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Answers
11. The mitral (bicuspid) and tricuspid valves between the atria and ventricles close to avoid back flow of the blood to the atria when the ventricles contract. This causes the first sound, S1, or as it is heard, “lub.”
The semilunar valves (at the exits of the ventricles) close to prevent blood backflow from arteries caused by lower pressure in the ventricles as the ventricles expand to fill with blood before pumping it. This causes the S2, or “dub” sound.
12. In the metaphase cell, there are 4
chromosomes (8 chromatids) total and two sets of homologous chromosomes that are
duplicated. In the anaphase cell, there are 8 chromosomes. The resulting daughter
cells will also be diploid and genetically identical to the mother cell.
This is a haploid cell in metaphase and anaphase of mitosis. There are 2 chromosomes
(4 chromatids); 1 big chromosome, 1 small chromosome in the metaphase cell. In the
anaphase cell, there are 4 chromosomes present. The resulting daughter cells would
be halploid and genetically identical to the mother cell.
There are two divisions in meiosis. The cell entering meiosis is diploid. In meiosis
homologous chromosomes pair (allows crossing over of genetic material), but
homologous do not pair in mitosis. Another difference is that after the first meiotic
division, the cells do not reenter interphase and DNA is not replicated.
metaphase 1 of meiosis, bivalents orient at the metaphase plate and homologous are
paired. Each chromosome of a homologous pair attaches to fibers from opposite poles.
The sister chromatids attach to fibers from the same pole. In anaphase 1, the
centromere does not divide and homologous chromosomes move to opposite poles.
This is the separation of
homologous chromsomes.
These are the products of the first
meiotic division. Only 1 of each
chromosome (long and short) is
present, therefore the daughter
cells produced from the first meiotic
division are haploid.
In between meiosis 1 and 2, the DNA does not replicate and the starting cells are
haploid.
In metaphase 2, the chromosomes
align at the metaphase plate and sister
chromatids attach to spindle fibers
from opposite poles.
In anaphase 2, the centromeres divide
and chromatids move to opposite
poles. This is the separation of sister
chromatids.
The daughter cells produced are
also haploid, having only 1 of each
chromosome (long and short).
14. Three major events occur in plant cells during photosynthesis: (1) absorption of light energy, (2) conversion of light energy into chemical energy, and (3) storage of chemical energy in sugars. Those three events occur in two distinct but interdependent sets of reactions.
Photosynthesis is a two stage process. The first process is the Light Dependent Process (Light Reactions), requires the direct energy of light to make energy carrier molecules that are used in the second process. The Light Independent Process (or Dark Reactions or Calvin Cycle) occurs when the products of the Light Reaction are used to form C-C covalent bonds of carbohydrates. The Dark Reactions can usually occur in the dark, if the energy carriers from the light process are present. Recent evidence suggests that a major enzyme of the Dark Reaction is indirectly stimulated by light, thus the term Dark Reaction is somewhat of a misnomer. The Light Reactions occur in the grana and the Dark Reactions take place in the stroma of the chloroplasts.
In the Light Dependent Processes light strikes chlorophyll a in such a way as to excite electrons to a higher energy state. In a series of reactions the energy is converted (along an electron transport process) into ATP and NADPH. Water is split in the process, releasing oxygen as a by-product of the reaction. The ATP and NADPH are used to make C-C bonds in the Light Independent Process.
