This is an OCR Gateway A level biology cheat sheet, Chapter 15 module 5. Specification reference: 5.1.1
|
Maintenance of internal environment in constant state despite external changes.
|
|
|
Fluctuations within normal range.
|
|
|
Types of dynamic equilibrium:
|
|
|
Negative feedback
|
Works to reduce change (e.g. body temperature control)..
|
|
Positive feedback
|
Works to increase change (e.g. release of oxytocin in childbirth to increase frequency of contractions).
|
|
Endotherms
|
Rely on metabolic processes to provide heat.
|
|
Ectotherms
|
Rely on surroundings to provide heat.
|
|
Ectotherms:
|
|
|
Behavioural adaptations
|
Move to shade / Sun, press bodies to heated surfaces.
|
|
Physiological adaptations
|
Change colour, alter heart rate.
|
|
Endotherms:
|
|
|
Cooling down
|
Sweating, vasodilation, relaxed erector pili muscles.
|
|
Heating up
|
Vasoconstriction, raising hair/feathers, shivering.
|
|
Carbohydrate metabolism
|
Control blood glucose, amino acid
|
|
Deamination
|
Transamination - Conversion of amino acids into another
Deamination - Removal of amine groups from molecules because body cannot store amino acids and proteins (ornithine cycle). |
|
Detoxification
|
Hydrogen peroxide (+ catalase) --> O2 + H2O
|
|
Liver cells = hepatocytes with adaptations such as large nuclei and golgi, lots of mitochondria.
|
|
|
Blood from hepatic artery and portal vein mix in sinusoids to increase overall O2 content of blood.
|
|
Happens in the glomerulus.
|
|
Blood comes from vein into narrower afferent arteriole which creates high pressures, so blood goes through capillary walls.
|
|
Arterioles surrounded by cells called podocytes with arm-like structures called pedicels.
These create slots to ensure molecules such as platelets that got through the epithelial and basement later do not enter the PCT (proximal convoluted tubule). |
|
In the PCT.
|
|
Glucose, amino acids, vitamins and hormones actively cotransported from filtrate back into blood.
|
|
Adaptations:
|
|
Microvili
|
|
Mitochondria - ATP for active transport.
|
|
In loop of Henle - descending limb
|
|
Top = impermeable to water, lower part = permeable to water.
|
|
Concentration of Na and Cl increases lower down the descending limb.
|
|
Water therefore moves out into capillaries.
|
|
Filtrate is very concentrated.
|
|
- ascending limb
|
|
Permeable to Na and Cl. Actively pumped out to medulla.
|
|
Impermeable to water, so more dilute.
|
|
Permeability varies with ADH.
|
|
Na+ can also actively be pumped out.
|
|
ADH (primary messenger) binds to receptors which trigger cAMP production.
|
|
cAMP triggered realise of aquaporin-containing vesicles.
|
|
Facilitates diffusion of water back into blood i.e. reabsorption of water.
|
No comments yet.
Cheatography n. The art of mapping complex subjects into clear, instantly navigable reference guides.
