Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
GCE BIOLOGY BY2 Transport of Respiratory Gases GCE BIOLOGY BY2 Transport of Respiratory Gases Fluid Mosaic Model of the Plasma Membrane Carbohydrate chain Glycoprotein GCE BIOLOGY BY2 Transport of Respiratory Gases Intrinsic protein Non-polar hydrophobic fatty acid chain Show/ hide labels Phospholipids GCE BIOLOGY BY2 Transport of Respiratory Gases One of the functions of the plasma membrane is to control the movement of substances in and out of cells. Why does this plasma membrane need to be semi-permeable? What’s the connection? What is the connection between the following structures? GCE BIOLOGY BY2 Transport of Respiratory Gases Hint: What do cells need to produce energy? Alveolus Red blood cells Small intestine Capillary Lungs Closed Circulatory System GCE BIOLOGY BY2 Transport of Respiratory Gases Humans have a closed circulatory system consisting of the heart, arteries, arterioles (narrow, thin walled arteries), capillaries, venules (small veins) and veins. The following diagram shows the relationship between these vessels and illustrates the movement of blood within them. GCE BIOLOGY BY2 Transport of Respiratory Gases The path of blood from an artery, to a capillary and a vein Blood in the capillaries GCE BIOLOGY BY2 Transport of Respiratory Gases Once the blood reaches the capillaries, it is in contact with the endothelium (the lining of the capillary) which is one cell thick. The plasma membrane of these cells are adapted for controlling the exchange of substances across them, as we will see in the following slides. Membrane Permeability Plasma membranes are semi-permeable – this means that some substances can pass through whilst others cannot. What determines which substances pass through this membrane? A substance has to be very soluble in the oily phospholipid bilayer. Steroid hormones, oxygen and carbon dioxide are examples of such molecules. Plasma membrane SOLUBLE GCE BIOLOGY BY2 Transport of Respiratory Gases steroid hormone oxygen carbon dioxide INSOLUBLE glucose protein lipid Click on the molecules to start their paths of motion Exchange of gases across a capillary GCE BIOLOGY BY2 Transport of Respiratory Gases In the following animation, we zoom into an alveolus and enter the capillary that surrounds it. Once inside the capillary, we will follow the exchange of gases that occurs in the red blood cell. Play Animation Formation of hydrogen carbonate and the transport of carbon dioxide in the blood Tissue cells CO2 Endothelium of capillary GCE BIOLOGY BY2 Transport of Respiratory Gases H2CO3 CO2 H2CO3 Diffusion Red blood cell First carbon dioxide (CO2) diffuses into the red blood cells where it is converted into carbonic acid (H2CO3). This reaction is catalysed by the enzyme carbonic anhydrase. CO2 Tissue cells Endothelium of capillary H2CO3 GCE BIOLOGY BY2 exchange Gas of Respiratory Gases Transport H+ + CO2 _ HCO3 H2CO3 Red blood cell H+ + _ HCO3 Carbonic acid dissociates, forming protons (H+) and hydrogencarbonate ions (HCO3-) Tissue cells GCE BIOLOGY BY2 Transport of Respiratory Gases Endothelium of capillary H2CO3 Red blood cell H+ + _ HCO3 Diffusion into plasma _ HCO3 The hydrogencarbonate ions diffuse out of the cell. They are transported in solution in the plasma. Tissue cells GCE BIOLOGY BY2 exchange Gas of Respiratory Gases Transport Endothelium of capillary H2CO3 Red blood cell H+ + _ HCO3 Chloride shift Diffusion into plasma _ Cl _ HCO3 _ Chloride ions (Cl ) diffuse inwards from the plasma to maintain electrical neutrality. This process is called the chloride shift. Tissue cells Diffusion Endothelium of capillary 4O2 Oxygen unloaded GCE BIOLOGY BY2 exchange Gas of Respiratory Gases Transport HHb Red blood cell _ H+ + HCO3 HbO8 The proteins left inside the cell are mopped up by haemoglobin to form haemoglobinic acid (HHb). This forces the haemoglobin to release its oxygen load, hence the Bohr shift. Tissue cells Diffusion Endothelium of capillary 4O2 Oxygen unloaded GCE BIOLOGY BY2 Transport of Respiratory Gases HHb Red blood cell _ H+ + HCO3 HbO8 By taking up excess protons haemoglobin is acting as a buffer. This is important in preventing the blood from becoming too acidic. The Effect of CO2 on the Oxygen Dissociation Curve How much oxygen is transported by a molecule of haemoglobin also depends on partial pressure of carbon dioxide. 100 Show hide CO2 line Saturation of Haemoglobin / % GCE BIOLOGY BY2 Transport of Respiratory Gases 80 CO2 60 From the graph we see that at high partial pressures of carbon dioxide, the oxygen dissociation curve shifts to the right. 40 This is called Bohr’s shift. 20 Higher partial pressure of carbon dioxide increases the dissociation of oxyhaemoglobin 0 0 2 4 6 8 Partial Pressure of Oxygen/ kPa 10 12 Haemoglobin This diagram shows how a model of haemoglobin reaches saturation with oxygen. GCE BIOLOGY BY2 Transport of Respiratory Gases haemoglobin The molecule is now saturated. Click on the numbered sections on the graph for an explanation of what happens at each stage Oxygen Dissociation Curve 100 5 4 80 3 Saturation of Haemoglobin / % GCE BIOLOGY BY2 Transport of Respiratory Gases 60 40 Haemoglobin’s The Under redconditions blood cells properties oftransport a lack allow of oxygen the it to oxygen (low bind partial with to arespiring lot pressure of oxygen tissues. ofoxygen oxygen), at The a high the The partial pressure of ispartial high The red blood cells collect oxygen inis pressure haemoglobin partial pressure of oxygen yields of oxygen, in its these oxygen but tissues to at low and the haemoglobin reaches the the capillaries the low, respiring partial as pressure, the cells oxygen –surrounding we only isrefer being a limited toused this lungs. as for saturation. respiration. dissociation. amount binds to it. 20 2 0 Show/ hide scale Show/ hide line 1 0 Show/ hide titles 2 4 6 8 Partial Pressure of Oxygen/ kPa 10 12 GCE BIOLOGY BY2 Transport of Respiratory Gases On the next slide we will see the path that the products of digestion take as they diffuse from the small intestine into the blood capillaries surrounding the gut. The cells must rely on more than diffusion to get all the glucose, amino acids and fatty acid and glycerol into the blood. What form of transport do you think is used? GCE BIOLOGY BY2 Transport of Respiratory Gases Absorption of digested food from the small intestine Click on the box to magnify the view Active Transport GCE BIOLOGY BY2 Transport of Respiratory Gases This is the movement of substances against a concentration gradient (from a region of low concentration to a region of higher concentration) across a plasma membrane. This process requires energy. This energy is provided by mitochondria in the form of ATP and cells performing active transport on a large scale contains numerous mitochondria. 4.8 How does Active Transport work? Active transport depends on proteins in the cell membrane to transport specific molecules or ions. These can move. These carriers can move: GCE BIOLOGY BY2 Transport of Respiratory Gases i) ii) iii) one substance in one direction (uniport carriers) two substances in one direction (symport carriers two substances in opposite directions (antiport carriers) The exact mechanism of active transport is unclear. Here are two hypotheses: 4.8 Cotransport Hypotheses Sucrose movement in glucose storing cells in a plant. Show animation GCE BIOLOGY BY2 Transport of Respiratory Gases Sucrose Proton pump Symport carrier H+ Sucrose Here the process of pumping protons drives sucrose transport in a plant cell. A pump using ATP as an energy source drives protons out of the cell, as they diffuse back into the cell, sucrose in this case is transported at the same time across a symport carrier. 4.8 Another Hypothesis This hypothesis suggests that one protein molecule changes its shape in order to transport solutes across a membrane. K+ K+ ATP K+ Na+ K+ GCE BIOLOGY BY2 Transport of Respiratory Gases Na+ K+ ATP Na+ Na+ Na+ PP- Na+ K+ Na+ Na+ K+ Na+ K+ Na+ Na+ Na+K+ Na+ K+ Na+ Na+ ADP P- ADP P- K+ Na+ Na+ As ATP is hydrolysed to ADP to release energy for the process, ADP binds to the protein and changes its shape. A sodium-potassium pump is an example of this. These pumps are vital in order to generate impulses in nerve cells. 4.8