Topic 4

• Single Celled organisms


  • Don't have specialised transport mechanisms, substances enter the cell through diffusion or active transport
• Multicellular organisms


  • Require specialised transport systems due to the diffusion distance is higher, the metabolic rate is higher and there is a smaller surface area-volume ratio
• Characteristics of mass transport systems


  • Vessels
  • Directional movement
  • Transport medium
• Efficient exchange surface


  • Large surface area
  • Thin with a steep concentration gradient
• Diffusion


  Net movement from a high low to concentration, they are nonpolar small molecules like CO2 and O2
• Osmosis


  The net movement of water across a partially permeable membrane from a high to low concentration
• Facilitated Diffusion


  Through channel proteins which are ions like nitrates, water, small molecules, they move through a water filled channel. Then carrier proteins which move small polar molecules like glucose, protein changes shape to move the molecules. They can also be voltage gated channels
• Active Transport


  Requires ATP, movement from low to high. It changes ATP to ADP +Pi which changes the shape of the pump and transports the molecule, it then goes back to its original shape after
• Endocytosis


  Cell intakes from the outside, with membrane forming a pit and then enclosing the particle. This occurs in phagocytosis
• Exocytosis


  From cell to outside, vesicle fuses with plasma membrane and releases, this occurs across synapses, but can also release hormones and neurotransmitters
• Turgor Pressure


  The inward pressure that's exerted by the plants cell wall, this is generated because water moves in by osmosis causing the protoplasm in the vacuole to push against the cell wall. The combination of these two forces can prevent too much water moving into a plant cell
• Gas exchange in mammals

  1. Gas exchange occurs through the lungs, where the contraction of the intercostal muscles and diaphragm causes the volume of the lungs to increase (therefore pressure decreases), so the air moves into the lungs through diffusion

  2. The gas then moves into the blood from the alveoli through diffusion, they are adapted to have a high surface area, small diffusion gradient and they are also moist

  3. The blood moving through the capillaries around the lungs is deoxygenated so therefore there is also a high diffusion gradient, and as the blood is constantly moving it maintains this concentration gradient
• Gas exchange in insects


  1. They have spiracles which can be opened and closed, they regulate the need for gas exchange and the need to retain water

  2. Oxygen diffuses into here and through into the Trachea, these are impermeable due to they are lined with rings of chitin, preventing form them collapsing

  3. Tracheoles - THese are smaller tubes that make up most of the respiratory system, where air enters the body, teacher moves air to the tracheoles and then enter into the body cells, water can often pool here but is removed if the insect is active as lactic acid builds up and decreases the water potential

  4. Air Sacs - These act as air reservoirs, increasing the volume of air that is mobbed through the system, they also have flexible walls so that the changes in pressure causes more gas exchange

  5. Abdomen movements - Rhythmic contractions of abdominal muscles compress air sacks which helps maintain concentration gradient, especially in vigorous activity like flying or if the CO2 concentration is increased
• Gas exchange in fish

  1. As they move the pump water over the gills allowing gas exchange to occur, they are made from filaments covered by folds called lamellae, increasing surface area, the continuous movement of water also prevents them from sticking together

  2. To move water water the floor of the mouth opens, closing the gill flap, it's then raised to increase the pressure, forcing more water over the gills

  3. To maintain the concentration gradient a countercurrent exchange system occurs, where the water flowing over the gills and the blood flowing through work in opposite directions, maintaining a steep concentration gradient. And unlike humans they only have a single circulatory system
• Gas exchange in plants


  1. The layers of the plant contain a waxy cuticle to prevent water loss

  2. The upper epidermis (often transparent to allow more light through)

  3. Palisade mesophyll layer (stacked vertically, high concentration of chloroplasts, close to the leaf surface)

  4. Spongy mesophyll (also have chloroplasts, have air sacs for gas exchange and to increase surface area, also moist to allow for gaseous exchange)

  5. Lower epidermis, guard cells and stomata( Guard cells swell to open stomata when CO2 is needed, it diffuses in for photosynthesis, they can close to reduce water loss, on the underside of leaf to reduce transpiration)

  6. The stomata open through mainly K+ ions moving into the guard cells through active transport which then causes water to move in due to the water potential being decreased, making the guard cell turgid and swell, opening the stomata

  7. Lentils - These are on the bark of a tree which acts as a pore to allow gas exchange in lignified plants, and helps maintain concentration gradient
• Heart


  • Made from Myogenic Cardiac Muscle
• Blood flow through the heart


  1. The vena cava pumps blood in from rest of the body, which then gets pumped out to the lungs through pulmonary artery

  2. The blood from the lungs then comes in through the pulmonary vein, then out through the aorta to the rest of the body

  3. The valves between the atrium and ventricle are called atrioventricular valves, and the valves in the base of aorta and pulmonary artery are called semilunar valves, and stops blood from 'falling back' into the heart, there is three in each

  4. The tendinous cords prevent the atrioventricular valves from turning inside out

  5. Coronary arteries supply blood to the heart muscle

  6. The septum is in the middle of the heart, prevents the oxygenated and deoxygenated blood from mixing
• Double circulatory system


  One is through the heart and to the lungs, and then from the heart to rest of the body, advantages of this is a concentration gradient is maintained, the blood pressure to body tissues is higher where as to the lungs its lower (to prevent damage), organisms can then develop larger bodies
• Cardiac cycle


  1. Cardiac Diastole: During this stage blood flows into the atria through the Vena cava and pulmonary veins, low pressure is created through elastic recoil of the atrial walls, the atrioventricular valves are closed here

  2. Atrial Systole: The atriums fill with blood so the pressure increases, the atrioventricular valves are pushed open, with then the two atria contract simultaneously, forcing the remaining blood into the ventricles

  3. Ventricular systole: After a slight delay the ventricles contract, increasing the pressure (atrioventricular valves are closed), the smiley luna valves open and blood is pumped through the Aorta and Pulmonary artery
• ECG


  • P wave is caused by the depolarisation of the SAN
  • QRS is caused by the repolarization of the ventricles, causing ventricular systole, this is the largest wave due to the ventricles have the most muscle mass
  • T wave is caused by the repolarisation of the ventricles
  • U wave is possibly caused by the repolarisation of the purjinke fibres
• Functions of blood


  • Transport
  • Defence against pathogens
  • Formation of lymph and tissue fluids
• Plasma


  It transports digested food products like glucose or amino acids, nutrient molecules, hormones and excretory products (like urea)
• Red Blood Cells (erythrocytes)


  • Transport oxygen and some CO2, they are adapted due to their biconcave shape and lack of nucleus
• Leukocytes (white blood cells)


  • Defence from pathogens, contains Neutrophils, basophils and eosinophils, or monocytes and impacts
• Platelets


  They are bone fragments, involved in blood clotting
• Blood clotting


  1. When a vessel is damaged platelets attach to exposed collagen fibres, and then a protein called thromboplastin is released, triggering the conversion of prothrombin into active thrombin

  2. The throbbin catalyses the conversion of soluble fibrinogen into fibrin

  3. This then makes a network, where red blood cells, platelets and debris form the blood clot
• Atherosclerosis


  • The hardening of arteries by the buildup of a place called an atheroma. This is the cause of many cardiovascular diseases
  • The endothelium is damaged, for example by high cholesterol levels, smoking or high blood pressure
  • This leads to an inflammatory response, causing white blood cells to move to the site of damage
  • Overtime this builds up, and calcium salts go over it, hardening it and leading to a atheroma
  • This narrows the artery, creating higher blood pressure which damages the endothelial lining and the process is repeated
  • The risk of this is affected by genetics, age, diet, blood pressure, obesity, high blood pressure
• Haemoglobin


  A water soluble globular protein which consists of 4 polypeptide chains and a heme group, it carries oxygen as it binds to the heme group, this then changes the shape of the protein and increases the affinity for oxygen
• Foetal haemoglobin


  Has a higher affinity for oxygen, due to the blood runs in a countercurrent exchange system through the placenta - this difference in affinity is needed so that when oxygen dissociates from the maternal haemoglobin it can bind to foetal haemoglobin
• Myoglobin


  Another respiratory pigment used, it has a higher affinity for oxygen and acts as a storage molecule for oxygen. This is mostly found in muscles
• Partial pressure of CO2


  In the presence of CO2 the affinity of haemoglobin for oxygen decreases causing it to be released
• Transport of CO2 in the blood


  1. A small amount of it is dissolved in the plasma, about 20% of it reacts with amino acid in the blood, making compounds, and about three quarters reacts with water in the blood to form carbonic acid which dissociates into hydrogen carbonate and hydrogen ions

  2. This reaction is catalysed by carbonic anhydrase

  3. To prevent the drop in pH the haemoglobin acts as a 'buffer', the oxygen that is taken out is used to repair tissues
• Tissue fluid


  • Forms as a result of the interaction of hydrostatic pressure and oncotic pressure in capillaries
  • Hydrostatic pressure: This is the residual pressure from the heartbeat, its higher at the arterial end of the capillary then the venous end
  • Oncotic pressure: This is the movement of the fluid out of capillaries due to the hydrostatic pressure, the water potential of the capillaries then becomes more negative
  • At the arterial end hydrostatic is greater so the fluid moves out of the capillaries, however at the venous end oncotic pressure is greater, however there is still a net movement out of capillaries, this forms the tissue fluid
  • Excess fluid drains into the lymphatic system to prevent swelling, this then goes into the subclavian vein. The lymph contains lymphocytes that produce antibodies which are also emptied into the blood
• Xylem


  • Transports water and minerals, also serve as structural support
  • They are long cylinders with open ends - creates a wide lumen
  • They also contain pits for water to move sideways
  • They are lignified when they die, which is deposited in spiral patterns to enable toe plants to remain flexible
• Phloem


  • Made of living cells, involved in translocation - the movement of nutrients to storage organs
  • The consist of sieve tube elements and companion cells
  • The sieve tube elements form a tube to transport sugars like sucrose (sap)
  • Companion cells are also involved in ATP production for active transport
  • Cytoplasm of sieve tube elements and companion cells are linked through plasmodesmata (gaps between the cell wall), allowing the movement
  • The ends of phloem are sieve plates, this means it forms direct connections for transport from one element to another
• Movement of water in xylem

  1. Water moves into the plant through osmosis in root hair cells

  2. It moves through the root by osmosis to replace water in the xylem, it either moves through the simplest or apoplast pathway

  3. The symplast pathway moves through the cytoplasm

  4. The apoplastic pathway moves through the cell wall until it reaches the casparian strip, then it moves into the apoplastic pathway

  5. The casparian strip is impermeable, made of suberin and is only in the roots

  6. The water then moves into the xylem, containing a column of water maintained through cohesion and adhesion

  7. Cohesion is the attraction between molecules, where water forms H bonds with other water molecules

  8. Adhesion is the attraction between unlike molecules, where water forms H bonds with other surfaces (like pores in the mesophyll cells)

  9. Transpiration occurs in the leaf, causing a hydrostatic pressure in the xylem, this then moves the whole column of water upwards due to cohesion

  10. It reaches the leaf and moves along via osmosis, it then can evaporate through transpiration and out the stomata
• Movement of substances in phloem


  1. This is a form of mass flow called translocation, the substances moved are called assimilates (mainly sucrose)

  2. It's always moved from the source to sink, and can be moved either direction

  3. The sucrose can be loaded into the phloem by either symplastic or apoplastic pathway

  4. It is moved through hydrostatic pressure, where there is movement of water into the phloem from xylem near the source, along with sucrose moving through a companion cell into the phloem, then the water with the dissolved organic solutes moves down the hydrostatic pressure gradient. It is then moved into a companion cell and into a sink (against a concentration gradient

  5. The water then goes back into the xylem through osmosis

  6. Symplast: The sucrose moves by diffusion from leaf cell to companion cell of phloem into the phloem sieve tube, this decreases the water potential so water moves in and generates hydrostatic pressure (so the water moves down the gradient

  7. Apoplast: Sucrose moves by diffusion from leaf cell wall to companion cell wall, then moved through active transport into the cytoplasm, ti them diffuses into sieve tube

  8. The phloem are unloaded possibly, due to the sucrose moving into the companion cell through diffusion, then is moved into the sink through active transport