A-level Biology - 3.1.4 Transport into and out of Cells Part 4
To find the water potential of potato cells, place identical potato chips in varying concentrations of sucrose solution. Measure the mass before and after soaking, calculate the percentage change, and plot a calibration curve. The point where mass change is zero indicates the water potential.
Describe how you can use serial dilutions to find the water potential of potato cells
Use cork borer to cut potatoes into 5 indentically size chips (1 cm in diameter)
Blot potato chips with paper towel
Weigh mass of each potato chip on mass balance & record these values
Place each potato chip into each sucrose solution
Leave chips in solution for 20 minutes
Remove chips and gently pat them dry with paper towel
Weigh each chip again and record these masses
Calculate % change in mass for each chip
Use results to make calibration curve, showing % change in mass against sucrose solution
Key Terms
Describe how you can use serial dilutions to find the water potential of potato cells
Use cork borer to cut potatoes into 5 indentically size chips (1 cm in diameter)
Blot potato chips with paper towel
Weigh mass of each ...
Potato chips will gain water (& thus mass) in solutions with ____ _____ ______ than the chips
higher water potential
Describe how you would find the water potential of potato cells from a calibration curve
Point at which curve crosses x-axis = point where water potential of sucrose solution = water potential of potato cells
Find concentration at...
Define Active Transport
Movement of molecules/ions into or out of a cell from an area of lower concentration to an area of higher concentration using energy from ATP and c...
Describe how carrier proteins move molecules in active transport
Molecules/ions bind to receptors on carrier protein
On inside of cell: ATP binds to carrier protein = causes it to split into ADP and phospha...
Name 2 differences between active transport and facilitated diffusion
Active transport = moves solutes from low to high concentration
Active transport requires energy
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| Term | Definition |
|---|---|
Describe how you can use serial dilutions to find the water potential of potato cells | Use cork borer to cut potatoes into 5 indentically size chips (1 cm in diameter) Blot potato chips with paper towel Weigh mass of each potato chip on mass balance & record these values Place each potato chip into each sucrose solution Leave chips in solution for 20 minutes Remove chips and gently pat them dry with paper towel Weigh each chip again and record these masses Calculate % change in mass for each chip Use results to make calibration curve, showing % change in mass against sucrose solution |
Potato chips will gain water (& thus mass) in solutions with ____ _____ ______ than the chips | higher water potential |
Describe how you would find the water potential of potato cells from a calibration curve | Point at which curve crosses x-axis = point where water potential of sucrose solution = water potential of potato cells Find concentration at this point & then look up water potential for that concentration of sucrose solution |
Define Active Transport | Movement of molecules/ions into or out of a cell from an area of lower concentration to an area of higher concentration using energy from ATP and carrier molecules |
Describe how carrier proteins move molecules in active transport | Molecules/ions bind to receptors on carrier protein On inside of cell: ATP binds to carrier protein = causes it to split into ADP and phosphate molecule Causes carrier protein molecule to change shape, releasing molecules/ions to other side of membrane Phosphate molecule is released from carrier protein & recombines with ADP to from ATP during respiration Causes carrier protein to revert to its original shape |
Name 2 differences between active transport and facilitated diffusion | Active transport = moves solutes from low to high concentration Active transport requires energy |
Describe how ATP enables active transport (as well as other biological processes) | Undergoes hydrolysis reaction = splits ADP and P¡ (inorganic phosphate) = releases energy so solutes can be transported |
Co-transporters are type of ___ _____ | carrier protein |
Describe how co-transporters enable molecules to move in active transport | Bind 2 molecules at a time Concentration gradient of one of the molecules = used to move other molecule against its own concentration gradient |
Name 3 factors that affect the rate of active transport | Speed of individual carrier proteins Number of carrier proteins Rate of respiration in cell & availability of ATP |
Glucose is absorbed by _ in mammalian ileum | Co-Transport |
Why is glucose absorbed from lumen (middle) of ileum by co-transport? | ∵ In ileum (final part of small intestine) = concentration of glucose is too low for glucose to diffuse into blood |
Describe how glucose is absorbed from lumen (middle) of ileum by co-transport | Sodium ions = actively transported out of ileum epithelial cells into blood by sodium-potassium pump = creates concentration gradient Higher conc. of Na+ ions in lumen than inside cell Causes sodium ions to diffuse into epithelial cell by facilitated diffusion (down their concentration gradient) Via sodium-glucose co-transporter proteins Glucose absorbed with Na+ ions against their concentration gradient = concentration of glucose inside cell increases Glucose diffuses out of cell into blood, down its concentration gradient through protein channel by facilitated diffusion |
ATP has _ ____ ___ | 3 phosphate groups (Bonds between phosphate groups = unstable ∴ low activation energy = easily broken) |
Describe how ATP is synthesised to produce immediate source of energy | Conversion of ATP to ADP = reversible reaction ∴ energy can be used to add an inorganic phosphate to ADP to form ATP |
ATP cannot be stored ∴ it has to be ___ | continuously has to be made |
Describe how ATP is used in metabolic processes | ATP provides energy needed to build macromolecules from their basic units (e.g. making starch from glucose) |
Describe how ATP is used in active transport | Provides energy to change shape of carrier proteins |
What is the function of a glycolipid? | Acts as a recognition site |
Describe what the terms hydrophobic and hydrophilic mean and explain why this property of membranes helps their structure (4) | Hydrophobic = water hating Hydrophilic = water loving Membrane is stable because heads always move towards the water And tails always move away from the water, filling any gaps/holes that may form |
Name the roles of glycoproteins on the cell membrane (6) | Acts as a receptor/binding site for hormones Can be used for recognition Cell adhesion Cell signalling Act as antigens Can act as a switch to trigger changes in membrane Attaches to water molecules Receptor to transfer proteins |
List some of the molecules that require channel proteins to cross the membrane and explain why (3) | Glucose – too large to pass across Ions like sodium and potassium as they’re not lipid soluble Any molecules moving against a concentration gradient that requires ATP for active transport |
Define Cell Signalling | Communication between cells using various signals, particularly hormones |
What is meant by recognition in plasma membranes? | Receptors can be used to target certain cells and to distinguish between self and non-self |
What is meant by receptors in plasma membranes? | A glycoprotein molecule on the surface of a cell that triggers a response to environmental changes, hormones and other cells |
Using serial dilutions to find the water potential of potato cells: Before weighing, why do you blot dry the outside of each potato cylinder? (2) | ∵ water will affect the mass Amount of water on cylinders varies /ensures same amount of water on outside |
Using serial dilutions to find the water potential of potato cells: Why do you calculate the % change in mass? (2) | ∵ allows comparison cylinders may have different starting masses |
Using serial dilutions to find the water potential of potato cells: Why should you carry out several repeats at each concentration of sucrose solution? (2) | Allows anomalies to be identified Makes the mean / line of best fit more reliable / allows concordant results |