▪️C1.3 -cell Memebranes and transport Flashcards
Why are phospholipids a important component of the cell surface membrane?
- they can form bilayers
- inner layer of phospholipids has its hydrophilic head pointing in towards the cell, interacting with the water in cytoplasm
- outer layer has its hydrophilic head pointing outwards, interacting with the water surrounding the cell
- hydrophobic tails point towards each other, to the centre membrane
- phospholipid component of a membrane allows lipid soluble molecules across but not water soluble molecules
Where are proteins in a cell membrane?
Name the 2 forms of protein present
Scattered throughout the phospholipid Bilayer of the membrane embedded as either extrinsic or intrinsic proteins
Describe extrinsic proteins and their purpose
On the surface of the bilayer.
Provide structural support
Form recognition sites by identifying cells and receptor sites for hormone attachment
Describe intrinsic proteins and their purpose
Extended across both layers of the phospholipid bilayer
Includes carrier and channel proteins
What do carrier proteins (intrinsic proteins) do?
They transport water soluble substances across the cell membranes
What do channel proteins (intrinsic proteins) do?
Allow active transport of ions across the membrane through forming channels
Why is the fluid mosaic structure called the fluid mosaic structure?
- the individual phospholipid molecules can move within a layer relative to one another (fluid)
- the proteins embedded into the bilayer vary shape and size and pattern (mosaic) lol
Where in the cell membrane is cholesterol found? What is it’s purpose?
In the membranes of animal cells, between the phospholipid molecules, making the membrane more rigid and stable
Where in the cell membrane are glycoproteins and glycolipids found?
In the outer layer of the membrane.
What is the outer layer around the cell membrane called? What is it’s role?
The glycocalyx
The molecules in the glycocalyx have roles as hormone receptors or in cell-to-cell recognition
What can diffuse across the membrane?
Lipid soluble substances such as vitamin A, small molecules like oxygen and carbon dioxide can dissolve in the phospholipid and diffuse across the membrane
How does the phospholipid layer being hydrophobic effect diffusion is different molecules
Lipid soluble molecules move through the cell membrane more easily than water soluble substances
Name molecules that struggle to diffuse through membrane
Why is this?
Glucose, polar molecules and jk s can’t readily diffuse through the phospholipids
This is because they are water soluble
How do water soluble substances pass through the cell membrane?
They pass through intrinsic protein molecules which form water filled channels across the membrane
What is the name for a membrane that picks what to diffuse in and out
Selectively permeable membrane
Define simple diffusion
The movement of molecules or ions from a region of high concentration to lower concentration down a concentration gradient until equilibrium is reached. It is a passive process it does not require atp
Name the factors affecting simple diffusion:
- the concentration gradient (greater difference the more molecules diffuse in a given time)
- thickness of the exchange surface/distance of travel where diffusion takes place (thinner=more molecules diffuse)
- the surface area is the membrane
- size of diffusing molecules (smaller diffuses faster)
- temperature
- nature of diffusing molecules (fats diffuse faster than water soluble molecules)
Name the rate of diffusion equation:
(Surface area x difference in concentration) divided by the length of diffusion pathway
Define facilitated diffusion.
The passive transfer of molecules or ions die. A concentration gradient, across a membrane by protein carrier molecules In the membrane
Where does facilitated diffusion occur?
At a specific sit on the plasma membrane wher there are transport protein molecules (intrinsic carrier/channel proteins)
Define channel proteins in detail
Molecules with pores lines with polar groups. As the channels are hydrophilic, water soluble ions can pass through. The channels open and close according to the needs of the cell
Define carrier proteins in detail
Allow diffusion of larger polar molecules such as sugar and amino acids across the membrane. A molecule attaches to its binding site, on the carrier protein. The carrier protein changes shape and released the molecule on the other side of the membrane
Describe how larger molecules e.g amino acids diffuse through a cell membrane
A molecule attaches to the binding site, on the carrier protein. The carrier protein changes shape and releases the molecule on the other side of the membrane
Does the use of carrier proteins use ATP
No, carrier and channel proteins increase the rate of diffusion down a concentration gradient without energy in the form of ATP
Define active transport
A process in which ions and molecules move from an area of low concentration to high concentration against a concentration gradient through a semi permeable membrane, it is an active process it requires ATP
Name some features of active transport
1- ions/molecules are moved from a lower to higher concentration against a concentration gradient
2- requires energy in the form ATP. Anything that affects respiration will effect active transport
3- process occurs through intrinsic carrier proteins spanning the membrane
4-rate is limited by the number and availability of carrier proteins
Name some processes involving active transport
Muscle contraction, nerve impulse transmission, reabsorption of glucose in the kidney nephron and mineral uptake into plant root hair cells
Describe the process of ATP
1) Molecule or ion combines with a specific carrier protein on the outside of the membrane
2) ATP transfers a phosphate group to the Carrie protein on the inside of the membrane
3) carrier protein changes shape and carried the molecule across the membrane, to the inside of the cell
4) molecule is realised into cytoplasm
5) phosphate ion is released from the carrier molecule back to the cytoplasm and recombined with ADP to form ATP
6) carrier protein returns to its original shape
What happens when an active transport graph Levels off?
The carrier proteins are saturated
Name something that can stop active transport
Why?
A respiratory inhibitor such as cyanide can stop active transport
This is because they prevent aerobic respiration and the production of ATP in the mitochondria
Define co-transport
A type of facilitated diffusion that brings molecules and ions into cells together on the same transport protein molecule
Name an example of co-transport
Sodium-glucose co-transport is significant In absorbing glucose and sodium ions across cell membranes and into the blood in the kidney nephron
Describe how co-transport occurs
1- a glucose molecule and two sodium ions outside the cell attach to a carrier protein In the cell membrane
2- the carrier protein changes shape and deposits the glucose molecule and the sodium ions inside the cell
3-the glucose molecule and sodium ion separately diffuse through the cell to the opposite membrane
What is the water potential of pure water
0
What happens to the value of water potential when you add a solute
Addition of solute to pure water lowers the water potential making it a negative value
Define osmosis
The net movement of water molecules from an area of High water potential to low water potential down a concentration gradient through a semi permeable membrane, it is a passive process it does not require ATP
Define water potential
The tendency for water to move into a system, from an area of higher water potential to lower water potential. Water potential is decreased by the addition of a solute. Pure water has a water potential of 0
What does solute potential measure?
Measures how easily water molecules move out of a solution
Define turgid
A plant cell that holds as much water as possible, preventing further entry of water as the cell can’t expand further
Name the 2 opposing forces in a plant cell
1) solute potential, due to diluted in the vacuole and cytoplasm, pulls water in to the cell meaning water is less likely to move out
2) pressure potential, a force which increases chance of water moving out
Name the osmosis pressure equation
Water potential of cell= pressure potential + solute potential
Describe when a hypotonic situation occurs
If the water potential of the external solution is less negative (greater) than the solution inside the cell.
Water would flow into the cell
Describe when a hypertonic situation occurs
If the water potential of the external solution is more negative (less) than the solution inside the cell
Water flows out of the cell
Describe how a isotonic situation occurs
If the cell has the same water potential as the external solution
No net water movement
Define the process of plasmolysis
What happens when complete?
Occurs when plants in s hypertonic solution lose water by osmosis and the vacuole shrinks
and cytoplasm draws away from cell wall
When complete the cell is flaccid and plant wilts
Define the process of incipient plasmolysis
Occurs when the external concentration is High enough so just enough water is lost do the membrane begins to pull away from the cell wall
What is the pressure potential of a cell in incipient plasmolysis?
Why?
0
Because the cell wall does not exert any pressure on the cytoplasm
What is the pressure equation of a cell in incipient plasmolysis
Water potential =solute potential
What is the value of water potential in a fully turgid cell?
0
What is the pressure equation in a fully turgid cell?
Pressure potential = - solute potential
Why is turgor important to plants
Provides support, maintains their shape and holds them upright
Name the water potential equation in an animal cell
Water potential = solute potential
Describe the process of haemolysis
If red blood cells are in distilled water, water enters by osmosis and they burst as they don’t have a cell wall
Describe the process of crenation
When red blood cells are placed in concentrated salt solution, water leaves the cells and they shrink
Name the 2 methods of bulk transport
Endocytosis
Exocytosis
When does endocytosis occur?
When material is engulfed by extensions of the plasma membrane and cytoplasm, forming a vesicles
Name the 2 types of endocytosis
Phagocytosis
Pinocytosis
Define phagocytosis
The Uptake of solid material that is too large to be taken in by diffusion or active transport
Describe the process of phagocytosis
When granulocytes engulf Bactria, a lysosomes fuses with the vesicle formed and enzymes digest the cells, products are absorbed into cytoplasm
Define exocytosis
Process where substances leave the cell, having been transported trough the cytoplasm in a vesicle, which fuses with the cell membrane.
Give an example of something that is secreted by exocytosis
Digestive enzymes
Why is endocytosis and exocytosis active processes
The cell membrane has to change shape which requires energy is the form of ATP, generated by the cells respiration
Why is the cell membrane being fluid vital to the cell?
Because the cell membrane flows with endocytosis decreasing the overall are of the cell membrane and exocytosis increasing it
Suggest two reasons why transport across the membrane is vital to the cell
- Maintains water potential in cells
- obtain oxygen/remove CO2
- obtain minerals/nutrients e.g glucose
Describe the role of the cell wall in generating pressure potential
Cell wall is inelatic/won’t stretch
Water passes into the cell via osmosis and the protoplast swells/expands
This pushes against cell wall and due to its resistance generate a pressure potential
Suggest 2 functions of membrane proteins
- Acts as recognition sites for cell-to-cell recognition of individual cells
- transport proteins allow water soluble/ polar substances to penetrate the membrane
How does oxygen enter the cell
-by simple diffusion, through the phospholipid bilayer
Describe how phosphate ions enter the cell
Phosphate ions travel by facilitated diffusion/active transport through carrier proteins
Describe how the solubility in lipid affects the rate of diffusion through a membrane
As lipid solubility increases, the rate of diffusion increases as membrane contains double layer of phospholipids :: lipids can diffuse through the membrane more easily
Describe how molecular size affects the rate of diffusion
The larger the molecule the slower the rate of diffusion as they are more difficult to pass between phospholipid molecules
