Botany: Metabolism, Respiration, Photosynthesis, and Water Transport

Activation Energy

The minimum energy required for a chemical reaction to begin; enzymes lower this energy.

Active Site

The region on an enzyme where the substrate binds and the reaction occurs.

Adenosine Triphosphate (ATP)

The main energy currency of the cell; releases energy when hydrolyzed to ADP.

Anabolic

Metabolic reactions that build complex molecules from simpler ones; require energy.

Catabolic

Reactions that break down complex molecules into simpler components; release energy.

Catalysts

Substances that speed up chemical reactions without being consumed in the process.

Coenzyme

An organic molecule (often vitamin-based) that assists enzymes in catalyzing reactions.

Feedback Inhibition

A regulatory mechanism where the end product of a pathway inhibits an earlier enzyme.

Free Energy

The energy in a system available to perform work; determines reaction spontaneity.

Hydrolysis Reaction

A reaction that breaks bonds using water, often releasing energy.

Intermediates

Compounds formed in the middle steps of a metabolic pathway.

Kinetic Energy

The energy of motion; increases with temperature and molecule speed.

Metabolic Pathway

A sequence of enzyme-controlled reactions converting substrates into final products.

Nicotinamide Adenine Dinucleotide Phosphate (NADPH)

An electron carrier that provides reducing power for biosynthesis.

Potential Energy

Stored energy due to an object's position or structure (e.g., chemical bonds).

Substrates

The reactant molecules that bind to an enzyme's active site.

Aerobic Respiration

Respiration that uses oxygen to completely oxidize glucose into CO2 and H2O, producing large amounts of ATP.

Alcoholic Fermentation

Anaerobic process where pyruvate is converted into ethanol and CO.

Anaerobic Respiration

Respiration that occurs without oxygen; produces less ATP and often generates alcohol or lactic acid.

Chemiosmotic Theory

Explains how ATP is synthesized using a proton gradient across membranes during electron transport.

Glycolysis

The first stage of respiration; breaks glucose into two pyruvate molecules, forming ATP and NADH.

Krebs Cycle (TCA Cycle)

A cyclic series of reactions in mitochondria that oxidizes acetyl-CoA to CO2 while producing NADH, FADH2, and ATP.

Oxidative Phosphorylation

The production of ATP using energy from electron transport and a proton gradient.

Terminal Electron Transport Chain

The final stage of respiration where electrons are transferred to oxygen to form water.

Tricarboxylic Acid (TCA) Cycle

Another name for the Krebs cycle, involving three carboxylic acid intermediates.

Absorption Spectrum

A graph showing which wavelengths of light a pigment absorbs.

Ribulose Bisphosphate Carboxylase/Oxygenase (Rubisco)

The enzyme that fixes CO2 in the Calvin cycle.

Carotenoids

Accessory pigments that absorb light in other wavelengths and protect chlorophyll.

Chemosynthesis

The synthesis of organic compounds using energy from chemical reactions instead of sunlight.

Compensation Point

The CO2 level at which photosynthesis and respiration rates are equal.

Crassulacean Acid Metabolism (CAM)

Photosynthetic process in which plants fix CO2 at night and use it during the day.

Cyclic Electron Transport

A light reaction pathway that produces ATP but not NADPH.

Electromagnetic Energy Spectrum

The range of all types of electromagnetic radiation, including visible light.

Grana

Stacks of thylakoid membranes in chloroplasts where light reactions occur.

Light-Harvesting Complexes

Groups of pigments that capture and transfer light energy to reaction centers.

Noncyclic Electron Transport

The main light reaction pathway that produces both ATP and NADPH.

Noncyclic Photophosphorylation

The process of forming ATP and NADPH using light energy and water.

Photons

Discrete packets of light energy that excite electrons during photosynthesis.

Photophosphorylation

Formation of ATP using energy from light during photosynthesis.

Photosystems I and II

Protein-pigment complexes that capture light and drive electron transport in photosynthesis.

Spectrophotometer

Instrument used to measure light absorption by pigments.

Stroma Lamellae

Membrane structures connecting grana and helping distribute energy in chloroplasts.

Thylakoids

Flattened sacs in chloroplasts containing chlorophyll; sites of light reactions.

Adhesion

When water sticks to other surfaces, like the walls of plant cells or tubes.

Apoplast

The spaces between cell walls in a plant where water can move freely without entering the cells.

Capillary Forces

The ability of water to move upward in narrow tubes (like in plant stems) because of cohesion and adhesion.

Casparian Strip

A waterproof barrier in the root that forces water to go through cell membranes before entering the plant's xylem.

Cohesion

When water molecules stick to each other because of hydrogen bonds.

Differentially Permeable

A membrane that allows some substances (like water) to pass through but blocks others.

Guttation

The release of small drops of water from the edges of leaves, usually seen in the morning.

Hydathodes

Tiny openings on leaves that let out water droplets during guttation.

Osmosis

The movement of water through a membrane from an area of low solute concentration to high solute concentration.

Osmotic Pump

The process that helps move water in or out of plant cells through osmosis, driven by differences in water concentration.

Symplast

The continuous path of cytoplasm between plant cells connected by small channels called plasmodesmata.

Translocation

The movement of food (like sugars) from the leaves to other parts of the plant through the phloem.

Transpiration

The loss of water vapor from a plant's leaves through tiny pores called stomata.

Turgor Pressure

The pressure of water inside a plant cell that keeps it firm and upright.

Water Potential

A measure of how likely water is to move from one place to another; water moves from high to low potential.

What is the role of enzymes in cellular chemical reactions?

Enzymes act as biological catalysts that speed up chemical reactions by lowering the activation energy required. Without enzymes, most cellular reactions would proceed too slowly to sustain life.

How do enzymes interact with substrates at the active site?

Enzymes have specific active sites—grooves or pockets—where substrates bind through weak forces. The shape and charge of the active site complement the substrate, forming an enzyme-substrate complex that facilitates the reaction.

why do cells require different enzymes

Cells require thousands of enzymes because each enzyme catalyzes a specific reaction. Different biochemical processes in a cell each need their own unique enzyme.

What is a metabolic pathway and how are reactions linked within it?

A metabolic pathway is a series of enzyme-catalyzed reactions where the product of one reaction serves as the substrate for the next. These pathways are interconnected, forming networks that control synthesis and breakdown of cellular molecules.

What is intermediary metabolism?

Intermediary metabolism refers to all the interconnected metabolic pathways within a cell that transform intermediate compounds into various products.

significance of branch points ?

Branch points in pathways are key intermediates used by multiple enzymes to produce different products. They allow metabolic flexibility and regulation of cellular resources.

what is a chemical reaction, how does it occur in cells ?

A chemical reaction involves breaking and forming covalent bonds, rearranging atoms into new configurations. In cells, these are biochemical reactions controlled by enzymes.

what is activation energy, what are its effects?

Activation energy is the energy needed to form an activated complex so the reaction can proceed. High activation energy slows reactions; enzymes reduce it, increasing reaction speed.

how does temp affect the rate of chemical reactions ?

Higher temperatures increase the kinetic energy of molecules, making collisions between substrates more frequent and energetic—thus speeding up reaction rates—until excessive heat damages enzymes.

What are cofactors and how do they assist enzyme function?

Cofactors are non-protein substances required for enzyme activity; they may be metal ions or organic molecules.

cofactor vs coenzyme

A coenzyme is a specific type of cofactor that is organic (often vitamin-derived) and transfers electrons or atoms between reactions.

what is free energy, how does it determine direction ?

Free energy is the portion of a system's energy available to do work. Reactions proceed spontaneously in the direction that decreases free energy.

How do coupled reactions help drive uphill reactions in cells?

Coupled reactions pair an energy-releasing (downhill) reaction with an energy-requiring (uphill) one, allowing the latter to proceed.

what role does atp play ?

ATP is the primary energy carrier in cells. Its hydrolysis releases free energy that drives processes like active transport, synthesis, and movement.

How does the oxidation of NADH and NADPH contribute to cellular energy?

NADH and NADPH oxidation releases large amounts of energy used to synthesize ATP and other macromolecules. NADPH mainly powers biosynthetic reactions.

What is feedback inhibition and how does it regulate enzyme activity?

Feedback inhibition occurs when the end product of a metabolic pathway inhibits the first enzyme in the sequence, preventing overproduction.

How does the concentration of a product influence its own synthesis in a cell?

When product concentration increases, it inhibits its own synthesis; when levels drop, inhibition lifts, allowing production to resume.

what is respiration why is it essential?

Respiration is the oxidation of organic molecules to release usable energy (ATP). It is essential because all cellular activities require energy.

how do cells obtain energy from food molecules

Cells extract energy by oxidizing food molecules through glycolysis, the TCA cycle, and the electron transport chain, forming ATP and NADH/NADPH.

Why can't cells synthesize nucleic acids, proteins, or fats without energy from respiration?

Energy from respiration is necessary to build complex biomolecules like proteins, fats, and nucleic acids; without it, synthesis cannot occur.

What roles do intermediate carbon compounds play in cell metabolism

Intermediate carbon compounds formed during respiration act as building blocks for other essential molecules such as amino acids and nucleotides.

What is the process of digestion in cells, and which molecules are produced?

Cellular digestion breaks large food molecules into simpler forms using enzymes and water (hydrolysis).

how does hydrolysis play a role in the breakdown of complex food

Hydrolysis uses water to split complex molecules into smaller subunits like sugars and amino acids.

How do green plants differ from animals in their approach to food and digestion?

Green plants synthesize their own food through photosynthesis, while animals must ingest and digest complex foods.

How is starch stored during photosynthesis, and how is it made usable for cells?

During photosynthesis, plants store energy as starch in chloroplasts; it's later converted back into soluble sugar for respiration.

What does it mean that respiration is an oxidation-reduction process?

Respiration is an oxidation-reduction process where electrons are transferred from food molecules to electron acceptors like oxygen.

How do some organisms obtain energy without molecular oxygen?

Some organisms perform anaerobic respiration without oxygen, producing energy less efficiently through processes like fermentation.

What are the main types of reactions involved in respiration?

Respiration involves three major reaction types: glycolysis, the Krebs (TCA) cycle, and the electron transport chain.

How are energy carriers like ATP and NADH/NADPH involved in respiration?

ATP and NADH/NADPH act as energy carriers, transferring energy from food oxidation to energy-requiring reactions.

Why is energy released from glucose in small steps rather than all at once?

Energy from glucose is released gradually through stepwise reactions, allowing controlled ATP synthesis and preventing damage from heat release.

What mechanisms regulate the rate of respiration in cells?

Respiration rate is regulated by enzyme activity and energy demand; high ADP levels stimulate ATP production.

15. How does ATP hydrolysis affect the rate of respiration?

ATP hydrolysis to ADP signals cells to increase respiration, replenishing ATP supplies.

What are the main phases of respiration, and what happens in each?

Main phases of respiration: glycolysis (cytoplasm), TCA cycle (mitochondrial matrix), and electron transport chain (inner mitochondrial membrane).

What is glycolysis, and what are its major steps?

Glycolysis breaks glucose into two pyruvate molecules, producing ATP and NADH through phosphorylation, cleavage, and oxidation steps.

How does aerobic respiration differ from anaerobic respiration in terms of energy yield and byproducts?

Aerobic respiration uses oxygen, producing CO₂, H₂O, and ~36 ATP per glucose; anaerobic respiration yields only 2 ATP and produces alcohol or lactic acid.

Why is anaerobic respiration considered less efficient?

Anaerobic respiration is less efficient because most of the energy remains locked in products like alcohol or lactic acid.

what is PPP, what are its products

The Pentose Phosphate Pathway (PPP) forms NADPH and ribose-5-phosphate, used for biosynthesis of nucleic acids.

Which cell structures are involved in respiration, and what roles do they play?

The mitochondria are the main sites of aerobic respiration, housing the TCA cycle and electron transport chain.

Why are mitochondria necessary for aerobic respiration?

2. Mitochondria are essential for aerobic respiration because their inner membrane hosts oxidative phosphorylation and ATP synthesis.

How do water content, temperature, and oxygen availability affect the rate of respiration in plant cells?

Respiration rate in plants varies with water, temperature, and oxygen availability; optimal conditions increase ATP production.

What happens to respiration in seeds with low water content or at extreme temperatures?

In seeds with low water or at extreme temperatures, respiration slows or stops because enzyme activity is impaired.

What are the two main characteristics of light that are important for photosynthesis?

The two important characteristics of light are its wavelength and intensity—these determine how much energy is available for photosynthesis.