Biology - Chapter 7: Mass Transport

Describe the structure of haemoglobin. (2)

• Quaternary Structure protein

• 4 iron ions

Describe the role of haemoglobin in loading, transporting and unloading oxygen. (5)

• Haemoglobin binds to oxygen

• At high partial pressures of oxygen

• Binding to one oxygen makes binding to other oxygens easier

• Oxygen transported as oxyhaemoglobin

• Haemoglobin unloads oxygen at the respiring tissues

• At low partial pressure of oxygen

Describe properties of iron that allows it to perform its role in red blood cells. (3)

• It is charged or polar

• Forms part of haemoglobin

• Binds to oxygen

Describe and explain the Bohr shift.(3)

• Increased carbon dioxide concentration lowers blood pH

• So greater dissociation of oxygen

• For aerobic respiration in tissues

Explain why blood pH decreases in active tissues. (3)

• Aerobic respiration produces carbon dioxide

• Carbon dioxide dissolves in blood forming carbonic acid

• Acid dissociates forming more hydrogen ions

Explain the advantage of different shaped oxygen dissociation curves. (4)

• Right-shifted curves for reduced affinity

• More unloading into respiring tissues for high metabolism

• Left-shifted curves for greater affinity

• More loading of oxygen in low-oxygen environments

Explain why affinity of haemoglobin increases when a molecule of oxygen binds to it. (2)

• Binding of oxygen causes shape change

• Causing another binding site to be exposed

Define partial pressure. (1)

• Concentration of a gas

Describe the path of blood through the heart. (6)

• From vena cava into right atrium

• Through atrioventricular valves into right ventricle

• Through semi lunar valves into pulmonary artery

• From pulmonary vein into left atrium

• Through atrioventricular valves into left ventricle

• Through semi lunar valves into aorta

Name the blood vessels that bring blood to and from the kidneys. (1)

• Renal artery and renal vein

Explain why atrioventricular valves open and close. (2)

• Atrioventricular valves open when atrial pressure is greater than ventricular pressure

• Atrioventricular valves close when ventricular pressure is greater than atrial pressure

Explain how the features of an aorta are related to its function. (4)

• Smooth muscle absorbs high pressure

• Elastic tissue stretches and recoils to maintain blood pressure

• Endothelium reduces friction

• Protein coat prevents artery wall splitting

Explain how the structure of a vein is related to its function. (2)

• Thinner wall since lower blood pressure

• Valves to prevent backflow

Explain how blood in a vein is returned to the heart. (6)

• Muscles around vein contract and press on vein and squeeze blood through

• Valves to backflow

• Heart systole pushes blood through veins • During diastole recoil of heart

• Draws blood from veins into atria

• Wide lumen and low friction

Explain how the structure of a capillary is adapted for exchange of substances. (4)

• Permeable capillary lining

• Single cell thick so short diffusion distance

• Flattened endothelial cells so short diffusion distance

• Narrow lumen so large surface area to volume ratio

• Narrow lumen so decreased flow rate and more time for diffusion

Explain how tissue fluid forms. (2)

• High hydrostatic pressure at arterial end

• Forces water and ions out of capillaries

Explain how water from tissue fluid is reabsorbed. (4)

• Proteins remain in the blood

• Creating a water potential gradient

• Water moves into blood by osmosis

• Or drains into the lymphatic system

Explain how an arteriole can reduce blood flow into capillaries. (2)

• Smooth muscle contracts

• Constricts arteriole

Explain how the structure of xylem is suitable to its function. (3)

• Forms hollow tubes with no end walls so allows continuous column of water

• No cell organelles or cytoplasm so no obstruction of water flow

• Cell walls made of lignin so withstands tension in the column

• Cell walls made of lignin so withstands tension in the column caused by transpiration and adhesion

Explain how water moves up xylem vessels by the cohesion-tension theory. (4)

• Transpiration

• Decreased water potential creates tension at the top of the xylem

• Hydrogen bonds cause cohesion between water molecules

• Maintains continuous water column

• Adhesion between water molecules and xylem walls by hydrogen bonds

Explain how sucrose is transported by mass flow. (6)

• Sucrose is actively transported into phloem sieve element

• By a companion cell

• Lowering water potential of the phloem sieve element

• Water moves into the sieve element by osmosis

• Increasing hydrostatic pressure

• Sucrose is metabolised at the sink cells

Explain how companion cells are adapted for the functions. (2)

• Lots of mitochondria to produce ATP for active transport

• Lots of carrier proteins to actively transport sucrose into phloem sieve elements