Homeostasis

Question 1

why do multicellular organisms need a communication system

Answer 1

to respond when internal and external environment changes
coordinate organ function

Question 2

what is cell signalling

Answer 2

communication between cells
electrical signals carried between by neurons or chemical signals as hormones

Question 3

what is homeostasis

Answer 3

internal environment in maintained within set limits around an optimum

Question 4

define negative feedback

Answer 4

self regulatory mechanisms return individual environment to optimum when there is a fluctuation

Question 5

define positive feedback

Answer 5

a fluctuation triggers changes that results in an even greater deviation from normal levels

Question 6

what are receptors and effectors

Answer 6

receptors=specialised cells located in sense organs that detect a specific stimulus
effectors=usually muscles or glands which enable a physical response to a stimulus

Question 7

what is an ectotherm

Answer 7

organism that cannot regulate own body temperature
rely on external sources and behavioural responses

Question 8

what is an endotherm

Answer 8

organisms that can regulate own body temperature
thermoreceptors send signals to hypothalamus triggering a physiological or behavioural response

Question 9

how does the autonomic nervous system enable endotherms to thermoregulate

Answer 9

negative feedback
peripheral thermoreceptors detect changes changes in skin temperature
thermoreceptors in hypothalamus detect changes in blood temperature hypothalamus sends impulses to effectors in skin and muscles

Question 10

explain the role of the skin in thermoregulation

Answer 10

vasodilation/constriction of arterioles supplying skin capillaries controls heat loss to surface
hair erector muscles contract and follicles protrude to trap air for insulation
evaporation of sweat cools skin surface

Question 11

what is excretion

Answer 11

process of removing metabolic wastes to maintain metabolism

Question 12

describe the gross structure of the liver

Answer 12

liver lobules: cylinders of hepatocytes arranged in rows and connected at the centre
hepatic vein: takes deoxygenated blood away from the liver
hepatic portal vein: contains product of digestion
hepatic artery: supplies oxygenated blood
bile duct: transports bile to gall bladder

Question 13

outline the functions of the liver

Answer 13

site of gluconeogenesis, glycolysis, and glycogenesis
stores glycogen
deaminates excess amino acids forming ammonia and organic acids
detoxifies chemicals

Question 14

describe the gross structure of the kidney

Answer 14

fibrous capsule:protects kidney
cortex:outer region consists of Bowman’s capsule, convulated tubules and blood vessels
medulla:inner region consists of collecting ducts, loop of henle and blood vessels

Question 15

describe the blood vessels associated with a nephron

Answer 15

wide afferent arteriole from renal artery enters renal capsule and forms glomerulus:branched knot of capilaries which combine to form efferent arteriole
efferent arteriole branches to form capillary network that surrounds tubule

Question 16

describe the sections of a nephron

Answer 16

bowmans capsule at start: cup shaped, surrounds golmerulus, inner layer of podocytes
PCT:series of loops surrounded by capillaries, walls made of epithelial cells with microvilli
loop of henle:hairpin loop extends from cortex to medulla
DCT:fewer capillaries than PCT
collecting duct: DCT from several nephrons empty into collecting duct leading to pelvis

Question 17

describe the process of ultrafiltration

Answer 17

occurs in Bowmans capsule
high hydrostatic pressure in glomerulus forces small molecules out capillary fenestrations against osmotic gradient
basement membrane acts as filter

Question 18

how are cells of the Bowman’s capsule adapted for ultrafiltration

Answer 18

fenestrations between epithelial cells of capillaries
fluid can pass between and under folded membrane of podocytes

Question 19

what happens during selective reabsorption

Answer 19

occurs in PCT
useful molecules from glomerular filtrate are reabsorbed into the blood

Question 20

how does the kidney produce urine

Answer 20

after selective reabsorption filtrate passes through loop of henle which acts as countercurrent multiplier and then through DCT where water and mineral ions are reabsorbed
more water is reabsorbed in collecting duct
remaining fluid (urine) contains only waste materials and water

Question 21

what happens in the loop of henle

Answer 21

active transport of sodium and chlorine out of ascending limb
water potential of interstitial fluid decreases
osmosis of water out of descending limb
water potential of filtrate decreases going down descending limb

Question 22

define osmoregulation

Answer 22

control of plasma water potential via negative feedback

Question 23

explain the role of the hypothalamus in osmoregulation

Answer 23

osmosis of water out osmoreceptor in hypothalamus causes them to shrink
triggers hypothalamus to produce more ADH