y5 bio: cluster 2

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 to hydrolyse 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 hypothesized to have given rise to LUCA?

alkaline hydrothermal vents characterized by high heat (60–90°C), anoxic conditions, and rich 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 characterized 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 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

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 visualization 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 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 is the main purpose of using immunofluorescence in microscopy?

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

what is the definition of a cellular organelle?

a discrete structure within a cell adapted to perform a specific, specialized function.

which common structures are classified as organelles, and which are excluded?

included: plasma membrane, nucleus, ribosomes, vesicles. excluded: cell wall, cytoplasm, cytoskeleton.

what is the key advantage of separating the nucleus from the cytoplasm in eukaryotic cells?

it allows post-transcriptional processing (e.g., splicing) and mRNA quality control to occur before translation begins.

what are the three main advantages of cytoplasmic compartmentalisation?

1. concentration of enzymes/substrates. 2. maintenance of optimal local microenvironments (e.g., pH). 3. iSolation of incompatible biological processes.

gIve an example of compartmentalisation isolating destructive processes in animal cells?

lysosomes isolate hydrolytic enzymes to prevent self-digestion of the surrounding cytoplasm.

how does the structure of the inner mitochondrial membrane support ATP synthesis?

highly folded cristae maximize surface area for electron transport chains, while the narrow intermembrane space allows rapid proton gradient buildup.

how are thylakoids structurally adapted for efficient light-dependent reactions in photosynthesis?

grana stack to provide a large surface area for photosystems and ETCs, while small internal lumen volumes allow quick proton accumulation.

what is the function of the stroma in chloroplasts?

it isolates and concentrates RuBisCO and other enzymes/substrates required for the light-independent Calvin cycle.

what is the functional difference between free ribosomes and bound ribosomes on the rough ER?

free ribosomes synthesize proteins intended for use within the cytosol

what is the path of a protein intended for secretion from synthesis to release?

rough ER -> Transport Vesicle -> Golgi Apparatus -> Secretory Vesicle -> Plasma Membrane (Exocytosis).

what are the main processing functions of the Golgi apparatus?

modifying, sorting, and packaging proteins (including post-translational modifications like glycosylation and phosphorylation).

what is the structural role of clathrin in endocytosis?

claritin forms a polymerised triskelion lattice/cage that bends the plasma membrane into an invaginated pit.

what is the role of dynamin in vesicle formation?

dynamin uses GTP hydrolysis energy to pinch off (cause scission of) the newly formed vesicle from the membrane.

what is the difference between constitutive secretion and regulated secretion?

constitutive secretion releases substances continuously, whereas regulated secretion stores vesicles until triggered by a specific extracellular signal.

what is cell differentiation, and what signaling molecules direct it?

the process by which unspecialised cells become specialized, directed by signal gradients of morphogens that provide positional cues.

what is a stem cell niche?

a specialized microenvironment within tissues that maintains stem cells and regulates their self-renewal and differentiation.

what are two specific examples of stem cell niches in humans?

the bone marrow niche (hematopoiesis) and the hair follicle niche (hair/skin regeneration).

how do totipotent, pluripotent, and multipotent stem cells differ in potency?

toti potent cells can form any cell type (including extra-embryonic tissues)

what are the three embryonic germ layers formed by pluripotent cells?

ectoderm, mesoderm, and endoderm.

why does a decreasing 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?

microvili, cell flattening, and membrane invaginations.

how are Type 1 and Type 2 pneumocytes structurally adapted for their functions?

type 1: extremely thin with minimal cytoplasm to shorten gas diffusion distance. type 2: cuboidal shape with dense vesicles that secrete surfactant to prevent alveolar collapse.

what are two key structural differences between cardiac muscle cells and striated (skeletal) muscle cells?

cardiac muscle cells are short, branched, and single-to-few nucleated

what is the function of intercalated discs in cardiac muscle tissue?

they contain gap junctions that allow rapid passage of ions between cells, enabling synchronized contraction.

how are the midpiece and head of a sperm cell adapted for fertilization?

the midpiece contains abundant mitochondria for flagellar movement

what is the function of cortical granules in an unfertilized egg cell?

they release enzymes via exocytosis immediately after sperm entry to harden the zona pellucida, preventing polyspermy.