Transport Across Cell Membranes Flashcards
Learning Objectives and Summary Questions from the textbook
Describe the structure of the Cell-Surface Membrane
The phospholipid bilayer with proteins, cholesterol, glycolipids and glycoproteins embedded in the bilayer
Explain the Fluid-Mosaic model
Fluid - each individual phospholipid can move. This gives the membrane a flexible structure
Mosaic - the proteins that are embedded in the bilayer vary in size and shape
State the overall function of the cell-surface membrane
Allows different conditions to be established in and out of the cell. Controls the movement of substances in and out of the cell
State which end of the phospholipid molecule faces inwards in the middle of the bilayer
The hydrophobic tail
State through which molecule in the cell surface membrane the following are likely to pass in order to get in or out of a cell
A. a molecule that is soluble in lipids
B. a mineral ion
A. through the phospholipid bilayer
B. through a carrier protein
What is the definition of Diffusion?
The net movement of molecules or ions from a region where they are more highly concentrated to an area where their concentration is lower until they are evenly distributed
What can affect the rate of Diffusion?
- the difference in concentration
- temperature
- surface area of the membrane
What is the difference between Facilitated Diffusion and Diffusion?
Small non-polar molecules like carbon dioxide and oxygen diffuse through membranes, while Facilitated Diffusion moves charged ions and polar molecules using channel and carrier proteins.
Why is Facilitated Diffusion a passive process?
It only relies on the inbuilt motion from the kinetic energy of the diffusing molecule
Why can’t glucose molecules pass easily through the phospholipid bilayer?
The molecule is too large
What is the definition of Osmosis?
The passage of water from a region of higher water potential to a region of lower water potential through a selectively permeable membrane
What is the water potential of pure water?
0
What is the effect of solutes on water potential?
The addition of a solute to pure water will lower its water potential
How does water potential affect water movement?
The selectively permeable membrane allows only water to pass through. Therefore, water moves down the concentration gradient from the higher water potential solution to the lower one to reach dynamic equilibrium
What happens to an animal cell when it is placed in a higher, equal, and lower water potential compared to the cell solution?
Higher - Water enters the cell, causing it to swell and burst
Equal - no water enters or leaves the cell so there is no change
Lower - Water leaves the cell, causing the cell to shrink
What happens to a plant cell when it is placed in a higher, equal, and lower water potential compared to the cell solution?
Higher - Water enters the cell, causing the protoplast to swell, making it ‘turgid’
Equal - No water enters or leaves the cell, so there is no change to the protoplast, this is called ‘incipient plasmolysis’
Lower - Water leaves the cell, causing the protoplast to shrink and the cell becomes plasmolysed
Why does an animal cell burst when placed in pure water but a plant cell doesn’t?
The plant cell has an inelastic cell wall, meaning it cannot burst
What is the definition of active transport?
The movement of molecules or ions into or out of a cell from an area of lower concentration to an area of higher concentration using ATP and carrier proteins
What are the conditions for active transport to take place?
Active transport needs energy, transport proteins and a concentration gradient in order to take place
What is a similarity between active transport and facilitated diffusion?
Both use transport proteins to operate
What is a difference between active transport and facilitated diffusion?
Active transport uses ATP in order to go against the concentration gradient
When urine is produced, glucose is initially lost from the blood but is reabsorbed by the kidneys. Why is it important that this reabsorption occurs by active transport and not diffusion?
If glucose diffused, it would move out of the blood due to lower concentration. However, with active transport, glucose can go against the concentration gradient.
How do villi and microvilli take part in absorption?
They provide more surface area for the insertion of carrier proteins for diffusion, facilitated diffusion and active transport to take place
How are the products of carbohydrate digestion absorbed into the ileum
Active transport via sodium-glucose-co-transporters (SLGT1)
