Basic Chemical Context of Life notes Flashcards

Question

triglycerides

Answer 1

describe structures consisting of three fatty acid chains attached to a glycerol backbone. Can be saturated or unsaturated

Answer 2

contain **no double bonds** and have straight chains; are **bad** for health since the straight chains stack densely and form fat plaques

Answer 3

contain double bonds that cause kinks in chains; are better for health since chains stack less densely **can be cis or trans**

Answer 4

comprised of **two fatty acids** and a **phosphate group** (+R) attached to a glycerol backbone * are amphipathic, which means has both hydrophobic and hydrophilic properties

Answer 5

comprised of three 6-membered rings and one 5-membered ring; include hormones and cholesterol

Answer 6

1. **phospholipids** 2. **waxes** - esters of fatty acids and monohydroxylic alcohols, used as a protective coating on the skin 3. **steroids** - sex hormones, cholesterol, corticosteroids - 4 ringed structures 4. **carotenoids** - fatty acid carbon chains with conjugated double bonds and five/six-membered carbon rings at each end. includes pigments which produce colors in plants and animals * subgroups are carotenes and xanthophylls 5. **porphyrins** - 4 joined pyrrole rings that often complex with a metal (porphyrin heme complexes with fe in hemoglobin; chlorophyll with Mg) 6. **adipocytes** - specialized fat cells in two categories * white fat cells - composed primarily of triglycerides with a thin layer of cytoplasm around it * brown fat cells - have considerable cytoplasm, lipid droplets scattered throughout, and lots of mitochondria 7. **glycolipids** - similar to phospholipids but they have a carbohydrate group instead of a phosphate group 8. **lipoproteins** - lipids are insoluble so they are transported in the blood via lipoproteins, which are lipids cores surrounded by phospholipids and apolipoproteins

Answer 7

cell membranes need to maintain a certain degree of fluidity and are capable of changing membrane fatty acid composition to do so * **in cold weather** - cell membranes become more rigid. in order to avoid rigidity, cholesterol and mono and polyunsaturated fatty acids are incorporated into the membrane, which increases fluidity * **in warm weather** - cell membranes become more fluid and flexible. in order to avoid cell membrane collapse, _cholesterol_ is added to restrict movement. the fatty acid tails are saturated so they become straight and pack tightly, thus decreasing fluidity

Answer 8

amino group carbon side chain carboxyl group

Answer 9

polymers of amino acids joined by peptide bonds.

Answer 10

1. **storage proteins** - casein in milk, ovalbumin in egg whites, and zein in corn seeds 2. **transport proteins** - hemoglobin carries oxygen, cytochromes carry electrons 3. **enzymes** - catalyze reactions in both forward and reverse directions * efficiency is determined by substrate and enzyme concentration, temperature, pH and presence/absence of any inhibitors * amylase catalyzes reactions that break alpha-glycosidic bonds in starch 4. **cofactors** - non-protein molecules that assist enzymes; the union of a cofactor + enzyme is a _holoenzyme_ (when an enzyme is not combined with a cofactor, it is called and _apoenzyme/apoprotein_) * if the cofactor is organic, it is a coenzyme * if a cofactor is covalently bound to an enzyme, it is called a prosthetic group

Answer 11

1. **simple** - formed entirely of amino acids - **albumins & globulins** - functional proteins that act as carriers or enzymes - **scleroprotein** - fibrous proteins, have structural function (e.g. collagen) 2. **conjugated** - simple protein + non-protein - **lipoprotein** - protein bound to lipid - **mucoprotein** - protein bound to carbohydrate - **chromoprotein** - protein bound to pigmented molecule - **metalloprotein** - protein complexed around metal ion - **nucleoprotein** - contains histone or protamine, bound to nucleic acid

Answer 12

sequence of amino acids connected by peptide bonds

Answer 13

3D shape resulting from hydrogen bonding between amino acid and carboxyl groups of adjacent amino acids (alpha helix or beta sheet)

Answer 14

3D structure that forms primarily due to non-covalent interactions between amino acid R groups * non-covalent interactions include H-bonds, ionic bonds, hydrophobic effect (R groups push away from water), and Van der Waals forces * includes disulfide bonds (strong type od covalent bond between cysteins) which contribute to tertiary structure

Answer 15

3D shape of a protein that is a grouping of two or more separate peptide chains

Answer 16

* somewhat water soluble * mostly tertiary * diverse functions: enzymatic, hormonal, inter and intracellular storage, transport, osmotic regulation, immune response

Answer 17

* not water soluble * mostly secondary * made of long polymers * function: maintain and add strength to cellular and matrix structure (collagen or keratin)

Answer 18

includes proteins that function as membrane pumps, channels, or receptors

Answer 19

when proteins are taken out of their ideal temperature, pH range, or solvent, denaturation can occur **means the protein is reversed back to its primary structure**

Answer 20

overall term for DNA and RNA, essential to all forms of life function: to encode, express, and store genetic information

Answer 21

monomers that make up nucleic acids and consist of a **nitrogenous base, 5C sugar, and a phosphate group**

Answer 22

states that * all living organisms are comprised of one or more cells * the cell is the basic unit of structure, function, and organization in all organisms * all cells come from preexisting, living cells * cells carry hereditary information

Answer 23

proposes that self-replicating RNA molecules were precursors to current life. also states that RNA stores genetic information like DNA and catalyzes chemical reactions, leads to the belief that RNA may have played a major role in evolution

Answer 24

states that biological information cannot be transferred backwards from protein to protein or nucleic acid. Rather, information must travel from: DNA --> RNA --> proteins

Answer 25

uses visible light to view the surface of a sample _pro_: can view living samples _con_: has low light resolution compared to a compound microscope

Answer 26

uses visible light to view a thin section of a sample _pro_: can view *some* living samples (single cell layer) _con_: may require staining

Answer 27

uses light phases and contrast for a detailed observation of living organisms, including internal structures if thin _pro_: has good resolution and contrast _con_: not ideal for thick samples and produces a "halo effect" around perimeter samples

Answer 28

used to observe thin slices while keeping a sample in tact; common method for viewing chromosomes during mitosis _pro_: can observe specific parts of cell using fluorescent tagging _con_: can cause artifacts can be used without fluorescence, dye specimen

Answer 29

_pro_: view surface of 3D objects with high resolution _con_: can't use on living samples, preparation is extensive as sample needs to be dried and coated; costly

Answer 30

similar to SEM _pro_: sample is not dehydrated so you can observe samples in their more 'natural form' _con_: can't use on living samples, samples must be frozen, which can cause artifacts

Answer 31

_pros_: can observe very thin cross-sections in high detail, and can observe internal structures with very high resolution _cons_: cannot be used on living samples, preparation of sample is expensive, and technique is costly

Answer 32

not a type of microscope, but a technique used to build up a 3D model of sample using TEM data _pro_: can look at objects in 3D and see objects relative to one another _con_: same as TEM, cannot be used on living samples, costly

Answer 33

common technique used to prepare a sample for observation or further experimentation. it spins and separates liquified cell homogenates into layers based on **density** for cell based on highest density to lowest: nuclei layer -> mitochondria/chloroplasts/lysosome -> microsomes/small vesicles -> ribosomes/viruses/larger macromolecules

Answer 34

forms continuous layers of sediment, where insoluble proteins are found in the pellet while soluble proteins remain in the supernatant, liquid above the pellet

Answer 35

recall that enzymes are globular proteins that act as catalysts

Answer 36

ATP is a common source of activation energy, and the compound stores its potential energy in the form of chemical energy. new ATP is formed via phosphorylation, ADP and phosphate come together using energy from an energy rich molecule like glucose

Answer 37

enzymes must be strictly regulated to ensure that they are only functional for specific use

Answer 38

Michaelis constant, and represents the substrate concentration at which the rate of reaction is **half** of the max velocity of the enzyme, or Vmax * a small Km indicates that an enzyme requires only a small amount of substrate to reach max velocity * a higher Km means the enzyme needs more substrate to reach max velocity

Answer 39

have both an active site for substrate binding and an allosteric site for the binding of an allosteric effector (can be an activator or inhibitor)

Answer 40

a substance that mimics the substrate and inhibits the enzyme by binding at the active site. the effect of competitive inhibition can be overcome by increasing substrate competition **Km raised but Vmax is not**

Answer 41

substance inhibits enzyme by binding elsewhere than the active sire, allowing the substrate to still bind, but the reaction is prevented from completing **Km is unchanged but Vmax is lowered**

Answer 42

occurs when an enzyme inhibitor binds only to the formed enzyme-substrate complex, preventing formation of product

Answer 43

when an enzyme becomes more receptive to additional substrate molecules after one substrate molecule binds to the active site * ex: hemoglobin is a quaternary protein with 4 subunits that each have an active site for oxygen. when oxygen binds to one site, the other sites are more likely to bind oxygen

Answer 44

loosely attached to the surface of one side of the membrane * generally hydrophilic * held in place by H bonding and electrostatic interactions * can disrupt/detach them by changing salt concentration or pH

Answer 45

embedded in the cell membrane * hydrophobic * can be destroyed using detergent

Answer 46

type of integral membrane that travels all the way through the cell membrane

Answer 47

provide a passageway through membrane for hydrophilic, polar, and charged substances

Answer 48

type of glycoprotein that is used to distinguish between self and foreign

Answer 49

used to pass ions across the membrane and referred to as gated channels in nerve and muscle cells * voltage-gated (respond to difference in membrane potential) * ligand-gated (chemically binds to open channel) * mechanically gated (respond to pressure or vibration)

Answer 50

allow the passage of certain ions and small polar molecules; increase the rate of water passing in kidney and plant root cells * tend to be less specific

Answer 51

specific to movement across the membrane via integral membrane protein * changes shape after binding to specific molecule that enables it to be passed across

Answer 52

proteins that can use ATP to transport material across the membrane * includes active transport (Na+ K pump) * facilitated diffusion

Answer 53

attach cells to neighboring cells and provide anchors for stability via internal filaments and tubules

Answer 54

serve as binding sites for hormones and other trigger molecules

Answer 55

* allows small, uncharged, non-polar, hydrophobic molecules to free pass the membrane (steroids) * polar molecules may cross if they are small and uncharged * every other substance needs a transporter

Answer 56

adds rigidity to animal cell membranes under normal conditions and maintains fluidity of the membrane at lower temperatures

Answer 57

adds rigidity to plant cell membranes

Answer 58

adds rigidity in prokaryotic cells

Answer 59

a carbohydrate coat that covers the outer face of bacterial cell walls and animal cell plasma membranes * consist of glycolipids attached to the plasma membrane, and glycoproteins that may serve as **recognition proteins** * functions include *adhesive capabilities, barrier to infection, or markers for cell-cell recognition*

Answer 60

* in nucleus * general packaging structure of DNA around proteins in eukaryotes; tightness in packaging depends on cell stage

Answer 61

tightly condensed chromatin when the cell is ready to divide

Answer 62

serve to organize DNA which coil around it into bundles called nucleosomes; these bundles are wrapped around 8 histone proteins

Answer 63

inside of the nucleus and serves as the site of ribosome synthesis

Answer 64

synthesized using rRNA and ribosomal proteins which are imported from the cytoplasm. exported to the cytoplasm for final assembly into completed ribosome * function to make proteins* * composed of two subunits: 60S + 40S = 80S in eukaryotes, and 50S + 30S = 70S in prokaryotes * the two subunits are produced inside of the nucleolus and moved into the cytoplasm where they are assembles * larger S value indicated a heavier molecule

Answer 65

a dense fibrillar network inside of the nucleus of eukaryotic cells that provides mechanical support; helps regulate DNA replication, cell division, and chromatin organization

Answer 66

the irregular shaped region within **prokaryote cells** that contains all or most of the cell's genetic material

Answer 67

most of the cell's metabolic activity and transport occur here, and the area includes the cytosol and organelles

Answer 68

the difference between the cytosol and cytoplasm is that the cytosol doesn't include the components suspended within the gel-like substance, it is JUST the gel-like substance

Answer 69

studded with ribosomes and creates glycoproteins by attaching polysaccharides to polypeptides as they are assembled by ribosomes * in eukaryotes, the rough ER is continuous with the outer nuclear membrane

Answer 70

ER without ribosomes that serves to synthesize lipids and steroid hormones for export. in liver cells, it breaks down toxins, drugs, and toxic by-products from cellular reactions * smooth and striated muscle have smooth ER's called sarcoplasmic reticulum that store and release ions like Ca2+

Answer 71

* vesicles produced from golgi * contain digestive enzymes with low pH * function in apoptosis * break down nutrients, bacteria, and cell debris

Answer 72

* transport various substances in vesicles * plays important role in modifying and packaging proteins * contains flattened sacs called cisternae - cis face = incoming vesicles, trans face = secretory vesicles

Answer 73

* common in liver and kidney * breakdown substances, fatty acids, and amino acids * in plant cells, they modify by-products of photorespiration * in germinating seeds, they are called glyoxysomes which break down stores fatty acids * peroxisomes produce H2O2, which they use to oxidize substrayes

Answer 74

made up of the protein tubulin * provide support and motility * act as spindle apparatus which guides chromosomes during division * can be found in flagella and cilia of all animal cells and lower plants like mosses and ferns in a 9+2 array - 9 pairs of microtubules with 2 singlets in the center

Answer 75

provide support for maintaining cell shape * keratin

Answer 76

* made of actin * cell motility * found in skeletal muscle, amoeba pseudopod, and cleavage furrows

Answer 77

* structures that include centrosomes and basal bodies * found at base of each flagellum and cilium * organize their development * 9x3 array * plants do have MTOCs

Answer 78

moves materials between organelles or between organelles and the plasma membrane

Answer 79

temporary receptacles of nutrients that merge with the lysosomes in order to breakdown food

Answer 80

* generally large * can occupy most of the plant cell interior * exert turgor when fully filled to maintain rigidity * store nutrients * carry out functions performed by lysosomes in animal cells * specialized membrane called a *tonoplast*

Answer 81

location where plants store starch, pigments, and toxic substances such as nicotine

Answer 82

found in single-celled Protista organisms like amoeba and paramecium * function to collect and pump excess water out of the cell via active transport to prevent bursting

Answer 83

* cellulose - plants * chitin - fungi * peptidoglycan - bacteria * polysaccharides - archaea

Answer 84

found in animals between adjacent cells; is occupied by fibrous structural proteins, adhesion proteins, and polysaccharides secreted by cells * function to provide mechanical support and helps bind adjacent cells * collagen is the most common protein, but we also see integrin and fibronectin * is a network of collagen and proteoglycans connected to integrins in the cell membrane via fibronectin and laminin * also function in transmitting mechanical and chemical signals between the inside and outside of the cell

Answer 85

connection of the ECM to actin filaments in the cell

Answer 86

connection of ECM to intermediate filaments like keratin

Answer 87

cells that produce collagen and other connective tissue elements

Answer 88

organelles found in plant cells

Answer 89

double-layered organelles that make ATP, and serve as the site of fatty acid catabolism, or Beta-oxidation; have their own circular DNA and ribosomes

Answer 90

includes microtubules (flagella and cilia), microfilaments, intermediate filaments; found in eukaryotic cells * aids in cell division, cell crawling, and the movement of cystoplasm and organelles

Answer 91

* in a hypotonic solution (their normal state), the vacuole swells and becomes *turgid* * in an isotonic solution, the plant cell is flaccid * in a hypertonic solution, the cell is plasmolyzed - the cytoplasm is pulled away from the cell wall

Answer 92

the network of organelles and structures, either directly or indirectly connected, that function in the transport of proteins and other macromolecules into or out of the cell * includes plasma membrane, ER, Golgi apparatus, nuclear envelope, lysosomes, vacuoles, vesicles, and endosomes, but **NOT the mitochondria or chloroplasts**

Answer 93

* _brownian movement_ ( random particle movement due to kinetic energy, spreads small suspended particles throughout the cytoplasm) * _cyclosis/streaming_: circular motion of cytoplasm within the cell to transport molecules * _endoplasmic reticulum_: provides channel through cytoplasm, provides direct continuous passageway from plasma membrane to nuclear membrane

Answer 94

* _diffusion_: if cells are in close contact with the external environment, diffusion can suffice for food and respiration needs. this is also used for transport of materials between cells and interstitial fluid around cells in more complex animals * _circulatory system_: required by complex animals with cells too far from the external environment

Answer 95

* includes desmosomes - keratin filaments attached to adhesion plaques which bind adjacent cells together via connecting adhesion proteins, providing mechanical stability by holding cellular structures together * present in animal cells in tissues with mechanical stress * including cells in the skin epithelium and cervix/uterus

Answer 96

* completely encircles each cell, producing a seal that prevents the passage of materials between cells * is characteristic of cells lining the digestive tract where materials are required to pass through cells into the blood * by doing this, tight junctions prevent the passage of molecules and ions through the space between cells

Answer 97

* narrow tunnels between animal cells (connexins) that prevent cytoplasms of each cell from mixing * allow passage of ions and small molecules * essentially channel proteins of two adjacent cells that are closely aligned * tissues like the heart include these to quickly pass electrical signals

Answer 98

* narrow tunnels between plant cells * narrow tube of endosplamic reticulum - desmotubule - that exchanges material through the cytoplasm surrounding the desmotubule

Answer 99

bacteria, cyanobacteria, and archaebacteria

Answer 100

1. no nucleus 2. single, circular, naked, double-stranded DNA ( no chromatin level organization) 3. ribosomes (50S + 30S = 70S) 4. cell walls (peptidoglycan); archaea (polysaccharides) - many have sticky capsules on the cell wall 5. flagella that are constructed from flagellin, not microtubules

Answer 101

collective movement of substances such as blood in response to a force or pressure

Answer 102

* simple diffusion * osmosis * dialysis (diffusion of different solutes across a selectively permeable membrane) * plasmolysis (movement of water out of a cell that results in its collapse) * facilitated diffusion * countercurrent exchange *diffusion by bulk flow in opposite directions such as blood and water in fish gills) diffusion is **net** movement

Answer 103

movement of molecules against concentration gradient, requiring energy * usually involves solutes like small ions, amino acids, monosaccharides three types: 1. primary 2. secondary 3. group translocation

Answer 104

energy is directly used to move against concentration gradients

Answer 105

* energy is indirectly used to move against concentration gradient (usually with an ion moving down its concentration gradient) * can be **antiport (exchange)** or **symport (cotransport)**

Answer 106

seen in prokaryotes when the substance being transported across the membrane is chemically altered in the process, which prevents it from diffusing back out

Answer 107

encompasses three different types of active transport 1. **phagocytosis** - undissolved material (solid) enters cell; white blood cell engulfs the material as the plasma membrane wraps outward around the substance 2. **pinocytosis** - the plasma membrane invaginated around dissolved material (liquid) 3. **receptor-mediated endocytosis** - a form of pinocytosis in which specific molecules called _ligands_ bind to receptors

Answer 108

encompasses transportation out of the cell

Answer 109

tell us whether a given chemical reaction can occur spontaneously *ΔG = ΔH - TΔS * H is enthalpy * T is temperature * S is entropy - if ΔG is negative, the reaction can occur spontaneously - an unfavorable reaction with a positive ΔG1 value can be driven be a second, highly favorable negative ΔG2 value - in a spontaneous change, the Gibbs free energy goes down, stability goes up, and work capacity goes down - Basal Metabolic Rate (BMR) increases as body size increases, but decreases *per kg* as size goes up

Answer 110

overall oxidative, exergonic process (ΔG= -868kcal/mol) that breaks down glucose in order to derive energy in the form of ATP

Answer 111

cell division in all body cells (somatic), except for germ/reproductive cells 5 steps: 1. prophase 2. metaphase 3. anaphase 4. telophase 5. cytokinesis

Answer 112

* nucleus disassembles * nucleolus disappears * chromatin condenses into chromosomes * nuclear envelope breaks down * mitotic spindle forms * microtubules (composed of tubulin) begin connecting to kinetochores

Answer 113

* chromosomes line up along the center of the cell and spindle fibers attach to the kinetochore of each chromatid * karyotyping is performed in metaphase

Answer 114

* microtubules shorten * each chromosome is pulled apart into two chromatids * once separated, it is a chromosome, and the chromosome number doubles * the microtubules pull the chromosomes to opposite poles of the cell (_disjunction_) * at the end of this phase, each pole has a complete set of chromosomes note: cohesin proteins are what bind the sister chromatids together and break down

Answer 115

* chromosomes arrive at opposite poles and begin to decondense * nuclear envelope material surrounds each set of chromosomes * mitotic spindle breaks down * nuclear division occurs in this step

Answer 116

1. _cleavage furrow_ forms in animal cells - shortening of actin and myosin microfilaments and the plasma membrane is pulled into the center of cell 2. a _cell plate_ forms in plant cells, which involves vesicles from Golgi bodies migrating and fusing to form a cell plate. As the plate grows, it merges with the plasma membrane, eventually separating the two new cells

Answer 117

G1, S, G2, and M (mitotic) phases **G1**: cell increases in size and lots of proteins and ribosomes are synthesized. the G1 checkpoint ensures that everything is ready for DNA synthesis, and the phase as a whole is the most variable in length. if G1 checkpoint fails, cell enter G0, a non-dividing state **S**: DNA synthesis occurs where a new DNA molecules is replicated from the first, providing for sister chromatids **G2**: rapid cell growth occurs, organelles are replicated, and genetic material prepares for cell growth. G2 checkpoint checks for sufficient Mitosis Promoting Factor (MPF) note: interphase occurs during G1, S, and G2. most time spent here - growth occurs in all 3 interphase phases - M checkpoint checks if all chromosomes are attached to kinetochores, triggers start of anaphase

Answer 118

* a CDK enzyme activates proteins that regulate the cell cycle via phosphorylation * activated by protein cyclins, which vary in type and concentration throughout each phase of the cell cycle cyclin D - increases then decreases cyclin E - increases in between G1 and S cyclin A - gradually increases, high point in G2 cyclin B - gradually increases, high point at start of mitosis

Answer 119

the plasma membrane contains receptors for growth factors that stimulate cell division, such as in a tumor cell

Answer 120

cells stop dividing when surrounding cells density reaches maximum

Answer 121

most cells only divide when they are attached to an external surface such as neighboring cells or placed on a culture dish

Answer 122

referred to as transformed cells. cancer drugs also inhibit mitosis by disrupting the ability of microtubules to separate chromosomes during anaphase, thus stopping replication

Answer 123

occurs exclusively in germ cells * meiosis I: reduction division, homologous chromosomes pair at the plate, migrate to opposite poles, yet there is no separation of sister chromatids * meiosis II: analogous to mitosis

Answer 124

nucleus disassembles, nucleolus disappears, nuclear envelope breaks down, chromatin condenses, and mitotic spindle develops. the microtubules begin attaching to kinetochores, and crossing over occurs, which allows for genetic recombination i . synapsis occurs, which involves homologous chromosomes pairing up, forming a tetrad (group of 4 chromatids) or bivalents ii. chiasmata - region where crossing over of non-sister chromatids occurs iii. synaptonemal complex - protein structure that temporarily forms between homologous chromosomes; gives rise to tetrad with chiasmata and crossing over

Answer 125

1. leptotene - chromosomes start condensing 2. zygotene - synapsis begins, synaptonemal complex forms 3. pachytene - synapsis complete, crossing over 4. diplotene - synaptonemal complex disappears, chiasmata still present 5. diakinesis - nuclear envelope fragments, chromosomes complete condensing, and tetrads are ready for metaphase

Answer 126

homologous pairs line up along the metaphase plate, and microtubules attach to kinetochores of one member of each homologous pair

Answer 127

homologues within tetrads uncouple and are pulled to opposite sides (disjunction)

Answer 128

* nuclear membrane develops and each pole forms a new nucleus that has half the number of chromosomes * cell is now haploid * interphase may occur after telophase I, depending on the species

Answer 129

involves chromosomes lining up on the metaphase plate and sister chromatids separating and migrating to opposite poles

Answer 130

nuclear envelope disappears and spindle develops, but no chiasmata or crossing over occurs

Answer 131

chromosomes align on metaphase plate like in mitosis, but now with half the number of chromosomes (no extra copy)

Answer 132

each chromosome is pulled into 2 separate chromatids and migrate to opposite poles of the cell

Answer 133

nuclear envelope reappears and cytokinesis -> 4 haploid cells form, with each chromosome consisting of one chromatid

Answer 134

fusion of two haploid gametes, results in a diploid zygote

Answer 135

1. crossing over during prophase I 2. independent assortment of homologues during metaphase I 3. random joining of gametes, aka germ cells

Answer 136

in plants, meiosis in sporangia produces spores (haploid), which undergo mitosis to become multicellular haploid gametophytes. their gametes fuse together to form a diploid zygote that grows via mitosis into a sporophyte. cells in the sporophyte (sporangia) undergo meiosis again to produce haploid spores that germinate and repeat the life cycle known as alteration of generations

Answer 137

1. **surface-to-volume ratio**: as cells grow, the volume grows much larger compared to the surface area. when SA:V is large, exchange across the cell becomes much easier. when SA:V is small, exchange is harder, leading to either cell death or cell division to increase SA 2. **genome-to-volume ratio**: genome size remains constant throughout life, as cell growth leads to only an increase in volume. G:V will be small and thus exceed the ability of its genome to produce sufficient amounts of regulation of activities. some large cells like paramecium and human skeletal muscle are multinucleated to deal with this

Answer 138

* mitosis does not contribute to genetic variation * if you are seeing chromosomes, that means the chromatin has condensed, so you're observing mitosis - therefore, if you're asked to determine the number of chromatids, assume they've already been doubled