C E L L S

C E L L S Q&A
Surface Area to Volume Ratio - (correct answer)The surface area to volume ratio (SA:V)
is the amount of surface are per unit volume of an object. The larger the object, the
higher the surface area to volume ratio. The higher the SA:V ratio, the more efficiently
the organisms can exchange materials such as wastes and nutrients with its
environment.



Plasma Membrane Surface Area - (correct answer)The surface area of the plasma
membrane around a cell affects the rate of exchange that is possible between the cell
and it's environment. This means that smaller cells are more efficient in exchanging
matter with their environment as they have a larger SA:V ratio.



Increasing Cell Area - (correct answer)Three ways of changing the membrane surface
area without changing the volume of the cell are:

- Cell compartmentalisation

- A flattened shape

- Plasma membrane extensions


Cell Compartmentalisation - (correct answer)Cell compartmentalisation allows
eukaryotic cells to be much bigger than prokaryotic cells, because:

- It reduces the amount of exchange that needs to occur across the plasma membrane
to maintain an environment that is fit for all cell functions.

- It creates more space for membrane bound enzymes, allowing increased activity in
the cell.



A Flattened Shape - (correct answer)A flattened shape means that there is a larger
surface area to volume ratio allowing a higher rate of exchange through the plasma
membrane, and also reducing the distance that substances need to be transported to
and from and plasma membrane. Example: Red blood cells



Plasma Membrane Extensions - (correct answer)Plasma membrane Extensions
increase the surface area of the cell membrane without increasing the volume of the

, cell. This is done differently in different cells however often it is increased through small
hairs or finger-like extensions attached to the plasma membrane. Example: Some
animal cells have microvilli and some plants have root hairs which allow the plant
absorb more water and nutrients from the soil, also the small intestine has larger finer
like projections called villi.



Compartmentalisation - (correct answer)Cell compartmentalisation can occur in
eukaryotic cells and is the formation in the cytosol of specialised structures enclosed by
membranes, including the nucleus, mitochondria, endoplasmic reticulum, Golgi
apparatus, endosomes, lysosomes and chloroplasts. The membrane of these
membrane bound organelles enable each organelle to have a different composition
from the surrounding cytosol and other organelles.



Benefits of Compartmentalisation - (correct answer)- It allows enzymes and reactants
for a particular function to be close together in high concentrations and at the right
conditions so that processes within the organelles are very efficient

- It allows processes that require different environment to occur at the same time, the
same cell.

- It makes the cell less vulnerable to changes to its external environment, because
changes will affect the cytosol much more than the membrane-bound organelles.



Enzymes - (correct answer)A protein molecule that catalyses biochemical reactions


Organelles - (correct answer)Any specialised structure in the cytoplasm of a cell,
including the Golgi apparatus, mitochondria, endoplasmic reticulum, vacuole,
chloroplast and nucleus. Organelles have different functions within the cell and require
different internal conditions, including enzymes which catalyse the various reactions that
occur there.



Cell Wall - (correct answer)The cell wall is a rigid external structure surrounding the
plasma membrane around the outside of plant, fungi, algae and most bacteria cells
(animals do not have a cell wall). The cell wall of plants consist mostly of cellulose,
whilst fungal and bacterial cell walls consist largely of chitin and peptidoglycan. It's
function s to provide the cell with structure and protection and prevent lysis or bursting