cell size Flashcards
(15 cards)
what is size and shape of cells depended on
the size and shape of cells vary greatly depending on the organism and the cell’s function.
* cells are limited in size by their ability to exchange substances with their envirnoment.
are cells small?
cells are typically microscopic.
cell shape
cells come in a variety of shapes are reflective of their functions.
for example;
* neurons - have a long axon, allowing eletrical signals to be trasferred over large distances quickly.
* red blood cells - concave shape, increases it’s surface area, allowing greater uptake of oxygen
1. bacteria can also come in many shapes.
changing shape
not all cells have a fixed shape. for example, some cells are able to move actively, and these self-propelled cells don’t have fixed shapes, because their outer boundary is their flexible plasma membrane. so as these cells move, their shapes change.
for example
* cancer cells
* white blood cells
* amoebas
(some cells have a rigid cell wall, which means that changing shape is impossible, but this doesn’t mean that they can’t move)
moving around - how do cells with a fixed shape move?
some cells can change shape as they move. how do cells with a fixed shape move? These cells are appendages such as cilia and flagella
flagella
whip-like cell organelles involved in movement; singular = flagellum
* the direction of motion for it is right
cilia
in eurkaryote cells, whip-like structures formed by extensions of the plasma membrane involved in synchronisied movement
* the direction of motion is left
why are cells small, Why are most cells microscopically small rather than one large macroscopic unit?
Cells need to exchange materials (nutrients in, wastes out) with their environment across the plasma membrane. This exchange must be efficient enough to support the cell’s metabolic needs, which are related to its volume.
SA:V ratio, What is the surface area to volume ratio (SA:V) and why is it important for cells?
The SA:V ratio is the amount of plasma membrane surface area available relative to the cell’s internal volume. A higher SA:V ratio allows for more efficient exchange of substances across the membrane relative to the cell’s needs.
Cube Example, Explain how the SA:V ratio changes as a cube-shaped cell increases in size.
As the side length (L) of a cube doubles, the surface area (6L
^2 ) increases by a factor of 4, while the volume (L^3) increases by a factor of 8. This results in a decrease in the SA:V ratio as the cell gets larger.
limit of cell size, How does the SA:V ratio limit cell size?
As a cell’s volume increases (leading to higher metabolic needs), the surface area needed for exchange doesn’t increase at the same rate. Eventually, the SA:V ratio becomes too low for efficient transport, limiting how large a metabolically active cell can be.
rate of movement, How does cell size affect the rate of nutrient and waste movement?
Generally, the rate at which nutrients enter and wastes leave a cell is inversely proportional to the cell size. Larger cells have slower rates of movement relative to their volume.
Compensation: Microvilli, How do some cells, like those in the small intestine, compensate for a decreasing SA:V ratio as they function in absorption?
They increase their surface area without a significant increase in volume by extensively folding their plasma membrane into structures called microvilli.
Compensation: Shape, How does the shape of an object or cell influence its SA:V ratio? (Think of the hand example).
Objects with more protrusions or extensions (like an outstretched hand compared to a fist) have a higher surface area for the same volume, leading to a higher SA:V ratio.
SA:V of Blood Cells, Red blood cells (small) and white blood cells (larger) are roughly spherical. Which would have a higher SA:V ratio, and what is the impact of this difference? (Use the formula SA:V ∝1/r)?
red blood cells, being smaller (smaller r), have a higher SA:V ratio. This is beneficial for their function of rapid oxygen uptake and release. White blood cells, with a lower SA:V ratio, are less focused on rapid diffusion across their membrane.
