Module 2Exchange and Transport Unit One Cells, Exchange and Transport AS Biology OCR Specification
Learning Outcomes • Explain, in terms of surface area:volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not.
Exchanges between organisms and their environment • Exchange can take place in two ways • Passively (no energy is required) • E.g. diffusion and osmosis • Actively (energy is required) • Active transport • Pinocytosis and phagocytosis
Surface area to volume ratio • Exchange takes place at the surface of an organism, but the materials absorbed are used by cells that mostly make up its volume. • For exchange to be effective, the surface area of the organism must therefore be large compared with its volume.
Learning outcomes • Explain, in terms of surface area:volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not.
Evolution of organisms • A flattened shape • A central region that is hollow • Specialised exchange surfaces • Large areas to increase the surface area to volume ratio
Why organisms need special exchange surfaces • Oxygen for… • Glucose as a source of … • Proteins for … and … • Fats • Water • Minerals • To remove waste materials
Features of a specialised exchange surface • Good exchange surfaces have: • A large surface area • Thin barrier to reduce diffusion distance • Large concentration gradient • Fresh supply of molecules on one side • Removal of required molecules on other side
Specialised Exchange Surfaces • Alveoli in the lungs • Small intestine • Liver • Root hairs in plants • Hyphae of fungi
Progress Question • Very small organisms such as the amoeba do not have specialised gas exchange systems. • Mammals are large, multicellular organisms and have a complex gas exchange system. • Explain why the mammal needs such a system when an amoeba does not.
Progress Question - suggestions • Why do we need gas exchange? • Oxygen is needed for respiration • Body needs to get rid of waste carbon dioxide. • How do simple animals take in the oxygen they need? • Diffusion through the surface membranes e.g. amoeba or flatworm
Progress Question - suggestions • Why can’t multi-cellular organisms do this? • Cells are too far away from the oxygen in the external environment. • Need a specialised exchange surface. • In humans the specialised gas exchange surface is the alveoli.
Learning Outcomes • Describe the features of an efficient gas exchange surface, with reference to diffusion of oxygen and carbon dioxide across and alveolus.
Gas Exchange • Gaseous exchange is the movement of gases between an organism and its environment. • Gas exchange takes place by diffusion. • The rate of diffusion depends on three factors. • The surface area of the gas exchange surface • Difference in concentration • The length of the diffusion pathway
Alveoli • Adaptations of alveoli to gas exchange • Large surface area • Thin walls of alveoli and blood capillaries • Steep concentration gradient • Good blood supply • Ventilation • Blood is constantly moving through the lungs to maintain the concentration gradients. • The air in the alveoli is continually refreshed by ventilation.
Alveoli and gas exchange • Large surface area – 70m2 • Extremely thin – lined with squamous epithelium – allows for rapid diffusion • 0.1μm to 0.5μm thick • Kept moist / surfactant • Extensive capillary network • Capillaries 7-10μm in diameter • Blood flow through capillaries is slowed • Ventilation
Applying your knowledge • Alf smoked for 40 years. He had a bad “smoker’s cough” and easily got out of breath. His health got worse so he went to see his doctor. The doctor said that he had emphysema. She explained that the coughing had damaged a lot of the alveoli in his lungs and reduced their surface area. • Explain as fully as you can why Alf got out of breath easily. • Alf’s illness got worse. He couldn’t walk very far and he had to breathe oxygen from a cylinder. Explain why.
Learning Outcomes • describe the features of the mammalian lung that adapt it to efficient gaseous exchange; • outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function of the rib cage, intercostal muscles and diaphragm;
Think!! • Why is the volume of oxygen that has to be absorbed and the volume of carbon dioxide that has to be removed in mammals so large? • Large organisms with large volume of living cells • Maintain a high body temperature • High metabolic rate • High respiratory rate
Mammalian Lungs • Structure of the lungs • Trachea • Rib cage • Intercostal muscles • Bronchi • Bronchioles • Alveoli (site of gaseous exchange) • 100μm – 300μm in diameter • 300 million in each lung
Revision Activity • Design a poster • Your poster should show the distribution of tissues and highlight the functions of each of the tissues • cartilage • Cilia • goblet cells • smooth muscle • elastic fibres
Learning Outcomes • 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 • describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the mammalian gaseous exchange system;
Cartilage • Flexible supporting material • Incomplete rings support the smooth muscle keeping the tubes open. • Prevents trachea and bronchi from collapsing when air pressure lowers during inhalation
Cilia • Synchronised movement to transport mucus towards the pharynx
Goblet cells • Produce the mucus that forms a thin layer over surface of the trachea and bronchi • The mucus is sticky and traps bacteria. Pollen and dust particles, the air is “filtered”.
Smooth muscle • Contraction of the smooth muscle allows the bronchioles to constrict. • This controls the flow of air to the alveoli.
Elastic fibres • Elastic fibres become stretched when the smooth muscle contracts, when the smooth muscles relaxes the elastic fibres recoil back into their original positions. • This dilates the bronchioles.
Difference in structure of Trachea, bronchi and bronchioles • Cartilage in trachea and bronchi keep airways open and air resistance low. • Trachea has c-shaped rings • Bronchi has irregular blocks • Bronchioles have smooth muscle which contracts and elastic fibres to control their diameter
Learning Outcomes • outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function of the rib cage, intercostal muscles and diaphragm;
Fill in the gaps Mammalian Lungs (1) • Two reasons why mammals require a large and constant supply of oxygen are (1) and (2). The main organs for gaseous exchange are the lungs, which are connected to the outside by a tube called the (3). This branches into two (4), one of which enters each lung.
Fill in the gaps Mammalian Lungs (2) • The actual site of gaseous exchange is in the alveoli, which have a diameter of (5) and have walls made of (6) which is very thin, being only (7) in thickness. The total number of alveoli for both lungs is around (8) giving them a very large surface area of about (9).
Fill in the gaps Gaseous Exchange in the alveoli (1) • Gaseous exchange occurs in the alveoli, with the gas called (1) moving into the blood and the gas called (2) moving in the opposite direction. The diameter of an alveolus is (3) and it is surrounded by squamous epithelial cells that are only (4) thick and so allow rapid (5) of gases across them.
Fill in the gaps Gaseous exchange in the alveoli (2) • Each alveolus is surrounded by a network of (6) that are around (7) in diameter, causing (8) within them to be flattened against their surface, thus improving the rate of exchange of gases between themselves and the alveoli.
Learning Outcomes • explain the meanings of the terms tidal volume and vital capacity; • describe how a spirometer can be used to measure vital capacity, tidal volume, breathing rate and oxygen uptake; • analyse and interpret data from a spirometer
Breathing Rate • Breathing refreshes the air in the alveoli so that concentration of O2 and CO2 remains constant
Lung Capacities • Tidal volume • The volume of air breathed in or out in a single breath • Residual volume • The amount of air that remains in the alveoli and airways after forced exhalation. • Vital Capacity • The volume of air that can be exchanged between maximum inspiration and maximum expiration
The effect of exercise on breathing is measured by calculating ventilation rate, which is the total air moved into the lungs in one minute. Ventilation rate = tidal volume X breathing rate • Ventilation brings about changes in lung volume, these changes can be ,measured by a spirometer.
Measuring Oxygen Uptake • If someone breathes in and out of a spirometer for a period of time, the carbon dioxide level increases to dangerous levels. • To avoid this, soda lime is used to absorb the carbon dioxide exhaled. • This means the total volume of gas in the spirometer will go down.
Measuring Oxygen Uptake • The volume of CO2 breathed out is the same as the volume of O2 breathed in. • This allows us to make calculations of oxygen used under different conditions.