Diffusion Flashcards
Diffusion is the spreading out of the particles of any substance in
solution, or particles of a gas, resulting in a net movement from an
area of higher concentration to an area of lower concentration.
Where does it happen in body
Some of the substances transported in and out of cells by diffusion
are oxygen and carbon dioxide in gas exchange, and of the waste
product urea from cells into the blood plasma for excretion in the
kidney
Why is diffusion efficient in unicellular organisms
A single-celled organism has a relatively large surface area to
volume ratio. This allows sufficient transport of molecules into and
out of the cell to meet the needs of the organism.
How is the small intestines adapted for diffusion
Role in the body:
Most absorption of digested food molecules into the bloodstream occurs across the wall of the small intestine.
How it’s adapted to its role:
It has a surface lined with specialised intestinal epithelial cells (millions of epithelial and 1000’s of villi\0 this increases SA
Only cell thick epithelial cell – this decreases diffusion distance
Each villus has a good blood supply – this maintains a concentration gradient
how is the alveolus adapted for gaseous exchange
role in the body:
Gas exchange between air in the alveoli and the blood, to supply cells with oxygen for aerobic respiration and to remove carbon dioxide
Millions of alveoli (singular: alveolus) which collectively provide a huge surface area - this increases SA
The wall of each alveolus is one cell thick ( short diffusion distance
with a moist lining( gases dissolve in the moisture helping them to pass across the gas exchange surface
and excellent blood supply - this maintains a concentration gradient
Ventilation is the process that moves air into and out of the alveoli.
ventilation must be sufficient to create a high partial pressure of oxygen in the alveoli
Fish gills how are they adapted
Role in the body:
Gas exchange between water flowing through the gills and the blood, to supply cells with oxygen for aerobic respiration and to remove the waste product carbon dioxide
Each gill is made from lots of smaller plates called filaments, which themselves are covered in projections called lamellae – this increases SA
Dense capillary network ensures a good blood supply which flows in the opposite direction to water passing through the gills – this maintains a concentration gradient
Thin surface layer to minimise diffusion distance
concentration oxygen in water higher in blood so much oxygen possible diffuses in
Roots hair cell
Role in the plant:
To absorb water and mineral ions (such as magnesium and nitrate ions) from the soil and anchor the plant
The root network is highly branched - this increases SA
The surface of the roots are covered in root hair cells, which have a specialised structure with root hair projections – this increases SA
Leaves
role in plant :
Role in the plant:
The leaves contain most of a plant’s photosynthetic cells
Photosynthesis requires efficient gas exchange between air surrounding the leaf and the photosynthetic cells, whilst minimising water loss
stomata are tiny openings that predominantly cover the lower side of the leaf, allowing air to circulate inside the leaf – this decreases diffusion distance for carbon dioxide and oxygen
The lower layer of the leaf is made from spongy mesophyll cells which allow air to circulate inside the leaf
