00:04

in order for us to use the molecules and

00:07

energy we get from food

00:09

we must transport them across cell

00:11

membranes transport of nutrients is

00:15

essential for all cells but we’ll use

00:18

cells in the small intestine to teach

00:20

the principles of membrane transport

00:22

let’s zoom into the surface of an

00:26

intestinal cell the plasma membrane is

00:29

selectively permeable some molecules can

00:33

move across it while others cannot

00:35

how do materials enter and leave cells

00:41

lipids such as these yellow molecules

00:44

can move freely across the lipid bilayer

00:48

notice that the lipid molecules move

00:50

down their concentration gradient from

00:53

where they are more concentrated to

00:56

where they are less concentrated this is

00:58

an example of simple diffusion diffusion

01:01

is a form of passive transport it does

01:04

not require energy from the cell but it

01:07

does depend on the concentration

01:09

gradient size in charge of the molecule

01:12

or ion

01:13

however most molecules cannot cross the

01:17

lipid bilayer instead molecules like the

01:20

sugar fructose move into intestinal

01:23

cells by facilitated diffusion moving

01:26

down their concentration gradient and

01:28

through transport proteins it also

01:31

differs because it acts only on specific

01:34

molecules and the transport proteins can

01:37

become saturated reducing the amount of

01:40

diffusion

01:41

however facilitated diffusion doesn’t

01:44

require energy from the cell so like

01:47

simple diffusion it’s a form of passive

01:50

transport the majority of water

01:53

molecules cross the plasma membrane by

01:56

facilitated diffusion also called

01:58

osmosis through specific protein

02:01

channels called aquaporins

02:10

some ions such as sodium and potassium

02:13

require transport against their

02:16

concentration gradients the sodium

02:18

potassium pump actively transports these

02:21

ions from where they are less

02:23

concentrated to where they are more

02:25

concentrated this process requires

02:27

energy from the cell and is known as

02:30

active transport energy from ATP is used

02:34

to move three sodium ions shown in red

02:37

out of the cell

02:40

and two potassium ions shown in blue

02:43

into the cell because the pump uses ATP

02:47

directly this type of transport is

02:50

called primary active transport

02:53

another type of active transport

02:56

secondary active transport also moves

02:59

chemicals against gradients it doesn’t

03:02

use ATP as a direct source of energy

03:05

instead it uses the downhill gradient

03:08

from one ion or molecule to drive the

03:11

uphill movement of another ion or

03:13

molecule for example sodium and glucose

03:17

move into the cell by secondary active

03:19

transport in a process called Co

03:22

transport or symport because both

03:24

substances are moving in the same

03:26

direction sodium ions move down their

03:29

concentration gradient created by the

03:32

sodium potassium pump but because

03:34

glucose concentrations inside the cell

03:37

can quickly exceed those outside the

03:40

cell glucose moves against its

03:42

concentration gradient

03:49

the cell moves larger materials such as

03:52

proteins from the intracellular fluid to

03:55

the extracellular fluid using vesicles

03:58

that fuse with the plasma membrane and

04:00

release their contents outside the cell

04:03

this process is called exocytosis and

04:07

endocytosis the plasma membrane pinches

04:11

in forming a vesicle that contains

04:14

material from outside the cell cells use

04:18

all these processes passive and active

04:21

transport exocytosis and endocytosis to

04:26

move materials across their membranes

00:12

Cell transport is the process of how things move in or out of the cell through the cell membrane

00:19

There are two broad categories of cell Transport

00:23

The first Category is passive transport, for a cell passive transport means

00:28

It’s an automatic process that doesn’t require any input of energy

00:34

for example

00:36

Diffusion is a passive process in which particles move either into or out of the cell from an area of higher

00:43

concentration to an area of lower concentration

00:46

The cell doesn’t use any energy when this happens

00:51

The second Category of cell Transport is active Transport

00:56

This is when particles move from an area of lower concentration to an area of higher concentration

01:05

when particles move against the concentration gradient

01:08

Energy is required often to allow protein pumps to assist in Particle Movement

01:15

why would the cell need to move particles from a low to high concentration and expend energy to do it

01:24

An Important example is seen in your heart muscle cells

01:28

In order for your heart to beat there are certain molecules that have to move from an area of low concentration

01:35

to an area of high concentration

01:38

for those cardiac muscle cells to work

01:42

So the main things to remember are passive transport happens automatically with no energy required

01:49

while active transport needs energy for it to occur

01:56