SPM Biology Form 4 Notes – Terminology and Concepts: Movement of Substances Across the Plasma Membrane (Part II)

by BerryBerryTeacher

in Berry Reference (Notes)

Berry Berry Easy presents Part 2 of the SPM Form 4 Biology notes for Movement of substances across the plasma membrane“. In Part 1, the uniqueness, importance, structure and permeability of plasma membrane were discussed. This part focuses on the gist of the topic, which is on ‘transport’. Both the passive and active transport process is examined in this post. One thing for sure that Berry Readers will remember long after you leave school (yup, 100% sure) is how Osmosis works. It’s a topic which for some unknown reasons will give students headache in the beginning but after you leave school, it all make sense to you. You may ask your elder siblings if they still remember osmosis. Anyway, let the notes begin.

SPM Biology Form 4 – Terminology and Concepts: Movement of Substances Across the Plasma Membrane (Part 2)

Permeability of the fruit skin

Permeability of the fruit skin

Materials must be able to move through the plasma membrane in order for the cell cytoplasma to interact with the external environment. Therefore, the movement of soluble substances can occur in several mechanisms:

  • A. Process of Passive Transport
  • B. Process of Active Transport

A. Passive Transport

i) Simple Diffusion

  • not selective: lipid-soluble molecules, gases and water.
  • not control by cell.
  • movement of the molecules from a region of higher concentration to a region of lower concentration.
  • Factors affecting the rate of diffusion are temperature, size of molecules/ions, diffusion gradient, surface area and diffusion medium.
  • example: diffusion of oxygen and carbon dioxide at the alveolus.

ii) Osmosis:

  • only water molecules.
  • not control by cell.
  • movement of water from a region of higher concentration to one of lower concentration and often occurs across a semipermeable membrane.
  • strong sucrose solution = less water molecule = low water potential.
  • weak sucrose solution = more water molecule = high water potential.
  • example: absorption of water by root hairs.

iii) Facilitated Diffusion:

  • very specific: glucose, nucleic aicds, amino acids, protein and mineral ions.
  • control by cell.
  • transport of molecules (only certain molecules) across the outer membrane of living cell by a process of carrier protein (hydrophilic group) / channel protein (Ions: Na+, Ca2+, K+) within the cell membrane.
  • normally take place from a region with higher concentration of molecules to a region of lower concentration.
  • example: absorption of digested food in the villus.

B. Process of Active Transport

  • very specific: minerals ions and amino acids.
  • control by cell.
  • This process needs carrier proteins and energy (due to against concentration gradient) from a region of lower concentration to a region of higher concentration).
  • Cell must expend energy that derived from ATP (adenosine triphosphate)
  • example: human nerve cells (sodium ions are constantly transport out of the cell) / ions intake by root hairs of a plant.

Finally, the end of this part. Stay tune for the final part (Part 3) of SPM Biology Form 4 notes on “Movement of substances across the plasma membrane“.

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