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Lecture 2: The Biosphere and Environmental Variation
The Biosphere
- everywhere where life exists on the planet
- between the lithosphere (Earth’s surface crust and upper mantle) and the troposphere (lowest
layer of atmosphere)
Major Terrestrial Biomes
- biomes
• large-scale terrestrial communities shaped by physical environment in which they’re found
• identified by dominant plant form — plants are sessile so they have to survive all variations
in an area, meaning you can identify a biome but its plants; plants give it physical structure
• plant forms show morphological similarities (due to shared evolutionary history or
convergence — evolution of similar growth forms among distantly related species in
response to similar selection pressures); eg. birds and mammals are both warm-blooded
but their common ancestor was cold-blooded
- types of biomes
• tropical rainforests
• tropical seasonal forests and savannas
• deserts
• temperate grasslands
• temperate shrublands and woodlands
• temperate deciduous forests
• temperate evergreen forests
• boreal forests (taiga)
• tundra
- average annual temp and precipitation determine biome distributions; seasonal variations
(esp. climate extremes) can also play a role because extremes dictate where organisms are
• reflect global patterns of rainfall across the planet
• e.g. deserts have a lot of variability in temperature but not in rainfall
- climograph of major biomes in North America
• biomes can have overlaps in suitable conditions
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• which biome is present often depends on factors such as disturbances (e.g. grazing, fires),
human activities, climate extremes
- some mountain zones can have latitudinal changes due to elevation, like biomes do
- human activities impact global biome distributions — e.g. getting rid of forests to get more
grassland to get species like deer because you want them
- land use change is one of the major impacts
• secondary growth is when forests today are different than forests in the past because they
were converted from one type to another and then reverted back to the original type but a
bit differently
• altering land to use it for something else and this causes potential and actual distributions
of biomes to be very different; temperate biomes and grasslands are the most in danger
Tropical Rain Forests
- 10N to 10S, found in the low-latitude tropics
- more than 2000mm annual precipitation; most in danger from climate change
- soil: nutrient-poor because they’re in trees, acidic, rapid decomposition; not much variation
- most diverse terrestrial biome: about 50% of earth’s species found here
- plant forms
• canopy: multilayered and continuous, low light penetration
• broadleaf evergreen and deciduous trees
• physical environment: high rainfall and low light conditions (have to grow tall)
- growth forms
• light: emergents (very tall trees), lianas (woody vines), epiphytes (plants that grow on tree
branches), and understory (grow in shade of canopy)
• water: smooth bark, leaves with drip tips and groves, buttressed roots (need to get water
off of them because there is too much on them)
Tropical Seasonal Forests and Savannas
- north/south of wet tropics
- wet/dry seasonality due to movement of ITCZ; large gradient in climate primarily associated
with seasonality of rainfall
- soil: nutrient-poor, acidic, rapid decomposition
- biome includes tropical dry forests, thorn woodlands, tropical savannas
- plant forms
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• canopy: shorter trees, deciduous in dry season (leaves fall), more grasses/shrubs
• physical environment: semi-arid, seasonal rainfall, fires are common
• land use — less than 50% of biome remains
• savannas
- dominated by grasses intermixed with trees and shrubs
- maintained and established by fires
- large herbivores also play a role in places like Africa (elephants, rhinos, etc.)
- seasonal flooding can also be important in establishment— trees are intolerant of long
periods of soil saturation
Hot Deserts
- high pressure zones 30N and 30S
- seasonal temp variations (warm to very hot)
- low rainfall, rains in bursts
- soil: very dry with no subsurface water, sandy to coarse-texture, fertile and mineral-rich (lack
of water prevents mineral leaching) — when you add water, you get wild flowers
- sparse animal/plant populations, can be species rich
- plant forms
• drought-deciduous shrubs (open growth forms), grasses, succulents, annuals
• physical environment: avoiding heat and saving water is a priority
• succulent stems to store water (convergence) — plant functions during dry periods
• few/no leaves to reduce transpiration, dense hairs to alter leaves reflective properties
• CAM and C4 photosynthesis because of the desert environment
- cactus and euphorb — both converged and their forms adapted to the hot desert environment
so they look similar even though they are not related
- desertification — long-term droughts in association with unsustainable grazing practices can
result in loss of plant cover and soil erosion; degradation of formerly productive land in arid
regions resulting in loss of plant cover and acceleration of soil erosion
Temperate Grasslands
- between 30 and 50N; some in the south but most are in the north because more land mass
- seasons: semi arid, seasonal rainfall (warm, moist summers and cold, dry winters)
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- soil: very fertile, nutrient-rich
- land use change: most central N American and Eurasian grasslands — agricultural lands
(irrigation — salinization of soils)
- overgrazing in arid grasslands can lead to desertification
- frequent fires and grazing by large herbivores prevent establishment of trees and maintain
dominance of grasses in these environments
- plant forms
• grasses dominate biome
• physical environment: need to cope with seasonal droughts
• grasses — larger root biomass to cope with low water conditions
• grasslands maintained by frequent fires and large grazers (e.g. bison)
Temperate Shrublands and Woodlands
- between 30 and 40N
- seasons: Mediterranean climates (hot, dry summers in which growth occurs and wet winters)
- soil: somewhat fertile, but nutrient poor compared to grasslands
- shrublands
• maintained by fires
• continental interiors — in rain shadows and cold seasonal climates
• some conversion to agricultural fields (esp. vineyards), but soils nutrient poor
- plant forms
• evergreen shrubs and trees dominate
• physical environment: semi-arid, dry/hot summers
• evergreen leaves — photosynthesis in cooler, wetter periods
• sclerophyllous leaves — prevent grazing and wilting (conserve water)
Temperate Deciduous Forests
- 30 to 50N, on some continental edges
- seasons: warmer summers, cooler winters, enough ppt for tree growth
- soil: fertile, rich with decaying litter (slow decay due to cool temps, dry soils); not good for
long-term agriculture but is okay for short-term periods
- flora: not much tree diversity, 3-4 species/km2
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- land use — rich soils, shift to agricultural lands, shift back to forests in many places
(secondary growth)
- plant forms
• canopy: light penetrates, diverse understory vegetation
• physical environment: seasonal variation can be challenging, winters are fairly mild
• broad leaves, lost annually (oaks, maples, beeches)
• thick bark to limit water loss
• nutrient depletion (agriculture) and invasive species — shifts in species composition
Temperate Evergreen Forests
- 30 to 50N and S, coastal, continental, and maritime zones
- seasons: high rainfall, mild winters
- soil: nutrient-poor, but richer than tropical rainforests (slower decay here)
- flora: low tree diversity compared to tropical and deciduous forests
- land use — deforestation (lumber), replaced with even age trees
- plant forms
• acidic needle-shaped leaves, canopy has low light penetration, limited understory
• also includes temperate forests (western coasts 45-50deg) but trees look different
• physical environment: seasonal variation can be challenging, winters are mild
• species include needle-leaved conifers, broad-leaved beech and eucalyptus (depends on
location)
• fire suppression and even age stands — increased fire severity, increased susceptibility to
pests and pathogens; even age stands are when you cut down all trees and replant them
so they are all the same age
Boreal Forest/Taiga
- 50 to 65N
- seasons: long, severe winters, summer droughts; snow melting drives summer which is dry
- soil: thin, nutrient-poor, acidic, permafrost prevents drainage (saturated soils)
- low-lying areas can form peat bogs (lack of drainage)
- susceptible to forest fires in summer droughts; climate change causes more droughts
- land use: less impacted, but logging and oil/gas development
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- plant forms
• canopy: low light penetration, limited understory
• physical environment: heavy winter snowfalls and short growing seasons, arid summers
• flora: mostly conifers, also birches
• leaf and tree shape to decrease risk of snow damage
• evergreen needles: to photosynthesize in early spring
Tundra
- above 65deg latitude, mostly in arctic
- season: extreme winters, low precipitation, short summers with long days
- soil: permafrost, poor drainage, organic matter builds up
- repeated freezing/thawing — soils sort by texture
- pingos — permafrost freezing creates hills
- plant forms
• simple vegetation structure: mosses, lichens, herbs, low shrubs, grasses, and sedges
• physical environment: warmth is the main priority
• low dense growth form and dark leaves
- dark leaves to absorb more heat
- low growth to reduce convective heat loss
- reduced surface area to volume ratio to reduce conductive heat loss
• depth of permafrost and length of growing season keeps conifers from invading
• climate change: taiga encroachment into this biome
Mountain Biological Zones
- mountains — temperature and precipitation change with elevation, creates climate gradients
that impact biological community distributions
- slope aspect, stream proximity, slope orientation with respect to prevailing winds also impact
biological community distribution on smaller scale
- can mirror latitudinal variations in biomes but not completely; biological communities growing
at the bottom to the top mirror the latitudinal variations somewhat
- create climate gradients that change more rapidly over given distance than those associated
with changes in latitude
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- temperatures decrease rapidly with elevation
Major Aquatic Communities
- freshwater communities
• about 2.5% of earth’s surface is freshwater but most of this is frozen (glaciers, permafrost)
or below ground
• lotic and lentic ecosystems are associated with velocity, depth, temp, clarity, and
chemistry of water
• biological assemblages characterized by BOTH plants and animals
• process chemical elements from terrestrial ecosystems and transport them to the oceans
• connect terrestrial and marine biomes
• lotic is flowing water whereas lentic is stillwater
- oceans
• 71% of earth’s surface oceanic (largest biome)
• contains rich diversity of unique biota
• marine biological zones categorized by location relative to shorelines/ocean floor
• dimensions determine distribution of nutrients, oxygen, and light
• nearshore zones influenced by local climate, tides, waves, terrestrial inputs
• tides produce unique transition zones
• determined by ocean depth and proximity to the substrates at the bottom
Lotic Ecosystems
- characteristics
• a body of water flowing constantly in one direction; e.g. rivers and streams
• shallow enough for light to penetrate to benthic zone (the bottom of a body of water,
including the surface and shallow subsurface layers of sediment)
• oxygen levels depend on current and water temp
• streams increase in size as they move down elevations; water speed has a large impact
• streams form patterns of riffles (fast-moving portions of the stream flowing over coarse
particles on the stream bed, which increase oxygen input into the water) and pools
(deeper portions of the stream where water flows more slowly over a bed of fine
sediments), with different biological communities
• 1 order = small, high elevation streams
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• 2 order = convergence of 1st order streams (2 first order streams meet)
• large rivers = 6+ order
- organisms
• small, fast moving streams can’t support photosynthetic organisms (have fishes, insect
larvae, mollusks, other animals); food web is driven by things falling into the soil
• slower moving streams build up nutrients and organic matter, support plant and algal
growth and animals that eat them
• benthic zone includes invertebrates (detritivores, predators) that consume detritus
• other invertebrates live in hyporheic zone — substrate below and adjacent to the stream,
where water, either from stream or from groundwater moving into the stream, still flows
• runoff from agricultural lands can cause pollution
- composition of biological communities in streams and rivers changes with stream order and
channel size
- river continuum concept — developed to describe changes in both physical and biological
characteristics of a stream; as a stream flows downslope and gets bigger, input of detritus
from vegetation adjacent to stream decreases relative to volume of water and particle size in
stream bed decreases so there is greater establishment of aquatic plants going downstream
Lentic Ecosystems
- characteristics
• still water ecosystems (wind and temp drives water movement); e.g. ponds, lakes, bogs
• occur where depressions in landscape fill with water
• littoral and limnetic zones are warmer/better oxygenated
• benthic zone is nutrient rich (decomposition) but lacks oxygen
- organisms
• photic zone: cyanobacteria, algae, plankton, fishes, small crustaceans — things that
photosynthesize and the things that feed on them
• benthic zone: invertebrates and fish detritivores
- layers with water depth
• littoral zone — near shore shallow waters within photic zone; has aquatic plants and
phytoplankton
• limnetic zone — offshore, water that receives enough light to support photosynthesis
(dominated by zooplankton); aka pelagic zone; open water
• benthic zone — substrate along bottom of lake
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- layers by light level
• photic zone — littoral and limnetic zones, and parts of benthic zone that receive light
• aphotic zone — parts that do not receive light
Nearshore Biological Zones
- marine biological zones adjacent to continents are influenced by local climate, rise and fall of
ocean waters associated with tides, and by wave action and influx of fresh water and
terrestrial sediments from rivers
- tides are generated by gravitational attraction between earth and the moon and the sun
- estuaries
• rivers flow into oceans (salinity varies with tides and river inputs); rivers meet oceans and
salinity varies and affects the density of the water
• terrestrial inputs = high productivity
• nurseries for many fishes, shellfish, and other invertebrates also present
- salt marshes
• shallow coastal wetlands dominated by grasses and rushes
• terrestrial inputs enhance productivity
• tides produce salinity gradients throughout marsh
• habitat for fish, crabs, birds, mammals
- mangroves
• dominate some tropical coastal zones
• mangroves — salt-tolerant, evergreen trees/shrubs (convergence, not closely related)
• roots of mangroves trap sediments — buildup modifies shoreline
• habitat for many animals, including unique ones (manatees, crab-eating monkey, fishing
cats, monitor lizard)
- all 3 of these act as flood protection by absorbing incoming salt water floods
Intertidal Zones
- intertidal zones — part of nearshore exposed to air at low tide and underwater at high tide;
part of the shoreline affected by rise and fall of the tides
- rocky intertidal zones
• rocky terrain provides stable substrate for organisms to attach to (protection from wave
action of tides) — good to be here if you want to stick to rocks
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• sessile organisms must cope with extremes of high and low tides (open air vs. underwater)
• mobile organisms can move with tides to avoid desiccation or drowning
- sandy shores
• sandy terrain is not stable, and has lots of wave action
• many invertebrates burrow into sands (clams, sea worms, mole crabs)
• smaller organisms can live on or among sand grains (polychaete worms, hydroids,
copepods)
Shallow Ocean Zone
- diverse and productive ocean along continental shelves; fully photosynthetic all throughout
- light penetrates to benthic layer, supporting sessile photosynthetic organisms
- photosynthetic organisms support diverse community (energy and physical support)
- coral reefs
• most diverse oceanic biological community
• provide natural barriers that prevent shoreline erosion
• corals and symbiotic Zooxanthellae — structural habitat plus energy for communities
- seagrass beds
• submerged communities of flowering plants in subtidal marine sediments
• algae and animals, larval stages of many organisms grow on grasses
- kelp beds
• large brown algae with leaf-like fronds, stems, found where a solid substrate is available for
anchoring, anchored to sediments
• support diverse marine communities (sea urchins, lobsters, mussels, abalones, other
seaweeds, sea otters)
Pelagic Zone
- open ocean beyond continental shelves; light availability determines where photosynthetic
organisms can occur
- photic zone
• extends 200m into ocean
• supports highest density of organisms
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• supports nekton (swimming organisms capable of overcoming ocean currents) which swim
and move on their own, phytoplankton (photosynthetic plankton) and zooplankton
(nonphotosynthetic) which move with the current
• pelagic sea birds spend most of their lives over this zone
• need to overcome gravity and water currents that could force them to go deeper — some
swim, some have bladders for buoyancy, decreased their density, adapted shape that
lowers their downward velocity
- aphotic zone
• energy supplied by falling debris
• temp drops and water pressure increases
• debris supports crustaceans (copepods)
• main predators are crustaceans, cephalopods, fishes
- benthic zone
• near freezing temps and high pressure
• sparsely populated, nutrient rich zone
• sea stars, sea cucumbers, bioluminescent predatory organisms lure prey; e.g. animals
where the male attaches to the female on the side and is just stuck there because no light
- as you go down, it gets colder, water pressure increases, and it gets darker — must adapt
Human Actions Have Impacted Oceans
- oceans provide food production, protection of coastal areas from erosion, uptake and
stabilization of pollutants and nutrients, recreational benefits
- sedimentation — nutrients and pollutants released into rivers from land-based activities
- climate change and increasing ocean acidity — greenhouse gas increase
Environmental Variation
- physical environment influences ecological success (its survival and reproduction)
• availability of energy and resources influences an organism’s ability to grow/reproduce
• extreme conditions can exceed an organism’s tolerance (ability to survive stressful
environmental conditions) limits
- organisms can either tolerate environmental variation or they can use avoidance (a
response to stressful environmental conditions that lessens their effect through some
behaviour or physiological activity that minimizes an organism’s exposure to stress)
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- energy supply can influence the ability of an organism to tolerate environmental
extremes — e.g. how much fat they can put on
- an organism’s actual distribution also depends on other factors (competition, predation,
disturbance, etc.) — some need fire but some don’t
- actual geographic distribution of species differs from its potential distribution
- physiological ecology — study of the interactions between organisms and the physical
environment that influences their survival, persistence, and geographic ranges
- climate envelope — range of conditions over which an organism occurs; nonliving
components of their niche; potential distribution is like a fundamental niche and the smaller,
actual distribution is like the resized niche; they just model the big factors
- stress — environmental variation associated with depression of physiological processes,
lowering organism’s ecological success; reduces fitness by impacting physiology
- organisms can adjust to stress through acclimatization, which is a short-term, reversible
process; individuals acclimatize, populations adapt
- populations dealing with long-term environmental stress can adapt through differential
reproductive success (involves genetic change)
- populations with adaptations to unique environments are called ecotypes — represent
responses to both abiotic and biotic environmental factors; can eventually become separate
species as the physiology and morphology of individuals in different populations diverge and
become reproductively isolated
- e.g. mountain climbing
• stress — hypoxia at high elevations
• climbers need to acclimatize
- stay at base camps (don’t climb the biggest one right away, just accustomed to it)
- increase breathing rate and red blood cell production
• Tibetan and Andean people show local adaptation
- Andes: increase red blood cells and lung capacity
- Tibet: increase breathing rate and blood flow
- adaptation and acclimatization aren’t free — they represent possible trade-offs with other
functions of the organisms that may also affect its survival and reproduction
- 3 types of variation that organisms must face
• variations in temperature
• variations in water availability
• obtaining energy
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Variations in Temperature
- an organism’s internal temp can impact its ecological success
- temp variations must be tolerated or an organism needs to modify its physiology, morphology,
or behaviour
- some organisms survive temp extremes through dormancy — little or no metabolic activity
occurs
- an organism’s temp is determined by its energy exchanges with the external environment
- temperature affects physiological processes because biochemical reactions depend on
enzymes, which can become denatured at high temperatures; some species produce
isozymes which have different temperature optima to acclimatize to env temp; it also
influences the properties of membranes at low temps because they can solidify and lose
function
- temperature changes in plants
• deltaHplant = heat energy change of the plant
• SR = solar radiation
• IR = infrared radiation (input and output)
• Hconv = convective heat transfer (heat E carried by wind/water)
• Hcond = conductive heat transfer (E transfer warmer — cooler molecules)
• Het = heat transfer by evapotranspiration
• positive means it’s going into the plant and negative means it’s leaving the plant
• if plant is warmer than surrounding air, Hconv and Hcond are negative
• if deltaH plant is positive, the plant’s temperature is increasing because sum of energy
inputs exceeds sum of energy outputs
• can modify energy balance to control their temp by adjusting energy inputs/outputs —
leaves are the most temperature-sensitive tissue so they change the rate of transpirational
water loss, the leaf surface reflective properties, and leaf orientation toward the sun; they
also change surface roughness to change convective heat transfer
• change Het through stomates opening/closing to control the rate of transpiration, or
through shedding leaves in dry seasons to avoid temperature and water stress
• pubescence can reflect solar energy (changing SR) and reduce Hcond — color of hair,
light reflects so there is less solar radiation absorbed by the leaf and dark absorbs; alters
reflective properties of leaves; used by plants who maintain their leaves during dry periods
!13
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• heat can be lost from a leaf by convection when air temp is lower than temp of leaf;
effectiveness of convective heat loss is related to speed of air moving across a surface
• boundary layer of leaf impacts Hconv (smooth leaves have thin boundary layers = more
heat loss)
• excessive heat loss by convection can be a problem in cold, windy environments — short
plants clinging to the ground, layer of insulating hair on surface, dense pubescent leaves
- temperature changes in animals
• Hevap = heat transfer by evaporation (sweating, panting); not widespread among animals
• Hmet = metabolic heat generation (endotherms)
• ectotherms — regulate body temp through energy exchange with external environment,
have greater tolerance for temp variations; with a larger surface area relative to volume
(smaller body size), they can have greater heat exchange but it’s hard to maintain a
constant internal temp when external temps are changing a lot; smaller surface area to
volume ratio decreases animal’s ability to gain or lose heat
• endotherms — rely primarily on internal heat generation (birds, mammals, some fishes,
insects, and a few plants); can expand their geographic ranges because they can maintain
relatively constant internal temps; maintain a constant basal metabolic rate over a range of
environmental temperatures known as the thermoneutral zone; when the environmental
temperature drops to a point at which heat loss is more than metabolic production, they
reach the lower critical temperature
• change Hevap through sweating or panting
• change surface area to volume ratio (Hcond)
• move (bask in sun, sit on warm rock, swim, etc.)
• some animals avoid temp extremes through torpor (state of dormancy in which
endotherms drop their lower critical temperature and associated metabolic rate) or
hibernation (slowing heat loss; torpor that lasts several weeks during the winter, only
possible for animals that have access to enough food and can store enough energy
reserves); some animals stop breathing, heart stops beating, freeze and thaw from the
inside out
Variations in Water Availability
- water is medium for all biochemical reactions
- organisms need to maintain water balance with respect to external environment (different
challenges in arid, saline, freshwater environments)
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- surface area/volume changes can also impact water retention/water loss — when trying to
conserve heat, you increase volume to surface area ratio by getting bigger and this reduces
the surface with which you can lose heat so you retain more heat
- water flows from high-energy to low-energy zones (energy gradients) determined by solute
concentration (osmotic potential), pressure or tension (pressure potential), and the attractive
force of surfaces (matric potential)
- plants and microorganisms can influence water potential by adjusting solute concentration in
their cells (osmotic adjustment)
- aquatic animals that are hypo-osmotic to water must spend energy to excrete salts against an
osmotic gradient; if they are hyper-osmotic to water, they take up solutes from the
environment to make up for the solute losses to the surrounding water
- terrestrial organisms can alter gains/losses of water by adjusting resistance to water
movement, by opening or closing stomates and making adaptations to skin in animals
Obtaining Energy
- energy exists in many forms
• radiant energy = sunlight
• chemical energy = E stored in bonds of chemical compounds, stored in food being
consumed; chemoautotrophs do this
• kinetic energy = E associated with movement of molecules; measured as temp so when
things are cold or warm to our touch
- autotrophs assimilate energy from sunlight (photosynthesis) or from inorganic compounds
(chemosynthesis) and convert it into chemical energy within organic compounds (e.g. carbs)
- heterotrophs obtain energy by consuming organic compounds created by other organisms;
include detritivores (consumes detritus, break down dead organic matter and waste
products), parasites (organisms that lives in or on a host organism and feeds on its tissues
or body fluids), herbivores (organism that obtains energy by consuming energy-rich organic
compounds made by other organisms), predators (organism that kills and eats other
organisms called prey)
- chemosynthesis harvests E from inorganic compounds
• earliest autotrophs were likely chemosynthetic bacteria/archaea because oxygen was low
and carbon dioxide, hydrogen, and methane were higher
• oxidize inorganic substrate — frees electrons from the inorganic substrate to generate ATP
and NADPH
• use energy from ATP and NADPH to fix carbon dioxide (take up carbon from gaseous
carbon dioxide) and synthesize carbs
• nitrifying bacteria are an essential part of nitrogen cycle and food webs because this is
where plants get their nitrogen
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- photosynthesis is a powerhouse for life on earth
• most food webs are based on photoautotrophs
• energy harvested from sun is used to free electrons and generate ATP and NADPH (lightdriven reaction)
• carbon fixation and synthesis of sugars (carbon reaction)
• 6CO2 + 6H2O + SR —> C6H12O6 + 6O2
- heterotrophs have adaptations to acquire/assimilate energy
• 3 steps to acquiring energy
- find and obtain food
- consume food
- absorb energy and nutrients from food
• most food energy is found in carbs, proteins, and fats
• amino acids can provide nitrogen (limited nutrient)
• plants offer less readily available E because we can’t break down plant matter easily, but
you don't have to catch them
- heterotrophs
• earliest organisms were probably heterotrophs that consumed amino acids and sugars that
were produced naturally by chemical reactions occurring in the oceans
• could’ve led to diverse strategies for obtaining food, some of it involving autotrophy
- heterotrophic bacteria, archaea, and fungi excrete enzymes into the environment to
break down organic matter externally; digest food outside their bodies; instead of
bringing things into their bodies, they digest it by excreting things into surroundings and
taking the parts they need
- small protozoans ingest food particles into cells to digest in special organelles
- multicellular organisms (us) have specialized tissues for absorption, digestion, transport,
and excretion because they must find their own food on their own by seeking it out; e.g.
we have stomach and different organs to digest
- omnivores can adjust their digestive morphology depending on if they are consuming
plants or animals — can change the ratios of enzymes within them based on what
they’re consuming
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