HomeostasisEdexcel GCSE Biology: Revision notes
Section 1
Why Constant Internal Environment?
Homeostasis maintains constant internal conditions. Thermoregulation keeps enzymes optimal; osmoregulation keeps blood water content stable (prevents cells bursting/shrinking).
Enzymes 'denature', not 'die', from heat.
Section 2
Thermoregulation and the Skin
Hypothalamus monitors/coordinates temperature. Cold: shivering, vasoconstriction. Hot: vasodilation, sweating.
vaso-CONSTRICTion=cold; vaso-DILATion=heat lost.
Section 3
Blood Glucose Control and Diabetes
Insulin lowers glucose (glucose→glycogen). Glucagon raises glucose (glycogen→glucose). Type 1: no insulin, treated with injections. Type 2: insulin resistance, treated with diet/exercise/medication.
Section 4
Body Mass and Type 2 Diabetes
BMI = mass(kg)÷height(m)². Higher BMI/waist:hip ratio correlates with type 2 diabetes risk.
84kg, 1.75m: BMI=84÷3.0625=27.4 (overweight).
Section 5
Urinary System and Nephron
Kidneys filter blood via nephrons: filtration at glomerulus/Bowman's capsule; selective reabsorption of all glucose; variable water reabsorption. Urea from liver deamination excreted in urine.
Protein/blood cells are NOT in normal filtrate/urine.
Section 6
ADH and Osmoregulation
ADH increases collecting duct permeability, increasing water reabsorption (concentrated urine) when blood too concentrated; less ADH = dilute urine.
More ADH=more reabsorption=concentrated urine.
Section 7
Kidney Failure Treatment
Dialysis: blood filtered via partially permeable membrane, repeated regularly. Organ donation: transplant, needs immunosuppressants.
Must Know
- Homeostasis keeps enzymes/cells functioning via thermoregulation/osmoregulation.
- Insulin lowers glucose; glucagon raises it. Type 1=no insulin; Type 2=resistance.
- BMI=mass÷height²; nephron filters at glomerulus, reabsorbs glucose/water.
- ADH controls collecting duct permeability. Dialysis/transplant treat kidney failure.
That's the notes covered.
Carry on to the next subtopic.