Mammal Lactation
Lactation in mammals is a positive feedback loop, because milk is continually produced until the offspring stops breastfeeding. The response increases the stimulus. It is not negative, because it does not seek to limit a detrimental stimulus. In this case, the stimulus is the baby suckling, which results in signals being sent to the hypothalamus that then releases oxytocin, which in turn results in continued milk production. This does not end until the baby is done suckling.
Monday, December 15, 2014
Sunday, December 7, 2014
12/1/14-12/5/14
This week, we spent most of our time on the diffusion and osmosis lab, with minimal notetaking or homework. I thought this was genuinely interesting; we had to apply our knowledge in the labs, reinforcing the material even without a lecture or a powerpoint. I wouldn't want to jump into this feet first, though; that is to say, I prefer having a solid foundation from notes and lectures before doing a lab. It won't be long before winter break, which will be a much needed respite from all my schoolwork; however, it won't be long after that until we have to take midterms. I'm going to look through my "5 Steps to a 5" book over break to review older material and get a glimpse of what lies ahead, so I can do well come the end of the semester.
Diffusion and Osmosis Lab Reflections
Investigation 1 dealt with surface area to volume, and why cells are as small as they are. We hypothesized that the 1cm cube would have the highest diffusion rate since it had the highest ratio of surface area to volume. The results supported our hypothesis, and the 1cm cubed was the only one that displayed full penetration. Cells remain small because a higher surface area allows for more cellular activity, and having a high ratio of surface area to volume provides an optimal surface area in a compact space.
In investigation 2, we created models of cells using dialysis bags and filled them with a solution (in our case, 10ml of 1M sucrose), and placed them into a beaker containing another solution (for our group, 100ml of 1M glucose). We weighed the models before placing them in the beakers and then again, after removing them after a 30 minute soak. For us, the cell gained 12.9% more of its' original mass. The underlying concept behind this investigation was tonicity; molecules will diffuse down a gradient until equilibrium is reached. Our cell gained mass, suggesting that molecules flowed into the "cell" from the solution; thus, this suggests that the solution was initially hypotonic.
Investigation 3 involved observing the cells of an onion through a microscope. First, we looked at the cells without placing water on them; then, we exposed the cell to both distilled water and saltwater. The distilled water resulted in water flowing into the cell, as the concentration in the cell was lower. When exposed to saltwater, however, the cell lost water and shriveled, as the concentration of water in the cell was higher than in the saltwater. This exemplifies both the effects of differing tonicities, and the fact that the amount of free water is more important than the total mass. There might have been just as many water molecules in the saltwater, but many of them were unavailable due to being bound to salt molecules, thus resulting in a hypertonic solution.
In investigation 2, we created models of cells using dialysis bags and filled them with a solution (in our case, 10ml of 1M sucrose), and placed them into a beaker containing another solution (for our group, 100ml of 1M glucose). We weighed the models before placing them in the beakers and then again, after removing them after a 30 minute soak. For us, the cell gained 12.9% more of its' original mass. The underlying concept behind this investigation was tonicity; molecules will diffuse down a gradient until equilibrium is reached. Our cell gained mass, suggesting that molecules flowed into the "cell" from the solution; thus, this suggests that the solution was initially hypotonic.
Investigation 3 involved observing the cells of an onion through a microscope. First, we looked at the cells without placing water on them; then, we exposed the cell to both distilled water and saltwater. The distilled water resulted in water flowing into the cell, as the concentration in the cell was lower. When exposed to saltwater, however, the cell lost water and shriveled, as the concentration of water in the cell was higher than in the saltwater. This exemplifies both the effects of differing tonicities, and the fact that the amount of free water is more important than the total mass. There might have been just as many water molecules in the saltwater, but many of them were unavailable due to being bound to salt molecules, thus resulting in a hypertonic solution.
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