Stem Growth question

Epidermis

Outermost layer of a young/primary stem; single layer of cells, often covered by a waxy cuticle for protection and water control

Cortex

Ground tissue layer just inside the epidermis in a stem; often contains collenchyma (support) and parenchyma (storage/photosynthesis)

Primary phloem

Food-conducting tissue formed by the procambium during primary growth; lies toward the outside of the vascular tissue

Vascular cambium

Lateral meristem located between primary xylem and primary phloem; becomes active during secondary growth to produce secondary xylem/phloem

Primary xylem

Water-conducting tissue formed by the procambium during primary growth; lies toward the inside/center of the vascular tissue

Pith

Ground tissue at the very center of the stem; mostly parenchyma, used for storage

Stem tissue order (primary, outside to inside)

Epidermis → cortex → primary phloem → (vascular cambium) → primary xylem → pith

Stem tissue order (with secondary growth, outside to inside)

Periderm → cortex → primary phloem (fibers) → secondary phloem → vascular cambium → secondary xylem → primary xylem → pith

Procambium

Primary meristem that gives rise to primary xylem, primary phloem, and (in stems that undergo secondary growth) the vascular cambium

Protoderm

Primary meristem that gives rise to the epidermis

Ground meristem

Primary meristem that gives rise to ground tissue (cortex and pith)

Apical meristem

Meristem at the tip of shoots and roots; responsible for primary growth (growth in length)

Primary growth

Growth in length, produced by apical meristems (shoot tip and root tip) dividing and elongating

Lateral meristem

Meristem running along the side of stems/roots; responsible for secondary growth (growth in width)

Secondary growth

Growth in thickness/girth, produced by the two lateral meristems: vascular cambium and cork cambium

How primary and secondary growth relate

Primary growth happens at the tips (elongation); secondary growth happens behind the tips in older tissue that has stopped elongating — both occur simultaneously in different parts of the same plant

Auxin

Plant hormone produced by developing shoot buds; moves downward in the stem and triggers reactivation of the vascular cambium in spring

Periclinal division

Cell division parallel to the stem surface; the way cambium cells add new xylem (inward) and phloem (outward) cells, causing growth in girth

Anticlinal division

Cell division perpendicular to the stem surface; the way cambium initials multiply to keep pace with increasing stem circumference

Cell wall

Rigid outer layer surrounding the plasma membrane in plant cells; made of cellulose, hemicellulose, and pectin (may also contain lignin or suberin)

Cellulose

Main structural polysaccharide of the plant cell wall; long chains of glucose forming strong fibers

Lignin

Rigid, waterproofing compound deposited in cell walls of xylem and support tissues, providing strength

Suberin

Waxy, water-repellent compound found in cork cell walls and the root endodermis; makes tissue impermeable to water/gas

Middle lamella

Pectin-rich layer that glues adjacent plant cell walls together

Plasma membrane

Selectively permeable membrane surrounding the cytoplasm, controlling what enters/exits the cell

Nucleus

Membrane-bound organelle containing the cell's DNA; controls gene expression and cell activity

Chloroplast

Organelle where photosynthesis occurs; contains chlorophyll and is organized into thylakoids (stacked as grana) surrounded by stroma

Chlorophyll

Green pigment in chloroplasts that absorbs light energy for photosynthesis

Mitochondrion

Organelle where cellular respiration occurs, producing ATP (energy) for the cell

Central vacuole

Large, membrane-bound organelle in plant cells that stores water, ions, and waste; maintains turgor pressure against the cell wall

Turgor pressure

Pressure of the cell contents (mainly from the vacuole) pushing against the cell wall; keeps plant tissues firm/rigid

Endoplasmic reticulum (ER)

Network of membranes involved in protein (rough ER, has ribosomes) and lipid (smooth ER) synthesis

Ribosomes

Small structures (free or on rough ER) that synthesize proteins

Golgi apparatus

Organelle that modifies, packages, and ships proteins and other molecules, often to the cell wall or vacuole

Plasmodesmata

Small channels through plant cell walls that connect the cytoplasm of adjacent cells, allowing transport between cells

Plastid

General term for a family of organelles including chloroplasts (photosynthesis) and other types (e.g., storage of starch)