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Broken bones are repaired by cells called osteoclasts and osteoblasts.Osteoblasts secrete a hormone called osteocalcin in an inactive form. Osteocalcin is a protein.The active form of osteocalcin binds to a receptor on beta (β) cells in the pancreas, stimulatingthem to release insulin. Osteoblasts have receptors for insulin.The diagram shows how the production of osteocalcin by osteoblasts is controlled by positivefeedback.The secretion of osteocalcin (in an inactive form) by osteoblasts is controlled by positivefeedback.Use information from the diagram to explain why this is positive feedback.
GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABAcauses negatively charged chloride ions to enter postsynaptic neurones.Explain how this inhibits postsynaptic neurones.
Complete achromatopsia is a form of complete colour blindness. It is causedby having only rods and no functional cone cells. People with completeachromatopsia have difficulty in seeing detail. Complete achromatopsia iscaused by an autosomal recessive allele and is usually very rare inpopulations with only one in 40 000 being affected. However on the Pacific 5island of Pingelap ten percent of the population are affected.One form of red-green colour blindness is caused by a sex-linked recessiveallele which affects more men than women. People with this red-greencolour blindness are unable to distinguish between red and green, and alsobetween other colours. They have green-sensitive cones but the 10photoreceptive pigment they contain does not function.Scientists investigated the use of gene therapy to correct red-green colourblindness in monkeys. They injected viruses containing the gene for thegreen-sensitive pigment directly into the eyes of the monkeys. Although themonkeys maintained two years of colour vision, there is debate on whether 15this form of gene therapy is worthwhile. No clinical trials of this procedurehave been carried out on humans. Current research into the treatment ofred-green colour blindness involves the use of induced pluripotent stem cells(iPS cells). The use of iPS cells could have advantages over the use of genetherapy. 20Use the information in the passage and your own knowledge to answer the following questions.3(a) People with complete achromatopsia have difficulty in seeing detail (lines 2-3).Explain why.
Dopamine has a role in numerous processes in the brain including pain relief. The releaseof dopamine can be stimulated by chemicals called endorphins produced in the brain.Endorphins attach to opioid receptors on presynaptic neurones that release dopamine.Morphine is a drug that has a similar structure to endorphins and can provide pain relief.Explain how.
When does Stanley say to Stella that she loved it when he pulled her down off those columns?
When does Blanche reveal the truth about her past and the Tarantula's Arms?
When does Stanley accuse Blanche of lying?
When does Mitch rip the paper lantern off the light and says she tells what ought to be the truth?
Dopamine is a neurotransmitter released in some synapses in the brain. The transmissionof dopamine is similar to that of acetylcholine.Dopamine stimulates the production of nerve impulses in postsynaptic neurones.Describe how.Do not include in your answer the events leading to the release of dopamine and theevents following production of nerve impulses at postsynaptic neurones.
When does Stanley defend that he is not a Polack, but all American?
The mean rate of flow of blood plasma is 60% of the mean rate of blood flow into thekidneys.How much greater is the flow of blood into the kidneys with furosemide than with group C(placebo) over the 4 hours of the investigation? Give your answer in cm3
Furosemide and CVT are drugs used to remove excess fluid from the body. Scientistsinvestigated the effect of these drugs on the volume of urine produced by human volunteers. Thescientists used the following method.• They divided volunteers into three groups, A, B and C at random.• They gave all the volunteers the same food for 3 days.• After 3 days, they gave the volunteers in group A a tablet containing furosemide, thevolunteers in group B a tablet containing CVT and the volunteers in group C a placebo (atablet that did not contain either drug).• They then found the mean volume of urine produced by each group in the 4 hours aftertaking the tablets.Some of the results the scientists obtained are shown in Table 1.A value of ± 2 standard deviations from the mean includes over 95% of the data.All the volunteers were given the same food for 3 days.Suggest and explain one reason why they were given the same food.
When does Blanche tell Stanley that she's going off to Shep Huntleigh?
When is Blanche fully insane, believing Shep Huntleigh's coming for her?
When does Stanley give Blanche a ticket back to Laurel?
When does Mitch come over and try to get with Blanche?
Furosemide is sometimes used to treat high blood pressure.Suggest how furosemide would cause a decrease in blood pressure.
When does Blanche say she's always depended on the kindness of strangers?
When does Blanche spill a drink on her skirt?
When does Stella tell Stanley about Allan?