Cell size | Structure of a cell | Biology | Khan Academy

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Thinking about the limiting factors of cell size. Focus on volume to surface area ratio.
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[@ananyajha9484]

I was struggling to understand this concept, but wasn't able to do it on my own. Thank you so much, it's very very clear now.

[@mahalyalinam1916]

i think the end part, (the diffusion part) could have been given a bit more attention. like how Ron Milo points out using the diffusion equation( t= d^2/6d) that big cell = more the distance molecules have to travel inside a cell(which occours by random diffusion) , and how this big distance actually requires more time, so processes inside a cell that depends on molecules moving long distances( ex signal transduction) drastically slow down

[@SuperLegoMiner99]

THANK YOU SO MUCH I didn't really understand what limited cell size and needed some last minute help b4 my science quiz tmrw and now I COMPLETELY UNDERSTAND IT

[@cameron3786]

Yep.. same here.

[@who5563]

Woa, thanks! Now I can pass 5th grade!

[@sejalpanchal115]

Thank you so much I passed in my biology test🥳🥳🥳🥳

[@cameron3786]

Yea me too 😀😄

[@xx_jesus_xx1982]

Very informative! Thank you!

[@row268]

Keep up the cell videos sal!

[@cailin5591]

What up Mr. warrens class :)

[@cameron3786]

Thanks this was helpful!

[@GoldenDoom]

perfect to binge watch for the test tmr

[@GhostMr99]

very intresting! thanks for posting it.

[@AnonymousAlien2099]

GhostMr99 *uploading

[@cameron3786]

@Anonymous alien it’s basically the same thing lol

[@MixolydianMode]

good video!

[@abuzarv7708]

thanks

[@coolbionicle]

What about bubble algae? They are unicellular organisms, they are spherical and they are huge on a celular scale.

[@DDoubleEDouble]

Yeah, I was thinking the same thing, they're huge.

[@ninjagaming2.018]

@@DDoubleEDouble 😒😒😒😒

[@TasyaAdzkiya]

There is an interesting reason on why cells must remain fairly small (with few exceptions) that I read on Khan Academy article titled "Prokaryotic cells". Feel free to discuss because I'm not sure if I understand it thoroughly.
I don't understand this paragraph, please correct me if I'm wrong on my understanding of this paragraph:
"Each patch of membrane can exchange only so much of a given substance in a given period of time - for instance, because it contains a limited number of channels. If the cell grows too large, its membrane will not have enough exchange capacity (surface area, square function) to support the rate of exchange required for its increased metabolic activity (volume, cube function)."
Disclaimer: in my understanding and in this explanation of mine, it doesn't necessarily mean that a cell will grow and it goes bigger and bigger continuously. It just means that if we were to compare cells with certain lengths to each other, it will have a pattern that shows us that the greater the surface area is, the volume will be more greater relative to the surface area.
OK, my question is:
Does it mean that the surface area (which, in this case is the area of the plasma membrane because it is the cell's interface with the environment) can't keep up with the more rapid increase in volume (which, in cubic units compared to the surface area that is in square units) as the length increases?
You can see that because of the more rapid increase in volume, the volume that, at first, is more "small" relative to the surface area (in this case, the plasma membrane), becomes greater relative to the surface area at some point when the length reached a certain point and onward.
For example, you substitute 1 into the volume formula (which is the length cubed) and do the same with the surface area formula (which is 6 times the length squared because the area of each face is the length squared [remember that it is a cube and each face of a cube is a square] and we have 6 faces in a cube). The ratio of surface-area-to-volume would be 6 to 1.
See that the volume will be greater than the surface area eventually as the length increases. In this case, it's going to start when the length is 7 and onward. But, when x is 6, they are going to be equal, that's when the volume catches up to the surface area. To prove it, try substituting 8 into the volume and surface area formula. The ratio of the surface area to the volume would be 384 (6 x 8 x 8) to 512 (8 x 8 x 8).
Now that the matter is clear, we can start to think about why is that a problem. Well, in the article, it says that:
"If the cell needs to take up nutrients, it must do so across the membrane, and if it needs to eliminate wastes, the membrane is again its only route. Each patch of membrane can exchange only so much of a given substance in a given period of time."
That's a problem because if a cell is bigger (and of course, if it's bigger, it will have more volume), it requires more substances to keep up with everything that it's doing and, of course, it will produce greater amount of waste. It means that it will have to take in and take out more substances. So, the combination of the nature of the plasma membrane that can only take a certain amount of substance for a given area in a given period of time AND the more rapid increase of the volume relative to the surface area makes cells must remain fairly small, regardless of whether they’re prokaryotic or eukaryotic (with few exceptions as the article said).

[@44suhaanpawle8d6]

Awesome

[@500KiloVolt]

Cool.

[@jessicalv6442]

Egg cell is not the largest sphere cell. Algea Caulerpa is! And it is an unicellular. Biology always makes people amaze!

[@gamerwithanxbox9448]

Cool

[@bixihernandez732]

I love this! so helpful :)

[@pendodaniel6931]

thank you

[@soliy2481]

The red blood cells look like sweets

[@cameron3786]

Ikr

[@digitaladdiction4583]

This video takes to long

[@vinceparis9587]

Too*

[@ninjagaming2.018]

😒😒