1)What part does the placenta play in the;
a)Nutrition of the embryo
b)Protection of the embryo
2)Explain why several auxiliary buds sprout when a terminal bud in a young tree is removed.
3)Account for loss in dry weight of cotyledons in a germinating bean seed.
4)State two advantages of metamorphosis to the life of insects.
5)During germination and early growth,the dry weight of endosperm decreases while that of the embryo increses. Explain
1) The placenta plays a crucial role in the nutrition and protection of the embryo during pregnancy.
a) Nutrition of the embryo: The placenta is responsible for transferring nutrients and oxygen from the mother's placental blood vessels to the developing embryo through the umbilical cord. It acts as a conduit for the exchange of essential substances, such as glucose, amino acids, vitamins, and minerals, required for the embryo's growth and development.
b) Protection of the embryo: The placenta acts as a barrier between the mother and fetus, protecting the embryo from potential harm. It filters out harmful substances, such as toxins and certain microorganisms, preventing them from reaching the developing embryo. Additionally, it provides a protective environment by cushioning the embryo and helping to maintain a stable temperature and pH level.
2) When a terminal bud is removed from a young tree, several auxiliary buds sprout as a compensatory mechanism.
Auxiliary buds are dormant buds present in the leaf axils of a plant or tree. They are kept in a dormant state by the hormonal dominance of the terminal bud. However, when the terminal bud is removed (due to pruning or damage), the hormonal dominance is lost, allowing the auxiliary buds to start growing.
The sprouting of several auxiliary buds is a survival strategy for the young tree. It ensures that even if the main terminal bud is damaged or removed, the tree can still continue to grow and develop. The auxiliary buds allow the tree to produce new branches and leaves, helping it to compensate for the loss and maintain its growth and survival.
3) The loss in dry weight of cotyledons in a germinating bean seed can be explained by their utilization as a source of energy for the growing embryo.
During seed germination, the embryo utilizes the stored food reserves present in the cotyledons, mainly in the form of starch, proteins, and lipids. These reserves are broken down into simpler molecules by enzymes, which are then transported to the growing regions of the embryo to provide energy and building blocks for its development. As a result, the cotyledons gradually lose their stored substances, leading to a decrease in their dry weight.
This loss of dry weight in cotyledons is a normal and essential process for the germinating bean seed. It ensures that the growing embryo receives the necessary nutrients and energy for its growth until it can establish a functional root system and start obtaining nutrients from the soil.
4) Metamorphosis provides several advantages to the life of insects:
a) Adaptation to different ecological niches: Insects go through different stages of metamorphosis, such as egg, larva, pupa, and adult. Each stage is adapted to fulfill specific ecological roles. For example, larvae often have specialized structures and behaviors suited for feeding and growth, while adult forms have features necessary for reproduction and dispersal. This allows insects to occupy diverse habitats and exploit different food sources.
b) Reduce competition between life stages: Metamorphosis helps to minimize competition for resources between different life stages of insects. The larval stage typically feeds and grows in a different niche or habitat than the adult stage, reducing competition between the two. This allows each stage to specialize in different ecological roles, making efficient use of available resources and increasing the chances of survival and reproduction.