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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.


3.1.2 Types of Cell Division

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Types of Cell Division
 
1. Mitosis is a cell division to produce two identical daughter cells which are genetically
similar and have the same number of chromosomes to the parent cell.
 
2. Mitosis is carried out
(a) in somatic cells (body cells) of animals
(b) at the tip of root and shoot of plants 



 



3.1.3 Stages of Mitosis in an Animal Cell















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.








3.1.1 Genes, Deoxyribonucleic Acids (DNA) and Chromosomes

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Cell Division

3.1.1 Genes, Deoxyribonucleic Acids (DNA) and Chromosomes
1. The nucleus of a cell contains many small thread-like structures called chromosomes.
 
2. Chromosomes always exist in pairs (except in gametes).
 
3. Each chromosome contains a molecule of a deoxyribonucleic acid (DNA).
 
4. On each chromosome, there are genes which are the basic hereditary units.
 
5. A gene is a small segment of the DNA molecule. It passes genetic information from one generation to another.
 
6. Genes exist in pairs. One gene is inherited from the father and one from the mother.
 
7. Examples of genes:
  (a) A gene for body height
  (b) A gene for hair colour
  (c) A gene for fingerprint
 
8. Each organism has a specific number of chromosomes in its cell as shown in the table below.

Organism
Chromosomes number
Housefly
12
Onion
16
Frog
26
Apple
34
Human
46
Potato
48
Cow
60

3.1 The Plasma Membrane

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The Plasma Membrane

The plasma membrane is a semi-permeable lipid bilayer found in all cells that controls water and certain substances in and out of the cell.

Function of the Plasma Membrane

  1. Protects the cell.
  2. Separates the intracellular components from the extracellular environment.
  3. Controls what enters and exits the cell

Necessities for the Movement of Substances across the Plasma Membrane

  1. To transport nutrients into the cell.
  2. For gases exchange
  3. To excrete metabolic waste.
  4. To maintain the pH value and ionic concentration of the cell.



Substances In and Out through the Membrane


Structure of the Plasma Membrane

Fluid Mosaic Model




Permeability of the Phospholipids Bilayer

The permeability of the phospholipids bilayer is determined by:
  1. the size
  2. the charge and
  3. the polarity
of the substances pass through it.




2.4.2 Cell Organisation (Structured Question 1 & 2)

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Question 1:
Diagram below shows four levels of cell organization in humans.



(a) Complete Table below by naming Level 2 and Level 3. [2 marks]



(b)(i) The cells undergo process P to become specific cells that perform a specific function.
Name process P. [1 mark]

(ii) What is the function of the structure in level 2? [1 mark]

(iii) The structure in level 4 is one of the body systems.
Name this system. [1 mark]

(iv) State one function of the system in (b)(iii). [1 mark]

(c)(i) Name and explain the condition which can cause a blockage in blood vessel W. [3 marks]

(ii) A person is suffering from the condition in (c)(i).
State three effects on the person’s health. [3 marks]



Answer:
(a)
Level 2: Tissue
Level 3: Organ

(b)(i)
Process P: Differentiation

(b)(ii)
Function: able to contract and relax to pump the blood

(b)(iii)
Blood circulatory system

(b)(iv)
Transport oxygen, nutrients and antibodies


(c)(i)
Thrombosis – Deposition of cholesterol inside the lumen of a blood vessel which clogs the blood vessel.
Or
Embolism – Movement of cholesterol inside a blood vessel which clogs the blood vessel and leads to thrombosis.
Or
Arteriosclerosis – Deposition of cholesterol/ fat/ calcium inside the lumen of a blood vessel which cause narrowing of the lumen and leads to clogging.

(c)(ii)
1. Chest pain
2. Stroke
3. Heart attacks


2.4.1 Cell Structure and Function (Structured Question 1 & 2)

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Question 1:
Diagram below shows a plant cell as seen under an electron microscope.

(a)(i) On the diagram, label the structures A, B, C and D. (2 marks)

(a)(ii) State the function of structure A and structure D. (2 marks)


(b) Explain the role of C to maintain cell turgidity. (2 marks)

(c) Every somatic cell which contains structure B has a potential to form a complete new organism.

(i) Name the technique used to produce new plants in large quantities. (1 mark)

(ii) By using one suitable part of the plant, explain the technique in (c)(i). (4 marks)



Answer:
(a)(i)
A: Chloroplast
B: Nucleus
C: Vacuole
D: Golgi apparatus

(a)(ii)
A: Absorbs light energy for photosynthesis.
D: Collects chemical produced and pack them in a membrane to form secretory granules.

(b)
- Maintain the osmotic concentration of the cell sap.
- If the cell is flaccid, more water will enter the cell by osmosis.


(c)(i)
Culture tissue / Cloning

(c)(ii)
- Use shoot / root / meristem issue
- Wash and treat with the sterilizing agent hydrogen peroxide.
- The tissue or explant is cultured in a nutrient medium, at a suitable temperature and pH value.
- Cells divide by mitosis to form a callus.
- The callus differentiates to form a clone.



Question 2:
Diagram below shows the structure of an animal cell.


(a)(i) On the diagram, label the structures R and T. (2 marks)

(a)(ii) Explain the function of the chromosomes. (2 marks)


(b) Explain what will happen to the production of extracellular enzymes if the Golgi apparatus and T are absent. (4 marks)

(c) Explain why the sperm cells contain more mitochondria. (2 marks)

(d) Explain why lysosomes help in eliminating damaged organelles in the cells. (2 marks)


Answer:
(a)(i)
R: Plasma membrane
T: Rough endoplasmic reticulum

(a)(ii)
Chromosomes carry genetic material which is transferred from the parent to the offspring.

(b)
If T (the rough endoplasmic reticulum) is absent, there will be less ribosomes in the cells. Only the free ribosomes in the cytoplasm will synthesise proteins/ enzymes. Without the Golgi apparatus, enzymes which are proteins cannot be packaged or processed to be transported out of the cell.


(c)
Sperm cells need a large amount of energy so that it can swim towards the uterus for fertilization.

(d)
Lysosomes contain hydrolytic enzymes/ lysosomes which will digest/ hydrolyse damages organelles, absorb the useful nutrients and eliminate the waste.

2.11.3 Hormonal Coordination in the Body (Structured Questions)

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Question 1:
Diagram 1 shows the location of endocrine glands of a woman.
(a) Name glands R and S in the boxes provided in Diagram 1.

(b) State one function of hormone secreted by glands R and S.

(c) State one effect to the woman if both glands S are removed.

(d) Label with letter X the thyroid gland in Diagram 1.


Answer:
(a)
R: Pituitary gland
S: Ovary

(b)
R: Simulates the production of hormone by thyroid gland
S: Control menstrual cycle

(c) Infertility


(d)


2.2.2e Involvement of Systems in Maintaining an Optimal Internal Environment

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Internal Environment of Multicellular Organism

  1. The internal environment of a multicellular cell is referring to the medium surrounding the cell.
  2. It consists of blood plasma and interstitial fluid. (also called the extracellular fluid)

Homeostasis

Homeostasis is the property of a system, especially a living organism, that regulates its internal environment so as to maintain a stable, constant condition.

Factors Affecting the Internal Environment.

  1. Body temperature
  2. pH value of the blood
  3. Sugar level of the blood
  4. Blood pressure
  5. Osmotic pressure of the blood
  6. Concentration of the oxygen and carbon dioxide in the blood

Importance of Homeostasis

Maintaining a suitable environment for all the enzyme function efficienly, and hence enable all biochemical reactions been carried out at their maximum rate.

Regulation of body temperature

Nervous system Detect changes in body temperature
Integumentary system Produces sweat when the surrounding is hot.
Circulatory system Transports and distributes heat evenly through out the body
Muscular system Shivering to produce heat when the surrounding is cool.