Transport Across Membranes Flashcards
What is a cell membrane?
A phospholipid bilayer
What can the cell membrane contain?
- Glycoproteins- Cholesterol- Transport proteins- Glycolipids
What are transport proteins?
Channel and carrier proteins
How is the phospholipid bilayer arranged?
- Hydrophilic heads face outwards- Hydrophobic tails face inwards
Why is the phospholipid bilayer fluid?
Phospholipids can slide over each other
What molecules can diffuse through the phospholipid bilayer?
Small non-polar ones e.g. CO2 and O2
How does water cross the phospholipid bilayer?
Water is polar so cannot diffuse straight through the phospholipid bilayer, instead it crosses through aquaporins
What is the role of cholesterol in the phospholipid bilayer?
It adds strength and support by making the membrane more rigid and less flexible. This is useful because animal cells have no cell wall and cells like haemoglobin nneed more strength as they travel alone
How does cholesterol strengthen the membrane?
It binds to the hydrophobic tails
What is diffusion?
The net movement of molecules from an area of high concentration to low concentration along a concentration gradient
What type of movement is diffusion?
Passive
Does diffusion require ATP?
No
What are the three features that increase the rate of diffusion?
- Short diffusion pathway- Large surface area- Concentration gradient
Give an example of how the body can maintain a concentration gradient?
- Ventilation- Circulation
Give an example of how the body maintains short diffusion pathways
- Thin capillary walls
Give examples of the body increasing surface area
- Villi- Microvilli- Alveoli- Cristae- Thylakoids
How are the lungs adapted to maintain a fast rate of diffusion?
- Ventilation of air and circulation of the blood maintains the high concentration gradient- Alveoli and capillaries have thin walls to keep the diffusion pathway short- Alveoli and highly folded to increase the surface area
What is facilitated diffusion?
The passive movement of molecules across the cell membrane via a specific transmembrane transport protein
What molecules use carrier proteins?
Large molecules e.g. glucose
What molecules use protein channels?
Small polar molecules like ions
How does facilitated diffusion interact with a concentration gradient?
It goes along it from high to low
What else can transmembrane transport proteins be used for?
Active transport
How are the different transmembrane transport proteins different?
Each molecule has a specific transmembrane protein with its a specific tertiary structure
Does active transport go with or against the concentration gradient?
Against
How does active transport work?
Using a carrier protein and energy from ATP
How does co-transport work?
Via a carrier protein which moves 2 molecules at once, one along the concentration gradient and one against the concentration gradient
What are the 3 stages of the absorption of glucose?
- Sodium-potassium pump2. Co-transport3. Facilitated diffusion
What is the first stage of the absorption of glucose?
The sodium-potassium pump1. Na is pumped from the epithelial cell into the capillary against its concentration gradient therefore using energy from ATP2. K is pumped from the capillary into the epithelial cell
What is the second stage of the absorption of glucose?
Co-Transport1. There is a low concentration of sodium in the epithelial cell so it enters via co-transport via a carrier protein from the lumen of the ileum2. The glucose also enters the epithelial cell from the lumen of the ileum via the same carrier protein as sodium against its concentration gradient
What is the third stage of the absorption of glucose?
Facilitated Diffusion 1. Glucose is in a high concentration within the epithelial cells 2. Glucose uses a carrier protein to diffuse out of the epithelial cell into the blood where it is absorbed
What is osmosis?
The passive movement of water molecules from an area of high water potential to low water potential
What is a high water potential?
- High % of water - Low % of solute - Low solute concentration- Hypotonic
What is a low water potential?
- Low % of water - High % of solute - High solute concentration- Hypertonic
Water move into the roots of a plant by which process?
Osmosis
In active transport using carrier proteins, what form of energy is used?
ATP
What type of cells are most likely to burst when placed in a hypotonic solution?
Animal - no cell wall
Within active transport, which proteins are not involved?
Channel
What is a similarity between the processes of active transport and facilitated diffusion?
They both use a protein
Within facilitated diffusion, which proteins are not involved?
Receptor
What is a solution called which has the same water potential as the cell?
Isotonic
What is a definition for water potential?
The likeliness of water to diffuse into or out of a solution
If a cell is placed into a hypotonic solution, what will the net direction of water be?
Into the cells
Which molecule diffuses within the process of osmosis?
Water
Which of the process provides the energy for active transport to occur in humans?
Respiration
Carrier proteins are involved in which processes?
Facilitated diffusion and active transport
Which of molecules are able to move via simple diffusion across a cell membrane?
Oxygen
