Biology 112 - Plants Diversity Important Key Terms

Apical meristem

Region of actively dividing cells at the tips of roots and shoots; responsible for primary growth (length)

Axillary bud

Bud located at the junction of stem + petiole; can form branches or flowers.

Primary growth

Increase in length of roots and shoots due to apical meristems.

Secondary growth

Increase in girth (thickness) due to lateral meristems; produces wood in eudicots.

Xylem

Vascular tissue that transports water + minerals w upward; composed of tracheids and vessel elements.

Phloem

Vascular tissue that transports sugars throughout the plant; composed of sieve‑tube cells + companion cells.

Guard cells

Paired cells that regulate stomatal opening and control gas exchange + water loss.

Stomata

Pores on leaf surface for gas exchange; open/close via guard cells.

Cuticle

Waxy layer on leaves/stems that prevents water loss.

Dermal tissue

Outer protective tissue; includes epidermis and cuticle.

Ground tissue

Tissue for photosynthesis, storage, and support (parenchyma, collenchyma, sclerenchyma).

Vascular tissue

Xylem + phloem; transports water, minerals, sugars.

Tracheid

Elongated xylem cell with thick walls; transports water.

Vessel element

Shorter, wider xylem cell; more efficient water transport.

Sieve‑tube cell

Phloem cell that transports sugars; lacks nucleus.

Companion cell

Phloem cell that supports sieve‑tube cells; has many mitochondria.

Root cap

Protective covering over root tip; protects apical meristem.

Root hair

Extensions of epidermal cells; increase surface area for absorption.

Fibrous root system

Dense network of roots; typical of monocots.

Taproot system

Single large root with lateral branches; typical of eudicots.

Node

Point on stem where leaves or branches attach.

Internode

Stem region between nodes.

Petiole

Leaf stalk connecting blade to stem.

Simple leaf

Leaf with a single undivided blade.

Compound leaf

Leaf divided into leaflets.

Rhizome

Horizontal underground stem.

Runner (stolon)

Horizontal aboveground stem that forms new plants.

Tuber

Swollen underground stem for starch storage.

Bulb

Underground stem surrounded by fleshy leaves (Ex. onion).

Cortex

Ground tissue between epidermis and vascular tissue.

Endodermis

Root layer that regulates entry of water/minerals into vascular tissue.

Casparian strip

Waxy barrier in endodermis forcing water through cell membranes.

Pericycle

Layer from which lateral roots arise.

Vascular bundle

Xylem + phloem in stems.

Vascular stele

Xylem + phloem in roots.

Pith

Ground tissue in center of stems/roots.

Macronutrient

Element required in large amounts (N, P, K, Ca, Mg, S, C, H, O).

Micronutrient

Element required in small amounts (Fe, Mn, Zn, Cu, etc.).

Nitrogenase

Enzyme that converts atmospheric nitrogen (N₂) → ammonia (NH₃).

Rhizobia

Nitrogen‑fixing bacteria that form nodules on legume roots.

Nodules

Root structures housing rhizobia for nitrogen fixation.

Humus

Decomposed organic matter in soil.

Loam

Ideal soil mixture of sand, silt, and clay.

Sand / Silt / Clay

Soil particles of decreasing size; affect drainage and nutrient retention.

Soil profile

Vertical layers of soil (O, A, B, C horizons).

O horizon

Surface layer rich in organic matter.

A horizon

Topsoil; mix of organic + mineral material.

B horizon

Subsoil; accumulation of minerals.

C horizon

Parent material; partially weathered rock.

Mineral soil

Soil formed from weathered rock.

Organic soil

Soil formed from decomposed organic matter.

Parasitic plant

Plant that obtains nutrients from a host.

Insectivorous plant

Plant that traps/digests insects for nutrients.

Epiphyte

Plant that grows on another plant but is not parasitic.

Saprophyte

Plant that obtains nutrients from decaying matter.

Gametophyte

Haploid plant stage that produces gametes.

Sporophyte

Diploid plant stage that produces spores.

Microsporangium

Structure producing microspores (pollen).

Megasporangium

Structure producing megaspores (embryo sac).

Microspore

Haploid spore that becomes pollen.

Megaspore

Haploid spore that becomes embryo sac.

Microgametophyte

Male gametophyte = pollen grain.

Megagametophyte

Female gametophyte = embryo sac.

Pollination

Transfer of pollen to stigma.

Double fertilization

One sperm → egg (zygote)

One sperm → polar nuclei (endosperm)

Endosperm

Triploid nutritive tissue for embryo.

Cotyledon

Seed leaf; stores nutrients.

Radicle

Embryonic root.

Hypocotyl

Embryonic stem below cotyledons.

Epicotyl

Embryonic shoot above cotyledons.

Plumule

Young shoot of embryo.

Micropyle

Opening where pollen tube enters ovule.

Stamen

Male flower part (anther + filament).

Carpel

Female flower part (stigma, style, ovary).

Perianth

Sepals + petals.

Simple fruit

Fruit from one carpel.

Aggregate fruit

Fruit from multiple carpels in one flower.

Multiple fruit

Fruit from multiple flowers.

Accessory fruit

Fruit derived from tissues other than ovary.

Pericarp

Fruit wall (exocarp, mesocarp, endocarp).

Cross‑pollination

Pollen transferred between different flowers.

Self‑pollination

Pollen transferred within same flower.

Dormancy

Period of low metabolic activity in seeds.

Scarification

Breaking seed coat to allow germination.

Vernalization

Cold exposure required for germination.