3 - Exchange and Transport

What are the three main factors that affect the need for an exchange system?

Size, surface area to volume ratio (SA:V), and level of activity.

Why do smaller organisms have a lower demand for oxygen than larger organisms?

Smaller organisms have a larger SA:V ratio, allowing simple diffusion to suffice for gas exchange.

Describe three features of a good exchange surface.

Large surface area (folded walls), thin and permeable barriers (reducing diffusion distance), and good blood supply (maintaining concentration gradients).

How are human alveoli adapted to reduce diffusion distances?

Alveolus walls are one cell thick and in close contact with capillary walls, minimizing diffusion distance.

What is the role of surfactant in alveoli?

It reduces cohesive forces between water molecules to prevent alveoli collapse.

Describe the mechanism of inspiration.

Diaphragm contracts and flattens, external intercostal muscles contract to push ribcage up, increasing thoracic volume and decreasing pressure to draw air in.

Why do alveolar walls contain elastic fibers?

To stretch during inspiration and recoil during expiration, aiding in airflow.

What tissue type comprises alveolar walls?

Squamous epithelium.

What functions do ciliated epithelial tissue and goblet cells serve in the trachea?

Goblet cells produce mucus to trap particles, and cilia move mucus away from the lungs.

Why are C-shaped rings of cartilage present in the trachea and bronchi?

To prevent collapse during inspiration while allowing food to pass down the esophagus.

How is the nasal cavity adapted for exchange?

Large surface area, moist surfaces, hair-secreting mucus to trap dust and pathogens, warming air to body temperature.

What are the roles of smooth muscle and elastic tissue in the airways?

Smooth muscle constricts airways involuntarily and elastic tissue helps return airways to their original shape.

What precautions should be taken when using a spirometer?

Ensure subject has no asthma, no air leaks in apparatus, sterilize mouthpiece, and use fresh soda lime.

What is 'vital capacity' and its dependents?

The maximum volume of air moved by the lungs; depends on person’s size, age/gender, and exercise levels.

What is the usual range for vital capacity?

2.5 - 5.0 dm³.

What is 'inspiratory reserve volume'?

The maximum volume of extra air that can be inhaled beyond tidal volume.

What is 'expiratory reserve volume'?

The maximum volume of extra air that can be exhaled beyond tidal volume.

What is 'residual volume' and its standard volume?

The air remaining in the lungs after forced expiration, typically 1.5 dm³.

What is 'tidal volume' and a typical value?

The normal volume of air breathed in and out at rest, around 0.5 dm³.

What is the difference between 'ventilation rate' and 'breathing rate'?

Breathing rate (BR) is the number of breaths per minute, while ventilation rate (VR) is the total volume of air inhaled per minute.

What is the equation for ventilation rate?

Ventilation Rate = Tidal Volume x Breathing Rate.

Calculate the tidal volume during strenuous exercise given a ventilation rate of 45000 cm³/min and a breathing rate of 30 breaths/min.

Tidal volume = 1500 cm³, which is 1 dm³ higher than normal.

What is the operculum and its function in bony fish?

The bony flap covering the gills, protecting them and ensuring constant water flow.

Describe the structure of gills in bony fish.

Two rows of gill filaments with primary lamellae attached to a bony arch and secondary lamellae for large surface area.

Explain the ventilation process in bony fish.

Volume changes in the buccal cavity draw water in, then water is pushed through the gills.

What is the tracheal system in insects?

A network of tubes used for air supply to respiring tissues.

How does air enter the tracheal system in an insect?

Through spiracles (small openings on the body).

What is the function of tracheal fluid in insects?

Facilitates gaseous exchange with air in tracheoles.

What changes occur in an active insect to increase oxygen supply?

Tracheal fluid is withdrawn to increase the exposed surface area of tracheole walls.

Describe three features of an effective transport system.

A fluid to carry substances (blood), a pump to create pressure (heart), and exchange surfaces (capillaries).

What are three disadvantages of single circulatory systems in fish?

Blood pressure drops at gill capillaries, slow blood flow, limited oxygen/nutrient delivery.

Why do fish not need as much energy as mammals?

They are less metabolically active and do not regulate body temperature.

What is meant by open circulation?

Blood circulates freely in body cavities rather than confined to vessels.

List two disadvantages of open circulatory systems.

Low blood pressure and slow flow; circulation affected by body movements.

What are four advantages of closed circulation over open circulation?

Higher pressure and faster flow; quicker supply of oxygen/nutrients and removal of wastes.

What is the inner tissue lining of a blood vessel called?

Endothelium, which reduces friction.

Describe the three structural layers of an artery.

Tunica intima (elastic tissue), tunica media (smooth muscle), and tunica adventitia (collagen and elastic tissue).

What is the role of arterioles?

To take blood from arteries to capillaries and regulate blood flow.

How are capillaries adapted for exchange?

Narrow lumen, walls of single endothelial cell layer, and high permeability.

What is the function of a venule?

To transport blood from capillaries to veins.

How are veins adapted to return blood to the heart?

Wide lumen, thin walls, and valves to prevent backflow.

Where is the hydrostatic pressure of blood created?

In the ventricles of the heart.

What is oncotic pressure?

The pressure created by solutes in the blood plasma.

What substances affect the oncotic pressure of blood?

Dissolved solutes, such as mineral ions, sugars, and proteins.

What cell types are found in blood plasma, tissue fluid, and lymph?

Blood plasma has red blood cells, neutrophils, lymphocytes; tissue fluid has neutrophils; lymph has lymphocytes.

Why can plasma proteins not leave the blood plasma?

They are too large to pass through capillary walls.

Why can neutrophils enter tissue fluid while erythrocytes cannot?

Neutrophils can change shape to pass between cells, unlike rigid erythrocytes.

Describe the role of lymph fluid.

It returns excess tissue fluid to the blood system.

How does tissue fluid facilitate exchange with body cells?

It surrounds body cells, allowing substances to exchange across plasma membranes.

Describe the structure of hemoglobin.

Four subunits, each with a polypeptide chain and a haem group containing an Fe2+ ion.

What is dissociation in the context of hemoglobin?

The release of oxygen from oxyhemoglobin to respiring cells.

What is the main difference between fetal and adult hemoglobin?

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin.

List three ways carbon dioxide is transported.

5% dissolved in plasma, 10% as carbaminohemoglobin, 85% as bicarbonate ions.

Describe how bicarbonate ions are formed from carbon dioxide.

CO2 combines with water to form carbonic acid, which dissociates into bicarbonate and protons.

How is charge maintained in RBCs when bicarbonate ions move out?

Chloride ions move into RBCs (chloride shift) to maintain charge.

How are hydrogen ions buffered in RBCs?

By combining with hemoglobin to form haemoglobinic acid.

What is the net result of the Bohr effect?

Increased oxygen release in areas of high carbon dioxide production.

How do increased hydrogen ion levels affect hemoglobin?

Lower pH decreases hemoglobin's affinity for oxygen due to structural changes.

What do semilunar valves do?

Prevent backflow of blood from arteries to ventricles.

Why is the left ventricular wall thicker than the right?

It must generate higher pressure to pump blood throughout the systemic circulation.

What is the purpose of mitochondria in cardiac muscle?

To supply energy for muscle contraction.

What is the function of intercalated discs in cardiac muscle?

To ensure synchronized contraction between muscle cells.

Briefly outline the events of atrial systole.

Atria contract, pushing blood through the AV valves into ventricles.

Briefly outline the events of ventricular systole.

Ventricles contract, raising pressure above arteries to open semilunar valves.

Briefly outline the events of diastole.

Heart muscle relaxes, allowing blood to fill the atria and ventricles.

What does myogenic mean?

Cardiac muscle can initiate its own contractions without neural stimuli.

What tissue initiates the heartbeat?

Sinoatrial node (SAN).

What tissue propagates the electrical signals to the ventricles?

Atrioventricular node (AVN).

Why is there a delay before the AVN depolarizes?

To allow the atria to finish contracting completely.

Describe the role of Purkyne tissue.

Conveys the wave of excitation from the AVN to the ventricles.

What do PQRST represent in an ECG?

P = atrial contraction, QRS = ventricular contraction, T = diastole.

What terms represent a slow and fast heart rate?

Bradycardia for slow; tachycardia for fast.

What occurs during atrial fibrillation?

Frequent atrial beats resulting in no distinct P wave on ECG.

What is an ectopic heartbeat?

An early ventricular heartbeat.

What two types of vascular tissue are present in plant transport systems?

Xylem (water and nutrients upward) and phloem (assimilates both ways).

What tissue is found between xylem and phloem?

Meristematic tissue, which is a source of stem cells.

What is the purpose of parenchyma cells in xylem tissue?

To support and separate xylem vessels.

What is the role of lignin in xylem vessels?

To strengthen the vessel wall and prevent collapse.

What are bordered pits in xylem vessels?

Gaps that allow water to move between adjacent vessels.

List three adaptations of xylem vessels that relate structure to function.

Dead cells forming continuous columns, narrow tubes for effective capillarity, bordered pits for water movement.

What components of phloem are involved in transport?

Sieve-tube elements and companion cells.

Why do sieve tube elements lack a nucleus?

To provide space for mass flow of sap.

How are companion cells adapted for active loading?

They have many mitochondria to supply ATP.

Describe the two major pathways for water movement between cells.

Apoplast pathway (through cell wall spaces) and symplast pathway (through cytoplasm).

What allows water to move via the symplast pathway?

Differently water potentials and osmotic movement.

Why does starch presence in the endodermis suggest active processes?

It indicates energy storage for active transport.

What is the Casparian strip?

A waterproof band in endodermis cells forcing water through cell membranes.

Explain the significance of the Casparian strip.

Filters water and solutes before entering the vascular system, ensuring selective absorption.

How is water lost via stomata?

Water vapor diffuses down its concentration gradient from high inside the leaf to lower outside.

How do light intensity, humidity, and wind speed affect transpiration?

Increased light increases transpiration; higher humidity decreases it; more wind increases it.

What precautions should be taken to avoid air bubbles in a potometer?

Set up underwater and cut the stem underwater.

Calculate rate of transpiration given a 45 mm movement in 5 minutes.

Rate of transpiration is 7.1 mm³/min.

How does water move up the stem due to transpiration pull?

Evaporation creates tension, pulling water upwards through cohesive forces.

What property of water causes cohesion?

Polarity resulting in hydrogen bonding.

Define translocation.

Transport of assimilates from source to sink.

Name two sinks in a plant.

Roots and actively dividing tissues.

What is the difference between active loading and active transport?

Active loading involves active transport along with other mechanisms to move solutes.

Describe the role of hydrogen ions in active loading.

Pump out of companion cells creates a gradient that allows cotransport of sucrose with hydrogen ions.

Why is sucrose transported in phloem and not glucose?

Sucrose is more stable and less likely to be metabolized during transport.

How does sucrose move from companion cells into sieve tube elements?

Sucrose concentration increases, causing water influx and creating turgor pressure that pushes sap.