Syllabus responses from http://www

Syllabus responses from http://www.geocities.com/BiologyIB/

5.5.1 List the features of alveoli that adapt them to gas exchange.

There is a large surface area, a dense network of capillaries.a wall consisting of a single layer of flattened epithelial cells separated from one another by a thin basement membrane, allowing for easy diffusion of substances across this wall (so that the barrier between the air in an aveolus and the blood in its capillaries and gases are exchanged between the air and blood by diffusion), and a thin membrane, the pleura, lines the thoracic cavity secrete a fluid to lubricate and keep aveoli moist.

5.5.2 State the difference between ventilation, gas exchange, and cell respiration.

Ventilation is a method of increasing contact between the respiratory medium and the respiratory surface. It maintains a high concentration of oxygen in the alveoli and low carbon dioxide as we breathe in and out. Gas exchange occurs between the aveoli and the capillaries by diffusion, oxygen passes from the alveoli to the capillaries and carbon dioxide passes from the capillaries to the alveoli. Cell respiration is the chemical reaction that occurs inside the cell and that results in the controlled production of energy in the form of ATP.

5.5.3 Explain the necessity for a ventilation system.

A ventilation or gas-transport, system is needed in order to obtain oxygen for the organism (which takes part in the oxidation of organic compounds that serve as cellular energy sources) and to get rid of carbon dioxide that is produced as a by-product. A true ventalation system is needed for larger animals when diffusion of oxygen through cells is not enough to supply all the oxygen needed in the organism. It is needed to maintain concentration gradients in the alveoli.

5.5.4 Draw a diagram of the ventilation system including trachea, bronchi, bronchioles, and lungs.

This will be answered at a later date

5.5.5 Explain the mechanism of ventilation in human lungs including the action of the internal and external intercoastal muscles, the diaphragm and the abdominal muscles.

To inhale, the diaphragm contracts and flattens and the external intercoastal muscles also contract and cause the ribcage to expand and move up. The diaphragm contracts drops downwards. Thoracic volume increases, lungs expand, and the pressure inside the lungs decreases, so that air flows into the lungs in response to the pressure gradient. These movements cause the chest cavity to become larger and the pressure to be smaller, so air rushes in from the atmoshere to the lungs. To exhale, the diaphragm relaxes and moves up. In quiet breathing, the external intercoastal muscles relax causing the elasticity of the lung tissue to recoil. In forced breathing, the internal inercoastal muscles and abdominal muscles also contract to increase the force of the expiration. Thoracic volume decreases and the pressure inside the lungs increases. Air flows passively out of the lungs in response to the pressure gradient. The ribs to move downward and backward causing the chest cavity to become smaller in volume and the pressure increases pushing air out of the lungs into the atmosphere.

5.6.1 State that homeostasis involves maintaining the internal environment at a constant level or between narrow limits, including blood pH, oxygen and carbon dioxide concentrations, blood glucose, body temperature and water balance.

Homeostasis involves maintaining the internal environment at a constant level or between narrow limits, including blood pH, oxygen and carbon dioxide concentrations, blood glucose, body temperature and water balance

5.6.2 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.

If body temperature falls below 37 degrees Celsius, then messages are sent by the hypothalamus to different parts of the body so temperature is increased to normal. Conversely, if body tempature rises above 37 degrees Celsius, messages sent decrease body temperature to normal. Therefore, a change in a variable is counteracted by the opposite change to return the body to a normal temperature.

5.6.3 State that the nervous and the endocrine systems are both involved in homeostasis.

The nervous and endocrine systems are both involved in homeostasis.

5.6.4 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves and is composed of special cells called neurons that can carry electrical impulses rapidly.

The nervous system consists of the central nervous system (CNS) and peripheral nerves and is composed of special cells called neurons that can carry electrical impulses rapidly.

5.6.5 Describe the control of body temperature including the transfer of heat in blood, the role of sweat glands and skin arterioles, and shivering.

First, the nerve cells beneath the skin, thermoreceptors, detect a change in the environment surrounding the human. These thermoreceptors send messages that are received by the hypothalamus. The hypothalamus is made of nerve cells andis considered a part of the nervous and endocrine systems. Hormones are released from the hypothalamus and they travel to the pituitary gland. The pituitary gland then releases a hormone bound for the thyroid-gland which in turn releases thyroxine. The release of thyroxine increases the metabolic rate of the body and in turn releases more heat. For example, when the weather is hot, less thyroxine is released and less heat is produced. The hypothalamus also plays a role in transmitting nerve messages to muscles, blood capillaries and sweat glands. The effect of this is the occurrence of responses such as shivering, vasoconstriction or vasodilatation and sweating.

5.6.6 State that the endocrine system consists of glands which release hormones that are transported in the blood.

The endocrine system consists of glands which release hormones that are transported in the blood.

5.6.7 Explain the control of blood glucose concentration, including the roles of glucagon, insulin, and alpha and beta cells in the pancreatic islets.

Insulin and glucagon regulate the sugar level in the body. These two hormones are manufactured in the pancreas and through circulation are carried to the liver where they perform their functions. Enzymes that convert glucose to glycogen though a condensation reaction are stimulated by Insulin. Enzymes that hydrolyze glycogen to glucose are stimulated by glucagon. Receptors in the pancreas are sensitive to the changes in sugar level, thus releasing the necessary requirements of insulin and glucagon depending on the needs of the body. The beta cells found in the islets of the pancreas make insulin and the alpha cells make glucagon.

5.6.8 Define excretion

Excretion is the removal of metabolic waste from the body.

5.6.9 Outline the role of the kidney in excretion and the maintenance of water balance.

The human body contains two kidneys located at the back of the abdominal cavity. A tube called the ureter connects each kidney and runs downward to empty in a sac-like structure called the urinary bladder. The renal artery supplies each kidney with urea or other unwanted material and also oxygen. The renal vein leaves the kidneys with blood that contains the correct amounts of urea, salts and water. Carbon dioxide is prevalent in the renal vein and this is released by the kidney as respiratory waste. The urinary bladder opens up to two things: the urethra which empties urine to the outside of the body and the sphincter muscles which guard the emptying of urine and provide that urination can be controlled under normal circumstances.

12.1.1 Outline the need for excretion in all living organisms.

Excretion removes metabolic waste from the body. In animals, nitrogenous waste is excreted from a specialized network of organs created to store and excrete wastes. It needs to be excreted because it is toxic. When wastes accumulate, they tend to damage cells and metabolic processes, largely by changing the pH balance in their surrounding environment. Excretion prevents accumulation of wastes. In plants, oxygen is excreted when released from photosynthesis. The excretion of wastes also serves to free up space needed for products used in metabolism.

12.1.2 State that excretory products in plants include oxygen, and in animals they include carbon dioxide and nitrogenous compounds.

The excretory products in plants include oxygen, and in animals they include carbon dioxide and nitrogenous compounds.

12.1.3 Discuss the relationship between the different nitrogenous waste products and habitat in mammals, birds and freshwater fish.

Surplus amino acids must be degraded to relatively harmless nitrogen-containing compounds. Freshwater fish can get rid of ammonia, although highly toxic (due to its basicity), because it can be diluted by the readily available water. Birds are unable to carry too much water so they excrete uric acid which is insoluble and expelled as a paste (most of the water is removed before excretion). Mammals excrete urea, which contains some nitrogenous wastes but is largely water and not very toxic. Some desert mammals produce very concentrated urine (having a long loop of Henle in their kidneys to filter out the majority of water and fluids).

12.2.1 Draw the structure of the kidney.

Drawing will be inserted at a later date.

12.2.2 Draw the structure of a glomerulus and associated nephron.

Drawing will be inserted at a later date.

12.2.3 Explain the process of ultrafiltration including blood pressure, fenestrated blood capillaries and basement membrane.

The renal artery branches inside the kidney and a branch enters each Bowman's capsule. This branch is called the afferent renal arteriole. The arteriole branches into a branch of capillaries called glomerulus inside each Bowman's capsule. The capillaries merge again into one blood vessel that leaves the Bowman capsule called the efferent renal artery. The blood pressure in the gloerulus is very high due to the fact that these capillaries are present between two arteries and not between an artery and a vein as is the case with other parts of circulation. Due to this high blood pressure in the capillaries, fluid is squeezed out. However only the substances that have sizes that enable them to pass oout of the capillary wall are squeezed out. This is called filtration ( or ultrafiltration).

12.2.4 Define osmoregulation.

Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living organism.

12.2.5 Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport.

Reabsorption in the kidneys is, under most conditions, very efficient, able to reabsorb the vast majority of water and salts from the fluid. The inside of the proximal tubule is lined with countless microvili, essentially the same in structure to those found in the small intestine but scaled down significantly in size. These microvili are the surface through which substances enter and exit the filtrate, or the fluid inside the proximal tubule. Some substances in the filtrate, such as the buffer molecule HCO3 (bicarbonate) and postassium, diffuse out of the filtrate passively. However, other substances, including amino acids and glucose, must be actively transported into the microvil and eventually back into the blood stream. The proximal tubule also functions in the reabsorption of salt molecules, which passively move out of the tubule and into the surrounding microvili. Due to the gradient now forms by the diffusion of salt, water follows the salt out of the tubule by osmosis, thus reclaiming the majority of water in the process. The proximal tubule also functions in expelling poisons or wastes collected from the liver by secreting them into the filtrate, where they will later be excreted.

12.2.6 Explain the roles of the loop of Henle, medulla, collecting duct and ADH in maintaining the water balance of the blood.

The descending loop of henle reabsorbs water by osmosis. At the bottom of the loop of henle, the loop enters the medulla section. When in the medulla, salts begin to diffuse, and continue to diffuse in the ascending loop of henle, and in the upper section of the loop of henle the salts are pushed out by active transport. In the collecting duct, reabsorption of water, glucose and salts occurs depending on the hormone ADH. The more there is in the collecting duct, the more permeable the collecting duct is to water.

12.2.7 Compare the composition of blood in the renal artery and renal vein, and compare the composition of glomerular filtrate and urine.

The renal artery enters the kidney with urea and other unwanted material and carries oxygen to the kidney. The renal vein leaves the kidney with blood that contains correct levels of urea, salt, and water. It is also rich in CO2. The glomeruler filtrate contains salts, glucose, and vitamins, urea, and other small molecules. Urine contains ammonia and carbon dioxide, as well as water.

12.2.8 Outline the structure and action of kidney dialysis machines.

This machine works on the basis of osmosis and diffusion. It is multiple layers of sheets of a cellophane material that allows small molecules to pass through. The blood passes between the sheets of the dialysis machine and as it does that, movement of the ions according to concentration gradient will start taking place. A patient with kidney failure must be connected to a dialysis machine in a hospital 2 days a week for about 12 hours each time.