4) Cell Transport Mechanisms Flashcards
What does the size of the organism, specifically the SA:V determine?
The efficiency of transport of substances by diffusion in an organism.
How do SA:V and efficiency correlate?
The higher the SA: V ratio, the more efficient diffusion is.
SA: V in large/small objects
Smaller objects have a larger SA/V
Larger objects have a smaller SA/V
How to calculate surface area? (A cube which has 6 faces and each side is 4cm)
6 x 4 x 4 = 96cm²
How to calculate volume? (A cube which has 6 faces and each side is 4cm)
4 x 4 x 4= 64cm³
Which is more efficient for diffusion, smaller or large objects?
Smaller objects
Give examples of organisms that are efficient for diffusion
Small single celled organisms (bacteria)
Very small multicellular organisms (worms)
What 3 factors determine why small organisms can expel waste and CO2 through diffusion?
The diffusion distance is short
The SA/V ratio is high
Metabolic demands are low
Why is diffusion for large organisms not adequate?
They have a low SA/V ratio
Can not meet demand and removal of waste due to the large distances involved
What 3 factors affect the rate of diffusion?
Area of diffusion
Difference in concentration
Thickness of diffusion surface
What is the optimum features of an organisms for diffusion?
Organisms that surfaces with a large area and are thin. Also, a high difference in concentration.
What is the function of the cell surface membrane?
Contains the cell
Controls movement of substances in and out of the cell
Maintains the osmotic balance of the internal environment
Allows the cell to be recognised e.g. by hormones
What is the chemical structure of the cell membrane?
Lipids (In the form of phospholipids and cholesterol)
Proteins
Carbohydrates (In the form of glycoproteins and glycolipids)
What are the properties of the cell membrane?
Flexible
Fluid
Selectively Permeable
Label fluid mosaic model
Refer to textbook or workbook
What does fluid lipid bilayer consist of?
It has a mosaic of proteins and carbohydrates (glycoproteins and glycolipids) floating in it
Why do phospholipids form bilayers in aqueous environments?
Phospholipids are both hydrophobic and hydrophilic.
What does microscope images of a cell membrane show?
Proteins sticking out of the cell membrane.
What substance passes in and out of the cell membrane sometimes?
Some water-soluble substances pass in and out of cells.
What substances pass through the membranes easily, and which substances don’t?
Lipid-soluble substances pass easily through membranes. Ionic and polar molecules do not pass easily through membranes.
What other models were there besides the fluid mosaic model?
The Davson-Danielli model was proposed in 1935, showing a phospholipid bilayer in between 2 protein layers.
What is the downside to the Davson-Danielli model?
The model does not explain the many known facts about membranes
What is the similarity between the fluid mosaic model and the Davson-Danielli model?
They both have a phospholipid bilayer with proteins
What are the 2 differences between the fluid mosaic and Davson-Danielli models?
The fluid mosaic model has proteins within the phospholipid bilayer, while the Davson-Danielli model has a protein layer outside the membrane.
The fluid mosaic model has glycoproteins, glycolipids and cholesterol, whereas the Davson-Danielli model doesn’t.
What is the difference between active transport and passive transport?
Passive transport doesn’t require energy whereas active transport requires energy.
What is passive transport?
When there is a high concentration of particles and a low concentration of particles, more particles move away from the high concentration area than the low concentration area, so the net movement is AWAY from the high concentration to the low.
What are the 3 kinds of passive transport/movement?
Diffusion
Facilitated Diffusion
Osmosis
What is equilibrium?
When the concentration is the same on both sides of the membrane, particles are still moving across in both directions but the net movement is ZERO.
What factors do there need to be in order for diffusion to occur?
Even if there is a higher concentration on one side than the other, diffusion can only occur when:
-The membrane is permeable
-The particle and/or pore is charged
-The particle is soluble
What is osmosis?
Osmosis is the diffusion of free water molecules.
What does osmosis involve?
-The net movement of water molecules from a solution with a high water potential (low solute concentration) to a solution with a low water potential (higher solute concentration)
-Movement through a partially permeable membrane (permeable to water but not the solute)
What is facilitated diffusion?
The process of passive transport of molecules across a membrane, with the help of membrane proteins
What type of molecules can pass through the lipid bilayer?
Small, non charged molecules like O2 and CO2
What do bigger, charged molecules like glucose or sodium ions need to pass through?
A channel in form of a channel protein
What are channel proteins?
A membrane protein that allows molecules through a pore
What are carrier proteins?
A membrane protein that the molecule causes it to change shape, so it carries the molecule across the membrane
What are the properties of carrier proteins?
They are passive or active when transporting molecules down a concentration gradient (high to low)
What is active transport?
A movement of molecules across a cell membrane from an area of low concentration to an area of high concentration, against the concentration gradient
How are channel proteins given energy?
From ATP
What is an ATP molecule made up of?
Ribose
3 Phosphate Groups
Adenine Base
How is energy released from an ATP molecule?
When the bond between the 3rd and the 2nd phosphate is broken by hydrolysis, energy is released
How do we create ATP again?
Energy is required to add a 3rd phosphate bond to ADP to create ATP again
What is endocytosis
Movement of large molecules into the cell by vesicles, requires energy in the form of ATP
What is exocytosis
Movement of large molecules out of the cell by vesicles, requires energy in the form of ATP
How is exocytosis and endocytosis possible?
Through the fluid nature of the cell membrane
Give an example of endocytosis
Phagocytosis (cell-eating)
What is phagocytosis?
A large structure e.g. molecule is surrounded by the cell membrane and engulfed in a vesicle which moves into the cell
What is pinocytosis?
Cell-drinking, if the material taken in is a liquid
How does exocytosis occur?
Large molecules in the cell is engulfed in the vesicle, which moves to the cell membrane where it fuses with the membrane. The contents that were engulfed are then released out of the cell
