Key Concepts in Plant Biology and Physiology

Monosaccharides

Simple sugars like glucose and fructose.

Disaccharides

Sugars formed by two monosaccharides, e.g., sucrose.

Polysaccharides

Carbohydrates composed of long chains of monosaccharides, e.g., starch, cellulose, hemicellulose.

Cellulose

A structural component of the plant cell wall.

Alkaloids

Secondary metabolites that defend against herbivores/pathogens.

Phenolics

Secondary metabolites that provide structural support and UV protection.

Vacuole

An organelle for storage (water, ions, pigments), maintaining turgor pressure, detoxification, and pH/ion homeostasis.

Primary cell wall

A flexible cell wall that allows growth.

Secondary cell wall

A rigid cell wall that contains lignin and is formed after growth.

Plasmodesmata

Microscopic channels connecting adjacent plant cells, allowing direct transport of molecules (symplastic transport).

Mitosis in plants

Differs from animals as plants lack centrioles/centrosomes; spindle fibers are organized by MTOCs; cytokinesis involves phragmoplast and cell plate formation.

Bryophyte sporophyte

Consists of three parts: foot (anchors to gametophyte), seta (stalk), and capsule (sporangium for spore production).

Sphagnum moss

Forms peat bogs, stores carbon, and creates acidic, anaerobic conditions that slow decomposition.

Vascular plants adaptations

Key adaptations include vascular tissue (xylem/phloem), stomata, lignin in cell walls, true roots/leaves, and dominant sporophyte generation.

Homospory

Produces one type of spore (bisexual gametophyte).

Heterospory

Produces two types of spores: microspores (male) and megaspores (female).

Gymnosperms

Plants with naked seeds, no flowers, pollen delivered via pollen tube, including conifers, cycads, and ginkgo.

Eudicots

Plants with flower parts in multiples of 4/5.

Monocots

Plants with flower parts in multiples of 3.

Double fertilization

In angiosperms, one sperm fertilizes the egg (zygote), the other fuses with polar nuclei to form triploid endosperm.

Plant hormone groups

Six major groups include auxins (cell elongation), cytokinins (cell division), gibberellins (growth), ABA (stress response), ethylene (fruit ripening), brassinosteroids (cell expansion).

Cohesion-tension theory

Explains water movement in plants: transpiration creates tension, water molecules cohere, and adhesion to xylem walls maintains the column.

Macronutrients for plants

Nitrogen (growth), phosphorus (energy transfer), potassium (enzyme activation), calcium (cell walls), magnesium (chlorophyll), sulfur (proteins).

Phototropism

Directional growth response to light (e.g., shoots grow toward light).

ABC model of flower development

A genes (sepals), A+B (petals), B+C (stamens), C (carpels).

Tropical rainforest soil

Unsuitable for agriculture due to being nutrient-poor, rapid decomposition, heavy leaching, and thin topsoil.

Nutrient-poor soil

Rapid decomposition, heavy leaching, and thin topsoil.

Rubisco in C3 plants

Fixes CO2 into RuBP but can also bind O2, leading to photorespiration.

Inputs and outputs of light reactions

Inputs: light, H2O, NADP+, ADP; outputs: O2, ATP, NADPH.

Agrobacterium-mediated transformation

A method to genetically modify plants using T-DNA from Agrobacterium to insert foreign genes.

Traits selected during plant domestication

Loss of seed shattering, larger seeds, reduced dormancy, compact growth, and improved taste/texture.

Difference between spices and herbs

Spices were exotic and expensive (tropical), while herbs were local and inexpensive (temperate).

Three primary tissue systems in plants

Dermal (protection), ground (storage/support), and vascular (transport).

Function of the root cap

Protects the root tip and secretes mucilage to ease soil penetration.

Lateral roots vs. branches

Lateral roots arise endogenously from the pericycle, while branches develop exogenously from axillary buds.

Role of the endodermis in roots

Regulates water/nutrient flow into the vascular cylinder via the Casparian strip.

Sun leaves vs. shade leaves in dicots

Sun leaves: thick, high chloroplast density. Shade leaves: thin, larger surface area for light capture.

Purpose of the abscission zone in leaves

Facilitates leaf detachment by breaking down cell walls and forming a protective layer.

Four floral organs in the ABC model

Sepals (A), petals (A+B), stamens (B+C), and carpels (C).

Benefits of transpiration for plants

Cools leaves, transports nutrients, and maintains turgor pressure via water movement.

Triggers of stomatal opening

Light, low CO₂, adequate water, and hormones like auxin/cytokinins.

Pressure-flow mechanism in phloem

Sugars loaded into phloem create osmotic pressure, driving sap from source (leaves) to sink (roots/fruits).

Importance of iron (Fe) for plants

Essential for chlorophyll synthesis (immobile; deficiency causes young leaf chlorosis).

Effect of soil pH on nutrient availability

Low pH: increases Fe/Mn but may cause toxicity. High pH: reduces Fe/Zn availability. Optimal: 6.0-7.0.

Vernalization

Cold treatment inducing flowering (e.g., winter wheat germinates in fall, flowers after winter).

Response of short-day plants (SDPs) to light

Flower when night length exceeds a critical period (e.g., late summer/autumn).

Role of phytochrome in seed germination

Pr (inactive) converts to Pfr (active) under red light, promoting germination. Far-red light reverses this.

Desert plant adaptations

Succulence, reduced leaves (spines), CAM photosynthesis, and deep roots.

Biodiversity near the equator

Stable climate, high productivity, evolutionary history, and niche diversity.

Plant mass gain

Comes from water, not soil (planted willow in dry soil; soil mass unchanged).

Why do plants use visible light for photosynthesis?

It's abundant, non-damaging, and provides optimal energy for electron excitation.

How do C4 plants minimize photorespiration?

Spatial separation: PEP carboxylase fixes CO₂ in mesophyll, Calvin cycle in bundle sheath cells.

What is the function of PEP carboxylase in CAM plants?

Fixes CO₂ at night into malate, releasing it for the Calvin cycle during the day to conserve water.

What are the risks of genetically modified crops?

Gene flow to wild plants, pest resistance, ecological impacts, and consumer concerns.

What is synteny in genetics?

Conservation of gene order between species (e.g., rice and Arabidopsis share similar gene blocks).

Why were compact growth traits selected in crops?

Ease of harvest, higher yield density, and reduced lodging (falling over).

What is the significance of domestication centers like the Fertile Crescent?

Source of genetic diversity for breeding (e.g., wheat, barley) and adaptation traits.

What is the role of the quiescent center in root apical meristem?

Acts as a stem cell reservoir, rarely dividing but replenishing surrounding cells.

What is the role of hyaline cells in sphagnum moss anatomy?

Dead cells that absorb and retain water, releasing hydrogen ions to acidify the environment.

How do leptosporangia differ from eusporangia?

Leptosporangia: single-cell origin, thin-walled, few spores. Eusporangia: multiple-cell origin, thick-walled, many spores.

What is the function of the peristome in bryophyte capsules?

Aids in controlled spore release by responding to humidity changes.

Why do gymnosperms like conifers dominate cold/dry environments?

Needle-like leaves reduce water loss, and tracheids provide frost-resistant water transport.

What is the evolutionary significance of microphylls vs. megaphylls?

Microphylls (single vein) evolved from enations; megaphylls (branched veins) from flattened lateral branch systems.

How does the phragmoplast facilitate cytokinesis in plants?

Guides Golgi-derived vesicles to form the cell plate, which matures into a new cell wall.

What is the role of the suspensor in embryogenesis?

Temporarily transports nutrients from endosperm to the developing embryo.

Why do some seeds exhibit epigeal vs. hypogeal germination?

Epigeal (cotyledons above ground) for early photosynthesis; hypogeal (below ground) for protection in harsh conditions.

What is the 'inhibitory field model' in leaf phyllotaxy?

Auxin depletion around new leaf primordia prevents adjacent leaves from forming too close.

How do trichomes contribute to plant survival?

Defend against herbivores, reduce water loss, and reflect excess light.

What distinguishes vessel elements from tracheids in xylem?

Vessel elements are wider, perforated (angiosperms); tracheids are tapered, pit-mediated (all vascular plants).

Why is the Calvin cycle called C3 photosynthesis?

The first stable product is 3-carbon 3-PGA (phosphoglycerate).

ATP expenditure for PEP regeneration

Making it less efficient in cool climates.

How does ABA close stomata during drought?

Triggers potassium efflux from guard cells, reducing turgor pressure.

What is the role of statoliths in gravitropism?

Starch-filled amyloplasts in root caps sediment to sense gravity, directing auxin flow.

Why do long-day plants flower in spring?

Require daylight longer than a critical threshold (e.g., >12 hours).

What is the function of the bundle sheath in C4 plants?

Isolates Rubisco from O₂, minimizing photorespiration by concentrating CO₂.

How does ethylene promote fruit ripening?

Triggers cell wall-digesting enzymes (e.g., cellulase) and converts starch to sugars.

What is the adaptive value of mycorrhizal associations?

Fungi enhance root surface area for nutrient (especially P) absorption in exchange for plant sugars.

Why are peat bogs ecologically important?

Store 30% of global soil carbon and preserve organic matter due to anaerobic conditions.

What is the role of the L1, L2, and L3 layers in shoot apical meristem?

L1 (epidermis), L2 (subepidermal tissues), L3 (internal tissues); maintain zonation for organ formation.

How does the Casparian strip regulate nutrient uptake?

Forces water/solutes to pass through endodermal cell membranes, enabling selective transport.

What is the significance of 'synteny' in crop breeding?

Conserved gene order helps transfer beneficial traits between related species (e.g., wheat and barley).

Why do some plants exhibit vivipary?

Seeds germinate on the parent plant (e.g., mangroves) to ensure survival in waterlogged habitats.

What is the role of flavonoids in plants?

Pigments for pollinator attraction, UV protection, and antioxidant defense.

Why is photorespiration wasteful for C3 plants?

Rubisco binds O₂ instead of CO₂, consuming ATP and releasing fixed carbon.

How does the 'Fibonacci sequence' relate to leaf arrangement?

Optimizes light capture by spacing leaves at 137.5° angles (golden angle).

What is the role of the pericycle in secondary growth?

Initiates lateral root formation and contributes to vascular cambium in woody plants.

Why do bryophytes require water for fertilization despite living on land?

Their motile sperm must swim through water to reach eggs in archegonia (vestigial aquatic trait).

What is the significance of 'lignin helices' in protoxylem vessels?

Provide structural flexibility during root elongation while preventing collapse.

How do cardenolides in milkweed demonstrate coevolution?

Toxic to most herbivores but sequestered by monarch butterfly larvae as a defense.

Why do cycads have flagellated sperm despite being gymnosperms?

Retained ancestral trait from fern-like ancestors; pollen tubes deliver sperm close to ovule for final swim.

What causes 'heartwood' discoloration in tree trunks?

Accumulation of phenolic compounds (tannins, resins) in non-functional xylem for pathogen resistance.

Why do some seeds exhibit 'double dormancy'?

Require sequential environmental cues (e.g., cold stratification THEN scarification) to break dormancy stages.

allelopathy

Releases juglone from roots/hulls, inhibiting mitochondrial respiration in nearby plants.

chloroplast genome of dinoflagellates

Organized into mini-circles (1-2 genes each), a relic of tertiary endosymbiosis.

jasmonate signaling in carnivorous plants

Mimics wound-response pathways to trigger enzymatic digestion of prey without immune costs.

reaction wood formation

Angiosperms produce tension wood (high cellulose) on upper side; gymnosperms form compression wood (high lignin) below.

hydathodes

Passive water-secreting pores at leaf margins (guttation), lacking guard cells or photosynthetic function.

resurrection fern (Pleopeltis)

Accumulates trehalose sugars to stabilize membranes and proteins in dried state.

corpus vs. tunica in shoot apical meristem

Tunica (L1/L2) divides anticlinally for surface growth; corpus (L3) divides multidirectionally for bulk tissue.

buttress roots

Radially flattened extensions increase mechanical support and nutrient absorption surface area.