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Summary CCEA A21 Biology Exam notes
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CCEA A21 exam notes for Biology. Includes, -Succession -Plant coordination and control -Homeostasis -Food chains and Food webs
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Homeostasis.The maintenance of a constant or steady state within the body.
3 basic features of most homeostatic mechanisms:
1. Control system which has a sensor (receptor) - monitors the factor.
2. Corrective mechanism -brings about changes → regulating the factor which has deviated
from normal levels.
3. Negative feedback system- stops corrective mechanism from overcorrecting.
Communication between sensors, monitor and effectors can be hormonal or nervous.
e.g. Temp = nervous blood glucose=hormonal.
Homeostatic control of the mammalian body systems is essential for:
Providing the optimum conditions for enzyme reactions in terms of temp (H-bonds) and pH
(ionic bonds). → denatured enzymes = slower reactions.
Avoid osmotic problems in cells and body fluids.
The kidney (Homeostatic organ) and excretion:
1. Excretion: Removal of toxic waste products of metabolism e.g. urea and creatinine.
2. Osmoregulation: Control of water potential of body fluids (under influence of ADH.) helps
regulate amount of water in the blood by controlling both the volume and concentration of
urine produced.
, Urea- Nitrogen containing compound. Produced in breakdown of excess AA’s and nucleic acids in the
liver.
Creatinine- Waste product breakdown of creatine phosphate in muscles during synthesis of ATP.
Gross structure of the urinary (excretory system.)
Removes metabolic waste products.
Regulates chemical composition of body
fluids. Fluids.
Regulates water content of body fluids.
Regulates pH of body fluids.
Blood travelling through the aorta and renal artery reaches the kidneys at a high pressure
(required for filtration.)
The kidneys act as a complex filter (keeps useful products in the blood + eliminates excretory
products and water.)
Filtered blood leaves the kidney via the renal vein.
Excretory products and excess water pass through the ureter as urine.
Urine taken to the bladder for storage.
Sphincter muscles in base of the bladder control release urine.
Urine leaves the body through the urethra.
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