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Gas exchange 1. Across the body surface of a single-celled organism 2. In the tracheal system of an insect (tracheae and spiracles) 3. Across the gills of a fish (gill lamellae and fi laments including the countercurrent principle) 4. By leaves of dicotyledonous plants (mesophyll and stomata). Unicellular organisms Unicellular Organisms do not have specialised gas exchange surfaces. Instead gases diffuse in through the cell membrane. The smaller something is, the smaller the surface area is but, more importantly, the bigger the surface area is compared to its volume. In other words, unicellular organisms have a large surface area to volume ratio. They are therefore efficient when it comes to exchanging gases through their membrane. Also, all parts of the organism are supplied with oxygen because the diffusion path is short. Gas exchange in Insects Insects have no transport system so gases need to be transported directly to the respiring tissues. There are tiny holes called spiracles along the side of the insect. Insects The spiracles are openings of small tubes running into the insect's body, the larger ones being called tracheae and the smaller ones being called tracheoles. The ends of these tubes, which are in contact with individual cells, contain a small amount of fluid in which the gases are dissolved. The fluid is drawn into the muscle tissue during exercise. This increases the surface area of air in contact with the cells. Gases diffuse in through the spiracles and down the tracheae and tracheoles. Ventilation movements of the body during exercise may help this diffusion. The spiracles can be closed by valves and may be surrounded by tiny hairs. These help keep humidity around the opening, ensure there is a lower concentration gradient of water vapour, and so less is lost from the insect by evaporation. Gas exchange in Fish A Bony Fish Lamellae Secondary Lamellae Gill Plates Counter Current Mechanism http://www.kscience.co.uk/animations/anim_3.htm Gas exchange Similarities Differences Dissection C.O.W!! Match the correct letter with the correct part; 1.Operculum 2.Buccal cavity 3.Gill arch 4.Opercular cavity In today’s lesson… 1. Identify the buccal cavity, opercular cavity, operculum and gills on a fish. 2. Recall the benefits of countercurrent to fish 3. Carry out a dissection Fish head dissection In pairs dissect the fish head. You must identify and remove the; Operculum Gill arch Identify the primary lamellae Use a light microscope to identify the secondary lamellae How would the pressure and volume of the buccal cavity and opercular cavity change as the fish swims through the water? Things to consider• Buccal cavity open and fills with water •Buccal cavity closes and water is forced over gills into opercular cavity •Operculum opens and water is forced out The graph shows the change in pressure in the mouth (buccal) cavity of a fish during ventilation of the gills. +0.1 Pressure / 0 kPa –0.1 A 0.2 0.4 0.6 0.8 1.0 B Time/s ) Calculate the rate of ventilation per minute. Show your working. Rate per minute ........ (2) (i (ii) Explain what causes the fall in pressure between points A and B. ........................................................................................................................... ........................................................................................................................... (1) The diagram shows the arrangement of the respiratory surface in the lungs of birds. Trachea Blood capillaries around bronchioles Bronchi Network of bronchioles forming gas exchange surface Air sacs Lungs (i) Give one similarity and one difference between the gas exchange surface of a bird and that of a mammal. Similarity........................................................................................................... ........................................................................................................................... Difference.......................................................................................................... ........................................................................................................................... (2) The efficiency of diffusion is increased if there is: • • • A large surface area over which exchange can take place. A concentration gradient without which nothing will diffuse. A thin surface across which gases diffuse. Fick’s law Rate of diffusion α Area of surface x Difference in conc Thickness of surface Qu.. What conditions maximise the rate of diffusion?? Gas exchange in plants Ψ Cell Ψ Cell = Movement? Ψ Solute= Distilled water? Ψ Pressure= Animal cells? Plant cells? The diagram shows the potassium (K+) ion concentrations in the cells around an open and closed stoma in Commelina. The concentrations are in arbitrary units. (i) Explain how the movement of K+ ions accounts for the opening of the stoma. (ii) Explain how K+ ions are moved against a concentration gradient. (i) K+ ions move into guard cells; Water potential of guard cells becomes more negative; Water enters; How uptake of water causes stoma to open; (ii) Energy/respiration/ATP/active transport; Intrinsic proteins/carriers/channels.