BSCI 207 exam 3

Changes in membrane potential • What happens if more Na+ ion channels open?

- Opening more Na+ channels makes membrane potential less negative (more positive) and depolarizes the cell -Note that when Na+ channels open, Na+ moves in to cell because of both concentration gradient & charge

Mycorrhizae

- fungal partner gets organic compounds such as sugars & amino acids from plant • up to 20% of photosynthate produced by terrestrial plants goes to arbuscular mycorrhizal fungi -fungal partner has huge surface-to-volume ratio and ability to penetrate fine structure of soil, dramatically increasing access to water and minerals, especially phosphorus • mycorrhiza increases effective root surface area 10-fold to 1000-fold and fungal hyphae are much finer than root hairs • Mycorrhizae are essential for normal growth of many plants - occur in > 90% of terrestrial plants • Some plants without chlorophyll form mycorrhizae that may be shared with photosynthetic plants, indirectly sponging off them - mycoheterotrophy"

genetic digression:

- genetic digression:

What do plants need to live?

- light - carbon, hydrogen, oxygen (from air and water) - mineral nutrients (from soil solution around roots)

If cell reaches threshold depolarization

- positive feedback opens lots of Na+ channels and E takes off toward ENa = +62mV - Gated potassium channels open & K+ flows out, hyperpolarizing cell - Na+ channels become inactivated (refractory period) -K+ channels close & back to resting potential

Capillary action

- water molecules have strong cohesion, so a column of water can indeed rise a short distance in a narrow tube (e.g., a straw or xylem vessel) by capillary action—but calculations have shown that capillary action in a xylem vessel, with a diameter of 100 um diameter, would raise a water column only around 0.15 m

Proton concentration in soil around root is increased two ways

1) Proteins in root cell membranes actively pump protons (H+) out of the cells 2) Cellular respiration in roots releases CO2, some of which dissolves in soil water, forms carbonic acid, and dissociates (ionizes) to form bicarbonate and free protons: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3 -

Key ideas for today - the neuron

1. Cell membrane has different concentrations of ions on either side - also has membrane potential (voltage) across it 2. Ions feel two forces which oppose each other, resulting in equilibrium: - diffusive "force" from concentration gradient - electrical force from membrane potential 3. This balance is disturbed during action potential, sending signal down axon

Basic steps for animal nutrient assimilation

1. Eat (macroscopic) 2. Digest (break down into small molecules + waste) 3. Absorb/import small molecules 4. Excrete what's left

osmoregulation & excretion

1. osmosis and fluids homeostasis 2. excretion of nitrogenous wastes

NOTE:

A "diuretic" substance increases urine flow An "antidiuretic" substance decreases urine flow

Osmolarity

A 1 osmolar = 1 Osm solution has 6 X 1023 dissolved entities (e.g., glucose molecules, protein molecules, Na+ ions) per liter - 1 osmolar = 1000 milliosmolar = 1000 mOsm • For compounds that dissociate in solution, osmolarity and molarity are different - 1 molar (1 mol/L) solution of NaCl is a 2 osmolar (2 osmol/L) solution - but 1 molar solution of glucose is also 1 osmolar because glucose does not dissociate in solution • Most marine invertebrates are isosmotic with seawater (with an osmolarity of ~1 Osm) • Marine bony fishes are strongly hyposmotic, with body fluid osmolarity of ~300-500 mOsm - freshwater bony fishes ~250-350 mOsm

External Parasite

A parasite that lives on the external parts of its host.

How ADH regulates blood osmolarity

ADH production also stimulated by large drops in blood volume & pressure (detected by receptors in heart & large blood vessels)

Speed of action potential

Action potentials travel faster in axons with larger diameter e.g., squid muscle cells used for escape swimming are innervated by giant axons that can be 1 mm in diameter • Many vertebrate axons are relatively small diameter but myelinated, with uncovered spaces call nodes of Ranvier voltage-gated ion channels are clustered at nodes myelin is an electrical insulator saltatory ("jumping") conduction is faster

Proton pumps & ion channels

Active transport needed to move mineral ions across cell membrane against electrochemical gradient - concentrations of many mineral ions are lower in soil solution than within plant cells - may need to move negatively charged ions into a negatively charged cellular compartment

Two limits to membrane potential

All Na+ channels open, all K+ channels closed Na+ channels closed but all K+ channels open

Action potential (nerve impulse)

Always the same size does not get smaller as it propagates along cell membrane of neuron's axon • A neuron can receive multiple signals and the resulting depolarizations & hyperpolarizations may sum to bring the membrane potential up to -50 mV trigger a far-traveling action potential that can be rapidly passed along to other neurons • Large, brief localized change in local membrane potential actually reverses polarity of cell membrane membrane depolarizes from -65mV to +40 mV depolarization lasts ~1 milliseconds, very local

big picture summary

Animal phyla with very different anatomies pattern the head-to-tail axis using Hox genes. Many other systems for sending and interpreting signals during development are conserved across animals as well. Changes in the way the conserved patterning "toolbox" is deployed allow new forms to evolve.

a generic excretory organ

As with organs for gas exchange and digestion, excretory organs are all about surface area!

What makes all this happen?

Differential gene expression - even before we can see any obvious differences

Ions move to balance two effects

Diffusion - ions moving from high to low concentration Electrical - positive ions moving towards negative charge Resulting membrane potential is the electrical difference across membrane at which diffusion and electrical forces balance Membrane potential is the electrical difference across membrane at which diffusion and electrical forces balance

Vertebrate neuromuscular junction: a well-studied (relatively simple) chemical synapse

Each muscle cell (fiber) in a vertebrate skeletal muscle is typically innervated by one neuron, called a motor neuron • Neuromuscular junction is a chemical synapse between a motor neuron & a skeletal muscle cell

Mineral cations vs. anions

Important anions such as nitrate (NO3 - ) and sulfate (SO4 2- ) are not bound to clay particles as cations are - more accessible, but more easily leached from soil

resting state

In resting state, voltage-gated potassium and sodium channels are closed The "leaky potassium channels are always open

Subsoil

Includes material from topsoil above & parent rock below

Human small intestine

Inner midgut wall highly folded & folds bear fingerlike projections (villi) surface cells have border of microscopic microvilli...result of all this villification is a surface of ~30 to 40 m2 (apparently not 200-300 m2 as long believed)

Ubx and abdominal appendages in arthropods

Insect Ubx suppresses expression of distalless, important in appendage development

Ion traffic control across cell membranes

Ion channels (passive) when open, allow selected ions to diffuse rapidly down electrical & concentration gradients Ion pumps (active) consume energy to pump ions in & out of cell, maintaining concentration difference despite ions diffusing through channels toward equilibrium • Relatively small number of ions need to move through channels to change membrane potential - of all ions within 1,000 nm of membrane surface, fewer than 100 out of a million account for membrane potential

Phloem

Living vascular tissue that carries sugar and organic substances throughout a plant

loop length

Longer loops tend to produce larger maximum end-to-end NaCl gradients - thus increasing inner medulla NaCl concentration • Among related species of similar body size, species with relatively thick medullas & prominent renal papillae tend to be capable of producing more concentrated urine - "renal papilla" is a projection of medulla into the renal pelvis (renal pelvis = expanded inner end of the ureter that drains the kidney) and is composed largely of long loops of Henle

If stranded on a desert island, should you drink seawater?

Maximum Cl- concentration in urine produced by human kidney is lower than Clconcentration in seawater - so must use additional water to excrete Cl- taken in with seawater! - some other animals can excrete salts at higher concentrations than humans can • thus able to take in seawater & excrete the salts in less water than they ingested • many marine bony fish excrete pure ions from gills

opening more K+ channels?

More open K+ channels makes the membrane potential more negative and hyperpolarizes the cell

Nitrogenous waste

Most water-breathing aquatic animals excrete ammonia - breakdown of proteins & nucleic acids yields ammonia groups (−NH2), which are easily converted to ammonia (NH3) or ammonium (NH4 +) with no energy investment - ammonia is quite toxic, so concentration in body fluids must be kept very low • Most terrestrial animals excrete urea, uric acid, or compounds related to uric acid •Mammals & most amphibians excrete waste nitrogen mainly as urea, which is very soluble in water & relatively low in toxicity • Insects, spiders, and many reptiles (including birds) excrete waste nitrogen mainly as uric acid (or related compounds) - uric acid has low solubility in water, so often excreted in solid or semi-solid form • e.g., whitish paste in bird droppings

Anions enter root hairs via cotransporters.

Movement of anions into cell does not offset the charge difference. To make this favorable, re-import of a proton (which is favorable) is coupled to import of the anion, so that the net effect is no change in charge. Proteins that move one cation and one anion at the same time are examples of "cotransporters."

Moving carbohydrates: translocation

Photosynthate is actively transported into sieve tube elements and moved throughout the plant • Carbohydrates and other solutes are translocated via phloem from sources to sinks - source: net producer of carbohydrate (e.g., photosynthesizing leaves or storage organs digesting stored reserves) - sink: net consumer of carbohydrate (e.g., flower, developing leaf) - sources and sinks may change roles (e.g., storage root such as sweet potato may be sink at one time and source at another)

Secondary active transport

Proton pump yields an electrical gradient and proton gradient • With inside of cell now more negative than outside - essential cations such as potassium (K+) move down electrical gradient into cell through specific membrane channels • Secondary active transport: a form of active transport that does not directly use ATP as an energy source - instead, transport is coupled to ion diffusion down a gradient that was established by primary active transport • With inside of cell now more negative than outside - essential cations such as potassium (K+) move down electrical gradient into cell through specific membrane channels - essential anions such as chloride (Cl- ) are moved into cell against electrochemical gradient by a membrane "cotransporter" transport protein that couples their movement with that of H+

Studying phloem using aphids

Researchers have studied phloem contents using aphids • Aphids are insects that feed on plants by drilling into a sieve tube element with a specialized organ, the stylet • Pressure potential in a sieve tube is higher than outside, so phloem sap is forced through the stylet and into the aphid's digestive tract • A feeding aphid can be frozen and separated from its stylet, leaving phloem sap flowing from the stylet for hours—to be analyzed by researchers! - phloem solute is 90% sucrose - flow rate can exceed 100 cm per hour - overall, movement in phloem is bidirectional, but individual sieve tubes believed to move fluid in just one direction - in contrast to xylem, movement of fluid in phloem requires living cells

Latitudinal variation in metabolic index

Researchers used temperature & O2 data from world's oceans to map latitudinal variation in metabolic index

Morphogenesis Early cell proliferation

Sea Urchin a) fertilized egg b) four-cell stage c) early blastula d) later blastula

Summary of non-urea solute concentration

Solute concentration increases toward medulla, peaks at bend • Solute concentration decreases toward cortex • Final non-urea solute concentration in definitive urine exiting collecting duct depends on NaCl concentration of innermost medulla - this concentration depends, in turn, on size of single effect, rate of flow through loops of Henle, and lengths of loops

Cell receives a stimulus which K+ opens some gated Na+ channels

This depolarizes the cell which lets more Na+ in which further depolarizes the cell...

antp

This is a gain-of- function mutation: expression of Antp in head (where it isnt normally expressed) turns antennae into legs. Antp is sufficient to specify leg identity

Ubx

This mutation eliminates Ubx expression in thorax, turning segment T3 into a second wingbearing segment like T2 Ubx is necessary to block wing formation in T3 -Ubx expression in segment T3 results in T3 structures -repressing Ubx expression in T3 results in T2 structures on T3

Transpiration

Transpiration is not only key to moving water through xylem, but also cools leaves (like human sweating)

Same genetic information in the different nuclei!

Unequal distribution of cytoplasmic factors could be established due to, e.g., - where sperm enters egg - orientation during pre-fertilization development of egg

Nitrogen and symbiosis

Unlike other soil nutrients, nitrogen in soil is not from weathering of rocks. Instead, it comes from: • bacterial decomposition of dead organisms • fixation of atmospheric nitrogen

Morphogen gradient provides positional information during vertebrate limb development

ZPA = zone of polarizing activity Shh = sonic hedgehog morphogen ZPA secretes Shh

Osmoregulators

actively maintain osmolarity of body fluids within narrow range.

For a neuron at its resting potential, the forces acting on potassium ions (K+) are

an electrical potential pulling K+ inward and a concentration gradient pushing K+ outward

• Isosmotic

animals have body fluids with same osmotic pressure as water in which they live - osmoconformers: incl. most marine inverts

Substrate Feeding

animals that live in or on their food source

Osmoconformers

body fluids isotonic with surrounding water

Cell-cell interactions

cells and tissues exchange signals to coordinate differentiation Ex: limb development in vertebrates

Dendrite

collect electrical signals

Topsoil

contains most of the soil's living & dead organic matter

Heterotopy:

differences in spatial distribution of gene expression BMP4 = bone morphogenetic protein 4 (signalling protein that triggers apoptosis) Gremlin gene encodes a BMP4- inhibiting protein

Heterochrony:

differences in timing of gene expression

How do cells in an embryo know where they are?

from mutant flies comes a big clue homeotic mutants have normal body parts in the wrong place!

Bird Droppings

half feces from gut (dark), half concentrated uric acid (white)

stomata regulate transpiration rate

high [K+] in guard cells: H20 flows IN by osmosis. Guard cells turgid, open. low [K+] in guard cells: H20 flows OUT by osmosis. Guard cell flaccid, closed. Think of two elongated balloons whose tips are joined at a fixed distance apart : when full, a big hole forms; when nearly empty, hole collapses.

Cell body

integrates incoming signals and generates outgoing signal to axon

Legumes

legumes (members of the bean family) harbor symbiotic nitrogen-fixing bacteria

conclusion

mammals and insects have very different anatomies but: both pattern the head-to-tail axis by Hox genes

Suspension Feeding

many aquatic animals sift small food particles from the water Gill rakers are skeletal elements, covered with ordinary epidermis, and not involved in gas exchange

Morphogenesis Cell migration (not in plants)

neural crest cell migration

fertilized egg (zygote)

one really big cell • no organs or tissues • not responsive to environment • tasty

Internal Parasite

parasite that lives inside its host

Axon

passes electrical signals to dendrites of another cell or to an effector cell

Neuron

reciever and sender of signals

Typically, stomata open during the day and close at night.

reverse pattern seen in CAM plants, which typically grow in arid conditions • Even in sun, stomata may close on a hot, windy day

Parent rock (bedrock):

rock from which soil arises

mOSm

sea water: ~1000 mOsm sea urchin body fluid: ~1000 mOsm human blood: ~300 mOsm freshwater bony fish body fluid: ~250-350 mOsm marine bony fish body fluid: ~300-500 mOsm

Avian nephrons

small glomerulus, short proximal & distal convoluted tubules, no Loop of Henle large glomerulus, long convoluted tubules, Loop of Henle

Xylem

vascular tissue that carries water upward from the roots to every part of a plant

soil solution:

water in the spaces between soil particles, with dissolved minerals in it.

Loop diuretics

• "Loop diuretics" suppress ion reabsorption from fluid in ascending limb - used, e.g., to rapidly reduce fluid build-up in lungs

Early discovery of role of phloem

• 1600s experiment by Marcello Malpighi - removed ring of tree bark (containing phloem); over time, region of tree above girdle swelled; eventually, roots and entire tree died

Essential elements

• 6 macronutrients (≥ 1g/kg plant dry matter) - Nitrogen (as NO3 - [nitrate] or NH4 + [ammonium]) - Phosphorus (as PO4 3-[phosphate]) - Potassium (as K+) - Sulfur (as SO4 2-[sulfate]) - Calcium (as Ca2+) - Magnesium (as Mg2+) 8 micronutrients (< 0.1 g/kg plant dry matter) include - Iron (Fe2+) - Chlorine (Cl- ) - Manganese (Mn2+) - Zinc (Zn2+) - Copper (Cu2+) - Nickel (Ni2+) [recognized as essential only in 1983!] - Boron (Bo3 3- ) - Molybdenum (as MoO4 2- [molybdate])

Action potential propagation

• Action potential causes current to flow, depolarizing neighboring regions of membrane to threshold & generating another action potential • At threshold, large numbers of voltage-gated Na+ channels in region open massive influx of Na+ due to both concentration & charge differences, moving membrane potential toward equilibrium for Na+ (+62mV), but before this is reached, Na+ channels start to shut down & the more slowly responding K+ channels finally start to open in large numbers K+ becomes the dominant ion crossing membrane, diffusing out of cell following both concentration gradient & temporary charge gradient K+ outflow puts brakes on depolarization, which peaks at +40 mV outflow of K+ (due to both concentration & electrical gradients) brings membrane potential back down to -65 mV

Summary of "single effect" in loop of Henle

• Active transport of NaCl out of ascending limb - decreases NaCl concentration & osmotic pressure of fluid in ascending limb - increases NaCl concentration & osmotic pressure of both adjacent interstitial fluid & adjacent descending limb fluid

Generation of "single effect" in loop of Henle

• Active transport of NaCl out of ascending limb - decreases NaCl concentration of fluid inside ascending limb and increases NaCl concentration in interstitial fluid - permeability of descending limb varies among spp., but fluid in descending limb approaches equilibrium (or near equilibrium) with interstitial fluid wrt osmotic pressure & ion concentrations

Guttation

• Active transport of ions into xylem continues at night, xylem sap swells with water. When soil is wet and humidity of air is high, root pressure can result in guttation. • In short plants with low evaporation rates, water is literally pushed out of the leaves. Guttation is often mistaken for dew in the morning.

Kangaroo rats

• Adults kangaroo rats typically don't drink at all! - live in deep, cool burrows during heat of day - very little evaporation from skin, dry feces - soluble waste highly concentrated (osmotic U/P: 10 − 20) - obtain small amount of water from seeds, but most important water source is metabolic water from oxidation of organic molecules! • e.g., glucose: C6H12O6 + 6O2 → 6 CO2 + 6 H2O

Electrical synapse

• All electrical, no neurotransmitter • Cell membranes joined by gap junctions • With electrical synapse, post-synaptic neuron limited to transmit same signal as presynaptic neuron delivers • Typically found where very fast, invariant signal is needed, e.g., neurons that control escape swimming in some fish & crustaceans tissues in which large numbers of cells must be stimulated synchronously such as fish electric organs

Freshwater animals: problems

• All freshwater animals are hyperosmotic to freshwater • Water-breathing freshwater animals face problems opposite to those of marine fishes - tend to gain water by osmosis from freshwater environment, bloating them - tend to lose ions (such as Na+ & Cl- ) by diffusion to the environment - body fluids tend to become too dilute

Distal tubule of nephron

• As in proximal tubule, Na+ & Cl- are pumped out of tubule back into blood (active transport) • Unlike proximal tubule, wall of distal tubule has variable permeability to water - where aquaporin proteins are inserted in epithelial cell membrane, water permeability is high - insertion of aquaporins is controlled by antidiuretic hormone (ADH = vasopressin) secreted by the hypothalamus of the brain

Calculating the Membrane Potential

• At 37°C Eion tells you about the sign and magnitude of the charge inside the cell relative to outside needed to balance diffusion of an ion down its concentration gradient

Stimulating vertebrate skeletal muscle

• Axon terminals contain synaptic vesicles filled with acetylcholine (Ach) • When action potential reaches axon terminal, causes Ca2+ channels in presynaptic membrane to open Ca2+ diffuses into axon terminal from higher concentration outside, causing synaptic vesicles to fuse with presynaptic membrane & release Ach into presynaptic cleft • Ach-gated ion channels open, allowing Na+ & K+ to pass through • Na+ influx causes large graded depolarization, inducing graded ionic currents in neighboring regions with voltage-gated Na+ & K+ channels • Depolarization in these adjacent regions produces action potential that propagates throughout cell membrane of muscle cell & stimulates contraction

Ultrafiltration

• Blood enters each glomerulus at a pressure high enough that fluid from blood plasma is forced through tiny openings in walls of glomerular capillaries & then through inner wall of Bowman's Capsule - fluid enters lumen (central cavity) of Bowman's Capsule: primary urine • Blood cells & proteins dissolved in plasma are left behind in plasma • Water, salts, and small organic molecules such as glucose & amino acids pass through freely, entering nephron

Salmon transition

• Born in freshwater, grow in ocean, return to freshwater to spawn • In freshwater, do not drink; in ocean, start to drink & activate intestinal ion transport • In freshwater, use ATP to pump ions from surrounding water into blood in gills; in ocean, use ATP to pump ions out of blood in gills into seawater

Kidneys & nitrogenous waste

• Carbohydrates & fats break down during metabolism to CO2 & H2O—easy to get rid of • Proteins & nucleic acids contain nitrogen atoms and nitrogenous waste can be toxic - in some types of animals, kidneys have important role in excretion of nitrogenous waste

Key Processes in Development

• Cell type determination ex: destined to become muscle cell • Differentiation ex: actually becoming muscle cell • Morphogenesis - organization of differentiated cells to form multicellular body and organs via cell proliferation, cell migration, and apoptosis (programmed cell death) • Growth: cell division and expansion

Neuron

• Cell with axon for rapid, long distance communication - long axon conducts action potentials away from cell body • Action potentials propagate along axons with velocity of 1 to 100 m/s - when you touch a hot stove, danger signal travels length of your arm to spinal cord in 0.02 seconds!

Neural connections: synapses

• Cell-to-cell contact points specialized for transmitting signal from one cell to another • Neurons synapse with other neurons (for sensory neurons or interneurons) or with muscle fiber or gland cell (for motor neuron) Chemical synapses Electrical synapse

Water and mineral ions must cross root cell cell membrane and enter cells

• Challenges - cell membrane is hydrophobic, but water and mineral ions are polar - some mineral ions must move against their concentration gradient • Solutions - aquaporin proteins ("water channels") increase membrane permeability to water, so rate of osmosis can be regulated (though direction is always toward region of more negative water potential) - ion channels and proton pumps...

Changes in membrane potential

• Changes in membrane potential can be either graded or all-or-none depending on whether threshold (~-50 mV) is exceeded

Why does opening more K+ channels move membrane potential closer to Nernst potential for K+?

• Concentration gradients are essentially constant • Net charge is zero in bulk solution both inside & outside cell • Shift is all about the same behavior seen in single ion Nernst case outflow of K+ in response to concentration gradient makes inside of membrane more negative, reaching electrochemical equilibrium... but with higher proportion of K+ channels, multiion electrochemical equilibrium is closer to that for K+

Countercurrent multiplication

• Countercurrent multiplier system uses energy plus countercurrent exchange - loops of Henle, which use energy to transport NaCl out of the ascending limb • generating the "single effect" (the concentration difference between the ascending & descending limbs) - plus countercurrent flow in descending & ascending limbs • accounting for the"multiplier effect" (the much higher "top-to-bottom" gradient)

What causes differential gene expression?

• Cytoplasmic segregation - asymmetric distribution of specific cytoplasmic determinants (RNA, proteins) that influence transcription of particular genes at particular stages of development • Signaling between cells - e.g., gradients of signaling molecules that help determine cell fate and trigger differentiation

Metabolic disorders resulting in high urine production

• Diabetes insipidus (rare) - abnormally low ADH production (or low response) results in low water reabsorption from nephrons to blood, so excessive urine • Diabetes mellitus (way too common) - high blood glucose results in too much glucose remaining in urine instead of being reabsorbed by blood, so water stays also

Marine bony fishes: solutions

• Drink seawater & pump ions across intestinal wall • Use active transport to excrete excess ions into sea • Marine bony fishes expend 8-17% of daily energy budget on osmoregulation

Plants in Dry Conditions

• Drought avoiders - e.g., drop leaves during dry period - e.g., seed-to-seed during wet season • Leaf adaptations, e.g., - thick waxy cuticle covered with trichomes - stomatal crypts - spines instead of typical leaves (photosynthetic fleshy stems) • Water storage (succulents) • Variant photosynthesis - CAM (evolved multiple times), which allows stomata to open at night and store carbon for use during day in light-dependent reactions - C4 photosynthesis (evolved multiple times), which involves spatial reorganization and biochemical elaboration of process within leaf to reduce water loss • Extensive fibrous shallow root systems (e.g., cacti) or deep taproots • Concentrating solutes in vacuoles - lower water potential below that in surrounding soil

EPSPs & IPSPs

• EPSP or IPSP produced by a single synapse usually < 1 mV and last 10-20 milliseconds • Membrane potentials present at a single time sum together summation determines whether postsynaptic cell produces action potential(s) if still depolarized above threshold after refractory period, get another action potential

Neurotransmitters & brain

• Each presynaptic neuron produces one or more of dozens of different known neurotransmitters • A postsynaptic neuron in human brain may have chemical synapses with hundreds or thousands of presynaptic neurons • Receptor proteins for any particular neurotransmitter in cell membrane of postsynaptic neuron may be of two or more types with different actions much more complex than neuromuscular junction, which has just one type of neurotransmitter & one type of receptor!

Countercurrent multiplication in Loop of Henle

• Fluid concentrated in descending limb moves around into ascending limb - single effect produces ever-increasing osmotic concentration in interstitial fluid & descending limb at inner (medullar) end of loop - osmotic pressure of interstitial fluid at outer (cortical) end of loop is kept near 300 mOsm by • steady influx of 300 mOsm fluid into start of descending limb • dilution of fluid in ascending limb as it flows from deep in medulla to top of ascending limb - difference in osmotic pressure between cortical & medullar ends of the loop becomes greater & greater to a point where it much exceeds the between-limb difference generated by the single effect

Empirical metabolic index values

• For several marine ectotherm species, researchers assessed index values across geographic range - lowest metabolic index values for occupied sites were between 2 and 5: lower limit for viable habitats - interestingly, sustained field metabolic rates of diverse terrestrial species have been reported to be typically 1.5 to 5 times resting rates Why does this critical metaboli

hot desert

• Human in hot desert - maintain 37 C by sweating profusely (up to 2 L/h) • Oryx, Dromedary (Camelus dromedarius), etc., in hot desert varies body temperature - essentially storing heat rather than panting or sweating to get rid of it, then losing it nonevaporatively at night - reducing temperature gradient during day between oryx tissue and very hot environment

Hyperosmotic

• Hyperosmotic animals have body fluids with higher osmotic pressure than water in which they live

Hyposmotic

• Hyposmotic animals have body fluids with lower osmotic pressure than water in which they live

Vasa recta maintains osmotic gradient

• If blood vessels flowed unidirectionally from cortex through medulla and out of kidney... - blood traveling deeper into medulla would encounter ever-more-concentrated interstitial fluids and would therefore lose water osmotically and take up NaCl & urea by diffusion - it would then exit the kidney, leaving the water behind and taking solutes away—thereby diluting medullar fluids • In actual mammal kidney... - vessels of vasa recta carry blood into medulla, then back out, so gradient between blood & medulla is maintained - blood entering medulla from cortex passively picks up solutes & loses water - blood returning to cortex from medulla passively loses solutes & gains water - blood vessels exit kidney at junction between cortex & medulla, where interstitial fluid is isosmotic to blood

How do more open K+ channels shift membrane potential?

• If the proportion of open channels that are K+ increases, then importance of K+ in setting net membrane potential increases membrane potential moves closer to K+ Nernst potential

Kidney's adjust U/P ratio to regulate blood plasma

• If urine is less concentrated than blood plasma (U/P ratio < 1), the kidneys are making the plasma become more concentrated • If urine is more concentrated than blood plasma (U/P ratio > 1), the kidneys are making the plasma become more dilute • Can consider individual ions rather than total solute

Urine/plasma (U/P) ratio

• Imagine that an animal's blood plasma has an overall osmotic pressure of 100 & that its urine has an osmotic pressure of 25 - U/P ratio = 0.25 • kidney must be pulling out more water than solutes from plasma, so plasma is becoming more concentrated (i.e., the kidney is increasing the osmotic pressure of the blood plasma) • What if U/P ratio = 2.0? - urine is less watery than blood plasma, so kidney is removing more solute than water from blood plasma, making blood plasma more dilute (i.e., the kidney is decreasing the osmotic pressure of the blood plasma)

Loop length

• In mammals that achieve high concentrations, at least 15-20% of nephrons have long loops of Henle - in contrast, hippos & muskrats, e.g., have only short loops & can't make highly concentrated urine

U/P ratio: phylogenetic diversity

• Kidneys of most animals can produce urine more dilute than blood plasma (U/P < 1) • But most animals cannot produce U/P > 1 • Mammals, birds, and insects can produce concentrated urine with U/P > 1 - some desert mammals can achieve U/P of 10 or even 20 (max known 26!) • why is this important to them? - some insects achieve U/P of 8 and birds reach 2 or 3

Phenotypic plasticity of digestion

• Lab rat switched from low-protein to highprotein diet increases production of proteindigesting enzymes within 24 hours - in a week, secretion rate of these enzymes may increase 5-fold - switched from high-protein to low-protein diet, production of protein-digesting enzymes will drop • Similar findings for carbohydrates & lipids • Absorption efficiency also ramps up and down

Riftia annelid worms

• Live around deep sea hydrothermal vents • Up to 1.5 m long - no mouth, no gastrointestinal tract, no anus... - ~20% of body filled with "trophosome" tissue, which harbors abundant populations of sulfur-oxidizing bacteria - Riftia hemoglobin transports not only oxygen but also H2S and CO2 for bacteria to make organic molecules • some of these molecules enter worm tissue, "feeding" it

Translocation (movement of phloem sap) requires metabolic energy for two steps

• Loading: transport of sucrose & other solutes from sources into companion cells and then into sieve tubes • Unloading: transport of sucrose & other solutes from sieve tubes into sinks - maintains gradient of solute potential (and hence pressure potential) - delivers sugars for storage (e.g., in fruits) or for growth (e.g., new shoots in spring)

Loop of Henle

• Loop of Henle is the portion of a mammalian nephron connecting the proximal & distal convoluted tubules - main function is to create a concentration gradient in the medulla (= innermost portion) of kidney, increasing the osmotic pressure around collecting ducts - nephrons in a mammalian kidney oriented so all loops of Henle are parallel • Bowman's capsules & convoluted tubules in renal cortex • Loops of Henle & collecting ducts in renal medulla

Loops of Henle

• Loops of Henle in a kidney work together to increase osmotic pressure of tissue fluids deep in medulla - do not themselves concentrate urine, but set stage by increasing osmotic pressure of tissue fluids around collecting ducts • Flow of tubular fluid in opposite directions in descending & ascending limbs multiplies effects of active ion transport - "countercurrent multiplier" (like countercurrent exchange but requiring active transport)

Marine bony fishes: problems

• Lose water to environment by osmosis, dehydrating them - for these hyposmotic fish, living in ocean is like living in a desert! • Gain ions (such as Na+, Cl- ) by diffusion from seawater, making body fluids too concentrated

Beyond kidneys: extrarenal salt excretion

• Many birds & non-avian reptiles associated with oceans or deserts have salt glands in their heads that excrete a highly concentrated salt solution • Some terrestrial lizards & birds have cranial salt glands that secrete Na+, K+, and Cl- with higher ion concentrations than urine • Marine fish have salt-excreting glands in their gills - but marine mammals manage with just their ordinary mammalian high-performance kidneys

Symbioses with gut microbes

• Microbes in ruminant guts - break down cellulose into usable molecules - produce essential vitamins & amino acids - recycle waste nitrogen from host metabolism into microbial protein; digested by host into amino acids used to make host proteins • Ruminant chews cud ("ruminates") to expose more surface to microbes; added saliva keeps pH from dropping too low in rumen • Growing evidence of major importance of gut microbes ("gut microbiome") in nutrition and health of all animals, not just ruminants

Leaky K+ channels

• Most ion channels are closed most of the time • Some K+ channels are always open • K+ ions move out of cell down concentration gradient • Makes inside of cell membrane more negative (less positive) relative to outside

Nonmigratory aquatic animals may also encounter varying salinity

• Most marine invertebrates are osmotic conformers (=osmoconformers), but a minority are osmotic regulators (=osmoregulators) - most osmoconformers can't survive at low salinity • of marine invertebrates that can do well in low salinity, most are hyperosmotic regulators when in such situations - most osmoconformers do not survive in water much more dilute than seawater • but marine mussels are osmoconformers that can thrive at a wide range of salinities

Plant vascular tissue

• Most plants have vascular tissue - Xylem conducting cells • wood is secondary xylem, adding layers causes increase in diameter - Phloem cells, which are generally living, transport carbohydrates (mainly sugars) from sources (e.g., leaves, tubers, seeds) to sites where they are used or stored (sinks, e.g., growing tissues, roots, developing flowers and fruits) • phloem is innermost layer of tree bark

Sharks

• Most sharks & relatives have ion concentrations similar to those of marine bony fishes and much lower than seawater (hypoionic) • But osmotic pressure of blood is slightly higher than that of seawater (hyperosmotic) - body fluids have high concentrations of two organic solutes, urea (mainly) and trimethylamine oxide (TMAO) • Because blood is hyperosmotic to seawater, sharks experience slight osmotic influx of water • Nearly all sharks & relatives synthesize urea as main nitrogenous product of protein catabolism - nearly all bony fish use ammonia, not urea • For sharks & relatives, ~40% of blood osmotic pressure is attributable to urea (& TMAO) - in most aquatic animals, blood osmotic pressure mostly due to inorganic ions dissolved in plasma, so if animal tends to gain water by osmosis, it tends to lose ions by diffusion (and vice versa) • Sharks tend to gain water by osmosis and gain ions by diffusion

Membrane potential - summary

• Na+/K+ pump sets up concentration gradients • Membranes are semi-porous to certain ions - ions will diffuse across membrane down concentration gradient • Selective diffusion of ions across membrane can lead to a charge difference across membrane • This charge difference produces a voltage gradient = membrane potential - ions will move until charge difference balances the movement down concentration gradient

Animal digestive systems are diverse

• Nearly all animal phyla characterized by a tubular through-gut • Most molecules ingested cannot pass through gut epithelium - food must be broken down with the help of enzymes to yield smaller molecules that can cross gut epithelium and enter blood capillaries

Amphibian nephron

• Nephrons of amphibians similar to those of freshwater fish, non-avian reptiles, and most bird nephrons

Postsynaptic potentials

• Neuromuscular junction: each presynaptic nerve impulse generates action potential • In contrast, at neuron-to-neuron synapses, when postsynaptic ligand-gated ion channel opens, change in membrane potential of postsynaptic cell usually less than 1 mV fast, small, short-lived effect exact nature of effect depends on neurotransmitter & receptor protein, including which ion fluxes are changed

Nitrogenase

• Nitrogenase is strongly inhibited by oxygen • Plant roots are typically an aerobic environment - O2 levels in nodules regulated by leghemoglobin, a plant-produced O2-carrier protein related to hemoglobin • O2 levels kept low enough for nitrogenase to function, but high enough for aerobic respiration by bacteria (necessary to supply energy for fixation reaction)

Nephron

• Open at one end, closed at other • Urine formation starts at closed end, which consists of the cup-shaped Bowman's capsule enclosing a dense cluster of blood vessels known as a glomerulus

Human kidney U/P ratios

• Osmotic U/P can range from 0.1 (very dilute urine) to 4.0 (very concentrated) - under what circumstances might U/P be at each of these extremes? • drink a lot, blood plasma too dilute, so kidneys make dilute urine (pulling more water than solutes from blood) • sweat a lot/don't drink enough, blood plasma too concentrated, so kidneys make more concentrated urine (pulling more solute than water from blood) - urine volume is also adjusted

Characteristics of body fluids

• Osmotic pressure - total concentration of solutes (dissolved matter) • Ionic composition - in biological solutions, Na+, K+, Cl- especially • Volume - goldfish gains (and must expel) ~a third of its weight per day by osmosis

Some other ways plants get nutrients

• Parasites - ~1% of flowering plant species get some or all of their nutrients (and sometimes energy) from other plants Carnivorous plants - >500 species of plants that get at least some of their nutrients (but not energy) by digesting insects & other arthropods -digest insects & other arthropods • often live In boggy soils where little nitrogen or phosphorus are available • most famous: venus flytrap (Dionaea), with folding leaves that entrap prey, which is then digested by enzymes • Both parasitic and carnivorous lifestyles have evolved independently in multiple plant lineages

Plant transport systems

• Plants are not very active... • Plants have no muscles, so no heart... • Plants have evolved other ways to move essential materials (H20, minerals, sugar) - "circulatory system" does not transport gases water: • always moves from roots to leaves • moves through xylem sugars: • can move up or down • made in leaves, stored in roots • moves through phloem.

In nephron

• Primary urine is ~ isosmotic with blood plasma • During passage through nephron, > half of water & ions are typically reabsorbed into blood plasma - for concentrated urine, can be > 99% • Equivalent of all the plasma water in body enters nephrons every 30 minutes • Human kidneys each day process ~180 liters of filtrate to 1.5 liters of urine - opportunity to remove wastes or toxins quickly & make rapid adjustments to plasma volume & composition

Proton pump

• Proton pump uses energy from ATP to move protons (H+) out of the cell against a concentration gradient (primary active transport), resulting in - an electrical gradient such that the region just outside the cell is more positively charged than the inside of the cel l - a proton concentration gradient, with more protons just outside the cell than inside

Proximal tubule of nephron

• Proximal tubule has nephron wall loaded with aquaporins, so highly permeable to water • Na+ and Cl- (also glucose, amino acids) are returned to blood by active transport & water follows by osmosis - result is that as fluid moves through proximal tubule, volume is greatly reduced, but osmotic pressure is unchanged & still ~ matches that of blood plasma

Example of hormonally regulated homeostasis: human insulin and glucagon

• Regulate storage & release of nutrients in body • Both hormones are released by endocrine portion of pancreas, known as "islets of Langerhans" - pancreas has major exocrine portion as well, secreting digestive enzymes and bicarbonate into the midgut via pancreatic ducts • As blood glucose rises, secreted insulin causes cells to take up glucose, stabilizing blood glucose concentration & stimulating glucose storage when it is abundant - liver & muscle cells store glucose as glycogen • Between meals, pancreas produces glucagon instead of insulin, with reverse effects - breakdown of glycogen into glucose & release into blood

What's actually happening?

• Relatively small number of ions need to move through channels to change membrane potential of all ions within 1,000 nm of membrane surface, fewer than 100 out of a million account for membrane potential A typical cell contains ~ 6 trillion K+ ions has ~10,000 K+ channels that can each pass ~100,000 ions/second • So typical cell can move ~1 million ions/second i.e., ~ a hundredth of a percent of ions present

Electrochemical equilibrium

• Resting potential is mainly set by K+ • K+ leaving leads to voltage difference across membrane • K+ diffuses out until the voltage difference (negative on the inside) pulls K+ back inside with exactly the same force as the concentration gradient pulls K+ out - this is the equilibrium potential (voltage) of K+

`Resting potential

• Resting potential is mainly set by K+ leak channels that are effectively open all the time - K+ leaks out due to concentration gradient set up by Na-K+ pump • K+ exiting leaves unbalanced negative charge on inner surface of membrane that attracts positive charges to outer surface of cell membrane - voltage difference across membrane

Plants In Saturated Soil

• Roots need oxygen, so root systems in saturated conditions often shallow & slowgrowing • Some mangrove species have pneumatophores extending out of water & into air; lenticels (openings) allow oxygen to diffuse through them • Some aquatic plants have air spaces known as aerenchyma - store O2 from photosynthesis, which can diffuse where needed - provide buoyancy - add bulk but not much metabolic demand

Salty Soil

• Saline environments (high in Na+, K+, Ca2+, Cl- ) have a very negative water potential - hard for plants to get water - Na+ can inhibit enzymes & protein synthesis • Halophytes (salt-adapted plants) typically take up Na+ (and often Cl- ) into their roots, transport to vacuoles of leaf cells - accumulated salts reduce water potential - some halophytes excrete salt through salt glands in leaves

Glucose Transport

• Secondary active transport of glucose (a polar molecule) from lumen of small intestine into intestine cells Na+−K+ pump keeps Na+ concentration higher outside cells This concentration gradient allows glucose + Na+ to move reliably into intestine cells by facilitated diffusion with cotransporter (symporter) carrier protein (Na−glucose symporter) glucose would usually enter intestine cells by diffusion anyhow—but more slowly • Glucose moves from intestine cells into blood by facilitated diffusion (glucose uniporter, a carrier protein) • Glucose transport in & out of blood & MOST cells in body (excluding small intestine & kidneys) does not involve active transport • Glucose moves from intestine cells into blood by facilitated diffusion (glucose uniporter, a carrier protein)

Chemical synapse

• Signals passed between cells by means of molecules • At chemical synapse, cell membranes of presynaptic & postsynaptic cells separated bysynaptic cleft • Action potentials cannot cross synaptic cleft when action potential reaches presynaptic cell, cell releases a neurotransmitter into synaptic cleft neurotransmitter (e.g., acetylcholine) diffuses quickly across, then binds to receptor proteins in cell membrane of postsynaptic cell • Receptors generate electrical (or other) change when bound to neurotransmitter entire process of synaptic signal transmission may take just a few milliseconds • Neurotransmitter molecules are rapidly removed from synaptic cleft, terminating signal

Action potential only goes one way

• Sodium channels are inactivated during falling phase • Can't fire again for 1-2 ms refractory period cell can fire "only" 500- 1000 AP / second

Nitrogen-fixing root nodules

• Some plants, especially legumes, can form symbiotic relationships with certain bacteria that live in nodules that form on the roots, capture atmospheric N2, and make this nitrogen available to plants - some free-living (non-symbiotic) bacteria in soil & water also fix nitrogen • Maintaining these nitrogen-fixing bacteria can cost as much as 20% of a plant's photosynthetic output • Nitrogen fixation uses nitrogenase to transform N2 into ammonia (NH3) N2 + 6H ->2 NH3 • Leguminous plants often planted as cover crop to help replenish soil • Soybean (a legume) often rotated with corn to cut fertilizer use and maximize overall profit

Stomata response

• Stomata can open and close quickly (in minutes) not only in response to light level, but also CO2 concentration and water loss • Over longer term (days to weeks), plants can change number of stomata in response to environmental conditions - shed leaves, make new leaves with more or fewer stomata

Pressure flow model

• Sucrose loading: at source, sucrose actively transported into phloem companion cells, then into sieve tubes, followed by water • Water influx creates positive pressure at source end of sieve tube, pushing contents toward sink end • Sucrose unloading: at sink, sucrose is unloaded both passively & by active transport - water moves back into xylem, maintaining gradient of solute potential & pressure potential

Maple syrup demonstrates bidirectional movement of sugar in the phloem:

• Summer and Fall: sugar made in leaves, stored in roots • late Winter: sap rises back to shoot to support leaf development (that's when trunks are tapped)

Postsynaptic potentials: excitatory

• Synapses that depolarize the postsynaptic membrane are called excitatory synapses depolarization shifts membrane potential toward threshold for action potential (i.e., makes less negative) • Excitatory synapses produce graded membrane potentials called excitatory postsynaptic potentials (EPSPs)

Postsynaptic potentials: inhibitory

• Synapses that shift the membrane potential away from threshold are called inhibitory synapses lower the likelihood of reaching threshold for action potential (i.e., makes more negative) • Inhibitory synapses produce graded membrane hyperpolarizations called inhibitory postsynaptic potentials (IPSPs)

Ontogenetic shifts in nitrogenous waste excretion

• Tadpoles (aquatic larvae of frogs and toads) excrete ammonia across their gill membranes, but after metamorphosis adult frogs & toads generally excrete urea

Vertebrate hindgut

• Temporarily stores indigestible waste • Completes reabsorption of water & salts - in humans, ~7 liters of watery solution with Na+, Cl- , and other ions is secreted from blood to gut each day as part of food processing—must be recovered! • failure to reabsorb can be deadly, e.g., in cholera or dysentery

Why does action potential travel in one direction?

• The region of axon membrane that has produced an action potential experiences a brief refractory period during which it cannot produce another currents can produce action potential only in neighboring region in direction of axon terminals

Sending messages around the body

• Time for signaling molecule to diffuse 1 meter (16 years) • Time for signaling molecule to circulate through circulatory system - blood velocity Time to go 1 m - Capillaries 0.03 cm/s 33 s - Veins 15 cm/s 6 s - Aorta 40 cm/s 2.5 s

Freshwater animals: solutions

• To maintain hyperosmotic state - kidneys produce large volume of urine each day to get rid of excess water • in most cases, kidneys produce urine far more dilute than blood plasma (U/P < <1.0) - lost salts replaced by active transport cells that use ATP to pump Na+ and Cl- directly from freshwater environment into blood--although these ions are scarce in freshwater • in gills of fish, crayfish, clams; in skin of adult frogs

Transpiration-Cohesion-Tension Model

• Transpiration: evaporation of water from cells within the leaves • Cohesion: cohesion of water molecules in the xylem sap as a result of hydrogen bonding • Tension: tension on the xylem sap as a result of transpiration

Mammal kidney collecting ducts

• Tubular fluid passes through a collecting duct just prior to exiting kidney - at start of collecting duct, osmotic pressure of surrounding tissue fluid is like that of blood plasma - moving through the collecting duct, however, surrounding tissue fluid has increasingly high osmotic pressure • Tubular fluid passes through a collecting duct just prior to exiting kidney - at start of collecting duct, osmotic pressure of surrounding tissue fluid is like that of blood plasma - moving through the collecting duct, however, surrounding tissue fluid has increasingly high osmotic pressure

Kidneys make urine from blood plasma

• Tubular structures that discharge a fluid directly or indirectly to outside environment - single tube in, e.g., crayfish or lobster - many microscopic tubules (" nephrons") in vertebrate kidney • ~1 million nephrons in a human kidney • nephrons ultimately discharge into a single tube, the ureter, that carries fluid out of the kidney (in mammals, via the bladder & urethra) • Primary function of vertebrate kidney is to regulate composition & volume of blood plasma - selectively removes water & ions from blood plasma

Neurotransmitter removal

• Two main mechanisms of removal: Enzymatic breakdown Uptake by nearby neurons or associated cells (even re- uptake by presynaptic cell)

Dehydration: a major challenge for terrestrial animals

• Typical terrestrial vertebrates have blood osmotic pressure ~300-350 mOsm • Some terrestrial animals have outer body covering highly permeable to water, so must stay moist • Many others have outer lipid layer that minimizes evaporation • Some animals can even live in deserts

Blue Whale

• Up to 30 m long, 180,000 kg - tongue can weigh as much as an elephant - heart can weigh as much as an automobile • Feed almost exclusively on krill - can consume >3,600 kg/day!

Plants get help from soil organisms

• Vast numbers of soil organisms (largely microscopic bacteria & fungi) break down organic material in soil, freeing up nutrients— and some have very important mutualistic relationships with plants, notably - mycorrhizae - nitrogen-fixing bacteria

Carnivory

• Venus fly traps and other carnivorous plants typically live in nitrogen-poor soils, like swamps, bogs.

How vertebrate kidneys work: big picture

• Vertebrate kidney tubule = nephron - ~1 million nephrons in a human kidney • Fluid from blood plasma enters nephron at one end (="primary urine") • Volume & composition of fluid are modified as it passes through kidney & final product (="definitive urine") is passed out of body - along way, materials can be both reabsorbed & secreted into the urine

Ion channels

• Voltage-gated depolarization of cell membrane causes ion channels to open • Ligand-gated binding of specific molecules (e.g., neurotransmitters) causes ion channels to open

Glomerular filtration rate (GFR)

• Volume of blood passing through glomeruli each minute - measured indirectly with blood tests for, e.g., creatinine levels • An important measure of kidney function

Regulation of water loss

• Waxy cuticle on leaves and stems impermeable to water • Stomata in leaves can open and close to allow water, O2, CO2 to move in and out of leaves - some leaves with as many as 1,000 stomata per square millimeter

ADH & aquaporins

• When ADH level is high, walls of distal convoluted tubule have high aquaporin density & are highly permeable to water - functions like proximal tubule (ions pumped back into blood & water follows, yielding reduced volume of urine that is ~isosmotic with blood plasma) • When ADH level is low, walls of distal convoluted tubule have low aquaporin density & thus low permeability to water - Na+ & Cl- still pumped back into blood, but water can't follow so urine is dilute & volume is high

Mammal kidney and ADH

• When ADH level is high, yields small volume of highly concentrated urine • When ADH level is low, collecting duct walls have low permeability to water, so little water is lost through osmosis to surrounding tissue fluid as tubular fluid moves through collecting duct - in addition, Na+ & Cl- are actively transported out of tubular fluid as it moves through collecting duct - this process yields a high volume of dilute urine

Depolarization & positive feedback

• When cell membrane becomes partly depolarized, some Na+ channels open Na+ ions rapidly enter, depolarizing membrane further Na+ is suddenly the dominant ion crossing membrane • This continues until all Na+ channels in local region are open, causing maximum depolarization

Large vs. small mammals & heat stress

• Why is large body size advantageous for conserving water? - surface-to-volume ratio (exogenous heat absorption, evaporative water loss for cooling) - allometric relationship between body size & mass-specific metabolic rate (respiratory water loss, endogenous heat production, evaporative water loss for cooling)

Walter Nernst

• Won Nobel prize in chemistry in 1920 • At equilibrium the diffusion of ions movement due to concentration = from electrical differences potential • Equilibrium membrane potential to balance concentration differences

Salmon

• Young salmon in freshwater takes up water by osmosis, loses salts to surroundings by diffusion - tends to make blood more dilute • Once migrates to ocean, gains salts by diffusion from surroundings and loses water by osmosis to surroundings - tends to make blood more concentrated

Evolution of digestive abilities

• e.g., plant-eating insect host-shift • e.g., lactase production in human babies, but usually not in adults - lactase breaks lactose molecule into monosaccharides galactose & glucose - several cattle-raising African tribes, as well as northern Europeans, have independently evolved the ability to digest lactose as adults

Colinearity of Hox gene order and expression

• expression of each Hox gene is normally largely restricted to segments transformed in loss-of-function mutants • expressed in same order in embryo as they lie on chromosome:

Homeotic mutations affect a cluster of Hox ("homeobox") transcription factors

• homeobox sequence found in all Hox proteins (and others) • forms a DNA-binding protein domain • Hox proteins regulate activity of other genes

Morphogenesis Later cell proliferation

• in larval and adult animals, proliferation requires feeding and/or recycling:

downward bulk flow from leaves by positive pressure

• osmotic swelling of sap at source of sugar loading pushes surrounding phloem sap away • unloading of sugar at sink allows sap to lose water • result is similar to water potential gradient in xylem, but driven all by osmosis. • direction of gradient reversible (just flip source and sink tissues)

xylem overview

• tension (pulling from above) on xylem accounts for most of flow • osmotic contribution (pushing from below) is limited to roots, contributes little to flow in tall plants

adult chicken:

• ~ 1012 cells • many organs and tissues • very responsive to environment • still tasty

How can a mammal kidney make such concentrated urine?

•PCTs function like those of other vertebrates - reduce volume of urine without changing osmotic pressure • DCTs concentrate urine more or less in response to ADH • However, in mammal kidney, deeper portions of collecting ducts are surrounded by tissue fluid that is far more concentrated than blood plasma