2015年5月IB生物SL真题下载-Paper2
1. Diabetes is often associated with the failure of the β (beta) cells in the pancreas, but it is unclear what actually causes this failure. FoxO1 is a protein which acts as a transcription factor to regulate the expression of genes involved in cell growth. FoxO1 also regulates increase in number and differentiation in cells such as pancreatic β cells.
A study was conducted using mice lacking the gene for FoxO1 in β cells (IKO) as well as normal (control) mice. Blood glucose levels after fasting were compared for four groups of mice: young (3 months old) male mice, young (3 months old) female mice, older females (who have had several pregnancies) and aging males (16–20 months).
(a) Compare blood glucose levels after fasting in young control mice and young IKO mice without FoxO1.
(b) (i) Estimate the difference between mean blood glucose levels in control and IKO older female mice.
. . . . . . . . . . . . . . . . . mg ml–1
(ii) Aging and having pregnancies are considered to be physiological stresses. Deduce the effect of stress on blood glucose levels.
(c) Outline the relationship between blood glucose levels after fasting and lack of FoxO1 in the mice studied.
The levels of pancreatic hormones and β cell mass in older female control mice and older female IKO mice lacking FoxO1 were then investigated.
(d) Calculate the percentage difference in β cell mass of the IKO mice compared to the control mice.
(e) State the correlation between lack of FoxO1 and pancreatic hormones in mice.
(f) Referring to the functions of insulin and glucagon, suggest how the differences in hormone levels help to explain the blood glucose levels.
2. Milk contains lactose which some people can digest but some cannot.
(a) State what type of sugar lactose is.
(b) State a function of lactose.
(c) Explain the production of lactose-free milk.
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