Mass transport

• Mass transport is the movement of substances from one place to another.
• Active transport requires energy input (ATP) and moves molecules against their concentration gradient.
• Specialised exchange surfaces are needed as the size of the organism and its surface area to volume ratio increases
• Single-celled organisms have short distances for substances to enter the cell, while multicellular organisms have larger distances due to a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen
• Features of an efficient exchange surface include:

  • Large surface area (e.g., root hair cells or folded membranes)
  • Thin to ensure short distance for substance crossing
  • Good blood supply/ventilation to maintain a steep gradient (e.g., alveoli)
• Fish have a small surface area to volume ratio for gas exchange and impermeable skin requiring specialised gas exchange surfaces
• Bony fish have four pairs of gills supported by arches with gill filaments and lamellae for gas exchange
• Fish ventilation involves opening mouth, lowering buccal cavity floor, closing mouth, raising buccal cavity floor, and using operculum as a valve and pump
• Insects use spiracles, trachea, and tracheoles for oxygen transport directly to tissues undergoing respiration
• Gases move in and out through diffusion, mass transport due to muscle contraction, and volume changes in tracheoles in insects
• Plants have adaptations in leaves for efficient gas exchange including stomata, air spaces, and proximity of cells to stomata
• Mammalian gaseous exchange system involves lungs with a large surface area, rib cage protection, and diaphragm for inflation and deflation
• Gaseous exchange occurs in alveoli with trachea, bronchi, and bronchioles facilitating air flow
• Structures and functions of mammalian gaseous exchange system include:

  • Cartilage supporting trachea and bronchi
  • Ciliated epithelium moving mucus to prevent lung infection
  • Goblet cells secreting mucus to trap bacteria and dust
  • Smooth muscle controlling airway diameter
  • Elastic fibres controlling air flow
• Ventilation involves inspiration and expiration with the help of intercostal muscles and diaphragm
• A spirometer measures lung volume including vital capacity, tidal volume, and breathing rate
• Digestion involves hydrolysis of large biological molecules into smaller molecules for absorption across cell membranes
• Carbohydrates, lipids, and proteins are digested by specific enzymes and processes
• Products of digestion are absorbed by cells lining the ileum through facilitated diffusion and co-transport
• Haemoglobin is a water-soluble globular protein with two beta polypeptide chains and two alpha helices, forming complexes containing haem groups
• Haemoglobin is a water-soluble globular protein consisting of two beta polypeptide chains and two alpha helices
• Each haemoglobin molecule contains a haem group and can carry four oxygen molecules
• The affinity of oxygen for haemoglobin varies depending on the partial pressure of oxygen, with higher partial pressure leading to higher affinity
• During loading in the lungs, haemoglobin binds oxygen tightly, and during unloading in respiring tissues, oxygen is released
• Dissociation curves illustrate the change in haemoglobin saturation as partial pressure changes
• Fetal haemoglobin has a higher affinity for oxygen compared to adult haemoglobin
• The affinity of haemoglobin for oxygen is also affected by the partial pressure of carbon dioxide, leading to the Bohr effect
• The circulatory system in mammals is a closed double circulatory system with two pumps in the heart
• The heart is made up of two pumps, each with an atrium and a ventricle
• Valves between the atria and ventricles prevent backflow in the heart
• The cardiac cycle consists of three stages: cardiac diastole, atrial systole, and ventricular systole
• Arteries are thick-walled and carry blood away from the heart, while veins carry blood back to the heart
• Arterioles branch off arteries and feed blood into capillaries, which are one cell thick for metabolic exchange
• Venules are larger than capillaries but smaller than veins
• Tissue fluid serves as a means of supplying tissues with essential solutes and exchanging waste products
• Hydrostatic pressure forces blood fluid out of capillaries, and osmosis helps maintain water balance between blood and tissue fluid
• The lymphatic system carries remaining tissue fluid back to the blood and contains lymph nodes for immune system defenses
• Plants use xylem tissue for passive transport of water and minerals, and phloem tissue for active transport of sugars
• Xylem and phloem are components of the vascular bundle in plants, providing transport and structural support