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Plasma Membranes
4. Membrane Transport
-Active Transport
-Cell size and shape
Active Transport
Moving molecules or ions against a concentration
gradient (one way)
Energy required – high numbers mitochondria
Occurs in intestines to absorb as much of the nutrient
molecules as possible
Occurs in cells to keep high K+ inside and high Na+
outside, and to expel metabolism wastes (eg H+)
Plants also do this eg seaweed example
Bulk Transport
Occurs when cells need to move
large quantities of materials into or
out of the cytoplasm at one time
Too large to pass out of the pores in
the plasma membrane
Large amounts of energy required
Two forms:
Endocytosis
Exocytosis
Endocytosis
Engulf solid and liquid
particles by extending
cytoplasm around the
particle, forming vesicles
Phagocytosis
WBC’s (macrophages) engulf
bacteria/foreign bodies to
defend against disease
Digested by lysosome
enzymes
Selective eg Amoeba & food
Pinocytosis
Cell’s plasma membrane
engulfs extracellular fluid
Eg fat droplets in small
intestine after a meal
Exocytosis
Used by secretory
cells to export
products eg glands
Used by cells to
remove harmful waste
Used to release
transmitter chemicals
from nerve cells
Exocytotic vesicles
often come from Golgi
apparatus
Diffusion, Cell Size and Shape
Many different cell types with different functions
Cell size is small
As it grows, volume (cytoplasm) to surface area
(membrane) ratio increases
Volume of cytoplasm determines waste removal
and supply requirements
Removal of wastes and supply of nutrients is
dependent on surface area size
So cell is limited in the size to which it can grow
Some cells have adapted to have multiple folds to
increase surface area
When cell size is too big for its input and output
needs, it has to divide
Cell Size & Shape Activity
In small groups (4-6), create 3 different sized
cubes
The lengths of the sides (of each cube) must
differ by at least 5cm
Calculate the surface area and volume of each
cube
Calculate the surface area:volume ratio of each
cube
What is occuring with increasing size of cube?
Would this continue to occur?
How does this relate to cell size and shape?
Small Intestine Villi
Have massively
increased surface area
to maximise
absorption of nutrients
from the small
intestine
Disease conditions
that damage villi
cause malabsorption
and nutrient
deficiencies
Plants have also
adapted in this way
(root systems)
Whole Class Activity
Measurement of Na and K
concentration inside and outside red
cells in blood
Outside cells – blood plasma
Inside cells – lysed red blood cells
Using a POCT device
How different are you expecting the
results to be? How would you explain
any differences?
Questions
What applications are there for this
information in real-life situations?
What advantages are there to many
small cells rather than one large
one?
Review questions (active transport)
BioZone questions (active transport)