Which factors change how quickly substances cross into or out of cells?
Reveal answer
Surface area to volume ratio, diffusion distance, temperature and concentration gradient.
Key words: surface area · distance · temperature · gradient
2(d) MOVEMENT OF SUBSTANCES INTO AND OUT OF CELLS · RECALL
2.16 Factors affecting movement into and out of cells
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What is meant by the term surface-area-to-volume ratio?
Reveal answer
Surface area divided by volume, expressing exchange area relative to internal volume.
Key words: surface-area-to-volume ratio
What is meant by the term diffusion distance?
Reveal answer
The path length particles must travel across an exchange barrier.
Key words: diffusion distance
What is meant by the term exchange surface?
Reveal answer
A specialised boundary across which substances move.
Key words: exchange surface
What is meant by the term ventilation?
Reveal answer
Movement of a medium such as air over an exchange surface.
Key words: ventilation
What is meant by the term perfusion?
Reveal answer
Flow of blood through vessels supplying a tissue or exchange surface.
Key words: perfusion
Rate factors and biological adaptations, Surface area. Effect on movement rate? Biological example?
Reveal answer
Effect on movement rate: Larger area increases total movement per unit time. Biological example: Many alveoli; villi and microvilli; root hairs.
Key words: Surface area
Rate factors and biological adaptations, SA:V ratio. Effect on movement rate? Biological example?
Reveal answer
Effect on movement rate: A larger ratio provides more exchange area relative to demand. Biological example: Small cells and flattened exchange cells.
Key words: SA:V ratio
Rate factors and biological adaptations, Distance. Effect on movement rate? Biological example?
Reveal answer
Effect on movement rate: A shorter pathway increases rate. Biological example: One-cell-thick alveolar and capillary walls.
Key words: Distance
Rate factors and biological adaptations, Concentration gradient. Effect on movement rate? Biological example?
Reveal answer
Effect on movement rate: A steeper difference increases net rate. Biological example: Blood flow and ventilation maintain oxygen gradients.
Key words: Concentration gradient
Rate factors and biological adaptations, Temperature. Effect on movement rate? Biological example?
Reveal answer
Effect on movement rate: Higher kinetic energy usually increases diffusion rate. Biological example: Faster molecular movement within a safe range.
Key words: Temperature
True or false, and why? “A larger organism has less surface area.”
Reveal answer
False. It has more total area, but less surface area relative to its volume.
True or false, and why? “Surface area and SA:V ratio mean the same thing.”
Reveal answer
False. Area is an absolute quantity; SA:V relates it to volume.
True or false, and why? “Thin surfaces create a steeper concentration gradient.”
Reveal answer
False. Thinness shortens distance; flow or consumption helps maintain the gradient.
True or false, and why? “Higher temperature always benefits exchange in organisms.”
Reveal answer
False. Extreme temperature can damage cells and proteins despite faster particle motion.