Lesson: How do Organisms Reproduce
In
the list of organisms given below, those that reproduce by asexual method are:
(i)
Banana
(ii)
Dog
(iii)
Yeast
(iv)
Amoeba
(a)
(ii) and (iv)
(b)
(i), (iii) and (iv)
(c)
(i) and (iv)
(d)
(ii), (iii) and (iv)
(b)
In
a flower, the parts that produce male and female gametes (germ cells) are:
(a)
Stamen and anther
(b)
Filament and stigma
(c)
Anther and ovary
d)
Stamen and style
(c)
Which
of the following is the correct sequence of events of sexual reproduction in a
flower?
(a)
Pollination, fertilisation, seedling, embryo
(b)
Seedling, embryo, fertilisation, pollination
(c)
Pollination, fertilisation, embryo, seedling
(d)
Embryo, seedling, pollination, fertilisation
(c)
Offspring
formed by asexual method of reproduction have greater similarity among
themselves because:
(i)
Asexual reproduction involves only one parent
(ii)
Asexual reproduction does not involve gametes
(iii)
Asexual reproduction occurs before sexual reproduction
(iv)
Asexual reproduction occurs after sexual reproduction
(a) (i) and (ii)
(b)
(i) and (iii)
(c)
(ii) and (iv)
(d)
(iii) and (iv)
(a)
Characters
transmitted from parents to offspring are present in:
(a)
Cytoplasm
(b)
Ribosome
(c)
Golgi bodies
(d)
Genes
(d)
Characters
that are transmitted from parents to offspring during reproduction show:
(a)
Only similarities with parents
(b)
Only variations with parents
(c)
Both similarities and variations with parents
(d)
Neither similarities nor variations
(c)
A
feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that:
(a)
They reproduce asexually
(b)
They are all unicellular
(c)
They reproduce only sexually
(d)
They are all multicellular
(a)
In
Spirogyra, asexual reproduction
takes place by:
(a)
Breaking up of filaments into smaller bits
(b)
Division of a cell into two cells
(c)
Division of a cell into many cells
(d)
Formation of young cells from older cells.
(a)
The
ability of a cell to divide into several cells during reproduction in
Plasmodium is called:
(a)
Budding
(b)
Reduction division
(c)
Binary fission
(d)
Multiple fission
(d)
The correct sequence of
reproductive stages seen in flowering plants is:
(a) Gametes, zygote,
embryo, seedling
(b) Zygote, gametes,
embryo, seedling
(c) Seedling, embryo,
zygote, gametes
(d) Gametes, embryo,
zygote, seedling
(a)
The number of chromosomes
in parents and offspring of a particular species remains constant due to:
(a) Doubling of chromosomes
after zygote formation
(b) Halving of chromosomes
during gamete formation
(c) Doubling of chromosomes
after gamete formation
(d) Halving of chromosomes
after gamete formation
(b)
In
Rhizopus, tubular thread-like
structures bearing sporangia at their tips are called:
(a)
Filaments
(b)
Hyphae
(c)
Rhizoids
(d)
Roots
(b)
Vegetative propagation
refers to formation of new plants from:
(a) Stem, roots and flowers
(b) Stem, roots and leaves
(c) Stem, flowers and
fruits
(d) Stem, leaves and
flowers
(b)
Factors
responsible for the rapid spread of bread mould on slices of bread are:
(i)
Large number of spores
(ii)
Availability of moisture and nutrients in bread
(iii)
Presence of tubular branched hyphae
(iv)
Formation of round shaped sporangia
(a) (i) and (iii)
(b)
(ii) and iv)
(c)
(i) and (ii)
(d)
(iii) and (iv)
(c)
Length
of a pollen tube depends on the distance between:
(a)
Pollen grain and upper surface of stigma
(b)
Pollen grain on upper surface of stigma and ovule
(c)
Pollen grain in anther and upper surface of stigma
(d)
Upper surface of stigma and lower part of style
(b)
Which of the following
statements are true for flowers?
(i) Flowers are always
bisexual
(ii) They are the sexual
reproductive organs
(iii)They are produced in
all groups of plants
(iv) After fertilisation,
they give rise to fruits
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)
(d)
Which
among the following statements are true for unisexual flowers?
(i)
They possess both stamen and pistil
(ii)
They possess either stamen or pistil
(iii)
They exhibit cross pollination
(iv)
Unisexual flowers possessing only stamens cannot produce fruits
(a) (i) and (iv)
(b)
(ii), (iii) and (iv)
(c)
(iii) and (iv)
(d)
(i), (iii) and (iv)
(b)
Which among the following
statements are true for sexual reproduction in flowering plants?
(i) It requires two types of
gametes
(ii) Fertilisation is a
compulsory event
(iii)
It always
results in formation of zygote
(iv) Offspring formed are
clones
(a) (i) and (iv)
(b) (i), (ii) and (iv)
(c) (i), (ii) and (iii)
(d) (i), (ii) and (iv)
(c)
In
the given figure, the parts A, B and C are sequentially:
(a)
Cotyledon, plumule and radicle
(b)
Plumule, radicle and cotyledon
(c)
Plumule, cotyledon and radicle
(d)
Radicle, cotyledon and plumule
(c)
Offspring
formed as a result of sexual reproduction exhibit more variations because:
(a)
Sexual reproduction is a lengthy process
(b)
Genetic material comes from two parents of the same species
(c)
Genetic material comes from two parents of different species
(d)
Genetic material comes from many parents
(b)
Reproduction
is essential for living organisms in order to:
(a)
Keep individual organism alive
(b)
Fulfil their energy requirement
(c)
Maintain growth
(d)
Continue the species generation after generation
(d)
During adolescence, several
changes occur in human body.
Mark one change associated
with sexual maturation in boys:
(a) Loss of milk teeth
(b) Increase in height
(c) Cracking of voice
(d) Weight gain
(c)
In human females, an event that reflects onset of reproductive phase is:
(a) Growth of body
(b) Changes in hair pattern
(c) Change in voice
(d) Menstruation
(d)
In human males, testes lie
in the scrotum, because it helps in the:
(a) Process of mating
(b) Formation of sperm
(c) Easy transfer of
gametes
(d) All the above
(b)
Which among the following is not the function of
testes at puberty?
(i) formation of germ cells
(ii) secretion of testosterone
(iii) development of placenta
(iv) secretion of estrogen
(a) (i) and
(ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
(c)
The correct sequence of organs in a male
reproductive system for transport of sperms is:
(a) Testis → Vas deferens → Urethra
(b) Testis → Ureter → Urethra
(c) Testis → Urethra → Ureter
(d) Testis → Vas deferens → Ureter
(a)
Which among the following diseases is not sexually
transmitted?
(a) Syphilis
(b) Hepatitis
(c) HIV - AIDS
(d) Gonorrhoea
(b)
In a
bisexual flower in spite of young stamens being removed artificially, the
flower produces fruit.
Provide a
suitable explanation for the above situation.
A flower
produces fruit when the process of pollination and fertilisation take place. In
absence of stamens, cross pollination can take place to facilitate
fertilisation and formation of fruit.
Can you consider cell division as a type of reproduction in unicellular
organism? Give one reason.
Yes,
because cell division results in the formation of two daughter cells, that is,
it results in the production of more individuals of that organism.
What is a clone? Why do
offspring formed by asexual reproduction exhibit remarkable similarity?
An exact copy of something
is called a clone. An offspring of an organism formed by asexual method of
reproduction possess exact copies of the DNA of their parent. Hence, the
offspring formed after asexual reproduction exhibit remarkable similarity.
Explain how, offspring and
parents of organisms reproducing sexually have the same number of chromosomes?
Gamete formation is the first step in sexual reproduction. Reduction
division (meiosis) during gamete formation halves the chromosome number in both
male and female gametes. When these two gametes fuse during fertilisation, the
original number of chromosomes (as in the parent) becomes equal in the
offspring. Therefore, the offspring and parents of organisms reproducing sexually
have the same number of chromosomes.
Colonies of yeast fail to
multiply in water, but multiply in sugar solution.
Give one reason for this.
For all life processes, an organism requires nutrition.
Yeast gets inadequate
nutrition in water which prevents its multiplication. On the other hand, yeast
gets all the energy required for sustaining all life activities including
reproductions in a sugar solution. Thus, colonies of yeast fail to multiply in
water, but multiply in sugar solution.
Why does bread mould grow profusely on a moist slice
of bread rather than on a dry slice of bread?
Moisture is an important factor for the growth of
hyphae. When compared to a dry slice of bread, the moist slice of bread offers
much needed water to the spores of the bread mould. Hence, bread mould grows
profusely on a moist slice of bread.
Give two reasons for the
appearance of variations among the progeny formed by sexual reproduction.1
The reasons for the
appearance of variations among the progeny formed by sexual reproduction are:
(a) Gene proof of a progeny
is contributed by two parents with different sets of characters
(b) The gene combinations
are different in both male and female gametes.
Would a Planaria cut
vertically into two halves regenerate into two individuals? Complete the given
figure D and E by indicating the regenerated regions.
Yes,
shaded part in Figures D and E represent the regenerated halves.
From the internet, gather information about the
number of chromosomes present in five animals and five plants.
Correlate the number of chromosomes with the size of
organism and answer the following questions.
(a) Do larger organisms have more number of
chromosomes/cells?
(b) Can organism with fewer chromosomes reproduce
more easily than organisms with more number of chromosomes?
(c) More the number of chromosomes/cells greater is
the DNA content. Justify.
(a) No, there is no
relationship between size of an organism and its chromosome number.
(b) No, the process of
reproduction is not dependent on the number of chromosomes. It depends on
various factors like availability of nutrients, water, conductive environment
and suitable mate.
(c) Yes, the major component
of chromosome is DNA. If there are more chromosomes in a cell, the quantity of
DNA will also be more.
In a tobacco plant, a male gamete has twenty-four
chromosomes.
What is the number of chromosomes in a female
gamete?
What is the number of chromosomes in the zygote?
Number of chromosomes in a female
gamete is 24.
Number of chromosomes in
zygote is 48.
Why fertilisation cannot take place in flowers, if
pollination does not occur?
Fertilisation
requires both male and female gametes. This can happen only when pollen grains
are transferred to the stigma through any means of pollination. Hence,
fertilization cannot take place in flowers if pollination does not occur.
Is the
chromosome number of a zygote, an embryonal cell and an adult of a particular
organism always constant?
How is the
constancy maintained in these three stages?
Yes, the chromosome number
of a zygote, an embryonal cell and an adult of a particular organism is always
constant.
The constancy is maintained because cells in all these three structural phases undergo only mitotic divisions.
Where is the zygote located
in a flower after fertilization?
After fertilization, zygote
is located, inside the ovule present inside the ovary.
Reproduction is linked to
stability of population, of a species.
Justify the statement.
Every
species on Earth has to constantly struggle for its survival. The natural cycle
of birth and death, natural predators and vagaries of nature will continue to remove
a large section of population of a particular species. So, living organisms
reproduce to replenish the lost section of their population. Thus, reproduction
helps in providing stability to the population of a species by producing new
individuals that resembles their parents.
How are general growth and sexual maturation
different from each other?
General
growth refers to the growth, where body parts become larger. Examples: Increase
in height, weight gain, changes in shape and size of the body.
Sexual maturation: These are certain changes that
occur when one attains a certain age. In human beings, this starts at an early age,
teenage years. These changes are signs of one
gaining more sexual maturity like the ability to reproduce. Examples: Cracking
of voice, new hair patterns, development of breast in females etc.
Trace the
path of sperms during ejaculation and mention the gland and their functions
associated with the male reproductive system.
Sperms
come out from testes into the vas deferens, and then passes through urethra
before ejaculation.
The
secretion from seminal vesicles adds fluid content to the semen, which
lubricates the sperms and provides a fluid medium for easy transport of sperms.
The
prostate gland makes the medium of semen alkaline.
What
changes are observed in the uterus if fertilisation does not occur?
The thick
and spongy lining of the uterus slowly breaks and comes out along with blood,
mucus, and the discarded egg.
What
changes are observed in the uterus subsequent to implantation of young embryo?
Once the
zygote is implanted in a uterine wall, the uterine wall thickens. So that it
gives support to the growing embryo. It is richly supplied with blood to
provide nourishment to the embryo. A special tissue called placenta develops and
it connects the embryo to the uterine wall to provide nutrients and oxygen to the
embryo.
What are
the benefits of using mechanical barriers during sexual act?
Benefits
of using mechanical barriers:
a) It prevents sperms from reaching the egg. Thus, it
helps avoiding unwanted pregnancy.
b) A condom on a penis or similar covering worn in a vagina,
and used as mechanical barriers also prevents transfer of sexually transmitted
diseases.
In the
given figure label the parts and mention their functions:
(a)
Production of egg
(b) Site
of fertilisation
(c) Site
of implantation
(d) Entry
of the sperms
a) Ovary (production of egg)
b) Oviduct (site of fertilisation)
c) Uterus (site of implantation)
d) Vagina (entry of the sperms)
What would
be the ratio of chromosome number between an egg and its zygote? How is the
sperm genetically different from the egg?
The ratio is 1:2. Sperms are genetically different
from an egg in a way that it contains either X or Y chromosome whereas an egg always
carries X chromosome.
Why are budding, fragmentation and regeneration considered
as asexual types of reproduction?
With a neat diagram explain the process of
regeneration in a Planarian.
Budding, fragmentation and regeneration are considered as asexual types
of reproduction because only one parent carries out the process of reproduction
and gamete formation does not happen during this mode of reproduction.
The
following diagram shows the regeneration in a Planarian:
When
the body of a Planarian is cut off into several parts, each part regenerates
its complimentary part to develop a new individual.
Write two
points of difference between asexual and sexual types of reproduction. Describe
why variations are observed in the offspring formed by sexual reproduction.
Asexual Reproduction |
Sexual Reproduction |
Involves only one parent |
Often involves two parents |
Gametes are not produced |
Gametes are produced |
No fertilisation and zygote formation |
Fertilisaton and zygote formation is observed. |
Reason for variations in
offspring produced by sexual reproduction:
During sexual reproduction,
two sets of genes are contributed by different parents. This brings different
sets of characters in the offspring.
Distinguish between
pollination and fertilisation.
Mention the site and
product of fertilisation in a flower.
Draw a neat, labelled
diagram of a pistil showing pollen tube growth and its entry into an ovule.
Pollination: Transfer of
pollen grains from anther to stigma is termed as pollination. It is a physical
process in which pollen grains move due to certain physical factors such as
air, water, birds or some insects.
Fertilisation: Fusion of
male and female gametes is termed fertilization. The site of fertilisation is
ovule. The product of fertilisation is zygote.
The following diagram shows
fertilisation in a plant:
Distinguish between a
gamete and zygote.
Explain their roles in
sexual reproduction.
Gamete: It is a sex or germ cell that takes part in
fertilization. There are two types of gametes male and female.
Zygote: The fertilisation of male and female gametes leads
to the formation of zygotes.
It is the first cell of a new
generation.
Role of gamete in sexual reproduction:
Gamete formation results in
halving of number of chromosomes. This is necessary to maintain the number of
chromosomes in an organism that reproduces sexually.
Role of zygote in sexual reproduction:
Zygote formation makes the
number of chromosome equal to the somatic cells. Further, it is the zygote
which undergoes mitosis to develop into an embryo and subsequently into a new
individual.
Draw diagram of a flower and label the four whorls.
Write the names of gamete producing organs in a
flower.
Male gamete forming part: anther/stamen
Female
gamete forming part: pistil/ovary/ovule
What is placenta? Mention its role during pregnancy?
Placenta is a tissue that connects embryo to the uterine wall. It is a
disc-like structure which is embedded in the uterine wall. Placenta contains
villi on the embryo’s side of the tissue, and blood spaces on mother’s side
surrounding the villi. Placenta works as a channel between the mother and the
embryo and provides nutrients and oxygen to the embryo. This also provides a
large surface from mother to the embryo and waste products from embryo to
mother.
What are various ways to avoid pregnancy? Elaborate
any one method.
The
various ways to avoid pregnancy are:
(i) Mechanical barriers
(ii) Drugs
(as pills)
(iii) Loop
or copper T
(iv) Surgical
method
Copper-T:
Copper-T is in the shape of ‘T’ and is made of copper. Copper-T makes a
barrier at the opening of the fallopian tubes in the uterus and thus prevents
sperms from entering the fallopian tubes and prevents fertilization.
How does
fertilisation take place? Fertilisation occurs once in a month. Comment.
During the ovulation cycle,
one egg is released by either of the two ovaries and it reaches the fallopian
tube. During sexual intercourse, sperms enter through the vaginal passage. Sperms
are highly active and mobile and thus move up through cervix into the uterus. From
there, it reaches the fallopian tube. Millions of sperms are released into the
vagina at one time, but only one sperm encounters the egg in the fallopian tube
and fertilization takes place.
Since only one egg is
released in a single ovulation cycle and ovulation cycle happens once in a
month, therefore, fertilisation occurs once in a month.
Reproduction is essentially a phenomenon that is not for survival of an
individual but for the stability of a species. Justify.
All organisms on Earth need
energy for survival and growth. This energy is obtained from life processes
such as nutrition and respiration. Compared to these life processes, reproduction
needs a lot of energy. Reproduction helps
in the production of new individuals of its own kind. During reproduction, genetic
material is transferred from one generation to the next through DNA copying,
with high constancy and considerable variations. Variations are important for
maintaining features that allow an organism to survive in the changing
environment. Therefore, reproduction is essential for the stability of a
species and for the survival of an individual.
Describe sexually transmitted diseases and mention different ways to
prevent them.
A disease that can be transmitted through sexual contact is called
sexually transmitted disease or STD. This includes bacterial infections such as
gonorrhoea and syphilis and viral infections like HIV.
Some of the ways to prevent STDs are as follows:
•
Being faithful to one’s life partner.
•
Avoiding sexual contact with unknown person.
•
Using condom during sexual intercourse.
•
Maintaining personal hygiene.