AP Biology

BELL RINGER [3 Minutes]• Mark New Vocabulary: K, S, H, or D

• Write a sentence using 1 AWL Word (Consume, Classify, Concise, or Distinct)

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MYP Biology: The Cell Membrane

What are the functions of the cell membrane?

The cell membrane controls what goes in and out of the cell and helps the cell to maintain homeostasis. The membrane also helps the cell maintain its shape and protects the cell.

What are phospholipids?• Phospholipids are molecules with a polar

phosphate ‘head’ and two nonpolar fatty acid tails.

Why do phospholipid bilayers form?

The polar heads of the phospholipids face outwards to be near polar water molecules (they are hydrophilic). The nonpolar tails of the phospholipids, which do not like to be near water molecules, face within the bilayer (they are hydrophobic).

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Phospholipid bilayer

polarhydrophilic

heads

nonpolarhydrophobic

tails

polarhydrophilic

heads

Label the cell membrane structure

Protein ReceptorPhospholipids Protein Channel

Cholesterol

What are the functions of the parts of the cell membrane?

Membrane Part Function

Phospholipids Makes up the basic bilayer structure of the membrane

Cholesterol Within the bilayer; gives structure to fluid membrane

Protein Channel Helps molecules pass through the membrane

Protein Receptor Sends and receives signals to and from other cells

Why is the cell membrane called a “fluid mosaic?”

The cell membrane is often described as a fluid mosaic since it is made up of many different molecules and it is flexible, not rigid.

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What does it mean that the membrane is selectively-permeable?

The cell membrane being selectively-permeable means that it allows some types of molecules to pass in and out of the cell space, but not others.

What factors determine how a molecule will cross the membrane?

• Size• Charge / Polarity• Concentration

Small, nonpolar molecules can pass through the membrane without assistance if they are moving from high to low areas of concentration.

All other types of particles need some sort of assistance, such as a protein channel in order to pass across the cell membrane.

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Any Questions??