B3.2 Transport (SL)

First Exams 2025

  • Theme: Form and Function

  • Level of Organisation: Organisms

  • Power of Science

Key Terms and Content (SL & HL)

  • Terms: Capillary, Artery, Vein, Lumen, Pulse, Correlation Coefficients, Coronary Heart Disease, Atherosclerosis, Transpiration, Xylem, Phloem, Vascular Tissue, Cortex, Epidermis

Capillaries

  • Definition: Small blood vessels connecting arteries to veins.

    • Function: Exchange materials between blood and cells.

Adaptations of Capillaries

  • Large Surface Area: Highly branched structure with narrow diameters.

  • Narrow Lumen: Just wide enough for one red blood cell at a time.

  • Thin Walls: Typically one cell thick, facilitating rapid exchange by diffusion.

Micrograph Analysis of Blood Vessels

  • Arteries vs. Veins: Definition and Characteristics

    • Artery: Thick wall, narrow lumen.

    • Vein: Thin wall, wide lumen.

  • Identification of Blood Vessels:

    • Blood vessel A (thick wall) is an artery.

    • Blood vessel B (thin wall) is a vein.

Arteries

  • Function: Transport blood away from the heart.

  • Adaptations for High Blood Pressure:

    • Thick Walls: Enable resistance to high pressure.

    • Collagen: Strengthens the artery's outer wall.

    • Smooth Muscle: Contracts to maintain pressure.

    • Elastic Fibers: Stretch and recoil to accommodate pressure changes.

    • Narrow Lumen: Maintains high pressure and reduces friction with smooth endothelial lining.

Measuring Pulse Rate

  • Definition: Caused by the heart's beating.

  • Methods for Measurement:

    • Manual counting at the radial or carotid artery.

    • Using technology like smartwatches and oximeters.

Veins

  • Function: Return blood to the heart.

    • Blood flow is slow and not under high pressure.

  • Adaptations to Assist Blood Return:

    • Valves: Prevent backflow.

    • Thin Walls: Can be compressed by surrounding skeletal muscles to aid blood movement.

    • Wide Lumen: Allows for increased blood volume transport.

Comparison of Arteries and Veins

  • Features:

    • Lumen: Arteries have narrow, veins have wide.

    • Wall Thickness: Arteries are thick, veins are thin.

    • Direction of Blood Flow: Arteries carry blood away from the heart, veins return it.

    • Valves: None in arteries, present in veins to prevent backflow.

Atherosclerosis

  • Definition: Hardening and narrowing of arteries due to cholesterol and other substances build-up.

  • Impact: Can lead to coronary artery occlusion and heart attacks.

Causes of Atherosclerosis

  • Biological Factors:

    • Damage due to high blood pressure attracts macrophages.

    • Macrophages release growth factors and consume cholesterol, leading to plaque formation.

    • Plaque may occlude arteries or break off, potentially causing clots.

Risk Factors for Atherosclerosis**

  • Uncontrollable Factors: Genetics, Age, and Gender (males more affected).

  • Controllable Factors: Obesity, Physical inactivity, Smoking, Diet high in fats/cholesterol.

Correlation Coefficients**

  • Pearson's Coefficient (r): Measures correlation strength between variables.

    • Close to zero indicates no relationship; not indicative of causation.

Saturated Fat and Coronary Heart Disease**

  • Study Findings: Increased saturated fat intake correlates with higher coronary heart disease deaths.

    • Important distinction: Correlation does not imply causation, but saturated fat is a known risk.

Transpiration**

  • Definition: Movement of water through a plant, evaporating from parts like leaves.

  • Process: Water enters roots via osmosis, travels through the xylem, and evaporates from mesophyll cells, creating a negative pressure that helps pull water upward due to hydrogen bonding.

Xylem**

  • Function: Transports water and minerals upwards; provides structural support.

  • Structure: Composed of dead, hollow cells forming long tubes devoid of end walls, allowing for efficient water flow.

Adaptations of Xylem**

  • Features:

    • No end walls for continuous water column.

    • Lack of cell contents and plasma membranes for unimpeded water flow.

    • Pits facilitate water movement between xylem cells.

    • Lignin fortifies cell walls to endure transpiration pressure.

Dicotyledonous Stem and Root Structure**

  • Epidermis: Provides protection.

  • Cortex: Offers structural support and starch storage.

  • Vascular Bundles (Xylem and Phloem): Transport materials throughout the plant.