WARM UP #2: Cells and Marcomolecules
Selected student responses

QUESTION 1: Cells are generally microscopic, ranging in size from about 50 microns for animal cells to as small as 1 micron for bacterial cells. Why do you think that cells - animal, plant, or bacteria - don't get any bigger than this? Why do you think we are made of 75 trillion very small cells, rather than just a bunch of very large cells?

From Ricca: Q1 = The reason cells are generally small in size is because with a smaller cell there is a higher amount of surface area. A tennis ball in size comparison to a basketball would be a much more efficient cell because the surface area to overall volume is higher than the ratio of the surface area to the volume of the basketball. The reason the surface area determines the optimum size of the cell is because it has to transfer oxygen and food into the cell and transport waste out of the cell. The total volume being smaller compared to being bigger makes the cell more efficient.

From DoodleBug: Q1 = The surface area does not increase as quickly as volume, so it would be difficult for the membrane to contain that much cytoplasm. The flow of nutrients into the cell and waste out of the cell would not be fast enough and the cell would die. It would also have trouble moving things through the cytoplasm.

From SweetPea: Q1 = If one very small cell dies then it doesn't harm the body, but if a very large cell dies then it can be very harmful to the body. Each cell is specific for maintaining life in a large organism.

From Dr. Marrs: Good answers – the bigger a cell gets in size, the more volume it has compared to its surface area. Why is surface area important? This is where the cell interacts with its environment – the bloodstream, the pond where it lives, etc. All cells need a constant supply of fresh oxygen and need a way to get rid of wastes like carbon dioxide. A cell with a huge amount of volume could not get fresh oxygen into the middle of the cell, and could not get rid of wastes easily. (Fun fact: there are ~75 trillion cells in a human body!)

QUESTION 2: Starch (like bread, pasta) is a glucose polymer that gives us energy, but cellulose, an almost identical glucose polymer, is indigestible. Why do you think that ONE of these almost identical molecules can be digested, while the other can't? Why is cellulose (non-nutritive and indigestible) a very necessary part of our diet?

From Jess Q2 = The reason starch and cellulose are different is because of the differences in bonding patterns in their monomers. In cellulose, the chains stretch out side-by-side making the chains strong and tight which also makes them hard to digest. In starch, the monomers are positioned at an angle, which makes the chain into a spiral pattern but also makes the chain more accessible to enzymes. Cellulose is a very necessary part of our diet because it is used as structural material in cell walls.

From HW Q2 = I'm not sure why one can be digested and the other cant but I do know that cellulose is used for structure purposes

From Q2 = Something to do with the glucose linkage of cellulose makes it indigestible, if I remember correctly. Cellulose is necessary for fibre which aids in digestion and prevents certain cancers.

From Dr. Marrs: Starch is a long chain of sugar molecules that plants link together to serve as an energy reserve for their cells. (Even though it is made of sugar, because it is a long chain it doesn’t taste sweet to us.) We eat the plants and get energy from their starches - ‘carbos’ like pasta, potatoes, bread - because in our body (or in a plant’s cells) the starches break down to sugar, which is broken down farther for energy.
Plants put sugar molecules together in a slightly different way to make cellulose. Cellulose is the main structural material in a plant cell wall – it is rigid and holds the plant up. (Wood is almost pure cellulose – we use it as a structural polymer too! Paper and cotton are also made of cellulose.) Because of the way the sugars are linked together, almost no living organisms can break it down – a good feature for a polymer that the plant is making to hold itself up!!! Even though we can’t digest it, cellulose serves a useful purpose in our diet, as “fiber”.

QUESTION 3: Butter and oil are both fats. Why is butter a solid at room temperature, but corn oil a liquid? What is "soft margerine"?

From Angie: Q3 = Butter is a solid at room temperature because it is an animal fat and has saturated fatty acids. Corn oil is a liquid beacuse it is a plant fat, which has unsaturated fatty acids.

From Zephyr: Q3 = The difference is whether the carbon chain on a fat molecule is saturated or unsaturated. Saturated fats are solid at room temperature where as unsaturated fats are liquid. Soft margerine is a mix between saturated and unsaturated fats.. I think.

From TP Q3 = The more double bonded hydrogens you add to a fat (replacing the single bonded ones) the more liquid it is at room temperature. If something is solid at room temperature it has more saturated fat, such as CRISCO, and if it is more liquid, it has less saturated fat. Either way it will have fat. I assume that "soft margerine" just has more double bonded hydrogens, so it is softer at room temp.

From Dave Q3 = …. I'm not sure what margerine is made of. It is one of the freakish side effects of technology much like Velveeta.

From Dr. Marrs: Good answers. Animal fats have saturated (“full of hydrogens”) fatty acids, which pack closely together, resulting in a solid at room temp. Plant fats, or oils, have unsaturated (loose, kinked fatty acids ) that don’t pack together into a solid at room temp. Margarine and Crisco are vegetable oils that are chemically turned into solids by adding hydrogens to the vegetable oil, ‘stiffening’ the fatty acids. Soft margarine has a few more hydrogens than oil, which adds some solidity, but not as much as regular margarine! As for Velveeta and American Cheese - there is no animal (dairy) component to these “cheese foods” - they are plant oils chemically converted to solids, plus some attractive orange coloring! Ooh yummy! What is Olestra, or “fake fat’? We’ll talk about it!

QUESTION 4: Voices of N100: Comments, suggestions...

Q4 = I like how our book gives only a small amount of information on each topic, but I really can't find anything that you are asking for in it. It doesn't really seem to relate much to the lecture notes and I don't really follow how I'm supposed to find the warm-up questions.
Note from Dr. Marrs : the answers to the WarmUps are usually NOT in the book – they are more like thought questions to get you thinking about what is in the book and what we will talk about in lecture. Do the readings, then answer the WarmUps to the best of your knowledge!

Q4 = Professor, I would appreciate it if you could:
1) talk a bit more slowly, especially when discussing a difficult concept.
2) repeat the questions asked by someone before answering him or her.
3) hand out a list of suffixes and prefixes and their meaning.

Q4 = You talk too fast.....suggestion: maybe slow down the information flow and provide a little more explanation?
Q4 = I like your voice it keeps me awake. You talk a little too fast but it's not to bad.
Q4 = I like the class but like you said yesterday you talk way too fast and I believe that not all things are completely understood before you switch to a different topic.
Q4 = I really enjoy this class. I am looking forward to learning new things and improve on the things I wasn't sure about. I have one suggestion and that is to have maybe more talking in between notes to let our hands rest.

OK! Points are well taken. : ) Remind me to Slow It Down if I get going too fast! Please don’t hesitate to ask me to repeat or go over things in class – if you have questions, probably others in the class do too!

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