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| Frage | Antworten |
| Give some examples of things that need to be exchanged between an organism and its environment. | Respiratory gases Nutrients Excretory products Heat |
| What are the two ways this exchange can take place? | Passively or actively |
| Give an example of each type of exchange | Passive - diffusion, osmosis Active - active transport |
| In terms of a surface area to volume ratio, what must it be for exchange to be effective and efficient? | The surface area of an organism must be larger compared to its volume (ie large sa:vol ratio) |
| Some organisms have a sa:vol ratio that is too large to ensure an efficient gas exchange rate (some cells too far away). What are the two features organisms may have evolved to overcome this problem? | - Flat shape so that no cell is ever far from the surface (e.g flatworm) - Specialised exchange surfaces with large areas to increase the sa:vol ratio (lungs and gills etc) |
| What are some of the features of a specialised exchange surface? | - large sa:vol - thin - partially permeable - movement of internal medium - movement of external medium |
| How can the relationship between these factors be expressed? (equation) | |
| Why are gas exchange surfaces often located inside an organism? | They are thin so easily damaged |
| What does this mean to organism needs? | Means of moving the external medium over the surface (means of ventilating the lungs in mammals) |
| What is the problem with all terrestrial organisms (live on land)? | Water easily evaporates from the surface of their bodies and they become dehydrated |
| What does this mean they need to do? | Conserve water |
| However what features of an efficient gas exchange surface contradict with this? | Thin + permeable surface |
| What two features do terrestrial organisms exhibit to reduce water loss? | - Waterproof coverings (in insects this is a rigid outer skeleton covered with a waxy cuticle) - Small s.a:vol ratio (minimise area over which water is lost) |
| This means that insects cannot use their body surface to diffuse gases in the same way as ______ ______ _________ | Single celled organisms |
| Instead they have developed an internal network of tubes called _______ | Tracheae |
| Why are the tracheae supported by strengthened rings? | To stop them collapsing |
| What do the tracheae divide into? | Smaller tubes called tracheoles |
| In which ways to respiratory gases move in and out of the tracheal system? | - Along a diffusion gradient - Ventilation |
| Explain how gases move through the tracheal system along a diffusion gradient | When cells respire they use O2 - O2 conc at end of tracheoles falls - O2 diffuses from atmosphere (high conc) to tracheoles (low conc) (diffusion gradient in opposite direction for CO2) |
| Diffusion in air is much quicker than in water. What does this mean? | Respiratory gases are exchanged quickly by this method |
| How does ventilation further speed up the exchange of respiratory gases? | Movement of muscles in insects can create mass movements of air in and out of the tracheae |
| Through which structures do gases enter and leave the tracheae? | Spiracles |
| The spiracles are open and closed by valves. What is allowed to happen when the spiracles are open? | Water is allowed to diffuse |
| So why do insects keep their spiracles closed most of the time? | To prevent water loss |
| What is a limitation of the tracheal gas exchange system? | Relies on diffusion - efficient diffusion requires a short diffusion pathway - this limits the size an insect can attain |
| Fish have a ____________ and ___ _____ outer covering | Waterproof and gas tight |
| Being relatively large they have a _____ sa:vol ratio | Small |
| This means their body surface is not adequate to supply & remove their respiratory gases. What is the name of the specialised internal gas exchange surface inside fish? | The gills |
| What are gills made up of? | Gill filaments |
| The gill filaments are stacked up in a pile. What structures are at right angles to the gill filaments? | Gill lamellae |
| What do gill lamellae increase? | The surface area of the gills |
| The position and arrangement of the gill filaments & lamellae mean that water flow over them and blood flow within them are in opposite directions. What name is given to this principle? | Contercurrent flow |
| What does the countercurrent exchange principle allow for? | Maximum possible gas exchange |
| Why is there a fairly constant rate of diffusion across the entire length of the gill lamellae? | |
| In plants, why is there a reduced need for gas exchange with the external air? | Plants respire and photosynthesise - the product of one is the reactant of the other |
| In which 2 ways is gas exchange in plants similar to gas exchange in insects? | - No living cell is far from external air - Diffusion takes place in gas phase (more rapid than if it were in water) |
| In addition, plants have a very _____ surface area compared to the volume of living tissue | Large |
| This means no specialised gas exchange system is needed. Where does most of the gas exchange in the plant happen? | The leaves |
| What are the three adaptations of the leaf that make it suitable for rapid diffusion? | - Thin and flat (large sa:vol) - Many small pores (stomata) - Many interconnecting air spaces (throughout the mesophyll) |
| Each stomata is surrounded by a pair of what? | Guard cells |
| What can these cells do? | Open and close the stomatal pore and therefore control the rate of gaseous exchange |
| Why is this important? | Terrestrial organisms lose water by evaporation - plants have to balance conflicting needs of gas exchange and control of water loss |
| How do they use the stomata to do this? | By completely or partially closing stomata at times when water loss would be excessive |
| ________ is adequate for transport over short distances | Diffusion |
| Mammals however have a very small s.a:vol ratio and therefore require a mass __________ _______ | Transport system |
| Whether or not there is a specialised transport medium and/or a pump depends on what two factors? | - The surface area to volume ratio - How active the organism is |
| How many features of a mass transport system are there? | 5 |
| One feature is that there needs to be a suitable medium in which to carry materials. What is this medium in mammals? | Blood |
| Why is this medium usually a liquid based on water? | Because water readily dissolves substances and can be moved around easily |
| Another feature is that there is a closed system of what that contain the transport medium? | Tubular vessels |
| Why do the vessels form a branching network? | To distribute the medium to all parts of the body |
| Moving the transport within vessels requires a _______ difference between one part of the system and another | Pressure |
| In which two main ways is this achieved? | - Animals - muscular contractions - Plants - passive natural physical processes e.g evaporation of water |
| Give an example of another feature of transport systems that maintains mass flow movement in one direction? | Valves |
| What is the final feature? | A means of controlling the flow of the transport medium to suit the changing needs of different parts of the organism |
| Mammals have a _______ circulatory system | Double |
| What does this refer to? | The fact that blood passes twice through the heart for each complete circuit of the body |
| Why is this necessary? (in terms of pressure) | Because when blood is passed through the lungs, pressure is reduced If blood was to be passed round the body straight from the lungs it would do so very slowly So instead blood is returned to the heart to boost its pressure before being circulated to the rest of the tissues |
| For what two reasons is it necessary that substances are delivered to the rest of the body quickly? | - Mammals have a high body temp - Mammals have a high rate of metabolism |
| What are the three types of vessels that make up the circulatory system of a mammal? | Arteries Veins Capillaries |
| The transport system is used to move substances longer distances. What process is the final part of the journey into the cells? | Diffusion |
| Why is the final exchange from capillaries into cells rapid? | - Large surface area - Short distances - Steep diffusion gradient |
| Arteries, arterioles (smaller arteries) and veins all have the same basic layered structure. What is this structure? | Tough outer layer Muscle layer Elastic layer Thin inner lining Lumen |
| What is the function of the tough outer layer? | To resist pressure changes from both within and outside |
| What is the function of the muscle layer? | It can contract so that it controls the flow of blood |
| What is the function of the elastic layer? | Maintain blood pressure by stretching and springing back |
| Why is the thin inner lining (endothelium) smooth? | To prevent friction To allow diffusion |
| What is the lumen? | The central cavity in which the blood flows |
| Out of arteries, arterioles, capillaries and veins, which has the thickest muscle layer? | Arterioles |
| Why is this necessary? | Arterioles control the blood flow between arteries and capillaries - thick muscle layer required to constrict lumen and restrict blood flow |
| However arterioles have a thinner elastic layer than arteries. Why is this? | Because blood pressure is lower in the arterioles. In arteries it is important that the blood pressure is high so it reaches the extremities of the body - the elastic wall is stretched at each beat of the heart creating smooth pressure surges |
| In which vessels are valves present throughout? | Veins |
| Explain why there are valves in veins but no valves in arteries (except leaving the heart) | Veins - valves ensure blood doesn't flow backward which it might do because the pressure is so low. Veins are compressed when body muscles contract, increasing the pressure. Valves direct blood towards the heart Arteries - Blood under constant high pressure- doesn't tend to flow backwards |
| Why is the muscle, elastic and overall thickness of the walls in veins relatively thin? | Pressure is too low to create any risk of bursting or to create a recoil action |
| Give some features of capillary structure that make it suited to its function of exchanging metabolic materials between the blood and the tissues | Thin Numerous, highly branched Narrow diameter + permeate tissues Narrow lumen Spaces between lining (endothelium) cells |
| Why are the spaces between the endothelium lining cells useful? | They allow white blood cells to escape in order to deal with infection |
| What name is given to the liquid which bathes the tissues? | Tissue fluid |
| Tissue fluid is formed of blood plasma. Why is blood plasma forced out the capillary wall at the arteriole end of capillaries? | Due to a high pressure |
| Tissue fluid is formed by ultrafiltration rather than diffusion. Explain why | Larger molecules such as proteins and cells are too large to fit through the permeable capillary walls |
| Give some examples of ways by which materials are now exchanged between the tissue fluid and the tissues | Lipid diffusion - lipid soluble substances and gases Osmosis - water Facilitated diffusion - ions Active transport - glucose and amino acids |
| Why does tissue fluid return by diffusion at the venous end of the capillary bed? | Since the pressure of the blood is much lower because it has lost most of its plasma |
| Solutes (salts, carbon dioxide etc) enter the blood by diffusion ____ their concentration gradient | Down |
| Why has a water potential gradient been set up between the tissue fluid and the blood? | The blood has lost much of its water but regained soluble proteins so its water potential is low So water moves into the capillary down its water potential gradient |
| Not all the fluid that left returns. Where does this excess tissue fluid drain to? | Lymph vessels in the capillary beds |
| Lymph vessels have ____ walls | Thin |
| So tissue fluid can easily _______ inside, forming lymph | Diffuse |
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