Biology (2nd Period) / Chemistry (4th Period)

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"Good morning, everyone. Please answer when I call roll and get out your notebooks--we have a lot to cover today."

There are two important ways a cell can harvest energy from food: fermentation and cellular respiration. Both start with the same first step: the process of glycolysis which is the breakdown or splitting of glucose (6 carbons) into two 3-carbon molecules called pyruvic acid. The energy from other sugars, such as fructose, is also harvested using this process. Glycolysis is probably the oldest known way of producing ATP. There is evidence that the process of glycolysis predates the existence of O2 in the Earth’s atmosphere and organelles in cells:

* Glycolysis does not need oxygen as part of any of its chemical reactions. It serves as a first step in a variety of both aerobic and anaerobic energy-harvesting reactions.
* Glycolysis happens in the cytoplasm of cells, not in some specialized organelle.
* Glycolysis is the one metabolic pathway found in all living organisms.

In fermentation these pyruvic acid molecules are turned into some “waste” product, and a little bit of energy (only two ATP molecules per molecule of glucose – actually four are produced in glycolysis, but two are used up) is produced. Out of many possible types of fermentation processes, two of the most common types are lactic acid fermentation and alcohol fermentation.

"Now, I want you to take one of these handouts and complete the lab listed in your manual on page 23. You may leave when you and your partner are finished."




"Good morning. Please turned in the homework I assigned last time."

The Combined Gas Law is a combination of Boyle's and Charles' Laws. The Combined Gas Law describes the relationship between pressure, volume, and temperature. For example, if the pressure increased, wither the volume would decrease or the temperature would increase.

The Combined Gas Law can be used to solve any Boyle's or Charles' Law problem. If one of the variables remains constant, disregard that variable by leaving it out of your equation or setting it to the same value on either side of the equals sign.

The pressure and volume of a gas are inversely proportional to each other, but directly proportional to the temperature of that gas.

Mathematically, this can be represented as:
Temperature = Volume x Pressure / Constant
or
Volume = Constant x Temperature / Pressure
or
Pressure = Constant x Temperature / Volume
or
Pressure x Volume/Temperature = Constant

Substituting in variables, the formula is:
PV/T=K

Because the formula is equal to a constant, it is possible to solve for a change in volume, temperature, or pressure using a proportion:
PV/T = P1V1/T1

Let's try a problem with the Combined Gas Law. For example, the pressure and temperature of a gas are changed to STP (101.3 kPa/0°C) from 22.0°C and 30.8 kPa. What will be the new volume if the original volume was 205 mL?

First, we must convert degrees Celcius to Kelvins. This means that our original temperature was 295 K and our target temperature is 273 K.

It seems that the pressure increases, but the temperature decreases. Because of their inverse relationship, the increased pressure will decrease the volume. Because of their direct relationship, the decreased temperature will decrease the volume, also. If we consider the amount that the pressure increases, it more than triples. The temperature decreases only slightly. Therefore, it is safe to assume that the new volume will be less than a third of its original volume, or less than 68.2 mL (205 x 0.3333 = 68.2).

Plug values into the formula
From the problem, we know that, for the original state of the gas, the conditions were:
Volume (V) = 205 mL
Temperature (T) = 295 K
Pressure (P) = 30.8 kPa

We also know the target temperature and pressure:
Temperature1 (T1) = 273 K K
Pressure1 (P1) = 101.3 kPa

The unkown is V1. Our equation is:
30.8 kPa x 205 mL / 295 K = 101.3 kPa x V1 / 273 K

Manipulating the equation, we get:
V1 = 30.8 kPa x 205 mL / 295 K x 273 K / 101.3 kPa

V1 = 57.68 mL

However, because our problem only was to three digits of precision, the answer is:
V1 = 57.7 mL

To check our answer, we must compare it to our earlier estimate. We estimated the value to be less than 68.2 mL. Because 57.7 mL is less than 68.2 mL, but not incredible much so (like 20 - 30 mL), we can assume the answer to be correct.

Homework: Please do the problems listed on page 33 of your textbook and be ready to discuss them next week. Have a nice day.

Comments

Re: Biology

[sooo_cute]

Quinn may have gone to the wrong class yesterday. Look, she has a lot. She's confused.