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3.4.2 The Movement of Substances Across the Plasma Membrane in Everyday Life (Structured Question 1 & 2)

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Question 1:
Diagram I and Diagram II show the movement of substances P and Q across the plasma membrane respectively. The movement of P needs energy but the movement of Q does not.
(a) Name the processes involved in the movement of P and Q. (2 marks)

(b)(i) Name one example of P and Q. (2 marks)
(b)(ii) Describe the movement of Q shown in Diagram II. (2 marks)


(c) Diagram III shows the condition of a plant cell before and after being immersed in a type of solution. (3 marks)

Explain the condition of the cell after being immersed in the solution.

(d) A housewife makes mango pickles by immersing mango slices in a concentrated sugar solution.
State one advantage and two disadvantages of the method used, compared to storing fresh mangoes. (3 marks)



Answer:
(a)
P: Active transport
Q: Simple diffusion

(b)(i)
P: Nitrate
Q: Oxygen

(b)(ii)
The partial pressure of Q is higher in the alveolus than in the blood capillary.  As a result, Q diffuses into the blood capillary following the concentration gradient.


(c)
The plasma membrane is pulled away from the cell wall, the vacuole becomes small, as a result the cell becomes flaccid and plasmolysis occurs.

(d)
Advantage: It keeps food for longer period.

Disadvantages:
1. The sugar content of the food is too high.
2. Some of the nutrients such as vitamin C are lost.



Question 2:
Diagram I below shows a plant cell that has been immersed in 30% sucrose solution.


(a)(i) On the diagram, label P and Q. (2 marks)
(a)(ii) Name the solution which filled the space between the cell wall and P.
Explain how the solution filled the space. (2 marks)

(b) The plant cell in the Diagram has undergone plasmolysis.
Explain how this happened. (2 marks)


(c) Diagram II and III below show the condition of two plants which are added with fertilizer. The plant in Diagram III is added with excess fertilizer.


Explain the condition of the plant in Diagram III. (3 marks)


(d) Diagram IV shows a method of preserving vegetables.


Explain the method used. (3 marks)



Answer:
(a)(i)
P – Plasma membrane
Q – Vacuole

(a)(ii)
Solution: Sucrose solution
Explanation: Cell wall is permeable to allow sucrose solution to pass through and fill up the spaces.

(b)
When water molecules diffuse out of the large vacuole by osmosis, the plasma membrane will be pulled away from the cell wall. The cytoplasm shrinks due to osmosis.


(c)
Excess fertilizer will cause the soil water to be hypertonic towards the root hair cells. As a result, water from the root hair cells diffuses out to the soil by osmosis. The cells become plasmolysed and this leads to wilting.

(d)
Salting – Concentrated salt solution is used to soak vegetables, The hypertonic solution causes vegetable tissues to be dehydrated. Microorganisms lose water by osmosis and cannot live without water.


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

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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.


3.2.3 Types of Solution – Hypertonic

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What is Hypertonic Solution?

Hypertonic solution is the solution that has lower water potential than the other solution.

Water Concentration and Solute Concentration of a Cell in a Hypertonic Solution


  1. Water concentration: Water concentration inside the cell is higher than outside the cell.
  2. Solute Concentration: Solute concentration inside the cell is lower than outside the cell.



Effect of Hypertonic Solution on Animal Cell




  1. If an animal cell such as red blood cell is placed into a hypertonic solution, water molecules is transported out from the red blood cells by osmosis (as shown in the diagram above).
  2. The red blood cells will shrink due to the lost of water from the cell and probably die.
  3. The red blood cells are said to undergo crenation .



The Youtube video above shows the effects of hypertonic solution on red blood cells. We can see that the cells finally shrink in hypertonic solution.



Effect of Hypertonic Solution on Plant Cell




  1. When a plant cell is placed in a hypertonic solution, water molecules is transported out from the cell by osmosis.
  2. The vacuole and cytoplasm are then shrink due to lost of water.
  3. The plasma membrane is pulled away from the cell wall..
  4. The process is called plasmolysed.



Summary:






3.2.2 Types of Solution – Isotonic

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What is Isotonic Solution?

In isotonic solutions, both solutions have equal water potential.

Water Concentration and Solute Concentration of a Cell in a Isotonic Solution

Water concentration and solute concentration are equal in both solutions.

Effect of Isotonic Solution on Animal Cell




  1. If an animal cell such as red blood cell is placed into a isotonic solution, amount of water molecules is transported into the red blood cells by osmosis is equal to the amount of water molecules transported out from the cell (as shown in the diagram above).
  2. Therefore the amount of water in the cell remain unchanged.
  3. The red blood cells maintain their shape.



The Youtube video above shows the effects of isotonic solution on red blood cells. All the cells remain unchanged in isotonic solution.



Effect of Isotonic Solution on Plant Cell


  1. When a plant cell is placed in an isotonic solution, solute concentration in the external solution is equal to the solute concentration i the cell sap.
  2. Therefore the rate of diffusion of water into the cell is equal to the rate of diffusion of water out from the cell.
  3. As a result, the shape of the cell remain unchanged.

3.2.1 Types of Solution – Hypotonic

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What is Hypotonic Solution?

Hypotonic solution is the solution that has higher water potential than the other solution.

Water Concentration and Solute Concentration of a Cell in a Hypotonic Solution


  1. Water concentration: Water concentration inside the cell is lower than outside the cell.
  2. Solute Concentration: Solute concentration inside the cell is higher than outside the cell.



Effect of Hypotonic Solution on Animal Cell




  1. If an animal cell such as red blood cell is placed into a hypotonic solution, water molecules is transported into the red blood cells by osmosis (as shown in the diagram above).
  2. The red blood cells will inflate and finally burst because the thin membrane cannot withstand the high pressure inside the cell.
  3. The red blood cells are said to undergo haemolysis.



The Youtube video above shows the effects of hypotonic solution on red blood cells. We can see that the cells finally burst and become "blur" under the microscope.



Effect of Hypotonic Solution on Plant Cell




  1. When a plant cell is placed in a hypotonic solution, water molecules is transported into the cell by osmosis.
  2. The water is then stored in vacuole causing it to expand and exerts pressure on the cell wall. This pressure is called turgor pressure.
  3. The turgor pressure caused the plant cell to become firm or turgid.
  4. The rigid cell wall prevents cell from bursting.

3.1.4 Active Transport

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What is Active Transport?


  1. Active transport is the movement of substances across the plasma membrane of cells against the concentration gradient (From lower concentration to higher concentration).
  2. Since it is against the concentration gradient, energy is needed in the process.
  3. Video below shows how particles are transported through the carrier protein in active transport. Take notes that the process only happens when the carrier protein receives energy from an ATP.





Basic Requirements in Active Transport

  1. Presence of the carrier protein
  2. Presence of ATP (Adenosine Triphosphate)

Function of the ATP

ATP is the source of energy in active transport. It supplies energy to the carrier protein to carry out the process. It is converted into ADP (Adenosine Diphosphate) after the reaction.

Mechanism of Active Transport

The video below shows how sodium ions and potassium ions are transported through the plasma membrane by a carrier protein.



Examples of Active Transport

Intake of mineral ions by the root hairs of a plant.

3.1.3 Passive Transport – Facilitated Diffusion

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What is Facilitated Diffusion?

Facilitated diffusion is the passive transport of substances across the plasma membrane with the help of transport proteins such as the channel protein and the carrier protein.

Substances Pass through the Plasma Membrane through Facilitated Diffusion

Particles undergo facilitated diffusion are the particles that cannot diffuse through the phospholipid bilayer such as
  1. Large particles such as glucose, amino acids, proteins and nucleic acids
  2. Some ions such as the sodium ions and chloride ions


2 Types of Transport Protein

Facilitated diffusion occurs through 2 types of transport protein, namely
  1. Channel Protein
  2. Carrier Protein



Mechanism of Facilitated Diffusion

Click on the links below to see how facilitated diffusion happen through the plama membrane of the cell.


Concentration Gradient

Facilitated diffusion happens down a concentration gradient.

Similarities between Simple Diffusion and Facilitated Diffusion

  1. Down the concentration gradient (From high concentration to low concentration)
  2. No energy is required

Differences between Simple Diffusion and Facilitated Diffusion




3.1.2 Passive Transport – Osmosis

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What is Osmosis?

Osmosis is the diffusion of a water through a semi-permeable membrane, from a solution of low solute concentration to a solution with high solute concentration.

It is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane separating two solutions of different concentrations.

Important Points:
  • It is the diffusion of water (normally) through a semi-permeable membrane.
  • It is from a dilute solution to a more concentrated solution.


3.1.1 Passive Transport – Simple Diffusion

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What is passive transport?

  1. Passive transport is the movement of substances across the cell membrane without the use of energy by the cell.
  2. During passive transport, substances move down their concentration gradient, hence no energy is required.
  3. Passive transports can happen through three different channels, namely
    1. lipid bilayer
    2. pore protein
    3. carrier protein

What is diffusion?

Diffusion is the movement of particles from a high density region to a low density region. No energy is needed and no membrane involves in diffusion.


The Dynamic Equilibrium

Diffusion will continue until the concentration in all region is the same. When this happen, we say it has reached the dynamic equilibrium.



Factors Affecting the Rate of Diffusion (How fast diffusion happens)




Particles that Move Through the Plasma Membrane Through Diffusion

  1. Substances soluble in fat: fatty acid, glycerol, some vitamins (A,D,E,K)
  2. Neutral particles: water, oxygen, carbon dioxide,

Example of Diffusion

Between alveoli and blood capillaries in the lung during gases exchange.