REVISION PACK Edexcel IAL Biology - Topic 1; Molecules, Transport and Health
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Course
Topic 1 | Molecules, Transport and Health (XBI11)
Institution
PEARSON (PEARSON)
Revision pack - perfect for exam practice!
Includes everything you need to be exam ready:
- ALL EXAM QUESTIONS concerning topic 1 from June 2018 to June 2021
- Znotes in the first few pages as a quick reference
- Answers at the end
How to use:
1. Read the Znotes
2. “Blurt” what y...
Topic 1 | Molecules, Transport and Health
Revision Pack
Specification Points 1.1 - 1.20
, EDEXCEL IAS-LEVEL BIOLOGY//WBI11 EDEXCEL IAS-LEVEL BIOLOGY//WBI11
o Sweet
1. MOLECULES, TRANSPORT AND HEALTH o Soluble in water • Role of triglyceride:
o They have an osmotic effect o Better energy reserves than carbohydrates as more CH
1.1.1 The Chemistry of Life o Crystalline in nature bonds
• Water is liquid at normal temperatures, while other • Examples of Monosaccharides: o Acts as an insulator and provides buoyancy
small molecules, like CO2 and O2, are gas. o α-glucose o A metabolic source of water as gives CO2 and H2O on
• Features of water and its significance to life: o Fructose These components are made from α-glucose molecules oxidation in respiration
o Hydrogen bonding: A water molecule contains two o Galactose and contain glycosidic bonds. Starch is highly compact
hydrogen atoms and one oxygen atom held together • Disaccharides form when two monosaccharides join in a and stores energy.
by hydrogen bonds. condensation reaction, releasing a water molecule. AMYLOSE AMYLOPECTIN
1.1.5 Proteins
o Solvent: Water is an effective solvent because of it’s • Properties of Disaccharides are similar to Proteins are made of amino acids which only differ in the
STRUCTURE 1,4 glycosidic 1,4 and α 1,6
polarity and so can form electrostatic interactions with Monosaccharides. R- groups/ variable side
bonds glycosidic
other polar molecules and ions. Thus it is a transport • The bond formed between the two monosaccharides is chains and will always
bonds, giving
medium and reagent for metabolic and other reactions called a glycosidic bond. contain an amine group
it’s branched
in plant and animal cells. DISACCHARIDE FORMING UNITS (basic), carboxyl group
structure
o High surface tension and cohesion: Cohesion refers to (acidic) and a hydrogen atom
Maltose α-glucose + α-glucose SHAPE Helical and more Branched
the attraction of one water molecule to each other. attached to the central carbon atom.
Sucrose α-glucose + Fructose compact
Water molecules have strong, cohesive forces due to • A peptide bond is formed by condensation between 2
Lactose α-glucose + Galactose • Glycogen: is a Polysaccharide that is used for the storage
hydrogen bonds, thus having high surface tension. of energy is animal cells and is also made from α glucose amino acids, forming a dipeptide. Many amino acids that
o High specific heat capacity: The amount of heat join together by peptide bonds form a polypeptide.
• Maltose: molecules. The structure of glycogen is very similar to
energy required to raise the temperature of 1 kg of that of amylopectin. However, it is much more
o Broken down by Maltase enzyme
water by 1 °C. Water has high SPC due to its hydrogen branched, allowing it to be hydrolysed rapidly.
o Contains 1,4 glycosidic bond
bonds. The temperature within organisms remains
• Sucrose:
constant compared to external temperature, and water
o Broken down by Sucrase enzyme 1.1.4 Lipids
bodies also have a slow change in temperature, • Triglyceride: forms by the condensation of 3 fatty acid
o Contains 1,2 glycosidic bond
providing stable aquatic habitats. chains and one glycerol molecule, forming ester bonds.
• Lactose:
o High latent heat of vaporisation: A measure of the Fatty acid chains are long hydrocarbon chains with a
o Broken down by Lactase enzyme
heat energy needed to vaporise a liquid. Water has a carboxylic head. Glycerol is an alcohol-containing 3 OH
o Contains 1,4 glycosidic bond
high LHV due to its high SPC as H bonds need to be groups.
• Disaccharides can also be broken down in a hydrolysis
broken before water can be vapourised, cooling the UNSATURATED SATURATED FATTY
reaction using a water molecule.
surrounding environment. Sweating is a good cooling FATTY ACID ACID • Peptide bonds are broken when hydrolysed into amino
mechanism. 1.1.3 Polysaccharides BOND At least 1 C=C No C=C double bond acids.
o Density and freezing properties: Ice is less dense than double bond • Structure of Proteins:
• Polysaccharides are made up of monomers joined
water and floats on it, insulating water and preventing STRUCTURE Contains bent Straight chain o Primary Structure: The sequence of amino acids held
together by glycosidic bonds.
it from freezing, preserving aquatic life underneath it. chains (kinks)
• Properties of Polysaccharides: Lower H:C ratio Higher H:C ratio
together by polypeptide bonds in a polypeptide chain.
Changes in the density of water with temperature H:C RATIO
o They are macromolecules with a large molecular mass
causes currents, which helps to maintain the
o Formed from a large number of monomers
circulation of nutrients in the oceans. • Kinks present in unsaturated fatty acids cause its melting
o Contains Glycosidic bonds between monomers
point to decrease due to weaker intermolecular bonds.
o No sweet taste
1.1.2 Monosaccharides and Disaccharides
o No Osmotic effect/insoluble in water
• Monosaccharides are made up of Carbon, Hydrogen,
• Starch: is a polysaccharide that is found in plant cells and
and Oxygen.
is made up of two components, amylose and
• They have the general formula Cn(H2O)n where n
amylopectin.
represents the number of carbon atoms. o Secondary Structure: the structure of a protein
• Due to their structure, they are able to be broken down molecule resulting from the regular coiling or folding of
quickly by living organisms to produce ATP energy. the chain of amino acids.
• Properties of Monosaccharides:
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, EDEXCEL IAS-LEVEL BIOLOGY//WBI11 EDEXCEL IAS-LEVEL BIOLOGY//WBI11
▪ α- helix: the polypeptide chain twists into a regular • Haemoglobin: a globular protein that has a quaternary pressure to prevent damage to the capillaries in the ▪ CO2 in plasma diffuses from the blood into the alveoli,
spiral and is maintained by hydrogen bonds between structure with 4 polypeptide chains, 2 α-globin and 2 β- alveoli, while the rest of the body requires a high blood and oxygen diffuses into the blood from the alveoli.
the (-NH) group of one amino acid and the (CO-) globin chains, each connected by disulfide bridges. Each pressure to provide blood to all tissues ▪ Carbaminohaemoglobin dissociates to form CO2 and
group. chain has one prosthetic haem group containing an iron o Maximise the rate of diffusion by sending Hb
▪ β- pleated sheet: the chain is not tightly coiled and atom that reversibly binds to an oxygen molecule. deoxygenated blood to the lungs and sending ▪ Hb then picks up O2, and HHb (haemoglobinic acid)
lies in a looser, straighter shape. Oxyhaemoglobin is bright red when the haem group is oxygenated blood to the rest of the body. This creates dissociates to form H+ and Hb.
combined with oxygen. Otherwise, it is purplish. a steep concentration gradient which increases the ▪ The H+ ions combine with HCO3- to form carbonic
Haemoglobin is an example of a conjugated protein. rate of diffusion acid, which dissociates to form CO2 and water
(catalysed by carbonic anhydrase).
1.2.2 The Roles of the Blood ▪ CO2 diffuses into alveoli.
• Blood is composed of 4 components: • The presence of a high pCO2 causes Hb to release
o Plasma: This is the liquid part of the blood. It is a dilute oxygen. This is called the Bohr Effect. High pCO2 are
solution of salts, glucose, amino acids, vitamins, urea, found in actively respiring tissues that need oxygen. This
protein, and fats. causes Hb to release oxygen even more readily than it
o Leukocytes (white blood cells): Involved in the would otherwise.
o Tertiary Structure: the precise folding and coiling of immune system.
alpha-helices and beta-pleated sheets of an amino acid o Platelets: Involved in blood clotting.
chain. They are held together by: 1.2.1 The Principles of Circulation o Erythrocytes (red blood cells): Involved in carrying
▪ Hydrogen bonds between a wide variety of R- groups • In small organisms, diffusion is sufficient for gaining oxygen and carbon dioxide.
▪ Disulfide bridges between two cysteine molecules nutrients and excreting waste due to: • Adaptations of red blood cells to carry out its function:
▪ Ionic bonds between R groups containing amine and o The short distance of diffusion between the deepest o Biconcave, allowing for a greater surface area to
carboxyl groups. part of the organism and the outside volume ratio to carry oxygen
▪ Hydrophobic interactions between non-polar R o The high SA:V ratio allowing for fast diffusion o No nucleus nor mitochondrion, allowing more space
groups. o Usually, small organisms have a low metabolism. for haemoglobin
Therefore, they don’t use much oxygen and food o Small diameter to allow it to squeeze through
• Larger organisms are unable to rely solely on diffusion • Fetal Haemoglobin: It is present in the blood of a
capillaries
due to their low SA:V ratio. Thus, to overcome their developing fetus. It has a higher affinity to oxygen
• Haemoglobin (Hb): is a red oxygen-carrying pigment compared to adult haemoglobin. Allowing it to “absorb”
limitations: found in RBCs and is a globular protein. It is made of 4 oxygen from the mother’s blood, ensuring proper
o They have a transport system that carries substances polypeptide chains each containing an iron ion. growth.
by mass flow from one part of the body to another. o In respiring tissues: The pCO2 is high, and the pO2 is
o They increase the surface area of parts of the body • The blood clotting mechanism:
low. o Upon injury, the platelets break
involved in an exchange with the environment, e.g. ▪ CO2 from the cells diffuses into the plasma. o This releases several chemicals that aid in the blood
Alveoli. ▪ CO2 combines with Hb to form clotting process, causing a cascade of reactions
• Features of Mass transport include: carbaminohaemoglobin. (10% carried this way) o Serotonin: is a chemical that causes smooth muscles
o A medium of transport, e.g. blood ▪ Most CO2 combines with water (catalysed by carbonic
o Quaternary Structure: the three-dimensional to contract, narrowing blood vessels
o A system of vessels anhydrase) to form carbonic acid, which then
arrangement of two or more polypeptides, or a o Thromboplastin: is a globular protein that catalyses
o A pump dissociates into H+ and HCO3- ions.
polypeptide and a non-protein component such as the reaction of prothrombin to thrombin in the
o A way to ensure substances moved in the right
haem, in a protein molecule. The polypeptide chains presence of Ca2+ ions
direction
o Prothrombin and thrombin are both soluble globular
are held together by bonds in the tertiary structure. • The mammalian circulatory system is a closed double
• Globular proteins: curl up into a spherical shape with proteins in the blood. Prothrombin is present in the
circulation. This is because blood passes through the
their hydrophobic regions pointing into the centre of the plasma
heart twice in one circulation of the body (pulmonary
molecule and hydrophilic regions pointing outwards. o Thrombin catalyses the reaction of Fibrinogen to Fibrin
circuit and systemic circuit), contained inside blood
They are soluble in water, e.g. enzymes and ▪ H+ ions combine with Hb to form Haemoglobinic acid o Fibrinogen is a soluble globular protein, while Fibrin is
vessels.
(HHb). an insoluble protein.
haemoglobin. • Advantages of a double circulatory system:
o In the lungs: pO2 high and pCO2 low. o Fibrin forms a mesh-like structure that traps red blood
• Fibrous proteins: form long strands, are insoluble in o Maintaining different pressures to the lungs and the
cells allowing the clot to dry up and form a scab
water and have structural roles, e.g. collagen, hair, nails. rest of the body. The lungs require a low blood
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, EDEXCEL IAS-LEVEL BIOLOGY//WBI11 EDEXCEL IAS-LEVEL BIOLOGY//WBI11
• Benefits of blood clotting include: more pressure. o Endothelium lining is damaged due to several reasons
o Preventing excess blood loss VESSEL ADAPTATIONS like high blood pressure and smoking
o Preventing the entry of pathogens • Tough collagen fibre wall prevents it from o The damage to the endothelium lining causes an
bursting inflammatory response
1.2.3 Circulation in the Blood vessels • Elastic fibres allow it to stretch and recoil, o This causes a buildup of cholesterol and calcium salt,
• Arteries and veins contain three layers of tissues known maintaining blood pressure forming plaque after hardening
as the tunica intima, tunica media, and tunica adventitia. ARTERY • Smooth endothelium lining reducing o Plaque causes the narrowing of the lumen, which
o Tunica intima: endothelium, smooth lining allowing resistance
restricts blood flow. Causing an increase in blood
• Small lumen aids to maintain high pressure
the easiest possible blood flow pressure
• Smooth muscles constrict and dilate to keep
o Tunica media: containing mainly smooth muscle and o Reduced blood flow causes decreased oxygen supply
the blood at a high pressure
elastic fibres with some collagen to tissues, resulting in anaerobic respiration
• Large lumens to carry more blood
o Tunica adventitia: containing mostly collagen, with • Thins walls allowing skeletal muscles to • Examples of Cardiovascular diseases:
some elastic fibres. VEIN
compress and pump blood towards the heart o Hypertension: A rise in blood pressure caused by the
• Arteries: These blood vessels transport oxygenated • Valves to prevent backflow of blood • The cardiac cycle is divided into 3 stages: formation of plaque in arteries
blood swiftly to the tissues at high pressures. They have CAPILLARIES • Narrow allowing it to reach tight places o Atrial Systole: This occurs when muscles in the atria o Coronary thrombosis: Platelets could stick to a
thick walls to withstand this high pressure. The • Forms a dense network increasing the surface contract and blood passes on to the ventricles. 70% of damaged artery wall, causing it to release
exception to this is the pulmonary artery, carrying area the blood flows passively down to the ventricles. The Thromboplastin, which starts a cascade of reaction,
deoxygenated blood to the lungs. As arteries reach • Pores allowing substances to move in and out bicuspid and tricuspid valves open while the semilunar forming a blood clot.
tissues, they branch into smaller vessels called arterioles. of tissue fluid valves are closed.
• Thin wall making it permeable to small o Ventricular systole: After Atrial Systole, the ventricles 1.3.1 Risk, Correlation, and Cause
• Veins: Many capillaries join to form venules, which then
substances
join to form veins. These blood vessels carry contract increasing the blood pressure and pushing it • Epidemiology: The study of disease patterns to find a
deoxygenated blood back to the heart. The exception is out of the heart. The blood passes through the Aorta correlation between a disease and certain risk factors.
1.2.4 The Mammalian Heart
the pulmonary vein, carrying oxygenated blood from the and pulmonary arteries. The semilunar valves open and • Risk: The probability of damage occurring
• External structure : Blood vessels that leave the heart
lungs to the heart. the bicuspid and tricuspid valves are closed. • Actual risk: Factors increasing the probability of getting a
are the Aorta and pulmonary artery. Blood vessels that
o Tunica media is thinner in veins when compared to o Diastole: All muscles of the heart relax, and the disease.
enter the heart are the superior vena cava, the inferior
arteries, as the blood in veins is at a lower pressure. pressure inside ventricles becomes lower than the • Perceived risk:
vena cava, and the pulmonary vein. The septum
o Valves are also present to prevent the backflow of atria. When this happens, most of the blood starts to o Overestimating the risk of something happening due
separates the left and right sides of the heart.
blood. flow from the atria to the ventricles even though the to the unfamiliarity of the risk
• Internal structure: The human heart has four chambers:
o To keep blood flowing upwards from legs, veins are atria is not contracting. However, the atria contracts o Underestimating the risk of something happening due
• Atria: 2 upper chambers are known as atria. They are
usually near muscles, so the pressure is increased towards the end to push out the last bit of blood into to it being in the far-future
thin-walled and receive blood at low pressure.
when muscles contract. the ventricles, and the cycle begins all over again. • Multifactorial diseases: A disease caused by interactions
• Ventricles: 2 lower chambers are known as ventricles.
o Veins also have a much larger lumen than arteries. of multiple factors.
They are thick-walled, receive blood from atria, and
• Capillaries: Arterioles continue to branch into capillaries. pump it out through arteries. • Causation: When a change in 1 variable is responsible
These are the smallest blood vessels and they take the o The left ventricle has a thicker muscular wall, as it has for a change in another variable.
blood as close as possible to the cells. This allows for to pump blood into the systemic circuit, which has a • Correlation: When a change in 1 variable is reflected by
rapid transfer of substances between cells and the a change in another variable.
higher resistance to blood flow than the pulmonary
blood. Due to the very small diameter of these blood
circuit. The systemic circuit is also longer and requires
vessels, blood travels very slowly. This increases the
opportunity for diffusion to occur.
o Walls of capillaries are made of a single layer of
endothelial cells with pores between individual cells
present to allow some components of blood to pass
through into the cells and tissues of the body. 1.2.5 Atherosclerosis
• Tissue fluid: It has almost the same components as • Atherosclerosis: it is a disease in which artery walls are
plasma but lacks large plasma proteins that are too large caused to harden. It could eventually lead to coronary
to diffuse through pores in capillaries. Osmotic pressure heart disease (CHD).
causes tissue fluid to move into and out of capillaries • Atherosclerosis is caused by a series of events:
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