IB Diploma · Biology B2.1
IB Biology B2.1: Mem. & Mem. Trans. — Practice Questions & Answers
IB Biology B2.1 study notes: the fluid mosaic model, phospholipid bilayer, membrane proteins, and passive and active transport across membranes.
Here are 10 practice questions with full answers and explanations.
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Practice questions with answers
1
Multiple choice
What forms the basis of cell membranes?
- Lipid bilayers
- Protein monolayers
- Hydrophilic tails
- Hydrophobic heads
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WhyThe lipid bilayer of phospholipids forms the basic structure of all cell membranes.
2
Multiple choice
Why do phospholipids naturally form bilayers in water?
- They are amphipathic
- They are hydrophobic
- They are hydrophilic
- They are ionic
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WhyBeing amphipathic, phospholipids arrange with tails inward and heads facing water, forming a bilayer.
3
Multiple choice
What property of the hydrophobic hydrocarbon chains in the membrane core makes it a barrier?
- Low permeability to large molecules and hydrophilic particles
- High permeability to all molecules
- High permeability to ions
- High permeability to polar molecules
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WhyThe hydrophobic hydrocarbon core resists passage of large and hydrophilic particles, making it a barrier.
4
Multiple choice
What is an example of simple diffusion across membranes?
- Movement of oxygen and carbon dioxide
- Movement of glucose
- Movement of ions via channel proteins
- Movement of water via aquaporins
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WhySmall non-polar gases such as oxygen and carbon dioxide cross the membrane by simple diffusion.
5
Multiple choice
What are the two main types of membrane proteins?
- Integral and peripheral
- Globular and fibrous
- Primary and secondary
- Conjugated and non-conjugated
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WhyMembrane proteins are classed as integral, embedded in the bilayer, or peripheral, attached to its surface.
6
Multiple choice
How are integral proteins positioned in the membrane?
- Embedded in one or both lipid layers
- Attached to the surface of the membrane
- Floating freely in the cytoplasm
- Bound to the cytoskeleton
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WhyIntegral proteins are embedded within one or both layers of the lipid bilayer.
7
Multiple choice
How are peripheral proteins positioned in the membrane?
- Attached to one or other surface of the bilayer
- Embedded in the lipid layers
- Floating freely in the cytoplasm
- Bound to the cytoskeleton
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WhyPeripheral proteins attach loosely to one surface of the bilayer rather than spanning it.
8
Multiple choice
What is the movement of water molecules across membranes called?
- Osmosis
- Diffusion
- Active transport
- Facilitated diffusion
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WhyOsmosis is the movement of water molecules across a selectively permeable membrane.
9
Multiple choice
What are aquaporins?
- Proteins that facilitate water movement across membranes
- Proteins that facilitate ion movement
- Lipids that form the membrane bilayer
- Carbohydrates that aid in cell recognition
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WhyAquaporins are channel proteins that let water cross membranes rapidly.
10
Multiple choice
What drives osmosis?
- Differences in solute concentration
- Differences in temperature
- Differences in pressure
- Differences in pH
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WhyOsmosis is driven by differences in solute concentration, so water moves toward higher solute concentration.
Key terms in Mem. & Mem. Trans.
Amphipathic: Having both a hydrophilic and a hydrophobic region; phospholipids are amphipathic, which drives bilayer formation.
Phospholipid bilayer: Two layers of phospholipids with hydrophilic heads facing the water and hydrophobic tails facing inwards.
Fluid mosaic model: The model describing the membrane as a fluid phospholipid bilayer with a mosaic of proteins that can move within it.
Integral protein: A protein embedded in the hydrophobic core of the membrane, often spanning the whole bilayer.
Facilitated diffusion: Passive movement of polar molecules or ions down their gradient through channel or carrier proteins.
Osmosis: Net movement of water across a partially permeable membrane from higher to lower water potential.
Active transport: Movement of substances against a concentration gradient using pump proteins and energy from ATP.
Aquaporin: A channel protein that allows rapid passage of water molecules across the membrane.
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