12th Class Biology Chapter 4 Reproduction Short Question Answers

There are two types of reproduction which are as follows: i) Asexual reproduction ii) Sexual reproduction

In some cases fruit development proceeds without fertilization and thus no seed formation takes place e.g.banana pineapples and some varieties of oranges and grapes.Such development is called parthenocarpy.

Germinating pollen grain is not only an important structure for safe transfer of gametes and insurance for fertilization but also a rich source of auxins as well as commonly stimulating the tissues of the style and ovary to produce more auxin.This auxin is necessary for fruit set i.e.retention of ovary which becomes the fruit after fertilization.

Diploid aprthenogenesis is that in which the egg-producing cells of the female undergo a modified from of meiosis involving total non-disjunction of the chromosomes they retain the diploid number of chromosomes.Egg develops into young females.

In some case the female produces more than one egg and all eggs are independently fertilized forming two or more zygotes.These zygotes develop into new offspring’s but with different genetic combinations.Such twins or triplets are called fraternal twins or triplets.

Organisms which contain both the sexes (testes and ovaries) in the same individual are known as hermaphrodite or bisexual.

Fertilization is the process which leads to union of gametes fertilization may occur outside the body or inside the body of the female.

In some mammals like duckbill platypus internal fertilization leads to internal development of the young one in a shelled egg and when development is completed shelled egg is laid which hatches the offspring.This is called ovoviviparous condition.

In human females the periods reproductive cycle is completed in approximately 28 days and involves changes in the structure and function of the whole reproductive system.It is called the menstrual cycle and can be divided into four phases.

It is thought that asexual method of reproduction is a primitive form of reproduction than the sexual reproduction.

Reproduction is the mechanism that produces new generations and maintains a species.

Asexual reproduction requires only a single parental organism which gives rise to offspring by mitotic cell division during which the complete adult number of chromosomes is exactly replicated and passed on so that the offspring are genetically identical to the parent.

Methods of asexual reproduction are fission sporulation budding vegetative propagation artificial propagation parthenogenesis apomixis etc.

sexual reproduction usually involves two parents.A fertilized egg is produced through the union of meiotically produced specialized sex cells from each parents.

Plants have diplohaplontic life cycle with alternating diploid sporophyte and haploid gametophyte generations.

If the two generations are vegetatively similar such alternation of generation is referred to as isomorphic and if they are dissimilar it is called heteromorphic.

It is special condition of rest which enables an embryo to survive the long periods of unfavourable environmental condition such as water scarcity or low temperature.During this period the embryo ceases or limits its growth.

Fruit set is the retention of the ovary which becomes the fruit after fertilization.After fertilization the ovary and the rips seeds continue to produce auxins which stimulate fruit development.

Fruit ripening is often accompanied by a burst of respiratory activity called the climatric.This is associated with ethane production which helps in ripening of the fruit.

The variations in day length are called photoperiod and the phenomenon is called photoperiodism.

Effect of photoperiodism was first studied in 1920 by garner and allard.They studied that tobacco plant flowers only after exposure to a series of short days.

It is light-controlled development of form and structure in plants.

The phytochromes are blue light sensitive protein pigments found in plants.Phytochromes exist in two forms i.e.P 660 and P730.

P 660 absorbs red light at a wave length of 660 nm and is converted to active p 730.P730 absorbs far red light at 730 nm and is converted to P660.In nature the P660 to P730 conversion takes place in day light and P 730 to P 660 conversion occurs in the dark.

Florigen is a hormone in leaves which travel through phloem to the floral buds and initiates flowering.

Biennial and perennial plants are stimulated to flower by exposure to low temperature.This is called vernalization.

The duration of low temperature treatment varies from four days to three months.

Temperature around 4ᵒC stimulates the production of Vernalin hormone which induces vernalistion.It is now believed that vernalin is not important but actually it is gibberellin.

Photoperiodism and vernalization encure reproduction at favourable of years.They also ensure that members of the same species flower at the same time encouraging cross pollination for genetic variability.

Vernalization is very important in agriculture.Now it is possible to grow the winter varieties under environmental conditions that ordinarily do not allow it to produce ripe seed.

Reproduction is the ability to produce new individuals of ones own kind or reproduction is the biological process which leads to the production of the new individuals.

Binary fission multiple fission budding parthenogensis cloning and identical twins are the common asexual mehtods of reproduction.

Parthenogenesis is defined as the development of an egg without fertilization.Ants bees and wasps are good examples.

The haploid egg develops into haploid offspring and it is called develop from unfertilized eggs.

In tissue culturing technique in plants cambium tissue excised from plants could be stimulated by the addition of nutrients cytokinis and IAA.These cells show continued growth and differentiate into a new plant genetically identically identical to their parents.

Organisms produced from a single cell by sub-culturing are called clones and phenomenon is called cloning.

i) Production of desirable animals. ii)Quantitative study of the action of hormones drugs and antibodies. iii)Identical offspring.

i) Offspring have environmental hazard. ii) Clone development not fully known.

When embryo of higher animals is at two celled stage the two blastomeres instead of remaining together may separate and each giving rise to a new individual.Both have identical genetic make up and are called identical twins.

Fertilization is the process which leads to union of gemetes.Fertilization may occur outside the body or inside the body of the female.

Frog Toad Fish etc.

Reptiles and birds lay shelled eggs to protect the developing embryo from harsh terrestrial conditions.Such animals are called oviparous animals.

In mammals development of embryo is accomplished inside the female body which give birth to young one-such animals are called viviparous.

External genitalia consist of a pair of testes which lie outside the body,in the sac like scrotum.

Each testis consists of a highly complex duct system called seminiferous tubules.In seminiferous tubules repeated division of the cells of the germinal epithelium produce spermatogonia

The spermatogonia present in seminiferous tubules differentiate into primary spermatocytes which undergo meiotic division to form Secondary spermatocytes and spermatids which ultimately forms sperms.

Sertoli cells are present in testes.They secrete fluid that provides liquid medium protection and nourishment to sperms while they are in the tubules.

The sperms are transferred from seminiferous tubules to the main duct of the male reproductive tract the vas deferens;which forms highly convoluted epididymis in the beginning.

The interstitial cells of testes secrete testosterone.This hormone is essential for the successful production of sperms and also controls the development of male secondary sexual characteristics during puberty.

The ovaries the oviducts uterus and the external genitalia.

Reproduction differs from all other functions of the animals in the respect that it is not necessary for the wall being of the individual.

Reproduction is the biological mechanism that produces new individuals. It serves to maintain the species.

Asexual reproduction is any method of producing off spring that does not involve meiosis and fusion of gametes. Sexual reproduction is the process of formation of new individuals (offspring) by the fusion of two gametes (sex cells) produced by meiosis.

These are fission, sporulation (spore formation) budding vegetative propagation, parthenogenesis and apomixes etc.

[toggle title=”The primitive algae and many fungi have haploid adult stages which arise by meiosis occurring in the haploid zygote. Such a lifecycle is called as haplontic.

Is some algae end fungi and in all the animals the adults are diploid and produce haploid gametes by meiosis. Such a lifecycle is called diplontic.

A life cycle having alternating diploid saprophytic and haploid gametophyte generation is known as diplohaplontic life cycle as in plants.

The alternation of generations are of two kinds in plants, isomorphic in which both the generations are morphologically similar and heteromorphic in which both the generations are morphologically dissimilar.

The development of the fruit from the ovary, without fertilization is called parthenocarpy. The parthenocarpic fruits differ from the normal fruits in having no seeds. The examples of parthenocarpic fruits are banana, pineapple and some varieties of oranges and grapes.

The parthenocarpy is due to hormonal imbalance, usually high auxin levels in the ovaries.

The developing seeds are rich sources of auxins, gibbereilins and cytokinins.

These growth substances are mainly associated with development of the embryo and accumulation of food reserves in the seed and sometimes in the pericarp (fruit wall).

The ripening of fruit is often accompanied by enormous respiratory activity called as the climatric. The climatric is associated with ethane production which helps in ripening of the fruit.

The light influences the plants through photosynthesis, phototropic and photo nastic response and photoperiodism.

The response of the plants to the relative length day or night, particularly with respect to flower production is called photoperiodism.

Garner and Allard studies photoperiodism for the first time in 1920.

The examples of short-day plants are cocklebur. Soybean and strawberry and those of long-day plants are henbane, cabbage and spring wheat.

These are the plants which bloom only when the day length (photoperiod) is below their critical photoperiod.

These are the plants which bloom only when the day length exceeds their critical photoperiod.

These are the plants in which flowering is not at all affected by the day length.

It is 15.5 hours.

It is 11:00 hours.

Phytochrome is a light sensitive pigment found in plant cells. It exists in two interconvertible forms; P₆₆₀ after receiving red light and P₇₃₀ after receiving for red light.

Long-day plants produce flowers when phytochrome in their cells is in the form of P₇₃₀ and short-day plants bloom when containing P₆₆₀. It is thought that phytochrome, P₇₃₀ in long-day plants and P₆₆₀ in short-day plants, stimulates te production of a hormone, Florien which induces flowering.

These are binary fission, multiple fission, budding, parthenogenesis, tissue culturing cloning and formation of identical twins.

These are the ants, male bees and wasps.

The males of honeybees are called drones.

Apomixis is a modified form of reproduction by plants in which seeds are formed without fusion of gametes.

An animal having both the testes and the ovaries is known as hermaphrodiis. The examples are tapeworm and earthworm.

It is formed by the fusion of the male and the female gametes.