Question

A student observes cell division in two different cells of a lily plant.

Answer 1

Answer:

Where I have used the term "chromosome complement," I am simply referring to the "complete" chromosome makeup of the nucleus of a cell in the flowering plant life cycle. The Merriam Webster Third New International Dictionary has many definitions for complement, but the one I am using is "the quantity or number required to fill a thing or make it complete." On the chromosome questions I want the "complete" chromosomes (represented by letters) for various cells and nuclei in the plant life cycle. For example, if ABCD refers to the chromosomes of an egg and abcd refers to the chromosomes of a sperm; then AaBbCcDd refers to the complete chromosomes of a fertilized egg or zygote (ABCD + abcd = AaBbCcDd). In a number of questions I have referred to the chromosome complement of a specific cell or nucleus, such as the zygote. In this case the chromosome complement of the zygote would be AaBbCcDd. The chromosome complement of the embryo would also be AaBbCcDd. Just think of the chromosome complement as the complete chromosome makeup of a cell where large and small case letters stand for the actual chromosomes. If there is one of each letter, then the cell is haploid (e.g. ABCD or abcd). If there are two of each letter, then the cell is diploid (e.g. AaBbCcDd). If there are three of each letter, then the cell is triploid (e.g. AAaBBbCCcDDd). If there are four of each letter, then the cell is tetraploid (e.g. AAaaBBbbCCccDDdd).

In the following questions, the term haploid (1n) refers to one set of chromosomes. This is typically the number of chromosomes found in the single nuclei of sex cells (gametes). In the flowering plant life cycle, this is also the chromosome number of the three nuclei within a germinated pollen grain (pollen tube) and the eight nuclei within an embryo sac. In plants, the haploid part of the life cycle is called the gametophyte. The normal haploid number for a human egg or sperm is 23 chromosomes (n = 23). The term diploid refers to two sets of chromosomes resulting from the union of the sperm and the egg. This is typically the number of chromosomes found in the nuclei of body cells (somatic cells) of a plant or animal. In plants, the diploid part of the life cycle is called the sporophyte. In a normal human, the diploid number is 46 chromosomes (2n = 46). The following link to life cycle patterns may be helpful in understanding the gametophyte and sporophyte parts of a life cycle. In the diagrams, everything above the red horizontal line is diploid (sporophyte) and everything below the red line is haploid (gametophyte). The terms sporophyte and gametophyte are used in the life cycles of plants, fungi and algae, but not animals.