diffusion Flashcards
What is diffusion?
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.
What does a bigger concentration gradient or a higher temp mean for the rate of diffusion?
Faster diffusion rate
How do substances move across the cell membrane?
Substances may move into and out of cells across the cell membranes via diffusion.
What kind of substances diffuse across cell membranes?
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.
What are some examples of molecules that can’t fit through the cell membrane?
Starch and proteins
What is a net movement?
An overall movement
How does SA affect diffusion?
The large the SA of the membrane the faster the diffusion rate because more particles can pass through at once.
Why do single celled organisms have large SA:V ratios?
To allow efficient transport of molecules in and out of the cell. gases & dissolved substances can diffuse directly in/out the cell across its membrane. The SA is large COMPARED to the volume so enough substances can be exchanged across the membrane to supply the volume of the cell - & short diffusion distance.
Why do multicellular organisms need an exchange surface?
For efficient diffusion. They have a smaller SA compared to their volume. So not enough substances can diffuse across their outside surface fast enough to supply their entire volume. So diffusion without an exchange surface would be very inefficient.
How are exchange surfaces adapted to maximise effectiveness in both plants and animals?
.Thin membrane - short diffusion distance
.Large SA - lots of substances can diffuse at once
Why do , surfaces and organ systems need to be specialised for exchanging materials in multicellular organisms?
In multicellular organisms, surfaces and organ systems are specialised for exchanging materials, to allow sufficient molecules to be transported into and out of cells for the organism’s needs.
How are exchange surfaces adapted to maximise effectiveness in animals?
. Lot’s of blood vessels - get stuff in/ out of blood quickly
. Gas exchange surfaces are often ventilated - air moves in and out e.g. alveoli
What is the function of the lungs?
to transfer oxygen to the blood and to remove the waste C02 from it.
How are the lungs adapted to meet their function?
Have lots of alveoli where gas exchange takes place
How are the alveoli adapted to maximise the diffusion of Oxygen and Carbon dioxide?
. Enormous SA
.Moist lining for dissolving gases
. Very thin walls
. A good blood supply
What is the inside of the small intestine covered in?
millions and millions of tiny little projections called villi.
What do villi do?
increase SA in a big way so that digested food is absorbed much more quickly in the blood
How are villi adapted for their purpose?
.single layer of cells - decrease diffusion distance
.good blood supply to assist quick absorption
.covered in micro villi - increases SA
How does carbon dioxide diffuse?
C02 diffuses into the air spaces within the leaf, then into the cells where photosynthesis happens
How is the leaf adapted to allow easy diffusion?
The underneath of the leaf is an exchange surface. It’s covered in little holes called stomata which the carbon dioxide diffuses through.
How do oxygen and water diffuse?
Oxygen and water vapour diffuse out of the stomata (water vapour is lost from all over the leafs surface but most of it’s lost thru the stomata)
How do the guard cells control the size of the stomata (as in when do they do this)?
They close it if the plants is losing water faster than it’s being replaced by the roots - without the guard cells, the plant would soon wilt
What about the shape of the leaf improves its effectiveness as an exchange surface?
The leaf’s shape is flat so the SA:V ratio is increased so its more effective as an exchange surface.
How are the inside of the leaves adapted to be good exchange surfaces?
The walls of the cells inside the leaf form another exchange surface, the air spaces inside the leaf increase the area of this surface so there’s more chance for C02 to get into the cells
