Gas exchange and adaptations PDF

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Exchange and transport Smaller organisms e.g. Amoeba have a lower energy demand than larger organisms e.g. Whale, so they don’t need special exchange surfaces. In amoeba (single celled organisms) they can uptake oxygen via DIFFUSION and do not need lungs. There are a few reasons why: - Metabolic activity of a single-celled organism is usually low, so the O2 demands and CO2 production is low = diffusion is enough to exchange these gases. o The distances these gases have to travel will be very small - SA:Volume ratio is large (because it’s very small, so its volume is very little however it has a big surface area) As organisms get larger, their surface area increases by power of 2, but volume increases by power of 3. Larger organisms e.g. Whales have specialised exchange surfaces to overcome this. Specialised exchange surfaces: 1. ↑ Surface area = more substances can be exchanged (e.g. villi, alveoli, root hair cells) 2. Thin layers = less diffusion distance (e.g. alveoli) 3. Rich blood supply = good blood flow ensures a constant steep diffusion gradient 4. Ventilation to maintain diffusion gradient – occurs for gas exchange in alveoli and gills (in gills its water carrying the gas)

Mammals:

Exchange and transport Nasal cavity: - Large SA - Good blood supply: warms air - Hairy lining: secretes mucous and traps dust/bacteria = prevents infection and damage - Moist surfaces = increases humidity of incoming air & reduces evaporation from exchange surfaces (there is a layer of water on alveoli which helps dissolve O2 and make it go into capillaries – don’t want this layer to get evaporated off) Trachea:  Carries clean, warm, moist air  Cartilaginous rings (stop trachea from collapsing when you breathe out)  The epithelium has cilia (little hair like projections which beat like a wave to move mucous back up into the throat) = any trapped bacteria will be coughed out or ingested  Surrounding epithelial cells there are some goblet cells = secrete mucous Bronchus Have incomplete cartilage Bronchioles Have smooth muscle. This muscle contracting helps the bronchiole to constrict. When the muscle relaxes, the bronchiole dilates  Important in asthma Alveoli: One cell thick - flattened epithelial cells. Also has collagen & elastic fibres (elastin) which help alveoli to stretch and recoil as air is breathed in. Adaptations: 1. Large SA: many alveoli 2. Thin layers: Alveolar epithelium and Capillary cells are both one cell thick 3. Rich blood supply: each alveolus has many capillaries and a constant flow of blood. 4. Good ventilation

Ventilation:

Exchange and transport 1. Inspiration: Active sucking of air into lungs via pressure gradient. a. Diaphragm contracts b. External intercostal muscle contracts = rib moves up and out 2. Expiration: Passive movement of air out of lungs a. Diaphragm relaxes b. External intercostal muscle relaxes = rib moves down and in

Measuring lung function:  Peak flow meter  Spirometry  Vitalographs Lung volumes: Tidal volume = Air moving in and out of lungs at rest Vital capacity = Volume of air inspired when taking deepest breath out & deepest breath in Inspiratory reserve volume = Extra air you can breathe in, AFTER the tidal volume Expiratory reserve volume = Extra air you can breathe out, AFTER the tidal volume Residual volume = volume of air in your lungs when you have exhaled has hard as possible. Total lung capacity = Sum of vital capacity + residual volume Ventilation rate = Tidal volume x Breathing rate (per minute)

Gas exchange in other organisms: 1. Insects

Exchange and transport a. They have a tough exoskeleton so they cannot absorb gas, and they cannot carry gas through their blood as they do not have Hb b. They instead have a system of tubes called Spiracles. These spiracles have openings along the thorax and abdomen (chest and tummy) of the insect. Air enters and leaves the system & it is controlled i. They need to control the water loss through these spiracles (limit it) c. More spiracles will open as the insect is moving or active. d. The spiracles split into tracheae. These are made of chitin. e. The tracheae split into tiny tracheoles which have no chitin i. These tracheoles will spread into the tissue and supply the respiring cells directly. ii. There is tracheal fluid at the end of tracheoles which prevents air from diffusing past  however when the insect is moving/active, it produces lactic acid and this fluid will move out of the tracheoles via osmosis = allows MORE oxygen to get to the tissue during exercise (as if the muscle is sucking the tracheal fluid which has lots of O2 dissolved in it). This sucking of fluid into muscles also lowers pressure in tracheoles which draws more air to move into them from outside air.

Some insects have extra adaptations to ↑ gas exchange: -

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Mechanical ventilation of tracheal system  via muscular pumping movements of the thorax/abdomen. Air is drawn into/forced out of the trachea due to change in pressures (due to change in volume of abdomen/thorax) Collapsible enlarged tracheae can act as air reservoirs & ↑ the amount of air moved through the gas exchange system

2. Fish a. Have ↑ O2 demand due to swimming b. They developed gills to extract O2 from water

Exchange and transport i. High SA, thin layers & rich blood supply c. The gill has a gill arch, where you have gill filaments which stack together. The gill filaments have gill lamellae (perpendicular) ↑ SA

Gill ventilation -

Water is a slower diffusion medium for gases than air Fish need to have a continuous water flow over gills even when they're not moving. o Whilst swimming this is easily done by keeping their mouth open and operculum o Some cartilaginous fish e.g. sharks just continually move to ventilate their gills (known as Ram movements), however most bony fish do not do this  Bony fish overcome this problem by:  Opening mouth and lower floor of buccal cavity = ↑ Volume  Water moves into mouth due to ↓ pressure in mouth  Now the opercular valve closes and opercular cavity expands = ↓ pressure in opercular cavity  Floor of buccal cavity moves up = ↑ Pressure = water moves over gills

Gill adaptations for effective gas exchange 1. The tips of adjacent gill filaments overlap = increases resistance to flow of water over the gill = longer time for gas exchange

Exchange and transport

2. Countercurrent flow of blood and water in gill  the blood and water move in OPPOSITE directions. a. This maintains a steep concentration gradient of OXYGEN and CO2 throughout the length of the gill. b. Freshest (most O2 rich) water meets most O2 rich blood (which is at slightly lower O2 concentrations – so there is diffusion), whilst the poorest O2 water meets blood with little O2, so there is still diffusion. Thus, there is a concentration gradient maintained throughout. c. If there was a parallel system (same direction movement) then eventually the blood and water would reach equal O2 concentrations (EQUILIBRIUM) and no more diffusion would occur.

Exchange and transport...