Question Set B

cbse 12th Standard Biology Human Reproduction Model Questions Papers Study Material - QB365

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Questions:

Case Study Questions

5 x 4 = 20

Study the pedigree chart showing the pattern of inheritance of blood group character in a family.

(a) Give the genotypes of the parents in generation I.
(b) State the possible genotypes of the individuals.
(i) X in generation II.
(ii) Y in generation III.
(c) How does the inheritance of this blood group explain codominance?

In pea plants, let symbol Y represent dominant yellow, symbol y, the recessive green, symbol R, the round seed shape, and symbol r, the wrinkled seed shape. A typical Mendelian dihybrid cross was carried out starting with homozygous dominant and recessive parents.
Answer the following questions.
(a) Write the genotype and phenotype of the F₁offspring.
(b) The genetic make up of the gametes produced by F₁individual.
(c) Give the phenotypic ratio of F₂ generation.

ABO blood group character in human population exhibits four possible phenotypes and six different genotypes. Explain the different mechanisms of inheritance involved in exhibiting the possibility of four phenotypes and six genotypes.

Two independent monohybrid crosses were carried out involving a tall pea plant with a dwarf pea plant. In the first cross, the offspring population had equal number of tall and dwarf plants, whereas in the second cross, it was different. Work out the crosses and explain giving reasons for the difference in the offspring populations.

Look at the cross given above and answer the following questions:
(a) Give the genotypes of A, B, C and D.
(b) Write the phenotypic ratio.
(c) What type of a cross is this?

Assertion and reason

17 x 1 = 17

Assertion: Reusable contraceptives are not full proof method of contraceptions.
Reason: Diaphragms, cervical caps and vaults are barrier methods which prevent conceptions by blocking entry of sperms through cervix. They are reusable.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Assertion: Barrier methods prevent physical meeting of sperms and ova.
Reason: This prevents conception.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Assertion: Periodic abstinence is a method in which couples avoid from coitus from day 17 to 27 of menstrual cycle.
Reason: It is a very effective method and 100% sure of birth control.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Assertion: Natality increases both population density and population size.
Reason: Natality increases the number of individuals in an area by births.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

10.

Assertion: Introduction of sex education in schools should be encouraged.
Reason: This will encourage children to believe in myths about sex related aspects.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

11.

Assertion : Chasmogamous flowers require pollinating agents.
Reason : Cleistogamous flowers do not expose their sex organs.
Codes:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

12.

The diagram given below shows a phenomenon known as epihydrophily (Pollination occurring over the water surface). Refer to the given diagram and comment upon the appropriateness of Assertion and Reason.

Assertion (A) :Hydrophily is an uncommon mode of pollination exhibited by aquatic plants.
Reason (R) : Pollens are distributed through water bodies to other plants.
(a) If both A and R are true and R is correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(d) If A is false, but R is true

13.

Assertion (A) : Cleistogamous flowers produce assured seed set in the absence of pollinators.
Reason (R) : Cleistogamous flowers do not open at all.
(a) If both A and R are true and R is correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(d) If A is false, but R is true

14.

Assertion (A) : Pollen grain of angiosperm is considered as the male gametophyte.
Reason (R) : Pollen grain contains stigma, style and ovary.
(a) If both A and R are true and R is correct explanation of A
(b) If both A and R are true, but R is not the correct explanation of A
(c) If A is true, but R is false
(b) If A is false, but R is true

15.

Assertion: The second meiotic division of the developing ovarian follicles is completed just after conception.
Reason: Conception is the onset of pregnancy when the implantation of blastocyst take place
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true butreason is false.
(d) Both assertion and reason are false.

16.

Assertion: In morula stage, the cells divide without any increase in size.
Reason: Zona pellucida remains undivided till cleavage is complete.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true butreason is false.
(d) Both assertion and reason are false.

17.

Assertion: Epididymis is divided into three parts.
Reason: Epididymis is the organ that stores spermatozoa.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true butreason is false.
(d) Both assertion and reason are false

18.

Assertion: Clitoris offemale is homologous to tip of penis.
Reason: Both have same origin and richly supplied with nerves and blood vessels.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true butreason is false.
(d) Both assertion and reason are false.

19.

Assertion: Cilia lining the fallopian tube helps to pick up and push the released ovum into the oviduct.
Reason: Cilia of fallopian tubes beat towards uterus.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true butreason is false.
(d) Both assertion and reason are false.

20.

Assertion: At puberty human male develops secondary sexual characters.
Reason: At puberty there is decreased secretion of testosterone in male.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true butreason is false.
(d) Both assertion and reason are false

21.

Assertion(A): Helobial endosperm is found in monocots.
Reason(R): Two chambers are formed in this endosperm
Cores:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

22.

Assertion: Colpa aurea is a specialised pollinating agent of orchid Ophrys speculum.
Reason: Male Colpa mistakes the Ophrys flowers for female partner
Codes:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false

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Answers Key:

Case Study Questions

5 x 4 = 20

(a) Father - I^Ai, Mother I^Bi
(b) (i) -I^Bi
(ii) I^Ai or ii
(C) (i) The alleles I^Aand I^Bofthe blood group character are equally dominant and both of them express themselves when present together, resulting in blood group AB.

(a) Genotype of F_I- YyRr
Phenotype of F_I - Yellow, round seeds
(b) Gametes:
(c) Phenotypic ratio of F2 generation: Yellow, round 9: Yellow, wrinkled 3: Green, round 3: Green, wrinkled I.

Mechanisms of Inheritance.
(i) Multiple allelism.
(a) The gene I controlling blood group character exists in three allelic forms, l^A, I^Band i.
(ii) Dominance.
(a) The allele IA is dominant over the allele i and the allele IB is also dominant over the allele, i.
(iii) Codominance.
(a) The alleles I^A and I^B are equally dominant and both of them express themselves, when they are present together; blood group AB results.

Cross 1
(i) Since dwarf individuals have appeared in the progeny, the tall plant must be heterozygous, i.e., its genotype is Tt.

Tall: Dwarf in the ratio 1: 1.
Cross 2
(i) If the tall pea plant were homozygous dominant (IT), all the offspring in the progeny will be tall; hence, different from the first cross.

(a) Genotype of:
A - Tt, B - TT, C - tt, D - Tt
(b) The phenotypic ratio is
3 Tall : I Dwarf
(c) It is a monohybrid cross.

Assertion and reason

17 x 1 = 17

(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Explanation:
Reusable contraceptives do not guarantee prevention from accidental pregnancy.

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Explanation :
Barrier methods include the diaphragm, cervical cap, male condom, and female condom and spermicidal foam, sponges, and film. Unlike other methods of birth control, barrier methods these are used only during sexual intercourse.

(d) If both Assertion and Reason are false.
Explanation:
Periodic abstinence is a natural method in which the couples avoid or abstain from coitus from day 10 to 17 of the menstrual cycle when ovulation could be expected. The effectiveness of this method is limited because only a few women have regular menstrual cycles and the actual time of ovulation can be produced as the ovulation in humans occurs about 14 days before the onset of the next menstruation.

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Explanation:
Natality is generally expressd as number of birth per 1,000 individuals of a population per year. It increase the population size and population density.

10.

(c) If Assertion is true but Reason is false.
Explanation:
Introduction of sex education in schools should be encouraged to provide right information to the young children and to discourage them from believing in myths and having misconceptions about sexrelated aspects. Proper information about reproductive organs, adolescence and related changes, safe and hygienic sexual practices, sexually transmitted diseases (STDs), AIDS, etc., would help people, especially those in the adolescent age group to lead a reproductively healthy life.

11.

(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Explanation :
The majority of angiosperms bear chasmogamous flowers, which means the flowers expose their mature anthers and stigma to the pollinating agents. There is another group of plants which set seeds without exposing their sex organs. Such flowers are called cleistogamous and the phenomenon is cleistogamy.

12.

(b) If both A and R are true, but R is not the correct explanation of A

13.

(a) If both A and R are true and R is correct explanation of A

14.

15.

(b) Both assertion and reason are true but reason is not the correct explanation of assertion.

16.

(b): In morula stage, the cells divide without any increase in size and becomes a solid mass of cells. Zona pellucida remains undivided till cleavage is complete. After damage it breaks down and morula formation starts.

17.

(b) : Epididymis lies along the top and side of testes and is divided into 3 parts - anterior caput epididymis: middle corpus epididymis and posterior cauda epididymis.
The epididymis, besides forming a part of tubular conducting system for sperm transport, in it serves as a storage reservoir for sperms

18.

(a) : Clitoris of female is the small, spongy and erectile structure which hangs freely from the front end of vulva. It represents the underdeveloped penis. Whereas penis is a finger-like cylindrical outgrowth of abdomen projecting in between the scrotal sacs. Clitoris and penis both originate from the same origin, therefore are homologous.
Homologous organs are those organs which have the same origin and mayor may not have the same function. Clitoris and penis both are the reproductive organs present in female and male respectively. They are originated from the mesoderm layer and both are supplied with the nerves and blood vessels.

19.

(a) Both assertion and reason are true and reason is the correct explanation of assertion.

20.

(c) : Puberty is the period of life at which the ability to reproduce begins and reproductive organs become functional. In male, the puberty is the period between 13-16 years. Puberty in male is controlled by male sex hormone called testosterone, which is secreted by interstitial or Leydig's cells of the testes under the stimulation of interstitial cells stimulating hormone (ICSH) secreted by anterior pituitary. After puberty the seminiferous tubules start producing sperms. The development of secondary sex organs like prostate, scrotum, penis, etc., starts and secondary sexual characters like growth of hair on face, chest, pubis and axillae, broadening of shoulders, deepening of voice due to enlargement of voice box occurs. In puberty (male), height increases due to rapid growth of muscles and bones.

21.

(b) Helobial endosperm is restricted largely to the monocotyledons. The primary endosperm nucleus moves to the chalazal end of the embryo sac where it divides forming a large micropylar chamber and a small chalazal chamber.

22.

(a) For its pollination the orchid Ophrys speculum has picked on the most selective attraction in the entire animal kingdom. It is pollinated by a hairy wasp, Colpa aurea. The wasp has a fixed habit whereby its males leave the burrows for above - ground existence about four weeks before the females emerge for the open air mating. The orchid opens its flowers about the same time the males appear and they possess an appearance and odour similar to those possessed by the female wasp. The inexperienced males mistake the Ophrys flowers for their female counterparts and land to perform the act of pseudo copulation. The insect repeats the act with a number of orchid flowers and carries pollinia from one flower to another.