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Specification reference. (a) explain, in terms of surface area:volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not (HSW1);
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Specification reference • (a) explain, in terms of surface area:volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not (HSW1); • (b) describe the features of an efficient exchange surface, with reference to diffusion of oxygen and carbon dioxide across an alveolus;
Little george Loss of appetite
Is it efficient? • Is the mammalian lung the most efficient design? • Discuss!! Firstly discuss what you already know about the mammalian lung. Can you come up with any flaws?
Classifying and analysing • Cut out these pictures and classify them in terms into groups of organisms that you think have similar respiratory functions. • Write a list. What features do they all have in common?
frog Carbon dioxide 2.5 times as fast!!
Features of an efficient gaseous exchange system • Large surface area Exchange surface should be thin Diffusion gradient Surfaces should be wet
Unicellular v multicellular • 1) Draw: • - a 1cm cube • - a 2cm cube • - a 3cm cube • 2) Calculate the surface area of each cube • 3) Calculate the volume of each cube • 4) Calculate the SA:V ratio • SA:V = SA • V
Exchange surfaces All organisms require nutrients and the ability to excrete waste. Many simple organisms, such as bacteria and sea anemones, can exchange substances directly across their external surfaces. Larger organisms require specialized gas exchange and transport systems to transport substances such as oxygen and nutrients to their cells efficiently. Fish exchange these substances across gills, while insects have openings called spiracles on their surfaces. Crop photo In mammals, gas exchange occurs in the lungs, and in particular the alveoli.
Exam specification • (c) describe the features of the mammalian lung that adapt it to efficient gaseous exchange; • (d) describe, with the aid of diagrams and photographs, the distribution of cartilage, ciliated epithelium, goblet cells, smooth muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli of the mammalian gaseous exchange system; • (e) describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the mammalian gaseous exchange system;
ISA skills • AIM: • Effect of surface area: volume ratio on diffusion rate • Procedure: • Work through the instructions with your learning buddies. • Follow through the practical writeup
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Pluck dissection Respiratory system video
Trachea cross section Trachea Cross Section One of the special features of the Trachea is the PCC (pseudostratified ciliated columnar) on the internal surface which keeps the air passage clear of debris. Another is the hyaline cartilage C-rings that keep the trachea open. Note also the mucous glands emptying mucous into a duct which carries it to the surface. This also aids in trapping debris that enters the trachea.
Trachea cross section-epithelial cells The ciliaon the surface along with mucus cause the debris that enters the trachea to move back up to the epiglottis -->esophagus --> to the GI tract. The lamina propriaunder the PCC is made of strong flexible fibro-elastic tissue
Trachea cross section-cartilage The dark violet hyaline cartilage C-ringswill not allow the tracheal air passage to collapse. The rings are open on the posterior side of the trachea which is adjacent to the esophagus. This open surface allows for more flexibility when functioning with the esophagus which is collapsed except when food is moving through
Trachea cross section – goblet cells Mucus is a thick sticky substance that acts in collecting debris for swallowing. Serous fluidis a thinner runny substance that is mainly for keeping the epithelial tissue moist and lubricated.
Maintaining the structure of the alveoli During inhalation, the chest cavity increases in volume, lowering the pressure in the lungs to draw in fresh air. This decrease in pressure leads to a tendency for the lungs to collapse. Cartilage keeps the trachea and bronchi open, but the alveoli lack this structural support. alveoli Lung surfactant is a phospholipid that coats the surfaces of the lungs. Without it, the watery lining of the alveoli would create a surface tension, which would cause them to collapse. surfactant
Keeping the airways clear The walls of the trachea and bronchus contain goblet cells, which secrete mucus made of mucin. This traps micro-organisms and debris, helping to keep the airways clear. The walls also contain ciliated epithelial cells, which are covered on one surface with cilia. These beat regularly to move micro-organisms and dust particles along with the mucus. They contain many mitochondria to provide energy for the beating cilia.
Why do we breathe? Animals need to maintain a concentration gradient across their exchange surfaces so that oxygen will diffuse into the blood and carbon dioxide will diffuse out. Fish manage this by keeping a continuous stream of oxygenated water moving over their gills. In animals such as mammals and birds, a concentration gradient is maintained in the alveoli by the mechanism of ventilation.
The pleural cavity Each of the lungs is enclosed in a double membrane known as the pleural membrane. The space between the two membranes is called the pleural cavity, and is filled with a small amount of pleural fluid. lung This fluid lubricates the lungs. It also adheres to the outer walls of the lungs to the thoracic (chest) cavity by water cohesion, so that the lungs expand with the chest while breathing. pleural membranes
