A membrane that only "lets" certain molecules in while keeping other molecules out is ___ ___.
1 answer:
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Explanation:
1. As cells increase in size, their surface area:volume ratios decrease rapidly; larger cells have a harder time moving molecules across the membrane. Thus, substances required for cell growth cannot permeate the cell; cell growth is limited as the cells grow further.
2.Surface area to volume ratio is 6 units of surface: 1 unit of volume
surface area= or (1 cm x 1 cm x 6 )
volume= (1cm x 1cm x 1cm)
With a high surface area to volume ratio, substances readily diffuse across the membrane of the cell, into the cytoplasm. The cell is able to obtain all the materials it requires.
3. Surface area to volume ratio is 3 units of surface: 1 unit of volume
surface area= or (1 cm x 1 cm x 3 )
volume= (1cm x 1cm x 1cm)
As cells increase in size, their surface area:volume ratios decrease rapidly; larger cells have a harder time moving molecules across the membrane, as there is less of a permeable surface for substances to diffuse across. In comparison to the other cell with a 6:1 ratio, this cell likely cannot obtain all the materials it requires.
Further Explanation:
Cells require all substances to cross the cell membrane. These are semi permeable -only allowing some molecules to pass cross the membrane or surface. Cell membranes contain lipids which form a barrier; polarity or arrangement can give these non-polar macromolecules hydrophilic and hydrophobic properties. Via diffusion, small water molecules can move across the phospholipid bilayer acts as a semi-permeable membrane into the extracellular fluid or the cytoplasm which are both hydrophilic and contain large concentrations of polar water molecules or other water-soluble compounds.
The hydrophilic heads of the bilayer are attracted to water while their water-repellent hydrophobic tails face towards each other- allowing molecules of water and water soluble molecules, to diffuse across the membrane along the concentration gradient. Thus in smaller cells, the rate of diffusion is higher as the surface area to volume ratio is higher; a substance can diffuse all the way to the center.
However as cells increase in size, their surface area:volume ratios decrease rapidly; larger cells have a harder time moving molecules across the membrane, as there is less of a permeable surface for substances to diffuse across. To combat this, eukaryotic cells have specialized mechanisms to transport molecules along with membrane-bound organelles like the endoplasmic reticulum that provide a higher surface area for absorption and enable more efficient transportation.
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