PYQ – MZO-003: Comparative Animal Physiology and Biochemistry (Solved Q&A) | MZO-003 | MSCZOO | M.Sc.Zoology | IGNOU | December 2024
M.Sc. (Zoology) (MSCZOO)
Term-End Examination
December, 2024
MZO-003 : COMPARATIVE ANIMAL PHYSIOLOGY AND BIOCHEMISTRY
Time : 2 Hours| Maximum Marks : 50
Note: Attempt any five questions.
1. (a) Explain with help of a diagram fluid exchange across the capillary wall. (5 Marks)
Fluid exchange through capillary walls is an important process that allows tissues to receive nutrients and remove waste. This exchange happens through two main processes: filtration (fluid moves out of capillaries) and reabsorption (fluid moves back into capillaries). The direction of fluid movement depends on the balance between capillary hydrostatic pressure and plasma oncotic pressure.
At the arterial end of a capillary, the hydrostatic pressure (pushing force of blood) is greater than the oncotic pressure (pulling force created by plasma proteins like albumin). This causes water and small molecules like glucose, amino acids and oxygen to move out of the capillaries into the interstitial fluid. This process is called filtration and it helps in delivering nutrients to tissues.
[Note:– Arterial end: It is the beginning part of a capillary connected to an artery where blood pressure is high and fluid moves out into tissues.]
At the venous end of a capillary, the hydrostatic pressure falls but the oncotic pressure remains almost the same. Now, the oncotic pressure becomes stronger than the hydrostatic pressure, so water along with some waste products moves back into the capillary. This is called reabsorption and it helps in removing waste materials from tissues.
[Note:– Venous end: It is the ending part of a capillary connected to a vein where blood pressure is low and fluid from tissues moves back into the capillary.]
Normally, large proteins and blood cells cannot pass through the capillary wall because the pores between endothelial cells are too small. However, a small amount of interstitial fluid still remains outside and is collected by the lymphatic vessels, which later return it to the blood circulation. This helps in preventing fluid accumulation and maintains proper tissue fluid balance.
(b) Explain RAAS (Renin Angiotensin Aldosterone System). (5 Marks)
Renin-Angiotensin-Aldosterone System (RAAS) is a hormone-regulated mechanism which helps the body to maintain normal blood pressure and fluid balance. It is mainly activated when blood pressure becomes low, blood volume decreases or when there is less sodium in the body. The overall aim of RAAS is to restore normal pressure and fluid by hormonal control of blood vessels and kidney functions.
There are five major steps in the working of this system. These steps involve a chain of hormonal conversions and target actions that help the body to conserve sodium and water, and to increase blood vessel resistance. The following are the main steps involved in the RAAS:
1. Renin Release
Juxtaglomerular cells of the kidney release renin in response to low blood volume, decreased sodium, or sympathetic stimulation.
2. Formation of Angiotensin I
Renin acts on angiotensinogen, a plasma protein from the liver and converts it into angiotensin I.
3. Conversion to Angiotensin II
Angiotensin I is converted into angiotensin II by angiotensin-converting enzyme (ACE) mainly in the lungs.
4. Actions of Angiotensin II
Angiotensin II causes vasoconstriction, stimulates the adrenal cortex to release aldosterone and promotes ADH release from the pituitary, all of which help raise blood pressure.
5. Aldosterone Effects
Aldosterone acts on the kidney tubules, increasing sodium and water reabsorption, and potassium excretion, thus restoring fluid volume and pressure.
2. (b) Explain how ATP generation occurs for skeletal muscle contraction in vertebrates. (5 Marks)
ATP is essential for skeletal muscle contraction in vertebrates. It is used in multiple steps like cross-bridge cycling between actin and myosin, calcium ion pumping into the sarcoplasmic reticulum and maintaining ion gradients across the muscle cell membrane. Since muscle activity can be short and intense or prolonged, ATP is generated by three main mechanisms that work at different timescales.
- Creatine Phosphate System
- This is the fastest way to generate ATP. In resting muscles, ATP transfers a phosphate group to creatine, forming creatine phosphate. During sudden contraction, this phosphate is given back to ADP to form ATP with the help of the enzyme creatine kinase. This system supports muscle activity for about 8 to 10 seconds.
- Anaerobic Glycolysis
- When oxygen is not available or during intense activity, glucose is broken down into pyruvate. In absence of oxygen, pyruvate is converted into lactic acid. This process occurs in the cytoplasm and gives 2 ATP per glucose molecule. It provides energy for short bursts of activity, but the buildup of lactic acid causes muscle fatigue.
- Aerobic Respiration
- This is a long-term and efficient ATP-producing system. It takes place inside mitochondria in the presence of oxygen. Glucose, fatty acids, or amino acids are broken down completely into CO₂ and water. This process gives about 36 ATP molecules per glucose. It supports sustained and moderate activities like walking or running.
These three pathways work together depending on the intensity and duration of muscle activity. At the start of contraction, creatine phosphate is used. Then anaerobic glycolysis takes over and finally, aerobic respiration supports long-term energy needs.
(b) What are the ion channels? Discuss their role in nerve impulse generation and conductivity. (5 Marks)
Ion channels are special protein pores found in the plasma membrane of cells. They help in the movement of ions like sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺) and chloride (Cl⁻) from one side of the membrane to the other. This movement always occurs from higher to lower concentration, so no energy (ATP) is used. Ion channels are highly specific, meaning each channel only allows one type of ion to pass. They play an important role in many cellular processes like nerve impulse generation, muscle contraction and maintaining the resting membrane potential. Ion channels can open and close in response to different signals. Based on how they open, they are of different types such as voltage-gated, ligand-gated, mechanically-gated and leak channels (Always open channels). These channels are very important in excitable cells like neurons and muscle cells.
Role of Ion Channels in Nerve Impulse Generation
The nerve impulse begins with a stimulus that causes the membrane potential to become less negative. When it reaches a threshold, voltage-gated Na⁺ channels open and sodium ions rush inside the neuron. This sudden inflow causes depolarization. After a few milliseconds, these Na⁺ channels close and voltage-gated K⁺ channels open, allowing potassium ions to exit. This leads to repolarization. The rapid and temporary change in membrane potential is called an action potential. Without ion channels, this sudden ionic movement would not be possible.
Role of Ion Channels in Impulse Conductivity
Once the action potential is generated, it travels along the axon. This is possible due to the sequential opening of voltage-gated ion channels along the axon membrane. In unmyelinated neurons, ion channels are spread evenly along the membrane and the impulse moves continuously. In myelinated neurons, the ion channels are concentrated at Nodes of Ranvier. The action potential jumps from one node to the next, which is called saltatory conduction. This type of conduction is faster and saves energy. The opening and closing of ion channels at these nodes helps in maintaining the speed and direction of the impulse.
3. (a) Describe the function of electric organs in fish. (5 Marks)
Electric organs are specialized biological structures present in certain fish species that can generate electric fields. These organs are mostly found in electric eel (Electrophorus electricus), electric ray (Torpedo) and electric catfish (Malapterurus). These organs are usually derived from modified muscle cells or sometimes nerve cells called electrocytes. These cells are arranged in rows or stacks and each cell can create a small electric charge. When all electrocytes discharge together in a coordinated manner, they produce a large enough electric potential.
These electric organs produce electric discharges that help the fish in different ways depending on the species. Their main functions are as follows:
1. Capturing Prey and Defense
In fishes like electric eel (Electrophorus electricus) and electric ray (Torpedo), electric organs can produce strong electric shocks. These shocks are used to stun or kill prey such as small fishes, frogs etc. They also help in self-defense against predators. The discharge can be as high as 600 volts in some cases.
2. Navigation and Object Detection
Some fishes live in dark or muddy water where eyesight is not useful. In such cases, certain fishes like Gymnotus and Apteronotus produce weak electric signals to scan their surroundings. These low-power signals form an electric field around the fish. When any object enters this field, the fish can detect its presence, size, shape and even movement. This process is called electrolocation.
3. Communication Between Individuals
These weak electric signals are also used to send messages to other fish of the same species. It helps them identify each other, attract mates, or avoid territorial fights. This is known as electrocommunication.
(b) Explain how absorption of fats differs from absorption of proteins and sugars. (5 Marks)
In vertebrates, the absorption of nutrients mainly occurs in the small intestine. However, the absorption of fats is quite different from that of proteins and sugars. These differences can be explained based on the following criteria:
1. Initial Processing and Site
Fats are first emulsified by bile salts in the duodenum. This converts large fat globules into small droplets. These are then broken down into fatty acids and monoglycerides by lipase.
Proteins are broken into amino acids by proteases like pepsin and trypsin, and sugars are broken into monosaccharides by enzymes like amylase. The digestion of both proteins and sugars mainly occurs in the duodenum and jejunum.
2. Form and Mechanism of Absorption
Fats form micelles with bile salts and get absorbed into intestinal epithelial cells. Inside, they are converted back to triglycerides and packed into chylomicrons.
Proteins and sugars are already in dissolved form and get absorbed as amino acids and monosaccharides without forming such complexes.
3. Pathway of Absorption
Fats are first converted into chylomicrons after digestion. These chylomicrons are too large to enter blood capillaries. So, they are absorbed into lacteals, which are lymphatic vessels present inside the intestinal villi.
On the other hand, proteins are absorbed as amino acids and sugars as monosaccharides. Both are small and water-soluble, so they directly enter the blood capillaries of the villi.
4. Transport and Destination
Fats are transported through the lymphatic system and reach the bloodstream via the thoracic duct, bypassing the liver at first.
Proteins and sugars go directly to the liver through the hepatic portal vein before entering systemic circulation.
4. Differentiate between the following pairs of terms: (2.5 × 4 = 10 Marks)
(a) Respiratory Acidosis and Alkalosis
Respiratory acidosis is a condition in which blood pH decreases due to excessive carbon dioxide (CO₂) buildup in the body. This usually happens because of hypoventilation or impaired lung function, where CO₂ is not properly exhaled. As CO₂ combines with water, it forms carbonic acid, which lowers the pH. Common causes include chronic obstructive pulmonary disease (COPD), respiratory muscle weakness and drug overdose that depresses the respiratory system.
Respiratory alkalosis, on the other hand, occurs when blood pH increases due to rapid loss of CO₂ from the body, often because of hyperventilation. As CO₂ levels drop, less carbonic acid is formed and blood pH rises. This may occur during anxiety attacks, fever, or at high altitudes. Both conditions affect acid-base balance and are usually compensated by the kidneys, which adjust bicarbonate reabsorption or excretion accordingly.
(b) Myelinated axon and Non-myelinated axon
Myelinated axons are covered by a fatty insulating sheath called myelin. In the peripheral nervous system, Schwann cells produce myelin, while in the central nervous system, oligodendrocytes perform this function. Myelin increases the speed of nerve impulse conduction by enabling saltatory conduction, where the impulse jumps from one Node of Ranvier to the next. Myelinated axons are usually found in motor neurons and long sensory pathways.
Non-myelinated axons do not covered by a fatty insulating sheath. The nerve impulse travels continuously along the axon, making conduction slower. These axons are generally found in autonomic nerves or in short interneurons where fast conduction is not essential. While slower, they are still efficient for short or local communication.
(c) Competitive enzyme inhibition and Uncompetitive enzyme inhibition
In competitive inhibition, the inhibitor molecule resembles the substrate and competes for the enzyme's active site. It blocks the substrate from binding, reducing enzyme activity. This type of inhibition can be reversed by increasing substrate concentration. In enzyme kinetics, competitive inhibition increases Km but does not change Vmax. A classic example is malonate inhibiting succinate dehydrogenase in the citric acid cycle.
Uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex, not to the free enzyme. This locks the substrate in the enzyme and prevents the reaction from completing. It cannot be reversed by increasing substrate concentration. Both Km and Vmax are reduced in this case. Uncompetitive inhibition is often observed in multi-substrate enzymatic reactions or in feedback control systems.
(d) Acclimation and Acclimatization
Acclimation is the physiological adjustment of an organism to a single environmental factor under controlled laboratory conditions. For example, a fish kept at a specific temperature in a lab tank for several days can adjust to that temperature. Acclimation is used in experimental settings to study individual factors in isolation.
Acclimatization refers to natural adaptation to multiple environmental factors in the wild. For example, humans gradually adapt to high altitudes by increasing red blood cell count and breathing rate to cope with low oxygen. It is a slower, complex process involving coordinated physiological changes and usually happens in natural ecosystems without experimental control.
5. Write short notes on the following: (2.5 × 4 = 10 Marks)
(a) Bohr effect
The Bohr effect refers to a physiological property of hemoglobin in which its affinity for oxygen decreases in the presence of high levels of carbon dioxide and hydrogen ions. This concept was first described by Danish physiologist Christian Bohr in 1904.
In the tissues, where cellular respiration occurs, carbon dioxide levels are high. CO₂ reacts with water to form carbonic acid, which dissociates into hydrogen ions and bicarbonate, lowering the pH. This acidic condition causes hemoglobin to change shape and release oxygen more easily.
In contrast, in the lungs, where carbon dioxide concentration is low and the pH is relatively high, hemoglobin binds to oxygen more efficiently.
This dual behavior allows oxygen to be released in metabolically active tissues and picked up again in the lungs, ensuring effective oxygen transport based on the body's needs.
(b) Green glands
Green glands are specialized excretory organs found in many crustaceans such as prawns, crabs and crayfish. They are called green glands because of their greenish color and are also known as antennal glands, as they are located near the base of the antennae. These glands serve a function similar to kidneys in vertebrates. They remove nitrogenous waste products, mainly in the form of ammonia, from the hemolymph (blood of arthropods) and help regulate osmotic balance. The gland consists of a labyrinth, a bladder and an excretory duct which opens to the exterior. The labyrinth filters the hemolymph, the bladder stores the excreted material and the duct releases it outside the body. In freshwater crustaceans, green glands also play an important role in removing excess water from the body to maintain internal salt concentration. Thus, they are vital for both excretion and osmoregulation.
(c) Xenobiotic function of liver
Xenobiotics are foreign substances not naturally produced or expected in the body. These include drugs, food preservatives, pesticides, pollutants and synthetic chemicals. The liver plays a key role in the metabolism and detoxification of xenobiotics. This process occurs in two main phases.
In Phase I, enzymes such as cytochrome P450 modify the xenobiotics by oxidation, reduction, or hydrolysis to make them more reactive.
In Phase II, these reactive compounds are conjugated with water-soluble molecules like glucuronic acid, sulfate, or glutathione. This makes them easier to eliminate from the body through urine or bile.
The liver's role in xenobiotic metabolism is crucial for preventing toxic accumulation and protecting other organs from damage. It also affects how long and how strongly a drug can act in the body.
(d) Fo-F1 ATP synthase
Fo-F1 ATP synthase is a complex enzyme that synthesizes ATP, the primary energy currency of the cell. It is located in the inner membrane of mitochondria in eukaryotes. The enzyme has two major components:
- Fo, which is embedded in the membrane
- F1, which extends into the mitochondrial matrix.
The entire system works like a molecular motor and is essential for cellular energy production. Without this enzyme, the cell cannot produce sufficient ATP to maintain its functions.
6. (a) Describe the various methods for regulating enzyme activity. (5 Marks)
There are four main methods for regulating enzyme activity: allosteric regulation, covalent modification, feedback inhibition and proteolytic activation. These regulatory methods allow precise control of enzyme action and help maintain homeostasis in the body.
1. Allosteric Regulation
In this type, enzymes have an additional site called the allosteric site. When specific molecules bind here, they change the shape of the enzyme and either increase or decrease its activity. This type of regulation is usually reversible. For example, phosphofructokinase in glycolysis is regulated allosterically by ATP and citrate.
2. Covalent Modification
This involves reversible chemical changes to the enzyme, most commonly phosphorylation. Protein kinases add phosphate groups from ATP, while phosphatases remove them. This can switch the enzyme on or off. For example, the enzyme glycogen phosphorylase becomes active after phosphorylation.
3. Feedback Inhibition (Negative Feedback)
In this method, the final product of a metabolic pathway inhibits the activity of an earlier enzyme in the same pathway. This prevents overproduction and maintains balance. For example, the amino acid isoleucine inhibits the enzyme threonine deaminase in its own biosynthesis.
4. Proteolytic Activation
Some enzymes are made in inactive forms called zymogens or proenzymes. These become active only after a specific part is cut off by another enzyme. This mechanism is seen in digestive enzymes like trypsin, which is activated from trypsinogen in the small intestine.
(b) Derive the Michaelis-Menten equation for enzyme catalysed reactions. (5 Marks)
Michaelis-Menten equation explains how the rate of an enzyme-catalysed reaction depends on substrate concentration. This model was developed by Leonor Michaelis and Maud Menten in 1913.
Let an enzyme (E) catalyse a reaction where a substrate (S) is converted into a product (P). The reaction occurs in the following two steps:
Step 1: Formation of enzyme-substrate complex
E + S ⇌ ES
This is a reversible step where the enzyme binds with the substrate.
Step 2: Breakdown of ES complex to form product
ES → E + P
This step releases the product and regenerates the free enzyme.
Steady-State Assumption
To derive the equation, we use the steady-state assumption. It means the concentration of the intermediate complex ES remains constant during the reaction. That is, the rate of formation of ES equals the rate of its breakdown.
Let:
- k₁ = rate constant for formation of enzyme-substrate complex (ES)
- k₋₁ = rate constant for dissociation of ES back to E and S
- k₂ = rate constant for conversion of ES to product (P) and enzyme (E)
Then,
Km (Michaelis constant) = (k₋₁ + k₂) / k₁
Let [E₀] be the total enzyme concentration and [S] be the substrate concentration. The initial rate of reaction is:
V₀ = Vmax × [S] / (Km + [S])
Where,
- V₀ = initial reaction velocity
- Vmax = maximum velocity when all enzyme is bound to substrate
- Km = substrate concentration at which V₀ is half of Vmax
This equation shows that at low [S], V₀ increases nearly linearly, while at high [S], it approaches a maximum velocity Vmax, forming a hyperbolic curve.
7. (a) Briefly describe how glucose homeostasis is maintained in humans. (5 Marks)
Glucose homeostasis means maintaining a steady level of glucose in the blood. This is very important because glucose is the main energy source for brain cells and many other body tissues. In humans, glucose level is mainly controlled by two pancreatic hormones: insulin and glucagon. These hormones are released by special cells in the islets of Langerhans in the pancreas and work in opposite ways to keep the glucose level stable.
When Blood Glucose Level Rises (Postprandial State)
After eating food, especially rich in carbohydrates, the blood glucose level increases. This rise is detected by beta cells of the pancreas, which respond by secreting insulin into the bloodstream. Insulin promotes the uptake of glucose by muscle and fat cells through special transporters called GLUT-4. It also stimulates glycogenesis, where glucose is converted to glycogen and stored in the liver and muscles. Along with that, insulin inhibits glycogenolysis (breakdown of glycogen) and gluconeogenesis (formation of new glucose) to avoid further increase in blood glucose. It also helps in lipogenesis, where excess glucose is converted into fat. All these actions bring down the glucose level to normal.
When Blood Glucose Level Falls (Fasting or Starvation State)
During fasting, prolonged exercise, or between meals, the blood glucose level starts decreasing. This fall is sensed by alpha cells of the pancreas, which release glucagon. Glucagon mainly targets liver cells and activates glycogenolysis, which converts stored glycogen back into glucose. It also promotes gluconeogenesis by using substrates like lactate, amino acids and glycerol to make new glucose. Additionally, glucagon helps in lipolysis, where stored fat is broken down to provide energy. These processes raise the glucose level back to normal and provide energy to essential organs like the brain and muscles.
(b) How do enzyme lower the activation energy? Discuss using suitable examples. (5 Marks)
Enzymes are biological catalysts that speed up chemical reactions in living organisms. They do this by lowering the activation energy, which is the minimum energy needed to start a chemical reaction. Without enzymes, many reactions in the body would happen too slowly to support life.
Enzymes lower activation energy by making the reaction path easier. They do this mainly through following ways:
1. Proper Orientation of Substrates
Enzymes hold the substrate molecules in the correct angle and position. This makes sure that the right parts of the molecules are close to each other, which increases the chances of reaction. For example, sucrase binds to sucrose and positions glucose and fructose in such a way that the glycosidic bond between them can break easily.
2. Stabilization of the Transition State
The enzyme binds more strongly to the transition state than to the normal substrate. This lowers the energy of the transition state, making the reaction go faster. For example, chymotrypsin helps in breaking peptide bonds by stabilizing the high-energy tetrahedral intermediate during protein digestion.
3. Providing Favorable Microenvironment
Enzymes may create a small chemical environment at the active site which supports the reaction. This includes acidic or basic conditions or keeping water away. For example, pepsin works well in the acidic conditions of the stomach, where its active site supports proton transfers that help in protein breakdown.
4. Applying Mechanical Strain on Substrate Bonds
Some enzymes slightly bend or stretch the bonds in the substrate. This strain makes the bonds weaker and easier to break. For example, lysozyme attacks bacterial cell walls by bending the sugar bonds in peptidoglycan. This distortion makes the bond more ready to break.
5. Direct Participation by Active Site Groups
Enzymes may use amino acid side chains or metal ions to take part directly in the reaction. These groups donate or accept electrons or protons, making bond changes faster. For example, carbonic anhydrase has a zinc ion that activates water molecules. This helps convert carbon dioxide into carbonic acid very quickly.
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