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AQA AS BIOLOGY 2015+ > 2 Transport across cell membranes > Flashcards

2 Transport across cell membranes Flashcards

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1
Q

Cell Surface Membrane

A

Membrane that surrounds cell and forms boundary to the outside.
Controls the movement of substances in and out of cell.

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2
Q

Features of Phospholipid in CSM

A

Hydrophilic head outside CSM - attracts water

Hydrophobic tail inside CSM - repels water

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3
Q

Function of Phospholipid in CSM

A
  • allow lipid-soluble molecules to enter and leave
  • prevent water-soluble molecules entering and leaving
  • make the membrane flexible and self-sealing
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4
Q

Extrinsic Proteins

A

Embedded in the surface of bilayer

Either used for mechanical support or in conjunction with glycolipids

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5
Q

Intrinsic Proteins

A

Embedded completely in the bilayer

1) Protein channels - allow water soluble ions through
2) Carrier Proteins - used for facilitated diffusion

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6
Q

Functions of Proteins in Membranes

A
  • provide structural support
  • act as channels for water-soluble substances
  • allow active transport across membrane
  • form cell surface receptors
  • help cells adhere together
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7
Q

Cholesterol Molecules

A

Occur throughout bilayer

Very hydrophobic

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8
Q

Function of Cholesterol Molecules

A
  • add strength to membranes
  • reduce movement of molecules
  • make membranes less fluid at high temperatures
  • prevent loss of water and ions
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9
Q

Glycolipid

A

Carbohydrate covalently bonded with a lipid

Carbohydrate section extends out of bilayer into watery environment outside (acts as a receptor)

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10
Q

Function of Glycolipids

A
  • act as recognition sites for hormones
  • helps maintain stability
  • helps cells attach to one another and form tissues
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11
Q

Glycoprotein

A

Carbohydrate chains attached to many extrinsic proteins on outer surface

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12
Q

Function of Glycoproteins

A
  • act as recognition sites for hormones and neurotransmitters
  • helps cells attach to one another and form tissues
  • allows cells to recognise each other (e.g. lymphocytes)
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13
Q

Why can’t some molecules diffuse through the membrane?

A
  • not lipid-soluble
  • too large
  • same charge as channel protein (they are repelled)
  • polar
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14
Q

Fluid-Mosaic Model

A

Fluid - phospholipid molecules can move around - gives a flexible structure
Mosaic - proteins embedded in bilayer are varied in shape and size

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15
Q

Simple Diffusion

A

Net movement of particles from high concentration to a low concentration, until evenly distributed.

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16
Q

Facilitated Diffusion

A

Movement of charged ions and polar molecules through the CSM
Passive process - relies on kinetic energy from molecules

17
Q

Facilitated Diffusion - Protein Channels

A
  • form hydrophilic channels

- allow specific water-soluble ions through

18
Q

Facilitated Diffusion - Carrier Proteins

A
  • molecule binds to carrier protein outside
  • causes change in shape
  • molecule is released on inside
19
Q

Osmosis

A

Movement of water molecules from high water potential to low water potential through a partially permeable membrane

20
Q

Solute

A

Substance that is dissolved in solvent

21
Q

Water Potential

A

Pressure created by water molecules

22
Q

Water Potential of Pure Water

A

Zero (this is the highest water potential everything else is negative)

23
Q

Addition of Solute to Pure Water

A

Will lower water potential (be negative)

24
Q

Osmosis in Animal Cells

A

Less negative water potential = water entering cell, cell swells and bursts (turgid)
Equal water potential = no change (incipient plasmolysis)
More negative water potential = water leaving cell, cell shrinks (plasmolysed)

25
Q

Active Transport

A

movement of molecules from low concentration to high concentration using ATP and carrier proteins

26
Q

ATP in Active Transport

A
  • directly move molecules

- in co-transport

27
Q

Process of Direct Active Transport

A
  • molecule binds to carrier protein
  • on the inside ATP binds to carrier protein causing it to split into ADP + inorganic phosphate
  • protein changes shape and molecule released on the inside
  • phosphate is released and protein changes back
28
Q

Sodium-Potassium Pump

A

Sodium ions are actively removed from cell while potassium ions are actively taken in

29
Q

Microvilli

A

Finger-like projections that line the ileum, provide more surface area for transport

30
Q

Role of Diffusion in Absorption

A

Greater concentration of glucose and amino acids in ileum than the blood
Concentration gradient formed
Glucose/amino acids transported into blood by facilitated diffusion

31
Q

Role of Active Transport in Absorption

A

Not all glucose and amino acids can be absorbed by diffusion
Example of co-transport

32
Q

Co-transport of Glucose Molecule

A

1) Sodium ions are actively transported out of epithelial cells by sodium-potassium pump (protein carrier molecule)
2) higher concentration of sodium ions in lumen of ileum
3) sodium ions diffuse into epithelial cells (by co-transport protein) carrying glucose molecule
4) glucose passes into blood by facilitated diffusion

33
Q

What factors affect the rate of facilitated diffusion?

A
  • the concentration gradient

- the number of channel and carrier proteins

34
Q

What factors affect the rate of osmosis?

A
  • water potential gradient
  • thickness of the exchange surface
  • surface area of the exchange surface
35
Q

What is a co-transporter?

A

type of carrier protein
they bind two molecules at a time
concentration gradient of one of the molecules is used to move the other molecule against its concentration gradient

36
Q

How is rate of active transport increased?

A
  • having microvilli

- increased number of protein channels and carrier proteins

37
Q

What factors affect the rate of active transport?

A
  • speed of individual carrier proteins
  • number of carrier proteins present
  • rate of respiration in the cell and availability of ATP

AQA AS BIOLOGY 2015+ (10 decks)

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