A2.1 Origins of cells, A2.2, A2.3 Flashcards
Conditions of early earth (6)
Surface Temp: 75-95 C
single global ocean (no land masses)
bombarded by asteroids/comets
no ozone layer
hotter liquid inner core –> weaker magnetic field –> high levels of cosmic + solar (UV) radiation
extreme weather - electric storms
Asteroids/Comets in influencing early earth conditions (3)
asteroid/comets brought water + other compounds
collisions + volcanoes released methane + ammonia gas
earth’s early atmosphere - methane, ammonia, water vapour, CO2
How were carbon compounds formed from early earth (4)
reducing atmosphere due to reducing gases (ammonia + methane)
able to donate electrons to other molecules –> enables chemical reactions
reactions formed more complex carbon compounds (amino acids + hydrocarbons)
carbon compounds could be joined to form building blocks of cells (proteins, nucleic acids, lipids)
Define metabolism (2)
chemical reactions that take place in the cells of an organism
enzymes speed up these chemical reactions
Define response to stimuli/sensitivity (2)
responding to changes/external stimuli in environment
e.g detecting chemicals in environment –> moving towards or away from area
Define homeostasis (2)
maintenance of constant internal conditions
e.g active transport to control concentration of ions
Define movement
organisms having control over their position and location
Define growth (2)
increase in cell size + number or dry mass over period of time
e.g cell division
Define reproduction
production of offspring + passing down of genes
Define excretion
removal of metabolic waste
Define nutrition (2)
intake/production of nutrients
nutrients obtained through external environment or produced from inorganic material
Necessary steps for the spontaneous origin of cells to be brought about by evolution (5)
formation of simple organic compounds (amino acids + hydrocarbons)
catalysis - control over chemical reactions
larger organic molecules formed from simpler ones
self-replication of molecules
compartmentalisation - membrane to enclose cell contents
Aim of Miller and Urey’s experiment (2)
proving spontaneous origin of cells
simulate earth’s prebiotic conditions
Miller and Urey’s closed system (3)
water - simulated ocean
gas inlet - to add reducing gases (methane, ammonia, hydrogen)
electrical sparks - simulate electric storms
Procedure of Miller and Urey (4)
water vaporised –> run through gases + electric sparks
cooling jacket to condense water
water droplets represented primordial soup
water droplets collected + analysed
Results of Miller and Urey (3)
water droplets contained basic organic monomers (amino acids)
proved that non-living synthesis of organic compounds was possible
could have been how carbon compounds originated
Explain the spontaneous formation of vesicles (2)
fatty acids spontaneously coalesce due to hydrophobic/hydrophillic traits
formed spherical bilayer - curved to reduce hydrophobic tail exposure
Function of spontaneous formation of vesicles (2)
interior provides different chemical environment to outside
allows cell to control/maintain conditions (e.g pH level, solute concentration)
RNA first genetic material hypothesis (2)
basis for formation of first cell-structure
acts as genetic material + catalyst
What is suggested if the hypothesis that RNA was the first genetic material is true (5)
RNA formed from inorganic sources
able to replicate using ribozymes (RNA molecules with enzymatic activity)
able to catalyse protein synthesis
RNA able to produce DNA + protein
DNA became main genetic material due to being more stable
Evidence to support RNA first hypothesis (3)
RNA can self-replicate - short RNA sequences can duplicate other RNA molecules
RNA has some catalytic activity - could have initially acted as genetic material + enzymes
ribozymes still catalyse peptide bond formation in protein synthesis
Miller-Urey hypothesis
spontaneous generation of simple organic molecules in pre-earth conditions (amino acids, carbohydrates, lipids)
Metabolism first hypothesis (4)
simple metabolic reactions –>
simple metabolic pathways –>
formed more complex molecules –>
formed basis of cells
“Sulfur world” hypothesis
forms of life based on ion-sulfur chemistry
“Lipid world” hypothesis (2)
lipid bilayers evolved before RNA
provide protective layer for RNA
Define LUCA (3)
last universal common ancestor
original life forms that gave rise to all species existing today
likely that there was more than one life form –> may have gone extinct through competition from LUCA
Features of LUCA (4)
single-celled autotrophic microbe
possible RNA genome
anaerobic
existed in hydrothermal vents in ocean - hydrogen, methane, sulfur used as an energy source
Evidence for LUCA
universal genetic code across all living organisms may have originated from LUCA
Why the universal genetic code was preserved (3)
genetic code has been conserved
essential for the transmission of genetic information
any change to this genetic code could be detrimental to organism
Relationship between LUCA, bacteria, archaea, eukaryotes (2)
bacteria + archaea arose from LUCA
eukaryotes - endosymbiosis of bacteria + archaea
Define a specimen
object being viewed under a microscope
Using a microscope (6)
start with lowest magnification + stage at the highest position.
adjust coarse + fine focus to get clear image of specimen
look through eyepiece
anticlockwise to move specimen further from lens, and clockwise to move it closer
use fine focus knob/wheel to image clearer
adjust magnification - rotating nosepiece to use different objective lens
Define cell theory (3)
all organisms made up of one or more cells
cells = smallest unit of life
all cells come from pre-existing cells
Making temporary mounts of cells/tissues (onion) (5)
scapel to cut piece off (onion)
tweezers to place onto glass slide
add drop of iodine
lower cover slip over specimen
gently press cover slip to push out bubbles
Define stains (3)
distinguish between parts of cells due to them usually being transparent
bind to particular structures - making it easier to identify
e.g iodine for plants
Define cover slips/slides (4)
small thin pieces of glass
hold specimen in place
prevent specimen from drying out
prevent specimen from touching lens of microscope
Define deductive reasoning (2)
starting with a rule/hypothesis
testing the rule through experiments
Define inductive reasoning (2)
starting with examples
attempting to form rule/hypothesis
Inductive reasoning in cell theory (2)
observation - parts of diverse organisms consist of cells
hypothesis - all organisms consist of ells
Define magnification
number of times larger an image is than an object
image size/actual size
Define resolution (2)
ability to distinguish 2 close points as separate rather than one
clarity of image
micrometers to millimitres (2)
1 micrometer = 0.001millimitres
1 millimeter = 1000 micrometers
micrometers to nanometers
1 micrometer = 1000 nanometers
Quantitative vs Qualitative data (2)
quantitative - numerical + objective
qualitative - observations/descriptions that are more subjective
Define transmission electron microscopes (3)
beam of electrons passed through specimen
electrons absorbed by denser parts of sample + scattered/pass through less dense areas
picked up by electron detector —> forms image
Advantages of electron microscopes (2)
shorter wavelengths than light –> higher resolution
magnification of 500,000x
Disadvantages of electron microscopes (2)
only give black and white images
electron beams kill specimen
Define freeze-fracture in microscopy (5)
sample frozen
then physically broken apart
vapour of carbon/platinum fired onto fracture –> replica of fracture
electron microscopy used to observe replica
gives image of cell’s internal structure
Define cryogenic electron microscopy (4)
flash-freezing sample to cryogenic temperatures (placed in liquid ethane) - makes molecules more firm/stable
specimen then viewed using electron microscopy
computer algorithms - create 3D image of protein molecules
primarily used for structure of proteins
Advantages of cryogenic electron microscopy (2)
freezing sample improves resolution + reduces damage that may occur from the electron beam
captures protein at instant time
Define immunofluorescence light microscopy (4)
fluorescent tag (fluorophore) - attached to antibodies specific for specimen
antibody binds to the antigen –> structure ‘tagged’ with immunofluorescence
certain wavelength of light shone onto fluorescence tag –> emits light of different colour
appear as brightly coloured spots –> can locate target molecules
Define fluorescent dye light microscopy (3)
dye added to sample –> attach to certain structures.
dye absorbs light at one wavelength –> re-emits fluorescence
labelled areas become brightly coloured spots –> can locate target molecules in specimen
Structures of typical cells (3)
plasma membrane
cytoplasm
DNA
Features of plasma membrane (2)
separates cell from external environment
controls what exits/enters cell
Features of cytoplasm (3)
water-based jelly-like fluid
suspends organelles of cell
site of enzymes that carry out metabolic reactions
Features of DNA (2)
contain information for cell to carry out its functions
hold instructions for making proteins
Define prokaryotes (3)
unicellular organisms that lack membrane bound organelles
no nucleus
e.g bacteria, archaea
Features of prokaryotes (6)
cell wall
plasma membrane
cytoplasm
naked DNA in a loop
70s Ribosomes
plasmid
Naked DNA as a component of prokaryotes (3)
single molecule of DNA as a loop
not associated with histone proteins
found in region called nucleoid
70S ribosomes as a component of prokaryotes (2)
protein synthesis
smaller mass than eukaryotic ribosomes
Plasmids as components of prokaryotes
small/circular pieces of DNA that can be transferred from one prokaryotic cell to another (horizontal gene transfer)
Define eukaryotes (3)
cells with a nucleus and membrane bound organelles
usually larger than prokaryotes
some are multicellular (organism consists of more than one cell)
