Biology Test 304

Metaphase is characterized by the alignment of chromosomes at the cell's equator, also known as the metaphase plate. This alignment ensures that each daughter cell will receive an equal and identical set of chromosomes when the chromosomes are pulled apart in the subsequent anaphase. The precise alignment and attachment of spindle fibers to the kinetochores on the chromosomes are crucial for the accuracy of chromosome segregation.

A key feature of meiosis that contributes to genetic diversity is the pairing of homologous chromosomes and the exchange of genetic material between them, known as crossing over. This process occurs during prophase I of meiosis and results in new combinations of genetic material on each chromosome. Crossing over is a fundamental mechanism that increases genetic variability within a population, which is essential for evolution and adaptation.

Auxins play a crucial role in initiating rooting in stem cuttings. They stimulate cell division in the cambium, promote cell elongation in shoots, and at higher concentrations, can inhibit root growth. An interesting fact about auxins is that they are involved in the process of apical dominance, where the main central stem of the plant is dominant over (grows more strongly than) other side stems.

actual number of enzyme decrease and hence Vmax decrease

Gibberellins are involved in various growth processes including overcoming seed dormancy, promoting flowering, and enhancing fruit size. However, inducing root hair formation is a function attributed to ethylene, not gibberellins. Gibberellins are particularly known for their role in promoting stem elongation and seed germination.

Cytokinins are crucial for promoting cell division and organ initiation, including the development of leaves, shoots, and roots. They work in conjunction with auxins to regulate growth and development. An interesting additional fact is that cytokinins can delay aging in plants by promoting nutrient mobilization, which keeps leaves green and delays senescence.

Ethylene is the phytohormone responsible for promoting fruit ripening and the abscission (shedding) of plant organs such as leaves and flowers. It is unique among the plant hormones because it is a gas. Ethylene also plays a role in overcoming seed and bud dormancy and in stress responses.

During S phase of the cell cycle, the histone proteins are synthesized in a eukaryotic cell. The major event in S phase is DNA replication. The goal of this process is to create exactly two identical semi-conserved chromosomes. The cell prevents more than one replication from occurring by loading pre-replication complexes onto the DNA at replication origins during G₁ phase which is dismantled in S phase as replication begins.

Abscisic acid (ABA) induces the closure of plant stomata, helping plants to conserve water during drought conditions. This role as a stress hormone showcases ABA's importance in plant responses to environmental stress. An additional fact is that ABA also plays a crucial role in seed dormancy, ensuring seeds only germinate under favorable conditions.