A2.1 Origin of Cells

Question 1

why was the Earth formed?

Answer 1

gravity caused dust and gas to come together

Question 2

describe the pre-biotic atmosphere

Answer 2

only traces of oxygen because it reacted with other elements; methane concs higher bc of intense volcanic activity and meteorites; CO2 concs higher bc of volcanic emissions

Question 3

why were temps higher than they are now?(4)

Answer 3

high concs of CO2 and CH4 which are heat-trapping greenhouse gases; comet and asteroid impacts; the ozone layer that now protects us wouldnt exist bc of lack of oxygen, without the layer more solar UV would have penetrated to earth’s surface; more lightening triggering other chemical processes

Question 4

where would carbon compounds be formed?

Answer 4

specialized environments eg hot springs on land or hydrothermal vents in oceans

Question 5

what would carbon compounds have formed?

Answer 5

droplets of water in the atmosphere, creating an ORGANIC AEROSOL HAZE which would have deposited into lakes/oceans creating a ‘soup’ of carbon compounds

Question 6

what happened as organisms came about?

Answer 6

they increases oxy conc and decreased CO2 conc so ozone layer formed giving protection against UV + greenhouse effect was reduced

Question 7

cells can be considered as…

Answer 7

the smallest units of self-sustaining life

Question 8

what are the 3 components of cell theory?

Answer 8

all living organisms are composed of one or more cells; the cell is the most basic unit of life; all cells arise from pre-existing cells by division

Question 9

what are the functions of life(Mr H Gren)

Answer 9

metabolism, response, homeostasis, growth, reproduction, excretion, nutrition

Question 10

which developments are needed for the origin or cells?

Answer 10

catalysis, self-assembly(carbon compounds eg amino acids need to assemble to form polymers), compartmentalisation(membrane to enclose cell contents), self-replication

Question 11

Miller-Urey experiment

Answer 11

passed steam through CH4, H, ammonia simulating earth’s atmo, used electricity to mimic lightening, found amino acids and carbon compounds could be formed, theorised these would then form polymers using energy from deep sea vents and trigger mechanisms for inheritance before becoming enclosed in a membrane to form a cell

Question 12

strengths of miller-urey experiment

Answer 12

repeatable-similar experiments have shown a diversity of carbon compounds can form spontaneously in an atmosphere lacking oxygen

Question 13

weaknesses of miller-urey experiment

Answer 13

miller and urey probs got some conditions wrong-pre-biotic Earth had more CO2 and N2 and less NH3 and CH4 and less lightning

Question 14

what is a vesicle?

Answer 14

small droplets of fluid, enclosed in a membrane

Question 15

what are exosomes?

Answer 15

extracellular vesicles which some cells produce

Question 16

what does the membrane of vesicles consist of?

Answer 16

mainly phospholipids, experiments show that bilayers spontaneously form stable spherical structures

Question 17

what would have happened if phospholipids were part of the ‘soup’ of carbon compounds?

Answer 17

they would have self-assembled into bilayers and vesicles would have likely formed but movement of pilar in and out would have been limited by hydrophobic membrane core so would have developed own internal chem(cell-like)

Question 18

what can RNA do?

Answer 18

store info like DNA but is self-replicating and can act as a catalyst

Question 19

what do some viruses use as genetic material?

Answer 19

RNA which supports theory that RNA could have been used before genes of DNA evolved

Question 20

LUCA

Answer 20

last universal common ancestor, the hypothetical organism from which all life on earth is believed to have descended

Question 21

what is convergent evolution?

Answer 21

when it’s possible for similar structures to evolve in organisms that don’t have a recent common ancestor

Question 22

conditions for luca?

Answer 22

would have used RNA to store genetic info and catalyse chemical reactions, would have been highly resistant to extreme environments

Question 23

evidence for luca?

Answer 23

universal genetic code in all cells, same building blocks for RNA and DNA in all cells, common molecular processes in all cells

Question 24

what is an emergent property?

Answer 24

characteristics of an organism not evident on a cellular level created by interactions between cells

Question 25

eg of minerals found in alkaline hydrothermal vents that act as catalysts to build organic molecules

Answer 25

iron and sulfur

Question 26

what is a micelle

Answer 26

an aggragate created through self-assembly of amphipathic molecules;hydrophobic ends face in and hydrophilic ends fce out

Question 27

what is a protocell

Answer 27

structures formed from the aggregation of abiotic components but has some similarities to living cells

Question 28

bc Earths early atmosphere was absent of O2 this suggests luca was…

Answer 28

anaerobic

Question 29

bc of earths hot thermal vents underwater it suggests luca was…

Answer 29

thermophilic bc thermal vents are v hot and autotrophic bc no organisms to take nutrition from and wouldnt use light as an energy source bc deep ocean is v dark

Question 30

fossils for the 3rd part of the timeline for early life

Answer 30

rocks in australia contain fossilized stromatolites which are rocky mounds formed by mats of cyanobacteria in shallow seawater which trap sediments and secrete CaCO3

Question 31

isotope ratios in rocks for the 2nd part of the timeline for early life

Answer 31

carbon originating from living organisms has a low 13C/12C ratio, banded iron rock dating from 3.8 Gya shows this, suggesting life had evolved by then

Question 32

genomic info for the 1st part of the timeline for early life

Answer 32

the no. of differences between the genomes of 2 species is proportional to the time since they diverged from a common ancestor. LUCA and the first living cells existed 4.5 Gya

Question 33

what kind of environment was it likely that LUCA lived in?

Answer 33

high concs of H, CO2 and iron and these conditions are found in and around hydrothermal vents in oceans

Question 34

which conditions do hydrothermal vents have that are needed for the 1st cells to form?

Answer 34

alkaline, white smoke that comes out is fluid at temps of 60 to 90 and contains high concs of H, methane, ammonia and sulfides. These chemicals could have been used to generate energy anaerobically which protocells could have used to assemble carbon compounds into polymers. CO2 needed by evolving protocells would have been abundant in the pre-biotic ocean water

Question 35

how did pasteur disprove spontaneous generation?

Answer 35

showed air was full of microorganisms, heated some broth in a flask to kill the microorganisms and left open to air through a swan-neck flask and nothing formed, broke the swan neck flask and saw microorganisms developed

Question 36

what are the 3 atypical cells and why are they atypical?

Answer 36

skeletal muscle bc they’re multinucleated; aseptate fungi bc they contain hyphae(cells) but no septa(cell walls); acetabularia bc they’re large single cells

Question 37

what happens as cells increase in size?

Answer 37

SA:V ratio decreases; reduces speed at which substances enter and exit the cell; reduces rate of both energy and heat transfer limiting rate of metabolism; this restricts the size of the cell which is why most cells are small

Question 38

define differentiation

Answer 38

development of cells in different ways to carry out specific functions; involves the expression of certain genes in a cell’s genome and enables emergent properties

Question 39

pluripotent

Answer 39

stem cell can differentiate to form any cell in an organism

Question 40

multipotent

Answer 40

stem cell can differentiate to form many different cells in an organism

Question 41

where can stem cells be found in humans?

Answer 41

embryonic(contained within embryo, pluripotent); cord blood stem cells(found in umbilical cord, multipotent); adult stem cells(found in bone marrow, multipotent)

Question 42

how can stargardt’s disease be treated with stem cells?

Answer 42

blindness in children due to a dysfunction of retinal cells in the eye, stem cells injected into the eye and differentiate into healthy retinal cells curing the blindness

Question 43

how can stem cells be used to treat leukaemia?

Answer 43

production of abnormal WBCs; stem cells extracted from bone marrow and chemotherapy kills the remaining cells; stem cells reintroduced and differentiate to form new healthy WBCs

Question 44

what does endosymbiotic theory provide evidence for?

Answer 44

provides evidence for the origin of eukaryotes

Question 45

which experiment disproved spontaneous generation?

Answer 45

Louis Pasteur

Question 46

what is the endosymbiotic theory?

Answer 46

states that larger prokaryotes engulfed smaller prokaryotes; have their og membrane and the membrane of larger prokaryotes

Question 47

what characteristic of a steroid shows it is a lipid?

Answer 47

it has a very low proportion for oxygen to carbon