Samacheer Class 10 Science - Reproduction in Plants and Animals

The germination of pollen grains, a crucial step in sexual reproduction in flowering plants, takes place on the stigma. The stigma is the receptive tip of the carpel, or of several carpels fused together, in the gynoecium of a flower. It is typically sticky or feathery to effectively trap pollen grains that land on it. Once a compatible pollen grain lands on the stigma, it absorbs moisture and nutrients, germinates, and grows a pollen tube down through the style to reach the ovary, where fertilization occurs.

Budding is a form of asexual reproduction where a new organism develops from an outgrowth or bud due to cell division at one particular site. This bud, when it detaches from the parent organism, grows into a new independent organism. Two common examples of organisms that reproduce through budding are yeast, a single-celled fungus, and Hydra, a small freshwater invertebrate belonging to the phylum Cnidaria. In yeast, a small bud forms on the parent cell, grows, and eventually separates. In Hydra, buds form on the body wall, develop into miniature Hydras, and then detach to lead an independent life.

The endosperm is a nutritive tissue formed within the seeds of most flowering plants after fertilization. Its primary function is to provide nourishment to the developing embryo during its growth, both before germination and in the early stages after germination begins. The endosperm is rich in stored food materials such as starch, oils, and proteins, which are essential for the embryo's development and eventual sprouting into a new plant. In some plants, like beans, the endosperm is completely absorbed by the cotyledons before the seed matures, while in others, like castor oil seeds, the endosperm remains a significant source of food for the seedling.

The hormone responsible for inducing and strengthening the vigorous contractions of the uterine muscles during childbirth is oxytocin. Oxytocin is a peptide hormone produced by the hypothalamus and released by the posterior pituitary gland. Its release is stimulated by the stretching of the cervix and uterus during labor. These powerful contractions are essential for dilating the cervix and pushing the baby out of the uterus during the delivery process. Oxytocin also plays a role in the milk let-down reflex during breastfeeding.

The enzyme present in the acrosome, a cap-like structure at the anterior end of a sperm, is primarily hyaluronidase. The acrosome also contains other enzymes like acrosin. Hyaluronidase plays a critical role in fertilization by breaking down the hyaluronic acid that holds the cells of the corona radiata, the outer layer of cells surrounding the egg, together. This enzymatic action helps the sperm penetrate through the corona radiata and reach the zona pellucida, the jelly-like layer surrounding the egg, facilitating fertilization.

World Menstrual Hygiene Day is observed annually on May 28. This day is dedicated to raising awareness about the importance of good menstrual hygiene management (MHM) and addressing the challenges faced by women and girls worldwide regarding menstruation. The date May 28 was chosen because it represents the 5th day of the 5th month, symbolizing the 5 days of menstruation and the 28-day average menstrual cycle. The day aims to promote the use of safe and hygienic menstrual products, provide access to sanitation facilities, and break the stigma and taboos associated with menstruation.

Contraception is essential for several vital reasons related to individual health, family well-being, and societal development. Firstly, it helps prevent unwanted pregnancies, giving individuals and couples control over their reproductive choices and family size. Secondly, effective contraception contributes significantly to controlling population growth, which can alleviate pressure on resources and the environment. Thirdly, it allows for the spacing of births, which is crucial for the health of both the mother and the child, enabling adequate recovery time for the mother and proper care for each child. Lastly, certain contraceptive methods, particularly barrier methods, can help reduce the transmission of sexually transmitted infections (STIs), thereby promoting sexual health.

If a planarian is cut into small fragments, each piece has the remarkable ability to regenerate into a complete, new, and genetically identical organism. This process is known as regeneration. It occurs because planarians possess a population of undifferentiated cells called neoblasts, which are pluripotent stem cells. When the planarian is injured or cut, these neoblasts proliferate rapidly at the site of injury and then differentiate into the various cell types needed to rebuild the missing parts of the body, ultimately forming a complete organism from each fragment.

Vegetative propagation is practiced for growing certain types of plants for two main reasons. Firstly, it is the only method of propagation for plants that do not produce viable seeds or are sterile, ensuring their continuation. For example, seedless varieties of fruits like bananas and some grapes cannot be propagated through seeds. Secondly, vegetative propagation allows for the preservation of desirable traits of the parent plant in the offspring. This is particularly important for high-yielding varieties or plants with specific characteristics, as the new plants produced are genetically identical to the parent, thus retaining qualities like disease resistance, fruit quality, or growth habit.

Binary fission and multiple fission are both forms of asexual reproduction, but they differ significantly in the number of daughter cells produced. In binary fission, a single parent cell divides into two approximately equal daughter cells. This is a common mode of reproduction in organisms like Amoeba and bacteria. In contrast, multiple fission involves the division of the parent cell into numerous daughter cells simultaneously or in quick succession. This process often occurs under unfavorable conditions, where the parent organism forms a protective cyst, and its nucleus divides multiple times before the cytoplasm divides, releasing many small daughter cells when conditions improve. Plasmodium, the parasite that causes malaria, reproduces through multiple fission within its host cells.

Insect-pollinated flowers, a process known as entomophily, exhibit several distinct characteristics to attract insects and facilitate pollen transfer. These flowers are typically large, brightly colored, and often possess a strong, pleasant fragrance to lure insects like bees, butterflies, and flies. They also produce nectar, a sugary liquid, which serves as a reward for the visiting insects. The pollen grains themselves are usually larger, heavier, and have a rough or spiny outer surface (exine) that helps them adhere to the bodies of insects, ensuring effective transport to the stigma of another flower. The stigma is often sticky to readily capture the pollen carried by insects.