(a) the need for communication systems in multicellular organisms
To include the need for animals and plants to respond to changes in the internal and external
environment and to coordinate the activities of different organs.
NOTES
o animals need to respond to changes in the internal and external environment and to
coordinate the activities of different organs,
o this allows for organisms to maintain their internal conditions,
o homeostasis is the maintenance of optimal conditions for enzyme action and cell
function,
o some physiological factors controlled by homeostasis include:
temperature,
blood pH,
glucose concentration in blood,
water potential of blood,
o two communication systems in mammals include the nervous system and the endocrine
system
o plants carry out homeostasis by stomata controlling the diffusion of gases in/out of
leaves,
o good communication system includes:
rapid and specific communication,
enable both short and long-term responses,
enable cells to communicate with each other.
(b) the communication between cells by cell signalling
To include signalling between adjacent cells and signalling between distant cells.
NOTES
o cell signalling allows multicellular organisms to control and coordinate bodies and to
respond to environments,
o cells in nervous system communicate by secreting neurotransmitters which send signals
to adjacent cells,
o hormonal system works by cells releasing hormones which travel in blood and trigger
responses in distant, target cells.
(c) the principles of homeostasis
To include the differences between receptors and effectors, and the differences between
negative feedback and positive feedback.
NOTES
o homeostasis - maintaining a relatively stable internal environment within narrow limits,
even though the environment is changing,
o factors that need to be kept constant include:
core body temperature,
enzymes function best at optimum temp and can denature at high
temps due to tertiary structure changes,
blood pH,
enzymes function best at optimum pH and can denature at extreme pHs
due to tertiary structure changes,
, blood glucose concentration,
glucose used as a respiratory substrate by cells,
water potential of blood (osmoregulation),
changes in W.P of blood may cause cells to shrink/expand via osmosis,
o negative feedback - effector causes a change that brings the environment back to its
normal conditions,
1.receptor detects increase/decrease in level,
2.effectors counteract change back to normal levels.
o positive feedback - situation is amplified until there is a change brought about,
3.in pregnancy, head of fetus pushes against cervix,
4.nerve impulses from cervix transmitted to brain,
5.brain stimulates pituitary gland to secrete oxytocin,
6.oxytocin stimulates contractions and continues pushing fetus towards cervix.
(d) the physiological and behavioural responses involved in temperature control in ectotherms
and endotherms
To include: • endotherms – peripheral temperature receptors, the role of the hypothalamus and
effectors in skin and muscles; behavioural responses • ectotherms – behavioural responses An
opportunity to monitor physiological functions in ectotherms and/or endotherms.
NOTES
o endotherms regulate their own internal temperature,
o organisms need a constant internal temperature for enzyme activity and aerobic
respiration,
o thermoregulatory centre in hypothalamus contains thermoreceptors which monitor
temp of blood,
o vasodilation - more blood flow closer to skin which allows for more heat loss through
radiation,
o shunt vessel narrows and prevents blood flowing away from skin, therefore blood flows
closer to skin,
o vasoconstriction - less blood flow closer to skin which prevents heat loss,
o hair erector muscles contract to trap an insulating layer of air.
b. increase in body temp detected by peripheral temperature receptors in skin,
c. increase in body temp detected by thermoreceptors in thermoregulatory centre in
hypothalamus,
d. neuronal impact:
vasolidation,
relaxation of hair-erector muscles,
sweating.
e. hormonal impact:
decreased production of adrenaline and thyroxine (metabolism) = decreased
heat production,
return to normal temp.
o ectotherms rely on behavioural adaptations to maintain their internal body
temperature,
rest/bask in warm locations to increase body temp,
, seek shade to cool down,
ectotherms can survive longer where food is limited.
(a) the term excretion and its importance in maintaining metabolism and homeostasis
To include reference to the importance of removing metabolic wastes, including carbon dioxide
and nitrogenous waste, from the body.
NOTES
o excretion - removal/processing of waste from the body,
o metabolic waste - waste produced from metabolism (CO2, urea),
o egestion - removal of undigested waste by defecation,
o deamination - removal of ammonia from amino acids,
o secretion - process by which substances are produced/discharged from a
cell/gland/organ for a particular function,
o excretion maintains homeostasis by keeping levels of certain substances in the blood,
o CO2 transported by:
5% in plasma,
10% as carbaminohaemoglobin,
85% as hydrogen carbonate ions,
o CO2 is toxic as hydrogen carbonate ions can reduce ability to transport oxygen,
o also carbaminohaemoglobin has a lower affinity for oxygen than normal,
o can lead to respiratory acidosis which is a drop in blood pH (headache, tremor),
o excess amino acids cannot be stored but they contain lots of energy,
o so liver deaminates = amino acid + oxygen → keto acid + ammonia,
o ammonia is then converted to a less soluble, less toxic compound,
o ammonia + CO2 → urea + water.
(b) (i) the structure and functions of the mammalian liver (ii) the examination and drawing of
stained sections to show the histology of liver tissue
To include the gross structure and histology of the liver AND the roles of the liver in storage of
glycogen, detoxification and the formation of urea (the ornithine cycle covered in outline only).
NOTES
o liver supplied by two different blood supplies,
o hepatic artery brings oxygenated blood from aorta,
o hepatic portal vein delivers deoxygenated blood from digestive tract (toxins and
nutrients),
o blood carried away by the hepatic vein to the vena cava,
o hepatic portal vein has a wider lumen than the hepatic artery,
o sinusoids connect hepatic artery to hepatic portal vein allowing hepatocytes to remove
harmful substances from blood,
o Kupffer cells (macrophages) attached to walls of sinusoids and break down RBCs to
make billrubin,
