The cell membrane is the boundary that.....
maintains conditions suitable for the life of the cell by regulating or controlling the passage of materials into and out of the cell
Plant cells are more of what shape, and why?
rigid and box-like, because of the presence of the cell wall
What shapes do animal cells come in, and why?
different shapes, because the fluidity of the cell membrane, which is their only outer structure
What is a semi-permeable membrane?
it allows certain substances to pass through freely, and restricts others completely
What do carbohydrates receive?
communications from other cells, and they detect chemical changes in their surroundings
What are the five functions of the cell membrane?
1. protects the cell by acting as a barrier
2. regulates the transport of substances in and out of the cell
3. receives chemical messengers from other cell
4. acts as a receptor
5. cell mobility, secretions, and absorptions of substances
What does the phospholipids portion of the cells membrane block the passage of?
most of the molecules except water and a few ions
Who won a Nobel Prize in 1973, and why did they win it?
Joseph Goldstein and Michael Brown, for their discovery of how carbohydrates present on the cell membrane control the level of cholesterol in the human blood
What did Joseph Goldstein and Michael Brown prove?
that glycoproteins protruding from the cell membrane bind to cholesterol particles that circulate in the blood and take them to the cell to make cell membrane
What is cholesterol a key factor in?
the production of hormones like testosterones, progesterone, and bile which, helps in the digestion of fat
What happens if these particles are not taken into the cell?
they could build up in blood vessels and lead to atherosclerosis or narrowing of the arteries which can lead to a heart attack
The greater number of ________ on the cell membrane, the more ___________ containing particles are removed from the blood
How many people out of how many people have an abnormally small number of glycoproteins on the cell membrane?
1 in 500 people
Can people with a normal gene have high cholesterol levels?
yes, because when the cell's cholesterol needs are met, the glycoproteins shut off
What happens during active transport?
substances move against the concentration gradient , from a region of low concentration to a region of high concentration
Since they move against the concentration gradient during active transport, what is used to move substances?
energy in the form of adenosine tri phosphate
Why is this type of transport called passive transport?
because energy is not required to move molecules
Does active transport take place in all cells?
yes, and in some cells it accounts for more than half of the cell's energy expenditure
What happens during this transport?
3 sodium ions are pumped to the outside of the cell for each 2 potassium ions that moves into the cell
What takes place in all human cells? And what cells is especially in
the sodium-potassium pump, especially nerve and muscle cells
What are two types of active transport that move large molecules across the cell membrane?
exocytosis and endocytosis
Before the molecules are sent out of the cell in exocytosis, they must first be what?
surrounded by a membrane which is called the secretion vesicle
What are some examples of exocytosis?
production and release of materials required for the construction of cell wall, and the production and release of hormones
What happens during pinocytosis?
small vesicles form out of the plasma membrane and carry liquid or smaller molecules into the cell from outside
What happens during phagocytosis?
large molecules or small unicellular organisms are taken into the cell
What is an example of phagocytosis?
the engulfing of bacterium by ameba. the ameba encloses the bacterium and releases enzymes to digest it. the nutrients are absorbed by the ameba, and the unabsorbed waste is discharged by exocytosis
What happens when a white blood cell sees a new bacteria?
it will locate, engulf, and disintegrate it slowly, the second time it goes much faster. this is called cell recognition
As molecules diffuse from a region of high concentration to a region of low concentration, what happens?
the concentration eventually becomes equal
What is able to diffuse through the cell membrane?
small molecules such as water, carbon dioxide, and oxygen
What are the factors affecting the rate of diffusion?
*state of matter
*concentration gradient and slope of concentration gradient
*size of molecules
The _________ the difference in concentration between the high and low regions, the _________ the molecules will diffuse.
What happens when heat is applied?
molecules absorb energy and tend to move along the concentration gradient
Smaller molecules are less likely to what?
collide with opposing larger molecules when they move from a region of more to a region of less
What happens during facilitated diffusion?
substances move along the concentration gradient, however during this, proteins called carrier proteins help in the transport of substances
Why are carrier proteins required during facilitated diffusion?
to move molecules larger than water, carbon dioxide, and oxygen into the cell
What do carrier proteins form?
channels through the cell membrane to facilitate the movement of larger molecules
the diffusion of water through a semi permeable membrane from a region of high concentration to a region of low concentration
How are water molecules able to move freely through the cell membrane?
because they are very small and can easily pass through
How is the direction of the flow of water determined?
by the amount of solute and solvent present inside and outside of the cell
When water moves into a cell as result of osmosis, it creates pressure within the cell, called what?
osmotic pressure or the force of osmosis
What does the amount of solute and solvent present in a solution determine?
the concentration of the solution
During osmosis, the direction of the flow of water depends on what?
the solute/solvent concentration
a solution that has a high solute concentration and less solvent concentration compared to the outside environment
What is an example of a hypertonic solution?
in a hypertonic salt solution, there is more salt than water
What happens when cells are placed in a hypertonic salt solution?
water molecules will move out of the cell and salt molecules will move into the cell
What do these animals have?
special mechanisms to prevent water from leaving their cell and hence prevent dehydration due to loss of water
where the plasma membrane pulls away from the cell wall as the cell shrinks due to loss of water
What happens to cells in a hypotonic solution?
they gain water because there is more water outside of the the cell than inside of the cell
Why will the animal cells rupture?
water diffuses into the cell as a result of osmosis, and since animal cells don't have a cell wall, the cell membrane will rupture due to increased osmotic pressure
the concentration of solute is the same on both sides of the membrane, inside and outside of the cell
red blood cells are very vulnerable to changes in concentration because...
they don't have any mechanism to remove excess water