Plant Biology - Energy and Plant Metabolism - Quick Guides

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Study GuidePlant Biology–Energy and Plant Metabolism1. Chemistry of Energy UseAll living organisms are constantly carrying out chemical reactions. Thesum of all these reactionsiscalledmetabolism. These reactions do not happen randomly. Instead, they follow specific step-by-step routes known asmetabolic pathways.Cells are able to carry out metabolism because they areseparate, organized systems. Each cell issurrounded by a membrane that separates it from the outside environment. This separation allows thecell to carefully control what enters, what leaves, and what reactions take place inside.To manage these reactions, cells useenzymes. Enzymes act like helpers that speed up reactionsand make sure they happen at the right time. Cells also useenergy carriersto move energy fromone part of the cell to another.Metabolic reactions are connected.Energy-releasing reactions (exergonic)provide energy forenergy-requiring reactions (endergonic). In this way, the cell efficiently uses energy withoutwasting it.1.1Oxidation–Reduction (Redox) ReactionsMost energy changes in plants and other organisms happen through special chemical reactions calledoxidation–reduction reactions, orredox reactions.What Is Oxidation?Oxidationoccurs when an atom or moleculeloses electrons. When this happens, the molecule alsoloses energy. The term “oxidation” is used because oxygen is often the substance that accepts theseelectrons.What Is Reduction?Reductionalways happens at the same time as oxidation. It occurs when an atom or moleculegainselectrons. Gaining electrons means gaining energy, so reduced molecules store more energy thanoxidized ones.A helpful way to remember this is:•Oxidation = loss of electrons•Reduction = gain of electrons

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Study Guide1.2Role of Hydrogen in Living CellsInside living organisms, electrons usually do not move by themselves. They are commonly transferredalong with aproton, forming ahydrogen atom.Because of this:•Oxidationoften meanslosing hydrogen atoms•Reductionoften meansgaining hydrogen atomsThis movement of hydrogen plays a key role in how cells store and release energy.1.3Energy Balance in Living SystemsThe molecules inside cells are usuallyreduced, meaning they are rich in electrons and contain a lotof stored energy. Their chemical bonds are relatively weak.In contrast, most molecules in the surrounding environment areoxidized, meaning they have fewerelectrons and stronger bonds.Living organisms mustconstantly add energyto their systems to stay organized. Without this energyinput, they would naturally move toward disorder, as described by theSecond Law ofThermodynamics. Continuous energy use helps organisms stay alive, structured, and functional.1.4Photosynthesis and RespirationBothphotosynthesisandcellular respirationare redox reactions.•Photosynthesisrequires energy to occur, making it anendergonic process. It storesenergy by reducing molecules.•Respirationreleases energy, making it anexergonic process. It releases energy byoxidizing molecules.Together, these processes allow organisms to capture, store, and use energy efficiently.

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Study Guide2. Energy Regulators: Enzymes and ATPLiving cells constantly carry out chemical reactions. These reactions release energy—but if all thatenergy were released at once, it would mostly turn into heat and damage the cells. To avoid this,organisms use special systems thatcontrol how energy is released and used step by step. Two ofthe most important energy regulators areenzymesandATP.2.1Enzymes: The Cell’s Speed ControllersWhy Enzymes Are NeededChemical reactions need a certain amount of starting energy, calledactivation energy. Without help,many reactions would happen too slowly—or not at all.Enzymes solve this problem.•Theylower activation energy•They allow reactions to happenquickly and safely•They prevent energy from being released all at once as heat2.2How Enzymes WorkEnzymes arebiological catalysts. This means:•They speed up reactions•They arenot used up or changedduring the reactionThey work by temporarily attaching to the reacting molecules (calledsubstrates). This weakens thechemical bonds in the substrate, making it easier for the reaction to occur.2.3Structure and Types of Enzymes•Almostall enzymes are proteins•Most enzymes need helpers calledcofactorsoThese can bemetal ions(like Mg²⁺or Fe²⁺)

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Study GuideoOrorganic moleculescalledcoenzymesEnzymes usually work inchains of reactions, where:•Each enzyme controlsonly one step•That’s why cells needthousands of different enzymesIf the same type of reaction happens in two different processes, cells usesimilar but differentenzymescalledisozymes.Each isozyme is specially adapted for its own process.2.4Models Explaining Enzyme ActionThere are two main models:Lock-and-Key Model•The enzyme has a specificactive site•The substrate fits exactly into this site•Like a key fitting into a lockInduced-Fit Model (More Accurate)•The active site isflexible•When the substrate binds, the enzymechanges shape slightly•This creates a tighter fit and helps start the reactionEven though the shape can adjust, enzyme action ishighly specific:one enzyme works with one specific substrate.2.5ATP: The Energy Currency of the CellWhat Is ATP?ATP stands foradenosine triphosphate.It is themain energy carrierin all living cells—just like money is used to buy things in daily life.

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Study GuideATP is made of:•Adenine(a nitrogen base)•Ribose(a sugar)•Three phosphate groups2.6Why ATP Stores EnergyThe energy of ATP comes from the bonds between its phosphate groups.•These bonds areweak and easy to break•When thelast phosphate bond breaks, energy is releasedThis process is calledhydrolysisand is helped by an enzyme calledATPase.2.7ATP Breakdown and RechargeStep by step:1.ATP → ADP + Pi + energy2.(one phosphate is removed)3.Sometimes:oADP → AMP + Pi + more energyAfter releasing energy:•ADP is recharged back into ATP•This happens duringcellular respiration•ATP is also made duringphotosynthesisThis constant breaking and rebuilding keeps energy flowing in the cell.

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Study Guide2.8Limits of ATP and Other Energy StoresATP is perfect for:•Quick, short-term energy needsBut it isnot suitable for:•Long-term energy storage•Processes that need very large amounts of energyFor those needs, plants use:•Starch and lipids→ long-term storage•Sucrose→ transport and larger energy demandsKey Takeaway•Enzymescontrolhow fastandhow safelyreactions happen.•ATPprovidesusable energyexactly when and where cells need it.•Together, they make sure energy is releasedefficiently, gradually, and productively—keeping cells alive and working smoothly.3. Movement of Materials in CellsCells live in a watery environment. Almost everything that happens inside a cell takes place in water.This watery mixture is called asolution.•Wateris thesolvent(the liquid doing the dissolving).•The substances dissolved in water are calledsolutes.Solutes include:•Small particles like hydrogen ions (H⁺)•Ions such as sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺)•Organic molecules like sugar (sucrose)•Both polar and non-polar moleculesThe chemical nature of these solutes determines how easily they can move across cell membranes.

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Study Guide3.1Diffusion: Movement from High to LowAll molecules havekinetic energy, which means they are always moving randomly. Because of thisconstant movement, molecules spread out over time.What is diffusion?Diffusionis the net movement of particles from an area where they are more concentrated to an areawhere they are less concentrated. This movement happensdown a concentration gradient.Key points to remember:•Thesteeperthe concentration gradient, thefasterdiffusion happens.•Diffusion continues until the particles are evenly spread out.•Diffusion does not need energy—it happens naturally.•Most substances move in and out of cells by diffusion.•However, diffusion is slow and not useful for moving materials over long distances.3.2Osmosis: Diffusion of WaterOsmosisis a special type of diffusion that involves onlywater.What makes osmosis different?Osmosis occurs across aselectively permeable membrane. This membrane allows water to passthrough but blocks most solutes.Water moves:•From an area withmore free water(fewer solutes)•To an area withless free water(more solutes)In other words, water moves fromhigh water concentration to low water concentration, or fromhigh pressure to low pressure.

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