Topic 8 Flashcards Preview

GCSE Edexcel Biology grade 9-1 course, topics 6-9 > Topic 8 > Flashcards

Flashcards in Topic 8 Deck (133)
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what must all organisms do?

take in substances that they need from the environment and get remove any waste products


why do cells need oxygen?

for aerobic respiration which produces carbon dioxide as a waste product


how do oxygen and carbon dioxide move between cells and the environment?

by diffusion


how is water taken up by cells?

by osmosis


what substances diffuse with water in animals?

food molecules (the products of digestion) and mineral ions


what are some examples of food molecules which diffuse with water in animal cells?

glucose and amino acids


what are three substances which organisms exchange with the environment?

oxygen, water and urea


where does urea diffuse from cells to? and why?

urea diffuses from cells to the blood plasma for removal from the body by the kidneys


what does an organism's ease to exchange substances with its environment depend on?

the organism's surface area to volume ratio (SA:V)


what does a ratio show?

how large one value is compared to another


how does an organism's SA:V vary with the size of the organism?

the larger an organism is, the smaller its surface area is compared to its volume


what is the equation for the area of a surface?

length x width


what is the equation for a volume of a block?

length x width x height


in single-celled/ unicellular organisms, how do substances diffuse into/ out of the cell?

the gases and dissolved substances can diffuse directly into/ out of the cell across the cell membrane because the cells have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of the cell


how do multicellular organisms diffuse/ exchange substances to supply to the volume of the organism?

multicellular organisms need exchange surfaces for efficient diffusion and a mass transport system to move substances between the exchange surface and the rest of the body. this is because multicellular organisms have a smaller surface area compared do to their volume which makes it difficult to exchange substances to supply to their entire volume across their outside surface alone.


what are alveoli?

an exchange surface found in the lungs of mammals which are well-adapted for the efficient exchange of oxygen and carbon dioxide. they are in the form of small "air sacs"


how are gases exchanged in the lungs?

by diffusion


what three factors affect the rate of diffusion of any substance?

•concentration difference / concentration gradient
• surface area


how can distance affect the rate of diffusion?

substances diffuse faster when the substances don't have to move as far


how can concentration gradient affect the rate of diffusion?

substances diffuse faster if there's a large difference in concentration between the area the substances are diffusing from and the area the substances are diffusing to. this is because there is a greater concentration of particles to move from one side of the membrane to the other.


how can surface area affect the rate of diffusion?

the greater the surface area, the more surface there is available for the molecules to move across so the faster the molecules can travel from one side to the other.


what is the function of the lungs?

to transfer oxygen to the blood and to remove waste carbon dioxide from the blood


where does gas exchange happen in mammals?

in the lungs, in the alveoli


what is the singular form of "alveoli"?



describe the process of gas exchange in the alveoli

- blood returning from the rest of the body and arriving at the lungs contains lots of carbon dioxide and a small amount of oxygen. this maximises the concentration gradient for the diffusion of the gases

- oxygen diffuses out of the air in the alveoli where the concentration of oxygen is is high and into the blood where the concentration of oxygen is low. carbon dioxide diffuses in the opposite direction to be breathed ou


how are the alveoli specialised to maximise the diffusion of oxygen and carbon dioxide?

•have a moist lining for dissolving gases
•have a good blood supply to maintain the concentration gradient of oxygen and carbon dioxide
•have very thin walls which minimises he distance that the gases have to move
•the alveoli have a huge surface area


what is the surface area of alveoli in humans?

75 m²


which cell membranes do oxygen and carbon dioxide diffuse across in the lungs?

the membranes of the cells which make up the walls of the capillary and alveolus.


what is Fick's Law?

the rate of diffusion ∝ (is proportional to)

surface area x concentration difference
thickness of membrane


what does Fick's Law describe?

the relationship between the rate of diffusion and the factors that affect the rate of diffusion