OCR GCSE Biology A B3.3 Maintaining Internal Environments Exam Questions

About OCR GCSE Biology A B3.3 Maintaining Internal Environments

B3.3 is about homeostasis: keeping conditions inside the body within narrow limits so cells and enzymes work properly. On the OCR Gateway Biology A course it completes Topic B3 Organism level systems, assessed in Paper 1 (Foundation) or Paper 3 (Higher). You study temperature control, blood glucose regulation and diabetes, and water balance by the kidneys. It draws on osmosis from B2.1, enzymes from B1.2 and hormones from B3.2. Examiners like extended answers on thermoregulation, the roles of insulin and glucagon, comparisons of type 1 and type 2 diabetes, and the structure and function of the nephron, including ADH for Higher.

What you need to know

• Homeostasis Homeostasis is the maintenance of a constant internal environment. It relies on receptors, a coordination centre and effectors working by negative feedback.
• Thermoregulation The thermoregulatory centre in the brain monitors blood temperature. When too hot, sweating increases and vasodilation of skin blood vessels increases heat loss; when too cold, shivering, hair erection and vasoconstriction reduce heat loss and increase heat production.
• Blood glucose control When blood glucose rises, the pancreas releases insulin, which causes liver and muscle cells to take up glucose and store it as glycogen. When blood glucose falls, the pancreas releases glucagon, which causes glycogen to be converted back into glucose.
• Diabetes In type 1 diabetes the pancreas does not produce enough insulin, so it is treated with insulin injections. In type 2 diabetes body cells stop responding to insulin; it is linked to obesity and treated with diet, exercise and sometimes medication.
• The kidney and nephron Kidneys filter the blood under high pressure in the glomerulus (ultrafiltration). Useful substances such as all glucose and some ions and water are selectively reabsorbed, and urea, excess ions and excess water leave in urine.
• ADH and kidney failure When blood is too concentrated, the pituitary releases more ADH, which makes the collecting ducts more permeable so more water is reabsorbed (Higher). Kidney failure is treated by dialysis or a kidney transplant.

Common mistakes in B3.3 Maintaining Internal Environments

• Saying blood vessels move closer to the skin surface in vasodilation. Arterioles supplying the skin capillaries widen so more blood flows near the surface; the vessels do not move.
• Confusing glucagon with glycogen. Glucagon is a hormone; glycogen is the storage carbohydrate in the liver and muscles.
• Stating that type 2 diabetes means no insulin is made. In type 2 the body cells no longer respond properly to insulin.
• Writing that glucose is filtered out and lost in urine in a healthy person. All glucose is filtered but then reabsorbed.
• Saying ADH makes more urine. More ADH means more water is reabsorbed, so a smaller volume of concentrated urine is produced.

Try three B3.3 Maintaining Internal Environments exam-style questions