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Plant Biology - Energy and Plant Metabolism

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    Study Guide Plant Biology – Energy and Plant Metabolism 1. Chemistry of Energy Use A ll living organisms are constantly carrying out chemical reactions. The sum of all these reactions is called metabolism . These reactions do not happen randomly. Instead, they follow specific step - by - step routes known as metabolic pathways . Cells are able to carry out metabolism because they are separate, organized systems . Each cell is surrounded by a membrane that separates it from the outside environment. This separation allows the cell to carefully control what enters, what leaves, and what reactions take place inside. To manage these reactions, cells use enzymes . Enzymes act like helpers that speed up reactions and make sure they happen at the right time. Cells also use energy carriers to move energy from one part of the cell to another. Metabolic reactions are connected. Energy - releasing reactions (exergonic) provide energy for energy - requiring reactions (endergonic) . In this way, the cell efficiently uses energy without wasting it. 1.1 Oxidation – Reduction (Redox) Reactions Most energy changes in plants and other organisms happen through special chemical reactions called oxidation – reduction reactions , or redox reactions . What Is Oxidation? Oxidation occurs when an atom or molecule loses electrons . When this happens, the molecule also loses energy. The term “oxidation” is used because oxygen is often the substance that accepts these electrons. What Is Reduction? Reduction always happens at the same time as oxidation. It occurs when an atom or molecule gains electrons . Gaining electrons means gaining energy, so reduced molecules store more energy than oxidized ones. A helpful way to remember this is: • Oxidation = loss of electrons • Reduction = gain of electrons

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    Study Guide 1.2 Role of Hydrogen in Living Cells Inside living organisms, electrons usually do not move by themselves. They are commonly transferred along with a proton , forming a hydrogen atom . Because of this: • Oxidation often means losing hydrogen atoms • Reduction often means gaining hydrogen atoms This movement of hydrogen plays a key role in how cells store and release energy. 1.3 Energy Balance in Living Systems The molecules inside cells are usually reduced , meaning they are rich in electrons and contain a lot of stored energy. Their chemical bonds are relatively weak. In contrast, most molecules in the surrounding environment are oxidized , meaning they have fewer electrons and stronger bonds. Living organisms must constantly add energy to their systems to stay organized. Without this energy input, they would naturally move toward disorder, as described by the Second Law of Thermodynamics . Continuous energy use helps organisms stay alive, structured, and functional. 1.4 Photosynthesis and Respiration Both photosynthesis and cellular respiration are redox reactions. • Photosynthesis requires energy to occur, making it an endergonic process . It stores energy by reducing molecules. • Respiration releases energy, making it an exergonic process . It releases energy by oxidizing molecules. Together, these processes allow organisms to capture, store, and use energy efficiently.

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    Study Guide 2. Energy Regulators: Enzymes and ATP Living cells constantly carry out chemical reactions. These reactions release energy — but if all that energy were released at once, it would mostly turn into heat and damage the cells. To avoid this, organisms use special systems that control how energy is released and used step by step . Two of the most important energy regulators are enzymes and ATP . 2.1 Enzymes: The Cell’s Speed Controllers Why Enzymes Are Needed Chemical reactions need a certain amount of starting energy, called activation energy . Without help, many reactions would happen too slowly — or not at all. Enzymes solve this problem. • They lower activation energy • They allow reactions to happen quickly and safely • They prevent energy from being released all at once as heat 2.2 How Enzymes Work Enzymes are biological catalysts . This means: • They speed up reactions • They are not used up or changed during the reaction They work by temporarily attaching to the reacting molecules (called substrates ). This weakens the chemical bonds in the substrate, making it easier for the reaction to occur. 2.3 Structure and Types of Enzymes • Almost all enzymes are proteins • Most enzymes need helpers called cofactors o These can be metal ions (like Mg² ⁺ or Fe² ⁺ )

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    Study Guide o Or organic molecules called coenzymes Enzymes usually work in chains of reactions , where: • Each enzyme controls only one step • That’s why cells need thousands of different enzymes If the same type of reaction happens in two different processes, cells use similar but different enzymes called isozymes . Each isozyme is specially adapted for its own process. 2.4 Models Explaining Enzyme Action There are two main models: Lock - and - Key Model • The enzyme has a specific active site • The substrate fits exactly into this site • Like a key fitting into a lock Induced - Fit Model (More Accurate) • The active site is flexible • When the substrate binds, the enzyme changes shape slightly • This creates a tighter fit and helps start the reaction Even though the shape can adjust, enzyme action is highly specific : one enzyme works with one specific substrate. 2.5 ATP: The Energy Currency of the Cell What Is ATP? ATP stands for adenosine triphosphate . It is the main energy carrier in all living cells — just like money is used to buy things in daily life.

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    Study Guide ATP is made of: • Adenine (a nitrogen base) • Ribose (a sugar) • Three phosphate groups 2.6 Why ATP Stores Energy The energy of ATP comes from the bonds between its phosphate groups. • These bonds are weak and easy to break • When the last phosphate bond breaks , energy is released This process is called hydrolysis and is helped by an enzyme called ATPase . 2.7 ATP Breakdown and Recharge S tep by step: 1. ATP → ADP + Pi + energy 2. (one phosphate is removed) 3. Sometimes: o ADP → AMP + Pi + more energy After releasing energy: • ADP is recharged back into ATP • This happens during cellular respiration • ATP is also made during photosynthesis This constant breaking and rebuilding keeps energy flowing in the cell.

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    Study Guide 2.8 Limits of ATP and Other Energy Stores ATP is perfect for: • Quick, short - term energy needs But it is not suitable for : • Long - term energy storage • Processes that need very large amounts of energy For those needs, plants use: • Starch and lipids → long - term storage • Sucrose → transport and larger energy demands Key Takeaway • Enzymes control how fast and how safely reactions happen. • ATP provides usable energy exactly when and where cells need it. • Together, they make sure energy is released efficiently, gradually, and productively — keeping cells alive and working smoothly. 3. Movement of Materials in Cells Cells live in a watery environment. Almost everything that happens inside a cell takes place in water. This watery mixture is called a solution . • Water is the solvent (the liquid doing the dissolving). • The substances dissolved in water are called solutes . 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 molecules The chemical nature of these solutes determines how easily they can move across cell membranes.

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    Study Guide 3.1 Diffusion: Movement from High to Low All molecules have kinetic energy , which means they are always moving randomly. Because of this constant movement, molecules spread out over time. What is diffusion? Diffusion is the net movement of particles from an area where they are more concentrated to an area where they are less concentrated. This movement happens down a concentration gradient . Key points to remember: • The steeper the concentration gradient, the faster diffusion 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. 3.2 Osmosis: Diffusion of Water Osmosis is a special type of diffusion that involves only water . What makes osmosis different? Osmosis occurs across a selectively permeable membrane . This membrane allows water to pass through but blocks most solutes. Water moves: • From an area with more free water (fewer solutes) • To an area with less free water (more solutes) In other words, water moves from high water concentration to low water concentration , or from high pressure to low pressure .

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