Transport Across Membranes

Question 1

What are the functions of a glycolipid?

Answer 1

Act as recognition sites, help maintain the stability of a membrane, helps attach to one another and so forms tissues

Question 2

What are the functions of a glycoprotein?

Answer 2

Act as recognition sites, help attach to one zntoher and so forms tissues, allows cells to recognise one another, for example lymphocytes can recognise an organisms own cells

Question 3

What is the function of cholesterol in the membrane?

Answer 3

Reduce lateral movement of other molecules including phospholipids, make the membrane less fluid at high temperatures, prevent leakage of water and dissolved ions from the cell

Question 4

What are the functions of proteins in the membrane?

Answer 4

Provide structural support, act as channels transporting water soluable substances across the membrane, allow active transport across the membrane through carrier proteins, form cell surface receptors for identifying cells, help cells adhere together, act as receptors for example hormones

Question 5

What are the functions of phospholipid bilayers?

Answer 5

Allow lipid soluble substances to enter and leave the cell, prevent water soluble substances entering and leaving the cell, make the membrane flexible and self sealing

Question 6

Why do molecules not freely diffuse move across cell surface membranes?

Answer 6

Not soluble in lipids and therefore cannot pass through the phopholipid bilayer, too large to pass through the channels in the membrane

Question 7

What is simple diffusion?

Answer 7

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distrubuted.

Question 8

What is facilitated diffusion?

Answer 8

A passive process down a concentration gradient

Question 9

Define facilitated diffusion

Answer 9

It is a passive process specific carrier proteins or channel proteins with complementary binding sites transport large and or polar molecules or ions down a concentration gradient

Question 10

What is the purpose of a calibration curve?

Answer 10

They are used to determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations

Question 11

How is a calibration curve used to find the concentration of plant tissue?

Answer 11

Plot a calibration curve of percentage change in mass against concentration. Find the X intercept where the plant tissue is isotonic to the sucrose solution

Question 12

What occurs when plant tissue is placed in a hypotonic solution?

Answer 12

Water moves into the plant tissue by osmosis, plant tissues increase in mass?

Question 13

What occurs when plant tissue is placed in a hypertonic solution?

Answer 13

Water moves out of the plant tissue by osmosis, plant tissue decreases in mass

Question 14

What are the potato discs left in solution for 20 minis ?

Answer 14

To allow time for osmosis until the paint tissue reaches equilibrium with its surrounding solution

Question 15

What is water potential determined by?

Answer 15

The concentration of solutes. The higher the solute concentration then the lower the water potential.

Question 16

Outline the procedure of investigating osmosis using potato tissue

Answer 16

1) make a simple dilution of 1m sucrose to produce 5 concentrations. Add 5 cm3 to 5 different test tubes. 2) cut a potato into equal sized chips and weigh 3) place a chip in each test tube and leave for 20 mins 4) take out, dab the excess water and weigh them again. 5) calculate the percentage change in mass

Question 17

Why is the percentage change used rather than the actual change in mass?

Answer 17

Potato chips may not all have same starting mass. Percentage change allows comparison

Question 18

What is indicated by the x-intercept of the calibration curve?

Answer 18

The concentration that is isotonic to the solution tested

Question 19

Explain the change in mass in the potato chips

Answer 19

The potato chips with concentration lower than the sucrose solution lose mass as there is a net movement of water out of the cells. The potato chips with concentration higher than the sucrose solution gain mass as there is a net movement of water into the cells.

Question 20

Why are the potato chips dabbed dry after removing from the sucrose solution?

Answer 20

To remove any excess water clinging to its surface

Question 21

What are the controlled variables?

Answer 21

Volume of sucrose solution, size of potato chips, length of time left in solution, dab each potato disc with paper towels