Summary BIOLOGY IB HIGHER LEVEL LEARNING OUTCOMES TOPICS 6.6 THROUGH TO TOPIC 11 AND HL UNITS FOR OPTION D
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Module
INTERNATIONAL BACCHALEURETTE
Institution
INTERNATIONAL BACCHALEURETTE
BIOLOGY IB HIGHER LEVEL LEARNING OUTCOMES TOPICS 6.6 THROUGH TO TOPIC 11 AND HL UNITS FOR OPTION D
TOPICS 6.6 to topic 11 and units for option D specifically for HL
Topic 7: Nucleic Acids and Proteins · Topic 8: Cell Respiration and Photosynthesis · Topic 9: Plant Science · Topic 10: Gene...
BIOLOGY IB HIGHER LEVEL LEARNING OUTCOMES TOPICS 6.6 THROUGH TO TOPIC 11 AND
HL UNITS FOR OPTION D
TOPIC 6 (HL)
6.6
Explain the control of blood glucose concentration, including the roles of glucagon, insulin
and the alpha and beta cells in the pancreatic islets.
If the glucose concentration deviates substantially from the set point of about 5 mmol L1,
homeostatic mechanisms mediated by the pancreatic hormones insulin and glucagon are
initiated.
There are small regions of endocrine tissue called islets of Langerhans dotted through the
pancreas that secrete hormones directly into the blood stream. The two cell types in the
islets of Langerhans secrete different hormones.
Alpha cells synthesize and secrete glucagon if the blood glucose level falls below the set
point. This hormone stimulates breakdown of glycogen into glucose in liver cells and its
release into the blood, increasing the concentration.
Beta cells synthesize insulin and secrete it when the blood glucose concentration rises above
the set point. This hormone stimulates uptake of glucose by various tissues, particularly
skeletal, muscle and liver, in which it also stimulates the conversion of glucose to glycogen.
Insulin therefore reduces blood glucose concentration. Like most hormones, insulin is
broken down by the cells its acts upon, so its secretion must be ongoing. Secretion begins
within minutes of eating and may continue for several hours after a meal.
Describe the structure and function of thyroxin.
Structure: chemical structure is unusual because the thyroxin molecules contains four atoms
of iodine
Function: regulates the body's metabolic rate
Outline thyroxin's role in body temperature regulation.
Thyroxin regulates the body's metabolic rate. Higher metabolic rate supports more protein
synthesis and growth and it increases the generation of body heat. In a person with normal
physiology, cooling triggers increased thyroxin secretion by the thyroid gland, which
stimulates heat production as body temperature rises.
List symptoms of thyroxin deficiency.
Lack of energy and feeling tired all the time
Forgetfulness and depression
Weight gain despite loss of appetite as less glucose and fat are being broken down to
release energy be cell respiration
Feeling cold all the time because less heat is being generated
Constipation because contractions of muscle in the wall of the gut slow down
Impaired brain development in children Leptin is a protein hormone
,State that leptin is a protein hormone.
Leptin is a protein hormone secreted by adipose cells (fat storage cells).
Outline the mechanism of action of leptin.
The concentration of leptin in the blood is controlled by food intake and the amount of
adipose tissue in the body. The target of leptin is groups of cells in the hypothalamus of the
brain which contribute to the control of appetite. Leptin binds to receptors in the membrane
of these cells. If adipose tis sue increases, blood leptin concentrations rise, causing longterm
appetite inhibition and reduced food intake.
Describe the role and discovery of the ob allele in obese mice.
Breeding experiments showed that obese mice had two copies of a recessive allel, ob. In the
early 1990s it was shown that the wildtype allele of this gene supported the synthesis of
a new hormone that was named leptin. Adi pose cells in mice that have two recessive ob
alleles cannot produce leptin. When ob/ob mice were injected with leptin their appetite
declined, energy expenditure increased and body mass dropped by 30% in a month.
Define circadian rhythm
The rhythms in behaviour which fit the 24hour cycle that humans are adapted to live in
Describe the secretion and action of melatonin.
Cells in the hypothalamus called the suprachi asmatic nuceli (SCN) control the secretion of
the hormone melatonin by the pineal gland. Melatonin secretion in creases in the evening
and drops to a low level at dawn as the hormone is rapidly removed from the blood by the
liver, blood concentrations rise and fall rapidly in response to these changes in secretion.
The most obvious effect of melatonin is the sleepwake cycle. High melatonin levels cause
feelings of drowsiness and promote sleep throughout the night. Falling melatonin levels
encourage waking at the end of the night.
Outline the mechanism that regulates melatonin secretion in response to the day / night
cycle.
Experiments have shown that melatonin contributes to the nighttime drop in core body
temperature, as blocking the rise in melatonin levels reduces it and giving melatonin
artificially during the day causes a drop in core temperature. Melatonin receptors have been
discovered in the kidney, suggesting that decreased urine production at night may be
another effect of this hormone.
Describe the mechanism by which the SRY gene regulates embryonic gonad development.
A special type of ganglion cell in the retina of the eye detects light of wavelength 460480 nm
and passes impulses to cells in the SCN. This indicates to the SCN the timing of dusk and
dawn and allows it to adjust melatonin secretion so that it corresponds to the day/night
cycle.
Outline role of testosterone in prenatal development of male genitalia.
If the gene SRY is present, the embryonic gonads develop into testes. This gene is located on
the Y chromosome, so is only present in 50% of embryos.
,SRY codes for a DNA binding protein called TDF (testis determining factor). TDF stimulates
the expression of other genes that cause testis development. 50% of embryos have two X
chro mosomes and no Y so they do not have a copy of the SRY gene. TDF is therefore not
produced and the embryonic glands develop as ovaries.
State testosterone's role in stimulating the prima ry sexual characteristic of males.
The testes develop testosterone secreting cells at an early stage and these produce
testosterone until about the 15th week of pregnancy. During the weeks of secretion,
testosterone causes male genitalia to develop.
List secondary sexual characteristics triggered by testosterone at puberty.
At puberty the secretion of testosterone increases. This stimulates sperm production in the
testes, which is the primary sexual characteristic of males. Testosterone also causes the
development of secondary sexual characteristics during puber ty such as enlargement of the
penis, growth of public hair and deepening of the voice due to growth of the larynx.
State the sources of estrogen and progesterone used in embryonic development.
At first estrogen and progesterone are secreted by the mother's ovaries and later by the
placenta.
Describe prenatal development of female reproductive organs.
In the absence of fetal testosterone and the presence of maternal estrogen and
progesterone, female reproductive organs develop. Ovaries develop from the embryonic
gonads due to estrogen and progesterone as well as there being no testosterone.
List secondary sexual characteristics triggered by estrogen and progesterone at puberty.
Enlargement of the breasts and growth of public and underarm hair.
Outline events occurring during the follicular and luteal phases of the menstrual cycle.
Follicular phase:
A group of follicles develops in the ovary. In each follicle an egg is stimulated to grow. At the
same time the lining of the uterus (endometri um) is repaired and starts to thicken. The
most developed follicle breaks open, releasing its egg into the oviduct. The other follicles
degenerate. Luteal phase:
The wall of the follicle that released an egg be comes a body called the corpus luteum.
Continued development of the endometrium prepares it for the implantation of an embryo.
If fertilization does not occur the corpus luteum in the ovary breaks down. The thickening of
the endometri um in the uterus also breaks down and is shed during menstruation.
State the source and lo cation of action of hormones in the menstrual cycle, including FSH
(follicle stimulating hormone), LH (luteinising hormone), estrogen and progesterone.
Outline the role of hormones in the menstrual cycle, including FSH (follicle stimulating
hormone), LH (luteinising hormone), estrogen and progesterone.
FSH and LH protein hormones produced by the pituitary gland bind to FSH and LH receptors
in the membranes of follicle cells.
, Estrogen and progesterone are ovarian hormones, produced by the wall of the follicle and
corpus luteum. They are absorbed by many cells in the female body (where they influence
gene expression and therefore development)
FSH: (rises to a peak towards the end of the menstrual cycle and) stimulates the
development of follicles (each containing an oocyte and follicular fluid) FSH also stimulates
secretion of estrogen by the follicle wall.
LH: (rises to a sudden and sharp peak towards the end of the follicular phase.) It stimulates
the completion of meiosis in the ooctye and partial digestion of the follicle wall allowing it to
burst open at ovulation. LH also promotes the development of the wall of the follicle after
ovulation into the corpus luteum which secretes estrogen and progesterone.
Estrogen: (rises to a peak towards the end of the follicular phases) It stimulates the repair
and thickening of the endometrium after menstruation and an increase in FSH receptors
that make the follicles more receptive to FSH, boosting estrogen production. When it
reaches high levels estrogen inhibits the secretion of FSH and stimulates LH secretion
Distinguish between causes of type I and type II diabetes.
Type I diabetes arises when beta cells are destroyed leading to insulin production stopping.
Type 2 diabetes is related to obesity and a poor diet. Type 2 diabetes is characterised by an
inability to process and respond to insulin because of a deficiency of insulin receptors or
glucose transporters on target cells.
Distinguish between treatment of type I and type II diabetes.
Type I diabetes is treated by testing the blood glucose concentration regularly and injecting
insulin when it is too high or likely to become too high. Injections are often done before a
meal to prevent a peak of blood glucose as the food is digested and absorbed. Type II
diabetes is treated by adjusting the diet to reduce the peaks and troughs of blood glucose.
Small amounts of food should be eaten frequently rather than infrequent large meals. Foods
with high sugar content should be avoided. Starchy food should only be eaten if it has a low
glycemic index, indicating that it is digested slowly. High fibre foods should be included to
slow the digestion of other foods. Strenuous exercise and weight loss are beneficial as they
improve insulin uptake and action.
Explain the double blind study that tested the effect of leptin treatment on hu man
obesity.
Seventy three obese volunteers injected them selves either with one of several leptin doses
or with a placebo. A double blind procedure was used, so neither the researchers nor the
volunteers knew who was injecting leptin until the results were analysed. The leptin
injections induced skin irritation and swelling and only 47 patients completed the trial. The
eight patients receiving the highest dose lost 7.1 kg of body mass on average compared with
a loss of 1.3 kg in the 12 volunteers who were injecting the placebo. However, in the group
receiving the highest dose the results varied very widely from a loss of 15 kg to a gain of 5
kg. Also any body mass lost during the trial was usually regained rapidly afterwards.
Outline role of leptin resis tance in human obesity.
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