Transport across membranes Flashcards
Is a simple diffusion is a passive transport or active transport?
It is a passive transport.
What does passive mean?
It means no energy is required by the cell.
What is diffusion?
It is the movement of molecules/ions from a region of high concentration to region of low concentration. It goes down a concentration gradient until there is equal distribution.
Give me an example of molecules which use simple diffusion
Oxygen and carbon dioxide.
Diffusion occurs when…
There is a concentration gradient, the molecules have kinetic energy, no ATP is required and no specific proteins are required.
What affects the rate of diffusion?
The concentration gradient, thickness of membrane, surface area, size of molecule, diffusion distance, lipid solubility, availability of carrier proteins and temperature.
Why does lipid solubility affect the rate of diffusion?
As fat soluble molecules diffuse faster than water soluble molecules so non polar molecules will diffuse faster than polar ones.
What happens when there is only a few proteins available for facilitated diffusion?
There is a decrease in rate of diffusion as there are only a limited number of proteins found within the membrane.
How will a greater concentration gradient difference affect the rate of diffusion?
A greater difference in concentration of molecules within two areas means that more molecules need to diffuse over a given time.
What is the equation for rate of diffusion?
Surface area x difference in concentration divided by length of diffusion path
What is facilitated diffusion?
It is a passive transfer of molecules or irons down a concentration gradient across a membrane by protein carrier molecules in the membrane.
Why does facilitated diffusion occurs?
It occurs when some ions and molecules can’t pass through the membrane. As they are relatively insoluble in the phospholipid bilayer. It occurs at specific sites and the plasma membrane where there are transport proteins available. The number and availability of the proteins limits the rate of facilitated diffusion.
What are the two types of transport proteins?
Carrier proteins and channel proteins.
What are channel proteins?
Channel proteins have molecules which are lined with polar groups making the channels hydrophilic this allows ions to pass through the membrane. These channels can open and close depending on the needs of the cell.
What are carrier proteins?
They allow diffusion of larger polar molecules e.g. sugars and amino acid across the membrane. A molecule attaches to the binding site on the carrier protein. The protein changes shape and releases the molecule on the other side of the membrane.
What is active transport?
It is the movement of molecules or ions across a membrane which goes against the concentration gradient this requires energy from the hydrolysis of ATP made by the cells during respiration.
Where does active transport occur?
It occurs for intrinsic proteins which span across the membrane, the rate is limited by the availability and number of carrier proteins.
What concentration does molecules move from during active transport?
They move from low to high concentration going against the concentration gradient.
Which processes involve active transport?
Protein synthesis, muscle contraction, nerve impulse transmission, reabsorption of glucose in the kidneys and mineral uptake into the plant root hairs.
What happens during active uptake?
The molecule combines with a specific carrier protein on the outside of the membrane, ATP transfers a phosphate group to the carrier protein on the inside of the membrane. The protein changes shape and carries the molecule across the membrane to the inside of the cell. The molecule and phosphate ion is then released into the cytoplasm where it re-combines with ADP to form ATP. Finally the protein returns back to its original form.
What happens if a respiratory inhibitor is present within active transport?
When a respiratory inhibitor is present the rate of uptake is decreased. It prevents aerobic respiration and ATP production in the mitochondria. Without ATP active transport can’t occur. Active transport is the uptake of ions and when more oxygen is present active transport is increased.
What is co-transport?
It is the type of facilitated diffusion which brings molecules and ions into cells together which are simultaneously transported across the membrane by one protein or protein complex which doesn’t have ATPase activity
What is an example of co-transport?
Sodium – glucose, co-transport is significant in absorbing glucose and sodium ions across the cell membrane and into the blood in the ileum and the kidney nephron
