Why do all the gametes formed in human
Question: Why do all the gametes formed in human females have an X-chromosome ? Solution: Human females are homogametic. Their generic constitution is 44 + XX The two sex chromosomes are similar. Their ova which are produced after meiosis carry a gametic constitution of 22 + X No other combination is possible....
Read More →Mention three important features
Question: Mention three important features of fossils which help in the study of evolution. Solution: Fossils are remains or impressions of past organisms that are found in the rocks. Fossils of lower strata belong to early periods while those of upper strata are of later periods. Arranging the fossils stratumwise will indicate the occurrence of different forms of life at different times. It is found that the early fossils generally belong to simple organisms. Complexity and elaboration increase...
Read More →Does genetic combination of mothers play
Question: Does genetic combination of mothers play a significant role in determining the sex of a new born ? Solution: No. Mothers have no role in determining the sex of the new born. Mothers are homogametic, that is, they produce only one type of ova (22 + X). Fathers are heterogametic, that is, they produce two types of sperms, gynosperms (22 + X ) and androsperms (22 + Y). If gynosperm (22 + X) fertilises the ovum (22 + X), the sex of new born will be female (44 + 2X). If androsperm (22 + Y) ...
Read More →How is a sex of new born determined
Question: How is a sex of new born determined in humans ? Solution: Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better adaptability to the existing environment. Peppered Moth of England has two forms, light grey and dark grey. Prior to industrial revolution, tree trunks in the forests around. Manchester were light greyish green due to presence of lichens. Most of the Peppered Moth found in the area ...
Read More →How is a sex of new born determined in humans ?
Question: How is a sex of new born determined in humans ? Solution: Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better adaptability to the existing environment. Peppered Moth of England has two forms, light grey and dark grey. Prior to industrial revolution, tree trunks in the forests around. Manchester were light greyish green due to presence of lichens. Most of the Peppered Moth found in the area ...
Read More →Describe sexually transmitted
Question: Describe sexually transmitted diseases and mention the ways to prevent them. Solution: It is a group of infections caused by different types of pathogens that are transmitted by sexual contact between a healthy person and an infected person. The sexually transmitted diseases are also called venereal diseases (VDs). Some 30 different types of STDs are known. It is caused by bacterium Neisseria gonorrhoeae. Gonorrhoea spreads through sexual contact, common toilets and under clothes. Incu...
Read More →Reproduction is essentially a phenomenon
Question: Reproduction is essentially a phenomenon that is not for survival of individual but for the stability of a species. Justify. Reproduction is not essential for survival of the individual. Solution: Survival of the individual depends upon input of nutrients and energy and elimination of wastes. Reproduction has ho role in these. It is, however, essential for the stability and survival of the species. Reproduction takes part in (a)Perpetuation of Species:Perpetuation or continuation of sp...
Read More →Flow does fertilization take place ?
Question: Flow does fertilization take place ? Fertilization occurs once in a month. Comment. Solution: In human beings, fertilization is internal. It can occur within 2-3 days of ovulation (between 14th and 16th day of menstrual cycle). Fertilization generally takes place in ampulla (ampulla-isthmus border) part of fallopian tube where ovum rests for several hours after entry into oviduct. The sperms have to reach there. Sperms deposited in the vagina reach there partly by their own movement an...
Read More →What are the various ways
Question: What are the various ways to avoid pregnancy ? Elaborate any one method. Solution: (a) Methods to Avoid Pregnancy: Prevention of pregnancy is called contraception. The techniques used in preventing the occurrence of pregnancy are called contraceptive devices.(b) Mechanical Barrier Methods of Contraception: Mechanical Barriers like condoms, cervical cap, diaphragm. Oral Contraceptives or oral pills like Mala D, Saheli Intrauterine Contraceptive Devices (IUCD) like loop, bow, Cu-T. Surgi...
Read More →What is placenta ?
Question: What is placenta ? Mention its role during pregnancy. (CCE 2011, 2014) Solution: Placenta:It is a special double layered, spongy tissue connection between the foetus and uternine wall found in pregnant females. It has finger-like outgrowths or villi which are in contact with blood sinuses present in the uterine wall. Role: Attachment: Placenta attaches the foetus to uterine wall. Villi: Placenta has finger-like outgrowths or villi which develop a large surface area for fixation and abs...
Read More →Draw the diagram of a flower and label
Question: Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower. Solution: (b) Male Gamete Forming Part. Pollen grain, produced in anther of stamen. Female Gamete Forming Part. Embryo sac developed inside ovule of ovary part of pistil....
Read More →Distinguish between a gamete and zygote.
Question: Distinguish between a gamete and zygote. Explain their roles in sexual reproduction. Solution: Differences between Gamete and Zygote Role of Gamete. Gamete is sex or germ cell which is specialized to take part in sexual reproduction. There are two types of gametes, male and female. Each of them carries one set of chromosomes which are randomly obtained from its parent. Fusion of male gamete with a female gamete produces a zygote. Role of Zygote. It is the firstcell of new generation. Z...
Read More →Distinguish between pollination and fertilization.
Question: Distinguish between pollination and fertilization. Mention the site and product of fertilization in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule. Solution: (a)Differences between Pollination and Fertilization (b) Site of Fertilization. Embryo sac in ovule. Product of Fertilization. Zygote, Primary endosperm cell....
Read More →Write two points of differences between asexual
Question: Write two points of differences between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction. Solution: (a)Differences between Asexual and Sexual Reproduction (b)Development of Variation in Sexual Reproduction:Sexual reproduction produces a number of variations in the population due to Chance separation of chromosomes at the time of meiosis. Crossing over during meiosis. Chance combination of chromosomes during fe...
Read More →Why are budding, fragmentation and regeneration
Question: Why are budding, fragmentation and regeneration all considered as asexual types of reproduction ? With neat diagrams, explain the process of regeneration in Planaria. Solution: (a)Asexual Reproduction:Budding, fragmentation and regeneration are all considered to be modes of asexual reproduction as they involve formation of new individuals from single parents without fertilization or fusion of gametes. (b)Regeneration in Planaria:...
Read More →What would be the ratio of chromosome
Question: What would be the ratio of chromosome number between an egg and its zygote ? How is the sperm genetically different from the egg ? Solution: Chromosome Number in Egg and Zygote. 1 : 2 Genetic Difference between Sperm and Egg. Sperms are genetically of two types, X-containing and Y-containing. Eggs are always of one type, X- containing....
Read More →In the female reproductive system,
Question: In the female reproductive system, name the parts that are involved in (a) Production of egg. (b) Site of fertilization (c) Site of implantation (d) Entry of sperms. Solution: (a) Production of Egg: Ovary (b) Site of Fertilization: Ampulla part of fallopian tube. (c) Site of Implantation: Uterus. (d) Entry of Sperms: Vagina....
Read More →What are the benefits of using
Question: What are the benefits of using mechanical barriers during sexual act ? Solution: Prevention of Pregnancy : Mechanical barriers (e.g., Condoms, diaphragms) prevent the passage of sperms into the genital tract of the female. Consequently, pregnancy does not occur. Non-transmission of Infections: There is no transfer of venereal diseases from the infected partner to the non-infected partner....
Read More →What changes are observed in the
Question: What changes are observed in the uterus subsequent to implantation of young embryo ? (CBSE Delhi 2017) Solution: Endometrium thickens, becomes glandular and highly vascular. The contact region between embryo and uterine wall grows into placenta. Placenta helps the embryo in obtaining nourishment and oxygen from blood sinuses of the uterus. It also helps in transfer of wastes from embryo to the blood of the mother....
Read More →What changes are observed in the uterus
Question: What changes are observed in the uterus if fertilization does not occur ? (CBSE Delhi 2017) Solution: Glands present in the mucosa of uterine endometrium begin to degenerate. This sloughs off the endometrial lining, releasing a lot of mucus and blood. It is called menstruation. Menstruation lasts for 3-5 days....
Read More →Trace the path of sperm during ejaculation
Question: Trace the path of sperm during ejaculation and mention the glands and their function associated with the male reproductive system. Solution: Ejaculated sperms are the ones which are stored in epididymes. They are formed regularly in seminiferous tubules from where they pass through vasa efferentia into epididymes. At the time of ejaculation, the sperms are first pushed through vasa deferentia, enter ejaculatory duct where they receive secretion of seminal vesicles and then urinogenital...
Read More →How are general growth and sexual
Question: How are general growth and sexual maturation different from each other ? Solution: General growth is the growth of an individual in size, height, shape, weight, etc. Sexual maturation is a set of changes in body of an individual that enable one to take part in reproduction, e.g., maturation of gonads, genitalia and other accessory structures. In human beings, beginning of sexual maturation is indicated by puberty changes like cracking of voice, new hair pattern, development of breast i...
Read More →Reproduction is linked to stability of population
Question: Reproduction is linked to stability of population of a species. Justify the statement. Solution: Reproduction maintains the size and composition of population of a species by regularly adding new individuals for replacing the ones getting killed due to ageing, disease or predation. It also adds variations that allow the individuals to adapt to changing environment....
Read More →Where is the zygote located in
Question: Where is the zygote located in the flower after fertilization ? Solution: Zygote is the fertilized oosphere which occurs in the embryo sac present inside an ovule located in the ovary part of the pistil....
Read More →Is the chromosome number of zygote,
Question: Is the chromosome number of zygote, emboryonal cells and adult of a particular organism always constant ? How is the constancy maintained in these three stages ? Solution: Zygote is the first diploid structure. It undergoes mitotic divisions to form embryonal cells. Embryonal cells further divide by mitosis to form the adult. Mitosis maintains the same chromosome number in the daughter cells....
Read More →