Bihar Board Class 12 Biology Solutions Chapter 1 Reproduction in Organisms Textbook Questions and Answers, Additional Important Questions, Notes.
BSEB Bihar Board Class 12 Biology Solutions Chapter 1 Reproduction in Organisms
Bihar Board Class 12 Biology Reproduction in Organisms Text Book Questions and answers
Why is reproduction essential for organisms?
Reproduction is the ability of all living organisms to produce young ones (offsprings) similar to themselves in most of characters. The offsprings grow, mature and produce new offsprings thus completing the cycle of birth, growth and death. This way reproduction enables the continuity of the species generation after generation.
Which is better mode of reproduction sexual or asexual? Why.
Sexual reproduction is a better mode of reproduction because though the events of sexual reproduction and elaborate and complex but they follow a regular sequence.
Why is the offspring formed by asexual reproduction referred to as clone?
Asexual reproduction does not involve the formation or fusion of gametes. Thus, a single parent is capable of producing offsprings. The offsprings so produced are identical to each other and are exact copies of their parent. They are morphologically and genetically similar individuals so they are referred to as clone.
Offspring formed due to sexual reproduction have better chances of survival, why? Is this statement always true?
Sexual reproduction involves the formation and fusion of gametes. These gametes are male and female either from same individual or by different individuals of the opposite sex. These gametes fuse (syngamy) to form zygote which develops to form new organism. This way the offsprings are not identical to themselves or to their parents.
These offsprings are genetically different from their parents as variations appear due to new combinations of genes during crossing over, chance seggregation of chromosomes and chance fusion of gametes. Thus there are more chances of elimination of unfavourable traits in sexual reproduction so giving better survival to the offsprings. No, the above statement is not always true. If the mother is suffering from any major disease or any other aliment the offspring may not survive.
How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
In asexual reproduction the participation of two organisms is not required, no gametes are formed. Somatic cells of the parent undergo mitotic divisions and produce the offsprings. So the next generation will be the exact copy of the parent.
Sexual reproduction is generally biparental. It involves the production of specialized sex cells i.e. male and female gametes. They undergo fusion and form zygote. It involves the process of fertilization. During fertilization both the parental traits fuse and variations appear. The offsprings are genetically different from the parents-. Thus giving better chances of survival for the most favourable ones. It plays important role in evolution.
Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
|Asexual reproduction||Sexual reproduction|
|(1) Always uniparental reproduction.||(1) Generally hiparental except Taenia. Fasciola.|
|(2) No gametes are formed.||(2) Male and female gametes are formed.|
|(3) It involves only mitotic divisions.||(3) Meiosis occurs at the time of gamete formation and mitosis occurs after fertilization.|
|(4) No fusion of gametes Occurs.||(4) Male and female gametes fuse to form zygote.|
|(5) Offsprings are genetically similar to the parents.||(5) Offsprings are genetically different from the parent.|
|(6) Rate of reproduction is faster.||(6) Rate of reproduction is slower.|
|(7) Units of reproduction can he whole parent body or bud or body fragment.||(7) Unit of reproduction are gametes.|
|(8) Occurs in lower invertebrates and lower chordates and plants with simple organisations.||(8) Found in higher plants and animals.|
In plants, the asexual mode of reproduction is referred to as vegetative reproduction. It takes place with the help of propagules such as runner, rhizome, sucker, tuber, offset and bulb. Formation of propagules does not involve two parents so vegetative reproduction is considered as asexual reproduction.
What is vegetative propagation? Give two suitable examples.
In plants, the term vegetative propagation is used to denote asexual mode of reproduction. This does not occur by gamete formation, single parent can reproduce by vegetative propagules for example runners, rhizome, sucker, tuber, offset and bulbs. Examples are eyes of potato; rhizome of ginger. These are nodes from the modified stems of these plants. Under favourable conditions, they produce roots and new plants.
8. Define:(i) Juvenile phase, (ii) Reproductive phase, (iii) Senescent phase.
(i) Juvenile phase: All organisms have to reach a certain stage of growth and maturity in their life before they can be sexually active. This first phase of growth is called the juvenile phase or vegetative phase in plants.
(ii) Reproductive phase: When the juvenile phase is over the organisms enter the period of reproductive phase or sexual maturity. It is indicated by showing various morphological and physiological changes such as development of secondary sexual characters in animals and by flowering in plants. This is the actual period of the life span of any organism when it is capable of producing offsprings. This phase is of variable duration in different organisms.
(iii) Senescent phase: This is the final and third stage of growth cycle. It can be considered as the end of reproductive phase. It is accompanied by reduction in functional capacity and increase in cellular break down and metabolic failures. It ultimately leads to death.
Higher organisms have resorted to sexual reproduction in spite of its complexity, why?
In sexual reproduction separate male and female gametes fuse to form, a zygote which develops to form embryo and later, a complete organism. It is an elaborate and complex process. It involves slow multiplication and units of reproduction are haploid gametes. Since, the offsprings are genetically different from the parents as variations appear due to new genetic combinations during crossing over, chance segregation of chromosomes and chance fusion of gametes so better chances of survival are there in the next generation. This leads to selection of better traits at each generation and ultimately to the evolution.
Explain why meiosis and gametogenesis are always interlinked?
Meiosis and gametogenesis both processes occur in sexually reproducing organisms. The parent body is deploid (2n) at the time of reproduction. Sexual reproduction involves fusion of male and female gametes, which must be haploid (n) to form a zygote (2n). So, meiosis occurs at gametogenesis stage to produce haploid gametes. This way meiosis and gametogenesis are always interlinked.
Identify each part in a flowering plant and write whether it is haploid (n) diploid (2n).
(a) Ovary – haploid (n)
(b) Anther – haploid (n)
(c) egg – diploid (2)
(d) Pollen – haploid (n)
(e) Male gamete – haploid (n)
(f) Zygote – diploid (2n)
Define external fertilization. Mention its disadvantages.
Fertilization involves the fusion of haploid male and female gametes to form diploid zygote. When fertilization takes place outside the parent body i.e. in external medium such as water, it is termed as external fertilization, e.g. majority of algae, fishes and amphibians.
Its major disadvantages are :
- A large number of gametes are required.
- A large number of offsprings are produced.
- Chances of gametic fusion are less.
- Offsprings are vulnerable to predators.
- Very few offsprings survive due to lack of proper parental care.
Differentiate between a zoospore and a zygote.
|(1) They are involved with asexual reproduction.||(1) They are involved in sexual reproduction.|
|(2) Zoospores are formed in simple plants, algae or fungi.||(2) Zygote is formed in complex organisms.|
|(3) They are microscopic motile structures formed from parent body. No gametic fusion is involved.||(3) This is formed as a result of fusion of male and female gametes.|
|(4) They are mobile structures.||(4) This is generally not mobile structure.|
Differentiate between gametogenesis from embryogenesis.
|(1) Gametogenesis involves the formation of haploid gametes in the gonads.||(1) Embryogenesis involves the transformation of zygote into a multicellular organism.|
|(2) It leads to fertilization.||(2) It leads to birth.|
|(3) It is of two types :
(a) spermatogenesis, and
|(3) It is a complex process which involves
|(4) It is variable in different organisms.||(4) It includes a definite series of phases which are fundamentally similar in all sexually reproducing organisms.|
Describe the post-fertilization changes in a flower.
After double fertilization, the major events during post-fertilization are as such :
- Development of endosperm.
- Development of embryo.
- Development of seed from ovule.
- Development of fruit from ovary.
(i) Development of endosperm is from triploid primary endosperm nucleus in the central ceil of embryosac. It is a food-filled tissue to provide nutrients to the growing embryo. It is formed as a result of triple fusion i.e. the fusion of a male gamete with secondary nucleus of the central cell. Based on its subsequent divisions it may be: nuclear endosperm, cellular endosperm and helobial endosperm.
(ii) Development of embryo: The fertilized egg or zygote divides into two cells, a large basal suspensor cell and a smaller terminal embryonal cell. Further divisions take place and embryonal or epileasal ceil divides separately to form a row of 4-8 ceils. The terminal cell divides to form a cluster of cells called proembryo. The hypobasal cell and other cells divide and form suspensor. The terminal cell enlarges and form hypophysis. The lowermost cell of suspensor develops into the apex or radicle. The proembryo cell divides and form embryo after two successive divisions. Further divisions in the embryo form embryo proper. Its terminal cells form plumule and cotyledons. The process is shown in the following figure.
(iii) Development of seed: After double fertilization ovule develops into seed In its development, the zygote develops into an embryo, and the endosperm is formed, the nucellus is either used up during embryo development or form a thin layer called perisperm; testa and tegmen, two seed coats are formed.
(iv) Development of fruit: A true fruit is formed in the ovary by cell division, expansion and differentiation. The ovules inside the ovary are transformed into seeds and wall of ovary makes pericarp (fruit wall).
What is a bisexual flower? Collect 5 bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
Flowers which contain both stamen and pistil are called hermaphrodite or bisexual flowers, e.g. Sweet potato. (For second answer consult your school teacher).
Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers.
Students are advised to do it themselves with the help of their teacher. Corn, papaya produce unisexual flowers.
Why are offsprings of oviparous animals at a greater risk as compared to offspring of viviparous animals?
In oviparous animals, the development of zygote takes place outside the body of the female parent i.e. they lay fertilized egg in safe environment. These egg are covered by hard calcareous shells and hatch young ones after a period of incubation. Because of lack of proper parental care and risk of predators the offsprings of oviparous animals are at a greater risk for survival.
On the other hand, in viviparous animals, the zygote develops into a youflgone inside the body of the female organism. After attaining a certain age of growth, the young ones are delivered out of the body of the female organism. Thus, due to proper embryonic care and protection, the chances of survival of young ones is greater in viviparous organisms.
Bihar Board Class 1 Biology Reproduction in Organisms Additional Important Questions and Answers
Very Short Answer Type Questions
Name different types of asexual reproduction.
Types of asexual reproduction are budding, fission and fragmentation.
What does regulate the growth, maintenance and functions of the primary sex organs?
The gonadotropins of the anterior pituitary regulate the functions of the primary sex organs.
What is Cryptorchidism?
It is failure of testes to descend into the scrotum.
What is Hyaluronidase?
Hyaluronidase assists the entry of sperm in the ovum.
Mammalian follicle was first discovered by?
Mammalian follicle was first discovered by De Graf.
In the life cycle of honeybee, which individuals are produced parthenogenetically?
In honey bees male i.e. the drones are produced parthenogenetically.
Puberty is the term used for the period when the sexual maturity is attained in the human male or human female.
Name the primary and secondary sex organs of female.
These are ovaries, uterus, vagina and fallopian tube.
What do you mean by polyembryony?
Polyembryony is when many young ones are formed from same zygote.
Name two basic processes involved in sexual reproduction.
These are gametogenesis and syngamy.
Where are Leydig’s cells located?
Leydig’s cells are located between the seminiferous tubules of the testis.
What is full form of AIH?
AIH stands for Artificial Insemination Husband.
What is gestation period?
This is the period between fertilization of ova and birth of young individuals.
Give the typical terms for birth canal and fertilization canal.
Birth canal: Vagina
Fertilization canal: Fallopian tube.
Why is ovum non-motile?
Ovum is non-motile because its fully laden with food material.
What is teratogen?
Teratogens are chemical agents which may cause malformations in the developing embryo.
Name three phases of gametogenesis?
Three phases of gametogenesis are multiplicative phase, growth phase and maturation phase.
What is the source of middle piece of sperm?
Mitochondria of spermatid is the source of its .middle piece.
What is Antrum?
Antrum is the cavity present in the grafifian follicle.
This is the degenerative process by which eggs are lost from the ovary.
Short Answer Type Questions
Define gametogenesis. List two types of gametogenesis. Tabulate the differences between them.
Gametogenesis is the process of formation and differentiation of haploid gametes (Sperms and ova) from the diploid primary germ cells, gametogonia present in primary sex organs called gonads.
Its of two types : (i) Spermatogenesis and (ii) Oogenesis.
|(1) It occurs in seminiferous tubules of testes.||(1) It occurs in ovaries.|
|(2) One spermatogonium forms 4 haploid sperms.||(2) One oogonium forms only one ovum.|
|(3) No yolk is synthesized in growth phase.||(3) Vitellogenesis occurs in growth phase.|
|(4) Sperm is much smaller than spermatogonium.||(4) Ovum is much larger than oogonium.|
|(5) Nucleus becomes condensed.||(5) Nucleus is bloated.|
Give reasons for the following :
(i) Amoeba is immortal.
(ii) Testes lie outside the body cavity in scrotal sacs.
(i) Amoeba is immortal: Amoeba reproduce asexually by binary fission. Thus the parent cell divides into two halves and each rapidly grows into an adult. This way the parent will never die, it will keep on splitting and producing exactly similar offsprings.
(ii) Testes lie outside the body cavity in scrotal sacs: Testes are present in thin-walled skin pouches called scrotal sacs and are hanging from lower abdominal wall. Scrotal sacs act as thermoregulators and keep the testicular temperature 2°C lower than body temperature for normal spermatogenesis, as high abdominal temperature kills the spermatogenic tissue.
Gonads possess both cytogenic as well as endocrinal function?
Gonads, i.e., the primary sex organs viz., testes in males and ovaries in females are cytogenic as they produce gametes, i.e., sperms and ova respectively. They are endocrinal as they also secrete sex hormones, i.e., testosterone in males and estrogen and progesterone in females.
Differentiate between the following :
(i) Asexual and sexual reproduction.
(ii) Binary fission and multiple fission.
(iii)Primary and secondary sex organs.
(i) Asexual and sexual reproduction :
|Asexual reproduction||Sexual reproduction|
|(1) Always uniparental.||(1) Generally biparental except Taenia, Fasciola.|
|(2) No gametes are involved.||(2) Male and female gametes are involved.|
|(3) Only mitotic divisions takes place.||(3) Meiosis occurs at game to- genesis. Mitosis occurs after fertilization.|
|(4) Somatic cells are involved.||(4) Germ cells are involved.|
|(5) Offsprings are genetically identical to the parent.||(5) Offsprings are genetically different from the parent.|
(ii) Binary fission and multiple fission :
|Binary fission||Multiple fission|
|(1) Parent divides in two daughters.||(1) Parent divides in many daughters.|
|(2) Takes place during favourable conditions.||(2) Takes place during un-favourable conditions.|
|(3) Whole parent body is consumed, nothing is left.||(3) Residual cytoplasm of parent is left.|
(iii) Primary and secondary sex organs :
|Primary sex organs||Secondary sex organs|
|(1) These form the gametes.||(1) These help in conduction of gambles.|
|(2) They secrete sex hormones.||(2) They do not secrete sex hormones.|
|(3) Their growth, maintenance and functions are controlled by gonadotropins of anterior pituitary.||(3) Their growth, maintenance and functions are controlled by sex hormones secreted by gonads.|
Name the harmonies that control the growth, maintenance and functions of duct system, accessory glands, penis, seminiferous tubules and Leydig cells.
- Testosterone promotes the growth, maintenance and functions of duct system, accessory gland and penis.
- FSH regulates the growth maintenance and functions of seminiferous tubules.
- L.H (Luteinizing Hormones) regulates the growth maintenance and functions of Leydig cells.
Mention the functions of (i) Fallopian tubes, (ii) Uterus and (iii) Vagina.
- Fallopian’ tubes: These conducts the ovum towards the uterus and ovum may be fertilized by a sperm in it.
- Uterus: The fertilized ovum at the blastocyst stage gets implanted on the wall of the uterus and develops into the growing foetus during pregnancy.
- Vagina: It receives the semen from the male during mating. During childbirth, it convey s chi Id to the outside.
Distinguish between Menstrual and Oestrous cycle.
|Menstrual cycle||Oestrous cycle|
|(1) It occurs only in primates.||(1) Occurs in most of the mammals.|
|(2) Menstruation occurs at the end of cycle.||(2) Menstruation does not occur.|
|(3) Endometrium goes out with menstrual flow.||(3) Endometrium is reabsorbed.|
|(4) Copulation can be any time of year.||(4) Copulation occurs only when female in oestrous or heat period.|
Write a note on puberty.
Ans. Puberty is the period of sexual maturity. It comes between 13 to 16 years in the male and between 10 to 14 years in the female. It is controlled by testosterone in the male and estrogens in the female. It is characterized by the development of secondary sexual characters.
What is parthenogenesis?
Parthenogenesis is the development of an unfertilized ovum into a fully formed haploid organism. It is monoparental Le. honey bees, wasps, aphids. The offsprings thus produced are exactly similar to the parents. It permits triploid and aneuploid chromosomal combination. At the same time, it stops the chances of new combinations of genes.
Draw well-labelled diagram of male reproductive system.
Give a diagrammatic representation of female reproductive system.
Name two basic processes involved in sexual reproduction.
Two basic processes involved in sexual reproduction are :
- Gametogenesis: It involves the formation of haploid gametes (sperms and ova) in the primary sex organs called gonads.
- Syngamy: Syngamy (fertilization) involves the complete and permanent fusion of two haploid gametes to form a diploid zygote.
Mention three advantages of sexual reproduction.
Sexual reproduction involves formation and fusion of sex called (gametes). Its main advantages are :
- The haploid (n) gametes fuse together and the chromosome; number of the species (2n) is restored
- Variations are produced in the off-springs.
- Off-springs are better adapted to the environment and leads to evolution.
Differentiate between fission and budding.
|(1) It involves the division of whole organism into more than one new organism. It may be binary fission or multiple fission.||(1) It involves the enlargement of a vegetative a’ bud, which detaches from the parent body to form a new organism.|
|(2) Binary fission may be longitudinal or transverse fission.||(2) A bud is constructed to the parent body.|
|(3) There is neither proliferation nor differentiation of some vegetative cells.||(3) Proliferation and differentiation of some ordinary vegetative ceils e.g. Planaria.
on the body surface form a bud. e.g. Hydra.
Draw diagram to explain the structure of human spermatozoa.
Long Answer Type Questions
What is menstrual cycle? Write down the hormonal control over the menstrual cycle.
The reproductive cycle of human female starts from the age of 13-15 at puberty and stops at the age of 45-49 on the onset of menopause. After the menopause, the ovarian cycle stops and the woman is not able to bear children. In this span of reproductive life, the ovary goes through a cycle of change every month.
This cycle is called the menstrual cycle which is characterised by menstruation, a process in which blood, mucus and uterine tissues are eliminated. The menstrual cycle is regulated by the action of hormones oestrogen and progesterone on the uterine tissue. Oestrogen stimulates the growth of myometrium and endometrium which consists of uterine epithelium glands and connective tissues.
Progesterone acts upon the oestrogen primed endometrium to convert it into actively secreting tissue- which provides favourable environment for implantation of the fertilized ovum. The endometrial changes throughout the normal non-pregnant menstrual cycle which are regulated by the action of oestrogen and progestrone.
Stages of M.C.: Normally a cycle is of 28 days but variations do occur. The cycle is divided into four stages.
1. The soft tissue of inner uterine epithelial lining disintegrates with the result bleeding occurs. The unfertilized eggs and soft tissues are discharged. The discharge continues for 3 to 5 days.
2. Uterine epithelial lining reappears. Maturation of Graafian follicle and ovum inside the ovary takes place. The stage starts at the end of menstration and continues upto 10 to 14 days from the first day of menstruation. ’
3. After 10 to 14 days the mature ovum is released from the Graafian follicle which comes in the fallopian tube.
4. At this stage corpus luteum is formed from the Graafian follicle of released ovum. This secretes hormones. This hormone prepares the uterus for receiving the fertilized ovum. If no fertilization occurs again the uterus lining breaks up and bleeding occurs.
Briefly describe the processes of oogenesis and sperma¬togenesis.
Oogenesis: Ovum is formed by the process of oogenesis in the germinal epithelial cells of the ovary. During oogenesis egg mother cells produces oogonia. Oogonia develops into primary oocytes. The primary oocyte undergoes meitotic division. As a result of which one functional ovum and three polar bodies are produced. From one oocyte only one ovum is produced. The process of oogenesis takes place in three stages :
- Multiplication phase,
- Growth phase, and
- Maturation phase.
Oogonium is diploid. It divides by mitosis division to form oocyte (2N). Only one oocyte enters in growth phase. It is known as primary oocyte. After a long growth phase it enters into maturation phase, where it divides by meiosis to form one secondary oocyte (N), and one polar body (N). Entry of sperm restarts cell cycle and breakdown MPF (M-phase promoting factor) and turning on the APC (Anaphase promoting complex). Secondary oocyte then divides to form one haploid ovum (N) and one polar body while the other polar body forms two polar bodies after dividing.
Spermatogenesis: The process of formation of spermatogoa from the spermatogonia in the male gonad, testis is called spermatogenesis. In it the geminal cell (spermatogonial cell) of testis form spermatogonia (2N). Some of these remain as stem cell (spermatogonia A-type). Some other differentiate into progenitor cells (spermatogonia B-type) after maturation into primary spermatocytes (2N). The primary spermatocytes undergo meiosis to form four spermatids which are transformed into spermatozoa by spermiogenesis. There are three stages of spermato-genesis followed by spermiogenesis.
- Multiplication phase
- Growth phase
- Maturation phase.
Spermatogenesis occurs in the seminiferous tubules of testis.