Which of the following describes a low gradient stream?

A stream with a gentle slope and slow-moving water

A stream with a steep slope and fast-moving water

A stream with a winding path and strong current

A stream with no slope and stagnant water

How does a low gradient stream differ from a high gradient stream?

A low gradient stream has a gentle slope, while a high gradient stream has a steep slope

A low gradient stream has no slope, while a high gradient stream has a winding path

A low gradient stream has a steep slope, while a high gradient stream has a gentle slope

A low gradient stream has fast-moving water, while a high gradient stream has slow-moving water

What is the primary factor that determines the gradient of a stream?

The change in elevation over a given distance

The presence of vegetation along the stream

The average width of the stream channel

The volume of water flowing through the stream

What is the main cause of the formation of low gradient streams?

Erosion caused by weathering and the movement of water over time

What is the primary factor that influences the velocity of water in a low gradient stream?

The gradient or slope of the stream

The presence of rocks in the stream

The width of the stream channel

What causes high gradient streams to have a turbulent flow?

Obstacles and irregularities in the streambed

High and Low gradient streams

PHOTOSYNTHESIS LIGHT DEPENDENT REACTION 1. Photosystem II (PSII) – Light Absorption & Water Splitting • Light energy (photons) excites electrons in chlorophyll molecules. • These high-energy electrons leave PSII and are passed into the electron transport chain (ETC). • Meanwhile, water molecules are split (photolysis) into: o O₂ (released as a by-product into the atmosphere) o H⁺ ions (protons, which build up inside the thylakoid) o Electrons (e⁻), which replace the ones lost by PSII. 2. Electron Transport Chain (ETC) • Excited electrons move through protein carriers embedded in the thylakoid membrane. • As they move, their energy pumps H⁺ ions into the thylakoid space, creating a proton gradient (high H⁺ inside, low outside). 3. ATP Production (ATP Synthase) • The buildup of H⁺ ions acts like a “waterfall” of potential energy. • These protons flow back across the membrane through ATP synthase, a protein complex that acts like a turbine. • This flow drives the conversion of ADP + Pi → ATP, which provides energy for the Calvin cycle. 4. Photosystem I (PSI) • Electrons arriving from the ETC enter PSI. • Sunlight excites them again, boosting them to a higher energy level. 5. NADPH Production • The energized electrons are transferred to NADP⁺. • Along with a proton (H⁺), this forms NADPH, another energy carrier. • NADPH is then delivered to the Calvin cycle to help build glucose. End Products of Light-Dependent Reactions: • ATP (energy source for Calvin cycle) • NADPH (reducing power for glucose synthesis) • O₂ (released into the atmosphere as waste) Light-Independent Reactions (Calvin Cycle) • These reactions do not directly require sunlight. • They occur in the stroma of the chloroplast (the fluid-filled space surrounding the thylakoids). • The inputs are ATP and NADPH (from light-dependent reactions) and CO₂ (from the atmosphere). • The outputs are glucose (C₆H₁₂O₆) and other carbohydrates. Think of the Calvin cycle as a factory that uses the energy and “raw materials” made in Stage I (ATP & NADPH) to build sugars. The 3 Main Steps of the Calvin Cycle 1. Carbon Fixation • CO₂ from the atmosphere enters the chloroplast and diffuses into the stroma. • Each CO₂ molecule attaches to a 5-carbon sugar called RuBP (ribulose-1,5-bisphosphate). • This reaction is catalyzed by the enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase — the most abundant enzyme on Earth!). • The result is a short-lived 6-carbon compound, which immediately splits into two 3-carbon molecules called 3-PGA (3-phosphoglycerate). Summary: CO₂ + RuBP → 2 × 3-PGA 2. Reduction Phase • The 3-PGA molecules are “energized” and converted into G3P (glyceraldehyde-3-phosphate), a more energy-rich 3-carbon sugar. • This transformation requires: o ATP (provides energy) o NADPH (provides high-energy electrons and hydrogen atoms). • Some of the G3P molecules will eventually be combined to form glucose and other sugars. Summary: 3-PGA + ATP + NADPH → G3P 3. Regeneration of RuBP • Not all G3P molecules leave the cycle. Most of them are used to regenerate RuBP so the cycle can continue. • This regeneration also requires ATP. • For every 3 turns of the cycle, 5 G3P molecules are recycled to regenerate 3 molecules of RuBP. Summary: G3P + ATP → RuBP The Full Cycle Balance • To make one G3P molecule that can exit the cycle (and later form glucose), the cycle must run 3 times, fixing 3 molecules of CO₂. • To make one glucose molecule (C₆H₁₂O₆), the cycle must run 6 times (since glucose needs 6 carbon atoms). Inputs (for 1 glucose): • 6 CO₂ • 18 ATP • 12 NADPH Outputs: • 1 glucose (C₆H₁₂O₆) • 18 ADP + 18 Pi • 12 NADP⁺ Day vs Night Clarification • The Calvin Cycle is called light-independent, but that doesn’t mean it only happens at night. • It usually happens during the day because it depends on ATP and NADPH, which are only produced in light-dependent reactions (when sunlight is available). Simplified Analogy • Carbon fixation = The factory brings in CO₂ as raw material. • Reduction = Workers use energy (ATP & NADPH) to shape the raw material into useful products (G3P). • Regeneration = Some products are recycled to keep the factory running (RuBP is re-formed). • Output = After enough cycles, the factory produces glucose, the “food” of the plant.

LESSON 4. Cellular Respiration • Define cellular respiration • Identify the stages of clan respiration You have just learned how the energy from the sun is captured, processed, and stored in the form of glucose. Cellular respiration, another important life process, is the means by which cells release the stored energy in glucose to make adenosine triphosphate (ATP). The primary goal of this life process is to convert stored energy into usable form, such as ATP, for the cells to carry out their functions. Cellular respiration involves several chemical reactions. The reactions can be summed up in the following equation: C6 H12 O6 + 602 ----- 6 CO₂ +6H₂O + ATP Glucose oxygen carbon dioxide water energy Aerobic respiration reactions, or cellular respiration that takes place in the presence of oxygen, can be grouped into three stages glycolysis, Krebs cycle, and electron transport chain (ETC). Stage 1: Glycolysis Glycolysis is the process that breaks down one molecule of 6-C glucose into 3-C pyruvates or pyruvic acids. It also releases four molecules of ATP. This process occurs in the cytoplasm of the cell. The following is the step-by-step process of glycolysis. Take note that several enzymes are involved in this process. 1. The first step of glycolysis requires energy. It can only proceed when the two ATP molecules donate energy to the glucose by transferring a phosphate group with the help of an enzyme, producing glucose 6-phosphate 2. Then, a specific enzyme promotes the rearrangement of the atoms, producing the fructose 6-phosphate. 3. The action of the enzyme in step 2 promotes the transfer of a phosphate group from another ATP molecule, forming fructose 1,6-bisphosphate. 4. The resulting fructose 1,6-bisphosphate molecules, with the help of another enzyme, splits into two molecules, each with three carbon backbones. These two sugars are dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. 5. Another important enzyme then rapidly interconverts the molecules of dihydro-xyacetone phosphate and glyceraldehyde 3-phosphate. This produces two molecules of glyceraldehyde 3-phosphate or 3-phosphoglyceraldehyde (PGAL) 6. The succeeding step involves another enzyme-mediated action. The hydrogen (H) from PGAL is transferred to the oxidizing agent, nicotinamide adenine dinucleotide (NAD), which forms NADH. A phosphate (P) is also added from the cytosol of the cell to oxidize the two molecules of PGAL, forming two 1.3-bisphosphoglycerate. 7. A phosphate (P) from 1,3-biphosphoglycerate is transferred to ADP to form ATP. This happens for each of the two 1,3-bisphosphoglycerate. resulting to a yield of two ATP and two 3-phosphoglycerate molecules. 8. A phosphate is transferred from 3-phosphoglycerate molecules from the third carbon to the second carbon, forming 2-phosphoglycerate molecules A hydrogen atom and a hydroxyl ((OH) group is released, which then combines to form water (H2O). The removal of H2O from 2-phosphoglycerate results in the formation of 2- phosphoglycerate molecules. 9. A hydrogen atom and a hydroxyl ((OH) group is released, which then combines to form water (H2O). The removal of H2O from 2-phosphoglycerate results in the formation of two phosphoenolpyruvic acid (PEP) 10. Phosphate (P) from PEP is transferred to ADP (and forms ATP) and the final product, pyruvic acid. This reaction yields two molecules of pyruvic acid and two ATP molecules In summary, a single glucose molecule that undergoes the process of glycolysis produces two molecules of pyruvic acid, four molecules of ATP, two molecules of NADEL and two molecules of H.O. However, only two molecules of ATP are counted as net products since two molecules of ATP are spent throughout the process. Stage II: Krebs Cycle The Krebs cycle, named after its proponent Sir Hans Adolf Krebs, is a cyclical series of enzyme-controlled reactions. This stage of cellular respiration occurs in the matrix of the mitochondria. It is sometimes. called the citric acid cycle (CAC) since it produces citric acid. Citric acid contains three carboxyl (COOH) groups; hence, it is also called the tricarboxylic acid cycle (TCA). This requires the pyruvic acids produced during glycolysis. The main function of this cycle is to produce high-energy-yielding molecules, namely, NADH and flavin adenine dinucleotide (FADH) that will later on be used in the electron transport chain reaction. Figure 6-7. Summary of glycolysis and corresponding products in each reaction presented (See Appendix F on page 285 for an enlarged and complete version of the image.) An initial process is needed for the Krebs cycle to begin. As a pyruvate molecule from glycolysis enters the mitochondrion, it undergoes an important preliminary ate to form acetyl-CoA reaction. Coenzyme-A (COA) combines with pyruvate help of an enzymatic complex. This conversion also produces CO, and NADH. The Krebs cycle is summarized as follows. Take note that several enzymes are involved in this process. 1. The Krebs cycle technically begins when the acetyl-CoA combines with oxaloacetic acid (OAA), a 4-C molecule, to produce citric acid, a 6-C molecule. 2. With the aid of an enzyme, the citric acid now goes through a series of reactions that releases energy. Water molecule is removed from the citric acid and is returned in a different location. The-OH group is repositioned, forming the molecule isocitrate. 3. Isocitrate is then oxidized, forming the a-ketoglutarate, a 5-C molecule. The byproducts of this reaction are NADH and CO, 4 The a-ketoglutarate loses its CO, and a coenzyme-A is added in its place. The decarboxylation occurs with the help of NAD, which then becomes NADH. The resulting molecule is called succinyl-CoA. 5. Succinyl-CoA is converted into succinate. Also in this reaction, a molecule of guanosine triphosphate (GTP) is synthesized. The GTP molecule has similar structure and energy properties to that of ATP and is used by cells the same way. The free phosphate group attacks the succinyl-CoA molecule, which detaches the COA. Then, phosphate is attached to GDP to come up with GTP, similar to the process that occur in ATP synthesis (from ADP to ATP). 6. Two hydrogens are removed from succinate, A molecule of flavin adenine dinucleotide (FAD), a coenzyme similar to NAD, is reduced to FADH, as it takes the hydrogens from the succinate. This reaction produces the fumarate. 7. Fumarate is then converted into malate as the addition of a water molecule is catalyzed. The final reaction is the regeneration of oxaloacetate. The resulting byproduct of this regeneration is NADH Recall that two pyruvate molecules were produced during glycolysis, causing the Krebs cycle to turn twice. Each tuts produces three molecules of NADH, single ATH one FADIH, and the by-product CO, which is exhaled. Stage III: Electron Transport Chain The electron transport chain (ETC) is a series of photon pumps on the inner membrane of the mitochondrion. Electron transport is the last stage of the cellular respiration. In this stage, the energy from NADH and FADH, from the Krebs cycle is transferred to ADP to produce ATP. This process is generally known as oxidative phosphorylation. This energy coupling mechanism in the cell was revealed by the work of Peter stored energy in the form of proton (1) gradient to phosphorylate (add phosphate) ADP and produce ATP. The pumping of hydrogen sons across the inner membrane creates higher concentration ions in the inner membrane than on the outside of the membrane. This chemiosmotic gradient causes the ions to flow back across the membrane where the concentration of ions is lower. ATP synthase lined in the matrix serve as a channel protein, helping the ions to move across the membrane. The chemiosmotic gradient powers the phosphorylation of ADP to ATP, which also occurs in the ATP synthase. After passing through the ETC, the oxygen, being the final hydrogen acceptor, combines with two electrons and two protons, forming a water molecule. Water is a by-product of cellular respiration and is excreted. MINI TEST 6-3 1. Which energy-releasing pathway yields the most ATF in each glucose molecule? 2. Briefly describe the two stages of aerobic respiration that follow glycolysis: (a) Krebs cycle (b) Electron transport chain Anaerobic Respiration Most cells carry out arrobic respiration when oxygen is present. Aerobic respiration is an efficient process that yields a lot of ATP. However, many organisms thrive in mud, marshes, animal gut, canned goods, sewage treatment pond, and deep oceans where oxygen is scarce. Organisms that can live without oxygen are called anaerobes. Cellular respiration that proceeds without the presence of oxygen is called anaerobic respiration. In the event that the oxygen supply becomes low, aerobic cells also perform fermentation and lactic acid fermentation anaerobic pathways. There are two common anaerobic pathways in these cells, alcoholic fermentation and lactic acid fermentation. In alcoholic fermentation, ethyl alcohol and carbon dioxide are produced by some cells using the pyruvate from glycolysis. Each pyruvate molecule is rearranged into acetaldehyde and carbon dioxide, which is eventually released. NADII gives up electrons to acetaldehyde to form ethanol Fermentation is widely used in the industry. Yeast, a fungus used in making bread. can undergo anaerobic respiration. Bakers aux sugar, flour, water, and yeast to form the bread dough. The dough rises due to the carbon dioxide and alcohol released by the yeast cells trapped in air bubbles. Beer and wine manufacturers, we yeast to ferment the sugars in wheat and grape juice, forming alcoholic beverages such as beer and wine. In some cells, glycolysis produces two pyruvates, two NADH molecules, and two ATP molecules. Pyruvate itself becomes the final acceptor of the electrons from the NADH that produces the final product: lactate. Oftentimes, this product is called lactic acid. Human skeletal muscles can carry out fermentation when the blood cannot supply the cells with adequate oxygen during strenuous activities. When lactic acid builds up in the muscles, fatigue, burning sensation, and cramps result. Lactic acid will continue to build up until there is adequate supply of oxygen. Lactic acid is then converted back into pyruvate in the liver. Muscles also restore normal functions. Have you ever wondered why milk or cream turns sour after some time? Bacterial cells that undergo fermentation are responsible in producing lactate that turns the milk sour. These bacteria are used in manufacturing yogurt and sour milk products. Fermentation pathways do not breakdown and utilize the glucose completely. ATP is no longer produced beyond the process of glycolysis. Thus, energy produced is just enough for some single-celled organisms, or the energy can only be used by multicellular organisms for a short period.

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