On page 42, Moalem mentions the revolutionary
reproductive medicine that allows people to freeze and preserve eggs and sperm.
This relates to Big Idea 3: Living systems store retrieve, transmit and respond
to information essential to life processes. Genetic information necessary for
the survival, growth, and reproduction of an organism, can be frozen in the
form of eggs and sperm and stored through vitrification, and then fertilized in
vitro. Similarly, embryos can be frozen and stored for later conception even
more successfully than eggs and sperm.
Please explain biologically why women would
want to freeze their eggs, and why men may not need to. Also, relate why it is
more successful to freeze embryos than freezing eggs and sperm, to mitosis
and meiosis.
Moalem also mentions the viability of large
human organs for transplants later on this page. This relates to Big Idea 4:
Biological systems interact, and these systems and their interactions possess
complex properties. Organ and organ system interaction are essential to
biological activities for organisms as a whole and cannot be stored for long
periods of time because of their complex properties. Generally, this is because
of the damage ice crystals can have on the tissues and organs and the effects of
freezing the flow of fluids into and out of the cell.
Explain specifically (on a molecular level) the
effect of osmotic pressure and the concentration gradient on the cells and
their environment (of organs). Also describe the role aquaporins play when
cells begin to react to colder temperatures and how they affect the water supply
inside the cell and outside the cell. Finally, briefly explain why the wood frog can effectively recover after being frozen during the winter, but human organs
cannot after more than a few hours.
Women would want to freeze their eggs because it would allow them to save their eggs in case they suddenly are diagnosed with a disease that will make them infertile, or if they want to have children at a later age where normal sexual reproduction may be dangerous to the women, according to the NYU Fertility Center. Men may not need to freeze their sperm because sperm is continuously made in the testes throughout the males' lives (Campbell 1007).
ReplyDeleteAlso, it is more successful to freeze embryos than freezing eggs and sperm because embryos are already fertilized cells, whereas with frozen sperm and egg, there's a chance that fertilization may not be completed properly. This is related to Big Idea 4 (biological systems interact, and these systems possess complex properties) in that the sperm and egg interact to fertilize into an embryo, and if the sperm or egg is frozen, the cryopreservation may disrupt normal fertilization.
The effect of osmotic pressure and the concentration gradient on cells and the organs is that when the cell is hypertonic to the environment, meaning the cell has less water than the environment, water molecules go into to cell and cause it to become turgid, or the cell shrivels up. When the cell is hypotonic to the environment, meaning the cell has more water than the environment, water molecules move out of the cell, or the cell just lyses. the concentration gradient effects the cell in that it establishes whether the cell is hypertonic or hypotonic to the environment. Thus, osmotic pressure and concentration gradient can disrupt the organ's proper function and structure by destroying cells.
According to Dr. Moalem's Survival of the Sickest on p. 42, aquaporins are responsible for regulating water concentration in the cell by acting as protein channels for facilitated diffusion. When the cell is in a colder temperature, aquaporins move water out of the cells to minimize ice formation inside the cell. Also according to Dr. Moalem on p. 43-44, wood frogs can effectively recover after being frozen during the winter because the water in the organ cells are "pooled in the abdomen" and the frogs' livers inject massive doses of glucose into the bloodstream to lower freezing point of blood. However, human organs cannot survive being frozen because they do not have the ability to move the water out of the cell like the wood frogs, and the ice crystals destroy cells by cutting cell walls or organ capillaries.
Unlike in cells where the body can save different resources such as carbohydrates for late use when needed, the body of a female does not save its eggs. Instead, eggs get released cyclically, but they cannot be saved after they are released. The female body also has a limited number of eggs that can be fertilized. Since there is only a certain amount in one body, it is logical for a woman to freeze some of their eggs for fertilization at a different time. Men, however, do not need to do this. Men can produce sperm throughout their entire life, so there is no need to preserve them. More can be produced for fertilization when needed.
ReplyDeleteFreezing an embryo, though, is a more reasonable thing to do than freeze gametes. An embryo is more stable than a gamete, so there is less of a chance of damaging the cell during the freezing and thawing processes. The implantation process is also “twice as likely” to succeed.
http://www.fertilityproregistry.com/article/embryo-freezing-vs-egg-freezing.html
The osmotic pressure and concentration gradients of a cell have a major influence on the cell due to its environment. Dr. Moalem explains on pages 39-40 that alcohol is”natural antifreeze”. But, when water is present, it does not allow the sugar in the cells to accumulate at a high enough concentration on one side to effectively decrease the freezing temperature of the solutions in the cells in the specific cold environment. This is why the body tries to remove as much water as it can when the environment is cold. It allows the body to increase the concentration of sugar in the cells to decrease the freezing temperature. This also prevents the water from freezing in certain places that propose potential dangers to the body. When water freezes, it forms a crystallized structure that expands. This would cause ruptures in certain places such as vital organs.
The wood frogs are able to remove the water from their cells and store it in the abdomen and moves high amounts of sugar into the cells. This, along with clotting factors, prevents damage to major organs. And when the temperatures begin to rise, the frogs are able to reinsert the water into the bloodstream when it melts due to the adaptation it has developed over time. Humans, though, have not developed such an adaptation. Removing organs and storing them is not what they are meant to do, so this will not work as well as preserving organs of wood frogs. This connects the big idea 1 because different environmental pressures over time have forced these diversifying adaptations between species.
By Daniel Majeed dmajeed4@students.d125.org