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7 May 2019

Phospholipids make up most of the lipid part of the cell membrane. Since water exists on both the outside and inside of a cell, which of the following phospholipid arrangements makes the most sense?

a single layer of phospholipids with the polar heads facing outside the cell

two back-to-back phospholipid layers with the non-polar tails facing out on both sides

a single layer of phospholipids with the polar heads facing inside the cell

two back-to-back phospholipid layers with the polar heads facing out on both sides

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Beverley SmithLv2

7 May 2019

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3. In an aqueous environment, the phospholipids of a membrane____.

a) are arranged in a single layer

b) are arranged in a bilayer with the polar heads of each layerlocated at the surface

c) are arranged in a bilayer with the fatty acid tails locatedat the surface

d) are arranged in a bilayer but the phospholipids have nospecific orientation

e) dissolve

4. which of the following molecules demonstrate dual solubilitycharacteristics

a) sterols only

b) proteins only

c) phospholipids only

d) sterols and phospholipids

e) sterols, phospholipids, and proteins

5. The "mosaic" part of the fluid mosaic model refers to themembrane ____.

a) proteins

b) phospholipids

c) cholesterol

d) functions

e) layers

9. Transport of a molecule across a cell membrane by facilitateddiffusion ____.

a) does not exhibit specificity for a particular type ofmolecule

b) requires the input of energy

c) depends on a concentration gradient

d) goes against the concentration gradient

e) allows non-polar uncharged molecules to diffuse across amembrane

13. A transport system in which transport of an ion in onedirection provides the energy for active transport in the oppositedirection is known as ____.

a) primary active transport

b) active diffusion

c) secondary active transport

d) cotransport

e) osmosis

14. Cells undergo exocytosis ____.

a) to pump protons down a concentration gradient

b) when replicating

c) to secrete protein and wastes from the cell

d) to ingest nutrients

e) as a means of cellular protection

15. What is the molecular basis of familialhypercholestremia?

a) HDL enters cells using a specific receptor on the cellsurface

b) LDL enters cells using a specific receptor on the cellsurface

c) HDL exits cells using a specific receptor on the cellsurface

d) LDL exits cells using a specific receptor on the cellsurface

e) receptor-mediated exocytosis

16. Carrier molecules are utilized for ____.

a) active transport only

b) passive transport only

c) both active and passive transport

d) osmosis

e) transport of all types of molecules

17. All of the following are functions of integral membraneproteins EXCEPT ____.

a) transport of polar molecules

b) reception of chemical signals form other cells

c) cell division

d) recognition of other cells as being "like"

e) cell-cell binding

olivecod348

1 In our hierarchy of levels of organization (from atom to biosphere), at which level does life begin? Can you relate form to function when it comes to cell structure of a plant cell like Elodea? A thin simple squamous epithelium like in the lining of the lungs? A thicker columnar epithelial layer like that found in the stomach/intestine?

2. Can you remember the architecture of the phospholipid bilayer that makes up the cell membrane? How the 2 phospholipids arrange themselves to form the bilayer? And how you produce a water-proof (hydrophobic) barrier from the bilayer architecture?

3. What are the 3 roles of the plasma membrane? How does the barrier or âfenceâ role of the plasma membrane relate to non-polar vs. polar vs. charged molecules? How does the membrane control the amounts of certain molecules inside the cell? How does this relate to class rule #4? How do cells communicate with one another?

4. How does the plasma membrane help with this function? Which macromolecule is critical to this function? How does this all relate to red blood cells and âA/B/AB/Oâ blood type?

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raspberryraven266

It's a pretty elementary concept, and when I first learned of itI don't think I had the foundations to even think of such aquestion, but I found myself the other day thinking about theamphipathic nature of the phospholipids in the plasma membrane andwhy it might be that lipid-soluble molecules don't stay in betweenthe layers (of the bilayer).

I know that simple diffusion is a response to a concentrationgradient, but consider a case where equilibrium is being restoredand lipid-soluble molecules are diffusing from whateverextracellular matrix through the membrane and into the cytosol.Towards the end of this process, when equilibrium is nearlyrestored and the last few molecules are making their way into thecell, the rate of diffusion for these last couple molecules will beslower than those that diffused when the concentration differencewas greater. Since the polar heads on the outside and inside of thebilayer are hydrophilic but the inner part, where the fatty acidtails are, is hydrophobic, what drives a molecule to leave thecozy, accepting, lipophilic environment of the middle (of thebilayer) to cross through the cytosolic-side rejecting polar headsand enter the cytosol?

I understand that initially these molecules were moving into thecell in response to a difference in intracellular vs extracellularconcentration, but I'm asking whether we would ever see a casewhere the gradient is nearly zero and a molecule in transit simplydecides to reside in between the layers instead of crossing all theway into the cell; as if moving through the cytosolic polar headside is not worth the effort to reduce a nearly-zero gradient tozero.

Please ask me if I can clarify my question in any way -- I'mfinding it difficult to phrase. I asked my professor (who has herdoctorate in toxicology & pharmacology) and she understood whatI was asking but didn't have an answer.