Exchange - Size and Surface Area Flashcards
Organisms need to exchange substances with their environment
- Cells take in oxygen (for aerobic respiration) + nutrients
- Cells excrete waste products including co2 + urea
- Organisms exchange heat with surroundings to keep at a constant temp
Surface area to volume ratio
This is how much of the surface is exposed compared to volume.
The higher the SA:V, higher rate of exchange
More of the organisms surface is exposed compared to volume
Exchange in single celled organisms
Single celled organisms do not need specialised exhange organs and mass transport systems. Substances move into their cells through the cell surface membranes via diffusion, this happens quickly. This is because there is a small distance for the substances to move across
Exchange in multi-cellular organisms
Multi cellular organisms require specialised exchange organs and mass transport systems. Larger animals have low SA:V. The distance between the outside environment and the cells in the organism is large. Diffusion would be too slow.
Mass Transport
Carries substances to and from individual cells in multi-cellular organisms
General adaptations of gas exchange surfaces
- Large surface area, increases rate of diffusionj
- Thin surface layer - usually one layer of epthilial cells. Short diffusion pathway. Increases rate of diffusion by decreasing distance over which it happens
- High conc gradient across gas exchange surface
Gas exchange in single celled organisms
- Gasses (O2, CO2) directly diffuse through outer surface
- Because large surface area + thin surface
- No need for gas exhange system
Gas exchange in multi-cellular organisms
- Fish
- Insects
- Plants
- Humans
Fish
Water contains less oxygen than air, therefore, fish haves special adaptations to gas exhange to ensure they get enough oxygen
- Water enters mouth of fish, then moves through gills
- Gills are made up of lots of thin plates called gill fillaments, which increase surface area
- Gill filaments are covered in tiny structures called lamellae which further increase SA
- Lamella have a thin surface and lots of blood capillaries
- Blood enters the lamellae in one direction and watere enters in the opposite direction. This is called counter current flow and maintains a high conc gradient of oxygen between water and blood. The conc of O2 in water is always more than blood, so O2 diffuses from water to blood
Insects
- Gas exchange occurs in tracheae
- Air enters trachea through pores on surface known as spiracles
- The trachea split into tracheaoles which have thin + permeable walls. They go to each cell
- Oxygen diffuses down its conc gradient, from air into trachea via spiracles then down tracheaoles to respiring cells
- CO2 diffuses down its conc gradient, from cells to tracheoles, then from tracheae to air via spiracles
- Insects use rythmic abdominal movements to move air in and out of spiracles
Tidal Volume
Volume of air in each breath
Ventilation rate
No. of breaths per min
FEV - Forced Expiratory Volume
max vol of air breathed out in 1 second
FVC - forced vital capacity
max vol of air forcefully breathed out after taking in deep breath
Spirometer
Machine used to measure vol of air breathed in and out. Can be used to work out tidal vol, ventilation rate etc
Residual air
Air in lungs which can not be expelled
Lung Diseases FAPE
Fibrosis
Asthma
Pulmonary Tuberculosis
Emphysema
Pulmomonary Tuberculosis
- Person infected with tubercuolsis bacteria
- Immune system cells form a wall around the bacteria in the lungs leading to formation of a hard tuberceles
- Tissue infected with tubercles dies. This damages gas exhange surface, reducing rate of gas exhange, reducing tidal volume. This means lower vol. of air can be inhaled in each breath, therefore, to ensure enough oxygen enters blood, person breaths faster, so increased ventilation rate
- Symptoms include persistant cough, coughing up blood and mucus, fatigue, shortness of breath + chest pain
Fibrosis
- Result of scarred tissue in the lungs. Caused by exposure to too much dust or asbestos
- Scarred tissue is thicker and less elastic than normal lung tissue
- Less elastic means lungs cannot expand as well as they normally do. Reduces tidal volume. Less air can be inhaled in each breath. So, person breaths faster to ensure that they get enough oxygen in blood, so higher ventilation rate. Also, lower FVC
- Scarred tissue is thicker meaning that the rate of gas exchange is reduced because rate of diffusion is reduced because thicker exhange surface so longer diffusion pathway
- Symptoms include: Chest pain, shortness of breath, fatigue, dry cough fatigue
Asthma
- Inflammation and irritation to airways (trachea, bronchi, bronchioles). Caused by allergic reaction to pollen, dust etc
- During asthma attack, smooth muscle lining in bronchioles contract, leading to production of lots of mucus.
- This leads to constriction of airways. Less air can be breathed in and out. This reduces tidal volume. Lower vol of air can be inhaled in per breath. So, person breatjs faster to ensure enough oxygen enters blood, therefore, higher ventilation rate. Lower FEV
- Symptoms include wheezing, tightning of chest, shortness of breath, fatigue
- Symptoms reduced by taking drugs in inhalers. Relax smooth muscle lining of bronchioles, less mucus production, clearing of airways
Emphysema
- Caused by smoking or long-term exposure to pollution.
- Foreign particles in air get trapped in alveoli
- This leads to inflammation which attracts phagocytes
- Phagocytes release an enzyme which breaks down elastin
- Elastin is an elastic protein in the alveoli walls which help the alveoli return to normal shape after inhaling air and exhaling air
- Loss of elastin means alveoli cannot recoil (return to normal shape) so cannot expel air therefore, air is trapped in alveoli
- Also, when the phagocytes release enzyme which breaks down elastin, this leads to damage of the alveoli walls. Therefore, damage to gas exhange surface, reducing surface area of alveoli / gas exhange surface, reducing rate of gas exhange. Lower tidal volume. Lower vol. of air inhaled in in each breath. Therefore, person starts to breath faster to ensure enough oxygen in blood, so higher ventilation rate
- Symptoms - shortness of breath, wheezing
Why is a common symptom of all lung diseases fatigue, weakness and tiredness?
- All lung diseases reduce rate of gas exchange
- Rate of diffusion of oxygen from alveoli to blood is lower
- Less oxygen absorbed into blood from alveoli
- Less oxygen recieved by respiring cells
- Rate of respiration drops
- Less energy released
Risk Factors
Factors which increase the chance of you actually getting the disease. e.g. smoking is a risk factor for cancer
