Plant Form and Function – Structure, Growth & Development

Comprehensive set of Q&A flashcards covering meristems, primary & secondary growth, tissue systems, water and nutrient transport, plant nutrition, reproduction, hormonal regulation, environmental responses, and defense mechanisms in vascular plants.

What are the two main organ systems in vascular plants?

The root system and the shoot system.

Where does primary growth occur in plants?

At the apical meristems located at root and shoot tips.

Name the three types of meristems found in plants.

Apical meristems, lateral meristems and intercalary meristems.

Which meristem is responsible for secondary growth that increases girth?

Lateral meristems (vascular cambium and cork cambium).

What characteristic shape do meristematic cells typically exhibit?

They are isodiametric (roughly spherical).

Give three shared features of all meristematic cells.

Living, densely cytoplasmic, centrally nucleated, undifferentiated, mitotically active.

Which zone of a growing root contains actively dividing cells?

The zone of cell division (root apical meristem).

What is the name of the tissue that protects the root apex as it pushes through soil?

Root cap.

In shoot primary growth, from what do leaves arise?

Leaf primordia on the sides of the shoot apical meristem.

List one structural difference between the shoot apex and root apex.

Shoot apex is protected by leaf primordia, root apex by a root cap.

What are the three major tissue systems in vascular plants?

Dermal, ground and vascular tissue systems.

Which epidermal outgrowths reduce water loss or defend against insects?

Trichomes.

What ground-tissue cell type is alive at maturity and has thin primary walls?

Parenchyma cells.

Which living support cells have unevenly thickened primary walls?

Collenchyma cells.

Name the two dead supporting cell types of sclerenchyma.

Sclereids and fibres.

Which two cell types conduct water in xylem?

Vessel elements and tracheids.

What special plates occur at the ends of vessel elements?

Perforation plates.

Which phloem cell lacks a nucleus at maturity but conducts photosynthates?

Sieve-tube element.

How do companion cells assist sieve-tube elements?

They load/unload sugars and provide metabolic support via plasmodesmata.

What is the primary function of the endodermal Casparian strip?

Blocks apoplastic flow, forcing water and minerals through a selectively permeable membrane.

Where does secondary xylem accumulate?

Produced inside the vascular cambium (wood).

Which lateral meristem produces the periderm?

Cork cambium.

Define heartwood.

Older, non-conducting secondary xylem that has become filled with resins and is darker.

What are annual rings and how are they formed?

Alternating layers of spring wood and summer wood produced during one growing season.

What term describes leaves arranged one per node?

Alternate phyllotaxy.

Why are grass leaves oriented nearly vertical?

To avoid damage from intense overhead light and reduce overheating.

Which leaf mesophyll layer is rich in chloroplasts and elongated cells?

Palisade mesophyll (in dicot leaves).

Where are stomata more numerous in most dicot leaves?

Lower epidermis.

What two ions are central to the stomatal opening mechanism?

K⁺ influx and Cl⁻/malate²⁻ balancing anions.

Which hormone triggers stomatal closure during drought?

Abscisic acid (ABA).

Give four environmental factors that close stomata.

Darkness, high ABA, drought/high temperature, high wind (drying).

Define water potential (Ψ).

A measure of potential energy of water; determines direction of water movement.

Write the water potential equation.

Ψ = Ψs (solute potential) + Ψp (pressure potential).

Why is Ψs always negative?

Solutes bind water molecules, reducing free water energy.

Explain plasmolysis.

Shrinking of protoplast from the cell wall when a plant cell is placed in a hypertonic solution.

Differentiate apoplastic and symplastic routes.

Apoplast: cell-wall continuum outside membranes; Symplast: cytoplasmic continuum through plasmodesmata.

What hypothesis explains upward pull of xylem sap?

Cohesion–tension hypothesis.

Name the driving force for phloem translocation.

Pressure flow generated by loading sugars at sources and unloading at sinks.

Define guttation.

Exudation of water droplets from leaf margins via hydathodes due to root pressure.

What are carnivorous plants and why do they capture insects?

Photosynthetic plants that obtain additional N and minerals by digesting animals in nutrient-poor soils.

State two mutualistic plant relationships.

Mycorrhizae (roots + fungi) and legume root nodules with Rhizobium.

List the nine macronutrients essential to plants.

C, H, O, N, P, K, S, Ca, Mg.

Which micronutrient deficiency causes interveinal chlorosis in young leaves?

Iron (Fe) deficiency.

What is alternation of generations?

Life cycle with multicellular haploid gametophyte and multicellular diploid sporophyte phases.

Which generation is dominant in mosses?

Gametophyte generation.

What type of spores are produced by Nephrolepis?

Homosporous spores.

Define heterospory and name a plant that exhibits it.

Production of micro- and megaspores; seen in Selaginella and seed plants.

In Cycas, what structure becomes the seed coat?

The integument of the ovule.

What is double fertilization in angiosperms?

One sperm fuses with egg forming zygote; second sperm fuses with two polar nuclei forming triploid endosperm.

Why is cross-pollination advantageous?

It increases genetic variation and reduces inbreeding depression.

Name three floral adaptations promoting cross-pollination.

Self-incompatibility, dioecy/unisexuality, heterostyly (different style/filament lengths).

What triggers fruit development in angiosperms?

Fertilization (or hormonal signals in parthenocarpy).

Define seed dormancy.

A period in which a viable seed does not germinate despite favourable conditions, often due to inhibitors or hard seed coat.

Which light receptor mediates shade-avoidance responses?

Phytochrome (red/far-red photoreceptor).

What colour light promotes seed germination via phytochrome?

Red light (~660 nm).

Describe the triple response induced by ethylene.

Reduced stem elongation, stem thickening, and horizontal growth when seedling encounters obstacle.

Which hormone promotes cell elongation, apical dominance and root initiation?

Auxin (indole-3-acetic acid).

Name the hormone that breaks seed dormancy and promotes stem elongation in bolting.

Gibberellin.

What hormone group delays leaf senescence and promotes cell division?

Cytokinins.

How does the statolith hypothesis explain root gravitropism?

Dense amyloplasts settle, redistributing Ca²⁺ and auxin, inhibiting cell elongation on lower side, causing downward bending.

Define thigmotropism with an example.

Directional growth in response to touch, e.g., coiling of pea tendrils around a support.

What is thigmomorphogenesis?

Altered growth form (shorter, stockier) in response to mechanical stress like wind.

Which plant hormone mediates drought-induced stomatal closure?

Abscisic acid (ABA).

How do halophytes cope with salt stress?

They secrete excess salt through salt glands and accumulate compatible solutes.

Name a pre-existing structural defense against pathogens.

The waxy cuticle or thick epidermal cell walls.

Give an example of an induced chemical defense in plants.

Production of phytoalexins or pathogenesis-related proteins after infection.

Which secondary metabolite from neem acts as an insecticide?

Azadirachtin (a terpenoid).

What is the role of tannins in plant defense?

They deter herbivores by reducing digestibility of plant tissues.

Explain facilitated diffusion in plant cells.

Passive movement of solutes down a concentration gradient through specific membrane transport proteins.

Why is bulk flow faster than diffusion?

It moves the entire solution driven by pressure gradients through xylem or phloem, independent of solute concentration.

What defines a source in phloem transport?

An organ that is a net exporter of sugar (e.g., mature leaf).

During phloem loading, what often provides the energy for active transport of sucrose?

A proton gradient generated by H⁺-ATPase co-transporters.

Which plant process is primarily responsible for evaporative cooling?

Transpiration.

Name two environmental factors that increase transpiration rate.

High light intensity, low humidity (or high temperature, wind).

What is cuticular transpiration?

Water loss through the cuticle—typically only a small fraction (~5%) of total leaf water loss.

Define imbibition.

Physical adsorption of water by hydrophilic colloids (e.g., cellulose cell wall) causing swelling.

Which macronutrient activates many enzymes and is part of chlorophyll?

Magnesium (Mg).

What deficiency symptom indicates potassium shortage?

Yellow or brown leaf margins and weak stems.

Which micronutrient is essential for nitrogen metabolism and is part of nitrogenase enzymes?

Molybdenum (Mo).

Describe root pressure.

Positive pressure in the xylem of roots generated by active ion accumulation, pushing water upward, seen at night or in low transpiration.

What structure releases water droplets during guttation?

Hydathodes at leaf tips or margins.

What is parthenocarpy?

Development of fruit without fertilization, leading to seedless fruits.

Which hormone is commonly used commercially to induce parthenocarpic fruits?

Auxin or gibberellin applications.

Name the blue-light photoreceptors influencing phototropism and hypocotyl inhibition.

Cryptochromes and phototropins.

What is photoperiodism?

A physiological response to the relative lengths of day and night, often controlling flowering.

In long-day plants, when does flowering occur?

When the night length is shorter than a critical duration.

How does vernalization promote flowering?

Exposure to prolonged cold reduces floral repressors, allowing flowering in certain plants.

Which part of the embryo becomes the shoot system during germination?

The plumule (embryonic shoot).

What is the first structure to emerge during seed germination?

The radicle (embryonic root).

Define photomorphogenesis.

Light-regulated developmental processes in plants mediated by photoreceptors.

Provide one example of commensalism in plants.

Epiphytic orchids growing on tree branches without harming the host.

What is the main photosynthetic cell type in C3 leaves?

Mesophyll parenchyma (palisade + spongy).

How do bundle-sheath cells differ in C4 plants?

They are large, chloroplast-rich cells surrounding veins where the Calvin cycle occurs.

Why are vessel elements absent in softwood?

Gymnosperms lack xylem vessels; their wood consists mainly of tracheids.

What is bark composed of?

All tissues external to the vascular cambium (secondary phloem + periderm).

Describe the process of apical dominance.

Auxin produced by the shoot tip suppresses growth of lateral (axillary) buds.

What effect does cytokinin have on apical dominance?

Cytokinins released from roots counteract auxin to promote lateral bud growth.

Name a hormone antagonist pair regulating seed germination vs dormancy.

Gibberellin (promotes germination) and ABA (promotes dormancy).

What structure in a leaf controls gaseous exchange?

Stomata guarded by two guard cells.

How do radial cellulose microfibrils affect guard-cell movement?

They constrain differential expansion, causing the pore to open when turgid.