Reproduction in Animals

Assessment Zone

A. Choose the correct answer.

A. 1. d 2. c 3. b 4. d 5. c

B. Fill in the blanks.

1. Male gamete, zygote

2. Vas deferens

3. Penis 

4. Sex cells or gametes

5. Embryo 

6. Semen

C. State True or false.

1. False 

2. False 

3. False 

4. False

5. False 

6. True 

7. False 

8. False

D. Answer in one word.

1. Asexual reproduction 

2. Oviparous

3. Metamorphosis 

4. Reproduction

5. Foetus

E. Differentiate between the following:

1. External and internal fertilisation 

External fertilisation Internal fertilisation

It is characterised by the release of

both sperm and eggs into an external

environment; sperm will fertilise the

egg outside of the organism, as seen in

spawning.

It is characterised by sperm fertilising the

egg within the female

In external fertilisation the fertilised egg

or embryo are more prone to predators

and harsh environments, which results in

lower survival rates

It ensures better chances of survival of the

young ones than external fertilisation.

Large number of gametes are produced Relatively lesser number of gametes are

produced

2. Oviparous and viviparous animals

Oviparous animals Viviparous animals

The animals that lay eggs are called

oviparous

Certain give birth to young

ones are called viviparous

 Their young ones develop inside the eggs. the development of an embryo

into an offspring takes place inside the

female’s body.

The young one hatches out of the egg after

its development is complete.

Once the offspring is fully developed, the

female gives birth to the baby.

Birds, reptiles and fish Human, cat, dog, cow and deer

3. Embryo and foetus

The difference between an embryo and a foetus has to do with the different phases of

baby’s development. The embryo is defined as the developing pregnancy from the time of

fertilisation until the end of the eighth week of gestation. At the end of eighth week, it

becomes foetus.

 During the embryonic period, cells begin to take on different functions. The brain, heart,

lungs, internal organs and arms and legs begin to form. Once baby is a foetus, growth

and development are aimed at prepping baby for life on the outside.

4. Sexual and asexual reproduction

  • The asexual reproduction is the process where there is no interaction between the

organisms of the same species and the organism alone is capable of producing the

offspring. Sexual reproduction involves the interaction of the two organisms (male

and female), to produce the zygote or the offspring.

  • Asexual reproduction is usually seen in lower forms of organisms like algae,

protozoans, bacteria, and fungi. Sexual reproduction is noticed in higher plants and

animals.

    • Asexual reproduction does not involve special cells called gametes. Sexual

reproduction requires production of gametes that fuse together and form zygote.

    • In asexual reproduction, young one produced is exactly like its parent. In sexual

reproduction, the young ones produced are not clones of parents.

5. Zygote and embryo

  • Zygote is formed when a male gamete i.e. sperm, fertilises with a female egg cell.

Embryo is the first stage of the zygote’s development where its cells multiply to form

their designated functions (differentiation).

  • Zygote has one-celled stage whereas embryo is a multicellular stage.

6. Male and female gametes

  • The male gametes or sperms are produced in a pair of testis. The female gametes are

produced by the ovaries.

  • Male gametes are known as sperms and female gametes are called eggs.

F. Match the following:

1. e 

2. c 

3. a 

4. b 

5. d

G. Answer the following questions in brief.

1. Reproduction is the process by which organisms, such as plants and animals, produce

offspring. In this process, organisms replicate themselves and bear offspring in order

to ensure the survival of their species. Reproduction can be a sexual or an asexual act,

dependent on the species. In sexual reproduction, the formation of a new organism

is created by the union of a male and female gamete, or reproductive cell. In asexual

reproduction, a single organism generates a new organism. This organism is genetically

identical to its parent.

2. In Vitro Fertilisation

3. The human male gamete or the sperm fuses with the human female gamete also called

the egg or the ovum, to produce a single-celled structure called the zygote. This fusion

between a male and a female gamete takes place in the fallopian tube. Zygote develops

into embryo. Development of embryo takes place inside the uterus or the womb.

  4. In external fertilisation, millions of gametes are produced and released into the water.

The main criteria for this type of fertilisation to be successful is that the gametes must

be produced in large numbers, because, there are always high chances of them getting

eaten by fish or getting washed away by water currents and rainfall.

5. Embryo is implanted in uterus or womb. Its development takes place in uterus.

6. Some organisms produce both male and female gametes in the same body. Such

organisms are called hermaphrodites. Snail, slug, leech and earthworm are examples of

hermaphrodites.

7. The testis produces millions of sperms which are male gametes and responsible for

fertilisation. Penis is the organ that transfers the sperms into the vagina—a part of

female reproductive system.

8. Horse – V, dolphin – O, Butterfly – O, polar bear – V

H. Answer the following questions in detail.

1. a. Refer to fig 9.2 on page no.126.

    b. Refer to fig 9.1 on page no.126.

  2. Refer to fig 9.5 on page no.128.

    To reach and fertilise an egg, sperm must move — wriggling and swimming through a

woman’s cervix, uterus and fallopian tubes. This is known as motility. Certain glands

secrete fluids that are poured into the sperm ducts. This gives better mobility to sperm

cells

3. Refer to fig 9.4 on page no.128.

  4. In case of frog, the eggs hatch into tadpoles that have tails to swim and gills to breathe

in water. As the tadpole matures, it loses its tail and starts resembling the adult frog.

  5. Refer to fig 9.6 on page no.128.

a. Uterus b. Fallopian tube

c. Endometrium or uterine lining d. Ovaries

6. It is a technique in which ova are collected from a female’s body and allowed to fuse with

sperms collected from a male’s body in an external medium or outside the body of the

female. The zygote so developed is allowed to grow in vitro (that is, in glass) for about a

week and then implanted in the female’s uterus where it further develops as a normal

embryo. A baby born of this technique is often called a ‘test-tube baby’.

  7. Fertilisation is the process by which male and female gametes are fused together,

initiating the development of a new organism. Male gametes (sperms) are introduced

into the female reproductive system by the penis. Both the gametes meet in the oviduct.

The fusion between a male and a female gamete in the fallopian tube results in the

formation of a fertilised egg or the zygote. This process of fusion of male and female

gametes is known as fertilisation. The zygote formed through fertilisation then grows

into a new individual.

8. All animals are not oviparous as being viviparous certainly have advantages. For

example,

  • Certain important developments occur before birth in viviparous animals.

    • Parents do not have to stay at a particular place to take care of the young ones all

the time as they can leave their habitat with their young ones inside them.

    • Less offspring can be produced as opposed to oviparous where large number of eggs

should be laid to ensure maximum survival.

  • Food and oxygen are readily available to the embryo.

  9. Let’s work it out, doubling each time:

 1) 2 2) 4 = 22 3) 8 = 23

 4) 16 = 24

 5) 32 = 25

 …so on.

The first power of two which is > 100,000,000,000,000 is 247, so our answer is 47

divisions. It would take about 47 cell divisions for one zygote to grow into an organism

with 100 trillion cells.

10. In humans, usually only one egg is released at a time from women ovaries. When two

are released, both may become fertilised by separate sperm and implant in the uterus.

They may be of the same or different sexes. Various types of assisted reproductive

technologies routinely create dizygotic twins, triplets and higher numbers of offspring.

     Monozygotic twins or identical twins arise from a single fertilised egg. At some point

after the zygote begins to divide, the cell mass splits into two, creating two embryos

from one. Monozygotic twins are always of the same sex and they look identical.