Transport

Simple diffusion

The net movement of small, non polar, lipid soluble substances from an area of high concentration to an area of low concentration. Does not require channel proteins/ carrier proteins and ATP

Faciliated diffusion

Requires a channel protein to transport polar molecules, charged and water soluble molecule across the membrane

Osmosis

The diffusion of water molecules from an area of high concentration to an area of low concentration across a partially permeable membrane

Osmosis RP : Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue : Determining the water potential of potato tuber cells

Label six boiling tubes 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol dm^-3 sucrose.

Use the 1 mol dm^-3 sucrose solution and distilled water to make up 20cm³ of sucrose solution of each concentrations with the equation C₁V₁= C₂V₂

Stand the boiling tubes containing the sucrose solutions in a water bath set at 30 degrees. Use a thermometer to ensure that the temperatures of each tubes reaches 30 degrees.

Use the potato cutter to cut six chips from the potato tuber. Remove any peel on the potatoes. Use a ruler to measure all potato chips to the same length.

Blot the potato chips dry with a paper towel and number the paper towel

Weigh each potato chips and record the initial masses in a table

At the water bath, set the stop clock to zero

Transfer each potato chips to its own boiling tube

After 20 minutes, remove the chips from the boiling tubes. Blot the chips dry. Reweigh them and plot the final masses in the results table

Calculate the change in mass and the percentage change in mass

Plot a graph of your processed data and use this to determine the concentration of sucrose which has the same water potential as the potato tuber cells.

Using C₁V₁= C₂V₂

C₁ = starting concentration (1 mol dm⁻³)

V₁ = volume of starting solution needed

C₂ = concentration you want

V₂ = final total volume

Active transport

Movement of molecules through a carrier protein against the concentration gradient from a region of lower concentration to a region of higher concentration, requires ATP. Reaches maximum rate when all carrier proteins are occupied and working at their maximum rate, increasing the concentration of the substance cannot increase transport further.

Key mechanisms of active transport

molecule or ion binds to specific carrier protein

ATP is hydrolysed into ADP and inorganic phosphate, releasing energy

this energy enables the carrier protein to change shape

the substance is moved against its concentration gradient across the membrane

the carrier protein returns to its original shape

Co-transport

The movement of two substances across a membrane via the same transport protein, where the movement of one substance down its concentration gradient or electrochemical gradient provide energy to move another substance against its gradient

Key mechanisms of co-transport

The sodium–potassium pump actively transports Na⁺ out of the epithelial cell using ATP into the surrounding tissue fluid, this creates a sodium ion gradient

Sodium ions move from the lumen into the epithelial cell through a sodium–glucose co-transporter.

Na⁺ and glucose bind to the same co-transporter, moving both into the epithelial cell. Glucose can move against its concentration gradient.

Glucose moves out of the epithelial cell through a GLUT carrier protein by facilitated diffusion, down its concentration gradient.

The sodium–potassium pump continuously removes Na⁺ from the cell, maintaining the gradient required for co-transport.

Co-transport of amino acid

Na⁺ is actively transported out of the epithelial cell using ATP.

A sodium ion gradient is established.

Na⁺ moves back into the epithelial cell through a specific sodium–amino acid co-transporter.

Amino acids enter the cell alongside Na⁺, potentially against their concentration gradient.

Amino acids leave the cell through transport proteins and enter the blood.