ch5 - movement of molecules across membranes

What is diffusion

the net movement of molecules down a concentration gradient from an area of high to low concentration until equilibrium is reached/ when particles are evenly distributed

What are the two types of diffusion

Simple diffusion 

Facilitated diffusion

What is simple diffusion and what molecules diffuse this way

when molecules diffuse directly across a plasma membrane 

> small nonpolar molecules e.g. oxygen, carbon dioxide

Is simple diffusion a passive or active process

passive process as it does not require added energy in the form of ATP hence molecules move due to kinetic energy

What is facilitated diffusion and what molecules diffuse this way

when molecules diffuse across cell membrane with the help of transport proteins (carrier & channel proteins)

> large polar molecules e.g. glucose

> ions e.g. calcium 

Is facilitated diffusion a passive or active process

passive process as it does not require added energy in the form of ATP hence molecules move due to kinetic energy

Name 4 factors that affect the rate of diffusion

-temperature 

-concentration gradient 

-thickness of membrane 

-surface area

How does temperature affect the rate of diffusion

at higher temperatures molecules have more kinetic energy so diffuse faster

How does concentration gradient affect the rate of diffusion

the steeper the conc gradient, the faster the rate of diffusion

How does thickness of membrane affect the rate of diffusion

the thinner the membrane the shorter the diffusion pathway hence making diffusion/osmosis faster

How does surface area affect the rate of diffusion

the larger the S.A, the more molecules can cross the membrane at once hence making diffusion/osmosis faster

What is active transport

the movement of molecules against the concentration gradient, going from an area of low to high concentration

Is active transport a passive or active process

Active process because it requires added energy in the form of ATP due to molecules moving against conc gradient

What transport protein is involved in active transport

Carrier proteins 

describe how a carrier protein works to transport a molecule AGAINST conc. gradient

large polar molecule and ATP bind to the protein 

> hydrolysis of ATP into ADP and Pi releases energy which causes a conformational/shape change

> allowing molecule to diffuse across membrane against the conc gradient

> Pi is released causing protein to return back to its original shape to be used again

What is bulk transport

the movement of large molecules e.g. hormones and enzymes in and out of cells by vesicles

Why is bulk transport needed

because large molecules are too big to be transported through channel or carrier proteins

What is endocytosis

transporting materials into cells 

What happens during endocytosis

cell surface membrane bends inward around the materials to engulf them, forming a vesicle which then moves into the cytoplasm so the contents can be processed

Name the two types of endocytosis

Pinocytosis

phagocytosis 

What is phagocytosis

When solid materials are taken in

What is pinocytosis

When liquid materials are taken in

Why is endocytosis an active process

requires added energy in the form of ATP so the cell can shape around and engulf the materials

What is exocytosis

transports materials out of cells by

What happens during exocytosis

materials are contained within a vesicle which moves towards and fuses with cell surface membrane, allowing the materials to be released out of the cell 

Why is exocytosis an active process

requires added energy in the form of ATP so the vesicles can move along cytoskeleton