excretion

how aquatic animals dispose of nitrogenous wastes

-readily diffuses in water

highly soluble in water and 100,000 times less toxic than ammonia

-excreted by mammals, amphibians, and a few fishes

this is how humans do it

less toxic than ammonia and excreted by birds, insects, many reptiles, and snails

-not soluble in water so it is excreted in crystalline form

-has the benefit of conserving water

liver makes urea

kidneys filter urea out of blood

chemically modifies substances absorbed from GI tract i.e. alcohol drugs

 -removes toxins/poisons and converts them to less toxic forms

-regulates some hormone levels

-produces proteins found in plasma

dumps everything out of the blood capillaries except cells and large proteins

-takes back only what is needed (glucose, water, amino acids, salts)

(-most ions and almost all water reabsorbed)

-leaves behind waste as urea and gets rid of it

-hypertonic (conc.) urine is formed to save water

renal pelvis

nephron

-streches from renal medula into renal cortex

capillary beds in nephrons

contained in bowman's capsule

everything is pushed out in glomeruli except large proteins and cells (because to big for filtration)

kidney arterioles have high blood pressure which forces filtration to occur

once filtrate has passed the glomerulus where does it go?

proximal convoluted tubule

descending limb of loop of Henle

loop of Henle

ascending limb of loop of Henle

distal convoluted tubule

collecting duct

endothelial cells in glomerulus

capillary in Glomerulus

have many pores

in (on) glomerulus: Bowman's capsule epithelial cells

podocytes

look like fingers surrounding the capillary

"interdigiting cell process with slits between them"

a) humans pass____L of blood through the kidneys daily 

b) ____L of water leaves the blood through filtration

c)we produce only ___L of urine per day, the rest of the water is reabsorbed

a) 2000

b) 180

c) 1-2

selective reabsorption: Proximal tubule

75% of Na⁺ is actively pumped out

-Cl^- (due to electrostatic forces) and 75% of water (due to hypertonic conc.) follows through osmosis

-glucose and amino acids also pumped out

-water, salt, glucose, and amino acids are picked up by peritubular capillaries

-water permeable

-not salt permeable

-as filtrate goes down LOH into medulla, extracellular fluid conc. increases, so water moves out passively (osmosis) due to hypetonic environment

-this increases the conc. of the filtrate

-water reabsorbed in peritubular capillaries

In the Distal tubule, only 3% of the initial water from Bowman's capsule is left

-filtrate from distal tubule enters collecting duct which goes into medulla where extracellular flued is very concentrated

vasopressin in the kidneys

same thing as antidiuretic hormone (ADH)

-released by posterior pituitary if more water is needed

-increases the permeability of collecting duct to water

-more water goes out of collecting duct and reabsorbed, urine more concentrated

solute gradient in kidneys, plasma levels (due to amount of water reuptake)

they are actively secreted (exo/endocytosis) from the peritubular capillaries into distal convoluted tubule

ex. penicillin and phenobarbitol

salt glands (marine bird), osmoregulation

-above beak between eyes

sea turtles, marine birds, crocs have no freshwater source, must drink salt water and get rid of salt from salt glands

live in deserts, never drink water or eat moist plants, only eat seeds that contain water

-produce water from respiratory metabolism

-must conserve

-i.e. no sweating/activity during the day, dry feces

-very concentrated urine, long loop of Henle

hormone

produced by actively growing parts (meristems)

-no special glands that do only hormone secretion, like endocrine glands in animals

auxins: cell elongation and division (and more)

gibberellins: cell elongation (and more)

cytokinins: cell division

inhibitors: (induce and maintain dormancy)

ethylene: (stimulate fruit ripening, thigmotropic response)

Auxins: what do they do

where do they do it

cell elongation in stems and shoots - positive phototropism

 roots - negative phototropism

found in apical meristem

investigated coleoptile

-1 control, 4 experimental groups

A: control -> top bended

B: cut off coleoptile -> no bend

C: covered coleoptile -> no bend

D: covered coleoptile with something clear ->bend

E: covered "trunk" ->bend

discovered relationship between coleoptile and phototropism

sunlgihts causes auxin to go to opposite side of shoot (originally equally present throughout)

-elongation is induced on the side, "pushing"/curving plant toward light source

Auxin Experiments: Boysen-Jensen

cut of coleoptile and place agar (gelatin) in between coleoptile and rest of shoot, the shoot still grew toward the light

-thought it must have been either a chemical that diffused through agar or an electrical signal

Auxin Experiment:

Wendt

cut off coleoptile and placed on agar block for one hour, then put block back on ONE side of stump

even in dark, plant grows away from agar because auxins have diffused into that side

what is the natural form of auxin

indoleacetic acid

most commonly studied form although there are many chemicals that are classified as auxins

auxins and gravitotropism

shoots show negative gravitotropsim

-compete for sunlight

roots show positive gravitotropism

-stabilize plant and absorb water

inhibits (restricts) lateral buds

-affects fruit development

-controls leaf abcission

fungus infects host and produces a surplus of gibberellin

-host grows to tall and can't support itself, eventually dies

stimulate rapid stem elongation

-has general affect unlike auxin

-move freely in plant, auxins only move one way

break dormancy in germinating seeds

-stimulates early foweing in biennials (every 2 years)

-stimulates flowering and fruiting in many plants

promote cell division

-if ratio of auxins to cytokinins favors auxins -> root growth

-if ratio of auxins to cytokinins favors cytokinins -> stem growth

-cut off apical bud (reduce auxins), no more cytokinins so stems grow more

can be used be pathogens to promote their own growth (like plant cancer)

-a bacterial infection can increase cytokinins an auxins which causes rapid cell division

ethylene

auxins (produced in flowers and developing fruits NOT APICAL SHOOT) stimulate ethylene production

-hastens fruit ripening

-tomatoes often picked green and ripened later with ethylene gas

-some tomatoes genetically modified to not produce ethylene on their own