Reproduction in Organisms Test - 2

In some lower animals both male and female sex organs are present in the same individual, such are called hermaphrodite, monoecious or bisexual, e.g tapeworm, earthworm and leech, etc.  

Organism shown in figure (d)  is Nereis. It is unisexual or dioecious and its reproductive phase is called ‘heteronereis’ Fertilization occurs in sea water.

Self-fertilization occurs in Taenia, while cross fertilization occurs in Pheretima, Periplaneta and Rana tigrina.

During favourable conditions, simple organisms like algae and funai multiply asexually but during unfavourable conditions gametes are formed. The gametes fuse to form zygotes which often develop a thick wall to become zygospores. The latter are dispersed. Under favourable zygospore germinates to form new organisms. Since fusion of gametes from different parents occur during sexual reproduction, hence genetic recombination takes place causing variations. Variations, being a major factor of natural selection, play an important role in evolution.

Juvenile phase is pre-reproductive phase in life cycle of an individual. It is the period of growth between the birth of an individual upto reproductive maturity. Juvenile phase is known as vegetative phase in plants. This phase is of different durations in different organisms.

Perennial plants live for a few to several hundred years, hence vegetative, reproductive and senescent phases cannot be observed clearly

cross-fertilisation occurs in Hydra. The testis matures earlier than the ovary. Spermatozoa released from the testis of one Hydra's swim in water with their tails and finally come into contact with the ovum of another Hydra.

Ovum lives inly for a short time after it is exposed. during this period, fertilization must take place. Thus, given figure is not showing self fertilization but cross fertilisation.

Continuous breeders continue to breed throughout their sexual maturity. Examples are honey bee, rabbit, mice. cattle, man, etc. Seasonal breeders reproduce at particular period of the year such as frog, lizard, most birds, deer, tiger, etc.

Strobilanthus kunthiana (Neelakuranji) flower once in 12 years, its juvenile phase is very long. The last time this plant flowered was during September - October 2006. It is found in hilly areas of Kerala, Karnataka and Tamil Nadu and attract a large number of tourists.

Chromosome number in meiocyte (2n) of onion cell is 32, while chromosome number in gamete (n) is 16.

In gymnosperms, endosperm is haploid and is formed Before fertilization. In angiosperms, the endosperm is a special tissue which is formed as a result of vegetative fertilization, triple fusion or fusion of a male gamete with diploid secondary nucleus of the central cell. It is triploid in nature.

In Agave, bulbils are modified floral buds that develop on the flowering axis, so chromosome number in a cell of bulbil will be equal to that of leaf cell of Agave, i.e., n=x.

Reproductive organs develop and mature during puberty. Changes that indicate reproductive maturity are development of external genitalia, breasts, body hair, pubic hair, changes in skeleton, etc

Oestrous cycle occur in non-primates such as cows, dogs, etc. Menstrual cycle occurs in primates only. Menstrual shows monthly recurrence but oestrous cycle does not.

The terminal irreversible stage of ageing is called senescence. This is the last phase of life span, that ultimately leads to death. In both plants and animals, hormones are responsible for the change over from one phase to another This phase can be recognised by slow metabolism, cessation of reproduction and decreased immunity.

Staminate flowers are those which have only male propagative organs, or stamens, or have infertile female organs. Staminate flowers produce only pollen (antherozoids) and are not capable of producing fruit.

Meiosis does not occur in asexually reproducing individuals. There is only mitotic cell division and multiplication occurs rapidly. On the other hand, sexual reproduction involves both meiosis and mitosis.

In Agave, bulbils are modified floral buds that develop on the flowering axis, so chromosome number in a cell of bulbil will be equal to that of leaf cell of Agave, i.e., n = x

Gametes are haploid whether the structures or cells producing them are haploid or diploid.
 

 When both male and female sex organs are present in the same individual, such animals are called hermaphrodite, monoecious or bisexual, e.g., tapeworm, earthworm and leech.
 

Ophioglossum is a fern having highest number of chromosomes. Chromosomes number in meiocyte (2n) = 1260. Chromosome number in gamete (n) = 630.

The germinal cells are diploid and act as meiocytes,which undergo meiosis to produce haploid gametes. Thus, meiocytes have diploid (2n) number of chromosomes, same as the somatic cells.

Cross-fertilisation occurs in many hermaphrodite animals as in earthworm. It is due to the fact that their male and female reproductive organs mature at different times.

Sex organs in human are formed before birth (during embryonic development).

Honey bees are attracted towards blue, purple-violet and yellow flowers. Bees use ultraviolet radiation for observation. Red appears black in ultraviolet radiation. Therefore, bees seldom visit red flowers. Honey bees visit flowers for nectar and pollen grains.

Depending upon the compatibility in sexual reproduction, fungi are of two types - homothallic and heterothallic. In homothallic forms, fusion occurs between genetically similar types. Fusion involves the union of cytoplasms as well as nuclei. In heterothallic forms, fusion occurs between gametes belonging to different parents.

Oestrous cycle occur in non-primates such as cows, dogs, etc. Menstrual cycle occurs in primates only. Menstrual shows monthly recurrence but oestrous cycle does not .

Sexual reprodction occurs in almost all types of animals and mostly in higher plants. It is usually biparental. Daughter organisms genetically digger from the parents. Since there are variations, it contributes to evolution of the species.

When fertilisation occurs outside the body of the organism, this type of gametic fusion is called external fertillisation or external syngamy. Organisms exhibiting external fertillisation produce a large number of both male and female gametes to enhance the chances of fertilisation e.g., algae, fish and amphibians.

Male sex organ in Chara is round in structure, called antheridium (B). It lies below the ovate shaped female sex organ called oogonium. Earthworm is bisexual or hermaphrodite organism. (C) show two pair of testis sacs, situated in the tenth and eleventh segments.