Biology Chapter 4 Flashcards
What is the cell surface membrane also known as?
The plasma membrane
What are the functions of the cell surface membrane?
- To form a boundary
- Allows different intracellular and extracellular conditions
- Controls movement of substances into and out of cell
What are the functions of the phospholipids in the membrane?
- Allow transport of lipid-soluble substances
- Prevent water-soluble substances from entering or leaving the cell
- Allow flexibility in the membrane
Define ‘extrinsic protein’
A protein that is either embedded in the cell surface membrane of a cell or on its surface, but does not completely pass through the membrane’s bilayer
What are the functions of an extrinsic protein?
- Mechanical support
2. Receptors
Define ‘intrinsic protein’
A protein that spans the entire phospholipid bilayer
What are the functions of an intrinsic protein?
- Carriers/channels
2. Enzymes
What are the functions of the membrane proteins?
- Structural support
- Carriers for water-soluble substances
- Active transport - form ion channels
- Recognition sites
- Help cells join together
- Receptors
What is the model of the plasma membrane structure called?
The fluid mosaic model
Why are the words ‘fluid’ and ‘mosaic’ used in the fluid mosaic model?
Fluid = the membrane is flexible as the phospholipid molecules are free to move within the membrane
Mosaic = The proteins in the membrane resemble the pieces of a mosaic, in that they vary in shape, pattern and size
Is diffusion passive or active?
Passive
Where does the energy in this type of diffusion come from?
The kinetic energy which all particles possess, rather than an external source
How would you describe the motion of particles in their natural state?
Random
Define diffusion
The net movement of molecules or ions from a region of higher concentration to one where the concentration is lower
3 factors that affect the rate of diffusion
- Area over which diffusion takes place
- Concentration gradient
- Thickness of exchange surface
What equation describes the relationship between 3 factors affecting the rate of diffusion?
Diffusion is proportional to:
length of diffusion pathway
What are 2 limitations of the diffusion equation?
- Affected by nature of plasma membrane
2. Affected by the nature of the diffusing molecules itself
Is facilitated diffusion a passive or active process?
Passive
Give 2 ways through which facilitated diffusion can occur
- Through protein channels
2. Through protein carriers
Define osmosis
The passage of water from a higher water potential to a region of lower water potential, through a partially permeable membrane
What is the water potential of pure water under standard conditions?
0
Will adding a solute to pure water lower or higher its water potential?
Lower
What is meant by ‘net movement of water’?
The overall movement of all the water molecules in the system
What would be the net movement of water if the cell is placed in a solution of equal water potential to that of the cell solution?
None
What would be the likely consequence of placing an animal cell in pure water?
It would burst
Define ‘turgid’ in terms of cell wall and protoplast
Where the protoplast is pushed against the cell wall
Define ‘incipient plasmolysis’ in terms of cell wall and protoplast
The protoplast begins to pull away from the cell wall
Define ‘plasmolyse’ in terms of cell wall and protoplast
The protoplast pulls away from the cell wall completely
Why do plant cells not burst when in contact with pure water?
Their tough cell wall prevents them from bursting
What soluble products are produced from carbohydrate breakdown?
Glucose
Fructose
Gallactose
What are villi?
Finger-like projections on the folded walls of the small intestine
How do villi increase the efficiency of absorption from the small intestine?
- Increase surface area
- Reduce diffusion distance
- Maintain diffusion gradient
- Good blood supply
What are microvilli?
Finger-like projections of the epithelial cells lining the villi
What 2 features help maintain the concentration gradient for glucose?
- Good blood supply, constant flow of blood
2. Smooth muscle contraction mixes contents
Why is active transport also necessary?
So that all glucose can be absorbed
Glucose is co-transported with:
Sodium ions
Do the sodium ions move up or down the concentration gradient?
Down
Do glucose molecules move up or down the concentration gradient?
Up
Is this type of active transport direct of indirect?
Indirect
Why?
Glucose movement is powered by the sodium concentration gradient, not ATP directly
Define active transport
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using energy and carrier molecules
How does active transport differ from passive transport?
- It requires ATP
- Materials are moved against a concentration gradient
- Carrier protein molecules act as pumps
- It is selective
How is ATP used?
- Moves molecules
2. Through co-transport
Where do the ions or molecules bind on the carrier protein?
Receptors on the channel
Does ATP bind to the channel inside or outside the cell?
Inside
What happens when ATP splits?
A shape change occurs in the carrier, and opens to the other side of the membrane
What happens to the phosphate molecule and ADP after the shape change?
They are released and recombine
Give an example of a pump that can transport 2 ions at the sample time:
Sodium-potassium pump
Explain how you could use a students results to find water potential of a potato tissue
- Plot a graph with concentration on the x-axis and the % change on the y-axis
- Find the concentration where the curve crosses the x-axis (where % change is 0)
- Use another resource to find water potential of sucrose concentration
Why can data in a table be described as processed results?
Calculations are made from raw data/ raw data would have recorded initial and final masses
Why would a student calculate the percentage change in mass instead of using results from the table when calculating the change in mass?
Results from the table have initial and final masses
As glucose and sodium ions enter the epithelial cell, water enters the cell from the lumen. Explain why
- Sodium ions and glucose lower water potential of cell
2. Water enters the cell by osmosis
Give a function of cholesterol in cell membranes
Stabilises the phospholipid membrane/bilayer
Is the head of the phospholipid hydrophilic or hydrophobic?
Hydrophilic (water-attracting)
Is the tail of the phospholipid hydrophilic or hydrophobic?
Hydrophobic (water-repelling)
Explain the effect of temperature on membrane permeability
Below 0 = phospholipids don’t have much energy, so they can’t move very much. Channel proteins and carrier proteins denature
Between 0 and 45 = phospholipids can move around and aren’t packed as closely together (partially permeable membrane)
Above 45 = phospholipid bilayer starts to melt (break down) and the membrane becomes more permeable. Channel proteins and carrier proteins denature
Describe the absorption of glucose into the bloodstream
- Sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium-potassium pump. This creates a concentration gradient- there’s now a higher concentration of sodium ions in the lumen of the ileum than inside the cell
- This causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell, down their concentration gradient. They do this via the sodium-glucose co-transporter proteins. The co-transporter carries glucose into the cell wall with the sodium. As a result the concentration of glucose inside the cell increases
- Glucose diffuses out of the blood, down its concentration gradient through a protein channel, by facilitated diffusion
What are the 3 factors affecting the rate of active transport
- The speed of individual carrier proteins
- The number of carrier proteins present
- The rate of respiration in the cell and the availability of ATP
Define ‘isotonic’
If 2 solutions have the same water potential (they won’t lose or gain water)
Define ‘hypertonic’
Solutions with a lower water potential than the cell
Define ‘hypotonic’
Solutions with a higher water potential compared with the inside of the cell
What are the 3 steps to investigating water potential?
- Make serial dilutions
- Measure change in mass
- Produce a calibration curve
