A Complete Notes
on Reproduction in Animals
by Md. Farrukh
Asif
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to know more……
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REPRODUCTION IN ANIMALS NIMALS
Chap 6 |
Modes of Reproduction
Reproduction is the biological process by which
organisms produce new individuals of their kind. It ensures the continuity of
life on Earth. There are two main modes of reproduction:
1. Asexual Reproduction
- Involves a single parent
- Offspring are genetically identical to the parent (clones)
- No fusion of gametes (reproductive cells)
- Fast and efficient
Examples of Asexual
Reproduction:
- Binary Fission: Bacteria split into two identical cells. Example: Amoeba
- Budding: A small growth, or "bud," forms on the parent
and detaches. Example: Yeast, Hydra
- Vegetative Propagation: Plants grow new individuals from roots, stems,
or leaves. Example: Potato, Strawberry
- Fragmentation: The body breaks into pieces, each forming a new
organism. Example: Starfish, Spirogyra
2. Sexual Reproduction
- Involves two parents
- Fusion of male and female gametes
- Offspring have genetic variation
- Slower but promotes adaptability
Examples of Sexual Reproduction:
- Humans & Animals: Fusion of sperm and egg
- Flowering Plants: Pollination leads to seed formation, e.g., Rose,
Mango
- Fish & Amphibians: External fertilization in water
Would you like me to generate images for these
concepts? Let me know your preferred style:
- Watercolor and Ink – Soft and artistic
- Whiteboard Doodles – Simple and sketch-like
- Low Polygon 3D – Stylized 3D shapes
- Plasticine – Clay-like textures
I'll generate images to illustrate both Asexual
and Sexual Reproduction concepts. Let’s start with the first image:
Image 1: Asexual Reproduction (Binary Fission & Budding)This image will show binary fission in bacteria and budding in yeast in a simple, visually appealing style.
Here’s an illustration of asexual reproduction, showing binary fission in bacteria and budding in yeast. Let me know if you want any adjustments!
Next, I’ll generate an image for sexual
reproduction. It will show the fusion of gametes in humans and flowering
plants. Generating now…
Here’s an illustration of sexual reproduction,
showing human fertilization (sperm meeting egg) and plant
fertilization (pollen reaching the ovule).
Sexual Reproduction: Male
and Female Reproductive Systems
Sexual reproduction involves the fusion of male and
female gametes, leading to genetic diversity in offspring. The reproductive
organs in males and females are specialized to produce and transport these
gametes.
1. Male Reproductive
System
The male reproductive system is responsible for
producing and delivering sperm.
Main Organs & Functions:
- Testes: Produce sperm and the hormone testosterone
- Epididymis: Stores and matures sperm
- Vas Deferens: Transports sperm from the testes
- Seminal Vesicles & Prostate Gland: Produce fluids that
nourish and protect sperm
- Penis & Urethra: Help in delivering sperm to the female reproductive
tract
Male
Reproductive System:
Here’s an illustration of the male reproductive
system, showing key structures like the testes, vas deferens, and prostate
gland.
Now, let’s move on to the female reproductive
system. Generating an image now…
Here’s an illustration of the female reproductive
system, showing key structures like the ovaries, fallopian tubes, and
uterus.
2. Female Reproductive
System
The female reproductive system is responsible for producing eggs and supporting fetal development.
Main Organs & Functions:
- Ovaries: Produce eggs (ova) and hormones like estrogen
- Fallopian Tubes: Transport eggs to the uterus, where fertilization can
occur
- Uterus: Supports fetal development during pregnancy
- Cervix: The lower part of the uterus, which opens into the vagina
- Vagina: The birth canal and passage for sperm entry
Female gametes called ova
(eggs) (Fig.). In human beings, a single matured egg is released into
the oviduct by one of the ovaries.
every month. Uterus is the part
where development of the baby takes place. Like the sperm, an egg is also a
single cell.
Fertilisation
The first step in the process of
reproduction is the fusion of a sperm and an ovum. When sperms come in contact
with an egg, one of the sperms may fuse with the egg. Such fusion of the egg
and the sperm is called fertilisation (Fig. 6.5).
During fertilisation, the nuclei of the sperm and the egg fuse to form a single
nucleus. This results in the formation of a fertilised egg or zygote
(Fig. ).
Fig: Fertilised egs
you know that the zygote is the beginning
of a new individual?
Fig: Zygote
The process of
fertilisation is the meeting of an egg cell from the mother and a sperm cell
from the father. So, the new individual inherits some characteristics from the mother and some from the father.
Look at your brother or sister. See if you can recognise some characters in
them similar to those of your mother or your father.
Fertilisation which takes place inside the
female body is called internal fertilisation.
Internal fertilisation occurs in many animals including humans, cows, dogs and
hens.
During spring or rainy season, frogs and
toads move to ponds and slow flowing streams. When the male and female come
together in water, the female lays hundreds of eggs. Unlike hen’s egg, frog’s
egg is not covered by a shell and it is comparatively very delicate. A layer of
jelly holds the eggs together and provides protection to the eggs (Fig. 6.7).
Development of Embryo
Fertilisation results in the formation of
zygote which begins to develop into an embryo [Fig. (a)]. The zygote divides
repeatedly to give rise to a ball of cells [Fig. (b)]. The cells then begin to
form groups that develop into different tissues and organs of the body. This
developing structure is termed an embryo. The embryo gets embedded in the wall
of the uterus for further development [Fig. (c)].
The embryo continues to develop in the
uterus. It gradually develops body
Fig.
: (a) Zygote formation and development of an embryo
from the zygote; (b) Ball of
cells
(enlarged); (c) Embedding
of the embryo in the uterus (enlarged)
parts such as
hands, legs, head, eyes, ears etc. The stage of the embryo in which all the
body parts can be identified is called a foetus (Fig. ). When the
development of the foetus is complete, the mother gives birth to the baby.
place inside the egg shell during this period? After the chick is completely
developed it bursts open the egg shell.
In animals which
undergo external fertilisation, development of the embryo takes place inside the egg shell during this period ?
After the chick is completely developed it bursts open the egg shell.
In animals which
undergo external fertilisation, development of the embryo takes place outside
the female body.
Fig. 6.9 : Foetus in
the uterus
Internal
fertilisation takes place in hens also. But, do hens give birth to babies like
human beings and cows? You know that they do not. Then, how are chicks born?
Let us find out.
Soon after
fertilisation, the zygote divides repeatedly and travels down the oviduct. As
it travels down, many protective layers are formed around it. The hard shell
that you see in a hen’s egg is one such protective layer.
After the hard shell is formed around the
developing embryo, the hen finally lays the egg. The embryo takes about 3 weeks
to develop into a chick. You must have seen the hen sitting on the eggs to
provide sufficient warmth. Did you know that development of the chick takes egg
coverings. After the embryos develop, the eggs hatch. You must have seen
numerous tadpoles swimming in ponds and streams.
Young Ones to Adults
The new individuals which are born
or hatched from the eggs continue to grow till they become adults. In some
animals, the young ones may look very different from the adults. The life cycle
of frog is shown in Fig. .
Observe the different stages of frog
starting from the egg to the adult stage. We find that there are three distinct
stages, that is, egg →
tadpole (larva) →
adult. Don’t the tadpoles look so different from the adults?
Can you imagine that these tadpoles would some day become frogs?
The tadpoles transform into adults
capable of jumping and swimming. The transformation of the larva into an adult
through drastic changes is called metamorphosis. What about the changes that we
observe in our body as we grow? Do you think we too undergo metamorphosis? In
human beings, body parts similar to those present in the adults are present
from the time of birth.
Asexual
Reproduction
So far, we have learnt about
reproduction in some familiar animals. But what about very small animals like
hydra and microscopic organisms like amoeba
? Do you know how they reproduce?
Let us find out.
Activity 6.3
Get permanent slides of hydra. Observe them using hand lens or a microscope.
Look out for any bulges from the parent body. Count the
number of bulges that
you see in different slides. Also, note the size of the bulges. Draw the diagram
of hydra, as you see it. Compare it with the Fig..
Fig. : AmoebaReproduction
In each hydra, there may be one or more bulges. These bulges are the developing new individuals and they are called buds. Recall the presence of buds in yeast.
In hydra too the new individuals develop as outgrowths from a single parent. This type of reproduction in which only a single parent is involved is called asexual reproduction. Since new individuals develop from the buds in hydra, this type of asexual reproduction is called budding.
Another method
of asexual reproduction is observed in the microscopic organism, amoeba. Let us
see how this happens.
You have already
learnt about the structure of amoeba. You will recall that amoeba is a
single-celled organism [Fig. (a)]. It begins the process of reproduction by the
division of its nucleus into two nuclei [Fig. (b)]. This is followed by
division of its body into two, each part receiving a nucleus [Fig. (c)].
Finally, two amoebae are produced from one parent amoeba [Fig. (d)].
========================
Exercises
Question 1 Explain
the importance of reproduction in organisms.
Answer
Reproduction
is an essential for the continuation of a species to existence. It ensures the
continuation of similar kinds of individuals like them, generation after
generation and prevents them from becoming extinct.
Question 2 Describe
the process of fertilisation in human beings.
Answer
When male sperms
come in contact with an egg of female, one of the sperms may fuse with the egg.
Such fusion of the egg and the sperm is called fertilisation. During
fertilisation, the nuclei of the sperm and the egg fuse to form a single
nucleus. This give the results in the formation of a fertilised egg or zygote.
Question 3
Multi
Choice Questions
(a) Internal
fertilisation occurs
I.
in female body.
II.
outside female body.
III.
in male body.
IV.
outside male body.
Answer
(i) in female body
Reason —
Fertilisation takes place inside the oviduct in the female body. Hence, it is
called internal fertilisation.
(b) A
tadpole develops into an adult frog by the process of
I.
fertilisation
II.
metamorphosis
III.
embedding
IV.
budding
Answer
(ii) metamorphosis
Reason —
The transformation of the larva into adult through drastic changes is called
metamorphosis. The tadpoles look like fish and are capable of swimming and
transform into adults capable of jumping and swimming.
(c) The
number of nuclei present in a zygote is
I.
none
II.
one
III.
two
IV.
four
Answer
(ii) one
Reason —
During fertilisation, the nuclei of the sperm and the egg fuse to form a single
nucleus. This results in the formation of a fertilised egg or zygote.
True
or False.
Question 4 Indicate
whether the following statements are True or False.
(a)
Oviparous animals give birth to young ones. (a) False
Corrected statement — Viviparous animals give birth to young ones.
(b) Each
sperm is a single cell. (b) True
(c)
External fertilisation takes place in frog. (b) True
(d) A new
human individual develops from a cell called gamete. (d) False
Corrected statement — A new human individual develops from a cell called
zygote.
(e) Egg
laid after fertilisation is made up of a single cell. (e) True
(f) Amoeba
reproduces by budding. (f) False
Corrected statement — Amoeba reproduces by binary fission.
(g)
Fertilisation is necessary even in asexual reproduction. (g) False
Corrected statement — Fertilisation is not necessary in asexual
reproduction.
(h) Binary
fission is a method of asexual reproduction. (h) True
(i) A
zygote is formed as a result of fertilisation. (h) True
(j) An
embryo is made up of a single cell. (j) False
Corrected statement — A zygote is made up of a single cell.
Question 5 Give
two differences between a zygote and a foetus.
Answer
|
Zygote |
Foetus |
|
Zygote is formed by the fusion of
sperm and egg during fertilisation. |
Foetus is the stage of the embryo
in which all the body parts can be identified. |
|
Zygote is unicellular. |
Foetus is multicellular. |
Question 6 Define
asexual reproduction. Describe two methods of asexual reproduction in animals.
Answer
Asexual
reproduction is the type of reproduction in which only a single parent is
involved. It takes place by different methods like budding, binary fission etc.
Two methods
of asexual reproduction in animals are:
Budding —
In budding, new individuals develop from buds. A bulge or outgrowth appears on
the parent's body that goes on to develop into a full organism. It then
detaches from the parent and continues to develop into a new individual.
Budding is seen in hydra and yeast.
Binary
Fission — In binary fission, a single-celled organism divides to form two
new individuals. The process begins with the division of its nucleus into two
nuclei. This is followed by division of its body into two, each part receiving
a nucleus. Finally, two cells are produced from one parent cell. It is seen in
Amoeba.
Question 7 In
which female reproductive organ does the embryo get embedded?
Answer
The embryo
gets embedded in the wall of the uterus of females for further development.
Question 8 What
is metamorphosis? Give examples.
Answer
The
transformation of the larva into an adult through drastic changes is called
metamorphosis. For example, it is seen in frog and butterfly. In frogs, there
are three distinct stages, that is, egg, tadpole (larva) and adult. In
butterfly the four distinct stages are egg, caterpillar, pupa and adult.
Question 9 Differentiate
between internal fertilisation and external fertilisation.
Answer
|
Internal Fertilisation |
External Fertilisation |
|
It takes place inside the body of
female. |
It occurs outside the body. |
|
It is observed in human beings
and other animals such as hens, cows and dogs. |
It is observed in aquatic animals
and amphibians such as fish, starfish and frogs. |
|
Lesser number of eggs are
released. |
Many more eggs are released. |
|
Survival rate is higher. |
Survival rate is low. |
Question 10
Complete the crossword puzzle using the hints given below.
Across
1. The
process of the fusion of the gametes.
6. The type of fertilisation in hen.
7. The term used for bulges observed on the sides of the body of hydra.
8. Eggs are produced here.
Down
2. Sperms
are produced in these male reproductive organs.
3. Another term for in vitro fertilisation.
4. These animals lay eggs.
5. A type of fission in amoeba.
The
solution of word puzzle is given below:
Across
1.
Fertilisation.
6. Internal.
7. Buds.
8. Ovary.
Down
2. Testes.
3. IVF.
4. Oviparous.
5. Binary.
***************
See You Again
**************
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