2. cells P1 Flashcards
describe the structure of the nucleus
surrounded by a nuclear envelope
nuclear pores allow substances to enter/exit
dense nucleolus made of proteins and RNA
describe the function of the nucleus
contains genetic code for each cell
site of transcription, mitosis
describe the structure and function of the cell membrane
‘fluid mosaic’ phospholipid bilayer with intrinsic and extrinsic proteins embedded
isolates cytoplasm from extracellular enviromment
selectively permeable to regulate transport of substances
describe the structure and function of the rough endoplasmic reticulum
sheets of folded membranes forming flattened sacs called cisternae
covered in many ribosomes for protein synthesis
describe the structure and function of the smooth ER
sheets of folded membranes forming flattened sacs called cisternae
lipid synthesis
describe the structure of the golgi apparatus
a group of fluid filled, membrane bound sacs called cisternae
vesicles made by it are seen at the edges
describe the function of the golgi apparatus
processes and packages proteins and lipids
modifies them ready for release
synthesises glycoproteins
describe the function of the golgi vesicles
stores lipids and proteins, transports them out of cell via cell membrane
describe the structure and function of a lysosome
small, round membrane bound organelle.
contains hydrolytic enzymes (lysozyme) which digests the contents of phagosome
describe the structure and function of a ribosome
very small organism
either floats free in cytoplasm or is attached to RER
made of proteins and RNA
not surrounded by a membrane
PROTEIN SYNTHESIS
describe the structure of a mitochondrion
surrounded by a double membrane, inner membrane folded to form cristae (site of ETC/ oxidative phosphorylation)
fluid matrix - contains mitochondrial DNA, respiratory enzymes, lipids, proteins
describe the function of the mitochondria
site of aerobic respiration and ATP synthesis
describe the structure of a chloroplast
thylakoids - flattened discs stack to form grana which contain photosystems with chlorophyll
lamellae - tubes attract thylakoids in adjacent grana.
stroma - fluid filled matrix
what’s the function of a chloroplast ?
site of photosynthesis
what’s the function of a chloroplast ?
site of photosynthesis
describe the structure of the cell wall
bacteria: made of polysaccharide murein
plants: made of cellulose microfibrils
fungi: chitin
describe the functions of the cell wall
mechanical strength and support
physical barrier against pathogens
describe the functions of the cell wall
mechanical strength and support
physical barrier against pathogens
describe the structure and function of the cell vacuole in plants
surrounded by a single membrane
tonoplast contains cell sap (mineral ions, water, enzymes etc)
absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
makes cell turgid and therefore provides support (prevents plants wilting)
contrast the structure of animal cells (A) and bacterial cells (B)
A has a nucleus, whereas B has free DNA
A has mitochondria, whereas B doesn’t
A has no cell wall, whereas B has a murein cell wall
A has larger ribosomes
A has no capsule whereas B has a capsule
A has DNA bound to histones, whereas B has DNA not associated with histones
name the 2 key differences between fungal and plant cells
fungal cell walls are made up of chitin rather than murein
fungal cells don’t have chloroplasts
name the 2 key differences between fungal and plant cells
fungal cell walls are made up of chitin rather than murein
fungal cells don’t have chloroplasts
explain some common cell adaptations
folded membrane or microvilli increase surface area e.g. for diffusion
many mitochondria- large amounts of ATP for active transport
walls one cell thick to reduce diffusion pathway
state the role of plasmids in prokaryotes
small ring of DNA that carries non-essential genes
can be exchanged between bacterial cells via conjugation
(not always present)
state the role of flagella in prokaryotes
rotating tail propels organism
state the role of the capsule in prokaryotes
provides protection against phagocytes and external chemicals
prevents cell from drying out (desiccating)
why are viruses referred to as particles instead of cells?
Acellular and non living - no cytoplasm
cannot self reproduce, no metabolism
state the role of a capsid on viral particles
surface sites enable viral particle to bind to and enter host cells or inject their genetic material
state the role of attachment proteins on virus
enable viral protein to bind to complementary sites on host cell
outline how a student could prepare a temporary mount of tissue for an optical microscope
obtain a thin section of tissue
place plant tissue on drop of water
stain tissue on a slide to make structures visible
add coverslip using mounted needle at 45degrees to avoid trapping air bubbles
suggest the advantages and limitations of using an optical microscope
- colour image
- can show living structures
- affordable apparatus
- but 2D image
- lower resolution than electron microscopes
describe how a transmission electron microscope works
pass a high energy beam of electrons through a thin slice of specimen
more dense structures appear darker since they absorb more electrons
suggest the advantages and limitations of using a TEM
- high resolution
- high magnification
- but 2D image
- requires a vacuum (can’t show living - - structures)
- no colour image
describe how a scanning electron microscope (SEM) works
focus a beam of electrons onto a specimens surface using electromagnetic lenses.
reflected electrons hit a collecting device and are amplified to produce an image
suggest the advantages and limitations of using a SEM
- 3D image
- high resolution
- but requires a vacuum (can’t show living structures
- no colour image
- only shows outer surface
define magnification
factor by which the image is larger than the actual specimen
define resolution
smallest separation distance at which 2 separate structures can be distinguished from one another
state the magnification equation
magnification = image size/ actual size
(I AM)
contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells [6]
TEM use elections and optical use light
TEM allows a greater resolution, so smaller organelles such as ribosomes can be observed
TEM view only dead specimens, and optical can view live specimens
TEM don’t show colour and optical can
TEM requires thinner specimens
TEM focuses using magnets and optical uses lenses
describe how a sample of chloroplasts could be isolated from leaves [4]
blend cells and filter in ice cold, isotonic and PH buffered solution. Spin in centrifuge and remove nuclei. Spin at higher speed and chloroplasts settle out
explain why the solution is ice-cold, buffered and isotonic
ice cold to slow/stop enzyme action to prevent digestion of organelles
buffered to maintain PH so enzymes/proteins aren’t denatured
isotonic - prevents osmosis, so no shrinkage of organelles
explain why you use a blender and filter the mixture
use a blender to break open the cells
filtered to remove larger debris
outline what happens during ultracentrifugation
blend cells to break open the cell and filter to remove larger debris
in ice cold, isotonic and PH buffered solution.
spin homogenise in centrifuge
the most dense organelles in the mixture form a pellet
filter off the supernatant and spin again at a higher speed.
state the order of sedimentation of organelles during centrifugation
nucleus —> mitochondria —> lysosomes —> RER —> plasma membrane —> SER —> ribosomes
state the order of sedimentation of organelles during centrifugation
nucleus —> mitochondria —> lysosomes —> RER —> plasma membrane —> SER —> ribosomes
the cell was stained. this caused parts of the structure of the cell-surface membrane to appear as two dark lines. suggest an explanation for the appearance of it. [3]
membrane has a phospholipid bilayer, stain bonds to phosphate/ glycerol, on inside and outside of membrane
describe how you could make a temporary mount of a peice of plant tissue to observe the position of starch grains in the cell using an optical microscope [4]
- add a drop of water to glass slide
- obtain a thin section of plant tissue and place on slide
- stain with iodine in potassium iodide
lower cover slip using mounted needle.
describe binary fission in bacteria [3]
replication of circular DNA, replication of plasmids, division of cytoplasm to produce daughter cells
suggest and explain how 2 environmental variables could be changes to increase the growth rate of cells [4]
increased temperature - increased enzyme activity
increased concentration of oxygen - increases respiration
increased concentration of phosphate - increased ATP
convert 1 micrometer to m
0.001 (divide by 1000)
what is mitosis needed for?
the growth of multicellular organisms and for repairing damaged tissues
(asexual reproduction)
what are the stages of the cell cycle
- interphase
- mitosis or meiosis
- cytokinesis
what happens during interphase?
G1 - cell synthesises proteins for replication and new organelles made
S - DNA replication
G2 - organelles divide, more proteins made, ATP made
outline what happens during prophase
chromosomes condense, becoming visible
centrioles move to opposite poles of cell and spindle fibres form.
nuclear envelope breaks down (chromosomes free in cytoplasm)
outline what happens during metaphase
sister chromatids line up at cell equator attached to the spindle by their centromeres.
outline what happens during anaphase
centromere’s divide, sister chromatids separate into 2 chromosomes and are pulled to opposite poles of cell (V shaped)
spindle fibres break down
outline what happens during telephase
chromosomes decondense, becoming invisible again (long and thin)
new nuclear envelopes form around each set of chromosomes (2 new nuclei- each with one copy of each chromosome)
describe the role of the spindle fire bed and the behaviour of the chromosomes during prophase, metaphase and anaphase [5]
- in prophase, chromosomes condense
- in metaphase/prophase, centromeres attach to spindle fibres
- in metaphase, chromosomes line up in centre of cell
- in anaphase, centromeres divide
- in anaphase, chromatids are pulled to opposite poles of cell
suggest why preventing the formation of spindle fibres stopped the cell cycle [2]
chromosomes can’t attach to spindle, so can’t line up on spindle, so no metaphase
explain the procedure for a root tip squash experiment
prepare a temporary mount of root tissue
focus an optical microscope on the slide.
count total number of cells in the field of view and number of cells in a stage of mitosis
calculate mitotic index (proportion of cells undergoing mitosis)
explain the procedure for a root tip squash experiment
prepare a temporary mount of root tissue
focus an optical microscope on the slide.
count total number of cells in the field of view and number of cells in a stage of mitosis
calculate mitotic index (proportion of cells undergoing mitosis)
for the mitosis root tip experiment explain why you only used the first 5mm from the tip of an onion root
it’s where dividing cells are found/ where mitosis occurs
explain why you pressed down firmly on the cover slip
to get a thin layer of cells so light passes through, making cells visible
describe the appearance and behaviour of chromosomes during mitosis [5]
- during prophase, chromosomes condense and become visible
- chromosomes appear as 2 sister chromatids joined at the centromere
- during metaphase, chromosomes line up on centre of cell, attached to spindle fibres
- by their centromere
- during anaphase, the centromere divides
- and the chromosomes are pulled to opposite poles of cell
- during telephase, the chromosomes unwind and become longer and thinner
describe 2 aseptic techniques you would have used when transferring a sample into an agar plate
open lid of petri dish as little as possible, to prevent unwanted bacteria contaminating the dish
wear gloves/ wash hands to prevent contamination from bacteria on hands.
describe the fluid mosaic model of membranes
fluid: phospholipid bilayer in which individual phospholipids can move
mosaic: intrinsic and extrinsic proteins embedded
explain the role of cholesterol in membranes
connects phospholipids and reduces flexibility to make bilayer more stable
explain the role of glycolipids in membranes
cell signalling and cell recognition
explain the role of glycolipids in membranes
cell signalling and cell recognition
explain the function of membranes within cells
selectively permeable to regulate passage of molecules into/ out of organelles
name and explain 3 factors that may affect membrane permeability
temperature: high temperature denatures membranes proteins
PH: changes tertiary structure of membranes proteins
use of a solvent: may dissolve membrane.
name and describe 5 ways substances can move across the cell surface membrane [5]
diffusion of small/non-polar molecules down a concentration gradient
facilitated diffusion down a concentration gradient via protein carrier/ channel
osmosis of water down a water potential gradient
active transport against a concentration via protein carrier using ATP
co-transport of 2 different substances using a carrier protein
the movement of substances across cell membranes is affected by membrane structure. describe how [5]
cholesterol affects permeability/ fluidity
carrier proteins allow active transport
channel/ carrier proteins allow facilitation diffusion/co-transport
phospholipid bilayer allows diffusion of non-polar/lipid soluble substances
phospholipid bilayer prevents diffusion of polar/charged substances
membrane surface area/ number of channel/ carriers determines how much diffusion
the movement of substances across cell membranes is affected by membrane structure. describe how [5]
cholesterol affects permeability/ fluidity
carrier proteins allow active transport
channel/ carrier proteins allow facilitation diffusion/co-transport
phospholipid bilayer allows diffusion of non-polar/lipid soluble substances
phospholipid bilayer prevents diffusion of polar/charged substances
membrane surface area/ number of channel/ carriers determines how much diffusion
suggest and explain 2 ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients [2]
- membrane folded, so increased surface area
- large number of protein channels/ carriers in membrane for facilitated diffusion
- large number of protein carriers in membrane for active transport
what does the rate of facilitated diffusion depend on?
the concentration gradient
the number of channel/carrier proteins
explain why simple diffusion of chloride ions across a cell-surface membrane would be extremely slow
ions are water soluble and the centre of the phospholipid bilayer is hydrophobic
chloride ions in the cell aren’t immediately used up. describe what will happen to the rate of facilitated diffusion of the chloride ions into the cell over time
the rate of facilitated diffusion will slow down/level off.
as diffusion progresses, the concentration gradient of the chloride ions will decrease over time until an equilibrium is reached
name factors that affect the rate of diffusion
temperature
diffusion distance
surface area
size of molecule
concentration gradient
contrast the processes of active transport and facilitated diffusion [3]
facilitated diffusion involves channel/carrier proteins, whereas active transport only involves carrier proteins
Facilitated diffusion doesn’t use ATP whereas active transport uses ATP
facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient
compare and contrast the processes by which water and inorganic ions enter cells [3]
- both move down concentration gradient
- both move through protein channels in membranes
- ions can move against a concentration gradient by active transport
explain the function of ATP hydrolase when linked to the action of a carrier protein [2]
breaks down ATP into ADP and Pi which releases energy
this energy allows the active transport of ions
the movement of sodium ions out of the cell allows the absorption of glucose into the cell lining the ileum. explain how [2]
it maintains a concentration gradient for NA+ from ileum into cell
NA+ moving in by co-transport, brings glucose with it
explain how co-transport is involved in the absorption of glucose/amino acids in the small intestine
Na+ is actively transported out of epithelial cells into bloodstream.
Na+ concentration is lower in epithelial cells than lumen of gut
transport of glucose/amino acids from lumen to epithelial cells is coupled to facilitated diffusion of Na+ down electrochemical gradient
what does the rate of osmosis depend on?
the water potential gradient
thickness of exchange surface
surface area of exchange surface
what are the factors affecting the rate of active transport?
the number of carrier proteins
the speed of the individual carrier proteins
the rate of respiration in the cell and availability of ATP
suggest one explanation for the faster rate of plasmid replication in cells growing in a culture with a high amino acid concentration [2]
- amino acids used in respiration
- so more energy/ATP for plasmid replication
OR
- amino acids are used in respiration
- so more energy/ ATP for plasmid replication
