single cell organisms rely on diffusion alone to get oxygen

multicellular organisms can’t because it will be way to slow so we have a specialised gas exchange system and a circulatory systems to get to those lungs but we need cells in our feet that have oxygen so thats why we have circulatory systems

surface area decreases as you increase in size —→ harder to get oxygen which is why they’re limited to size for unicellular organisms.

carbon dioxide and oxygen need to be exchanged in multicellular organisms because oxygen is needed for respiration and co2 is a waste product. co2 can’t stay in the body because it lowers ph level of blood and it takes up space. for plants, they need co2 for photosynthesis.

key terms:

ventilation - the active breathing, exhange of air between atmosphere and the lungs — taking oxygen in

gas exhange: exchange of gasses in the lungs between the alveoli and the bloodstream where its moving in the cells via passive diffusion

cell respiration: the release of energy (atp) from organic molecules it is enhanced by the precense of oxygen (aerobic)

to maximised diffusion of gases, gas exchange surfaces must have specialised adaptations.

these properties include: large surface area, permeable membranes, thin tissues and moist linings

1. large surface area

   more surface area you have, the more efficient it will be, these surfaces have some sort of feature that increases surface area, for example there are gill filaments in the fish which increase surface area. for humans whe have alveoli for increased surface area for gas exhange to occur

2. permeable membranes or openings that can easily get through

   membrane has to be permeable so diffusion can occur. where gas exchange can occur, the gas will actually pass it. it is one cell thick so it makes it easy for gasses to go through that. for plant cells, because they’re cell wall is thick, they have stomata in thier leaves for gas exhange.

3. thin tissues

   physical distance they have to transfer from, makes it easier as distance is shorter

   for example, alveoli has flattened cells in shape

4. moist linings

   gas exchange is easier when oxygen or co2 is dissolved in a liquid because they can diffuse across surface easier. therefore gas exchange surfaces are moist to increase rates of diffusion. in alveoli , there is a thin layer of liquid inside of their leaves to mantain a very moist environment. its humid inside like a sauna !!

our bodies rely on diffusion, for diffusion to occur we need a concentration gradient, from high concentration to low concentration. our body needs to make sure that those conc gradients can occur so diffusion can continue going.

for example, in human lungs, alveoli are surrounded by blood making that conc gradient and the continual blood flow brings in co2 all the time and bcs its low in o2, o2 can easily diffuse in our blood. we also breathe, so that constant inhale and exhale of air allow for that constant change of concentration gradient.

another example of this is in gills in fish. so the fish drink water, goes across the gills and go to the back, and that constant inhale and exhale of water, it allows for a concentration gradient as it is a dense network of cappilaries

ventiliation/breathing

air enters the ventilation system through the nose or mouth and then passes down the trachea

the trachea then divides into 2 bronchi. bronchi also have walls strengthened with cartilage. each bronchus leads to each lung

inside the lunhs the bronchi divide repeatedly to form a tree-;like structure of naarrower airways. thses are called bronchioles

at the very end of the narrowest bronchioles there are there

adaptations of mamillian ungs

presence of surfacent - surfacent helps to lower surface tension and keep lungs moist and stop collapsing

bronchioles - smooth muscle that can expand and open up the diameter of the chronioles when we need to take in more air for example when we’re excerciding

extensive capillary beds - every aveolus is surrounded by a netwrok of capillariies which allow for maximum gas exhange between the lungs and the blood

high surfacer areas- lots of aveoli increases the surface area of the lungs and proicde a large surface for gas exchange to occur