Plant Biology Test 1

Why learn about the diversity of life on Earth?

many plant species make specific types of medicine, many biologists agree we’re in the middle of a human-caused mass extinction episode and learning how to describe the diversity of life on Earth can help us know what we have and have lost

Why learn about life cycles?

if you understand an organism’s life cycle you can manage populations more effctively

What are the main factors thought to be responsible for the origin of life on Earth and what evidence supports the hypothesis that life arose in the oceans?

• Early Earth had heat, lightning, volcanoes, sunlight, and energy from thermal vents, which acted on gases to form organic molecules.

• These molecules accumulated in the oceans, where they were close together and able to form more complex molecules through abiogenesis.

• Proteinoid microspheres formed in water, acting as early cell-like structures.

• The oldest evidence of life, such as stromatolites and microbial mats, dates to about 3.5 billion years ago and is found in marine (ocean) environments, supporting the idea that life began in the oceans

Why do biologists believe that all living things on Earth today share a common ancestor?

• Nearly all organisms use the same universal genetic code to translate DNA into proteins.

• There are 64 codons that code for 20 amino acids across almost all life forms.

• This strong similarity suggests that life emerged only once and that all organisms descended from one common ancestor, a DNA-based microbe that lived over 3.5 billion years ago.

What is the principle difference between a heterotroph and an autotroph and what role did each play on the early Earth?

• Heterotrophs depend on external organic molecules for energy.

  • The first life forms were heterotrophic prokaryotes that used organic molecules already present in the oceans.

• Autotrophs make their own energy-rich molecules from inorganic materials.

  • Early photosynthetic autotrophs later evolved and became crucial by producing organic matter and oxygen, forming the base of food chains.

Why is the evolution of photosynthesis thought to be such an important event in the evolution of life in general?

• Photosynthesis produced oxygen (O₂), which slowly accumulated in the atmosphere.

• Oxygen led to the formation of an ozone (O₃) layer, protecting organisms from harmful UV radiation.

• Oxygen made cellular respiration possible, allowing organisms to produce ATP more efficiently.

• These changes enabled the evolution of eukaryotic cells and more complex life.

What were some of the problems encountered by plants as they made the transition from the sea to the land, and what structures in terrestrial plants evolved to solve these problems?

Problems and solutions:

• Water loss → Cuticle (waxy coating), epidermis

• Gas exchange → Stomata with guard cells

• Support → Stems

• Anchorage and nutrient uptake → Roots

• Transport of materials → Vascular tissues

  • Xylem transports water

  • Phloem transports organic molecules

These adaptations allowed plants to survive and reproduce on land.

What are biomes and what are the principal roles of plants in an ecosystem?

• Biomes are large geographic regions defined by climate and characteristic plant and animal life (e.g., forests, tundra).

• An ecosystem refers to interactions between living organisms and nonliving factors in an environment.

• Plants play a fundamental role by:

  • Acting as primary producers

  • Making organic molecules through photosynthesis

  • Forming the base of food webs

  • Regulating oxygen, carbon dioxide, and energy flow within ecosystems

What are organic molecules?

those made of carbon and hydrogen but can include other elements, must contain carbon atoms covalently bonded to hydrogen atoms

What is abiogenesis?

the natural process by which life has arisen from non-living matter like simple organic compounds; by virtue of being close to one another, more and more complex molecules form

What were the first cell-like structures?

aggregations of molecules called protenoid microspheres, not living yet, spherical protein-like aggregates that could form polymers

What is the difference between prokaryotes and eukaryotes?

Prokaryotes: lack nuclear envelope, genetic material not organized into complex chromosomes

Eukaryotes: cells with nuclear envelope, complex chromosomes, and organelles like mitochondria (sites of respiration) and chloroplasts (sites of photosynthesis), surrounded by membranes

What is endosymbiotic theory?

eukaryotic cells evolved from a symbiotic relationship between different species of prokaryotes

How did life first colonize land?

ocean shores provided richer sources of nutrients than the open ocean so biodiversity flourished there, early multicellular organisms anchored themselves to rocky shores

What is the vascular system in plants?

Xylem: water passes upward through the plant body

Phloem: transports organic molecules manufactured in leaves and other photosynthetic parts throughout the plant body

What are apical meristems?

growth region in plants found within the root tips and the tips of new shoots, involved in the extension of the plant body

What are primary and secondary growth?

Primary: growth that originates from apical meristems

Secondary: growth that results in a thickening of stems and roots, originates from two lateral meristems (vascular and cork cambium)

What are the four main types of organic molecules found in plant cells, and what are their basic structural subunits and their principal functions?

Carbohydrates: monosaccharides are a ready energy source, disaccharides are a transport form found in plants, polysaccharides are energy storage or structural components

Lipids: triglycerides are 3 fatty acids and 1 glycerol and function as energy storage, phospholipids are 2 fatty acids + 1 glycerol + 1 phosphate group and are a major component of all cell membranes, steroids are four linked hydrocarbon rings and form membranes and hormones

Proteins (polypeptides): made of amino acids, numerous functions including structural and catalytic

Nucleic Acids: DNA is made of nucleotides and carries genetic information, RNA is made of nucleotides and is involved in protein synthesis

By what process are all four types of organic molecules split into their subunits and by what process can these subunits be joined together?

Dehydration Synthesis: builds molecules, requires energy, loss of water molecule (loses 2H and 1O and forms water)

Hydrolysis: break molecules down by adding water molecule, releases energy

How do energy-storage polysaccharides and structural saccharides differ from one another? What are some examples of each?

Energy-storage polysaccharides

• Function: Store energy that cells can use later

  • Amylose: linear chain of repeated alpha-glucose monomers

  • Amylopectin: branched chain of repeated alpha-glucose monomers

Structural saccharides

• Function: Provide support, strength, and protection to cells and organisms

  • Cellulose: polymer of beta-glucose monomers

What is a consequence of beta-glucose monomers in cellulose?

the structure of beta-glucose has alternating hydroxyl groups which makes the bonds less accessible to be broken down, this strengthens the cell wall and makes it less permeable

What is an enxyme and why are enzymes important to cells?

enzymes are proteins that, by virtue of its charges and shape, can recognize certain molecules and interact with the molecule substrate to cause a reaction like bringing molecules together or splitting them up

How is ATP different from ADP, and why is ATP important to cells?

ATP is the cell’s major currency; ATP (triphosphate), ADP (diphosphate) → extra phosphate group in ATP; ADP is recharged to ATP during photosynthesis; the energy from ATP is used to drive the catalysis of many enzymes; ADP is a product of ATP hydrolysis

How does the structure of a prokaryotic cell differ from that of a eukaryotic cell?

prokaryotic cells lack nuclei and membrane-bound organelles and the chromosome consists of a single circular molecule of DNA localized in the nucleoid; eukaryotes have DNA contained in a true nucleus and have distinct organelles with membranes

What are the various types of plastids and what role(s) does each play in the cell?

chloroplasts contain chlorophyll and carotenoid pigments, they convert light to chemical energy in photosynthesis; chromoplasts contain/store carotenoid pigments; leucoplasts are non-pigmented and there are three different types, amyloplasts store starch, the others store lipids and proteins respectively

What developmental and functional relationships exist between the endoplasmic reticulum and the Golgi bodies of the plant cell?

• The ER and Golgi membranes originate from the same endomembrane system.

• Transport vesicles bud off from the ER and move to the Golgi bodies.

• These vesicles form and maintain the Golgi apparatus, linking the two organelles structurally

• The ER produces proteins and lipids.

• The Golgi modifies, sorts, and ships them to their final destinations.

• Vesicle transport links the two, making them interdependent in cell growth, maintenance, and secretion.

What is the ‘cytoskeleton’ of the cell and with what cellular processes is it involved?

complex network of protein filaments of which there are two types: actin filaments and microtubules; play a role in cell division, growth of cell wall, and movement of flagella

How do primary cell walls differ from secondary cell walls?

• Primary walls: thin, flexible, pectin-rich, allows growth

• Secondary walls: thick, rigid, lignin-rich, provides strength and support, lack pectins

What is the cell cycle and what key events occur in the G1, S, G2, and M phases of the cell cycle?

Cell cycle: sequential series of events that take place in a cell that causes it to divide into two daughter cells

Interphase: G1 (cell doubles in size), S (DNA replication), and G2 (make sure chromosome replication is complete and repair damaged DNA)

M phase: mitosis and cytokinesis

What is the role of mitosis? What events occur during each of the four mitotic phases?

Role of mitosis is to divide the nucleus

Prophase: duplicated chromosomes shorten and thicken

Metaphase: chromatid pairs come to lie in the center of the cell with centrosomes on equatorial plane

Anaphase: sister chromatids separate and move to opposite ends of the spindle

Telophase: nuclear envelopes form around each set of chromatids

What is cytokinesis and what roles do the phragmosome, the phragmoplast, and the cell plate play during the process?

cytokinesis is the division of the cytopl

Phragmosome

• Creates a plane across the cell where the new cell wall will form

Phragmoplast

• Guides vesicles (from the Golgi apparatus) to the center of the cell

Cell plate

• Becomes the new cell wall (including the middle lamella) separating the cytoplasm and the two daughter cells

What is water potential and what value does the concept of water potential have for plant physiologists?

water potential determines the direction in which water moves, from higher to lower potential energy (from lower solute concentrations to higher solute concentrations); the concept of water potential is useful because it enables plant physiologists to predict how water will move under various conditions

Distinguish between diffusion and osmosis. What kinds of substances enter and leave cells by each process?

Diffusion

• Definition: Movement of substances from an area of higher concentration to lower concentration

• What moves:

  • Small molecules and ions

  • Examples: oxygen (O₂), carbon dioxide (CO₂), some small nonpolar molecules

  • Role in cells:

  • Gas exchange (O₂ enters cells; CO₂ leaves cells)

Osmosis

• Definition: Diffusion of water across a selectively permeable membrane

• What moves:

  • Only water molecules

Role in cells:

• Controls cell volume and turgor pressure in plant cells

What is the fluid-mosaic model of membrane structure and what role is played by its two major components?

fluid-mosaic model describes the structure of the cell membrane as a dynamic, flexible layer made of different molecules that move within it

Phospholipids

• Form a phospholipid bilayer

• Have hydrophilic (water-loving) heads facing outward and hydrophobic (water-fearing) tails facing inward

• Create a selectively permeable barrier that separates the cell from its environment

Proteins

• Embedded in or attached to the bilayer

• Provide specific functions, such as:

  • Transport of substances (channels and carriers)

  • Cell signaling (receptors)

  • Cell recognition

  • Enzymatic activity

  • Anchoring the cytoskeleton

What are transport proteins and of what importance are they to plant cells?

• Proteins embedded in the cell membrane

• Form channels, carriers, or pumps

• Allow specific ions and molecules to cross the membrane

enable plant cells to control what enters and leaves the cell, making nutrient uptake, water balance, growth, and overall plant survival possible

What are the similarities and differences between facilitated diffusion and active transport?

facilitated diffusion: diffusion assisted by carrier or channel proteins, passive transport (no energy required)

active transport: transport requiring energy expenditure, can move against concentration or electrochemical gradient

What role is played by vesicle-mediated transport? Compare movement out of the cell with movement into the cell?

movement of large molecules in or out of cell occurs by endocytosis or exocytosis, where substances are transported within vesicles; three types of endocytosis: phagocytosis (solid particles), pinocytosis (liquids), receptor-mediated endocytosis (molecules/ions bound to receptors in plasma membrane)

What are the roles of signal transduction and plasmodesmata in cell-to-cell communication?

• Signal transduction allows cells to communicate using chemical signals and receptors, even over long distances.

• Plasmodesmata allow direct physical connections between plant cells, enabling fast and coordinated communication.

What are the first and second laws of thermodynamics and how do they relate to living organisms?

1st: energy can be converted but neither created nor destroyed

2nd: in the course of energy conversions, if no energy enters or leaves a system, the final potential energy will always be less than initially

to maintain the order on which life depends, living systems must have a constant supply of energy to overcome the tendency toward increasing disorder

Why are oxidation-reduction reactions important to biology?

an atom/molecule that loses electrons is oxidized while one that gains electrons is reduced; these always occur simultaneously; this is important for energy transformations in cells as that requires the transfer of electrons from one energy level to another

How do enzymes catalyze chemical reactions and what are some of the factors that influence enzyme activity?

enzymes lower the free energy of activation and increase the rate at which reactions take place;

• Enzymes have a specific region called the active site.

• The substrate binds to the active site, forming an enzyme–substrate complex

Their activity is influenced by temperature, pH, substrate and enzyme concentration, and inhibitors.

How does feedback inhibition regulate cellular activities?

in feedback inhibition, the regulatory enzyme (first in the pathway) is inhibited by an excess of the end product, which accumulates when the cell’s needs have been met; the entire pathway shuts down as the substrates need for the intermediate enzymes are depleted

What are coupled reactions and how does ATP function as an intermediate between exergonic and endergonic reactions?

cells are able to carry out endergonic (energy-requiring) reactions by coupling them with exergonic (energy-yielding) reactions; the energy released by one reaction is used to drive another reaction that requires energy

• ATP transfers a phosphate group to another molecule (phosphorylation).

• Phosphorylation makes the target molecule more reactive, allowing an endergonic reaction to occur.

What is the overall reaction, or equation, for respiration, and what is the principal function of this process?

C6H12O6 + 6O2 → 6H2O + Energy

this is the source of energy in most cells

What are the main events that occur during glycolysis?

six-carbon glucose molecule is split into two three carbon molecules of pyruvate, forms 2 molecules of ATP and two of NADH; occurs in cytosol

Where in the cell does the citric acid cycle occur and what are the products formed?

occurs in the mitochondrial matrix; yields 2 molecules of CO2, 1 molecule ATP, 4 molecules of reduced electron carriers; purpose is to extract high-energy electrons from acetyl-CoA and transfer them to electron carriers, while releasing CO₂

How does the flow of electrons in the electron transport chain result in the formation of ATP?

• High-energy electrons from NADH and FADH₂ are passed along a series of proteins in the inner mitochondrial membrane.

• As electrons move from one carrier to the next, they lose energy and release it

• The released energy is used to pump H⁺ ions (protons) from the mitochondrial matrix into the intermembrane space.

• This creates an electrochemical gradient (high H⁺ concentration outside, low inside).

• Protons flow back into the matrix through ATP synthase.

  • This flow powers ATP synthase to convert ADP + Pi into ATP (chemiosmosis).

• Electrons combine with oxygen and protons to form water, keeping the chain running.

How and why does the net energy yield under aerobic conditions differ from that obtained under anaerobic conditions?

in the absence or shortage of oxygen, pyruvate produced by glycolysis may be converted either to lactate or to ethanol and carbon dioxide in a process called fermentation which yield 2 ATP for each glucose molecule as opposed to the 36 generated by aerobic respiration

What is the central role played by the citric acid cycle in the metabolism of the cell?

The central role of the citric acid cycle in cell metabolism is that it acts as a metabolic hub connecting catabolism and anabolism.

• The citric acid cycle receives breakdown products from carbohydrates, fats, and proteins, not just glucose.

• These molecules are converted into intermediates that enter the cycle at different points.

What is the role of light in photosynthesis?

Light provides the energy that drives photosynthesis. When light is absorbed by pigments in the chloroplast, its energy excites electrons. This energy is used to power the light reactions, which convert light energy into chemical energy stored in ATP and NADPH. These energy carriers are then used to make sugars.

What are the principal pigments involved in photosynthesis and why are leaves green?

The principal photosynthetic pigments are:

• Chlorophyll a (primary pigment)

• Chlorophyll b (accessory pigment)

• Carotenoids (yellow, orange pigments)

Leaves appear green because chlorophyll absorbs red and blue light but reflects green light, which is what we see.

What are the main products of the energy-transduction, or light, reactions of photosynthesis?

The main products of the light reactions are:

• ATP (energy)

• NADPH (reducing power)

• Oxygen (O₂) as a byproduct from the splitting of water

What are the main products of the carbon-fixation reactions of photosynthesis?

The carbon-fixation reactions (Calvin cycle) produce:

• G3P (glyceraldehyde-3-phosphate), a sugar that can be used to form glucose and other carbohydrates
  They also regenerate RuBP to keep the cycle going.

What are the main events associated with each of the two photosystems in the light reactions and what is the difference between antenna pigments and reaction center pigments?

• Photosystem II (PSII):

  • Absorbs light and excites electrons

  • Splits water to replace lost electrons, releasing oxygen

  • Creates a proton gradient used to make ATP

• Photosystem I (PSI):

  • Absorbs light again to re-energize electrons

  • Produces NADPH

Antenna pigments:

• Collect light energy and pass it to the reaction center

Reaction center pigments:

• A special pair of chlorophyll molecules that transfer excited electrons to the electron transport chain

What are primary metabolites? How do they create secondary metabolites?

metabolites that are required for cell survival and proliferation; occur in all plant cells (simple sugars, amino acids, proteins, and nucleic acids); they enter synthetic pathways that produce many different types of molecules

What are secondary/specialized molecules?

cell itself does not need them to survive but the plant needs it to survive in the ecosystem; restricted to certain cell types; may act as signals that enable the plant to respond to environmental cues, or have anti-herbivore/other defensive/dispersal roles

What are the kinds of secondary compounds?

alkaloids, terpenoids, phenolics

what are alkaloids? what are some examples?

alkaline nitrogenous compounds with an amine group present always; morphine, cocaine, caffeine, nicotine, atropine

what does allelopathic mean? what secondary compound has this trait?

prevents seed germination of other species and reduces inter-specific competition; caffeine

what are terpenoids? what are some examples?

made of isoprene units, a hydrocarbon that is synthesized in chloroplasts from CO2 recently converted to organic compounds; essential oils (monoterpenoids and sesquiterpenoids), cannabis, mint, rubber

What are phenolics? What are some examples?

consist of a hydroxyl ring attached to an aromatic/benzene ring of 6 carbons with a double bond; flavonoids, tannins, lignins, salicylic acid

What are lignins? What is lignification?

polymers formed of 3 types of monomers: p-coumaroyl, coniferyl, and sinapyl alcohols; lignification stiffens and waterproofs the cell and likely plated a major role in plant evolution since it allowed plants to grow taller and support large surfaces

What are phytoalexins?

secondary metabolites synthesized in response to pathogens; type of phenolic

How does plant cell differ from animal cell?

cell wall, chloroplasts/plastids, vacuoles

Describe the structure of a plastid

bound by a double membrane; inside has a system of membranes (thylakoids) and a homogenous matrix (stroma); photosystem I and ATP synthase are mostly located in the stroma thylakoids while photosystem II is located mostly in the grana thylakoids (photosystems are complex protein matrices that are integral in photosynthesis); semi-autonomous organelles that contain one or more nucleoids or circular DNA

What pigments are found in chromoplasts, and how do these pigments affect plant appearance?

carotenoids; responsible for yellow, orange, and red colour of leaves and flowers and fruits

Describe how chromoplasts can develop from chloroplasts.

mature chloroplasts can develop into chromoplasts, losing their chlorophyll and thylakoid membranes

what does chlorophyll do?

absorbs light

Describe leucoplasts and proplastids

lack pigments and an elaborate system of inner membranes; amyloplasts are leucoplasts that synthesize starch; proplastids are undifferentiated plastids that occur in root and shoot meristems

Where do light reactions and ‘dark’ reactions occur?

light: thylakoids, calvin cycle: stroma

Where does most ATP come from in plant cells?

from the stroma thylakoid because that is where ATP synthase is

where is the highest concentration of protons in chloroplasts?

the thylakoid lumen because the light reactions of photosynthesis actively move and generate protons there, creating a proton gradient used to make ATP

what is chlorophyll a

very prominent granum thylakoid that absorbs a lot of the light/wavelengths the drive photosynthesis, identifiable by a CH3 group; responsible for oxygen generating photosynthesis (stripping electrons out of water)

what is chlorophyll b

accessory pigment that absorbs light at different wavelengths to chlorophyll a, it transfers the absorbed energy to chlorophyll a; CHO group instead of CH3

what is chlorophyll c

accessory pigment, transfers energy to chlorophyll a; found in brown algae and diatoms

what are some traits of carotenoids and phycobilin?

carotenoids are fat soluble so they localize in membranes, they scavenge reactive oxygen species; phycobilin is water soluble and has a limited distribution in nature

What is the structure of the chlorophyll molecule, and what role does the magnesium atom play in its porphyrin ring?

• The chlorophyll molecule has a porphyrin ring made of carbon rings at its head.

• A magnesium atom is located at the center of the ring and coordinates the structure, helping chlorophyll absorb light efficiently.

What are the main components of a photosystem and their functions?

Each photosystem has an antenna complex (250–400 pigments, captures light) and a reaction centre (2 special chlorophyll a molecules, carries out photochemistry).

Which chlorophyll types are in PSI and PSII reaction centres?

PSI: P700 chlorophyll a/a’ heterodimer; PSII: P680 chlorophyll a/a homodimer

Where are PSI and PSII located in the thylakoid membrane?

PSI: stroma thylakoids and grana margins; PSII: grana thylakoids.

Describe the path of electrons in light-dependent reactions

Water → PSII → PSI → NADP+, with photolysis at PSII producing protons and oxygen

What is photolysis and why is it important?

It splits water, releases electrons for the ETC, produces protons for a proton gradient, and generates oxygen

How can PSI function independently of PSII and what does it produce?

Through cyclic photophosphorylation, generating only ATP.

How is ATP generated in photosynthesis?

Protons from photolysis create a proton gradient across the thylakoid membrane, driving ATP synthase to make ATP.

How are PSI and PSII linked and why are they spatially separated?

Linked by an electron transport chain; spatial separation ensures efficient electron flow and prevents interference between the two photosystems

How do we know chlorophyll a is the main photosynthetic pigment?

Because photosynthesis rates are highest across chlorophyll a’s action spectrum

How did Engelmann measure the rate of photosynthesis and what did he find?

He measured oxygen production using oxygen-seeking bacteria, which clustered where violet and red light hit the algal filament.

Why were carbon-fixation reactions once called the “dark reactions,” and why is this misleading?

They don’t require light directly, but they depend on ATP and NADPH from the light reactions. the reactions don’t happen in the dark.

In what form do photosynthetic organisms obtain carbon?

As CO₂—from air in plants and dissolved in water for algae and photosynthetic bacteria.

What is the Calvin cycle and what does it produce?

It is C3 photosynthesis that uses ATP and NADPH to fix and reduce carbon, producing simple sugars.

What role does RuBP play in the Calvin cycle?

The cycle starts and ends with RuBP, a 5-carbon sugar with two phosphate groups.

What is Rubisco and why is it important?

Rubisco catalyzes the first step of carbon fixation, is the most abundant enzyme on Earth, and acts as both a carboxylase and an oxygenase.

describe what happens in the light reactions of photosynthesis

The light reactions of photosynthesis occur in the thylakoid membranes and convert light energy into chemical energy.

Light is absorbed by chlorophyll in Photosystem II, exciting electrons. Water is split to replace these electrons, releasing oxygen and protons. The excited electrons move through an electron transport chain, creating a proton gradient that drives ATP synthesis.

The electrons are re-energized in Photosystem I and used to reduce NADP⁺ to NADPH.

Main products: ATP, NADPH, and oxygen.

describe what happens during the calvin cycle of photosynthesis

The Calvin cycle (carbon-fixation reactions) occurs in the stroma of the chloroplast and uses ATP and NADPH to make sugars.

CO₂ is fixed when it attaches to RuBP by the enzyme RuBisCO, forming a 3-carbon compound.
Energy from ATP and NADPH is then used to reduce this compound to G3P, a sugar.
Some G3P leaves the cycle to form glucose and other carbohydrates, while the rest is used to regenerate RuBP so the cycle can continue.

Main product: G3P (sugar).

What are the principal differences among the C3, C4, and CAM pathways for carbon fixation, and what features do they have in common?

C3 plants:

• Use the Calvin cycle directly

• CO₂ is fixed by RuBisCO

• Prone to photorespiration

C4 plants:

• Separate CO₂ fixation and the Calvin cycle spatially

• CO₂ is first fixed into a 4-carbon compound

• Reduces photorespiration

CAM plants:

• Separate CO₂ fixation and the Calvin cycle temporally

• Stomata open at night to reduce water loss

• Store CO₂ for use during the day

Features in common:

• All fix carbon using CO₂

• All ultimately use the Calvin cycle

• All produce sugars using ATP and NADPH from light reactions

What does most of PGAL (glyceraldehyde 3-phosphate) become after being exported to the cytosol?

either converted to sucrose (the major transport sugar in plants) or to starch (the major storage carb in plants)