7th Grade Life Science Stumpers

I'm a TA in such a class. These questions got me.

1) Are teeth made of cells?

2) Is there pigment in tree bark making it brown?

3) Why don't animal cells have cell walls? (I have an idea, but am not sure).

4) Are there blood vessels in bones (e.g. in the marrow)?

5) If you break a piece of celery or a carrot in half, do you rupture cells (vs. breaking cells apart from one another)?

6) Why do starving people have big bellies?

Originally posted by AThousandYoung
I'm a TA in such a class. These questions got me.

1) Are teeth made of cells?

2) Is there pigment in tree bark making it brown?

3) Why don't animal cells have cell walls? (I have an idea, but am not sure).

4) Are there blood vessels in bones (e.g. in the marrow)?

5) If you break a piece of celery or a carrot in half, do you rupture cells (vs. breaking cells apart from one another)?

6) Why do starving people have big bellies?

1. Yes, so are bones, so is every part of our bodies.
2. Yes, the pigment makes the bark brown. However, this is not "melanin" that makes our skin brown or tan. The "brown" is just a color. Whatever "the pigment", it's the coloring substance.
3. Plant cells have walls. Animal cells have "membranes." Think of it this way: Plants are immobile (in the animal sense), and the "structure" benefits them. Animals "move." There are many more fundamental biochemical principles involved. These are 7th grade answers.
4. Yes, there are blood vessels in bones. In fact, if a doctor or a nurse or a paramedic cannot put a needle into a vein, they can insert one into the bone - right into the marrow - and give fluids into the veins that way.
5. A few celery cells will break, sure. Just like a swift kick in the bum kills a few muscle cells. Not enough to matter.
6. Starving people have big bellies from gas bloating, or poor nutrition, bad nutrition balance. A big belly is not a sign of health. Those starving people have underdeveloped other parts of their bodies.

Caveat: All of these answers are just off the top of my head. I don't have a clue if i'm right or wrong, except on a few of them . .like the bones and cells.

Originally posted by coquette
1. Yes, so are bones, so is every part of our bodies.
2. Yes, the pigment makes the bark brown. However, this is not "melanin" that makes our skin brown or tan. The "brown" is just a color. Whatever "the pigment", it's the coloring substance.
3. Plant cells have walls. Animal cells have "membranes." Think of it this way: Plants are immobile (in the animal ...[text shortened]... clue if i'm right or wrong, except on a few of them . .like the bones and cells.

1. Partly. The enamel and AFAIK the dentine are mineral excretions of the tooth pulp, which is made of cells.
2. No, there are several pigments, not a single one is responsible on its own for the brown colour of the bark; some are green, some brown, some reddish; the combination is what forms the bark's brown.
3. All cells have membranes, in animals and plants as well as fungi and other organisms. The cell wall attaches to it.
6. AIUI, it's usually oedema, not gas. Mainly caused not so much by lack of food, as (as you write) unbalanced nutrition; specifically, a lack of proteins.

Richard

Originally posted by Shallow Blue
1. Partly. The enamel and AFAIK the dentine are mineral excretions of the tooth pulp, which is made of cells.
2. No, there are several pigments, not a single one is responsible on its own for the brown colour of the bark; some are green, some brown, some reddish; the combination is what forms the bark's brown.
3. All cells have membranes, in animals a ...[text shortened]... of food, as (as you write) unbalanced nutrition; specifically, a lack of proteins.

Richard

Cool. Thanks!

Originally posted by Shallow Blue
Mainly caused not so much by lack of food, as (as you write) unbalanced nutrition; specifically, a lack of proteins.

Richard

That is what I thought, the subjects abs are weak and therefore do not contain the intestines and other organs, resulting in a "pot belly"

Originally posted by Drew L
That is what I thought, the subjects abs are weak and therefore do not contain the intestines and other organs, resulting in a "pot belly"

That was my thought too.

Originally posted by Drew L
That is what I thought, the subjects abs are weak and therefore do not contain the intestines and other organs, resulting in a "pot belly"

No


The cause of the "pot belly" not simple, there are many reasons for it. I'll outline 2 reasons i consider to be most significant. The first is most significant.

(1) Chronic malnutrition, especially a deficit of protein, decreases the liver's capacity to synthesis proteins. As a result the liver cannot make enough albumin* to maintain the oncotic pressure of the blood (the oncotic pressure of the blood is the tendency for fluid to move into the vascular space). A decrease in the oncotic pressure of the blood (when albumin is low) causes fluid (mostly water) to move out of the blood stream and into the extra-vascular space. For some reason this occurs mostly in the portal system and you get fluid accumulating in the peritioneum (the cavity in which the intestines and abdominal organs sit). The presence of fluid in the peritoneum is called ascites. When large amounts of fluid accumulate you see a "pot belly".

For more info look up kwashiorkor.


(2) A severe deficiency of thiamine (as seen in chronic malnutrition) can cause heart failure (wet beriberi). As the heart fails fluid backs up in the venous system and the pressure in the venous system increases. This increased pressure causes fluid to leak out of the blood vessels and into the extra-vascular space. It often accumulates in the legs causing oedema but it also backs up into the liver and the portal system, in this case the fluid leaks into the peritoneum and you get ascites, as in case (1).



Another cause is changes in capillary wall permeability due to catabolism and derangement in cell function.

Also you can get a massively enlarged liver which can give a "pot bellied" appearance.






*Albumin is a protein of large molecular weight which circulates in the blood. Its role is mostly to maintain plasma oncotic pressure but it also acts as a transfer protein for bilirubin, some ions like calcium, fatty acids, hormones and some drugs.

4. Yes, there are blood vessels in bones. In fact, if a doctor or a nurse or a paramedic cannot put a needle into a vein, they can insert one into the bone - right into the marrow - and give fluids into the veins that way.

Bones are surprisingly vascular.
Not only is the marrow full of blood but even the hard dense cortical bone is full of tiny microscopic channels called canaliculi. Tiny veins, capillaries and nerves run in these channels.

The integrity of the bone is dependent on adequate blood supply. If the blood supply to a portion of bone is interrupted (commonly seen in neglected fractures of the scaphoid bone) that part of the bone will become brittle and crumbly. A process called avascular necrosis.