B3.2 Transport - UWCSEA - IB Biology 2025 Topic

B3.2.1—What are the adaptations of capillaries

Capillaries are adapted for efficient material exchange:

Large surface area due to extensive branching and narrow diameters, which brings them close to almost every cell.

Thin walls consisting of a single layer of endothelial cells, reducing the diffusion distance.

Presence of fenestrations (small pores) in some capillaries, allowing rapid exchange where necessary.

B3.2.2— What are the features of arteries?

Arteries have thicker walls

with more muscle and elastic tissue

relative to their narrower lumen

to withstand high pressure

B3.2.2— What are the features of veins?

return blood to the heart;

have valves to avoid backflow;

have relatively thinner walls and a larger lumen (to reduce resistance to flow);

pressed by adjacent muscles to move blood;

do not support high pressure (as they carry blood to heart);

Three layers - tunica externa, media and intima

Variable size, but much larger than 10μm

B3.2.2 How can you distinguish between arteries and veins in micrographs based on the structure?

Thicker wall compared to lumen = artery

Thinner wall compared to lumen = vein

B3.2.3—What are the adaptations of arteries for transport?

carry blood leaving heart;

have relatively thicker walls to withstand high pressure; have muscles to contract to increase and maintain blood pressure;

have elastic fibres stretching and recoiling to maintain blood pressure; have relatively narrower lumen to maintain high blood pressure;

Three layers, tunica externa, media and intima.

Larger than 10μm

B3.2.4—How can measurement of pulse rates be achieved? How do different methods compare?

Traditional method: Feel the carotid (neck) or radial (wrist) pulse using fingertips and count the beats per minute.

Digital methods: Use electronic devices like heart rate monitors or smartwatches for automatic measurement.

Comparison: Digital methods offer continuous and more precise readings, while traditional methods are simple and require no equipment.

B3.2.5—What are the adaptations of veins for the return of blood to the heart?

Valves to prevent backflow of blood

Flexible walls that can be compressed by surrounding muscle action, aiding blood flow

Large lumen to reduce resistance to blood flow.

B3.2.6 — What are the causes and consequences of occlusion in the coronary arteries

Causes: Build-up of atherosclerotic plaques due to factors like high saturated fat intake, leading to narrowed arteries.

Consequences: Reduced blood flow can cause angina (chest pain), myocardial infarction, or heart attacks.

Epidemiological data: Used to find correlations between risk factors and incidence of coronary heart disease;

however, correlation does not imply causation.

How is epidemiological data used to evaluate the causes of CHD?

Data is used to find correlations between risk factors and incidence of coronary heart disease;

however, correlation does not imply causation.

there may be many confounding variables

B3.2.7—How is water transported from roots to leaves?

In the process of transpiration, water is lost from cell walls in leaf cells (spongy mesophyll)

creating a demand that draws water out of xylem vessels through the cell walls by capillary action

generating tension (negative pressure potential)

This tension pulls water upwards in the xylem, with cohesion maintaining a continuous column

allowing transport from roots to leaves.

B3.2.8—Adaptations of xylem vessels for transport of water

Xylem vessels are adapted for efficient water transport with lack of cell contents and incomplete or absent end walls

allowing unimpeded flow.

Their lignified walls provide strength to withstand the tension from water movement pits in the walls enable water entry and exit allowing distribution between cells and tissues.

B3.2.9—Distribution of tissues in a transverse section of the stem of a dicotyledonous plant

Vascular bundles contain xylem and phloem for support and transport in plants

Xylem, which is in the center, transports water

phloem on the outer edge distributes nutrients including sucrose and amino acids

Surrounding the bundles, the cortex provides support and storage,

the epidermis serves a protective function.

B3.2.10—Distribution of tissues in a transverse section of the root of a dicotyledonous plant

A root cross-section reveals central vascular bundles containing xylem and phloem

Here, xylem is a central cross shape that moves water upwards, while phloem distributes sucrose and amino acids

The cortex stores nutrients, and the epidermis protects and absorbs water from the soil

B3.2.11—How is tissue fluid released from and reabsorbed into capillaries?

Formation: High hydrostatic pressure at the arteriole end forces plasma out, forming tissue fluid.

Reabsorption: Lower pressure at the venule end allows tissue fluid to drain back into capillaries.

Balance: Ensures exchange of nutrients and waste between blood and tissues.

B3.2.12—Discuss the composition of plasma and tissue fluid and how substances are exchanged.

Plasma: Liquid component of blood, contains water, ions, nutrients, proteins.

Tissue fluid: Similar to plasma but lacks large proteins.

Exchange: Nutrients and oxygen diffuse from tissue fluid into cells; waste products diffuse from cells into tissue fluid.

B3.2.13—How is excess tissue fluid drained into lymph ducts, and what are the features of these ducts?

Lymph ducts collect excess tissue fluid (lymph) through gaps in their thin walls.

Valves prevent backflow, ensuring one-way movement toward the circulatory system.

Lymph is eventually returned to the blood circulation via the subclavian veins.

B3.2.14—What are the differences between the single circulation of bony fish and the double circulation of mammals?

Single circulation (fish):

Blood passes through the heart once per circuit; sequence is heart → gills → body → heart.

Double circulation (mammals):

Blood passes through the heart twice per circuit;

sequence is heart → lungs (pulmonary circuit) → heart → body (systemic circuit) → heart.

B3.2.15—Describe the adaptations of the mammalian heart that allow it to deliver pressurized blood to the arteries.

Cardiac muscle: Specialized, strong muscle for continuous contractions.

Pacemaker (sinoatrial node): Initiates heartbeat.

Atria and ventricles: Chambers that receive (atria) and pump (ventricles) blood.

Atrioventricular and semilunar valves: Ensure unidirectional blood flow.

Septum: Separates left and right sides, preventing oxygenated and deoxygenated blood from mixing.

Coronary vessels: Supply the heart muscle with oxygen and nutrients.

B3.2.16—What are the stages of the cardiac cycle following the initiation by the sinoatrial node, and how are blood pressure measurements interpreted?

Sinoatrial node: Sends out electrical signal for contraction of the atria

Atrial systole: Atria contract, pushing blood into ventricles.

Ventricular systole: Ventricles contract, forcing blood into arteries.

Diastole: Heart muscle relaxes, chambers fill with blood.

Blood pressure readings

Systolic pressure: Pressure during ventricular contraction.

Diastolic pressure: Pressure during relaxation.

Interpretation: High systolic/diastolic values indicate hypertension;

low values indicate hypotension.

B3.2.17—Generation of root pressure in xylem vessels by active transport of mineral ions

Root pressure is a positive pressure potential generated in roots to aid water movement

Created by active transport of mineral ions into roots

this pressure becomes critical when transpiration is low, such as in high humidity or early spring when there are not enough leaves/leaves haven't opened;

Root pressure supports hydration needs when transpiration alone is insufficient.

B3.2.18—Adaptations of phloem sieve tubes and companion cells for translocation of sap

Phloem sieve tubes and companion cells are adapted for sap translocation

Sieve plates allow smooth sap flow between tubes, which have reduced cytoplasm and no nucleus for minimal resistance Companion cells, connected to sieve tubes via plasmodesmata, are rich in mitochondria for active transport energy

These adaptations facilitate loading of carbon compounds at sources (e.g., leaves) and unloading at sinks for growth and storage