6.6 Hormones, Homeostasis & Reproduction

The graph below shows blood leptin concentration and body fat percentage in adult humans.

Calculate the percentage increase in blood leptin concentration when body fat percentage increases from 20 % to 60 %.

[2]

Research carried out in mice has shown that high levels of leptin can induce weight loss in mice with a high body fat percentage.

State how high levels of leptin can lead to weight loss in mice.

[1]

Suggest why humans with a high body fat percentage might continue to gain weight despite the results shown in part a) above and the evidence collected from research with mice.

[2]

Levels of the hormone leptin were recorded, along with levels of some reproductive hormones, in a group of 250 regularly menstruating, healthy women. The average results over one menstrual cycle are shown below.

One conclusion from the results of the study was that leptin could be involved with the process of ovulation.

Evaluate this conclusion.

Suggest, with a reason, one other possible conclusion that could be drawn about the role of leptin in reproduction from the results in part c).

A group of scientists studied the effect of exposure to bright bathroom lights late in the evening on melatonin levels. Subjects attended a sleep clinic where they were allocated to three different light exposure groups; dim light, bright yellow light, and bright blue light.

Over the course of a week, all of the subjects spent most of each evening carrying out normal activities under dim light, before each group was exposed to a 30 minute period of either continuing dim light, bright yellow light, or bright blue light between 10:30 and 11 pm to simulate exposure to bathroom light.

The saliva melatonin levels of all groups were measured at 30 minute intervals throughout the evening and an average is taken for each light condition. The results are shown below.

Describe the effect of the 30-minute period of light exposure on melatonin levels.

A student was changing the light bulb in their bathroom and concluded, after reading the data in part a), that the best bulb type for improving their sleep would be a bright, yellow bulb.

Evaluate the student's conclusion using information from part a).

One of the roles of melatonin is to bind to cell membrane receptors on pancreas cells and slow down the secretion of insulin.

[2]

Suggest a benefit of the effect described in part i) during the period at which melatonin levels are high.

[1]

A mutation known as the G allele has been identified in some individuals. The G allele is thought to increase the sensitivity of cells to melatonin. Individuals who regularly undertake shift work at night and who also have the G allele are thought to be at particularly high risk of diabetes.

Use the information provided in parts c) and d) to suggest why individuals with the G allele who regularly work night shifts are thought to be at greater risk of type 2 diabetes.

The image below shows some of the gene pathways that could be involved with sex determination in mammals. Note that 'switching on' a gene refers to activation, while 'switching off' refers to inhibition, e.g. the diagram shows that the gene WT1 activates expression of the gene SOX9.

Including information in the image above, outline the role of SRY in determining biological sex.

Suggest, with a reason, a possible outcome resulting from mutations in the following genes shown in part a).

SF1

[2]

FOXL2

[2]

Biological sex in some species of reptile is determined by the temperature at which the reptile eggs are incubated during a thermosensitive period of development. There has been some suggestion among scientists that the enzyme aromatase may be involved in temperature-related sex determination in these reptiles.

A possible example of this is in sea turtles. The graphs below show the effect of developmental temperature on sea turtle sex (top) and on the activity of the enzyme aromatase (bottom).

Use information provided here and in part a) to suggest how aromatase activity may determine sex in sea turtles.

Suggest, with a reason, how the current global warming trends may impact populations of the sea turtles described in part c).

One mark is available for clarity of communication throughout this question.

Draw a labelled diagram of the male reproductive system.

Describe the role of hormones in the regulation of the menstrual cycle.

The diagram shows the female reproductive system in front view

Identify structures 1 and 2.

State the function of structure 3 from part (a).

Outline the role of the SRY gene in the development of female embryonic reproductive organs

Ethinylestradiol is a synthetic form of the naturally occurring female hormone oestrogen. A group of scientists found that exposing fish eggs in the lab to ethinylestradiol resulted in fewer male offspring compared to control fish.

The scientists then exposed the fish and their eggs to water from different sources and found that the eggs exposed to river water had similar results to those exposed to ethinylestradiol.

The table gives information on the amount of oestrogen found in different sources of water.

Use your knowledge of hormones and the data provided to suggest an explanation for the scientists' results.

The graph below shows data collected on mice exposed to the hormone leptin. One group of mice were treated with leptin injections. The control mice received no leptin. Both groups of mice were fed the same diet over an eight week period.

Describe the results shown in the graph above.

Explain the results shown in part (a).

Another hormone is thyroxine, released from the thyroid gland. Thyroxine contains iodine as part of its chemical structure. 

Suggest, with a reason, two effects that iodine deficiency may have on the human body.

In vitro fertilisation, known as IVF, involves fertilisation of a female egg outside of the human body. The hormones FSH and LH are used in IVF.

State the functions of FSH and LH in IVF.

A fertility clinic investigated the effect of body mass index (BMI) on the outcome of the percentage of women who had successful implantation, became and remained pregnant, and were able to take home a healthy baby following IVF treatment.

Their results are shown in the graph below.

The clinic advised women with a BMI greater than 30kg/m² to lose weight before embarking on IVF treatment.

Use the data to explain why.

State what is meant by the term superovulation.

William Harvey conducted observational research on sexual reproduction in deer in the 1600s. 

State what Harvey was and was not able to observe in the deer.

One mark is available for clarity of communication throughout this question.

Outline the events that occur, including the hormones involved, during days 14-28 of the menstrual cycle in the absence of fertilisation.

The hormone oestrogen is involved in both positive and negative feedback loops within the menstrual cycle.

Explain how oestrogen functions in both positive and negative feedback within the menstrual cycle.

Describe the role of the pancreas and associated hormones in the control of blood glucose concentration.