Exchange and Transport in Organisms

Introduction to Topic 3: Exchange and Transport

• Topic 3 focuses on adaption for efficient gas exchange and transport across surfaces.
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Surface Area to Volume Ratio

• Surface area to volume ratio is calculated by dividing an organism's surface area by its volume.
• This ratio affects how efficiently organisms can transport substances across their surfaces.
• Larger organisms have a smaller surface area to volume ratio.
• Small organisms, like amoeba, have a large surface area to volume ratio, allowing them to meet their needs through simple diffusion.
• Larger organisms require adaptations for mass transport due to their smaller surface area to volume ratio and higher metabolic needs.

Adaptations for Efficient Exchange

• Key adaptations to maximize the absorption of digested food includes villi & microvilli.
• Alveoli and bronchioles serves this purpose for gas exchange in mammals.
• Spiracles and tracheals are gas exchange adaptations in terrestrial insects.
• Gill filaments and lamellae enable effective gas exchange in fish.
• Plants exchange gases through stomata on their leaves.
• Many gas exchange surfaces have a nearby capillary network to facilitate transport, except for plants.

Key Terms in Gas Exchange and Ventilation

• Breathing involves moving air in and out of the lungs, aka ventilation.
• Respiration refers to the chemical reaction that releases energy in the form of ATP.
• Gas exchange involves the diffusion of oxygen and carbon dioxide in and out of cells.

Human Gas Exchange System

• Key structures include the alveoli, bronchioles, bronchi, trachea, and lungs.

Ventilation in Humans

• Ventilation involves the diaphragm and antagonistic muscles surrounding the ribs, notably the external and internal intercostal muscles.
• Antagonistic muscles work in pairs, with one contracting while the other relaxes.
• External intercostal muscles contract, causing the rib cage to move out during inhalation or inspiration.
• Internal intercostal muscles contract, pulling the rib cage inwards during exhalation or expiration.
• During inhalation, the external intercostal muscles contract, the internal intercostal muscles relax, and the diaphragm contracts and moves downwards.
• During exhalation, the external intercostal muscles relax, the internal intercostal muscles contract, and the diaphragm relaxes and domes upwards.
• Pulmonary ventilation calculation: Tidal Volume × Ventilation Rate.

Gas Exchange in the Alveolar Epithelium

• Gas exchange occurs between the alveolar epithelium and the blood.
• Alveoli are tiny air sacs (~300 million in each lung).
• Alveoli epithelium cells are very thin to minimize diffusion distance.
• Each alveolus is surrounded by a network of capillaries to maintain concentration gradients.

Gas Exchange in Terrestrial Insects

• Insects have a waterproof exoskeleton, which prevents gas exchange across it.
• Insects do not have lungs.
• They uses a tracheal system (trachea, tracheals, and spiracles) for ventilation and gas exchange.
• Spiracles are small openings along the abdomen where oxygen and carbon dioxide enter and leave.
• Trachea are tubes with rings to prevent collapse, connecting to spiracles.
• Tracheals are smaller tubes that branch throughout the insect tissue to deliver oxygen to cells.
• Gases move into the tracheal system through diffusion, mass transport, and muscle cell respiration.
• Diffusion occurs due to the concentration gradient between tracheals and the atmosphere.
• Mass transport involves abdominal muscles contracting and relaxing to move gases in and out.
• In flight, muscle cells respire anaerobically, producing lactate, which lowers water potential, drawing water from tracheals and pulling in more air.
• Adaptations for gas exchange includes fine tracheals for large surface area, thin tracheal walls, a short diffusion distance between spiracles and tracheals, and maintaining a steep concentration gradient.
• Terrestrial insects limit water loss through small gas exchange surface area, a waterproof exoskeleton, and the ability to open and close spiracles.

Gas Exchange in Fish

• Fish have gills for gas exchange because they are waterproof and have a small surface area to volume ratio.
• Water contains 30 times less oxygen than air, so fish require additional adaptations.
• Key features are a large surface area, short diffusion distance, and a mechanism to maintain the concentration gradient.
• Fish gills are are made up of gill filaments covered in gill lamellae which are positioned at right angles to the filament.
• Each gill filament is covered in gill lamellae, increasing the surface area.
• Water rushes over the gills as the fish opens its mouth while swimming.
• A maintains a short fusion distance through anetwork of capillaries in every gill lamellae.
• The concentration gradient is maintained by the counter current flow mechanism, where water flows over the gills in the opposite direction to blood flow.
• The counter current flow ensures that equilibrium isn't reached, allowing oxygen to diffuse from water into capillaries across the entire gill lamellae.

Gas Exchange in Leaves

• Key structures include the palisade mesophyll (photosynthesis), spongy mesophyll (air spaces), and stomata (gas diffusion).
• Oxygen diffuses out of the stomata; carbon dioxide diffuses in for photosynthesis.
• Stomata close at night and open in the daytime, linked to the light-dependent reactions of photosynthesis.
• Xerophytic plants have adaptations to minimize water loss, such as rolled leaves, deep and sunken stomata, and tiny hairs.

Digestion and Absorption

• Large biological molecules are hydrolyzed into smaller soluble molecules for absorption across cell membranes.
• Three biological molecules: Carbohydrates, Lipids, and Proteins.

Carbohydrate Digestion

• Carbohydrates are hydrolyzed by amylases and membrane-bound disaccharidases.
• Digestion begins in the mouth, continues in the duodenum, and is completed in the ilium.
• Salivary amylase starts digestion in the mouth.
• Pancreatic amylase in the duodenum hydrolyzes polysaccharides into the disaccharide maltose.
• Membrane-bound enzymes, such as sucrase and lactase, hydrolyze disaccharides into monosaccharides.

Protein Digestion

• Proteins are hydrolyzed by endopeptidases, exopeptidases, and membrane-bound dipeptidases.
• Digestion begins in the stomach, continues in the duodenum, and is fully digested within the ilium.
• Endopeptidases hydrolyze peptide bonds between amino acids in the middle of a polymer chain.
• Exopeptidases hydrolyze peptide bonds between amino acids at the end of the chains.
• Membrane-bound dipeptidases break the peptide bonds between two amino acids to hydrolyze dipeptides

Lipid Digestion

• Lipids are digested by lipase and bile salts.
• Lipase, produced in the pancreas, hydrolyzes ester bonds in triglycerides to form monoglycerides and fatty acids.
• Bile salts, produced by the liver, emulsify lipids to form micelles, increasing the surface area for lipase to bind.
• Lipids are coated in bile salts to create an emulsion.
• Many small droplets of lipids provide a larger surface area to make hydrolysis faster.
• Micelles are vesicles formed of fatty acids, glycerol, monoglycerides, and bile salts.

Absorption of Lipids

• Lipids are digested into monoglycerides and fatty acids by lipase and bile salts in tiny micelles.
• Fatty acids and monoglycerides diffuse across the cell surface membrane into the epithelial cells of the ilium due to their non-polar nature
• Once in the cells, they are modified back into triglycerides inside the endoplasmic reticulum and Golgi body, forming vesicles.
• Vesicles are released from the cell into the lacteal (lymphatic vessels in the small intestine) for transport around the body.

Absorption in Mammals

• Absorption occurs in the ilium, which links to the villi and microvilli.
• The ilium wall is covered in villi with thin walls surrounded by a network of capillaries.
• Epithelial cells covering the villi have microvilli, creating a large surface area.
• Walls are thin, providing a short diffusion distance.
• The network of capillaries maintains the concentration gradients.
• Monosaccharides (like glucose) and amino acids are absorbed by active transport in the form of co-transport.

Hemoglobin and Oxygen Transport

• Hemoglobin is a quaternary structure protein involved in the mass transport of oxygen.
• Myoglobin is found in muscle tissue in vertebrates and in fetuses.
• The oxyhemoglobin dissociation curve illustrates how hemoglobin behaves under different conditions.
• Oxygen is loaded in regions with a high partial pressure of oxygen, such as the alveoli.
• In regions with a low partial pressure of oxygen, such as respiring tissues, hemoglobin unloads the oxygen.
• The sigmoidal shape of the curve is caused by cooperative binding; the first oxygen that binds makes it easier for the others to bind.
• The Bohr effect shifts the curve to the right w/high carbon dioxide concentration or partial pressure, causing a decrease in the affinity for oxygen which affects the shape of hemoglobin.
• Different animals have hemoglobin adapted to their particular needs and environments, such as high affinity in fetus' and low affinity in doves.

Circulatory Systems

• The mammalian circulatory system is closed and double.
• Closed: Blood stays within blood vessels.
• Double: Blood passes through the heart twice per circuit.
• Mammals require a double circulatory system to manage the pressure of blood flow.
• Blood flows through the lungs at lower pressure to prevent damage to capillaries in the alveoli and goes slower for gas exchange.
• Oxygenated blood from the lungs returns to the heart and is pumped out at a higher pressure to reach respiring cells.
• Key blood vessels include coronary arteries, vena cava, aorta, pulmonary artery, and pulmonary vein.
• Coronary arteries supply the heart muscle with oxygenated blood.
• "Pulmonary" refers to blood vessels connected to the lungs.
• Arteries, arterioles, capillaries, and veins connect the major blood vessels.
• Major blood vessels are connected within this double circulatory system via arteries, arterioles, capillaries, and veins.

Cardiac Muscle

• Walls of the heart have a thick muscular layer to contract with high force.
• Cardiac muscle has unique properties: myogenic (contracts and relaxes without nervous or hormonal stimulation) and never fatigues.
• Coronary arteries supply the cardiac muscle with oxygen and glucose.
• If a coronary artery becomes blocked, it can lead to a myocardial infarction (heart attack).
• Four chambers: two atria and two ventricles.
• Atria have thinner muscular walls; ventricles have thicker muscular walls.
• The right ventricle pumps blood to the lungs at lower pressure; the left ventricle pumps blood to the body at higher pressure.
• "Pulmonary" means lungs.
• Veins carry blood into the heart; arteries carry blood away from the heart.
• Valves prevent backflow of blood: semilunar and atrioventricular valves.
• Septum separates the deoxygenated and oxygenated blood.

Blood Vessels

• Arteries carry blood away from the heart towards the arterioles.
• Arterioles (smaller than arteries) connect to capillaries.
• Capillaries then connect arterioles to veins.
• Veins then then carry blood into the heart.
• Arteries have a much thicker muscular layer compared to veins because of constriction & dilation of the blood traveling though them, and do not have any valves.
• Arteries also have thicker elastic layers than veins to help maintain blood pressure.
• Veins have a much thinner muscular layer than arteries because the the blood is already low pressure, and contain valves.
• Arterioles have a thicker muscular layer to restrict capillaries.
• Capillaries do not have any muscular or tissue layer, and have one thin wall for exchange to occur.
• Arterioles are thicker than in the arteries the muscular layer & elastic layer; the wall is thinner with no valves.

Cardiac Cycle

• Three stages: diastole, atrial systole, and ventricular systole, where some people pronounce diastole as distally and systole as sistally.
• Diastole occurs first, where atria and ventricular muscles will relax as blood enters into the atria through the vena cava and the pulmonary vein which increases the pressure and volume.
• Atria Systole occurs when the atria muscles contract, increasing pressure in the blood, which will cause the atrioventricular valves to open while ventricle muscles stay relaxed.
• Ventricular Systole occurs after a short delay, where ventricular muscles will contract, increasing pressure, and then the semilunar valves will open.
• Cardiac output = Heart rate × Stroke volume

Tissue Fluid

• Tissue fluid contains water, glucose, amino acids, fatty acids, ions, and oxygen.
• Fluid is forced out of capillaries to bathe the cells.
• Capillaries have small gaps between cells that make up walls, so molecules that are too big cannot get out.
• As blood enters capillaries from arterioles, the smaller diameter results in high hydrostatic pressure.
• Water and small molecules are forced out through ultrafiltration.
• Molecules like red blood cells, platelets and large proteins cannont get out and stay out.
• Hydrostatic pressure decreases towards the venule end of the capillary.
• Towards the venule area, hydrostatic pressure has lowered the water pressure.

Mass Transport in Plants

• Mass transport of water involves transpiration.
• Transpiration is the water evaporating out of the stomata.
• Four key factors that affect transpiration:
  • More Light: More light means more transpiration
  • Hotter: Evaporate faster
  • Humidity: When humidity is higher, it reduces transpiration
  • Wind: More wind means more transpiration
• Water moves from the roots all the way up the xylem to transpire out of the stomata through cohesion tension theory

Cohesion Tension Theory

• Water moves up the plant from the roots against gravity via cohesion, capillarity or adhesion, and root pressure.
• Cohesion is where water becomes dipolar, and hydrogen bonds can form between the hydrogen and oxygen to move up a continuous column of water.
• Adhesion describes the molecules sticking to the walls of the xylem.
• Root Pressure describes water moving into the roots by osmosis and increasing the volume above it.
• It includes the water column whereby all the water molecules are stuck together.

Mass Transport In Plants: Phloem

• Transports organic molecules.
• Two key cells involved.
• Sieve tube elements: living cells with no nuclei and few organelles.
• Companion cells: are outside, have ATP for active transport of organic substances.
• Transport of organic molecules in solution is called the source to sink model, where glucose produced in photosynthesis is transported.

Translocation steps

• Photosynthesis in chloroplasts of leaves is the source.
• Increases concentration gradients in companion cell via facilitated diffusion.
• Active transport of protons from companion cell into space within cell walls.
• Protons move down concentration gradient into sieve tube elements, and co-transport of sucrose.
• Soluble organic substances movement due to difference in pressure.

Investigations that prove translocation

• Tracers: 2-D process where plants provided radioactively labeled carbon dioxide are cut into thin slices stems for X-ray films.
• Ringing Experiments: removal of rings by peeling away the bark and pholem off the phloem.

Explore adaptations for efficient gas exchange and transport in organisms. Learn how surface area to volume ratio impacts transport efficiency. Discover adaptations that maximize absorption for sufficient metabolic activity.