Biology by Bradford
2.6.AChannel and carrier
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2.6 Facilitated Diffusion: revision map
The subtopic in the middle and four tasks round it: label a diagram, complete a table and fill 10 gaps. Every box rests on a learning objective of the topic in the AP Biology course and exam description. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Facilitated Diffusion
AP Biology ยท Unit 2 Cell Structure and FunctionHover over a box to see it. Untick it to leave it off this sheet and its printout.
Name2.6.AHelping polar molecules across
Ions and polar molecules cannot cross the hydrophobic core of the membrane quickly, so they travel through proteins. In facilitated diffusion the solute still moves its concentration gradient and the cell spends no ATP. The protein only gives the solute a route. Each protein is specific, so a membrane with different proteins lets different solutes pass.
Topic 2.6Facilitated Diffusion
2.6.AChannels and carriers
| Channel protein | Carrier protein | |
|---|---|---|
| How it works | forms a the solute passes through | binds the solute and to release it on the other side |
| Specificity | by size and charge | binding site fits one solute |
| Gated? | often opens and closes | no |
| Example | aquaporin for water; ion channels | glucose transporter |
2.6.ASpeed and limits
As the concentration gradient steepens, the rate of simple diffusion rises in proportion. Facilitated diffusion rises too, but then levels off, because there is a limited number of proteins and all are working at once: they are . Water moves through the bilayer slowly, but cells that need to move it fast, such as kidney tubule cells, have many .
Word bank aquaporinscarrier proteinchanges shapechannel proteindownphospholipid bilayerporesaturatedspecific solutetransport
Answer key
Every box on the sheet with its gaps filled in, as the subtopic reads in full.
LabelChannel and carrier
- channel protein
- carrier protein
- specific solute
- phospholipid bilayer
GapsHelping polar molecules across
Ions and polar molecules cannot cross the hydrophobic core of the membrane quickly, so they travel through transport proteins. In facilitated diffusion the solute still moves down its concentration gradient and the cell spends no ATP. The protein only gives the solute a route. Each protein is specific, so a membrane with different proteins lets different solutes pass.
TableChannels and carriers
Channel protein Carrier protein How it works forms a pore the solute passes through binds the solute and changes shape to release it on the other side Specificity by size and charge binding site fits one solute Gated? often opens and closes no Example aquaporin for water; ion channels glucose transporter GapsSpeed and limits
As the concentration gradient steepens, the rate of simple diffusion rises in proportion. Facilitated diffusion rises too, but then levels off, because there is a limited number of proteins and all are working at once: they are saturated. Water moves through the bilayer slowly, but cells that need to move it fast, such as kidney tubule cells, have many aquaporins.