Transport across cell membranes

Question 1

what are cell membranes made of

Answer 1

Made of phospholipid bilayer with hydrophobic tails facing towards each other and hydrophilic heads outwards

Question 2

what else are cell membranes made of (3)

Answer 2

• Protein channels: for larger substances to go in and out of cell
• Antigens: cell needs to have visible recognition made out of glycoprotein for hormones
• Cholesterol: add stability to shape and reduces permeability/ movement of other molecules

Question 3

function of phospholipid bilayer (3)

Answer 3

• Allow lipids soluble substances to enter and leave the cell
• Prevent water soluble substances to enter or leave the cell
• Gives fluidity

Question 4

why is the cell membrane described as a fluid mosaic

Answer 4

not static, molecules can move, lots of pieces, a mixture of phospholipids and proteins fitted together

Question 5

functions of membranes within cells (4)

Answer 5

• Controls entry and exit of substances in organelles
• Separates organelles from cytoplasm
• Insulates enzymes which can damage cell e.g. lysozymes in lysosomes
• Provides a surface for reactions to take place e.g. protein synthesis using ribosomes on rough endoplasmic reticulum

Question 6

diffusion definition

Answer 6

passive transport of substances from a high to low concentration until equilibrium is reached

Question 7

Fick’s law

Answer 7

rate of diffusion α (surface area x concentration gradient)/(length of diffusion pathway )

Question 8

factors affecting rate of diffusion

Answer 8

Surface area
Concentration gradient
Thickness of diffusion pathway
Temperature

Question 9

facilitated diffusion definition

Answer 9

passive transport of certain larger substances from a high to low concentration at channel proteins and carrier proteins without the use of energy until evenly distributed

Question 10

how substances pass through channel proteins

Answer 10

Specific ions bind to protein causing it to change shape and allow it to pass through
Some are non-specific so allow several ions through
Some are always open, other have gates (gated channels) that open and close

Question 11

what type of things to channel proteins allow through

Answer 11

hydrophilic so allows water soluble things

Question 12

how substances pass though carrier proteins

Answer 12

Medium sized molecules bind to protein causing it to change shape and allow molecule to pass through
Specific glucose carrier proteins allows facilitated diffusion of glucose to be faster

Question 13

how does rate of entry of substances by facilitated diffusion change with increasing concentration of substance

Answer 13

After a certain concentration of substance outside the cell, rate of entry of substance would decrease because channels are saturated with the certain substance.

Question 14

osmosis

Answer 14

water moves from a solution of higher water potential to a solution of lower water potential through a partially permeable membrane

Question 15

water potential

Answer 15

adding solutes makes water potential more negative so more concentrated

Question 16

active transport

Answer 16

substances are carried against the concentration gradient involving the use of carrier proteins and energy

Question 17

what is the source of energy for active transport and adaptation

Answer 17

Source of energy is mostly from the hydrolysis of ATP produced by respiration in mitochondria
Adapted by having many mitochondria

Question 18

why are carrier proteins specific for active transport and adaptation

Answer 18

due to their tertiary structures of the binding site being complementary
• Adapted by having more carrier proteins and having a higher surface area by having villi

Question 19

co-transport absorption of glucose steps (5)

Answer 19

1. Na+ leaves epithelial cell and into blood by active transport
2. Creates low concentration of Na+ in epithelial cell
3. Na+ from small intestine binds to carrier protein specific to glucose and passes through by facilitated diffusion
4. Glucose is able to pass through by co-transport with sodium
5. Creates a high concentration of glucose inside epithelial cell so glucose moves out into the blood