Download 1 The Cell Membrane Exchanged Materials cytoplasm: the cell

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The Cell Membrane
Exchanged Materials
cytoplasm: the cell interior; a solution of many different substances in the cell interior
cytoplasm is surrounded by a membrane and sometimes a wall
in plants: cell wall and cell membrane
in animals: only cell membrane
wall and membrane enclose the cell like a wall encloses a room where the membrane would be the
paint
the cell is like a protected compartment
materials must enter the cell:
water – most important; many chemical reactions use hydrophilic molecules
oxygen – for releasing the energy needed chemical reactions
ions – like sodium, calcium, chloride, and potassium
carbon dioxide – for autotrophs to build food molecules
nutrients – like sugars and amino acids to supply energy and building material for cell
components
hormones- need access to the interior of cells to transmit messages
wastes- must exit
Membrane as Barrier
the membrane is selectively permeable
selectively permeable or semipermeable: only lets some, not all, materials
this means that membranes regulate the exchange of materials in a very specific way
not all molecules are equally soluble in a membrane
determined by polarity, size, and electric charge
can’t get in:
charged ions– the nonpolar phospholipid tails repel charged particles like sodium, potassium
big particles– they can’t fit through the membrane
larger uncharged polar molecules – amino acids, glucose, nucleotides
can get in:
small hydrophobic molecules – oxygen, nitrogen, carbon dioxide
small uncharged hydrophilic molecules— water, glycerol
phospholipid bilayer:
phospholipids: filter things in and out according size, charge, chemical makeup
fluid, not rigid, and move around proteins like ice cubes in a punch bowl
cholesterol:
within the phospholipid bilayer
keeps it fluid and liquid-like
transmembrane proteins:
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big and globular – tertiary structure
through the membrane or attached on outside
helps transport materials like ions and small polar molecules like amino acids and sugars in and out of
the membrane
other proteins involved in ATP synthesis are situated in the membranes of specialized compartments
within cells
glycoprotein:
glucose chain attached to protein
function like receptors/cell markers
receptors:
act like chemical receptors that receive chemical materials from other cells
act like an address (kind of like a mailbox—has the address of the cell)
a person’s receptors are the same, but different from somebody else
glycolipid:
glucose chain attached to the phospholipid head
function like receptors/cell markers (just like glycoproteins)
cytoskeleton:
proteins
anchors membrane to cell
runs through the whole cell
Passive Transport
molecules move from areas of high concentrations to low concentrations
molecules move due their own kinetic energy
they move down the concentration gradient
3 types:
1. diffusion- general movement from high to low
2. osmosis- diffusion of water
3. facilitated diffusion- diffusion using transmembrane proteins
Active Transport
molecules move from areas of low concentrations to high concentrations
molecules move up the concentration gradient
this requires energy from ATP
types:
1. protein pumps- active transport using transmembrane proteins
2. endocytosis - moves materials into cells
-pinocytosis- moves liquids into cells
-phagocytosis- moves solids into cells
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exocytosis- moves materials out of cells
Types of Passive Transport
passive transport: no energy and moves molecules from high to low
Diffusion
concentration: the amount of molecules in one are – high concentration is lots of molecules and low
concentration is fewer molecules
diffusion: the general movement of molecules from areas of high concentration to areas of low
concentration
molecules move from high to low concentrations due to their kinetic energy – molecules are in constant
motion and the movement of each molecule is random but there are more molecules in an area of
higher concentration  the molecules will move and spread out to lower concentrations
the entropy of a system increases as diffusion occurs
equilibrium: the same number of particles come in and leave (*this doesn’t mean the concentrations
are equal)
its like a classroom: 4 students leave, at the same time 4 students come in
at equilibrium molecules still move but there is no longer a lower-concentration area into which to
diffuse and the increase in disorder is associated with an increase in entropy
entropy favors rapid diffusion down a concentration gradient, when the gradient is steep
diffusion in liquids effectively moves substances only for short distances
concentration gradient: when there is a difference in concentration of molecules across a distance
it’s like a ramp: going up the ramp requires energy but coming down doesn’t
because molecules diffuse from regions of higher concentration to regions of lower concentration , they
are described as moving down their concentration gradient
because membranes are selectively permeable and don’t allow everything to pass through them,
concentration gradients can build up across the membrane
the membrane may hold back ions  potential energy is stored this way and is based on the
concentration gradient of substances  if the substance is charged, an electric potential also forms
across the membrane
concentration gradients provide potential energy to drive many cellular processes, including some types
of membrane transport
Osmosis
osmosis: the diffusion of water
water tends to diffuse from regions of high to low concentrations
responsible for the movement of water across membranes
doesn’t use proteins
water will never stop moving across the membrane – it just moves into and out of the membrane once it
reaches equilibrium
osmosis exerts a pressure on the side of the membrane that has the greater pressure gradient
turgor: the outward pressure of a cell against its cell wall
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osmosis can drive water out of cells, causing the cell to shrink  contractile vacuoles in some singlecelled organisms squeeze this excess water out of the cell
the rate of diffusion, including osmosis, depends on several factors like:
the size of the concentration gradient—a steeper gradient makes it go faster
the surface area—a greater surface area relative to the enclosed volume makes it go faster
isotonic- the cell solute concentration = the environment solute concentration
two solutions are the same strength
the cell composition = the environment composition
equilibrium: the amount of materials coming in and out is equal
animal cells
plant cells
97% water
3% solute
97% water
3% solute
97% water
3% solute
water moves in and
out the sameequilibrium
hypertonic- solution is above strength in solute
high in solute concentration, low in water concentration
water moves from high to low concentrations
animal cell
plant cell
water OUT
97% water
animal cell
3% solute
shrinks once
water diffuses out
hypertonic env.
90% water
10% solute
water OUT
97% water
3% solute
the cell is hypotonic
plant cell doesn’t
shrink once water
diffuses out because
the of its cell wall
water diffuses out of cells
cell water conc. is higher than env. water conc.
hypotonic- solution is below strength in solute
high in water concentration, low in solute concentration
water moves from high to low concentrations
animal cell
plant cell
water IN
hypotonic env.
90% water
10% solute
97% water
3% solute
animal cell
swells once
water diffuses in
and may burst
water IN
97% water
3% solute
plant cell expands
creating turgor
pressure
the cell is hypertonic
water diffuses out of cells
cell water conc. is higher than env. water conc.
Facilitated Diffusion
uses transmembrane proteins to help materials travel through the membrane
moves molecules from areas of high to low concentrations
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doesn’t need energy because molecules move down the concentration gradient, which doesn’t require
energy
the proteins can carry small charged ions across the membrane
makes transport more specific and speeds up the rate, but doesn’t work against the gradient
the transport proteins either form an open channel or attach to and carry specific molecules across the
membrane
big channel allows ions to move along on its own
carrier protein has binding site for molecule  molecule enters binding sit  carrier protein changes
shape, transporting molecule across membrane  carrier protein resumes original shape
Types of Active Transport
active transport: the energy-requiring process that moves molecules and ions across a cell membrane
against a concentration difference
requires energy and moves molecules from low to high against their concentration gradients
its energy source is the hydrolysis of ATP
requires transport proteins during the process
maintaining specific gradients across cell membranes is essential to keep internal conditions in a range
that permits life functions
many necessary substances couldn’t enter or leave cells without active transport
ex: plants need a constant supply of nitrate which is transported using active transport
protein pumps
moves materials from low to high concentrations
ATP binds with the protein  protein changes shape  material goes through
ATP becomes ADP and P with the process of hydrolysis
proteins are selective: only allow things that bind to it to come in the cell
bulk transport
to transport large molecules—endocytosis or exocytosis (they are both known as bulk transport)
in the process of bulk transport, large molecules, food, and other substances are packaged and moved
across the membrane
the cell membrane actually folds around the substance to be transported, making a pocket to carry it in
or out of the cell
endocytosis- brings materials in the cells
during endocytosis, the pocket in the cell membrane breaks loose from the membrane, creating a
structure called a vesicle which is a membrane bound sac
cell membrane pinches in and engulfs the substance
decreases size of cell
materials in the vesicle are broken down by enzymes
two types of endocytosis:
pinocytosis- brings liquids into cells
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phagocytosis- brings solids into cells
exocytosis- brings materials out of the cells
increases size of cell
exocytosis removes wastes from cells and also removes specific molecules so they can function in the
external environment, like digestive enzymes and some hormones
Gas Exchange
gas exchange is important because it supplies energy
an important supply of energy is cellular respiration
C6H12O2 + O2  H2O + CO2 + ATP
oxygen is needed for this process, and carbon dioxide is given off as a waste product
gas exchange regulates these materials very carefully
the exact mechanisms of gas exchange depend of the environment of the organism
ex: terrestrial or aquatic
the basic process of gas exchange are the same: diffusion
the gases involved, like oxygen and carbon dioxide, must be dissolved in water for diffusion to take place
gas exchange takes place in:
o fish
in water: aquatic  need oxygen
o plants
o humans
on land: terrestrial  need water
o birds
o earthworms
Fish
always in a water environment – not much oxygen concentration
need more oxygen and must carry out gas exchange
structure for gas exchange: gills
gill filaments – increase surface area of gills which makes it more efficient
lots of surface area makes diffusion faster
capillaries – surround filaments and absorb oxygen into blood
as water passes constantly over the gill surface, oxygen and carbon dioxide are exchanged between the
blood circulating through these capillaries and the water surrounding the filaments
oxygen diffuses from the water into the blood down its concentration gradient and is carried into cells
carbon dioxide- waste: diffuses from the gills into the water
water- lots of O2 as water flows over gills, oxygen goes into fish, carbon dioxide comes out
gills- lots of CO2
countercurrent exchange
gills are very efficient gas-exchange organs
water comes in through the mouth of a fish  forced over the gills  passes out of the body through an
opening in the body cavity that surrounds the delicate gill filaments
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gills make the water’s oxygen concentration a lot higher than the blood’s – maximize the difference
gill filaments are made of thin, disk-like structures – inside these disks, the blood, lower in oxygen, flows
from the back to the front, the opposite direction of the water
water, higher in oxygen, flows over these disks from front to back
the low concentration of the blood and the high concentration of the water flow in opposite directions
this process is called countercurrent exchange
oxygen diffuses from the water into the blood because water is higher in concentration than the blood
the blood continues to pick up oxygen from the water using diffusion – the capillaries absorb the oxygen
more than 80% of the dissolved oxygen in water diffuses into the blood
water
blood
oxygen diffuses from water to blood
water concentration = high
blood concentration= low
Terrestrial organisms
have the tendency to dry out
for oxygen and carbon dioxide to enter or leave the cell, they must be dissolved in water
earthworms and planaria
have no special gas-exchange organs
gases are exchanged directly through their skin
skin: is thin and moist so air can reach capillaries under the skin
this is why earthworms must live in a moist environment and die when the rain washes them on
land  if their skin dries out they can’t get oxygen and water
insects
have an exoskeleton and gas exchange can’t occur directly through their skin
use a system of branched air ducts called tracheae to carry oxygen through the body
birds
many birds beat their wings rapidly for long periods of time = flying
flying uses energy very quickly
flying needs lots of ATP  bird need large amounts of food and oxygen
special structures for gas exchange: air sacs ventilate the lungs
two cycles of inhalation and exhalation are required for the air to pass all the way through the system
a bird’s lung works like a two-cycle pump:
when it inhales – air passes directly into a set of chambers called the posterior air sacs
when it exhales – air passes into the lungs
on the following inhalation—air passes from lungs to a second set of air sacs called the anterior
air sacs
on the second exhalation—air flows from the anterior air sacs out of the body
posterior
air sacs
humans
lungs
anterior
air sacs
birds
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lungs
benefit:
the air passing through is always oxygen-rich
like fish, the flow of blood past the bird lung runs in the direction opposite to the air flow in the lung
(countercurrent flow)  this means that bird lungs are very efficient at picking up oxygen from the air
humans
gas exchange organs: alveoli in lungs
lungs are mucusy and on the inside of the body so they don’t dry out
the diaphragm is the muscle that controls the breathing
air moves from the mouth and nose  larynx  trachea  bronchus  bronchioles  lungs and then
back out the reverse way
nose: hairs filter, moisten, and warm the air
larynx
trachea
bronchi- 2 tubes that branch off to the two lungs
bronchioles- smaller tubules that are passageways to alveoli
air reaches alveoli
walls of alveoli are covered with capillaries that actually carry out gas exchange
oxygen and carbon dioxide diffuse into the capillaries
the alveoli increases surface area so gas exchange is more efficient
barriers can also conserve water by limiting the permeability of the outside of the organism itself
glands in human skin secrete oils and waxes as protective barriers
exercise:
pH = 7
pH = 6.8
 becomes slightly acidic – but only slightly because buffers prevent
CO2 + H2O  H2CO3 (carbonic acid)
extreme change
blood plasma –
liquid part of
blood
messages are sent to the brain (medulla oblongata) to the diaphragm to bring in more oxygen
diaphragm: moves up – increases pressure  air goes out
moves down – decreases pressure  air can come in
brain:
medulla oblongata – carries out automatic functions like breathing, heart beating, etc.
plants
cuticle: a waxy substance that forms a water-repellent covering secreted by cells along the surface of a
leaf
it reduces water loss from the leaf surface and blocks gas exchange between air and these cells
water can only leave through stomates, because the cuticle protects it
stomates: pores on the leaf surface where gases move in and out
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each stomate is surrounded by a pair of guard cells, which function as gates
low amount of water
guard cells shrink and close the stomate – minimizes water loss
high amount of water
guard cells swell up and open the stomate – allows carbon dioxide to
diffuse in and water vapor and oxygen to exit
water comes
out
guard cells shrink  stomate is closed
*loses turgor pressure*
guard cells swell  stomate is open
water is lost when a stomate opens, and this loss of water is called transpiration
transpiration: helps move water up a plant  when water evaporates, water is pulled up to replace it
Waste Removal
excretory system: maintains the water balance – keeps water you need and gets rid of the excess
the exchange of materials, including the removal of wastes, is essential to maintaining homeostasis
homeostasis: the balanced and controlled conditions in the internal environment of an organism
3 types of toxic waste: all contain nitrogen from proteins
1. ammonia
2. urea
3. uric acid
these nutrients lose nitrogen when they are converted to carbs or fats
ammonia is more toxic than urea and is a common nitrogenous waste
only organisms living in water can excrete ammonia directly because it’s very toxic to body tissues and
gets diluted in the water
some organisms convert their nitrogenous wastes to urea, which is much less toxic than ammonia
urea can be excreted safely when diluted in a moderate amount of water, which conserves body water
uric acid – pasty waste and is almost insoluble and a nontoxic form of nitrogenous waste
benefit of uric acid- requires almost no loss of water
the different forms of nitrogenous wastes show important patterns
unicellular organisms like paramecium
use contractile vacuoles to squeeze excess water from the cell
ammonia directly through their cell membranes or body coverings
simple organisms like sponges
simply excretes its wastes directly through the external surface
for larger animals, not enough of the cells are in contact with the environment for them to excrete
their own waste  there are too many cells that need to remove wastes to directly excrete through the
low surface area of the skin
fish
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gills: the excretion of carbon dioxide
in saltwater fish, special cells in the gills also excrete salt, helping maintain the body’s water-salt balance
excretes ammonia directly
birds and reptiles
excrete uric acid
it requires almost no loss of water
Human Urinary System
urinary system: made up of the kidneys, the blood vessels that serve them, and the plumbing that
carries fluid formed in the kidneys out of the body
path:
renal artery  kidneys, which contain nephrons  renal vein  ureter  urinary bladder  urethra
urine: the waste fluid
kidneys: compact organs and major organs responsible for processing the waste from metabolism
blood cycles through these kidneys, and nitrogenous wastes are removed
the removal of these wastes regulates the water balance by adjusting the concentrations of various salts
in the blood
surrounded by capillaries in the nephrons
nephrons: in the kidneys and filter the blood
renal artery: where blood that needs to be filtered enters the kidney
renal vein: where filtered blood exits
the kidneys process the entire blood supply of the human body about once every 5 minutes
ureter: a tube where the urine leaves the kidneys into
urinary bladder: a holding tank that the ureter drains into
urethra: where the urinary bladder periodically drains into
nephron: filters blood
is made of a coiled tube with one cuplike end that fits over a mass of capillaries and the other end which
opens into a duct that collects urine
found in kidney
each kidney has about 1 million nephrons
glomerular capsule or Bowman’s capsule: the cup of the nephron
where filtration occurs
glomerulus: the ball of capillaries beneath the cup
it filters the blood
most of the blood proteins are retained in here, in capillaries
collecting tubes: eventually empty into the ureter
where reabsorption and secretion take place
capillaries cover the wall of the collecting tubes
nephrons have three functions:
1. filtration- fluid from plasma membrane passes into nephron
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occurs in the glomerulus, where the blood plasma is forced into the glomerular capsule
blood cells and most of the blood proteins are retained in the capillaries of the glomerulus
(filtrate: materials that cross from the capillaries to the glomerulus capsule)
the filtrate includes the blood plasma, nitrogenous wastes from cells, urea, salts, ions, glucose, and
amino acids
only some of the filtrate is eliminated from the bladder – 90% is returned to the blood
2. reabsorption- molecules are reabsorbed into the capillaries
takes place in the tube of the nephron
cells of the tube walls reabsorb substances needed by the body from the filtrate and return them to
the blood
ex: salt and water in the tube are reabsorbed into the capillaries – the water returns by osmosis, but
active transport is needed for reabsorption of ions like the salt, glucose, amino acids, and urea
3. secretion- molecules from blood are secreted into nephron tubules
occurs as filtrate moves through the tube
cells of the tube wall selectively remove from the surrounding capillaries substances that were left
in the plasma after filtration or returned by reabsorption
the cells then secrete these substances into the filtrate
ex: excess potassium ions are excreted this way
Labs
Diffusion
the dialysis bag = cell membrane
they are both selectively permeable
starch in the dialysis bag started out white and changed to black/blue
this means that the iodine must have gotten into the starch bag, which means the bag has pores making
it selectively permeable
the water in the beaker stayed yellow, the color of the iodine solution
this means that starch didn’t move out of the bag because if it did the water in the beaker would have
changed to black/blue too
the iodine on the outside was lighter after the experiment because if iodine moves into the bag, its color
on the outside would become lighter
a membrane is permeable to a substance if that substance can move through the membrane, and its
impermeable if that substance can’t move through the membrane
the bag is permeable to iodine because the iodine was able to get inside the bag, which turned black 
the iodine was small enough to get through the bag
the bag is impermeable to starch because the water on the outside of the beaker stayed yellow, the
color of the iodine and if the starch had gotten out of the bag the water would have turned black  the
starch chains were too big to get through the bag
diffusion is the movement of chemicals from areas of high to low concentrations
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iodine moved into the bag by diffusion – iodine concentration was high outside the bag at the start and
iodine concentration was low inside the bag at the start
some scientists believe that membranes contain very small pores which determine why some chemicals
can or can’t pass through a cell membrane
the pores of the dialysis bag were probably very similar in size to the iodine molecules because
the iodine was able to get through the bag
the pores of the dialysis bag were probably smaller than the starch molecules because the
starch wasn’t able to get through the bag