GK: Class 12 General Q&A · Page 150
3,658 free answers on GK (General) for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
1. What term is used for the secretions of endocrine glands?
The secretions of endocrine glands are called hormones. These chemical messengers are released directly into the bloodstream and travel throughout the body to reach specific target organs or tissues. Unlike exocrine glands that release their secretions through ducts, endocrine glands are ductless and rely on the circulatory system to transport hormones to where they're needed. Hormones regulate a wide range of bodily functions including growth, metabolism, reproduction, mood, and slee
- GeneralClass 12All
How does a Hydra reproduce? Explain with the help of labeled diagrams.
Hydra reproduces primarily through asexual budding when environmental conditions are favorable, though it can also reproduce sexually under stress conditions. During asexual reproduction, a small outgrowth or bud emerges from the parent Hydra's body wall, typically in the middle region of the organism. This bud initially appears as a small protrusion of the body column, containing extensions of both the outer ectoderm and inner endoderm layers along with the central gastrovascular cavity. As
- GeneralClass 12All
Define the term ovulation and implantation.
. Ovulation is the process by which a mature egg (ovum) is released from the ovary into the fallopian tube, typically occurring approximately midway through the menstrual cycle in human females (around day 14 of a 28-day cycle). This release is triggered by a surge in luteinizing hormone (LH) secreted by the pituitary gland, which causes the mature follicle housing the egg to rupture and expel the ovum. The released egg is swept into the fallopian tube by finger-lik
- GeneralClass 12All
Name three modes of asexual reproduction in animals. Name an animal that shows two such modes of asexual reproduction.
Three common modes of asexual reproduction in animals are budding, fragmentation (regeneration), and binary fission. Budding involves the formation of a small outgrowth or bud on the parent's body, which develops into a new individual before detaching—seen in organisms like Hydra and certain sponges. Fragmentation occurs when an organism breaks into distinct pieces, each capable of regenerating into a complete individual, as observed in Planaria (flatworms) and some starfish species. Bi
- GeneralClass 12All
Name the organs where male and female gametes are formed in human beings.
In human beings, male gametes (sperms) are formed in the testes, while female gametes (eggs or ova) are formed in the ovaries. The testes are a pair of oval-shaped organs located outside the body cavity in the scrotum, where temperature remains approximately 2-3 degrees Celsius lower than core body temperature—a condition essential for healthy sperm production. Within each testis, millions of sperms are continuously manufactured in tightly coiled seminiferous tubules through the process
- GeneralClass 12All
What are oviparous animals? Give two examples of oviparous animals.
Oviparous animals are organisms that reproduce by laying eggs, with embryonic development occurring entirely outside the mother's body within the protective egg structure. After fertilization (which may be internal or external), the developing embryo receives all necessary nutrients from the yolk and other egg components rather than directly from the maternal body. The egg provides a self-contained environment with food reserves, water, and a protective shell or membrane that shields the deve
- GeneralClass 12All
Define asexual reproduction. Name two methods of asexual reproduction in animals. Name two animals which reproduce by these asexual reproduction methods.
Asexual reproduction is a mode of reproduction involving a single parent organism that produces offspring without the fusion of gametes, resulting in progeny that are genetically identical to the parent. This process relies on mitotic cell division, where DNA is precisely duplicated and distributed to create new individuals with the same genetic composition as the parent. Asexual reproduction bypasses the complexities of sexual reproduction—no mate-finding, no gamete production through
- GeneralClass 12All
Define gestation period. What is the duration of gestation period in human beings?
The gestation period is the time interval between fertilization and birth during which an embryo develops inside the mother's uterus in viviparous animals. This period encompasses all stages of prenatal development, from the single-celled zygote through embryonic differentiation and organ formation, continuing through fetal growth and maturation until the offspring is sufficiently developed for independent survival outside the womb. The gestation period varies dramatically across species, cor
- GeneralClass 12All
Give an example of metamorphosis in animals. What are the changes observed during metamorphosis of this animal?
The frog provides a classic example of metamorphosis, undergoing dramatic transformation from aquatic tadpole to terrestrial or semi-aquatic adult. Frog metamorphosis begins when eggs hatch into tadpoles—small, fish-like larvae with streamlined bodies, long muscular tails for swimming, and gills for extracting oxygen from water. During this larval stage, tadpoles are primarily herbivorous, feeding on algae and plant matter using specialized scraping mouthparts, and possess a simple, sin
- GeneralClass 12All
What advantage do viviparous animals have over oviparous animals?
Viviparous animals—those giving birth to live young after internal development—gain significant survival advantages through enhanced offspring protection and developmental support. The developing embryo remains inside the mother's body throughout gestation, shielded from predators, environmental extremes, dehydration, and physical damage that threaten externally developing eggs. This protective environment dramatically increases individual offspring survival rates, allowing vivipa
- GeneralClass 12All
Write two characteristics in which male gametes are different from female gametes.
Male gametes (sperms) are motile and produced in enormous quantities, while female gametes (ova or eggs) are non-motile and produced in limited numbers. Sperms possess a tail (flagellum) that propels them through the female reproductive tract toward the egg, actively swimming distances that are thousands of times their own length. A healthy adult male produces hundreds of millions of sperms daily, with each ejaculation containing 200-500 million sperm cells, compensating for the high attritio
- GeneralClass 12All
In viviparous animals, how does embryo get nutrition and oxygen?
In viviparous animals, particularly placental mammals like humans, the embryo receives nutrition and oxygen through a specialized temporary organ called the placenta that forms during pregnancy. The placenta develops where the embryo implants in the uterine wall, creating an interface between maternal and fetal circulatory systems. Blood vessels from the embryo extend through the umbilical cord to the placenta, where they branch into extensive networks of tiny capillaries. These fetal blood v
- GeneralClass 12All
Both in human beings and hen, fertilization is internal but there is a difference in further development of the zygote. Explain that difference.
Although both humans and hens experience internal fertilization where sperms meet eggs within the female reproductive tract, the subsequent developmental pathways differ fundamentally. In humans, after fertilization in the fallopian tube, the zygote undergoes cleavage while traveling toward the uterus, developing into a blastocyst that implants in the nutrient-rich uterine lining approximately 6-7 days post-fertilization. The embryo then develops entirely within the mother's uterus for approx
- GeneralClass 12All
Write a short note on cell wall.
The cell wall is a rigid, protective outer layer found in plant cells, fungi, bacteria, and some protists, but absent in animal cells. In plants, the cell wall is primarily composed of cellulose, a complex polysaccharide made of glucose molecules arranged in strong, fibrous chains. This structure is located outside the plasma membrane and provides mechanical strength and support to the cell. The plant cell wall is not a single uniform layer but typically consists of three parts: the middle la
- GeneralClass 12All
Who proposed cell theory? State its principles.
Cell theory was proposed through the collective work of three scientists in the mid-19th century: Matthias Schleiden (a German botanist), Theodor Schwann (a German zoologist), and Rudolf Virchow (a German physician). In 1838, Schleiden concluded that all plants are composed of cells, followed by Schwann in 1839, who extended this idea to animals, proposing that all living organisms are made of cells. Later, in 1855, Virchow added the crucial concept that all cells arise from pre-existing cell
- GeneralClass 12All
Which type of fertilization takes place in frogs? What is the disadvantage of this type of fertilization?
Frogs undergo external fertilization, where eggs and sperms are released into water and fusion occurs outside the female's body. During breeding season, male frogs clasp females in an embrace called amplexus, and as the female releases eggs into the water, the male simultaneously releases sperms over them to maximize fertilization chances. This process typically occurs in ponds, streams, or temporary pools where environmental conditions trigger synchronized reproductive activity. The
- GeneralClass 12All
How is an embryo different from a foetus?
An embryo represents the early developmental stage immediately following fertilization, characterized by rapid cell division, differentiation, and formation of basic body structures and organ systems. In humans, the embryonic period extends from conception through approximately the eighth week of pregnancy. During this critical phase, the single-celled zygote undergoes cleavage to become a ball of cells, which implants in the uterine wall and develops into recognizable structures including th
- GeneralClass 12All
Why are gametes formed in large numbers in organisms exhibiting external fertilization?
Organisms exhibiting external fertilization produce enormous quantities of gametes—often millions—to compensate for the extremely low probability of successful fertilization in aquatic environments. When fish, frogs, or marine invertebrates release their eggs and sperms into surrounding water, the gametes face numerous challenges: they may be swept away by currents, diluted across vast water volumes, consumed by predators, or fail to encounter each other within the limited time wi
- GeneralClass 12All
Which of the following animals undergoes metamorphosis and which do not? Cow, Butterfly, Silk moth, Humans, Frog, Housefly, Sparrow, Hen, Mosquito, Monkey
Animals that undergo metamorphosis from the given list are: Butterfly, Silk moth, Frog, Housefly, and Mosquito. Metamorphosis is a biological process where an animal's body structure changes dramatically during development from juvenile to adult form. Insects like butterflies, silk moths, houseflies, and mosquitoes undergo complete metamorphosis, progressing through distinct life stages—egg, larva (caterpillar or maggot), pupa (chrysalis or cocoon), and adult—with each stage looki
- GeneralClass 12All
How is the progeny formed from asexual reproduction different from those formed by sexual reproduction?
Progeny from asexual reproduction are genetically identical to their single parent, forming clones with no genetic variation except rare mutations, whereas offspring from sexual reproduction are genetically unique, inheriting a combination of traits from both parents. This fundamental difference arises from the mechanisms involved: asexual reproduction uses mitotic cell division to create offspring with identical DNA copies, while sexual reproduction employs meiosis to produce gametes with sh