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Biology A LEVEL > Transport across membranes > Flashcards

Transport across membranes Flashcards

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1
Q

What are the 4 key types of transport across a membrane?

A

1.) Simple diffusion.
2.) Facilitated diffusion.
3.) Active transport
4.) Osmosis.

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2
Q

Definition of simple diffusion.

A
  • Net movement of small, non-polar molecules from an area of high to low concentration, down a concentration gradient.
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3
Q

True or False

Simple diffusion requires ATP. If not, what does it require?

A
  • False, does not require ATP (it’s a passive process.)
  • Molecules must have kinetic energy so that they can constantly move (ie. liquids and gases can diffuse but solids cannot.)
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3
Q

What type of molecules can diffuse across membrane by simple diffusion?

A
  • Small, non-polar, lipid-soluble (due to the limitation imposed by the phospholipid bilayer- large/ polar molecules cannot pass through by simple diffusion. )
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4
Q

How do channel proteins transport water-soluble ions?

A
  • They form tubes filled with water.
  • Enabling water- soluble substances to pass through the membrane.
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5
Q

True or False

All channel proteins will transport all ions across a membrane.

A
  • False.
  • Channel proteins only open in presence of certain ions (when they bind to the protein.)
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6
Q

True or False

Channel proteins transport glucose by facilitated diffusion.

A
  • False.
  • Carrier proteins will transport glucose by facilitated diffusion.
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7
Q

Definition of facilitated diffusion?

A
  • Movement of charged ions/ larger molecules from area of high to low concentration using channel/ carrier proteins.
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8
Q

True or False

Facilitated diffusion is an active process.

A
  • False. Facilitates diffusion is a passive process - it does not require ATP.
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9
Q

Definition of osmosis?

A
  • Movement of water from area of higher water potential to area of lower water potential, across a partially- permeable membrane.
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10
Q

True or False

Water potential of -3.1kPa means there is LESS solute dissolved in the water than solute dissolved in water with water potential of -0.5kPa.

A
  • False.
  • More negative value means there is more solute dissolved.
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11
Q

How does osmosis in cells occur?

A
  • Osmosis in cells happens through channel proteins - called aquaporins.
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12
Q

Definition of active transport.

A
  • Movement of molecules/ ions from area of low concentration to high concentration, against a concentration gradient using carrier proteins.
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13
Q

Does active transport require ATP?

A
  • Yes, it is an active process that requires ATP.
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14
Q

True or False

All carrier proteins can pump ALL molecules/ ions from area of low to high concentration.

A
  • False.
  • It is a very selective process.
  • Only certain molecules can bind to (receptor/ carrier site of) carrier proteins to be pumped.
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15
Q

What happens to the ATP in active transport by carrier proteins?

4 main stages.

A

1.) ATP will bind to the protein (on inside of the membrane.)
2.) ATP is hydrolysed into ADP and Pi.
3.) This hydrolysis releases energy that is used to change shape of the carrier protein (so that it can
open/ release the molecules on other side of membrane.)
.4.) The Pi molecule is released from the carrier protein: this results in protein reverting back to its original shape.

16
Q

What is endocytosis? Does this process require ATP?

A
  • Engulfing by cell membrane to form a vesicle (this process requires ATP.)
17
Q

What is exocytosis? Does this process require ATP?

A
  • Fusion of vesicles with the cell membrane - releasing contents (within vesicle) to outside of the cell.
  • This process requires ATP.
18
Q

How can cells be adpated for rapid transport across their internal/ external membranes?

A
  • Increase in surface area of membranes.
  • Increase in number of protein channels and carrier molecules in the membranes.
19
Q

HypERtonic def and hypOtonic def and isotonic def.

A
  • Hypertonic: water potential of solution is more negative than water potential of fluid in cell.
  • Hypotonic: water potential of solution is more positive than water potential of fluid in cell.
  • Isotonic: Water potential of solution is the same as water potential of fluid in cell.
20
Q

What is the name of the site on the carrier protein that a molecule will attach to in active transport?

A
  • Called the “receptor site” of carrier protein.
21
Q

What is the ileum?

A
  • The ileum is the last part of the small intestine.
22
Q

What is the lumen of the small intestine?

A
  • The hollow tube of the small intestine.
23
Q

If you want to absorb glucose from the lumen to the gut (ie the epithelial cells in wall of small intestine) what must the concentration of glucose in the lumen be like for facilitated diffusion to occur?

A
  • Concentration of glucose in lumen must be higher than concentration of glucose in epithelial cell for facilitated diffusion to occur.
24
Q

Why can’t glucose diffuse from the lumen to the gut (ie the epithelial cells in wall of small intestine) by facilitated diffusion? How do the glucose molecules need to be transported?

A
  • There is usually a higher concentration of glucose in epithelial cells than in the lumen.
  • This is why active transport/ co- transport are required -requires energy to transport glucose against concentration gradient. (Active T - requires energy directly. Co - requires energy indirectly. )

() - extra info for clarification

25
Q

True or False.
Co- transport and active transport are 2 completely different processes.

A
  • False.
  • Co- transport is a TYPE of active transport.
26
Q

What are epithelial cells in the small intestine?

A
  • Layers of cells lining the walls of the small intestine.
27
Q

What are the 5 steps for the co- transport of glucose and sodium ions from the ileum to the blood within the capillary?

A

1.) Sodium ions are transported out of the epithelial cell into the blood (within the capillary) by active transport by a carrier protein.
2.) This reduces the sodium ion concentration in the epithelial cell.
3.) Sodium ions diffuse from the lumen (down concentration gradient) into epithelial cell by facilitated diffusion.
4.) Protein sodium ions diffuse through is co- transporter protein. So when sodium diffuses, glucose can also attach to the protein and be transported into epithelial cell against its concentration gradient.
5.) Glucose will then move by facilitated diffusion from the epithelial cell to the blood (within capillary. )

28
Q

Why isn’t there a build up of glucose in the blood within the capillary during the facilitated diffusion of glucose from the epithelial cells (lining walls of small intestine) to the blood in capillary? Why is this useful?

A
  • Because the blood is constantly flowing/ carrying away any glucose.
  • Maintains concentration gradient between epithelial cells (lining wall of small intestine) and the blood in the capillary.
29
Q

Why is it useful that epithelial cells (lining the walls of the small intestine) have micro-villi?

A
  • Micro-villi on epithelial cell increase the surface area for co- transporter proteins (ie. a large number of co- transporter proteins on epithelial cells/ a large number of molecules can be co- transported. )
30
Q

What are the cells lining the mammalian ileum called?

A
  • Epithelial cells.
31
Q

What is water potential?

A
  • Water potential is the pressure created by water molecules.
32
Q

What is the unit and symbol for water potential?

A
  • Unit = kPa.
  • Symbol = ψ
33
Q

What happens to plant cells when they are placed in hypotonic solutions VS what happens to animal cells when they are placed in hypotonic solutions?

A
  • Water will move from solution into cell by osmosis.
  • Plant cells become turgid (as they have a strengthened cell wall to withstand the pressure) WHEREAS, animal cells will burst (do not have a cell wall to withstand the pressure.)
34
Q

What things do you need to include in Q’s that ask what happens to plant/ animal cell when placed in: hypertonic, isotonic, hypertonic solutions?

A

1.) Where water is entering from to.
2.) Say “by osmosis.”
3.) State whether fluid in cell/ solution it is placed in have higher/ lower water potential compared to one another.

Biology A LEVEL (22 decks)

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