Cell Physiology Flashcards
What are the 4 methods of moving across membranes?
Diffusion
Active transport
Osmosis
Cyotosis
What is diffusion?
Diffusion is the movement of molecules or ions from a region of high concentration to an area of low concentration until they are spread out evenly.
What affects the rate of diffusion?
- Greater difference in concentration = faster the rate of diffusion
- Smaller particles diffuse faster than larger particles
- Shorter the distance between A and B, the faster the rate
- Greater the temperature, greater the diffusion (greater KE in particles)
The rate of diffusion in a given direction across the exchange surface:
- Is directly proportional to the area of the surface
- is directly proportional to the concentration gradient
- is inversely proportional to the distance
State Fick’s Law
Rate of diffusion is proportional to surface area x difference in concentration/ length of diffusion path
What is simple diffusion?
Random mixing of ions and molecules in a solution due to KE
How can simple diffusion occur?
Phosopholipid bi-layer: diffusion of lipid soluble molecules (steroids, glycerol).
Pores of channels that are formed by integral proteins: diffusion of substances that are not lipid soluble (ions for example).
Is diffusion quicker through the bi-layer or the pores of channels formed by integral proteins?
Bi-layer
What is facilitated diffusion?
substances too big for simple diffusion moving through selective proteins in the membrane
What are the two types of selective proteins?
Channel proteins
Carrier proteins
How do channel proteins work?
Channel proteins open to let ions through. Their polar surface pushes the ions through. When they close the gap and the opposite charge make the channel protein impossible to pass through.
How do Carrier proteins work?
The proteins have binding sites to which the molecules (like sugar) attach. The carrier protein then changes shape, closing like a scissor to stop molecules from the outside streaming in, and allowing only the bound molecules to move into the cell.
What is active transport?
It is the transport of ions or molecules across a membrane AGAINST the electrochemical gradient.
Active transport requires energy, unlike
Diffusion and osmosis; these are passive processes
Active transport is:
- Highly selective
- Involves special molecules called pumps
What are the pumps?
They are globular proteins situated across the phosopholipid bilayer. Energy is required to move the pump (ATP). Most pumps are specific to certain molecules. The pump picks up the molecule and transports it to the other side of the membrane, it is then released on the other side of the membrane.
What affects the ability to take up molecules/ions?
- Temperature
- Oxygen conc.
- Poisons present
List some examples of active transport
Nerve impulse transmission
Muscle contraction
Protein synthesis
What is the sodium/potassium ion pump
A pump that transports Na and K only
What is Endocytosis?
Importing substances into cells
Describe endocytosis
The cell wraps the cell surface membrane around the material (invagination) and brings it into the cyctoplasm inside a vesicle (vee see kill)
what are the two types of endocytosis?
Phagocytosis and Pinocytosis
Describe phagocytosis
Solid material taken into the cell inside a vesicle. Lysosomes fuse with the vesicle and send enzymes into the vesicle. They digest the material and the products are absorbed into the cytoplasm.
Describe pinocytosis
Liquid material is taken into the cell inside a vesicle. same process as phagocytosis.
