Transport across membranes

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18 Terms

1

Water potential

The pressure created by water molecules

- measured in kPa

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2

Osmosis in plant cells

Into cell: protoplast swells

- cell becomes turgid

Out of cell: protoplast shrinks

- cell becomes flaccid

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3

Osmosis in animal cells

Into cell: lysis

Out of cell: crenation

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4

Define simple diffusion

Passive process

(requires no energy from ATP hydrolysis)

movement of small, lipid-soluble molecules down a concentration gradient

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5

Define facilitated diffusion

Passive process

Movement of molecules down a concentration gradient via channel proteins

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6

how channel proteins work

Hydrophilic channels bind to specific ions

- one side of the protein closes and the other opens

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7

How do carrier proteins work?

Binds to complementary molecule

conformational change releases molecule on other side of membrane

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8

Five factors that affect the rate of diffusion

1. Temperature

2. Diffusion distance

3. Surface area

4. Size of molecule

5. Difference in concentration

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9

Ficks law

surface area x difference in concentration / diffusion distance

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10

How are cells adapted to maximise the rate of transport across their membranes?

1. many carrier/ channel proteins

2. folded membrane increases surface area

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11

Active transport

Active process

Movement of molecules against a concentration gradient via a carrier proteins

- using ATP

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12

Compare and contrast active transport and facilitated diffusion

● Both may involve carrier proteins.

Active transport requires energy from ATP hydrolysis whereas facilitated diffusion is a passive process.

Facilitated diffusion may also involve channel proteins.

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13

Features of a cell specialised for absorption

1. Large number of mitochondria

- to release energy for ATP in the form of ATP

2. Large number of channel and carrier proteins

- for facilitated diffusion

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14

Co-transport

The movement of 2 substances using a carrier protein

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15

How the movement of Na+ molecules out of the cell allows for the absorption of glucose into the cell

1. The movement of Na+ out of the cell maintains a concentration gradient

2. Na+ moving in by co-transport

- bringing glucose with it

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16

Explain how co-transport is involved in the absorption of glucose / amino acids in the small intestine.

1. Na+ actively transported out of epithelial cells & into bloodstream

2. Na+ concentration lower in epithelial cells than lumen of gut

3. Transport of glucose/ amino acids from lumen to epithelial cells is 'coupled' to facilitated diffusion of Na+ down concentration gradient

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17

How the movement of substances is affected by membrane structure

1. Phospholipid bilayer allows for the movement of non-polar/lipid-soluble substances

2. Phospholipid bilayer prevents movement of polar/lipid-insoluble substances

3. Carrier proteins allow active transport

4. Channel/carrier proteins allow facilitated diffusion/co-transport

5. Shape/charge of channel/carriers determines how much movement

6. No. of channels/carriers determines how much movement

7. Membrane SA determines how much movement

8. Cholesterol affects fluidity/permeability

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18

Osmosis definition

Movement of water molecules down a water potential gradient

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