2Material Needs...What sort of things do living things need to obtain from the environment?What sort of things do they need to remove from their cells?
3Organisms are differently adapted so gas exchange can take place whether it be in water or on land. In particular oxygen is needed to convert organic molecules into energy through the process of respiration.
4NB: Gas exchange is the process by which oxygen reaches cells and waste products are removed, don’t confuse with respiration which is energy production in cells.By what process does gas exchange take place?
5Diffusion and problem of size Diffusion occurs according to Fick’s Law:Rate of DiffusionSurface Area x concentration differencedistanceThink about this for a moment What does it mean?
6An organism’s requirements may be proportional to volume ...however diffusion is proportional to surface area
7organismlengthSA (m²)vol (m³)SA/vol(m-1)bacterium1 μm(10-6 m)6 x 10-1210-186,000,000amoeba100 μm(10-4 m)6 x 10-810-1260,000fly10 mm(10-2 m)6 x 10-410-6600dog1 m(100 m)6 x 1001006whale100 m(102 m)6 x 1041060.06
8As organisms get larger their volume to surface area increases meaning they cannot rely on diffusion alone as the diffusion path would be too long.
9Exchange in Protozoa Protozoa – single celled, hetrotroph, which does not have a cell wall.E.g. paramecium, amoeba(eukaryote)
10In small, unicellular organisms the surface area to volume ratio is so large that diffusion through the body surface is sufficient to supply their needs.An example of this is an amoeba where the cell membrane acts as the exchange surface, It is thin and moist so is efficient at its job
12Multicellular organisms are an aggregation of cells. Cells aggregate together to increase their size but decreases their surface area to volume ratioDiffusion path increasesMaterials are needed to be exchanged between different organs as well as the organism and the environment.So diffusion is no longer a viable process of exchange.
13Larger organisms therefore possess special surfaces for gaseous exchange, gills for aquatic environments, lungs for terrestrial environments.Gas exchange surfaces such as the gills of a fish, the alveoli in the lungs of a mammal, the trachae of an insect and the spongy mesophyll cells in the leaves of a plant are effective exchange surfaces.
14Exchange surfaces a large surface area a thin permeable surface Most are moist to allow a medium for gasses dissolve in before diffusiona mechanism to maximise the diffusion gradient by replenishing the source and/or sink.
15Systems that increase rate of Exchange large surface areasmall distancehigh concentration gradienthuman lungs600 million alveoli with a total area of 100m²each alveolus is only one cell thickconstant ventilation replaces the airFish gillsfeathery filaments with lamellaelamellae are two cells thickwater pumped over gills in countercurrent to bloodLeavessurface area of leaves of 1 tree is 200m², surface area of spongy cells inside leaves of 1 tree is 6000m².gases diffuse straight into leaf cellswind replaces air round leaves, and photosynthesis counteracts respirationThe large moist area for gaseous exchange is a region of potential water loss
16WormsSimple multicellular animals such as worms have a low oxygen requirementThey have an extremely low metabolic rate as they move very slowly.Oxygen and carbon dioxide are able to diffuse across the skin surfaceNo specialised gas exchange surface is required
17EarthwormElongated shape ensures a larger surface area to volume ratio enabling diffusion to take place.Low metabolic rate so does not require much oxygen.Mucus is secreted to keep the skin moist
18They possess a simple circulatory system: a closed blood system containing blood within vessels . The blood contains a respiratory pigment that transports oxygen.Oxygen is carried to the cells whilst carbon dioxide is transported in the opposite direction, thus maintaining the diffusion gradient at the respiratory surface.
19FlatwormsFlattened shape increases the SA: V and ensures a short diffusion path for exchange.Lives in aquatic environments
20Fish Fish are more active In fish gaseous exchange happens at the gill.At the gill a specialised pumping mechanism pumps a one way current of water over the surface.
21Gills are made up of many folds providing a large surface area. The density of the water keeps the gills from collapsing in on themselves which would reduce surface area.Gills are made up of many folds providing a large surface area.Fish can be further classified into two groups according to the material that makes up their skeleton:Cartilaginous fishBony Fish
22Cartilaginous fish Skeletons are made entirely of cartilage. Normally live in the sea e.g. sharkCharacterised by five gill clefts that open at five gill slits.Gas exchange involves parallel flow.Therefore blood travels through the capillaries in the same direction as the sea water.This is relatively inefficient as a diffusion gradient is not maintained.
23Bony Fish Internal skeleton made of bone Gills are covered by the operculumGas exchange involves Counter current flow.Blood in the capillaries flow in the opposite direction to the water flowing over the gill surface.This is more efficient as the gradient is maintained and exchange is able to happen over the whole gill surface
25Water is a dense medium with a low oxygen content To increase efficiency, it needs to be forced over the gill filaments by pressure differencesThis maintains a continuous, unidirectional flow of waterSo how does a fish do this?
26A lower pressure is maintained in the opercula cavity than in the bucco-pharynx. The operculum acts as a valveIt also acts as a pump drawing water over the gill filaments.The ventilation mechanism for forcing water over the gill is:mouthOpensoperculumClosesFloor of buccal cavityloweredvolumeincreasespressuredecreasesWater flows in
27Compared with parallel flow, counter current flow increases efficiency because the diffusion gradient between the adjacent flows is maintained over the whole surface. Blood flows between the gill plates under pressure in the opposite direction the blood in the capillaries.The blood always meets water with higher oxygen content than itself.It removes 80% of the oxygen from the water.This high level of extraction is important as there is 25% less oxygen in water than in air.
28Terrestrial Vertebrates What classes does this include?Amphibians, reptiles, birds and mammalsTerrestrial vertebrates have adapted for exchange with air, a less dense medium, instead of water, so have internal lungs.Internal lungs minimise loss of water and heat.
29AmphibiansThis was likely the first vertebrate group to colonise the land.They have lungs for use on land but in water gas exchange occurs through diffusion as they have permeable moist skin which acts as a respiratory surface.Tadpoles have gills for use in water.
30How then do frogs sit at the bottom of a pond for hours on end? Can use its skin as a respiratory surface but ONLY when it is inactive
31Reptiles and Birds Reptiles and birds have more efficient lungs than amphibians.Reptiles:Ribs protect the inner organs and provide ventilation to the lungs.Tissues in lungs provide a greater surface area.
32Birds:Large volumes of oxygen are needed for flight.ventilation of the lungs are assisted by air sacsthe action of flight muscles ventilate the lungs.
34Ventilation What is ventilation? Why do we need it? Ventilation is movement of air into and outside the bodyWhy do we need it?
35So what is the respiratory system???? The respiratory system includes everything we use to breath and supply our bodies with oxygen.We breath air intoOur lungsOxygen is then transferred into the bloodBlood then takes the oxygen around the body supplying vital organs and limbs with oxygen
38AlveoliSingle layer of flattened epithelial cells Capillaries run close by (1 cell thick) Layer of elastic tissue holds them together Secrete surfactant to stop alveoli collapsing SIMPLE DIFFUSION – oxygenated air in alveoli; deoxygenated blood in capillaries
39Gaseous exchange in the alveoli CO2 moves from the blood into the alveoli (alveolar air)O2 moves from oxygen-containing air, across to the red blood cells (tidal air)
40Ficks Law How does this apply to alveoli? Rate of DiffusionSurface Area x concentration differencedistanceHow does this apply to alveoli?Large surface area – ‘grape’ like structure of alveoliShort diffusion distance – alveoli are 1 cell thickConcentration gradient – continuous blood flow maintains gradient on capillary side; air in the alveoli is constantly refreshed
41Breathing… INHALING Diaphragm contracts and lowers Chest cavity volume increasesPressure in the lungs decreasesAir is drawn in
42Breathing… EXHALING Diaphragm relaxes and moves up Chest cavity volume decreasesPressure in the lungs increasesAir is forced out
43Different types of lung capacity Tidal volume:Is the amount of air you breath in or out with each breathInspiratory capacity:is the most air you can breath in after breathing out normally.Expiratory reserve volume:Is the most air you could force out after breathing out normallyVital Capacity:Is the most air you could possible breath in or out in one go.Residual VolumeIs the amount of air left in your lungs after you’ve breathed out as much as possible.A SPIROMETER is used to measure these
44InsectsInsects have a relatively inefficient, open circulatory system with no vessels to carry oxygen to different parts of their body.A centralised respiratory system, such as lungs, would not meet the respiratory demands of the insect's cells.Insects have evolved a very simple tracheal system that relies on a network of small tubes that channel O2 directly to the different parts of the body
45The tracheal system is composed of chitin-ringed tubes called tracheae these connect directly to the air through openings in the body wall called spiracles.The tracheae are reinforced with rings of chitin, the same material that makes up the exoskeletonSmall inactive insects rely solely on diffusionBigger active ones may ventilate the tracheae
51Xeromorphic adaptations in flowering plants Xeromorphic adaptations reduce water loss from aerial partsThicker CuticlesReduction in leaf sizeCurling or rolling of leavesNumber of stomataEpidermal hairs
52Hydrophytes Grow where water freely available: in, around or on ponds lakes and streamsSome live completely submerged:Canadian Pond weed (Elodea sp.)Water Milfoil (Myriophyllum sp.)
54These leaves have special adaptations: Some Hydrophytes like water lilies are rooted to bottom, leaves float on surfaceThese leaves have special adaptations:Stomata on upper surfaceNo stomata on lower surfaceElongated lignified cells (sclerids) stop leaves rolling upThick palisade mesophyll
56Stomata Opening: Hydrogen ions (or products) leave the guard cells. Potassium ions enter the guard cells.Chloride ions subsequently enter the guard cells.The osmotic pressure of the cell increases (water potential decreases).Water enters the guard cells.The guard cells become turgid.Because of the construction of the cells, the stomata open.
57Closing:Potassium ions leave the guard cells.Chloride ions also leave the guard cells.The osmotic pressure decreases (water potential increases).Water leaves the guard cells.The guard cells become flaccid.Because of the construction of the cells, the stomata close.