Question

the phospho- (13-) pid molecule:
polar portion (hydrophilic),
charged group,
alcohols,
phosphate,
glycerol.
nonpolar portion (hydrophobic),
fatty acid chain.

• the cell membrane is composed of a double layer of ______
• the head portion is hydrophilic (____) and is ____ to water
• the tail portion is hydrophobic (____) and ____ water.
• the two layers always orient so the tails face the ____ and the heads face ____.

the cell membrane:
lipid bilayer,
polar,
nonpolar,
protein,
channel,
carbohydrate.
the cell membrane is ______
parts of the membrane:
carbohydrate chain

• ______

surface proteins

• ______ & identificati

channel proteins

• allow materials ______

(diagrams: phospholipid structure, cell membrane structure with extracellular fluid, cytoplasm, glycoprotein, sugar molecule, etc.)

Explanation:

For the first blank (cell membrane composition):

Step1: Recall cell membrane structure

The cell membrane is made of a phospholipid bilayer. So the first blank (after "double layer of") should be "phospholipids".

Step2: Head hydrophilic meaning

Hydrophilic means "water - loving", so the first blank in the head section is "water - loving". And a hydrophilic substance is attracted to water, so the second blank there is "attracted".

Step3: Tail hydrophobic meaning

Hydrophobic means "water - fearing", so the first blank in the tail section is "water - fearing". A hydrophobic substance repels water, so the second blank there is "repels".

Step4: Bilayer orientation

In the phospholipid bilayer, the hydrophobic tails face each other (inside the bilayer, away from water), and the hydrophilic heads face the water - containing environments, which are the extracellular fluid and the cytoplasm (so the heads face "outward (towards extracellular fluid and cytoplasm)").

For the cell membrane description (the blank under "The cell membrane is"):

The cell membrane is a "semi - permeable membrane" (or "fluid mosaic model" but semi - permeable fits the context of allowing some materials through).

For "Parts of the Membrane":

• Carbohydrate Chain: Often involved in cell - cell recognition, so can be described as "Involved in cell - cell recognition".
• Surface Proteins: Can have functions like "Protection" & identification.
• Channel Proteins: Allow materials "to pass through the membrane" (like facilitated diffusion for specific substances).

Answer:

s (filling the blanks):

• The cell membrane is composed of a double layer of $\boldsymbol{\text{phospholipids}}$.
• The head portion is hydrophilic ($\boldsymbol{\text{water - loving}}$) and is $\boldsymbol{\text{attracted}}$ to water.
• The tail portion is hydrophobic ($\boldsymbol{\text{water - fearing}}$) and $\boldsymbol{\text{repels}}$ water.
• The two layers always orient so the tails face the $\boldsymbol{\text{inside (each other)}}$ and the heads face $\boldsymbol{\text{outward (towards water - based fluids)}}$.
• The cell membrane is $\boldsymbol{\text{a semi - permeable membrane}}$.
• Carbohydrate Chain: $\boldsymbol{\text{Involved in cell - cell recognition}}$
• Surface Proteins: $\boldsymbol{\text{Protection}}$ & identification
• Channel Proteins: Allow materials $\boldsymbol{\text{to pass through the membrane}}$