# Tutor profile: Jordan S.

## Questions

### Subject: SAT

The system of equations below has solution (x,y). What is the value of x + y? 2/3(3x-2y) = 25/3 x=6y

You can solve any system of equation using two different methods: substitution or elimination. In the example above, substitution is the preferred method because we can substitute x=6y for x in the first equation. We can also simplify the first equation by multiplying both sides of the equation by 3. This gives us... 2/3(3x-2y) = 25/3 (3){2/3(3x-2y)] = (25/3)(3) The 3's on both sides will cancel the 3's in the denominator of the fractions giving us: 2(3x-2y) = 25 Now we will substitute x=6y 2(3x-2y) = 25 2(3(6y)-2y) = 25 2(18y-2y) = 25 2(16y) = 25 32y = 25 y= 0.78 Now plug the value of y into the second equation to find x x=6y x=6(0.78) x=4.69 Now we must find x+y 0.78 = y x=4.69 4.69+0.78 = 5.47

### Subject: Chemistry

Using Le Chatelier's principle, describe what happens when there is increased H+. CO2 + H20 <-> H2CO3 <-> HCO3- + H+

Le Chatelier's principle states that in dynamic equilibrium, if there is a change made, the position of equilibrium will move to counteract the change. In the example above, the change made is the increased H+. In order to counteract this increase in H+, the equilibrium will shift to the left, thereby using more H+ and increasing CO2 and H2O. In general for Le Chatelier's principle: A + B <-> C If you increase A or B, the reaction will shift to the right (use more of A and B to make more of C) If you decrease the amount of A or B, the reaction will shift to the left (to make more of A and B)

### Subject: Biology

What change in afferent arteriolar resistance would lead to an increase in renal plasma flow (RPF), increase in glomerular capillary hydrostatic pressure (PGC), and an increase in glomerular filtration rate (GFR).

The glomerulus is the system of capillaries where blood is filtered at the nephron. There is one blood vessel entering the glomerulus and one exiting the glomerulus (one taking blood to the filter, one taking blood away from the filter). These blood vessels are the afferent (towards) and efferent (exiting) arterioles, respectively. Increases in afferent or efferent arteriolar resistance refers to vasoconstriction. Increased afferent arteriole resistance (vasoconstriction) leads to decreased blood through the afferent arteriole. Vasoconstriction can be thought of as stepping on a garden hose. When you step on a garden hose, you decrease the amount of water coming out of the hose downstream from where you are applying pressure. Therefore, increasing the resistance of the afferent arteriole (vasoconstriction) leads to decreased flow of blood through this arteriole. We refer to this blood flow as renal plasma flow. Vasodilation (decreased resistance) has the opposite effect, allowing increased renal plasma flow. In the question stem above, we are told the RPF is increasing. Therefore, the afferent arteriole must be dilated. Similarly, because there is increased blood reaching the glomerulus, there will be increased glomerular capillary hydrostatic pressure (PGC). Hydrostatic pressure is the pressure the blood in the capillary exerts on the capillary wall. It increases with increased renal plasma flow. Finally, glomerular filtration rate (GFR) is determined by net filtration pressure. It is helpful to remember the equation: filtration pressure = (PGC-PBS)-(Osmotic pressure GC-Osmotic pressure BS) PBS = Hydrostatic pressure bowman's space Osmotic pressure GC (Glomerular capillaries) Osmotic pressure BS (Bowman's space) = 0 (effectively zero, assumed to be 0 for calculations) When discussing GFR, we are looking at 2 different types of pressure: hydrostatic pressure and osmotic pressure. Hydrostatic pressure is due to blood flow, and blood wants to flow from high pressure to low pressure. The hydrostatic pressure is generally greater in the glomerular capillaries than Bowman's space. As discussed above, in afferent arteriole dilation, the hydrostatic pressure in the glomerular capillary is increased. Therefore, there is an increased driving force for filtration (increased filtration pressure) and the GFR will be greater.

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