IAL Edexcel Biology (2018) Unit 1 (WBI11) Last Minute Revision: Molecules, Diet, Transport and Health [Part 1]

 Preface

• This series contains 5 pars which are divided into 2 videos for topic 1 - molecules, transport and health; 2 videos for topic 2 - membranes, proteins, DNA and genes expression; and biology practical.
• The revision will be based on the syllabus for (WBI11) IAL Edexcel Biology (2018) Unit 1
• The first part contains the first half of the syllabus for topic 1

Syllabus Checklist

1. Understand the importance of water as a solvent in transport, including its dipole nature 
2. Know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin) 
3. Be able to relate the structures of monosaccharides, disaccharides and polysaccharides to their roles in providing and storing energy 
4. Know how monosaccharides (glucose, fructose and galactose) join together to form disaccharide (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions 
5. Know how a triglyceride is synthesised by the formation of ester bonds during condensation reactions between glycerol and three fatty acids 
6. Know the differences between saturated and unsaturated lipids 
7. Understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms) 
8. Understand how the structures of blood vessels (capillaries, arteries and veins) relate to their functions 
9. Know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function 
10. Understand the role of haemoglobin in the transport of oxygen and carbon dioxide 
11. Understand the oxygen dissociation curve of haemoglobin, the Bohr effect and the significance of the oxygen affinity of fetal haemoglobin compared with adult haemoglobin
12. Understand the course of events that leads to atherosclerosis (endothelial dysfunction, inflammatory response, plaque formation, raised blood pressure) 

1. Understand the importance of water as a solvent in transport, including its dipole nature

• Structure of water molecules
• Made of two hydrogen atoms and one oxygen atom
• Each molecule is slightly polarized and separation of charge is called dipole
• Oxygen atom is slightly negative
• Hydrogen atom is slightly positive
• This charge separation allows the molecule to form hydrogen bonds with other molecules hence they have higher boiling and melting temperatures than other substances of similar size
• Importance of water molecules
• Water is an unusual and excellent solvent
• Can dissolve polar substances such as ionic salts or glucose (due to formation of hydrogen bonds) which normally don’t dissolve in non-polar solutions
• Can carry non-polar substances which may form colloids
• For example triglycerides:
• Triglycerides are insoluble in water
• Are transported as lipoproteins 
• Formed into vesicles

• Hence water is a suitable solvent because insoluble molecules can be transported throughout the body and can be turned into soluble substances used by the cells, the soluble substance can also be converted into insoluble substance to act as the components of a cell 
• For example:
• Fats are insoluble in water hence are transported as emulsions in blood plasma
• Upon utilization, fats can be broken down to soluble forms which could be transported throughout the body to target places where they can be converted to insoluble form
• Water has one of the highest known surface tensions
• Hence places a great importance in the transportation system in plants e.g. during photosynthesis where water can be drawn up from the roots to the leaves 
• Water molecules is amphoteric
• It can react with both acids and bases 
• Hence, can act as a buffer, helping to prevent reactions in progress from changing the pH inside the cell
• Why water molecules are effective in transportation?
• Water is a solvent
• Water is slightly charged
• Polar molecules can dissolve in water
• Water is viscous
• Water as a liquid assists mass flow
• Presence cohesion between water molecules

2. Know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
3. Be able to relate the structures of monosaccharides, disaccharides and polysaccharides to their roles in providing and storing energy 
4. Know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions

• Difference between mono-, di- and poly-saccharides

• Example of monosaccharides
• Alpha glucose and Fructose

• Example of disaccharides

• Examples of Polysaccharides
• Made of many monosaccharide units joined by glycosidic bonds as a result of many condensation reactions 
• Molecules with 3-10 monosaccharides are known as oligosaccharides 
• Molecules with 11 or more are called polysaccharides 
• Act as storage molecules because it is compact and insoluble 
• Examples include: starch and glycogen
• Difference between lactose and starch

• Difference between amylose, amylopectin and glycogen

• Starch vs Glycogen

• Why some molecules are good storage mediums

• Condensation
• 2 monosaccharides can join together to form a disaccharide and several monosaccharides can join together to form an oligosaccharide or polysaccharide through condensation reaction by making glycosidic bonds
• For example: glucose + glucose —> maltose
• During the reaction H2O is given off and a glycosidic bond (-O-) is formed

• Hydrolysis
• The glycosidic bond between disaccharides or polysaccharides can be split by hydrolysis of the molecule to produce monosaccharides or shorter chain molecules 
• For example: Sucrose —> Glucose + Fructose

5. Know how a triglyceride is synthesised by the formation of ester bonds during condensation reactions between glycerol and three fatty acids 
6. Know the differences between saturated and unsaturated lipids

• Formation of triglyceride
• Glycerol can combine with three fatty acids through the formation of ester bond to form triglyceride
• Carboxyl group (-COOH) of the fatty acids react with hydroxyl group (-OH) of the glycerol molecules forming an ester bond (-COO-) and releasing a molecule of water 
• This reaction happens thrice and is called esterification

• Difference between saturated and unsaturated lipids 

7. Understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms) 

8. Understand how the structures of blood vessels (capillaries, arteries and veins) relate to their functions

• Double circulation
• Systemic circulation carries oxygenated blood from the heart to the cells of the body where the oxygen is used, and carries the deoxygenated blood back to the heart. 
• Pulmonary circulation carries deoxygenated blood from the heart to the lungs to be oxygenated, and carries the oxygenated blood back to the heart
• Why animals need a heart and circulatory system
• Animals have small surface area to volume ratio and have a high metabolic rate —> diffusion alone is not sufficient 
• Heart needed to pump blood around the body for mass flow 
• To transport of heat and glucose molecules around the body quicker to meet demands
• Components of blood

• Main functions of blood
• Transportation of nutrients
• Transportation of excretory products
• Transportation of hormones
• Maintain body temperature
• Acts as buffer
• Structure and function of capillaries, arteries and veins

9. Know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function

• Structure of the heart

• Cardiac Cycle

• Blood flow

• Why heart is divided into left and right side?
• It keeps oxygenated and deoxygenated blood separate —> keeps concentration gradient steep —> sufficient oxygen being carried to the tissues 
• There is also a need for different pressure in each side —> left side pumps to body; right side pumps to lungs
• Role of heart valves in the cardiac cycle

10. Understand the role of haemoglobin in the transport of oxygen and carbon dioxide 
11. Understand the oxygen dissociation curve of haemoglobin, the Bohr effect and the significance of the oxygen affinity of fetal haemoglobin compared with adult haemoglobin

• Role of haemoglobin in the transport of oxygen and carbon dioxide
• Oxygen
• Each haemoglobin molecules can pick up four molecules of oxygen
• The concentration of oxygen in the blood is low compared to the lungs hence oxygen diffuses into blood 
• The concentration gradient is maintained by the haemoglobin
• The haemoglobin molecule binds to the oxygen molecule hence the concentration of oxygen within the red blood cell cytoplasm would not be altered and is maintained at low concentrations
• So oxygen in the air can easily diffuse into the red blood cell cytoplasm down the concentration gradient
• Carbon-dioxide
• 10-20% of the carbon dioxide respired combines with carbaminohaemoglobin
• Others are transported in the cytoplasm of red blood cells as hydrogencarbonate ions

• Carbon dioxide passes into the plasma and red blood cells by diffusion. It combines with water to form carbonic acid, catalyzed by the enzyme carbonic anhydrase 
• Carbonic acid dissociates to give hydrogen ions and hydrogencarbonate ions

• Oxygen dissociation curve
• A graph with oxyhemoglobin (% Saturation) against partial pressure of oxygen
• The position on the lower left is the situation in the respiring cells
• The amount of oxygen in the surrounding is low (low partial pressure of oxygen) hence the amount of oxygen bounded hemoglobin will also be low as most of the oxygen molecules have diffused out of the red blood cells
• The position on the upper right is the situation in the lungs
• The amount of oxygen in the surrounding is high (high partial pressure of oxygen) hence the amount of oxygen bounded hemoglobin will also be high as most of the oxygen molecules have diffused in to the red blood cells
• The steep part of the graph shows a small change in partial pressure of oxygen results in a drastic change in oxyhemoglobin
• Bohr’s Effect
• Describes how the oxygen dissociation curves relates to carbon dioxide.
• As carbon dioxide and/or acidity increases, the binding affinity of haemoglobin for O2 decreases resulting in the shift to the right 
• Carbon dioxide forms carbonic acid due to action of carbonic anhydrase in RBC. 
• The increase in H+ ions bind oxyhaemoglobin to form HHb which decreases affinity due to an allosteric conformational effect.
• This mechanism helps provide the areas which are most oxygen demanding because
• Cells with greater respiration produces more amount of CO2 —> reduces affinity of hemoglobin —> oxygen less likely to bind to hemoglobin and more likely to diffuse to the demanding cells for respiration
• Significance of oxygen affinity of fetal haemoglobin compared with adult haemoglobin

• Fetal hemoglobin has high affinity than adult hemoglobin —> ensures that oxygen is transferred to the fetal blood through the placenta from the maternal blood 
• Fetal cells have high respiring rate —> very low oxygen partial pressure —> oxygen is unloaded rapidly into fetal cells

12. Understand the course of events that leads to atherosclerosis (endothelial dysfunction, inflammatory response, plaque formation, raised blood pressure)

Link to the youtube video: https://youtu.be/aQ5iLMRfd9k

Click this for Part 2