Unit 3.1.3 - Cells and Plasma Membranes Flashcards
What is the difference between a prokaryotic cell and a eukaryotic?
Eukaryotic cells are big complex cells where as prokaryotic cells are usually single celled organisms
Name three organelles you wouldn’t find in a prokaryotic cell and the main reason why?
Nucleus, mitochondria and ER because they are too large and wouldn’t fit it
Label the diagram of a eukaryotic cells?
See flash card 8
Label the diagram of a nucleus?
See flash card 9
Label the diagram of a mitochondria?
See flash card 10
What is the function of a nucleus?
Controls the cell activity
What is the function of the nucleolus?
Makes ribosomes
What is the function of mitochondria?
Produce energy by aerobic respiration
What is the function of smooth ER?
Makes and transports lipids
What is the function of rough ER?
Makes and transports proteins
What is the function of Golgi apparatus?
Modifies proteins
What is a vesicle?
A sack of protein that is used to transport the protein
What is the function of a ribosome?
To make protein
What is the function of the plasma membrane?
Control which substances enter and leave the cell
What is the function of the cytoplasm?
Where chemical reactions take place
What is the function of lysosomes?
Destroys (digests) dead organelles
What are microvilli?
Folds in the plasma membrane
Name two adaptations of an epithelium cell which makes it suitable for its function an why?
Microvilli - increase surface are for food absorption
Lots of mitochondria - to provide energy for the active transport of food molecules against the concentration gradient
What is the difference between magnification and resolution?
Magnification - how much bigger the image is than the specimen
Resolution - how detailed the image is
How do you calculate magnification?
Length of image / Length of specimen
How do you convert mm into µm?
x1000
What are the three types of microscopes?
- ) light microscope
- ) scanning electron microscope (SEM)
- ) transmission electron microscope (TEM)
How do transmission electron microscopes work?
They use electromagnets to focus a beam of electrons through a specimen, denser parts of specimen absorb more electrons which make them look darker on the image
How do scanning electron microscopes work?
They scan a beam of electrons across a specimen, this knocks of electrons from the specimen which are gathered in a cathode ray tube to form an image
Why cant you use either electron microscope on a living specimen?
You have to dehydrate the specimen and use heavy metals to stain it so you can see it under the microscope which kills any living cells
What are two advantages of a light microscope?
- ) can see living cells
2. ) can see actual colour
What are two disadvantages of a light microscope?
- ) low magnification
2. ) poor resolution
What are two advantages of a TEM?
- ) high magnification
2. ) good resolution
What are three disadvantages of a TEM?
- ) can only be used on thin specimens
- ) can’t be used on living specimens
- ) must be in a vacuum
What are four advantages of a SEM?
- ) can be used on thick specimens
- ) 3D image
- ) high magnification
- ) good resolution
What are three disadvantages of a SEM?
- ) must be in a vacuum
- ) cant be used on living specimens
- ) lower resolution than TEMs
What process can you use to separate cells?
Cell fractionation
What are the three steps in cell fractionation?
Homogenisation, filtration and ultracentrifugation
What happens during homogenisation?
The cells are broken up - by vibrating them or putting them in a blender - this is to break up the plasma membrane and release organelles
What two things does the solution have to be during homogenisation?
Ice cold and isotonic
Why does the solution have to be ice cold during homogenisation?
To reduce enzyme activity
Why does the solution have to be isotonic during homogenisation?
To prevent water moving in or out of the cell by osmosis
Why is a buffer usually added to the solution during homogenisation?
To prevent any damaging pH changes
What happens during filtration?
The solution is filtered through a gauze to remove large lumps of unbroken cells and cell debris
What happens during ultracentrifugation?
The solution is spun at a centrifuge at various increasing speeds, the heaviest organelles like the nuclei will form the pellet first
What are the four main things the plasma membrane consists off?
Phospholipid bilayer, proteins, carbohydrates and cholesterol
Draw a picture of a phospholipid bilayer?
see flash card 11
Why does the phospholipid bilayer contain cholesterol?
The cholesterol reduces the permeability and fluidity off the membrane making it more stable
Why does the phospholipid bilayer contain glycoproteins on its surface?
They act like antigens and tell your white blood cells that the cell is your own
Why is the model for the plasma membrane called the fluid mosaic model?
Because the phospholipid bilayer is fluid because the phospholipids are constantly moving and the proteins are scattered throughout the layer like tiles in a mosaic
Why do phospholipids arrange them selves into a bilayer?
They have a hydrophilic head and a hydrophobic tail, as the tail repels water they all automatically face inwards
Why does the phospholipid bilayer act as a barrier to water soluble substances?
They cant get through the centre of the bilayer as it is all hydrophobic
What four molecules do triglycerides consist of?
One glycerol molecule and three fatty acid molecules
Draw the structure of a triglyceride?
See flash card 12
What is the general structure of fatty acid?
See flash card 13
What reaction joins fatty acids to the glycerol molecule?
Condensation reaction
Draw the condensation reaction between a glycerol molecule and a fatty acid molecule?
See flash card 14
What bond forms between glycerol molecules and fatty acid molecules?
Ester bonds
Can the hydrocarbon tail of a fatty acid is it saturated or unsaturated?
Can be either
What is the difference between a phospholipid and a triglyceride?
A phospholipid only has two fatty acids instead of three, and instead it has a phosphate group attached
Draw a phospholipid?
See flash card 15
In a phospholipid which part forms the hydrophobic tail and the hydrophilic head?
The fatty acid forms the hydrophobic tail and the phosphate group forms the hydrophilic head
What is the test called you can do to test for lipids?
The emulsion test
Describe what happens during the emulsion test for lipids?
Pour ethanol into the solution and shake for about a minute
Then pour the solution into water
If there are lipids present there will be a milky emulsion, if there are no lipids present there will be no visible change
Define what diffusion means?
The passive movement of particles from an area of high concentration to an area of low concentration
What three factors can increase the rate of diffusion?
Steeper concentration gradient - which is maintained, thinner exchange surface and a greater surface area
What are the names of the two proteins which help facilitated diffusion?
Channel proteins and carrier proteins
What is facilitated diffusion for?
For when large molecules and charged particles can’t diffuse through the phospholipid bilayer
Describe what happens when a carrier protein transports a molecules across the plasma membrane during facilitated diffusion?
A large molecule attaches to a carrier protein, the protein changes shape and the molecule is released on the opposite side of the membrane
Which type of molecule do carrier proteins transport across the plasma membrane?
Large ones
Which type of molecules do channel proteins transport across the plasma membrane?
Charged molecules
Describe what a channel protein is and what its function is?
It is a pore in the membrane which allows the charged molecules to diffuse through
Does facilitated diffusion require energy?
No
Define what osmosis means?
It is the diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential
What is the water potential of pure water?
0
Why are all values for water potential negative apart from pure water?
Pure water has a water potential of 0, so as you lower the lower potential of a solution the value decreases and so becomes negative
What is meant by the term isotonic?
When two solutions have the same water potential and therefore there is no net movement of water particles
Define what active transport means?
It is where energy is used in the form of ATP to transport molecules against the concentration gradient, from an area of low concentration to an area of high concentration
What two proteins are involved in active transport?
Carrier proteins and co transporters
Describe how carrier proteins are used in active transport?
A molecule attached to a carrier protein as well as ATP, the carrier protein then uses this energy to change shape and move the molecule against its concentration gradient
Describe how co transporters transport molecules in active transport?
They transport two molecules at a time, they use the concentration of one molecule to move the other molecule against its own concentration gradient
Give an example of when co transporters are used?
When sodium ions move into the cell down their concentration gradient taking glucose molecules with it
What are the 4 steps for how glucose is absorbed from the small intestine lumen to the blood?
- ) to begin with glucose is absorbed from the small intestine into the epithelial cells and then into the blood down it concentration gradient
- ) This decreases the concentration of glucose in the small intestine lumen so diffusion stops
- ) Then the remaining glucose is transported by the co transporters with sodium ion from the small intestine lumen into the epithelium cells
- ) Then the glucose diffuses down its concentration gradient from the epithelium cells to the blood
When glucose is being transported what are the three steps which maintain a high concentration of sodium ions in the small intestine lumen?
- ) To begin with sodium ions are transported from the epithelium cells to the blood by active transport through the sodium potassium pump
- ) This decreases the concentration of sodium ions in the epithelium cells
- ) This means sodium ions diffuse down their concentration gradient from the small intestine lumen to the epithelium cells via the co transporters taking the glucose with it
Label the diagram of a cholera bacterium?
See flash card 16
Is a cholera bacterium a prokaryotic cell or a eukaryotic?
Prokaryotic
What is the capsule made of and what is its purpose?
Secreted slime and to protect the bacteria from attack by the cells immune system
What is a plasmid?
A small loop of DNA that aren’t part of the circular DNA in the centre of the bacterium
Why does the cholera bacterium cause diarrhoea in three steps?
- ) It produces a toxin which causes chloride ions to move into the small intestine lumen
- ) This lowers the water potential within the small intestine lumen and so water moves into it by osmosis
- ) There is then too much water to be absorbed by the large intestine and so there is an excessive amount of water in your faeces causing the diarrhoea
Why is used to treat diarrhoeal diseases?
Oral rehydration solution
What is a ORS?
A drink that contains large amounts of salts (chloride and sodium ions) and sugars (glucose) dissolved in water
How does ORS prevent diarrhoea in 3 steps?
- ) The sodium ions increase the glucose absorption into the epithelium cells
- ) This lowers the water potential in the epithelium cells and so water moves from the small intestine into the cells by osmosis, and then from the cells into the blood
- ) this decreases the water content in the faeces and replaces water lost from the blood
What is an advantage and a disadvantage for testing the ORS on children?
Advantage - the disease mainly affect children so it has to be seen if the treatment is effective for them
Disadvantage - children don’t get to decide if they do the trial or not the parents do
