Prove that mitochondria and the chloroplast were once prokaryotic cells.

Hey Luma, good to see you again. Thanks for sending the image again with the crops. I can now see all the questions clearly and will answer the remaining ones. 2. b) An extreme form of symbiosis witnessed in eukaryotic cells is endosymbiont theory which states that prokaryotic cells that invaded the eukaryotic cells at early stage in the history of life. Prove that mitochondria and the chloroplast were once prokaryotic cells. The endosymbiotic theory proposes that mitochondria and chloroplasts originated from free-living prokaryotic cells that were engulfed by ancestral eukaryotic cells. Evidence supporting this theory includes: • Similar size and shape: Mitochondria and chloroplasts are similar in size and shape to typical bacteria. • Circular DNA: Both organelles possess their own circular DNA molecules, similar to bacterial chromosomes, and distinct from the linear DNA in the eukaryotic nucleus. • Ribosomes: They contain ribosomes that are structurally similar to prokaryotic ribosomes (70S type) and different from eukaryotic cytoplasmic ribosomes (80S type). • Binary fission: Mitochondria and chloroplasts reproduce by binary fission, a process characteristic of bacteria, independent of the host cell's division. • Double membranes: Both organelles are enclosed by two membranes. The inner membrane is thought to be derived from the original prokaryotic cell membrane, while the outer membrane is believed to be from the host cell's engulfing vesicle. • Similar enzymes and transport systems: The inner membranes of mitochondria and chloroplasts have enzyme systems and transport proteins that are homologous to those found in the plasma membranes of prokaryotes. c) Describe how movement of materials in and out of the cell is achieved by i) Facilitated diffusion Facilitated diffusion is a type of passive transport that allows substances to cross cell membranes with the assistance of specific transport proteins (channel proteins or carrier proteins). It does not require metabolic energy (ATP) and occurs down a concentration gradient, meaning substances move from an area of higher concentration to an area of lower concentration. This mechanism is used for molecules that are too large or too polar to pass directly through the lipid bilayer, such as glucose and ions. ii) Bulk transport Bulk transport is a process that moves large quantities of materials, large molecules, or even whole cells across the cell membrane, often involving the formation of vesicles. This process requires metabolic energy (ATP). There are two main types: • Endocytosis: The cell takes in substances by engulfing them in a vesicle. This includes phagocytosis (cell eating, for solids like bacteria) and pinocytosis (cell drinking, for liquids and dissolved solutes). • Exocytosis: The cell releases substances by fusing vesicles containing the materials with the plasma membrane, expelling the contents outside the cell. This is used for secreting hormones, enzymes, or waste products. 3. a) What do you understand by; i) Bohr effect, The Bohr effect describes the phenomenon where an increase in the partial pressure of carbon dioxide (PCO2) or a decrease in pH (increase in acidity) in the blood reduces hemoglobin's affinity for oxygen. This causes hemoglobin to release more oxygen to tissues that are actively metabolizing and producing CO2 and H+ ions, such as exercising muscles, ensuring efficient oxygen delivery where it's most needed. ii) Chloride shift? The chloride shift (also known as the Hamburger phenomenon) is a process that occurs in red blood cells to maintain electrical neutrality during the transport of carbon dioxide. As bicarbonate ions (HCO_3^-), formed from CO2 and water, move out of the red blood cell into the plasma, chloride ions (Cl^-) move from the plasma into the red blood cell. This exchange prevents a buildup of negative charge inside the red blood cell and facilitates the continuous uptake of CO2. b) How is carbon dioxide transported in the blood of mammals? Carbon dioxide is transported in the blood of mammals in three main forms: • As bicarbonate ions (approx. 70%): CO2 diffuses into red blood cells, where it combines with water to form carbonic acid (H_2CO_3), catalyzed by the enzyme carbonic anhydrase. Carbonic acid then dissociates into hydrogen ions (H^+) and bicarbonate ions (HCO_3^-). Most HCO_3^- diffuses out into the plasma, while H^+ binds to hemoglobin. The chloride shift occurs to maintain electrical neutrality. • Bound to hemoglobin as carbaminohemoglobin (approx. 23%): CO2 binds directly to the amino groups of hemoglobin, forming carbaminohemoglobin. This binding does not occur at the same site as oxygen binding. • Dissolved in plasma (approx. 7%): A small amount of CO2 dissolves directly in the plasma as a gas. c) How does the heart control heart beat? The heart's beat is controlled by a specialized conduction system within the heart itself, making it myogenic (originating in muscle tissue). • The primary pacemaker is the sinoatrial (SA) node, located in the wall of the right atrium. It spontaneously generates electrical impulses at a regular rhythm. • These impulses spread across the atria, causing them to contract. • The impulses then reach the atrioventricular (AV) node, located between the atria and ventricles. The AV node delays the impulse slightly, allowing the atria to fully empty before ventricular contraction. • From the AV node, the impulses travel down the Bundle of His and then through the Purkinje fibers into the ventricular walls, causing the ventricles to contract. • The rate of the SA node can be modulated by the autonomic nervous system: the sympathetic nervous system increases heart rate, while the parasympathetic nervous system (via the vagus nerve) decreases it. Hormones like adrenaline also increase heart rate. 4. a) Briefly explain what you understand by the following terms: i) C4 plants C4 plants are plants that have evolved a specialized photosynthetic pathway to minimize photorespiration and maximize carbon fixation, especially in hot, dry environments. They initially fix carbon dioxide into a four-carbon compound (oxaloacetate) in mesophyll cells using the enzyme PEP carboxylase, then transport this compound to bundle sheath cells where CO2 is released and enters the Calvin cycle. This spatial separation of carbon fixation and the Calvin cycle improves efficiency. ii) Limiting factors Limiting factors are environmental conditions or resources that restrict the growth, abundance, or distribution of an organism or population. When a factor is in short supply, it limits the rate of a process, even if other factors are optimal. Examples in plants include light intensity, CO2 concentration, water availability, and nutrient levels. iii) Compensation point. The compensation point is the light intensity at which the rate of photosynthesis exactly equals the rate of respiration in a plant. At this point, there is no net exchange of gases (CO2 uptake equals CO2 release), and the plant is neither gaining nor losing biomass. Below the compensation point, the plant respires more than it photosynthesizes, leading to a net loss of organic matter. b) How is the Calvin cycle carried out in C4 plants? In C4 plants, the Calvin cycle is carried out exclusively in the bundle sheath cells, not in the mesophyll cells where initial carbon fixation occurs. • In the mesophyll cells, CO2 is fixed by PEP carboxylase into a 4-carbon compound (e.g., malate). • This 4-carbon compound is then transported from the mesophyll cells into the adjacent bundle sheath cells. • Inside the bundle sheath cells, the 4-carbon compound is decarboxylated, releasing CO2. • This released CO2 then enters the Calvin cycle (C3 pathway) within the bundle sheath cells, where it is fixed by RuBisCO and converted into sugars. This mechanism ensures a high concentration of CO2 around RuBisCO, minimizing photorespiration. c) Describe how digestion of protein occur in a rodent. Protein digestion in a rodent, similar to other mammals, begins in the stomach and continues in the small intestine. • Stomach: In the stomach, hydrochloric acid denatures proteins, unfolding their complex structures. The enzyme pepsin, secreted as inactive pepsinogen and activated by HCl, then breaks down proteins into smaller polypeptides. • Small Intestine: In the small intestine, pancreatic enzymes like trypsin and chymotrypsin (secreted as inactive zymogens and activated by enterokinase) further break down polypeptides into smaller peptides. • Brush Border: Enzymes on the brush border of the small intestine, such as peptidases (e.g., aminopeptidases and dipeptidases), hydrolyze these smaller peptides into individual amino acids. • Absorption: The amino acids are then absorbed through the intestinal wall into the bloodstream and transported to the liver and other cells for protein synthesis or energy. d) State the role of hormones in digestion. Hormones play crucial roles in regulating digestion by controlling the secretion of digestive juices, motility of the gastrointestinal tract, and absorption of nutrients. Key hormones include: • Gastrin: Secreted by the stomach, it stimulates the secretion of hydrochloric acid and pepsinogen. • Secretin: Released by the duodenum in response to acidic chyme, it stimulates the pancreas to release bicarbonate-rich fluid to neutralize the acid and inhibits gastric acid secretion. • Cholecystokinin (CCK): Released by the duodenum in response to fats and proteins, it stimulates the gallbladder to contract and release bile, and the pancreas to release digestive enzymes (e.g., amylase, lipase, proteases). It also promotes satiety. • Gastric Inhibitory Peptide (GIP): Released by the small intestine in response to glucose and fat, it inhibits gastric motility and acid secretion, and stimulates insulin release. • Motilin: Stimulates gastric and intestinal motility, particularly during fasting, to clear the digestive tract. 5. a) Explain what you understand by the following: i) Vernalization. Vernalization is the process by which exposure to a period of cold temperature is required for a plant to undergo flowering or to accelerate flowering. This physiological requirement ensures that plants flower at an appropriate time of year, typically after winter, when conditions are more favorable for reproduction. Many temperate zone plants, especially biennials and winter annuals, exhibit vernalization. b) Describe how photoperiodism is experienced in i) Flowering plants In flowering plants, photoperiodism is the physiological response to the relative lengths of day and night, which influences flowering time. Plants are categorized as short-day plants (flower when day length is shorter than a critical period), long-day plants (flower when day length is longer than a critical period), or day-neutral plants (flowering is not affected by day length). The perception of day/night length occurs in the leaves, involving the pigment phytochrome, which then signals the shoot apical meristem to initiate flowering. ii) Animals In animals, photoperiodism refers to the physiological and behavioral responses to changes in day length, which serve as a reliable environmental cue for seasonal changes. These responses include seasonal breeding, migration, hibernation, changes in fur color, and molting. The pineal gland, influenced by light perceived by the eyes, secretes melatonin, which plays a key role in mediating these photoperiodic responses by affecting hormonal cycles and biological rhythms. c) Describe the mechanism of clotting in the human blood Blood clotting (hemostasis) is a complex process that prevents excessive blood loss after injury. It involves several steps: 1. Vascular Spasm: Immediately after injury, the damaged blood vessel constricts to reduce blood flow. 2. Platelet Plug Formation: Platelets adhere to the exposed collagen in the damaged vessel wall, become activated, release chemicals (e.g., ADP, thromboxane A2) that attract more platelets, and aggregate to form a temporary platelet plug. 3. Coagulation (Blood Clotting): This involves a cascade of enzymatic reactions leading to the formation of a fibrin clot. • Intrinsic pathway (