Biology Test 328

The assertion is true as actinomorphic flowers do exhibit radial symmetry, allowing them to be divided into two equal halves along any radial plane. The reason is also true; however, it does not directly explain why actinomorphic flowers can be divided in such a manner. Instead, it provides an ecological advantage of radial symmetry, which is attracting a broader range of pollinators

Contraceptives are substances or methods that interfere with ovulation's natural action, fertilization of egg and sperm cells, and implantation to stop pregnancy. The features of a perfect contraceptive are:

• It should be easily accessible by both males and females.

• It should be easily removable.

• It shouldn't have any side effects.

• It should be inexpensive and cost-effective.

• It should be effective for preventing sexually transmitted diseases or STDs.

Reversible methods of contraception are considered to be the foremost effective.

Oscillatoria brevis is known for its ability to survive in hot water springs, with temperatures ranging from 50-70°C. This adaptability is due to its lack of a well-organized nucleus, allowing it to withstand extreme environmental conditions. This characteristic makes Oscillatoria brevis a fascinating subject for studying extremophiles and their adaptations.

In IVF, the fusion of ovum and sperm is done outside the body of women, to form a zygote which is allowed to divide to form embryo. This embryo is then implanted in uterus where it develops into a foetus which inturned develops into a child. This is called test tube baby.

In this method, ova from the wife or donor female and sperms from the husband or donor male are induced to form zygote in the laboratory. The zygote is allowed to divide forming 8 blastomeres. The zygote or early embryo is then transferred into the fallopian tube, this is known as zygote intra fallopian transfer (ZIFT).

Gamete intra fallopian transfer (GIFT) is the transfer of an ovum from a donor into the fallopian tube of another female, who cannot produce ovum but can provide environment for fertilisation and further development.

In Bryophytes, the sporophyte does not have a free-living stage. It is dependent on the gametophyte for nutrition and support. This contrasts with other plant groups like Pteridophytes and Gymnosperms, where the sporophyte is the dominant, free-living stage of the life cycle. Bryophytes represent an evolutionary step towards the land plant life cycle, where the sporophyte becomes increasingly independent.

Gemmae in liverworts play a crucial role in asexual reproduction. These green, multicellular buds develop in structures called gemma cups on the parent plant. When mature, gemmae are dispersed by environmental factors like raindrops, leading to the formation of new individuals. This method of reproduction allows for the rapid colonization of suitable habitats.

Chlorella is known for being used as a food supplement due to its high protein content. It is a unicellular, non-motile green alga that has gained attention for its nutritional benefits, including a high concentration of vitamins, minerals, and antioxidants. Chlorella's ability to grow rapidly under controlled conditions makes it a sustainable source of nutrients.

• Progestogens or estrogen-progestogen combinations are effective for emergency contraception. These pills prevent pregnancy if taken within 72 hours of coitus or copulation. Also, they are found useful to avoid possible pregnancy due to rape or casual unprotected intercourse.

• These medicines are used for sexual assault (like rape), treatment for unprotected sex, missed pills and other reasons which have a risk of pregnancy.

• Progestogens or estrogen-progestogen combinations either suppress or prevent ovulation by inhibiting the follicle-stimulating hormone and luteinizing hormone.

• They also bring a change in the lining of the uterus to prevent implantation and increase the thickness of mucus in the cervix region to prevent sperms from entering the womb.

Arthropods, which include insects, arachnids, crustaceans, and myriapods, are characterized by their chitinous exoskeleton, jointed limbs, and segmented bodies. The presence of a notochord is unique to Chordata, radial symmetry is a feature of Cnidaria and Echinodermata (in their larval stage), and the water vascular system is specific to Echinodermata. An interesting fact about arthropods is that they undergo molting, shedding their exoskeleton to grow.

Pteridophytes, like ferns and horsetails, indeed require water for fertilization to occur. This is because their male gametes, or antherozoids, are motile and need a film of water to swim through to reach the female gametes housed within the archegonia. This dependency on water for fertilization is a characteristic feature of their life cycle and highlights the evolutionary transition from aquatic to terrestrial life.