Slides in this set
Substances can get into and out of cells via three methods. These are:
Diffusion the net movement of molecules along a concentration gradient i.
e. from an area of high concentration to an area of low concentration.
Osmosis the net movement of water molecules from a dilute to a
concentrated solution through a partially permeable membrane.
Active Transport the net movement of molecules against a concentration
gradient through a partially permeable membrane. This process requires
ATP energy from respiration and involves carrier proteins in the cell
Exchange of Gases in the Lungs
· The main job of the lungs is to exchange oxygen , needed
for aerobic respiration, and carbon dioxide a waste
product of respiration with the atmosphere.
· The lungs are well adapted to their job as they contain
millions of alveoli.
· Oxygen diffuses into the capillaries surrounding the
alveoli and carbon dioxide passes out of the blood into
Below are the features of the lungs that
make them well adapted to their job:
Has millions of alveoli which provides a large
Has very thin cell walls which provides a short
diffusion pathway into the blood.
Rich blood supply provides a steep concentration
gradient for diffusion which means the rate of
diffusion will be quicker.…read more
Exchange in the Gut
· The food we eat is digested into small, soluble
molecules in the gut.
· In the small intestine these molecules are
absorbed by the blood.
· Food can be absorbed either by diffusion
(primarily used) or active transport. (Active
Transport is only used when there is a higher
concentration of food molecules in the blood
than in the small intestine.)
· The small intestine has finger like projections
Below are the features of the small
intestine that makes it well adapted to its
Villi increase surface area for absorption.
Thin cell walls provide short diffusion
pathway into the blood.
Rich blood supply gives a steep
concentration gradient for diffusion.…read more
Exchange of Materials in other Organisms
· In the exam you may be asked
questions about exchange in
other animals such as fish or
· But don't worry all you need to
know are the basic adaptations
that will be seen whenever gas or
solute exchange is important.
These are :
A large surface area.
A rich blood supply.
Short diffusion pathway ( thin cell
Exchange in Plants
· Plants exchange gases through
· Leaves have stomata on their
underside which gases diffuse
into and out of.
· Leaves are flat and thin so there
is a large surface area and short
pathway for diffusion.
· Water and minerals are taken up
through the roots.
· Root hair cells give a large surface
area for osmosis and active