Transcript Cell in its environment - Somerset Academy North Las Vegas

Cell in its
environment
Coulter
Diffusion
 The cell membrane is selectively permeable, which
means that some substances can pass through the
membrane while others cannot.
 Diffusion- is the process by which molecules move
from an area of higher concentration to an area of
lower concentration.
 Concentration- is the amount of a substance in a
given volume.
What causes diffusion?
 Molecules are always moving. As they move they
bump into each other.
 The more molecules in an area the more they will
collide.
 Collisions cause molecules to move away from each
other.
 The molecules will continue to spread out until they
are eventually evenly spread out throughout the area.
Diffusion of oxygen
 There is higher concentration of oxygen molecules in
water than inside the cell.
 The cell membrane is permeable to oxygen
molecules.
 Oxygen molecules diffuse from the higher
concentration to lower concentration
Osmosis!!
 Osmosis- is the diffusion of water molecules through a
selectively permeable membrane
 Because cells cannot function properly without
adequate water, many cellular processes depend on
osmosis.
Osmosis and diffusion
 In osmosis water molecules move by diffusion from an
area where they are highly concentrated through the
cell membrane to an area where they are less
concentrated.
Effects of osmosis on plants
 Plant cells are enclosed by a rigid cell wall.
 When the plant cell is placed in a hypotonic solution , it takes up
water by osmosis and starts to swell, but the cell wall prevents it
from bursting.
 The plant cell is said to have become "turgid" i.e. swollen and
hard.
 The pressure inside the cell rises until this internal pressure is equal
to the pressure outside.
 This liquid or hydrostatic pressure called the turgor pressure
prevents further net intake of water .
 Turgidity is very important to plants as it helps in the maintenance
of rigidity and stability of plant tissue and as each cell exerts a
turgor pressure on its neighbor adding up to plant tissue tension
which allows the green parts of the plant to "stand up" into the
sunlight.
Effects of osmosis in animals
 Animal cells do not have cell walls. In hypotonic solutions, animal
cells swell up and explode as they cannot become turgid
because there is no cell wall to prevent the cell from bursting.
 When the cell is in danger of bursting, organelles called
contractile vacuoles will pump water out of the cell to prevent
this.
 In hypertonic solutions, water diffuses out of the cell due to
osmosis and the cell shrinks.
 Thus, the animal cell has always to be surrounded by an isotonic
solution.
 In the human body, the kidneys provide the necessary regulatory
mechanism for the blood plasma and the concentration of water
and salt removed from the blood by the kidneys is controlled by
a part of the brain called the hypothalamus.
Effects of osmosis
Active transport
 Active transport describes what happens when a cell uses energy
to transport something.
 Active transport usually happens across the cell membrane.
There are thousands of proteins embedded in the cell's lipid
bilayer.
 Those proteins do much of the work in active transport.
 They are positioned to cross the membrane so one part is on the
inside of the cell and one part is on the outside.
 Only when they cross the bilayer are they able to move
molecules and ions in and out of the cell.
 The membrane proteins are very specific.
 One protein that moves glucose will not move calcium (Ca) ions.
 There are hundreds of types of these membrane proteins in the
many cells of your body.
Active transport
 Many times, proteins
have to work against a
concentration gradient.
That term means they
are pumping something
(usually ions) from areas
of lower to higher
concentration.