Chapter 3: The Plasma Membrane Flashcards
What is the purpose of the plasma membrane?
The cell membrane acts as a barrier and is semi-permeable, meaning it allows some substances through.
What cells have a plasma membrane?
All cells have a cell membrane however, plant, bacteria, fungal and most algae cells also have a cell wall. Animal cells only have a cell membrane.
The fundamental structure of the membrane is…
the phospholipid bilayer, which forms a stable barrier between two aqueous environments.
What is the lipid bilayer composed of?
Phospholipids which can be represented by a head and two tails
The Phosphate Head
The phosphate head is hydrophilic meaning they can absorb and attract water
The Fatty Acid Tails
The tails are hydrophobic meaning they avoid water and are unable to absorb water
What happens when these molecules form a bilayer?
The fatty acid tails turn inwards and face each other
Membrane protein types
Transport proteins
Recognition proteins
Receptor proteins
What is the purpose of transport proteins?
They act as passageways to allow certain molecules to pass through the membrane
What is the purpose of recognition proteins?
They allow cells to communicate with each other
What is the purpose of receptor proteins?
They bind hormones and other substances that can vary the activities of a cell essentially enabling them to respond to certain signals
What is the difference between active and passive transport?
Active transport requires energy whereas passive doesn’t
What are the two types of passive transport?
Diffusion and osmosis
What is diffusion?
Diffusion is the movement of particles from an area of high concentration to and area of low concentration
Concentration gradient definition
The difference in particle concentration between two regions
When does diffusion stop?
When an equilibrium is achieved between the two regions, diffusion will stop
What is facilitated diffusion?
Facilitated diffusion is when molecules are too large to diffuse with the use of the initial three proteins and require the assistance of specialised proteins
What are the proteins required for facilitated diffusion?
Channel and carrier proteins
How do carrier proteins assist diffusion?
They bind to specific molecules on one side of the membrane, change its shape and release the substance on the other side
How do channel proteins assist diffusion?
They create a narrow pathway for specific ions to pass through
What is osmosis?
Osmosis is a specific type of diffusion that relates to water and is the movement of water through a semi permeable membrane from areas of high concentration to areas of low concentration
Isotonic definition
Equal amount of solute in both regions
Hypotonic definition
When cells are surrounded by a solution with less solute concentration
Hypertonic definition
When cells are surrounded by a solution with higher solute concentration
What is haemolysis?
Haemolysis occurs when an animal cell is put into pure water and the particles diffuse into the cell causing it to swell and burst
What is crenation?
Crenation is the shrinkage of an animal cell when placed in a solution with a surrounding hypertonic solution in comparison to the cellular cytoplasm
When does active transport occur?
Active transport occurs when particles are needed in the high concentration area and must move in the opposite direction
What happens when molecules are too large for active transport?
The use of macromolecules come to play as vesicles to allow these molecules to pass through
What are the two types of vesicle tranpsort?
Endocytosis and exocytosis
Endocytosis
This is the process of capturing a substance in the cell membrane from outside the cell and creating a membrane-bound sac for the substance to then be moved into the cytosol within
What are the two main types of endocytosis?
Phagocytosis (cellular eating) or pinocytosis (cellular drinking).
Exocytosis
The process of fusing the plasma membrane to release the substance outside the cell. This occurs to remove waste or release a protein
