3.4.1 The Movement of Substances Across the Plasma Membrane (Structured Question 1 & 2)

Question 1:
Diagram I and Diagram II show two different types of movement of substances across the plasma membrane.


(a) In Diagram I. label the following structures:

• Phospholipid bilayer, with letter R
• Carrier protein, with letter S [2 marks]

(b) State two characteristics of the phospholipid bilayer. [2 marks]

(c) Name the process of the movement of substances across the plasma membrane as shown in Diagram I and Diagram II. [2 marks]

(d)(i) Glucose molecules are transported across the plasma membrane into the cell through the process shown in Diagram I. Explain why. [2 marks]

(ii) If the substances in Diagram II are calcium ions, describe how they are transported into the cell. [4 marks]

Answer:
(a)

(b)

1. It consists of hydrophilic heads and hydrophobic tails
2. The hydrophilic heads are facing the exterior and the interior of the cell
3. The bilayer is dynamic/ not static

(Choose any 2)

(c)
Process in Diagram I – Facilitated diffusion
Process in Diagram II – Active transport

(d)(i)

• Glucose consists of uncharged large sized molecules which cannot pass through the phospholipid bilayer.
• It needs a specific carrier protein to transport it across the phospholipid bilayer.

 

(d)(ii)

• By active transport – The movement of calcium ions is against the concentration gradient
• And it needs energy which is produced by cellular respiration ( in the form of ATP molecules)
• Carrier proteins bind with the calcium ions and change their shape, thus carrying the ions across the plasma membrane.