y5 bio: cluster 2 (origin of cells + cell structure)

what were the main atmospheric and environmental conditions of early earth?

higher CO₂, methane, lightning, UV radiation, and temperature

what are the four main requirements for the formation of protocells via abiogenesis?

catalysis, self-replication, self-assembly, and compartmentalisation

what was the main conclusion of the Miller-Urey experiment?

simple organic molecules, including amino acids, can form spontaneously under abiotic conditions simulating early earth

what were two major limitations or criticisms of the Miller-Urey experiment?

it used incorrect atmospheric gases (too little CO₂/N₂) and the conditions tended tohydrolyse chemical bonds, inhibiting polymerisation

why do scientists hypothesize that RNA was the genetic material in protocells?

RNA can both store genetic information (self-replicate) and catalyze chemical reactions (via ribozymes)

what are two key pieces of evidence supporting a last universal common ancestor (LUCA)?

the universal genetic code (64 codons) and hundreds of shared genes/biochemical pathways across all living organisms

what type of environment is hypothesised to have given rise to LUCA?

alkaline hydrothermal vents characterised by high heat (60–90°c), anaerobic conditions, and high concentrations of H₂, CH₄, and minerals

how do carbon isotope ratios indicate whether a material originated from a living organism?

living organisms selectively incorporate a higher ratio of carbon-12 relative to carbon-13

what do ancient carbon isotope ratios tell us about the timeline of life on earth?

they suggest that biological life existed on earth approximately 3.8 to 4.1 billion years ago

what is the definition of abiogenesis?

the natural process by which living organisms arose from non-living matter, such as simple organic compounds

what metabolic features characterised LUCA?

anaerobic metabolism capable of carbon dioxide and nitrogen fixation

what role did compartmentalisation play in protocell evolution?

it enclosed internal chemical reactions within a boundary, separating the internal microenvironment from the external surroundings

what four pieces of structural evidence support the endosymbiotic origin of mitochondria and chloroplasts?

they have their own naked circular DNA, possess 70s ribosomes, have double membranes, and divide independently via binary fission-like processes

what are the three core principles of cell theory?

1. all living organisms are composed of cells

2. cells are the smallest unit of self-sustaining life

3. all cells come from pre-existing cells

how do you calibrate an eyepiece graticule under a light microscope?

align the eyepiece graticule with a stage micrometer (a slide with a known scale) to calculate the distance per graticule unit for each objective lens

what is the formula for calculating magnification?

magnification = image size / actual size

what are the typical size ranges for prokaryotic VS eukaryotic cells?

prokaryotic cells are typically 1–10 µm and eukaryotic cells are 10-100 µm

why do electron microscopes provide higher resolution than light microscopes?

electron beams have much shorter wavelengths than visible light, allowing smaller structures to be distinguished clearly

what did freeze-fracture electron microscopy reveal about cell membrane structure?

it showed fracture lines passing through the middle of the bilayer, proving proteins are embedded within the lipid bilayer (singer-nicolson model) rather than forming outer layers (davson-danielli model)

what is cryo-electron microscopy (cryo-em) and its primary advantage?

a technique where samples are flash-frozen in liquid ethane, allowing 3d visualisation of proteins and cellular structures at near-atomic resolution in their native state

what three structural features are present in all living cells?

DNA, cytoplasm, and a plasma membrane

what are two examples of atypical, multinucleate animal/fungal structures?

skeletal muscle fibers and aseptate fungal hyphae

what are two functional advantages of a cell being multinucleate?

increased mRNA production and enhanced protein synthesis capacity to support large cell sizes

what is the main purpose of using immunofluorescence in microscopy?

to tag specific proteins or antigens using fluorescently labeled antibodies, visualising their precise locations within a cell

why does an increasing surface area to volume (SA/V) ratio limit maximum cell size?

as volume grows faster than surface area, transport across the membrane becomes insufficient to meet the cell's metabolic needs or remove waste

name three cellular adaptations that increase the SA/V ratio?

microvilli, cell flattening, and membrane invaginations