Theory works but not every single time. and law is something found in nature
Most animal and plant species we see in the fossil record are extinct, or no longer living. In fact, of all the species that ever lived, 98% are extinct. Animals and plants become extinct over time as a result of natural processes. Their habitat might change or a disease might wipe out a species.
Answer:
Explanation:
Guard cells are located in the leaf epidermis and pairs of guard cells surround and form stomatal pores, which regulate CO2 influx from the atmosphere into the leaves for photosynthetic carbon fixation. Stomatal guard cells also regulate water loss of plants via transpiration to the atmosphere.
Answer:
B. Crossover formation is a necessary step in meiosis I to ensure proper chromosome segregation
Explanation:
Crossing-over is a unique phenomenon that occurs in the prophase I stage of meiosis I, where non-sister chromatids of homologous chromosomes exchange their chromosomal segment. The physical point where this exchange occurs is called CHIASMATA. Hence, a mutation that affects the gene associated with the chiasmata will affect the occurrence of crossing over or homologous recombination.
Crossing-over, through the formation of the chiasmata, is responsible for the physical alignment and proper segregation of chromosomes into gametes. Naturally, the chiasmata formed as a result of recombination during meiosis helps ensure that the chromosomes stay together until it is the right time to separate. This way, any chromosomal defect in the resulting gamete is prevented.
However, an error or defect in homologous recombination might give rise to gametes with chromosomal disorder, a condition known as ANEUPLOIDY i.e. missing or additional chromosomes in gametes. This can affect the fertility of the involved human.
