Gas Exchange and Surface Area to Volume Ratio 3.1 + 3.2

• How does an organisms size relate to its surface area to volume ratio?

  The larger the organism, the lower the surface area to volume ratio.
• Surface area and volume of spheres and cylinders


  SphereSurface area= 4πr²Volume= 4/3πr^3CylinderSurface area= 2πrh + 2πr²Volume= πr²h
• How does surface area to volume ratio relate to metabolic rate?

  The smaller the surface area to volume ratio, the higher the metabolic rate.
• How might an organism adapt to compensate for a small surface area to volume ratio?

  -body parts become larger (eg elephants ears)-elongating shape-developing a special gas exchange surface
• Essential features of an exchange surface

  -large surface area to volume ratio-short diffusion distance-selectively permeable -maintains a steep concentration gradient
• Insect adaptions to prevent water loss

  1. Small surface area to volume ratio2. Waterproof exoskeleton made of chitin (polysaccharide)3. Spiracles (where gases can enter and exit - open and close to reduce water loss)This is why they can’t use their bodies as exchange surface
• Three main features of an insect's gas transport system

  1. Spiracles = holes on the body’s surface which can be open and closed to allow gases in and out2. Tracheae = large tubes extending through the body, supported by rings of chitin to prevent collapsing2. Tracheoles = smaller branches dividing off to reach to every single tissue to provide oxygen and remove carbon dioxide
• Process of gas exchange in insects

  First Method - Diffusion● Gases move in and out of the tracheae through the spiracles.● A diffusion gradient (as oxygen is used during respiration) allows oxygen to diffuse into the body tissue while waste CO2 diffuses out.● Contraction of muscles in the tracheae allows mass movement of air in and out.Second Method - Mass transport● Abdominal muscles contract and relax to move gases on massThird Method - Anaerobic Respiration● Produces lactic acid● Lowers water potential● Therefore water moves into cells via osmosis● Lower pressure in tracheoles so more air in
• Adaptations for efficient diffusion in insects

  1. Large number of trachioles2. Short diffusion distance (thin walls)3. Steep concentration gradient (use and production of oxygen and carbon dioxide)
• Why can't fish use their bodies as an exchange surface?

  -waterproof, impermeable outer membrane-small surface area to volume ratio
• Two main features of a fish's gas transport system

  Gills= supported by arches (multiple projections of gill filaments), stacked up in pilesLamellae= at right angles to gill filaments, increases surface area, blood and water flow across them in opposite directions (countercurrent exchange system)

  
• Explain the process of gas exchange in fish


  ● The fish opens its mouth to enable water to flow in, then closes its mouth to increase pressure. ● The water passes over the lamellae, and the oxygen diffuses into the bloodstream. ● Waste carbon dioxide diffuses into the water and flows back out of the gills.

  
• How does the countercurrent exchange system maximise oxygen absorbed by the fish?

  1. Water and blood flow in opposite directions2. Maintains a concentration gradient as water is always next to blood with a lower concentration of oxygen3. Along whole length of gill4. Enables 80% of oxygen to be absorbed
• Two types of fish

  Cartilaginous -no ventilation mechanism-have to keep swimming in order for oxygenated blood to flow over gills-parallel flowBony -water in through mouth-forced over gills-countercurrent flow
• Parallel flow graph

  
• Countercurrent flow graph

  
• Three adaptations of a leaf that allow efficient gas exchange

  1) Thin and Flat ( short diffusion distance)2) Many small pores on underside (stomata) to allow gases to easily enter3) Air spaces (spongy mesophyll) allow gases to move around leaf (facilitating photosynthesis)
• How do plants limit water loss while still allowing gases to be exchanged?

  Stomata regulated by guard cells to allow them to open and close as needed
• How do plants levels of respiration and photosynthesis differ?

  - During the day, levels of photosynthesis are higher- At night, levels of respiration are higher
• Structure of a leaf

  Waxy Cuticle: A waxy, waterproof layer which cuts down the water lost by evaporation and protects against parasitic fungiUpper epidermis: A single layer of cells that are transparent and contain no chloroplast allowing light to pass straight throughPalisade layer: Made up of palisade cells which contain chloroplasts, where most of the photosynthesis takes placeVein: Contains tubes called the xylem and phloem. The xylem brings water and salts to the leaf for photosynthesis. The phloem transports the dissolved foods awaySpongy mesophyll: consists of irregularly shaped cells with large air spaces between them allowing gas exchange (diffusion) between stomata and photosynthesising cellsLower epidermis: contains lots of tiny holes or pores called stomata at regular intervals which allow gases to diffuse in and out of the leaf

  
• Similarities and differences between gas exchange in plants and insects

  Similarities 1. Obtain the gases they need from the air by diffusion down a concentration gradient2. Movement of gases is controlled by pore- like structuresDifferences 1. Insects deliver air through tubes which aren't present in leaves2. Muscle contraction in insects can assist with movement of air whereas leaves cant
• Describe the pathway taken by air as it enters the mammalian gas exchange system

  Nasal cavity --> trachea --> bronchi --> bronchioles --> alveoli
• The lungs diagram

  
• Function of the naval cavity

  -Warms and humidifies -Goblet cells in the membrane secrete mucus which traps dust and bacteria
• Structure and function of the trachea


  -Wide tube supported by C-shaped cartlidge to keep airway open during pressure changes-Lined ciliated epithelial cells which move mucus towards the throat to be swallowed to prevent lungs from infecfion-Carries air to bronchi
• Structure and function of the bronchi

  -Supported by rings of cartilage -Lined by epithelial cells-Allow passage of air into the bronchioles
• Structure and function of the bronchioles


  -Narrower than the bronchi-Not kept open by cartilage so only have muscle and elastic fibres which contract and relax during ventilation -Allow passage of air into the alveoli.
• Features of the alveoli

  1. provide large surface area 2. wall of alveoli and wall of capillary are only 1-cell thick - short diffusion distance3. moist surface allows the gases to dissolve in water then pass in and out of the alveoli4. network of capillaries surround each alveolus5. concentration gradient between alveoli & capillary is high due to capillaries being narrow and blood flowing
• Pulmonary surfactant


  A mixture of phospholipids and proteins that coats the alveoli and prevents them from collapsing during exhalation.
• Process of inhalation


  -External intercostal muscles contract- Internal intercostal muscles relax- diaphragm contracts- ribs move upwards and outwards- diaphragm moves down-volume of the thorax increases
• Process of exhalation

  -External intercostal muscles relax- Internal intercostal muscles contract- diaphragm relaxes- ribs move downwards and inwards- diaphragm moves up-volume of thorax decreases
• Lung disease