water, swells
and burst through seed coat . The water helps the enzymes to function in the
seed. The enzyme digest the stored food in cotyledons ad make it soluble. The
soluble food makes the radical and plumule present in the seed to grow .
The embryo grows a new root or radical and new shoot
or plumule. The radical and plumule need food for growth and they get this food
from the food store in the cotyledons.
SEXUAL
REPRODUCTION IN ANIMALS
Sexual Reproduction is the fomation of the new
individuals by a process which involves the fusion of male and female gametes.
Reproduction
in human beings
An
animal having male sex cells called sperms in its body is called male.
An
animal having female sex cells called ova in its body is called female.
The
cells involved in sexual reproduction are called gametes. The male gamete is
called sperm and female gamete is called or ovum or egg.
Fusion
of gametes gives rise to a single cell called zygote.
Fertilization-
The
fusion of a male gamete with a female gamete to form a zygote during the sexual
reproduction is called fertilization.
Puberty:
The
age which the sex hormones (or gametes) begin to be produces and the boy and
girl become sexually mature (able to reproduce) is called puberty.
The
testes produce the male sex hormone called testosterone, and the ovaries
produce two female sex hormones, oestrogen and progesterone.
The various changes which occur in boys at puberty are:
Hair
grows under armpits and in pubic regions (genital area) between the thighs. Hair
also grows on other parts of the body like chest and face (moustaches, beard,
etc). Body becomes more muscular due to the development of muscles. The voice
deepens (or cracks). Chest and shoulders broaden. The penis and testes become
larger. The testes start to make sperm.
The various changes which occur in girls at puberty are:
Hair
grows under armpits and in pubic regions (this change is the same as in boys).
Mammary glands (or breasts) develop and enlarge. The hips broaden. Extra fat is
deposited in various parts of the body like hips and thighs. Fallopian tubes,
uterus and vagina enlarge. Ovaries start release eggs. Menstruation (monthly
period) start. Feeling and sexual drives associated with adulthood begin to
develop. All these changes in girls are brought about by the female sex
hormones ‘oestrogen’ and ‘progesterone’ made in ovaries. Please note that the
hormones ‘oestrogen’ is also written and spoken as ‘estrogen’.
Human reproductive system:
The reproduction systems in human beings
become functional (or start functioning) at a definite age called puberty.
The male reproductive system
The
human male reproductive system consists of the following organs: testes,
scrotum, epididymis, vas deferens (or sperm duct), seminal vesicles, prostrate
gland and penis. Testes are the primary reproductive organs in man (or males).
The function of testes is to make the male sex cells (or male gametes) called
sperms and also to make the male sex hormone called testosterone. The secretion
of seminal vesicles and prostrate gland provide nutrition to the sperms and
also make their further transport easier.
The female reproductive system
The
human female reproductive system consists of the following organs: ovaries,
oviducts (which are also called fallopian tubes, uterus and vagina. Ovaries are
the oval shaped organs which are inside the abdominal cavity of a woman near
the kidneys. A woman has two ovaries. Ovaries are the primary reproductive
organs in a woman (or female). The function of ovaries is to make mature female
sex cells ( or female gamates) called ‘ova’ or ‘ eggs’, and also to make the
female sex hormones ( called oestrogen and progesterone).
Menarche and Menopause
Menarche: The
begininning or commencement of menstruation at puberty is termed as menarche.
In other words, the first monthly period or menstruation is called the menarche.
It marks the beginning of the reproductive life of a woman. Normally it occurs
between 11-13 years.
Menopause: At about
the age of 50-55, the ovulation stops and the menstrual cycle is permanently
discontinues. The ovarian as well as uterine cycles stop. This is known as
menopause.
Menopause
is marked by the stoppage of menstrual flow and other cycle events related to
it.
After
menopause the female loses the ability to reproduce.
Menopause also brings about a hormonal
imbalance in the body( decreased oestrogen level), and hence is accompanied by
other changes like loss of bone matter, increased body weight etc.
Reproductive life: The period
between menarche and menopause i.e. between 12-50 years is called the normal
reproductive life of human female.
Fertilization
Fertilization
involves the fusion of a sperm and an ovum and restores the diploid number of
chromosomes. The fertilized ovum formed is called zygote.
In
human beings, the fertilization is internal. During mating, millions of sperms.
About 200,000,000 are deposited in the vagina but only one out of these
fertilizes the ovum. The sperms are highly active and motile but remain fertile
for only about 12-24 hours in the female reproductive tract.
The
sperms released in vagina, move up the uterus and then the fallopian tubes.
Only a very small number of sperms reach the fallopian tubes because the female
reproductive tract is strongly acidic. Finally only one sperm fertilizes an
ovum. Fertilization occurs high up in the fallopian tube. A sperms may
fertilize an ovum if mating takes place during the ovulatory phase.
The
union of a sperm and am ovum gives rise to a zygote.
Fertilization
is marked by the absence of menstrual flow.
Development of zygote after
fertilization
-Immediately after
fertilization, the zygote begins with repeated mitotic division. Also it starts
moving down slowly , along the fallopian tube towards the uterus. In about 4-5
days, as a result of repeated divisions, it becomes a multicellular structure called
an embryo and reaches the uterus.
-At about the 7th
day after ovulation, the embryo gets attached ( embedded ) to the thickened
inner wall of uterus . this is called implantation.
-After
implantation, a special tissue develops between the embryo and the uterine
wall. This tissue is called placenta.
Placenta:
Placenta is a disc- shaped connection between the mother and the embryo
(foetus). When the embryo takes the characteristic human form, it is termed as
foetus till birth.
-It is through
placenta that the foetus exchanges respiratory gases, nutrients and excretory
wastes with the maternal blood. Placenta supplies the foetus everything it
needs for development. ( in the placenta , blood of the mother and the foetus
never mix since exchange always takes place through the membrane. CO2 and wastes move from the foetus to maternal
blood, and O2 and nutrients
from the maternal to foetal blood by diffusion).
Umbilical cord:
it is during the development of embryo, that
along with placenta, develops another structure called umbilical cord.
Umbilical cord is a long and thick cord that runs between the foetus and the
placenta( placenta is attached to the uterus).
-Umbilical cord is
attached to the belly of the foetus. It contains the blood vessels taking
foetal blood to and from the placenta.
Gestation:
Pregnancy
or gestation refers to the condition of carrying developing foetus inside the
uterus till birth. It begins with conception i.e. the fertilization of the ovum
by a sperm, and continues until the birth of the baby.
Duration of pregnancy :
in
human beings, the average duration of pregnancy is about 280 days ( or 40
weeks) i.e. approximately nine months.
It
is calculated from the 1st day of the last menstrual cycle. The
newborn baby after 40 weeks of gestation weighs about 3.5 kg.
Parturition:
On
completion of pregnancy or gestation, the birth of the fully formed foetus is
called parturition.
Population control:
Human
population is increasing at an enormous rate. It is estimated to become double
in next 30-35 years. The increase in human population is not only adding to the
already exploding population but is also causing a number of socio-economic problems.
Also the frequent pregnancies have an adverse effect on the health of a woman.
Birth control or fertility regulation methods:
To
control over- population, the best method is the birth control. For this a
number of scientific techniques have been developed to prevent pregnancy. These
methods of birth control can be broadly classified into the following three categories.
1.
Barrier
methods
2.
Chemical
methods
3.
Surgical
methods
Some common birth- control or fertility regulation methods
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s.n
|
Birth control
Methods
|
Working of the birth- control method
|
Examples
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|
1.
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Barrier methods
|
-They prevent the entry of sperm in
the female genital tract. Hence fertilization cannot take place.
-They include physical
devices that act as barriers.
|
Condoms –used by male
Diaphragm and cervical caps – used
by females
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2.
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Chemical methods
|
-These are specific drugs used by females.
-They are in the form of oral pills and
vaginal pills
-Oral pills also known as birth control pills
or oral contraceptives (OCs) conatain a combination of hormones. They prevent
the production of ova in ovaries by acting on hypothalamus, pituitary and
ovaries. Since ovulation does not occur, pregnancy cannot take place.
-Vaginal pills are chemical spermicides i.e.
kill a large number of sperms.
-Intrauterine contraceptive devices (IUCDs)
like copper T. Copper T is a small plastic device shaped like a letter T,
with a fine copperwire wrapped around it. It is placed inside the uterus by a
qualified doctor. It prevents implantation of ovum in the lining of uterus.
The copper of copper T is slowly and continuously released into the uterus.
Because of the presence of copper t, copper T is considered to be a drug.
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Oral pills also called as oral
contraceptives (OCs) and vaginal pills.
Intrauterine contraceptive devices
(IUCD) like copper T
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3.
|
Surgical methods
|
-Surgical methods involve birth control by
sterilization.
-They can be performed on either males or
females and are almost 100% effective and are irreversible.
-In males, sterilization involves vasectomy
i.e the removal of a portion of vas deferens from each testis. It prevents
sperms from entering the urethra.
- In females, it involves tubectomy i.e the
removal or ligation (tying ) of a section of each fallopian tube. It prevents
ova from reaching the uterus.
Vasectomy and tubectomy , both prevent contraception permanently.
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Vasectomy in males.
Tubectomy in females.
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Reproductive health and sexually transmitted diseases (STDs)
The
term health includes the physical, mental and social well being of a person.
Reproductive
health includes aspects that ensure a responsible, safe and satisfying
reproductive life.
1. Importance of studying reproductive health
i.
It aims at providing awareness
regarding the fertility regulation methods to both males and females.
ii. It
gives the right, the freedom and choice to control child birth.
iii. It
gives people the ability to prevent and control sexually transmitted diseases
(STDs).
iv. It
helps people to manage disorders related to reproductive system.
2. Sexually transmitted diseases (STDs)
Sexually transmitted diseases (STDs) are
highly infectious diseases that spread form an infected person to a healthy person
by sexual contact.
These
diseases are caused by micro-organisms like viruses, bacteria, protozoans or
fungi that are passed from one human being to another by sexual contact. Most
of these diseases are curable, though there is no definite cure for AIDS( a
sexually transmitted disease) till now. In most cases the common symptoms are
burning sensation at urination and discharge from urethra or genital tract.
Some common sexually transmitted
diseases (STDs)
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Name of sexually transmitted diseases
|
Causative organism
(micro- organism)
|
Symptoms
|
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Gonorrhea
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Bacterial
|
-Infects mucous
membranes of the urino genital tract.
-Genital
discharge, painful urination.
-Children born
to afflicted mothers often suffer eye infections.
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Syphilis
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Bacteria
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-Causes sores
and lesions in the genital tract
-Burning
sensation at urination
-Later causes
sores in mouth.
-Can be deadly
if not treated.
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Trichomoniasis
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Protozoa trichomonas
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Vaginal irritation, itchining and discharge
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AIDS
(Acquired Immuno
Deficiency syndrome)
|
HIV
(Virus)
Human Immuno deficiency
virus
|
-Destroy the
immune system of body.
-Persistent
cough and fever
-Body attacked
by other diseases like pneumonia, T.B. and certain cancers.
AIDS is a life
threating disease. At present there is no vaccine to prevent and there is no
cure. However AIDS is preventable.
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