Homeostasis

Question 1

homeostasis

Answer 1

the maintenance of a relatively constant internal environment in the cells of the body

Question 2

why is homeostasis important?

Answer 2

optimal conditions for enzyme action and cell function
for cells, surroundings is tissue fluid

temp : too low can cause metabolic reactions to slow down; high can cause enzymes denatured

wp: wp decrease, water exits cells and metabolic reactions can slow down/stop; wp increase, water enters the cells and causes them to burt

blood glucose conc : lack causes less or no respiration/ no energy source; too much can cause decrease in wp and again disrupt metabolic reactions

Question 3

principle homeostasis/ how does it work

Answer 3

usually uses negative feedback
involves a stimuli, receptors, effectors , coordination systems (nervous and endocrine)
try to maintain at a set point
internal/external stimuli = receptor/sensor detects a stimuli that is involved with the condition/physiological factor
–> receptor relays the infor through the nervous system to CNS (input )
–> CNS instructs an effector to carry out an action (corrective actions)
–>stimulus is continously monitored by receptors so that is fluctuates around a set point or ideal value (output)

Nervous : electrical impusles along neurones
Endocrine : chemical messengers (hormones) in blood

Question 4

what is urea

Answer 4

produced in the liver, from excess amino acids
amino group is removed from amino acid/-NH2 (deamination) and a hydrogen atom
this forms ammonia and a keto acid
keto acid is respired = glucose or glycogen/ fat for storage
NH3 is soluble and toxic so it is converted in a less soluble and toxic urea by combining with CO2
2NH3 + CO2 –> CO(NH2)2 + H2O

Question 5

what is excretion?

Answer 5

the removal of unwanted products of metabolism from the body
excretes CO2 and urea

Question 6

structure of kidney

Answer 6

a fibrous capsule outside
then cortex
then medulla
then renal pelvis
then ureter
branches of renal vein and arteries

Question 7

look at the textbooks for some cross sections of:
• glomerulus
• Bowman’s capsule
• proximal convoluted tubule
• loop of Henle
• distal convoluted tubule
• collecting duct

Answer 7

-

Question 8

how is urine formed from nephrons

Answer 8

nephron consists of a glomerulus (a network of capillaries)
glomerulus is supplied by the afferent and efferent arterioles.

• the formation of glomerular filtrate by ultrafiltration in the
Bowman’s capsule
• selective reabsorption in the proximal convoluted tubule

Question 9

ultrafiltration

Answer 9

1st = endothelium of capillary
2nd = basement membrane
3rd = epithelium of bowman’s capusle/ podocytes

1st and 3rd = fully permeable as they have gaps allow substance to be dissolved into bowman’s capsule
= forms the glomerular filtrate
= amino acids, water, glucose, urea and inorganic ions (Na+, K+, Cl-)

2nd = basement membrane acts as a filter as it stops large protein molecules like red/white blood cells and platelets entering bownman’s capsule

Question 10

what is in the glomerular filtrate

Answer 10

amino acids, water, glucose, urea and inorganic ions (Na+, K+, Cl-)

Question 11

factors affecting ultrafiltration

Answer 11

??affected by water potential

Question 12

selective reabsorbtion
proximal convoluted tuble

Answer 12

proximal convoluated tuble (PCT) have epithelial cells
there are blood capillaries near the PCT.
Basal membranes is the part closet to blood capillaries
Sodium-potassium pumps in the basal membranes actively move Na+ out of epithelial cells and into blood.
Na+ conc decrease inside epi cells.
= passive transport Na+ from filtrate moves down conc gradient into epi cells.
= fuels the co-transport of glucose into the cell -Go through co-transporter proteins and glucose is transported against conc gradient.
glucose cannot return to filtrate so it diffuses down conc gradient into blood.
no more glucose in urine anymore

filtrate has less solutes in it than blood so H2O diffuses from filtrate into blood

Question 13

osmoregulation

Answer 13

control of the wp of body fluids
specialised sensory neurones that monitor wp called osmoreceptors in the hypothalamus.
when wp decrease in blood, hypothalamus sends nerve impulses to make posterior pituitary gland release anti-diuretic hormone (ADH)
The ADH reduces loss of water through urine and makes the kidney reabsorb the water
enters through the blood capilarries

when wp increases in blood, no ADH is stimulated, aquaporins are removed from the membrane

Question 14

how does ADH workd

Answer 14

ADH is primary messenger
acts on the lumial membrane of collecting duct cells
receptor proteins send signal to G protein
G protein makes cAMP (secondary messenger)
cAMP causes a signalling cascade to activate phosphorylase A enzymes
phosphorylase A enzyme moves the vesicles containing aquaprins to the luminal sides of the membrane (vesicles allows for unrestricted flow of water through a phospholipid bilayer)
so water can exit through them into tissue fluid and blood plasma

Question 15

decrease in blood glucose concentration

Answer 15

a cells begin secreting glucahon
B cells stop secretion of insulin
no insulin stops the use of glucose.
GLUCAGON binds to receptors in the cell surface memrbanes which activates a G protein
receptor proteins activaes enzyme adenylyl cyclase which causes ATP –> cAMP
cAMP binds to protein kinase A enzymes to create active protein kinase
—> active phosphorylase kinase enzymes (phosphate groups are added to activate them)
–> glycogen phosphorylase enzymes
–> glycogen -> glucose
known as glycogenolysis
glucose diffuses out of GLUT 2 transporter proteins into blood

Question 16

increase in blood glucose conc

Answer 16

B cells are used and releases insulin
insulin binds to receptor in cell surface membrane which signals so vesicles with GLUT4 move towards membrane
allowes glucose to enter through faciliated diffusion into cell down conc gradient
insulin also increases use of glucose in respiration
insuline then stimulates active enzyme glucokinase
–> phosphorylates glucose which now cannot exit cell as cannot pass through same transporters
phosphofructokinase and glygoen synthase are activated to catalyse glucose–>glycogen
=glycogenesis

Question 17

test strips

Answer 17

Test strips
glucose oxidase + peroxidase onto a small pad and immersed in the urine sample for a short time
if glucose present =
-glucose oxdiase causes glucose oxdisied to form gluconic acid + H2O2
-peroxidase catalyses H2O2 and colourless chemical in pad to form brown compound+H2O
darker colour = higher conc

Question 18

stomata

Answer 18

control the diffusion of gases in and out of leaves
Regulation of stomatal aperture balances the need for carbon dioxide uptake by diffusion with the need to minimise water loss by transpiration

Question 19

why do stomata have rhythms of opening daily and nightly

Answer 19

despite when plant is in constant light or constant darkness, the daily rhythm of opening and closing of the stomata continues
Day = open
- maintaids inward diffusion of CO2 and O2 exits
-Water vapour exits
Night = close
-reduces rate of transpiration
-saves water and prevents water loss

Question 20

structure and function of guard cells

Answer 20

thick cella walls facing air and stoma; thin cell walls facing adjacent epidermal cells
cellulose microfibrils arranged in bands around the cell
no plasmodesmata
high density of chloroplasts/mitocrhondria
thyloakoids but few grana
many cristae
several small vacuoles

Question 21

how guard cells open

Answer 21

In response to light, ATP powered proton pumps in membrane actively pumps H+ out of guard cell
low H+ conc and negative charge(starch = maltose = malate-) causes K+ channels to open so K+ can diffuse into cell by electrochemical gradient
High K+ conc causes low wp and so water moves in by osmosis down wp gradient
more water increases volume so it expands, cells curve against each other/increase in length and opens

Question 22

how guard cells close

Answer 22

hydrogen pump proteins stop and K+ leave and enter neighbouring cells.
malate ions are returned to chloroplasts to be converted to starch
water potential oustide so water leaves, guard cells become flaccid and close the stoma.

Question 23

abscisic acid during water stress

Answer 23

guard cells have ABA receptros in membrane
ABA binds to recpetors inhibiting proton pumps and stops the active transport of hydrogen ions out
Ca2+ moves into guard cells and acts as a second messenger to make K+ leave and so water leaves guard ccells and becomes flaccid

Question 24

selective absorption
distal convoluted

Answer 24

amino acids, vitamins and inorganic ions are also reabsorbed by the body.
wp in filtrate increases and there is less water in blood capillaries = water potential gradient causes water to move into blood by osmosis.
urea has higher conc in filtrate so diffuses down into blood
NaCl is actively transported out of the thick part of the acsending limb of loop of Henle
Distal convoluted tuble works the same way as the acsending limb of loop of Henle = NaCl are pumped out of tuble and K+ is pumped into tuble

Question 25

gluconeogenesis

Answer 25

glucagon also causes gluconeogenesis (fatty acids, glyercol, pyruvate, lactate)

adrenaline can also increase glucose by binding to different receptors on the liver cells to create the same signalling cascade and also cause muscles to breakdown glycogen stores

Question 26

Biosensor

Answer 26

for diabetes to show current blood glucose conc
- uses glucose oxidase/ no peroxidase immobilised on a recognition layer
Covering the recognition layer is a partially permeable membrane that only allows small molecules(glucose) from the blood to reach the immobilised enzymes
When a small sample of blood is tested, glucose oxidase catalyses a reaction in which any glucose in the blood sample is oxidised to form gluconic acid and hydrogen peroxide
The hydrogen peroxide produced is oxidised at an electrode that detects electron transfers
The electron flow is proportional to the glucose concentration of the blood sample
The biosensor amplifies the current, which is then read by a processor to produce a digital reading for blood glucose concentration
This process is complete within a matter of seconds

Question 27

adrenaline

Answer 27

attaches to adrenaline receptor
G protein activated
adenylyl cyclase which activates ATP to cAMP
cAMP acts as a secondary messenger
cAMP binds to kinase enzyme
enzyme cascade = amplifies signals