1
Q
Explain why digestion of large food molecules is essential. (2)
A
- Food needs to be broken down and reassembled as may not be suitable originally.
- Large food molecules need to be broken down into smaller ones in order for absorption to occur
2
Q
Explain the need for enzymes in digestion. (3)
A
- Enzymes break down large food molecules into smaller ones.
- As biological catalysts, they speed up the process of digestion by lowering the activation energy for the reaction.
- Work at body temperature.
3
Q
Outline the function of the mouth (3)
A
- Chewing (mechanical digestion)
- Saliva from the saliva glands moistens food to make a bolus for swallowing
- Amylase begins chemical digestion of starch (polysaccharide digestion)
4
Q
Outline the function of the Oesophagus (1)
A
- A wave of muscles contractions (peristalsis) pushes the bolus into the stomach
acids
5
Q
Outline the function of the stomach (3)
A
- Muscular contractions continue mechanical digestion
- HCL Acids kills bacteria and provides optimum pH for pepsin
- Pepsin begins digestion of proteins
6
Q
Outline the function of the small intestine (4)
A
Duodenum
1. Bile from the liver and gall bladder neutralizes acid and emulsifies fats
2. Pancreatic amylase and lipase digest carbohydrates and fats ( enzymes from pancreas and intestinal walls)
3. Trypsin digests polypeptides to amino
Ileum
4. Lower half of small intestine absorbs nutrients into the blood, via the villi
7
Q
Outline the function of the large intestine (2)
A
- Water is absorbed and returned to the blood, leaving semi-solid faeces. This is stored in the rectum
- Egestion - faeces (containing undigested food, dead cells and other waste) is forced out of the anus
8
Q
What is mechanical digestion? (2)
A
Food is physically broken down into smaller fragments via:
- Chewing (teeth->tongue->bolus->oesophagus)
- Churning (Stomach->chime->duodenum)
- Segmentation (contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestine)
9
Q
What is chemical digestion? (3)
A
Food is chemically broken down by chemical agents such as:
- Stomach Acids (gastric glands->digestive acids -> mucous membrane->pancreas->alkaline compounds)
- Bile (liver->gall bladder->intestine->emulsifies lipids)
- Enzymes (pancreas->amylase->protease->lipase)
10
Q
Definition of digestion
A
Breaking down of complex molecules into simpler molecules to transport around the blood stream
11
Q
What the anatomy of the digestive system consist of? (2)
A
- The alimentary canal consists of organs which food passes through (oesophagus, stomach, small/large intestine)
- The accessory organs aid in digestion but do not actually transfer food (salivary glands, pancreas, liver, gall bladder)
12
Q
Definition of peristalsis and its importance (3)
A
Muscular contractions (both around and down the alimentary canal) that moves food through the digestive tract
- Contraction of smooth muscles behind the bolus forces it forward
- Waves of muscle contractions move bolus towards the stomach
- This is important because food travels in one direction only. This ensures that it only moves forward. Also in the intestine it enables the chyme to mix and churn with enzymes.
13
Q
Describe the structure of the small intestine
A
The small intestine contains four distinct tissue layers from the lumen
1. Mucosa: Inner lining, includes villi
2. Submucosa: Connective tissue (between the mucosa and muscle)
3. Muscular layer: Inner circular and outer longitudinal muscle perform peristalsis
4. Serosa: Protective outer layer
It also contains the inner epithelial cell and villi
14
Q
Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion (8)
A
- Many villi increase the surface area for absorption.
- Epithelium is only one cell layer thick and so food is quickly absorbed.
- Microvilli on the villi increase the surface area for absorption further.
- Protein channels and pumps are present in the microvilli for rapid absorption.
- The mitochondria in the epithelium provide ATP needed for active transport.
- Blood capillaries are very close to the epithelium so diffusion distance is small.
- The lacteal takes away fats after absorption.
- Rich blood supply maintain concentration gradients between lumen and the blood
15
Q
What is the difference between absorption and assimilation? (2)
A
- Absorption refers to the uptake of broken down molecules into the blood (e.g function of the small intestine).
- Assimilation occurs when the food molecules becomes part of the bodies tissue and are used.
16
Q
Give an example for every transport mechanism in the digestive system (5)
A
- Simple diffusion - Fatty acids passing through the plasma membrane into the epithelial cells
- Facilitated Diffusion - When the concentration of glucose is higher in the lumen than in the epithelial cells
- Membrane Protein Pumps - When the concentration in the lumen is lower than in the epithelial cells but the cells need more glucose
- Endocytosis - Larger molecules that haven’t been fully digested
- Osmosis - The absorption of water and dissolved molecules occurs in both the small and large intestine
17
Q
Describe the process of starch digestion (4)
A
- Begins in the mouth with salivary amylase.
- Yet this doesn’t completely breakdown the starch because the enzyme is destroyed by the acidic environment of the stomach
- The pancreases then secretes pancreatic amylase into the small intestine which finishes breaking down the starch into maltose (a disaccharide)
- Within the small intestine, there is another enzyme (maltase) that finishes breaking down maltose into 2 glucoses
18
Q
What is the structure and function of arteries? (4)
A
Arteries carries high pressure blood away from the heart and to the rest of the body
They have:
1. Thick outer layer of longitudinal collagen and elastic fibres to prevent leaks and bulges and keep blooding flowing. Also allows expansion and contraction
2. Thick wall of collagen to withstands high pressure and prevent rupture
3. Thick layers of circular elastic fibres and muscle fibres to pump blood.
4. Narrow lumen to maintain high pressure.
19
Q
What is the structure and function of veins? (3)
A
Veins carries low pressure blood back to the heart using valves to ensure blood flows in the correct direction
They have:
1. A very wide lumen (relative to wall thickness) to maximize blood flow for more effective return
2. A thin wall containing less muscle and elastic fibres as blood is at low pressure
3. Valves to ensure blood only flows one way to prevent back-flow of the blood and therefore ensures that blood moves towards the heart
20
Q
What is the structure and function of capillaries? (3)
A
Capillaries exchange materials between cells in tissues and blood while travelling at low pressure
They have:
1. Blood slowly moves through them under low pressure providing opportunities for exchange of substances
2. Very small diameter (~5 μm) which allows the passage of only a single red blood cell at a time (optimal exchange)
3. Outer wall is only 1 cell thick which allows for easy diffusion of substances in and out of the capillary. Due to this distance many capillaries contain pores to aid in the transport of materials between tissue fluid and blood
21
Q
Outline the structure of the heart (3)
A
1. Chambers Two atria (receives blood) Two ventricles (pumps blood) 2. Heart valves Atrioventricular valves Semilunar valves 3. Blood Vessels Pulmonary artery:Sends blood to heart, low O2 concentration, Pulmonary vein: Sends blood away from heart, high O2 concentration Vena cava Aorta
22
Q
What are the structural and function differences between
the atria and the ventricles?
A
- The atrium is a chamber in where blood enters the heart, the ventricle is a chamber where blood is pushed out of the heart
- The walls of the ventricle are thicker than the atria because:
o They have to pump blood all the way from the heart to the whole body
o A strong muscle contraction is needed to produce enough pressure to carry the blood the whole way
o The right ventricle only has to pump to the lungs, which is closer, and the left ventricle has to pump all the way to the rest of the body
23
Q
Outline the stages occurring within the heart? (6)
A
- Atria collect blood from veins.
- Atria contract, atrioventricular valves open.
- Blood is pumped into ventricles.
- Ventricle contracts, atrioventricular valves close and semilunar valves open.
- Blood is pumped into arteries, semilunar valves close.
- Cycle repeats.
24
Q
What is the definition of diastole?
A
When a chamber is relaxed, it causes a decrease in pressure and allows blood to fill the chamber
25
What is the definition of systole?
When a chamber contracts, it causes an increase in pressure and forces blood out of the chamber through any available opening
26
What is a cardiac cycle? (2)
1. A cardiac cycle is a series of events from the beginning of one heart beat to the beginning of the next, commonly referred to as one heartbeat. This includes atrial and ventricular contractions (average of 72 cardiac cycles per minute, 1 every 0.8 seconds)
2. It is comprised of a period of contraction (systole) and relaxation (diastole)
27
Outline the control of the heartbeat (5)
1. Heart muscle can contract by itself (myogenic muscle contraction = spontaneous, independent of nervous system)
2. Pacemaker initiates contractions.
3. The medulla oblongata senses the increase CO2 levels due to respiration
3. One nerve carries messages from the medulla to SA node/pacemaker to speed up the beating of the heart.
4. One nerve carries messages from the brain to the pacemaker to slow down the beating of the heart.
5. Adrenaline signals the pacemaker to increase the beating of the heart.
28
What was the significance of William Harvey's discovery? (2)
1. People use to think that blood was produced by the heart and was slowly used up by tissues in the body (Therefore doctors would use leeches to suck out the diseased blood)
2. William discovered that the blood is circulated and recirculated through the body (not used up) and that the heart is a double pump.
29
What is blood composed of?
Blood is composed of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes) and platelets while nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat are all transported by the blood.
30
What is atherosclerosis? (3)
1. Atherosclerosis is the hardening and narrowing of the arteries. This happens due to the build up of cholesterol in damaged areas which forms a plaque
2. As build-ups of cholesterol and plaque form, the lumen narrows, restricting blood flow. If plaque ruptures, blood clotting is triggered. Blood clots are known as coronary thrombosis
3. Therefore, if atherosclerosis can lead to blood clots, and if these clots occur in myocardial tissue, it is called coronary heart disease. Coronary muscle tissue dies as a result of a lack of blood and oxygen
31
What are the risk factors of atherosclerosis?
| A.G.O.D.D.E.S.S.S
Age: Blood vessels become less flexible with advancing age
Genetics: Having hypertension predispose individuals
Obesity: Increasing in blood pressure/Leads to plaque formation in arteries
Diet: Increases fat/cholesterol/LDL in blood/leads to plaque formation in arteries
Diseases – Certain diseases increase the risk of CHD (e.g. diabetes)
Exercise: Lack of exercise increases risk que to weakened circulation
Sex – Males are at a greater risk due to lower oestrogen levels
Smoking – Nicotine causes vasoconstriction, raising blood pressure
Stress: Stress has been linked to increased cortisol hormones in the blood, causing increased atherosclerosis
32
What is the definition of a virus?
Any living organism or virus capable of causing a disease
33
Explain why antibiotics are effective against bacteria but no viruses (4)
1. Antibiotics block specific metabolic pathways in bacteria.
2. Bacteria are very different to human cells so human cells are not affected.
3. Viruses require host cell to carry metabolic processes for them and so antibiotics cannot be used to treat viruses.
4. Harming the virus would harm the human cells.
34
Outline the role of skin and mucous membranes as the primary defence against pathogens. (5)
Skin
1. The skin is made of several layers. The top layer is mostly dead cells so dry, thick and tough, which provides a good barrier
2. The skin also secretes lactic acid and fatty acids to lower the pH (5.6 – 6.4 depending on region)
Mucous membranes
1. Mucous contains lysozyme enzymes.
2. Mucous can be sticky and trap pathogens
3. Can release fluids to wash away pathogens (mucus, saliva, tears)
35
Explain the importance of blood clotting (5)
Blood clots prevents pathogens from entering the blood stream:
1. Blood vessel is ruptured /damaged
2. Damaged blood vessel cells release chemicals that cause platelets to undergo a structural change and stick to the damaged area
3. The damaged tissue released chemicals called clotting factors that convert prothrombin into thrombin
4. Thrombin acts as an enzyme to convert fibrinogen from being soluble (dissolved in the plasma) to its insoluble form called fibrin
5. Fibrin forms a mesh that traps cellular debris and forms a clot
36
Describe the process of phagocytosis (4)
Phagocytes/macrophages circulate in the blood and move into the body tissue in response to infection
1. The macrophage reads the protein on the outside of the pathogen and recognize that the pathogen isn’t suppose to be there
2. The macrophage then engulfs the pathogen via phagocytosis
3. The many enzymes found in the lysosomes of the macrophage destroy the pathogen
4. This is a non-specific response.
37
What is the difference between antibodies and antigens? (3)
1. Antibodies are proteins that defend the body against pathogens by binding to antigens on the surface of these pathogens and stimulating their destruction.
2. Antigens are foreign substances which stimulate the production of antibodies.
4. Antibodies usually only bind to one specific antigen.
38
Explain the process of antibody production (7)
1. Each B lymphocyte makes one type of antibody.
2. Antibodies are found on the surface of the lymphocyte.
3. Pathogen have antigens on their surface.
4. The antigens bind to the antibodies.
5. Lymphocyte becomes active (via helper T lymphocytes) and makes clones of itself, to produce more antibodies
6. Antibodies will target their specific antigen, enhancing the capacity of the immune system to recognise and destroy the pathogen
7. A small proportion of activated B cell (and activated TH cell) will develop into memory cells to provide long-lasting immunity
39
Outline the effects of HIV on the immune system and how it is transmitted (3)
1. Reduction in the number of active lymphocytes
2. Loss of the ability to produce antibodies, leading to the development of AIDS.
3. HIV is transmitted through the exchange of body fluids e.g. sexual intercourse or hypodermic needles
40
What was the significance of Florey and Chain's work? (3)
1. Florey tested penicillin on infected mice
2. Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
3. The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential
41
Describe physiological respiration? (3)
It consists of three distinct process:
1. Ventilation: the exchange of air between the atmosphere and the lungs – achieved by the physical act of breathing. (Fresh air in, stale air out)
2. Gas Exchange: The exchange of oxygen and carbon dioxide between the alveoli and bloodstream (via passive diffusion)
3. Cell Respiration: The release of energy (ATP) from organic molecules – it is enhanced by the presence of oxygen (aerobic)
42
Explain the need for a ventilation system (4)
1. To maintain the concentration gradients of oxygen and carbon dioxide in the alveoli
2. The body needs oxygen to make ATP via cell respiration.
3. The body needs to get rid of carbon dioxide which is a product of cell respiration.
4. Oxygen needs to diffuse from the alveoli into the blood. Carbon dioxide needs to diffuse from the blood into the alveoli. Requires an appropriate concentration gradient. (High 02 low CO2)
43
Describe the structure of the lungs (5)
1. Air enters the respiratory system through the nose or mouth and passes through the pharynx to the trachea
2. The air travels down the trachea until it divides into two bronchi (singular: bronchus) which connect to the lungs
3. The right lung is composed of three lobes, while the left lung is only comprised of two (smaller due to position of heart)
4. Inside each lung, the bronchi divide into many smaller airways called bronchioles, greatly increasing surface area
5. Each bronchiole terminates with a cluster of air sacs called alveoli, where gas exchange with the bloodstream occurs
44
Describe the features of alveoli that adapt them to gas exchange.
1. Great numbers increase the surface area for gas exchange.
2. Wall made up of single layer of cells and so are the walls of the capillaries so diffusion distance is small allowing rapid gas exchange.
3. Covered by a dense network of capillaries which have low oxygen and high carbon dioxide concentrations. This allows oxygen to diffuse into the blood and carbon dioxide to diffuse out of the blood.
4. Some cells in the walls secret fluid allowing gases to dissolve. Fluid also prevents the sides of alveoli from sticking together.
45
Outline the two types of pneumocytes
Type 1 Pheumocytes - thin and flat - Makes up the alveolus wall, easy for diffusion
Type II Pheumocytes - cube shaped - Produces a surfactant that keeps the alveoli moist and prevents them from sticking together (reduces surface tension)
46
Outline the mechanism within inhalation
1. Diaphragm and exterior intercostal contract
2. Abdominals and interior intercostal relax
3. Volume of the chest cavity increases
4. The increase in volume causes a decrease in air pressure
5. Air moves through the trachea into the lungs to fill the alveoli
47
Outline the mechanism within exhalation
1. The diaphragm and exterior intercostal relax
2. The abdominals and interior intercostal contract
3. The volume of the chest cavity decreases
4. The decreases in volume causes an increase in air pressure
5. Air is forced out of lungs through the trachea
48
Describe two lung related diseases
Emphysema: A disease in which the alveoli of the lungs are gradually damaged (lung tissue develops holes, destroying entire alveolar sacs)
Symptoms: Shortness of breath; persistent coughing
Causes of emphysema: Smoking, chemical fumes, coal dust, air pollution
Lung cancer: The spreading of tumours that originate in the lung tissue
Potential Causes: Smoking, asbestos exposure
49
What is the nervous system?
The nervous system includes both the central nervous system (CNS) and the peripheral nervous system (PNS)
• The CNS is made up of the brain and spinal chord
• The PNS is made up of the somatic and automatic nervous systems
50
What are the functions of neurons?
1. Neurons are specialized cells that function to transmit electrical impulses within the nervous system
2. There are three classes of neurons: sensory, motor and interneurons. All these neurons have the following functions:
o Receive signals (or information)
o Integrate incoming signals (to determine whether or not the information should be passed along)
o Communicate signals to target cells (other neurons or muscles or glands)
51
What is the structure of a neuron?
Soma (Cell Body) – A cell body containing the nucleus and organelles, where essential metabolic processes occur to maintain cell survival
Dendrites – Short branched fibers that convert chemical information from other neurons or receptor cells into electrical signals. Dendrites bring information to the cell body
Axon – An elongated fiber that transmits electrical signals to terminal regions for communication with other neurons or effectors. Axons take information away from the cell body
Synaptic terminal – Neurotransmitters are manufactured in the cell body but released from synaptic terminals. The neurotransmitters stimulate other neutrons
Synapse – A synapse is the junction between the synaptic terminal and another cell. The other cell is called a postsynaptic cell
52
What is myelination?
1. The main purpose of the myelin sheath is to increase the speed of electrical transmissions via salutatory conduction
2. The disadvantage of myelination is that is takes up significant space within an enclosed environment and requires additional energy
53
Define resting potential and action potential
Resting potential: the electrical potential (difference between inside cell and surrounding extracellular fluid) across the plasma membrane of a cell that is not conducting an impulse. Negative charge.
Action potential: the reversal and restoration of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it (depolarization and repolarization). Positive charge.
54
Explain how a nerve impulse passes along a non-myelinated neuron. (8)
1. Resting potential rises above threshold level.
2. Voltage gated sodium channels open.
3. Sodium ions flow into the cell, more sodium channels open.
4. Inside of cell develops a net positive charge compared to the outside and results in depolarization.
5. Voltage gated potassium channels open.
6. Potassium ions flow out of the cell.
7. Cell develops a net negative charge compared to the outside and results in repolarization.
8. Concentration gradients restored by sodium-potassium pumps.
9. Resting potential is restored.
55
Explain the principle of synaptic transmission (9)
1. Action potential reaches the end of a presynaptic neuron.
2. Voltage gated calcium channels open.
3. Calcium ions flow into the presynaptic neuron.
4. Vesicles with neurotransmitters inside the presynaptic neuron fuse with the plasma membrane.
5. Neurotransmitters diffuse in the synaptic cleft and bind to receptors on the postsynaptic neuron.
6. The receptors are channels which open and let sodium ions into the postsynaptic neuron.
7. The sodium ions cause the postsynaptic membrane to depolarize.
8. This causes an action potential which passes down the postsynaptic neuron.
9. Neurotransmitters in the synaptic cleft are degraded and the calcium ions are pumped back into the synaptic cleft.
56
Define homeostasis
The process in which organ systems work to maintain a stable internal environment inside the body
57
What is the endocrine system?
The endocrine system consists of glands that release hormones that are transported in the blood.
58
What is negative feedback?
Negative feed back is used to keep the internal environment between limits as it keeps a variable close to a set value. Positive feedback is when a response to an event increases the likelihood of the event to continue
59
What is the function of insulin and glucagon? (3)
1. High levels of glucose in the blood can damage cells (creates hypertonicity) and hence glucose levels must be regulated
2. When blood glucose levels are high (e.g. after feeding): Insulin is released from beta (β) cells of the pancreas and cause a decrease in blood glucose concentration through glycogenesis, promoting glucose uptake by the liver and adipose tissue, or increasing the rate of glucose breakdown (by increasing cell respiration rates)
3. When blood glucose levels are low (e.g. after exercise): Glucagon is released from alpha (α) cells of the pancreas and cause an increase in blood glucose concentration through glycogenolysis, promoting glucose release by the liver and adipose tissue, or decreasing the rate of glucose breakdown (by reducing cell respiration rates)
60
What is the function of thyroxin? (2)
1. Secreted by the thyroid gland in response to signals initially derived from the hypothalamus
2. It controls basal metabolic rate and body temperature
Too much: Hyperthyroidism. Leads to increased metabolism and temperature
Too little: Hypothyroidism. Leads to decreased metabolism
61
What is the function of leptin? (3)
1. Leptin is produced by adipose cells
2. It decreases appetite
3. Can become desensitized to leptin where it doesn’t work in controlling appetite anymore
62
What is the function of melatonin? (3)
1. Secreted by the pineal gland in the brain
2. Regulates day/night cycle (melatonin levels are highest at night). Circadian rhythm
3. Taking melatonin pills at night in the new time zone can help with jet lag (headaches, irritability, lethargy)
63
Explain the debunking of Aristotle's Soil and Seed Theory (3)
1. Aristotle proposed the “soil and seed” theory where a male will produce a “seed” which forms an “egg” when mixed with menstrual blood “the soil”. The “Egg” will then develop into a fetus inside the mother with the information contained within the male “seed” alone
2. William Harvey debunked this theory by studying the sexual organs of female deer after mating in an effort to identify the developing embryo. He was unable to detect a growing embryo until approximately 6 – 7 weeks after mating had occurred
3. He therefore concluded that Aristotle’s theory was incorrect and that menstrual blood did not contribute to the development of a fetus. However, Harvey was unable to identify the correct mechanism of sexual reproduction due to lack of effective microscopes and incorrectly asserted that the fetus did not develop from a mixture of male and female “seeds”
64
What is the SRY gene? (3)
1. Virtually all X chromosomes are unrelated to sex, unlike the Y chromosomes which contains genes that do determine sex
2. A single Y chromosome gene, called SRY (Sex-determining region) triggers an embryo to develop into a male
3. Without a Y chromosome, an individual develops into a female
65
Outline the functions of testosterone (4)
1. Stimulates the development of prenatal genitalia.
2. Stimulates the development of the male secondary sexual characteristics such as growth of the skeletal muscle and pubic hair.
3. During adulthood it maintains the sex drive.
4. Involved in sperm production during the on set of puberty
66
Outline the functions of oestrogen and progesterone (3)
1. They promote the pre-natal development of the female reproductive organs
2. They are responsible for the development of secondary sex characteristics (including body hair and breast development)
3. They are involved in monthly preparation of egg release following puberty (via the menstrual cycle)
67
Outline the structure of the male reproductive system (6)
1. Testis: The testis is responsible for the production of sperm and testosterone
2. Epididymis: Site where sperm matures and develops the ability to be motile. Mature sperm is stored here until ejaculation
3. Vas Deferens: Long tube which conducts sperm from the testes to the prostrate gland
4. Seminal Vesicle: Secretes fluid containing fructose (to nourish sperm), and prostaglandin (triggers uterine contractions)
5. Prostate Gland: Secretes an alkaline fluid to neutralize vaginal acids (necessary to maintain sperm viability)
6. Urethra: Conducts sperm/seman from the prostrate gland to the outside of the body via the penis
68
Outline the differences between Type I and Type II diabetes (2x4)
Type I
The onset is usually early, sometime during childhood.
β cells do not produce enough insulin.
Diet by itself cannot be used to control the condition. Insulin injections are needed to control glucose levels.
Type II
The onset is usually late, sometime after childhood.
Target cells become insensitive to insulin.
Insulin injections are not usually needed.
Low carbohydrate diet can control the condition.
69
Outline the structure of the female reproductive system
| 6
1. Ovary: The ovary is where oocytes mature prior to release (ovulation). It is also responsible for estrogen and progesterone secretion
2. Fimbria: Fimbria are a fringe of tissue adjacent to an ovary that sweep an oocyte into the oviduct
3. Oviduct: The oviduct (or fallopian tube) transports the oocyte to the uterus. It is also typically where fertilization occurs
4. Uterus: The uterus is the organ where a fertilized egg will implant and develop (becoming an embryo)
5. Endometrium: The mucous membrane lining of the uterus. It thickens in preparation for implantation or is otherwise lost (via menstruation)
6. Vagina: Passage leading to the uterus by which the penis can enter (uterus protected by a muscular opening called the cervix)
70
Outline the menstrual cycle (10)
The menstrual cycle:
1. FSH is secreted by the pituitary gland and its levels start to rise. This stimulates the follicle to develop and the follicle cells to secrete oestrogen.
2. Oestrogen then causes the follicle cells to make more FSH receptors so that these can respond more strongly to the FSH.
3. This is positive feedback and causes the oestrogen levels to increase and stimulate the thickening of the endometrium (uterus lining).
4. Oestrogen levels increase to a peak and by doing so it stimulates LH secretion from the pituitary gland.
5. LH then increases to its peak and causes ovulation (release of egg from the follicle).
6. LH then stimulates the follicle cells to secrete less oestrogen and more progesterone. Once ovulation has occurred, LH stimulated the follicle to develop into the corpus luteum.
7. The corpus luteum then starts to secrete high amounts of progesterone. This prepares the uterine lining for an embryo.
8. The high levels of oestrogen and progesterone then start to inhibit FSH and LH.
9. If no embryo develops the levels of oestrogen and progesterone fall. This stimulates menstruation (break down of the uterine lining). When the levels of these two hormones are low enough FSH and LH start to be secreted again.
10. FSH levels rise once again and a new menstrual cycle begins.
71
Outline the IVF Process (10)
1. For a period of three weeks, the women has to have a drug injected to stop her normal menstrual cycle.
2. After these three weeks, high doses of FSH are injected once a day for 10-12 days so that many follicles develop in the ovaries of the women.
3. HCG (another hormone) is injected 36 hours before the collection of the eggs. HCG loosens the eggs in the follicles and makes them mature.
4. The man needs to ejaculate into a jar so that sperm can be collected from the semen. The sperm are processed to concentrate the healthiest ones.
5. A device that is inserted through the wall of the vagina is used to extract the eggs from the follicles.
6. Each egg is then mixed with sperm in a shallow dish. The dishes are then put into an incubator overnight.
7. The next day the dishes are looked at to see if fertilization has happened.
8. If fertilization has been successful, two or three of the embryos are chosen to be placed in the uterus by the use of a long plastic tube.
9. A pregnancy test is done a few weeks later to find out if any of the embryos have implanted.
10. A scan is done a few weeks later to find out if the pregnancy is progressing normally.
72
Outline the ethical arguments surrounding IVF
Arguments for IVF
Many types of infertility are due to environmental factors rather than genetic which means that the offspring would not inherit the infertility.
The infertility of the parents may be inherited by their offspring passing on the suffering to the next generation.
The embryos that are killed during the IVF process cannot feel pain or suffering as they do not have a developed nervous system.
More embryos are produced than needed and the ones that remain are usually killed which denies them the chance of a life.
Suffering caused by genetic diseases can be decreases by screening the embryos before placing them into the uterus.
Arguments against IVF
Since the IVF process is not an easy one emotionally and physically, is costly, takes time and there are no guarantees, parents who are willing to go through it must have a strong desire to have children and therefore are likely to be loving parents.
IVF is not a natural process which takes place in a laboratory compared to natural conception which occurs as a result of an act of love.
Infertility should be accepted as God’s will and to go against it by using IVF procedures would be wrong.
IB Biology SL
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