Biology: Cells Flashcards
how do electron microscopes work and what are the conditions they have to be in?
- electrons fire through the sample, the reflected electrons are observed.
- it must be in a vacuum
- TEM microscope: sample is sliced and stained with a heavy metal
- SEM microscope: specimen is coated with a thin layer of gold.
how does centrifugation happen in order to obtain a small organelle?
- cell is homogenated (broken up)
- it’s filtered to remove whole cells and membrane debris.
- it’s put in a supernatant, it’s isotonic, ice cold and buffered to prevent pH or temp. change.
- it’s spun at a slow speed, a pellet containing large organelle forms at the bottom.
- it’s spun at a faster speed for a longer time and smaller organelle collect at the bottom.
what is an eyepiece graticule?
- it’s a glass disc that rests on the rim of the eyepiece.
- the stage micrometer is used alongside the graticule to measure the size of the sample.
how do you find image size?
actual size x magnification
what is the structure of the mitochondria?
- the inner membrane is folded into cristae.
- this maximises surface area so there’s more transport over the organelle.
what is the structure of the chloroplast?
-the thylakoid membranes are stacked to increase surface area for maximum light absorption.
what do the RER and SER do?
RER:
- it’s rough due to ribosomes on its surface.
- it’s used to sythensise proteins
SER
- lacks ribosomes so it’s smooth
- lipid synthesis.
what is cell differentiation?
- the cells of an embryo at an early stage are all the same.
- cells become different from each other.
- differentiated cells are specialised so they carry out specific functions.
what is a tissue?
a group of cells of the same type.
what are the uses of tissues?
- protection of internal organs from damage
- diffusion of substances across the surface of the epithelium
- absorption of materials, such as the products of digestion.
- secretion of substances onto the surface of the epithelium.
what are prokaryotic cells?
- cells with no membrane bound organelle.
- no true nucleus.
- DNA is in a strand which is freely floating inside the cell
how does the virus invade cells and replicate?
- attachment proteins bind to receptors on the cell.
- it releases a capsid into the cell.
- this releases its RNA into the cell, which changes the DNA of the cell.
- it replicates viruses
- the cell bursts due to overcrowding.
describe the process of mitosis
interphase: DNA replicates so there’s 2 chromatid per chromosome.
prophase: the chromosomes ondense and become more visible, the nuclear membrane breaks down.
metaphase: the chromosomes line up along the middle of the cell and attach to spindle fibres at the poles.
anaphase: the spindle fibres shorten, pulling the chromosomes apart to each of the poles.
telophase: it begins so constrict down the middle and new nuclear membrane forms around both groups of chromosomes. chromosomes decondense and become less visible
what is the fluid mosaic model?
- it shows the structure of the phospholipid bilayer
- it’s fluid mosaic as it’s flexible and consists of many parts, each of different shapes and sizes.
what is the purpose of the phospholipid bilayer?
- the hydrophilic head and hydrophobic tail doesn’t let water in.
- intrinsic proteins allow the passage of certain molecules through
what is the purpose of the channel and carrier proteins?
CHANNEL:
-water filled tubes to allow the passage of water-soluble molecules into the cell.
CARRIER:
- used in active transport
- change shape to let larger molecules enter the cell.
what is the purpose of cholesterol in the phospholipid bilayer?
- increases resistance to temp. change
- keeps the membrane structurally strong
what is diffusion and what factors can affect it?
the movement of a substance from high to low concentration down a concentration gradient until it reaches equilibrium. it’s a passive process as it doesn’t require energy.
factors:
- conc. of substance
- length of diffusion pathway
what is facilitated diffusion?
diffusion using the channel proteins. it’s still passive etc.
what is osmosis?
the net movement of water molecules through a partially permeable membrane until equilibrium is reached. high to low concentration
what is water potential?
the pressure exerted by water molecules. measured in kPa.
what is the water potential of pure water?
0
what does fick’s law state?
rate of diffusion proportional to:
(surface area x gradient) / length of diffusion pathway
how does active transport work?
- molecules go into carrier protein
- a phosphate from ATP phosphorylates the protein and it changes shape.
- this releases the molecules out of the other end of the membrane and into the cell
how does the sodium-potassium pump work?
3 sodium out, 2 potassium in
- 3 sodium ions bind using ATP
- phosphate binds, changing the tertiary structure
- 3 sodium released from cell
- higher affinity for potassium
- 2 potassium bind
- phosphate dissocated
- 2 potassium carried into the cell as well as glucose and amino acids etc.
what does hypertonic mean?
concentration of solute in a solution surrounding the cell is greater than that inside the cell
what does isotonic mean?
solutes in solution = solutes in cell
what does hypotonic mean?
conc. of solute in solution surrounding the cell is less than that inside the cell.
what happens to a cell in a:
hypertonic solution
hypotonic solution
isotonic solution
hypertonic:
cell deflates as water potential outside the cell is lower so water leaves the cell
hypotonic:
cell lysis as water enters the cell
isotonic:
nothing happens
how do barriers prevent us against pathogens?
-prevent pathogens from entering the body
- eyes: tears, eyelashes, blinking
- skin: oily substance called sebum
describe the process of phagocytosis
- phagocyte attracted to pathogen by chemoattractants
- it engulfs the pathogen and puts it in a vesicle called a phagosome
- lysosomes line up around the vesicle
- they release lysozyme, a digestive enzyme, into the vesicle
- it hydrolyses the pathogen
- it leaves the phagocyte by exocytosis.
what to cytotoxic t-cells do?
- they use an enzyme to break down the membrane of a cell
- water enters the cell, causing cell lysis
what do b-cells do in response to phagocytosis?
- divide and produce clones of cells.
- most of these cells are plasma cells and produce monoclonal antibodies
- monoclonal antibodies are complementary to a certain antigen
how do antibodies destroy antigens?
agglutination: easier for phagocytes to engulf them
precipitation: facilitates phagocytosis
markers: signal phagocytes
neutralisation of toxins
lysis: breaks down bacteria
what’s the difference between artificial and natural immunity?
natural: the body’s response to the antigen
artificial: brought about by vaccinations
