Edexcel International A Level Biology Topic 1: Molecules, Transport & Cardiovascular Health

Comprehensive revision flashcards covering key concepts from Topic 1: Molecules, Transport & Cardiovascular Health, including water properties, biological macromolecules, circulation, cardiac mechanics, gas exchange, blood clotting, CVD pathology, and experimental design.

Why is water a polar molecule?

Oxygen attracts the shared electrons more strongly than hydrogen, giving oxygen a partial negative charge and the hydrogens partial positive charges.

How does water's high specific heat capacity help organisms?

It buffers temperature changes and helps maintain stable conditions for enzyme-controlled reactions.

How does cohesion help water transport in xylem?

Cohesion helps maintain a continuous column of water as it is pulled up through the plant.

Why is water described as a metabolite?

It is used in reactions such as hydrolysis and photosynthesis and produced in reactions such as condensation and respiration.

What is the molecular formula of glucose?

$$\text{C}_6\text{H}_{12}\text{O}_6$$

What is the structural difference between alpha-glucose and beta-glucose?

They differ in the orientation of the hydroxyl group on carbon 1.

Which monosaccharides combine to form maltose, sucrose, and lactose?

Maltose is formed from two alpha-glucose molecules; sucrose is formed from glucose and fructose; lactose is formed from glucose and galactose.

How do amylose and amylopectin differ in structure?

Amylose is an unbranched chain of alpha-glucose with 1,4 glycosidic bonds that coils into a helix; amylopectin is branched with 1,4 glycosidic bonds and 1,6 glycosidic bonds at branch points.

Why is glycogen more highly branched than amylopectin?

It provides many ends where enzymes can act so it can be broken down rapidly to meet animals' energy demands.

How does cellulose provide strength to plant cell walls?

Alternate beta-glucose molecules are inverted to form straight chains with beta-1,4 glycosidic bonds; adjacent chains form hydrogen bonds to create microfibrils that resist stretching and prevent cells from bursting.

What is the difference between a condensation reaction and a hydrolysis reaction?

A condensation reaction joins two molecules together with the release of a molecule of water; a hydrolysis reaction breaks a chemical bond by the addition of water.

How do you test for a reducing sugar using Benedict's solution, and what indicates a positive result?

Add Benedict's solution to the sample and heat it in a hot water bath; the solution changes from blue through green/yellow/orange to a brick-red precipitate depending on concentration.

How do you test a sample for non-reducing sugars?

First test for reducing sugar; then boil a fresh sample with dilute hydrochloric acid, neutralise with sodium hydrogencarbonate, add Benedict's solution, and heat in a hot water bath.

What reagent tests for starch and what are the positive and negative results?

Iodine solution (usually iodine in potassium iodide); turns blue-black for a positive result and remains yellow-brown/orange-brown for a negative result.

How is a triglyceride formed?

Condensation reactions between one glycerol molecule and three fatty acids form three ester bonds and release three water molecules.

What is the difference between a saturated fatty acid and an unsaturated fatty acid?

A saturated fatty acid has no carbon-carbon double bonds in its hydrocarbon chain; an unsaturated fatty acid has one or more carbon-carbon double bonds.

What is the emulsion test for lipids?

Add ethanol to the sample and shake, then add water; a milky-white emulsion indicates the presence of lipid.

Why do large multicellular organisms require a mass transport system?

They have a low surface-area-to-volume ratio and long diffusion distances, making diffusion alone too slow to supply cells.

What is the advantage of a double circulatory system?

It allows blood to be pumped to the lungs at lower pressure to prevent damaging delicate capillaries and to the body at higher pressure to supply tissues efficiently.

How is an artery wall adapted to withstand and maintain high blood pressure?

It has thick muscular and elastic walls; elastic tissue stretches when blood is pumped and recoils to maintain pressure, while smooth muscle changes vessel diameter.

How are capillaries adapted for exchange between blood and tissues?

Their walls are one endothelial cell thick to provide a short diffusion distance, and they are numerous and highly branched to provide a large surface area.

How is tissue fluid formed at the arterial end of capillaries?

High hydrostatic pressure forces water and small dissolved substances out through gaps in the capillary wall, while red blood cells and large plasma proteins remain inside.

Why is the left ventricle wall thicker than the right ventricle wall?

It must generate higher pressure to pump blood through the long systemic circulation around the body.

What causes the 'lub' and 'dub' heart sounds?

The 'lub' sound is caused by the closure of the atrioventricular valves; the 'dub' sound is caused by the closure of the semilunar valves.

What is the function of the atrioventricular node (AVN)?

It delays the electrical impulse so that the atria finish contracting before the ventricles contract.

What do the P wave, QRS complex, and T wave represent on an ECG?

The P wave represents atrial depolarisation; the QRS complex represents ventricular depolarisation; the T wave represents ventricular repolarisation.

How is cardiac output calculated?

$$\text{Cardiac output} = \text{heart rate} \times \text{stroke volume}$$

Why is the oxygen dissociation curve of haemoglobin S-shaped?

The binding of the first oxygen molecule changes haemoglobin's shape and increases its affinity for subsequent oxygen molecules, a process known as cooperative binding.

What is the Bohr effect and how does it occur?

An increase in carbon dioxide reduces haemoglobin's affinity for oxygen, promoting oxygen release; carbon dioxide forms carbonic acid, lowering blood pH and decreasing oxygen affinity.

How is most carbon dioxide transported in the blood?

As hydrogencarbonate ions in plasma, formed after carbon dioxide and water react in red blood cells catalysed by carbonic anhydrase.

How does the oxygen dissociation curve of fetal haemoglobin compare with adult haemoglobin, and why is this advantageous?

The curve is shifted to the left because fetal haemoglobin has a higher affinity for oxygen, enabling it to take up oxygen from maternal blood across the placenta.

What is atherosclerosis?

The build-up of fatty material and other substances in artery walls, forming plaques (atheromas) that narrow the lumen and increase resistance to blood flow.

How does blood clotting occur following damage to a blood vessel?

Platelets adhere to the damaged area and become activated; prothrombin is converted into thrombin, which catalyses the conversion of soluble fibrinogen into insoluble fibrin to trap blood cells.

What is a confounding variable in cardiovascular disease research?

A factor associated with both the exposure and the outcome that can distort the apparent relationship between them.

What is a free radical and what role do antioxidants play?

A free radical is a highly reactive particle with an unpaired electron that can damage cellular components; antioxidants reduce oxidation by reacting with free radicals.

How is DCPIP used to measure vitamin C concentration in a sample?

Vitamin C reduces blue DCPIP to colourless; the volume of juice needed to decolourise a fixed volume and concentration of DCPIP is recorded and compared using a calibration curve.

What is the difference between disease incidence and disease prevalence?

Incidence is the number of new cases of a disease over a specified period; prevalence is the total number or proportion of individuals with the disease at a given time.

What is a double-blind trial and why is it used?

A trial where neither the participants nor the researchers assessing them know who receives which treatment; it prevents bias caused by expectations.

What is the difference between relative risk and absolute risk?

Absolute risk is the actual probability of an event occurring in a specified population over time; relative risk compares the probability of an outcome in an exposed group to an unexposed group.

How do LDL and HDL differ in their transport of cholesterol and their relation to CVD risk?

LDL transports cholesterol from the liver to tissues and is associated with plaque formation and increased CVD risk; HDL transports cholesterol from tissues back to the liver and is associated with lower CVD risk.

How is Body Mass Index (BMI) calculated?

$$\text{BMI} = \text{mass (kg)} \div [\text{height (m)}]^2$$

How do statins reduce the risk of cardiovascular disease?

They inhibit an enzyme involved in cholesterol synthesis in the liver, prompting the liver to remove more LDL cholesterol from the blood, which slows plaque development.

How do antiplatelet medicines differ from anticoagulants?

Antiplatelet medicines act mainly by preventing platelet aggregation and clumping, whereas anticoagulants interfere directly with the blood-clotting cascade.