Biology-Ecology

Question 1

Ecology

Answer 1

study of distribution+abundance of organisms and their interactions w/ other organisms + their physical environment

Question 2

Abiotic

Answer 2

nonliving (temp, climate, light and water availability, topology)

• Sunlight –
  
  • Photic zone in water = light penetrates; all aquatic photosynthesis
  • Aphotic zone – only animal and other heterotrophs
• Oxygen – air is ~ 80% nitrogen, 20% oxygen

Question 3

Biotic

Answer 3

all living things that directly or indirectly influence the life of the organism

Question 4

Population

Answer 4

group of individuals of same species living in the same area.

Question 5

Community

Answer 5

: group of populations living in the same area

Question 6

Ecosystem

Answer 6

describes interrelationships between organisms in a community and their physical environment

Question 7

Biosphere

Answer 7

composed of all regions of earth that contain living things. (ex. Atmosphere, hydrosphere, lithosphere, etc)

Question 8

Habitat

Answer 8

type of place where organism usually lives; including other organisms as well as physical, chemical environment

Question 9

Niche

Answer 9

describes all biotic and abiotic resources in the environment used by an organism. When an organism is said to occupy a niche, certain resources are consumed or certain qualities of environment are changed in some way by presence

Question 10

Population Ecology

Population Ecology

Answer 10

study of growth, abundance, and distribution of populations.

1. Size: N, total number of individuals in population.
2. Density: total number of individuals per area or volume occupied.
3. Dispersion: describes how individuals in a population are distributed; may be clumped, uniform, or random.
4. Age structure: description of the abundance of individuals of each age. 3 2 1 (% male) 0 (% female) 1 2 3 with horizontal bars for each age group.
5. Survivorship curves: how mortality of individuals in a species varies during their lifetimes.
   a. Type I: most individuals survive to middle age and dies quicker after this age (human).
   b. Type II: length of survivorship is random (invertebrates-hydra).
   c. Type III: most individuals die young, with few surviving to reproductive age and beyond (oysters).

Question 11

Population Growth

Answer 11

a. Biotic potential: maximum growth rate under ideal conditions (unlimited resources and no restrictions). The following factors contribute to biotic potential of a species: age at reproductive maturity, clutch size (# offspring produced at each reproduction), frequency of reproduction, reproductive lifetime, survivorship of offspring to reproductive maturity.
b. Carrying capacity (K): maximum number of individuals of a population that can be sustained by habitat.
c. Limiting factors: density-dependent (limiting effect becomes more intense as population density increases-competition, spread of disease, parasites, predation) and density-independent (occur independently of density of population such as natural disasters or big temp changes).

Question 12

Growth rate of population

Answer 12

r = (births – death)/N

Question 13

Change

Answer 13

∆N/∆t = rN = births - deaths

Question 14

Intrinsic rate

Answer 14

of growth is when the reproductive rate (r) is maximum (biotic potential).

Question 15

Exponential growth

Answer 15

occurs whenever reproductive rate (r) is greater than zero (J-shaped)

Question 16

Logistic growth

Answer 16

occurs when limiting factors restrict size of population to the carrying capacity of habitat.

change N/change t = rN (K-N/K)

K is carrying capacity. When population size increase→ growth rate decreases and reach 0 when population size reach carrying capacity→ S-shaped.

Question 17

Population cycle

Answer 17

fluctuations in population size in response to varying effects of limiting factors. when population grows over carrying capacity, it may be limited (lower) than the initial K due to the damage caused to the habitat à lower new carrying capacity K or it may crash to extinction.

Question 18

Population Ecology

Exponential and logistic growth patterns are associated with two kinds of life-history

Question 19

K-selected population

Answer 19

members have low reproductive rates and are roughly constant (at K) in size (ex. human population). Have a carrying capacity that population levels out at. Carrying capacity is a density dependent factor

Question 20

R – selected population

Answer 20

rapid exponential population growth, numerous offspring, fast maturation, little postnatal care (ex. bacteria). Generally found in rapidly changing environments affected by density independent factors. Characterized by opportunistic species (e.g. grasses, insects that quickly invade a habitat, reproduce, then die)

Question 21

Human Population Growth

Answer 21

enabled by:

• increase in food supply
• reduction in disease (medicine)
• reduction in human wastes
• habitat expansion (advancements now allow inhabitance of previously uninhabitable places)

Question 22

Ecological footprint

Answer 22

amount of raw land necessary to sustain an individual’s lifestyle habits (consider eating, traveling, housing habits)

Question 23

species richness

Answer 23

reflects the diversity of a community in regards to the total number of different species present

Question 24

Community Ecology

Answer 24

concerned with interaction of populations; such as Interspecific competition (different species).

1. Competitive exclusion principle (Gause’s principle): two species compete for exactly the same resources (or occupy the same niche), one is likely to be more successful (no two species can sustain coexistence if they occupy the same niche).
2. Resource partitioning: two species occupy same niche but pursue slightly different resources or securing their resources in different ways, individuals minimize competition and maximize success (multiple species-slightly different niches).
3. Character displacement (niche shift): as a result of resource partitioning, certain traits allow for more success in obtaining resources in their partitions→reduces competition →divergence of features (character displacement) such as different beak of birds on the same island. The mating calls of 2 species of frogs are different when they occupy the same island. On separate islands, the mating calls are the same.
4. Realized niche: niche that an organism occupies in absence of competing species is its fundamental niche. When competitors are present, one/both species may be able to coexist by occupying their realized niches, that part of their existence where niche overlap is absent (occupy areas of niche that don’t overlap so no competition for resources)

Example: One barnacle species can live on rocks that are exposed to full range of tides (fundamental). In natural environment, 2nd species of barnacle outcompetes the 1st, but only at lower tide levels where desiccation is minimal. The 1st species then only survive in its realized niche, the higher tide levels.

Question 25

Predation

Answer 25

another form of community interaction

• True predator: kills and eats another animal.
• Parasite: spends most of its life living on host, host usually doesn’t die until parasite complete one life cycle.
• Parasitoid: an insect that lays its eggs on host (insect or spider). After eggs hatch, larvae obtain nourishment by consuming host’s tissues. Host eventually dies, but not until larvae complete development and begin pupation.
• Herbivore: animal that eats plants. Granivores are seeds eater (act like predators totally consume organism). Grazers (animals that eat grasses) and browsers (eat leaves) and eat only part →weaken it in process.

Question 26

.Symbiosis

Answer 26

intimate, often permanent association b/w two organisms; may or may not be beneficial; some may be obligatory (one or both organisms cannot survive w/o the other)

Question 27

Symbiosis

Commensalism (+/o)

Answer 27

one benefits, the other is unaffected

• Remora and shark – remora gets food shark discards
• Barnacle and Whale – barnacle gets wider feeding opportunities

Question 28

Symbiosis

Mutualism (+/+)

Answer 28

– both organisms benefit

• Tick bird and Rhinoceros – bird gets food (ticks) and rhino loses ticks
• Lichen (fungus + algae) – algae produces food for itself and fungus via photosynth; fungus provided CO2 and nitrogenous wastes
• Nitrogen Fixing Bacteria and Legumes – legumes provides nutrients for bacteria and bacteria fixes nitrogen
• Protozoa and Termites – protozoa digests cellulose for termites, termites protect and provide food
• Intestinal Bacteria and Humans – bacteria utilized food and provide vitamin K

Question 29

Symbiosis

Parasitism (+/-)

Answer 29

benefits at the expense of the host; bacteria and fungi; live with minimum expenditure of energy

• Parasites can be ectoparasites (cling to exterior of host) or endoparasites (live within the host)
• Virus and Host cell – all viruses are parasites
• Disease Bacteria and Animals – diphtheria is parasitic upon man; anthrax on sheep; tuberculosis on cow or man
• Disease Fungi and Animals – ringworm is parasitic on man
• Worms and Animals – tapeworm and man (less dangerous = more survival; better for parasite not to kill its host)

Question 30

Saprophytism

Answer 30

protists and fungi that decompose dead organic matter externally and absorb nutrients

Question 31

Scavengers

Answer 31

consume dead animals directly (ex. Vulture, hyena, bacteria of decay)

Question 32

intraspecific interactions

Answer 32

between members of the same species are influenced by disruptive (competition) and cohesive (reproduction and protection from predators and weather) forces

Question 33

Interactions between organisms and their Environment

Osmoregulation

Answer 33

• Freshwater fish – live in hypoosmotic environment which causes excess intake of water; thus the fish seldom drink and excrete dilute urine
• Saltwater fish – live in hyperosmotic environment; constantly drinking and excreting salt across their gills
• Arthropods – secrete solid uric acid crystals to conserve water
• Plants – possess waxy cuticles on leaf surface and stomata and have stomata on the lower leaf surfaces only; leaves shed in winter; desert plants have extensive root systems, fleshy stems, spiny leaves, extra thick cuticles, and few stomata

Question 34

Interactions between organisms and their Environment

Thermoregulation

Answer 34

• Cold-blooded (poikilothermic) –vast majority of plants and animals; body temp. is close to that of surroundings, so metabolism is radically affected by environmental temp.
• Warm-blooded (homeothermic) – make use of heat produced by respiration; physical adaptations like fat, hair, and feathers retard heat loss (Ex: mammals and birds)

Question 35

Coevolution

Answer 35

evolution of one species in response to new adaptation that appear in another species.

1. Secondary compounds: toxic chemicals produced in plants that discourage would-be herbivores (tannins in oaks/nicotine/ tobacco are toxic)
2. Camouflage (cryptic coloration): is any color, pattern, shape, or behavior that enables an animal to blend in with its surroundings. Both prey and predator benefit from camouflage.
3. Aposematic coloration (warning coloration): conspicuous pattern or coloration of animals that warns predators that they sting, bite, taste bad, poisonous, or are other wise to be avoided.
4. Mimicry: occurs when two or more species resemble one another in appearance. There are two kinds:
   a. Mullerian mimicry: occurs when several animals, all with some special defense mechanism, share the same coloration à effective with single pattern such [predator only has to learn one pattern is bad instead of lots of variants] as yellow and black body markings (dangerous) from bees, yellow jackets, and wasps.
   b. Batesian mimicry: occurs when animal without any special defense mechanism mimics the coloration of an animal that does possess a defense.
5. Pollination: of many kinds of flowers occur as result of Coevolution of finely-tuned traits between flowers + pollinators
   - red tubular flower coevolves with hummingbird attracted to red à provides nectar to hummingbird in exchange for pollen transfer

Question 36

passive defenses

Answer 36

Coloration, camouflage, mimicry etc

Question 37

Active defenses

Answer 37

hiding, fleeing, defending but can be costly in energy.

Question 38

Ecological Succession

Answer 38

change in composition of species over time

It describes how one community is replaced by another gradually consisting of different species. As it progresses, diversity (# of species in community) and total biomass increase. A final successional stage of constant species composition (climax community), is attained (usually never-random occurs)→ unchanged until destroyed by catastrophic event (blowout).

Question 39

Succession has a factor of randomness that makes it hard to predict; resident species can also change a habitat

Answer 39

• Substrate texture: may change from solid rock, to fertile soil, to sand/others (because rock erodes, plants+animals decomp)
• Soil pH: may decrease due to decomposition of organic matter such as acidic leaves.
• Soil water potential: ability of soil to retain water, changes as soil texture changes.
• Light availability: may change from full sunlight to shady to darkness as trees become established
• Crowding: increases with population growth, may be unsuitable to certain species.

Question 40

Pioneer species

Answer 40

plants and animals that are first to colonize a newly exposed habitat (usually opportunistic, r-selected species); can tolerate harsh conditions. (ex. Lichens and mosses)

As soil, water, light change, r-selected will be replaced by stable K-selected species (live longer, slow succession) and reach climax where it remains for hundreds of years.

1. Primary succession: occurs on substrates that never previously supported living things (volcanic islands, lava flows). Essential and dominant characteristic of primary succession is soil building.
2. Secondary succession: begins in habitats where communities were entirely/partially destroyed by damaging event; begins on substrate that already bear soil (may contain native seed bank).

Question 41

dominant species

Answer 41

A community stage is identified by a dominant species; Ex: grass in grassland community

Question 42

Ecological succession in a Pond

Answer 42

1. Pond: Plants such as algae, pondweed. Animals such as protozoa, insects, fish
2. Shallow water-pond fills in: Reeds, cattails, water lilies
3. Moist land: grass, herbs, shrubs, willow trees. Frogs, snakes
4. Woodland: climax tree – perhaps pine or oak

Question 43

Ecosystems

Answer 43

have trophic levels that categorize plants/animals based on their main energy source

1. Primary producers: autotrophs that convert sun energy into chemical energy; plants, photosynthetic protists, cyanobacteria, and chemosynthetic bacteria.
2. Primary consumers: herbivores (long digestive tract w/ greater surface area and time for more digestion; symbiotic bacteria in digestive tract break down the cellulose which the herbivore itself cannot), eat primary producers.
3. Secondary consumers: primary carnivores, eat primary producers.
4. Tertiary consumers: 2nd carnivores, eat 2nd consumers. (example of primary producer à tertiary consumer chain here)
5. Detritivores: consumers that obtain energy by consuming dead plants/animals (detritus). smallest ones are decomposers (fungi and bacteria). Also includes nematodes, earthworms, insects, + scavengers (vultures, jackals, crab), saprophytes

Question 44

Ecological pyramids

Answer 44

show relationships between trophic levels

Question 45

Ecological efficiency

Answer 45

describes the proportion of energy represented at one trophic level that is transferred to the next. On average, an efficiency of about 10% is transferred to the next. 90% is for metabolism and to detritivores when they die.

Question 46

Food chain

Answer 46

linear flow chart of who’s eaten by whom (grass à zebra à lion à vulture).

Question 47

Food web

Answer 47

is an expanded, more complete version of food chain (greater number of pathways in a community food web, the more stable the community is)

Question 48

Energy/biomass/quantity

Answer 48

is greatest at primary producer level, lowest at tertiary consumer level. Tertiary is least stable + most sensitive to population fluctuations of lower levels

Question 49

Biogeochemical Cycles

Answer 49

1. **Hydrologic cycle (water cycle) **
   a. Reservoir: oceans, air, groundwater, glaciers.

b_. Assimilation_: plants absorb water from soil; animals drink and eat other organisms.

c. Release: plants transpire; animals and plants decompose.
* *2. Carbon cycle:** required for building organic materials. Basis for this is photosynthesis + respiration
a. Reservoirs: atmosphere (CO2), fossil fuels (coal, oil), peat, cellulose.
b. Assimilation: plant uses CO2 in photosynthesis, animals consume plants (this is carbon fixing – reduced from its inorganic form of CO2 to organic compounds) (just like in N-fixing: N2 is relatively inert, N-fixing frees it up for use)
c. Release: release CO2 through respiration and decomposition + when organic material is burned
3. Nitrogen cycle: required for amino acid and nucleic acids. (this cycle is important, memorize this)
a. Reservoirs: atmosphere (N2), soil (NH4+, NH3, NO2, NO3)
b. Assimilation: Plants absorb nitrogen as either NO3- or NH4+., animals obtain nitrogen by eating plants/animals
1. Nitrogen fixation: nitrogen-fixing bacteria in soil (N2 → NH4+); Lighting + UV (N2 à NO3-)
2. Nitrification: NH4+ → NO2- and NO2-→ NO3- by nitrifying bacteria.
c. Release: denitrifying bacteria (convert NO3 → N2; denitrification), detrivorous bacteria convert organic compounds back to NH4+ (ammonification), animals excrete NH4, urea, or uric acid, decay (nitrogen in the form of NH3 is released from dead tissues)
4. Phosphorus cycle: required for manufacturing of ATP and all nucleic acids. Cycles for other minerals (Ca, Mg) are similar to phos cycle.
a. Reservoirs: rocks and ocean sediments (erosion transfers P to water and soil)
b. Assimilation: plants absorb inorganic PO43- (phosphate) from soil; animals obtain organic phosphorus when they eat.
c. Release: plants and animals release phosphorous when they decompose, and animals excrete in waste products

Question 50

Biomes

Answer 50

regions with common environmental characteristics

1. Tropical rain forest: high (but stable) temperature and humidity, heavy rainfall, (tall trees with branch at tops à little light to enter). Most diverse biome.
   - Epiphytes are plants that grow commensally on other plants (like vines)
2. Savannas: grasslands with scattered trees. similar to tropics in that they have high temperature, but they get very little rainfall
3. Temperate grasslands: receive less water (+ uneven seasonal occurrence of rainfaill) and are subject to lower temperatures than savannas (e.g. north American prairie)
4. Temperate deciduous forests: warm summers, cold winters, and moderate precipitation. Deciduous trees shed leaves during winter. Soil is rich due to leaf shed. Vertical stratification: plants+animals live on ground, low branches, and treetops. Principal mammals hibernate through cold winter.

Temperate coniferous: cold dry forests; vegetation has evolved adaptations to conserve water (needle leaves)

5. Deserts: hot and dry; most extreme temp fluctuations (hot day, cold night); growth of annual plants is limited to short period following rare rain, plants and animals adapt to conserve as much water as possible (urinate infrequently, cacti spines, etc)
6. Taigas: coniferous forests (and trees with needles for leaves). Very long cold winters and precipitation in form of heavy snow. Largest terrestrial biome.
7. Tundras: cold winters (ground freezes), top layer thaws during summer à support minimal vegetation (grasses). but deeper soil (permafrost) remains permanently frozen. Very little rainfall that can’t penetrate frozen ground.

Chaparral: terrestrial biome along California coastline characterized by wet winters, dry summers, scattered vegetation

Polar region: frozen w/ no vegetation or terrestrial animals

Aquatic Biomes:

8. Fresh water biomes: ponds, lakes, streams, and rivers. Hypotonic to organisms, affected by climate/weather variations.
9. Marine biomes: the largest biome covering ¾ of world surface. Provides most of earth’s food + oxygen. Includes estuaries (where oceans and river meet), intertidal zones (where ocean meet land), continental shelves/littoral zone (shallow oceans bordering continents), coral reefs, and pelagic ocean (deep). Have a relatively constant temperature (water’s high heat capacity + volume), amount of nutrient materials and dissolved salts. Divided into regions classified by amount of sunlight received, distance from shore, depth, open water vs ocean bottom.

Question 51

Two major divisions to the marine biome

Answer 51

benthic zone is lowest layer of a body of water, including sediment surface and sub-surface layers. In ocean water (deep) light doesn’t penetrate; most organisms are scavengers and detritivores.

Second major zone is the pelagic, the water that is neither close to shore nor the very bottom. It is broken down from top to bottom in layers.

Epiplagic (surface layer of water, only photic zone since enough light for penetration, nearly all primary production of ocean occurs here)→(all zones from here on out are aphotic) mesoplagic (not enough light for photosynthesis, minimal oxygen)→bathypelagic (pitch black, no plant life, most organisms here consume detritus)→abyssopelagic (cold, high temp, most species have no eyes due to lack of light)→ hadopelagic (most life here exists in hydrothermal vents).

Question 52

Human Impact on Biosphere

Answer 52

1. Global climate change
2. Ozone depletion
3. Acid rain
4. Desertification
5. Deforestation
6. Pollution
7. Reduction in species diversity
8. Introduction of new species:

Question 53

Global climate change

Answer 53

burning of fossil fuels and forests increase CO2 in atmosphere à more heat trapped (greenhouse effect; normally a good thing for maintaining heat on Earth but this is overkill) à global temp rises à raise sea level by melting ice and decrease agriculture output (affecting weather patterns).

Question 54

Ozone depletion

Answer 54

O2 + UV in atmosphere→O3 is ozone which absorbs UV radiation, preventing it from reaching surface of earth (UV damages DNA). CFCs (chlorofluorocarbons) enter upper atmosphere and break down O3.

Question 55

Acid rain

Answer 55

burning of fossil fuels (e.g. coal) releases into air SO2 and NO2. When they react with water vapor à sulfuric acid and nitric acid (HNO3) à kills plants and animals when they rain to earth.

Question 56

Desertification

Answer 56

overgrazing of grasslands that border deserts transform the grasslands into deserts à agricultural output decreases, or habitat available to native species are lost.

Question 57

Deforestation

Answer 57

clear-cutting of forests causes erosion, flooding, and changes in weather patterns.

Question 58

Pollution

Answer 58

air, water, and land pollution contaminate materials essential to life; many remain in environment for decades. Eutrophication is the process of nutrient enrichment in lakes and subsequent increase in biomass (lakes polluted with fertilizer runoff àabundant nutrients (especially phosphates) stim algal blooms (massive algae/phytoplankton growth) which respire and deplete oxygen + breakdown and detrivous bacteria deplete even more oxygen→many animals die of oxygen starvation à lakes fills with carcasses of dead animals/plants).

Note: phytoplankton does photosynthesis, but at night they reduce oxygen when they respire + the detrivores continue to multiply as stuff dies

• Biological magnification: as one organism eats another, toxin (e.g. pesticide) becomes more concentrated at higher trophic level.
• Toxins: antibiotics, hormones, carcinogens, tetratogens (cause birth defects) which get into food chain cause biomag

Question 59

Reduction in species diversity

Answer 59

result of human activities

Question 60

Introduction of new species

Answer 60

killer honeybee introduced; stung + killed people. Zebra mussel outcompeted residents.

Question 61

Pesticides vs biological control

Answer 61

pesticides effective but dangerous to humans; biological control alternatives safer: crop rotation, natural enemies, natural plat toxins, insect birth control.

Question 62

rain shadows

Answer 62

areas of dry land that form on the leeward side (downwind) of a high mountain. Rain cloud approaches mountain range → rise in elevation→surrounding air becomes cooler→due point eventually reached →precipitation occurs as cloud gains precipitation, continues to rain towards peak→cloud begins to descend leeway side of mountain →decrease in elevation→ air temperature increases→precipitation decreases→rain shadow is dry

Question 63

Glycine

Answer 63

is the only optically inactive amino acid, since it has no chiral carbons.

Question 64

Enterogastrone

Answer 64

is any hormone secreted by duodenum when fatty food present à slow down stomach muscular movement (probably close pyloric sphincter) (slow peristalsis).

Question 65

Sporazoans

Answer 65

division of Protozoan; diverse group of parasites (ex. plasmodium), cause malaria in humans

Question 66

pKa

Answer 66

pKa = half-equivalence pH. Amino acid deprotonates @ higher pH & becomes protonated @ lower pH.

Question 67

In a typical antibody, the heavy and light chains are linked by disulfide bonds

Answer 67

Streptococci – can be virulent, form chains; staphylococci form clusters

Question 68

Purple/green bacteria

Answer 68

in the anaerobic sediments of lakes/ponds, carry out photosynthesis with H2, H2S, or D as the electron donor, oxygen is not a byproduct

Question 69

pH of lysosome is 5, pH of cytosol is 7

Answer 69

Starch and glucose are polymers of alpha glucose. Polysaccharides are branched/linear. Peptides can only be linear. Polysaccharides can have alpha or beta linkages.

Question 70

Nerve gas

Answer 70

inhibitors of acetylcholinesterase, and cause death respiratory paralysis

Question 71

Dynein

Answer 71

motor protein; used for movement in 9+2 flagella & cilia; may also be used in chromosomal movement

Question 72

Cells of PCT & DCT are very rich in mitochondria because of active transport.

Answer 72

Parasite & host population densities mimic each other

Question 73

Necrosis

Answer 73

traumatic cell death

Question 74

ruminants

Answer 74

animals w/ stomachs of alkaline pH; usually 4 chambers capable of digesting cellulose

Question 75

Albumin

Answer 75

carry bilirubin (can be made from heme of old-red-blood cell) to the liver from spleen (removes dead RBC). Bilirubin is converted by liver to soluble form that become part of bile. Both Liver and Spleen are involved.

Question 76

Diapause

Answer 76

resting condition in life of an insect such as hibernation in vertebrates

Question 77

Isoelectric focusing

Answer 77

• technique for separating different molecules by differences in their isoelectric point (pI). A type of zone electrophoresis, usually performed on proteins in a gel, utilizes the fact that overall charge on the molecule of interest is a function of the pH of its surroundings. Uses a pH gradient, loses H’s as it moves through, eventually remains static at its isoelectric point where its net charge is 0. (more on this in orgo notes)

Question 78

C. elegans (nematode: fully sequenced genome, good analysis of genetic control of development) and D. melagaster (fly: easy to raise, rapid generations, easy to mutate, easy to observe mutations) are (model organisms)

Answer 78

C. elegans (nematode: fully sequenced genome, good analysis of genetic control of development) and D. melagaster (fly: easy to raise, rapid generations, easy to mutate, easy to observe mutations) are (model organisms)

Question 79

B-cells

Answer 79

develop in fetal liver and spleen and produce antibodies. T-cells are involved in immune system and develop in thymus.

Question 80

Autophagy

Answer 80

lysosomes recycle old or degraded cell material

Question 81

Somatic hypermutation

Answer 81

genes responsible for antibody synthesis are intentionally mutated à lots of variety