OCR Biology Module 3 Notes

Exchange Surfaces

  • Smaller organisms have a large surface area to volume ratio, allowing simple diffusion for metabolic needs.
  • Larger organisms need adaptations to increase the efficiency of exchange due to their smaller surface area to volume ratio and higher metabolic rates.
  • Key adaptations involve a large surface area, maintained concentration gradient, and reduced diffusion pathway.

Mammalian Gas Exchange System

  • Structures include trachea, bronchi, bronchioles, and alveoli.
  • Trachea: C-shaped cartilage rings, ciliated epithelial cells, goblet cells, smooth muscle, and elastic fibers.
  • Bronchi and Bronchioles: Cartilage for support.
  • Alveoli: Site of gas exchange; oxygen diffuses into blood, carbon dioxide diffuses into alveoli.
  • Large surface area: Millions of alveoli.
  • Short diffusion distance: Single layer of squamous epithelial cells in alveoli and capillaries.
  • Steep concentration gradients: Capillary network and ventilation.

Ventilation

  • Inhalation: Thorax volume increases, pressure decreases, air flows in.
  • Exhalation: Thorax volume decreases, pressure increases, air flows out.
  • Inhalation: Diaphragm contracts (flattens), external intercostal muscles contract (ribs up and out).
  • Exhalation: Diaphragm relaxes (domes), external intercostal muscles relax, internal intercostal muscles contract (ribs in and down).

Lung Volume Measurement

  • Spirometer measures air volume during breathing.
  • Vital capacity: Maximum air volume inhaled/exhaled in a deep breath.
  • Tidal volume: Air volume inhaled/exhaled at rest.
  • Residual volume: Air remaining in lungs to prevent collapse.
  • Ventilation rate: Tidal volume x breathing rate.

Ventilation and Gas Exchange in Fish

  • Water flows in through the mouth and over the gills.
  • Buccal cavity volume changes drive water flow.
  • Gills: Site of gas exchange, composed of gill filaments covered in gill lamellae.

Gill Structure

  • Large surface area: Many gill filaments covered in gill lamellae.
  • Short diffusion distance: Thin gill lamellae with capillary network.
  • Steep concentration gradient maintained with a countercurrent flow mechanism.

Countercurrent Flow Mechanism

  • Water flows over gill lamellae in the opposite direction to blood flow in capillaries.
  • Maintains a steep concentration gradient along the entire gill lamella, maximizing diffusion.

Gas Exchange in Insects

  • Tracheal system: Spiracles, trachea, and tracheoles.
  • Spiracles: Open and close to regulate gas exchange and water loss.
  • Tracheoles: Site of gas exchange.
  • Large surface area: Branching tracheoles.
  • Short diffusion distance: Thin tracheole walls.
  • Steep concentration gradient: Cell respiration and abdominal muscle contractions.
  • Anaerobic respiration and lactate production lower water potential, drawing air in through spiracles.

Transport in Animals

Circulatory Systems

  • All systems transport gases and nutrients in a liquid using vessels and a pump.
  • Open Circulatory System: Hemolymph pumped to body cavity (hemocoel).
  • Closed Circulatory System: Blood remains in vessels.
  • Single Closed: Blood passes through the heart once per cycle (e.g., fish).
  • Double Closed: Blood passes through the heart twice per cycle (e.g., mammals).
    • Pulmonary circuit: Heart to lungs.
    • Systemic circuit: Heart to body.

Blood Vessels

  • Arteries, arterioles, capillaries, venules, and veins.
    Note: Refer to the video transcript for detailed info in the table of the blood vessels
  • Capillaries: Narrow diameter to slow blood flow, single layer of squamous epithelial cells for short diffusion distance.

Tissue Fluid Formation

  • Liquid and small molecules forced out of capillaries due to high hydrostatic pressure form tissue fluid.
  • Hydrostatic pressure: Pressure exerted by a liquid.
  • Oncotic pressure: Tendency of water to move into the blood by osmosis.

Tissue Fluid Dynamics

  • Formation: High hydrostatic pressure at the arteriolar end forces water and small molecules out.
  • Reabsorption: Lowered water potential at the venular end draws water back in by osmosis. Excess fluid absorbed into the lymphatic system as lymph.

Mammalian Heart

  • Cardiac muscle, myogenic, coronary arteries for oxygenated blood.
  • Pericardial membranes prevent overfilling.

Internal Structures

  • Left ventricle has thicker muscle for higher pressure.
  • Right ventricle has thinner muscle for lower pressure to protect lung capillaries.
  • Atria have thin muscle walls.

Cardiac Cycle

  • Diastole: Atria and ventricles relaxed, blood flows in.
  • Atrial Systole: Atria contract, blood flows into ventricles.
  • Ventricular Systole: Ventricles contract, blood to pulmonary artery and aorta.

Key Stages

  • Diastole: Atria and ventricular muscles are relaxed. Blood enters the atria, increasing pressure and opening the atrioventricular valves so blood can begin to flow into the ventricles.
  • Atrial systole: Atrial muscular walls contract, increasing the pressure further to cause the blood to flow into the ventricles through those open atrioventricular valves.
  • Ventricular Systole: Ventricles contract, increasing the pressure beyond that of the atria, so the atrioventricular valves close and the semilunar valves open.

Cardiac Output

  • Cardiac Output = Heart Rate
    eq Stroke Volume
  • Cardiac output is the volume of blood that leaves one ventricle in one minute.

Control of Cardiac Cycle

  • SAN (sinoatrial node) releases a wave of depolarization across the atria.
  • AVN (atrioventricular node) releases another wave of depolarization.
  • Bundle of His conducts the wave.
  • Purkinje fibers cause apex and ventricle walls to contract.

Electrocardiogram (ECG)

  • Measures electrical activity in the skin to diagnose heart rhythm irregularities.
  • Tachycardia: >100 bpm
  • Bradycardia: <60 bpm
  • Fibrillation: Irregular or chaotic rhythm.
  • Ectopic heartbeat: Extra beats out of rhythm.

Hemoglobin

  • Globular protein with a quaternary structure that transports oxygen.
  • Oxyhemoglobin dissociation curve: Shows percentage saturation relative to partial pressure of oxygen.
  • High partial pressure = high saturation; low partial pressure = low saturation.
  • Cooperative binding: First $O_2$ binding changes hemoglobin shape for easier subsequent binding.

Bohr Effect

  • High $CO2$ (low pH) shifts curve right, decreasing affinity, unloading more $O2$ at respiring tissues.
  • Different Hemoglobins
    • Fetal hemoglobin (HBF) shows a curve shifted to the left, so even at the same partial pressure of oxygen, it is more saturated with oxygen than adult hemoglobin (HBA).
    • The fetus's hemoglobin has a higher affinity than the adult hemoglobin because it can then remove oxygen from the hemoglobin of an adult and bind it to the fetus's hemoglobin instead.

Carbon Dioxide Transport

  • Dissolved in blood plasma.
  • As carbaminohemoglobin.
  • As hydrogen carbonate ions in red blood cells.
  • CO2 + H2O
    eq H2CO3
    eq H^+ + HCO_3^-
  • Chloride shift: Exchange of $HCO_3^-$ and Cl^- to maintain electrical balance.

Transport in Plants

Vascular Bundles

  • Xylem and phloem transport water and organic substance.
  • Root: Xylem in the center in star shape, phloem between the arms of the xylem star.
  • Stem: Xylem inside, pholem outside plus cambium in the middle.
  • Leaf: Xylem at the top, phloem at the button inside to the vascular bundle.

Phloem

  • Sieve tube elements (no nucleus) and companion cells.
  • Companion cells provide ATP for active transport.

Xylem

  • Dead, hollow cells with lignin-strengthened walls.
  • Allows for a continuous column for transporting water and mineral ions.

Water Uptake

  • Osmosis from soil into root hair cells (thin walls, increased surface area).
  • Symplast pathway: Through cytoplasm and plasmodesmata.
  • Apoplast pathway: Through cell walls (cohesion of water molecules).

Plant Adaptations

Xerophytes reduce water loss:
* curled leaves.
* increased humidity.
* sunken stomata.
* thick cuticle.
* longer root network
Hydrophytes manage excess water:
* thin cuticle.
* always open stomata at the top surface of the leaf.
* short roots
* wide leaves

Transpiration

  • Evaporation of water vapor from stomata.
  • Factors affecting rate:
    • Light intensity - higher rate when light is higher.
    • Temperature - higher rate when temperature is higher.
    • Humidity - lower rate when humidity is higher.
    • Wind - higher rate when wind is higher.

Cohesion-Tension Theory

  • Cohesion: Water molecules stick together due to hydrogen bonds.
  • Adhesion: Water molecules adhere to the lignin of xylem walls.
  • Root pressure: Positive pressure in roots pushes water up.

Transpiration Pull

  • Water evaporates from stomata, tension pulls water up xylem.
  • Adhesion to xylem walls and root pressure contribute.

Translocation

  • Active transport of sucrose from source to sink (requires energy).
  • Sucrose is made during photosynthesis.
  • Mass flow from source (photosynthesizing cells) to sink (respiring tissues).
  • Source releases hydrogen ions being actively transported, Co-transport of sucrose with the hydrogen ions then occurring via protein co-transporters
    *When water from the xylem moves in, osmotic pressure increases, thus liquids is forced through the phloem towards areas of of lower pressure.