Answers Homeostasis Structured Questions 1.

(a) (b)

(c)

(d)

(e)

2.

a)

b) c)

Ultrafiltration - The afferent arteriole has larger diameter than the efferent arteriole - A hydrostatic pressure is generated which forces the fluid through the pores of capillary wall of glomerulus into the Bowman capsule - The descending limb is more permeable to water. As the filtrate moves down, water diffuses out of the descending limb by osmosis. The filtrate becomes more concentrated - The ascending limb is relatively impermeable to water but more permeable to salts. As the filtrate moves up, sodium and chloride ions diffuse out passively at first and then higher up actively transported out into the surrounding tissue - This creates an area of high solute concentration in the medulla interstitium - More water is reabsorbed from the ducts and distal convoluted tubules into the region of high solute concentration. The water is carried away by the vasa recta. A small volume of concentrated urine is produced - Diabetes mellitus is caused by failure of beta cells in pancreas to produce insulin - The liver and other cells unable to take up and metabolise glucose. The blood glucose level rises above normal level - The kidney tubules are unable to reabsorb the high level of glucose. Excess glucose is removed in the urine Consumption of large amount of alcohol inhibits the release of antidiuretic hormone (ADH) from pituitary gland

i) ii)

Antidiuretic hormone ADH is a nine amino acids peptide produced by the neurons in the hypothalamus and passes to the posterior pituitary gland ADH increases the permeability of distal convoluted tubules and collecting ducts to water 1: ADH is transported by blood to the targeted organ, the kidney. 2: ADH binds to receptors in plasma membrane of epithelial cell lining in the distal convoluted tubules and collecting ducts 3: It activates a series of enzyme-controlled actions. Enzyme phosphorylase becomes activated 4: The phosphorylase causes vesicles with aquaporins to move to the plasma membranes of epithelial cells 5: The vesicles fuse with plasma membrane 6: Water diffuses freely through the aquaporins, down its concentration gradient, from the collecting ducts into the surrounding medulla interstitial fluid and then into the capillary

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3.

a) b)

4.

a)

b)

c)

d)

5.

a) b)

c)

S: sinusoid U: hepatocytes T: Canaliculus W: branch of hepatic vein P: Transport blood from hepatic portal vein carrying absorbed substances from alimentary canal Q: Transport deoxygenated blood that contains glucose and glycogen for gluconeogenesis or glycogenolysis R:

A: capillary / glomerular capillary B: Bowman’s capsule C: podocytes - Diameter of the efferent arteriole is larger than the diameter of efferent arteriole - High hydrostatic pressure in the glomerulus - Plasma contains large protein molecules that are not found in the glomerular filtrate - These molecules are too large to pass through the basement membrane of glomerular capillaries - Tightly packed cells increase the rate of reabsorption - Numerous microvilli that increase the surface area for reabsorption - Numerous mitochondria to provide ATP for active uptake of substances

S: 99.17% U: 28 g T: 0 g V: 52.83% - Na+ and Cl- ions are moved out from R by diffusion and active transport - These ions accumulate in the interstitial fluid creating a region of high salt concentration in the medulla - This causes water to diffuse out from Q by osmosis, producing concentrated urine i) - Costly / time-consuming / require frequent trip to hospitals or dialysis centre / disruption of daily life - Patients have to follow a strict diet to prevent waste substances from accumulating to a dangerous level / protein restriction ii) Kidney transplant

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Essay Questions 1.

a)

Ultrafiltration - the structures involved are the glomerulus, a mass of blood capillaries - supplied with blood from afferent arteriole of the renal artery - the Bowman’s capsule consists of basement membrane and podocytes - the force for ultrafiltration to occur is due to the larger diameter of the afferent arteriole - the force from the blood pressure enables substances to pass through the filters formed by the basement membrane and podocytes Selective reabsorption - proximal convoluted tubule (active removal of substances) have many microvilli forming a brush border along the closely packed layer of epithelial cells, increasing the surface area for absorption - PCT has many mitochondria to provide ATP for active uptake - the structure of the loop of Henle that has a narrow descending limb with water permeable walls and a wider ascending limb with less water permeable walls create a countercurrent multiplier system - the permeability of the walls of distal convoluted tubules and the collecting ducts affected by hormones such as ADH

2.

b)

- ADH is involved in water content regulation in the kidney - A decreased in water content of the body fluids by excessive sweating or reduced water intake increases the blood osmotic pressure - The increase is detected by osmoreceptors in the hypothalamus and impulses are transmitted to stimulate the posterior pituitary gland to release ADH - The presence of ADH causes the walls of DCT and collecting ducts to be more permeable to water and urea - This allows uptake of water to occur osmotically from the filtrate into the medulla and vasa rectae - Active uptake of sodium from the ascending loop of Henle coupled with movement of urea out from the collecting duct creates a hyperosmotic condition in the surrounding interstitial fluids - Urine that is hypertonic to the blood will be formed - An increase in water content of the body fluids because of little sweating or excessive intake of water reduces blood osmotic pressure - ADH production is inhibited. DCT and collecting duct remain impermeable to water and urea - Less water will be drawn out from the tubules resulting in the formation of urine that is hypotonic to the blood

a)

Refer answer in a)ii)

b)

- Almost 80% of the glomerular filtrate is reabsorbed at proximal convoluted tubule (PCT) - All glucose, amino acids, vitamins and hormones are reabsorbed actively into the peritubular capillaries

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- Almost 70% of the sodium and chloride ions in the filtrate are reabsorbed actively into the peritubular capillaries - This reduces the solute potential in the tubular filtrate - Hence, 70-80% of water is reabsorbed through osmosis - About 50% urea in the filtrate diffuse into the peritubular capillaries - This urea is then transported to all over the body - The remaining urea in the tubule is excreted in the urine - Small protein molecules that have passed into the tubule during ultrafiltration are digested into amino acids that can diffuse into the peritubular capillaries

3.

a)

- Loop of Henle passes from cortex down into medulla - Where high salt concentration is maintained in the interstitial fluid / low water potential created - Increased concentration achieved by movement of salt from ascending limb into surrounding fluid - This is carried out by active transport - The ascending limb is impermeable to water - Osmotic movement of water out of descending limb (permeable to water) - Diagram of loop of Henle with arrows showing movement of ions and water and relative concentration

- Collecting duct passes from second tubule (cortex) down through medulla - where salt level concentration detected by osmoregulation cells in the hypothalamus - Rise in osmotic pressure stimulates the release of ADH - ADH increases the permeability of walls of DCT and collecting duct to increase water retention b)

- Beta cells in the Islet of Langerhans in pancreas secrete insulin - Insulin increases the permeability of plasma membrane of target cells to glucose - An increase in the supply of glucose to the cells increases the rate of cellular respiration and oxidation of glucose occurs - Speed up the rate of glycogenesis, the conversion of glucose into insoluble glycogen - Which is stored in the liver and muscle SMK Sultan Ibrahim Kulai, Johor

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- Increase the rate at which excess glucose is converted to fats and stored in adipose tissues - Inhibits glycogenolysis, the conversion of stored glycogen into glucose

4.

5.

a)

- In skeletal muscles, glycogen store is converted into glucose - Glucose is converted to pyruvate during glycolysis - During anaerobic respiration, pyruvate is reduced to lactate by NADH + H+ - Lactate is transported by the blood from the muscles to the liver - In the hepatocytes, lactate is oxidised to pyruvate using NAD+ - Pyruvate is converted to glucose-6-phosphate and then to glucose - Glucose is converted to glycogen and stored in the liver - Glucose can be transported back to the muscles and used for cellular respiration - Importance: prevents an increase in lactic acid / H+ concentration in muscles - Prevents a decrease in pH which will affect most metabolic reactions that are catalysed by enzymes - Reduces muscle fatigue

b)

- Occurs in the liver where excess amino acids undergo deamination - Amino group is converted to ammonia - From cellular respiration, CO2 is produced. CO2 combines with NH3 in the presence of water and ATP to form carbomyl phosphate - Carbomyl phosphate combines with ornithine to form citrulline - Citrulline combines with aspartate, NH3 and ATP to form argininophosphate - Argininophosphate cleaves to form arginine and fumarate - Arginine is hydrolysed to form urea and ornithine - Urea is transported by the blood to kidney to be excreted - Importance: Ammonia is toxic and must be excreted - Prevents an increase in CO2 concentration / H+ concentration / decrease in pH - so that optimal conditions are maintained for metabolic reactions

a)

- Liver consists of many lobules - Each lobule contains many liver cells / hepatocytes - Arranged in row / liver cords radiating from the centre to the side / arranged radially around the central vein (a branch of hepatic vein) - Between liver cords, there are minute channels / canaliculi which contain / channel bile - Sinusoid, minute blood-filled space in the liver connects arteriole branches and hepatic portal vein with the central vein - Blood supply comes from hepatic artery and hepatic portal vein - Branches of the hepatic artery and hepatic portal vein are found between the liver lobules

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- Each liver cell is not differentiated. It has distinct nucleus and Golgi body, many mitochondria and lysosomes and richly contain glycogen granules and fat droplets b)

i)

ii)

6.

a)

- Regulation of blood glucose level: remove excess glucose from the blood if in excess or to raise the glucose level when it decreases - When blood glucose level is high, more glucose is absorbed into liver cells and respired / broken down to CO2 and water - Glucose is converted to glycogen under the effect of insulin - Glucose is converted into fat - When blood glucose level is low, glycogen store in liver cells is broken down to glucose under the effect of glucagon - Regulation of amino acids: amino acids are taken up by liver cells to synthesise protein - Transaminated to other amino acids - Deaminated - Regulation of lipid: Fat is converted by liver cells into glycogen - Producing cholesterol when the uptake through the diet is inadequate - Excess blood cholesterol is removed via bile - Regulation of blood osmotic pressure / water content in body fluid: high blood osmotic pressure causes pituitary gland to release ADH - ADH increases the permeability of DCT and collecting duct - More water is reabsorbed in DCT and collecting duct - Regulation of blood pH: excess hydrogen ions in the blood is excreted actively through DCT - Regulation of mineral ions concentration: excess mineral ions are not reabsorbed, they are eliminated in the urine - Inadequate sodium ions in the blood, sodium ions are reabsorbed via DCT and collecting duct under the influence of aldosterone

Ultrafiltration - Blood in the glomerulus undergoes ultrafiltration - In the glomerulus, hydrostatic pressure is higher compared to the osmotic pressure - Caused by the diameter of efferent arteriole which is smaller than the diameter of afferent arteriole - The numerous tiny pores / fenestrations between the endothelial cells of capillary wall permit many smaller molecules to pass through - Bigger molecules such as plasma proteins and red blood cells are retained in the blood - Glomerular filtrate has a chemical composition similar to blood plasma / contains glucose, amino acids, vitamins, hormones, urea, uric acid, creatinine, ions and water but not contain white and red blood cells, platelets and plasma proteins (albumin)

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Reabsorption - All glucose and amino acids are actively reabsorbed from the filtrate into PCT cells - Some sodium ions are actively reabsorbed here - A large volume of water is reabsorbed by osmosis from the tubule into the blood - Water is drawn out by osmosis to the interstitial fluid in the medulla at the descending loop of Henle, which is impermeable to water - The loss of water concentrates sodium and chloride in the descending limb - Sodium and chloride ions diffuse out from the thin ascending loop of Henle, which is impermeable to water - The thick ascending limb actively transport sodium and chloride ions from the filtrate to the medulla - This raises the osmotic concentration of the tissue fluid in the medulla - As a result water is reabsorbed from the collecting duct and descending limb by osmosis - Loop of Henle functions as countercurrent multiplier - Active reabsorption of sodium, chloride and calcium ions occur in DCT

7.

b)

- Due to uptake of water by osmosis from the glomerular filtrate into blood capillaries - Occurs as a result of increased in permeability of walls of DCT and collecting duct to water - Caused by the release of ADH - Diffusion of urea out of the collecting tubules into the interstitium of medulla - Increase the osmotic concentration resulting in the removal of water

a)

- Liver helps to maintain blood glucose level at 80 – 100 mg/100 cm3. - High level of glucose stimulates beta cells of Islets of Langerhans in the pancreas to secrete insulin - Insulin increases the rate of cellular respiration. Glucose is oxidised into CO2 and water - Insulin increases the rate of glycogenesis, that is the conversion of glucose into insoluble glycogen for storage in the liver and muscles - Insulin increases the rate of conversion of glucose into fats to be stored in adipose tissue - Low level of blood glucose results in glucagon secretion by alpha cells of islets of Langerhans - Glucagon increases the rate of glycogenolysis, that is the conversion of glycogen into glucose by glycogen phosphorylase enzyme - Glucagon stimulates gluconeogenesis, which is the conversion of non carbohydrate sources such as amino acids, glycerol and lactate into glucose as a result of hormone cortisol - Lactate produced by anaerobic respiration in active skeletal muscles is carried by the bloodstream to the liver - In the hepatocytes, lactate is oxidised into pyruvate, which is then converted into glucose-6-phosphate and then into glucose

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8.

b)

- Excess amino acids from protein metabolism are sent to the hepatocytes - The amino acids undergo deamination to produce ammonia - Amino acids combine with CO2 to form carbomyl phosphate - Carbomyl phosphate reacts with ornithine to form citrulline - Citrulline reacts with aspartate to form argininosuccinate - Argininosuccinate cleaves into arginine and fumarate - Fumarate can enter the Krebs cycle - Arginine is hydrolysed to form urea and ornithine - Urea produced is carried in the bloodstream to the kidney to be excreted

a)

- The mechanism occurs in the loop of Henle - Mechanism involves optimum absorption of water into the peritubular capillaries - Descending limb is permeable to water but impermeable to NaCl - Water from the glomerular filtrate in the descending limb leaves the tubule into the interstitial fluid osmotically - The interstitial space has high osmotic concentration due to the secretion of Na+ at the ascending limb - NaCl which remain in the tubule causes the osmotic concentration of the filtration within the tubule to increase - The osmotic concentration at the loop tip is at its highest osmotic concentration - Thin ascending limb is impermeable to water but permeable to NaCl - Thin ascending limb secretes NaCl into the interstitial space, leading to increase in osmotic concentration of the interstitial space - Thick ascending limb is impermeable to both water and NaCl so it secretes Cl- actively - To balance the ions, Na+ shifts out of the tubule passively - Water remains in the tubule to form urine

b)

- Xerophytic plants survive in arid conditions (desserts or artic regions) where they have difficulty to obtain sufficient water

Plants have twisted stem to achieve smaller surface area Thick and succulent stems Has parenchyma cells with high osmotic pressure Leaves modified into thorns for smaller surface area Shallow and widely spread roots Stomata are sunken, less, as crypt like depression or only at lower leaf surface Vegetative reproduction

This helps plants to reduce water loss via transpiration For water storage To absorb more water by osmosis To reduce water loss by transpiration To absorb water over a large area from soil surface To ensure stoma close during day so water loss by transpiration during daytime is minimised Reproduction is independent of water

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