3. Surface Area to Volume Ratio Flashcards
Do multicellular organisms have a large or small SA:V ratio?
Small
Do unicellular organisms have a large or small SA:V ratio?
Large
What do cells need to do to survive (in terms of importing/exporting products)?
Import molecules and expel waste products through its plasma membrane
If a cell’s surface area is too small compared to its volume…
not enough of the necessary molecules can get in, and not enough waste (including heat) can get out
Why is a large SA:V ratio beneficial?
- Shorter diffusion pathways: takes less time (& energy if active transport) for molecules to move in/out of cells
- Easier to generate concentration gradients: makes diffusion more efficient
Why would a large SA:V ratio not be beneficial?
- Small, warm-blooded mammals lose heat very quickly: need to eat almost constantly
- Desert plants would lose water quickly with flat leaves, so they minimise their SA:V ratio to conserve water
Unicellular organisms exchange materials by _____ with their environment
diffusion
A large SA:V ratio gives a ______ for diffusion
short distance
Most large, multicellular organisms have specialised…
exchange systems
Adaptations of polar bear (there are 4)
- Round structure: reduces SA to prevent heat loss
- Tiny ears - prevents heat loss
- Black skin
- Hollow fur - traps air as an insulating layer
What does cell division allow for?
Cell differentiation
Specialised functions
More complex multicellular life
Cells compartmentalise - what does this mean?
They use membranes to carry out metabolic processes. In eukaryotes, these are called organelles.
What are organelles made of?
Membranes. This maximises the SA for reactions.
What do some organs (eg. intestines) do?
Fold up to maximise SA:V ratio, making absorption of food molecules more efficient
Adaptations of roots
They are long and branched, with root hairs on the cells to maximise the SA for water uptake
What else do multicellular organisms need to exchange apart from nutrients and gases, and why is this important?
Heat!
This helps to maintain bodies at a constant temperature at a certain range, regardless of external temperature.
2 factors that influence heat exchange
Size and shape
Rate of heat loss is dependent on the ______ of the organism
surface area
Effect of size on heat exchange
Large organism = large volume = smaller SA relative to its size, so heat loss is harder.
Small organism = small volume = high SA. Since there is a high SA where heat exchange can happen, these organisms need to have a HIGHER METABOLIC RATE to generate more heat for it to stay warm
Effect of shape on heat exchange
More compact shape = small SA = no need for high metabolic rate to minimise heat loss from the body
Less compact shape = high SA = high metabolic rate to produce more heat to maintain body temp
Small desert mammals
High SA:V ratio: fast loss of water. To control this, they develop smaller kidneys to produce less urine.
Elephant
Low SA:V ratio: hard to cool down during hot months. Large ears to increase SA.
