Biology For Class X - Chapter No. 5 - Reproduction- Long Question Answers

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CHAPTER 5: REPRODUCTION
DETAILED NOTES

C. EXTENSIVE RESPONSE QUESTIONS

Q.No1: Define Reproduction and its types? Also Describe natural asexual reproduction in plants.
Ans: REPRODUCTION:
Reproduction is the most fundamental function of living things. It is essential for continuing and survival of the species.
Definition:
The process through which organisms produce young ones of their own kind to maintain their species is called Reproduction.

TYPES OF REPRODUCTION:
There are two types of reproduction.
1. Asexual Reproduction
2. Sexual Reproduction

1. Asexual Reproduction:
The type of reproduction in which fusion of gametes does not take place and requires only a single parental organism and the offspring produced are exact copies of their parents is called Asexual Reproduction.

2. Sexual Reproduction:
The types of reproduction which takes place by the fusion of male and female gametes (specialized haploid sex cells) to form a zygote (single diploid cell), and usually two parents of opposite sexes are involved and the off springs are not exactly similar to any one of the parent is called sexual reproduction.

NATURAL ASEXUAL REPRODUCTION IN PLANTS:
Plants reproduce asexually by following methods

1. By Fission
2. Budding
3. By spores
4. Vegetative propagation

1. By Fission (Splitting):

• It is the simplest and fastest mode of asexual reproduction.
• It is also called fission because the cell splits into two or more cells.
• In this method there is replication of genetic material (Prokaryotes) or division of the nucleus (Eukaryotes) followed by division of cell (parent body) into independent daughter cells.
• Each daughter cell receives equal amount of nucleic or genetic material.

Types Of Fission:
Fission is of two types:

• a) Binary fission:
  When a mother cell divides into two daughter cells under favorable conditions of temperature, nutrition and moisture it is called binary fission.
  Example:
  It takes place in bacteria, single bacterium divides into two bacteria within 20 minutes and numerous bacteria are produced within very short interval of time.
• b. Multiple fission:
  When a mother cell divides into more than two daughter cells it is referred as multiple fission.

(ii) Budding:

• Budding is the method of asexual reproduction where a small out growth or bud is formed by parent cell.
• This bud is detach from parent cell and grows into new organism.
• Example:
  It takes place in yeast and plants.
  

(iii) By Spores:

• An asexual reproductive structure called sporangium is developed on the body of an organism.
• These sporangia produce numerous unicellular spores.
• Spores are very small and light and are dispersed easily by wind. Their thick, resistant walls enable them to survive in unfavorable conditions.
• When these spores drop on proper substratum, they develop into new organism in favorable conditions.
• Example:
  This type of reproduction occurs in bacteria, protozoans, algae, fungi, mosses and fern as well as in plants.

 

iv) Vegetative Propagation:

• When a new plant develops from tissue or organs of a plant or outgrowth of a plant. This type of reproduction is called Vegetative Propagation.
• It occurs usually due to the accumulation of large amount of reserve food and consequent growth of the vegetative parts.
• New plants can be produced from vegetative structures (non-reproductive part of plant) like thallus, roots, stems, suckers and leaves.
• These parts sooner or later separated from parent plant. These specialized vegetative organs are morphologically different in different cases but usually in all cases they bear one or more bud which develops into new plants.

By stem: In many plants, the stem has buds that can start new offspring .These type of stems that can reproduce are recognized as runners, bulbs, rhizome, tubers, and suckers.
e.g.

• Runner (Grass and strawberry), stolen (mint), rhizomes (ginger), daffodils etc.
• Bulb (onion and garlic), stem tuber (potato), Bulbil (Bryophyllus)

Leaves: Some leaves have bud on their margin which give rise to an adventitious root when fall on ground or come in contact with soil. After some time these parts of leaves develop into an independent plant.
e.g.

• Bryophyllum

Roots: new plant emerges out of swollen modified root known as tuber.
e.g.

• Root tubers (sweet potato),
• Phylloclades (Opuntia)

Suckers:
Suckers are root sprouts. These are plants stem that arise from buds on the base of stem or root of parent plant that use suckers. Suckers grow and form a dense compost mats that is attached to parent plant. Too many suckers can lead to a small crop.
e.g.

• Apple,
• Elm and
• Banana tree etc.

Q No.2: Describe artificial vegetative propagation and discuss its methods?
Ans: Artificial Propagation:
It is the method of development of new plant with the help of human efforts. Artificial propagation can occur from cells, tissues, cutting of stem etc.

Methods of Artificial Vegetative Propagation:
It takes place by:

1. Cutting,
2. Grafting and
3. Cloning (Tissue culture technology)
4. Apomixes (Parthenogenesis)

i. By Cutting:

• In this method stem or branch having 2-3 nodes and buds is cut from the plant obliquely .
•  It is then embedded in soil with at least one node above the soil.
•  The adventitious roots and shoots grow from buds below and above the soil respectively forming a new plant.
• Examples include: Sugar cane, sweet potato and rose.

ii. By Grafting:

• This is a technique a branch from a desired variety of plant is joined to another plant with well-established root system. 
• The plant from which the branch is taken is called Scion and the plant to which it is joined is called Stock.
• The two plants involved are normally the different varieties of same species.
• Examples are Orange, lime and mango.

iii. Cloning (Tissue Culture Technology or Test Tube Cloning):

• Tissue culture or cloning is a special technique which is used to produce varieties of plants.
• By this technique, a group of genetically identical offspring produced by asexual method called Clones.
• The tissue of selected plants are cultured using their ability of asexual reproduction in test tube or dishes.
• To speed up the growth, hormones are added in the growth medium. After some time the baby plant is transferred to field for large commercial scale production.

iv. Apomixes (Parthenogenesis)
The modified form of asexual reproduction in which seeds are formed without fertilization is called Apomixis.

OR

Apomixes is the type of seed production in which embryo develops without fusion of male and female gametes (i.e in the absence of fertilization.). It is the type of Parthenogenesis which is a natural form of asexual reproduction.

Mechanism:
In apomixis, a diploid cell in the ovule gives rise to the embryo without any fertilization and the ovules mature into the seeds. The resulting offspring can be either haploid or diploid depending on the process and the species.
It is considered as asexual reproduction, because this process does not require fusion of male and female gametes to produce offspring and new genetic combination does not occur.
Example:

• Most commonly found in plants and invertebrates.
• In Dandelions and other plants seed formation take place without fertilization.

Q No.3: Define angiosperm? Describe the structure of a sexual reproductive organ of a plant?
Ans: Angiosperms:
The group of plants that give rise to traditional flowers are called angiosperms. Therefore all angiosperms are called flowering plants. In these plants sexual reproduction takes place through flower.

Structure Of A Flower:
Flower is the reproductive part of plant, which is actually the modified form of shoot.
Function:
Flower is highly modified shoot and is responsible for reproduction by producing seeds within fruits.
Structure:
Pedicle: It is a small stalk on which flower is borne.
Thalamus Or Receptacle: It is a base of a flower on which all the four whorls of a flower are attached.

External wheels of leaves
A flower comprises the following parts:
1. Calyx:

• It is the outermost whorl of a flower. It comprises of units called sepals.
• Function: It protects the flower when in bud.

2. Corolla:

• It consists of many numbers of petals and it is the second whorl of the flower.
• Function: It attracts insects for pollination.

Inner wheels of leaves:
3. Androecium:

• It is the male reproductive part of a flower, comprising of stamens.
• Each stamen consist of filament (stalk) and anther.
• Anther contains pollen grains.
• Function: The stamens are responsible for the production of pollen grains which are male gametes.

4. Gynoecium:

• It is the female reproductive organ and the last whirl of the flower. It is composed of carpel or pistil.
• Each carpel consists of stigma (stalk), style and ovary.
• Funstion: Carpels produce ovule in ovary.

Q No.4: Describe the structure of ovule with the help of a labelled diagram.
Ans: Structure of Ovule:

• Nucellus:
  It is the main cellular body of ovule.
• Integuments:
  The outer and inner coats which surround the nucellus are the outer and inner integuments.
• Micropyle:
  It is a small opening present at the apex of the integument.
• Funicle:
  The stalk of the ovule with which it is attached to ovary wall is called the funicle.
• Chalaza:
  These are the tissues between nucellus and funicle.
• Embryo sac:
  There is a large oval cell embedded in the nucellus which form embryo sac (female gametophyte). The mature embryo sac consists of 7 cells i.e. one Ovum, two synergids, three antipodals cells and one secondary nucleus in numbers while a diploid cell is a fusion nucleus in the center.

Q No.5: Describe the structure of pollen grains? Also Describe the process of sexual reproduction in a flowering plants?
Ans: Structure of pollen grain:

• The pollen grains are loose ,dusty powder which develop from microspore in the pollen sac of anther.
• Each pollen grain is 4 celled structure, bounded by a wall of 2 layers.
  Exine: It is the outer layer of wall.
  Intine: It is the inner layer of wall.

Process Of Sexual Reproduction In A Flowering Plants:
In angiospermic plants the main part is sporophyte which consists of two parts:
Vegetative Parts:
They include

1. Root,
2. Stem and
3. Leaves

Floral parts:
These include

1. Flower,
2. Fruit and
3. Seed

The floral part is the reproductive part. After two processes i.e. pollination and fertilization, it produces seed within fruit. The seeds when disperse germinate into baby plant called seedling, when matures, it become a new plant like its parents. In flower androecium and gynoecium takes part in sexual reproduction.

Androecium:

• In flower androecium (male part) consists of stamen (microsporophyll) and has 2 to 4 pollen sac (microsporangia) in its anther.
• These pollen sacs are filled with microspore mother cells which produce microspore by meiotic cell division.
• Each unicellular microspore divide its cells by mitosis and produce 2 to 4 cells, in this way unicellular microspore become pollen grain (multicellular) but each of its cell is haploid.
• When anther burst these pollen grains disperse in nature.

Gynoecium:

• On the other hand each carpel (megasporophyll) has one or more ovules (megasporangium) in its ovary.
• Each ovule has single megaspore mother cell.
• This megaspore mother cell is divided by meiosis to produce 4 haploid megaspores.
• Only one will survive and develops into embryo sac (female gametophyte) inside ovule, which consists of 7 cells.
• The pollen grain disperse if dropped at the stigma of carpel, fertilization takes place and zygote (2N) is formed which develop to form embryo and the life cycle remain continues.

Q No.6: Define pollination and its types in detail.
Ans: POLLINATION:
Definition
The transfer of pollen grains from another to the stigma of carpel is called pollination.

Types of Pollination
There are two types of pollination

1. Self pollination
2. Cross pollination

1. Self Pollination:
The transfer of pollen grains from anther of stamen to the stigma of same flower or flowers on same plant is called self pollination.

2. Cross Pollination:
The transfer of pollen grains from anther of one flower to the stigma of another flower belongs to another plant of same species is called cross pollination.

Agents of cross pollination:
Cross pollination is more common than self pollination, the pollen grains are carried from one flower to another through following agents.

• Wind
• Water
• Insects
• Animals

Mechanism :

1. Pollen grain drops at stigma, it starts its development into pollen tube (male gametophyte).
2. The pollen tube consists of 6 haploid cells, among them two are prothallial cells, two are male gametes, one stalk nucleus and one tube nucleus.
3. The pollen tube grows from stigma to ovule through style and transfers two male gametes in ovule through micropyle which ultimately reach to embryo sac.
4. One sperm nucleus fuses with ovum to produce diploid (2N) zygote while other gamete fuses with secondary nucleus to form 3N (Triploid) cell which later develop into endosperm of seed. This type of fertilization is called double fertilization, which is the characteristic feature of angiospermic plant.
5. The 2N zygote after successive mitotic divisions develops into an embryo within the embryo sac.
6. The triploid (3N) secondary nucleus develops into endosperm.
7. The endosperm provides nourishment to the developing embryo.
8. During this development the ovule develops into seed.
9. The integument develop into seed coat.
10. Zygote form small embryo and cotyledon.
11. The ovary outside ovule become swollen due to mitotic cell division and become fruit. The fruit is eaten by animal or decay, the seeds come out, disperse or dropped in soil. In favorable conditions, it germinates and grows into new baby plant.

Q No.7: How is fruit formed?
Ans: Mechanism Of Fruit Formation:

1. The ovary enlarges to form a fruit, containing seed or seeds.
2. The stigma and style disappear.
3. The stamens and petals are usually lost after pollination.
4. In some cases, sepals remain attached with fruit e.g. brinjal.
5. The endosperm provides nourishment to develop embryo.
6. It also stores energy in grains which can be utilized by us or other animals.

Q No.8: Discuss the adaptation in the structure of wind and insect pollinated flowers. OR Give adaptive characters of wind and insect pollinated flowers.
Ans: Plants have adapt themselves according to the agent of pollination in the following ways:

Adaptive characters of wind and water pollinated plants:

1. The flowers of these plants are non- attractive, small in size and do not bear any odour.
2. They produce pollen grains in high quantity.
3. The pollen grains are very light in weight, some of them bear wings and some have parachute like structure.
4. They do not produce high quantity of nectar.

Adaptive character in insect pollinated plants.

1. The flowers are large in size.
2. They have bright coloured petals or sepals or bracts.
3. The pollen grains have sticky substance or hooks.
4. They produce special odour.
5. They produce high quantity of nectar.

Q No.9: Describe the structure of seed with reference to maize grain
Ans: SEED:
Seed may be defined as a ripened ovule or a part of a plant body in which embryo lives in dormant condition.

STRUCTURE OF SEED
Seed can be divided into the following parts:

1. Seed coat
2. Embryo
3. Cotyledon
4. Sometimes endosperm

1. Seed Coat:
The seed is covered from outside by a coat called Seed Coat. The seed coat is formed by integuments. It is made up of two layers.

• Testa: The outer thicker layer is called Testa.
• Tegmen: The inner thin layer is called Tegmen.

Hilum: The hilum is a scar, present at seed coat.
Micropyle: It is a very small hole through which the water enters the seed coat.

2. Embryo:
The embryo develops from diploid zygote. It is a small axis, lying between two Cotyledons.
Plumule: the upper end called plumule and
Radicle: the other lower end is called radicle.
During germination plumule develops into shoot while radical develops into root.

3. Cotyledon:
The seed also contain leaf like structure called cotyledon . These are either one or two. On the basis of these numbers the seeds are classified into

• Monocot: Seeds having one cotyledon
• Dicot: Seeds having two cotyledons

4. Endosperm:
In endospermic seeds the cotyledons are thin and paper like.
In many of the seeds endosperm is not present than food is stored in cotyledons therefore they become swollen and thick e.g pea.

STRUCTURE OF BEAN SEED

(DICOT)

MAIZE GRAIN:

• In maize grain which has monocot seed, the ripened ovary wall get fused permanently with seed coat is called pericarp.
•  Internally maize grain is divided into two unequal parts by a thin layer of cells called epithelium.
• The larger portion is the endosperm and the smaller is embryo.
• In the embryonic part, a shield shaped cotyledon is present called scutellum.
• Moreover the plmule and radicle are enclosed in protective sheath called coleoptile and coleorhiza, respectively.

STRUCTURE OF MAIZE GRAIN

(MONOCOT)

Q No.10: What is germination and its types . Also write about conditions necessary for germination. OR What is germination? Give the condition of germination also describe the methods of different germination.
Ans: GERMINATION:
The process in which dormant or sleeping embryo awakes up renews its life and develops into a seeding is called as Germination.

OR

Breaking of seed dormancy is called seed germination. As a result of germination seed develops into seedling.

KINDS OR METHODS OF GERMINATION:
Seed can germinate in two ways i.e.

1. Epigeal Germination
2. Hypogeal Germination

1. Epigeal Germination:

• Epi = above, geo = earth.
  The cotyledons are brought on the surface of the soil along with the shoot.
• The hypocotyl has a curved terminal part to protect the plumule as it comes out of the soil.
• The hypocotyl grows excessively to bring the cotyledons out of the soil.
• The hypocotyl grow in the form of arch.
• The plumule comes out of the seed by the elongation of the hypocotyl.
• The growth rate of hypocotyl is higher than epicotyl.
• The energy for the growth comes from the cotyledons.
• Epicotyl is short.
• The cotyledons turn green when come above the soil and work as first foliage leaves and perform photosynthesis.
• It is generally shown by the dicot seeds.
• It occurs in beans, onion, papaya, castor, etc.

2. Hypogeal Germination:

• Hypo = below, geo = earth.
  Cotyledons remain below the soil surface.
• The epicotyl has a curved terminal part to protect the plumule from friction in soil particles.
• The hypocotyl does not show much elongation.
• The hypocotyl does not grow in the form of arch.
• The plumule comes out of the seed by the elongation of the epicotyl.
• The growth rate of epicotyl is higher than hypocotyl.
• The energy primarily comes from the endosperm.
• Epicotyl is long.
• The cotyledons do not turn green and have no role in photosynthesis.
• It is generally shown by the monocot seeds.
• It occurs in coconut, gram, maize, etc.

CONDITIONS NECESSARU FOR SEED GERMINATION:
Only living seeds can germinate, require optimum condition of water, oxygen and favourable temperature for germination.

(i) Role of water (Moisture):

• All metabolic activities depend on water, therefore water has vital importance for life. During germination the presence of water has the following effects:
• Seed coat become soft by water.
• Cotyledons and endosperm absorb water become swollen and exert pressure on seed coat to break.
• The embryo comes out to grow.
• Enzymes become activated by water.
• Solid reserve food changes into solution.

(ii) Role of oxygen:
The metabolic activities require energy. Energy is produced during respiration which requires oxygen.

(iii) Temperature:

• Enzymes activity require certain range of temperature.
• Most of the seeds require the temperature range between 25 to 37 °C.
• Seeds do not germinate at temperature below 0 °C or above 45 °C.

Q No.11: Write a note on Asexual reproduction in animals? OR Describe different types of asexual reproduction in animals?
Ans: ASEXUAL REPRODUCTION IN ANIMALS:
Asexual reproduction occurs in many ways. The common type in animals are:

1. Fission (Spitting)
2. Budding
3. Fragmentation

1. Fission (Spitting):
The simplest type of asexual reproduction in which parent body divides into two or more parts and each of which develop into a new individuals is called Fission.

OR

Splitting of cell into two or many cells or organisms called fission.

Types of Fission
There are two types of fission

1. Binary Fission:
   The type of fission where an organism divides into two organisms is called binary fission.
   During this process the nucleus of the parent organism divides into two nuclei, both of them move in opposite directions in the cytoplasm. Meanwhile, a constriction appears in cytoplasm which deepens from outside to inside finally organism divides into two organisms.
   Example: It is commonly observed in unicellular organisms like protozoa.
   
   
2. Multiple Fission:
   The type of fission in which parent body divides into more than two daughter organisms is called multiple fission.
   
   OR
   Multiple fission involves the division of an organism into many small sized daughter organisms.
   Example: It occurs in unicellular organisms like amoeba, paramecium and plasmodium during unfavourable conditions.

2. Budding:
The type of asexual reproduction in which one or two small outgrowth develops on the body surface of parent body (organism) called bud which after some growth, separates from the parent body and develops into new individual is called budding.
Example: Budding is common in sponges, hydra and corals.

3. Fragmentation:
The type of asexual reproduction in which parent body (living organism) splits off into fragments (many pieces) and each fragment recovers its lost part by regeneration and develops into new complete individuals is called fragmentation.
Example: It is found in lower, multicellular animals like liver fluke and nematodes. It is also common in sponges.

Q No.12: Explain Sexual reproduction in animals?
Ans: SEXUAL REPRODUCTION:
The process of sexual reproduction involves fusion of specialized haploid sex-cells or gametes to form a single diploid cell, zygote (2N).

Necessities of Sexual Reproduction:
Sexual reproduction is a complicated process and it occurs in following steps:

1. Gametogenesis
2. Mating
3. Fertilization

1. Gametogenesis:
The process of formation of sex-cell (gametes) is called Gametogenesis.

Types of Gametogenesis:
There are two types of gametogenesis
i. Spermetogenesis:
The process of gametogenesis which involves the formation of male gamete i.e. sperm is called spermatogenesis.

ii. Oogenesis:
The process of gametogenesis which involves the formation of female gamete i.e. ovum or egg cell in female gonads (ovary) is called Oogenesis. This involves meiosis which reduces number of chromosomes to half in gametes. It also results variation in genes by process called crossing over .These gametes mostly do not have identical genetic make up.

2. Mating:
the process of union of male and female organisms to collect their gametes at same place is called mating.

3. Fertilization:
Fusion of male and female gametes to form diploid zygote (2N) is called fertilization.

Q No.13: Name the male and female reproductive organs of rabbit. Also draw diagram.
Ans: Male and Female Reproductive Organs Of Rabbit

S.NO.	Male	Female
Gonads  (Gametes producing organs)	Testes two in numbers. Hanging outside, in a sac called scrotal sac. Contain seminiferous tubules. Epididymis to collect sperm.	Ovaries two in numbers. Located in abdominal cavity. Produce ovum.
Duct  (Gametes collecting tubes)	Vas deferens, two in number.	Oviduct or fallopian tube collect ovum from ovary. Two in number
Genitals  (Gametes depositing or receiving organs)	Penis, a muscular organ to transfer semen into female genital.	Vagina, a tube which receive semen containing many sperms.
Glands	Prostate gland Cowper's gland Seminal vesicle	Ovary works as gland as well

MALE REPRODUCTIVE ORGANS OF RABBIT

FEMALE REPRODUCTIVE ORGANS OF RABBIT

Q No.14: What do you know about fertilization and its types?
Ans: FERTILIZATION:
The process of fusion of male and female gametes from diploid zygote is called fertilization.

Types of fertilization:
On the basis of location of fertilization there are two types of fertilization,

• external fertilization and
• internal fertilization.

S.NO.	EXTERNAL FERTILIZATION	INTERNAL FERTILIZATION
1.	It takes place outside the body.	It takes place inside the body of female.
2.	It takes place in water.	It takes place inside female body.
3.	Both gametes mature at same time.	Gametes may mature after each other.
4.	Gametes are produced in large numbers.	Gametes are produced in limited numbers.
5.	It takes place in fishes and amphibians.	It takes place in reptiles, aves and mammals.

Q No.15: Describe the process of Spermetogenesis.
Ans: SPERMATOGENESIS:
A male gametogenesis process in which formation of sperm in male gonads (Testis) from germ cells takes place is called spermatogenesis.

PROCESS OF SPERMATOGENESIS:
It undergoes following steps:

1. Spermatogonia (2n):
   Spermatogonia in the testis can undergo repeated rounds of mitosis to produce more spermatogonia (singular: Spermatogonium).
   
   
2. Primary Spermatocyte (2n):
   A Spermatogonium (2n) may enter prophase I (first stage of meiosis I) becoming a primary spermatocyte (2n).
   
   
3. Secondary Spermatocyte (n):
   Each primary spermatocyte (2n) completes meiosis I to produce two secondary spermatocyte (n).
   
   
4. Haploid Spermatids (n):
   Secondary spermatocyte (n) then undergoes meiosis II toproduce two haploid spermatids (n).
   
   
5. Sperm (n):
   Each spermatids (n) mature into sperms (n), which are male gametes.