AP Biology Unit 6

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236 terms · Unit 6 from the textbook Campbell Reece Biology, by chapter, in the order they appear. Unit name: Plant Form and Function Unit pages: 712-817 Chapters: 35-39


an organism's ability to alter or molditself in response to local environmental conditions


an integrated group of cells with a common function, structure, or both


a specialized center of body function composed of several different types of tissues

root system

all of a plant's roots that anchor it in the soil, absorb and transport minerals and water, and store food

shoot system

the aerial portion of a plant body, consisting of stems, leaves, and (in angiosperms) flowers


an organ in vascular plants that anchors the plant and enables it to absorb water and nutrients from the soil

taproot system

a root system common to eudicots, consisting of one large, vertical root (the taproot) that produces many smaller lateral, or branch, roots

lateral root

a root that arises from the outermost layer of the pericycle of an established root

fibrous root system

a root system common to monocots consisting of a mat of thin roots spreading out below the soil surface


a term describing any plant organ that grows in an atypical location, such as roots growing from stems

root hair

a tiny extension of a root epidermal cell, growing just behind the root tip and increasing surface area for absorption of water and minerals


a vascular plant organ consisting of an alternating system of nodes and internodes that support the leaves and reproductive structures


a point along the stem of a plant at which leaves are attached


a segment of a plant stem between the points where leaves are attached

axillary bud

a structure that has the potential to form a lateral shoot, or branch. The bud appears in the angle formed between a leaf and a stem

terminal bud

embryonic tissue at the tip of a shoot, made up of developing leaves and a compact series of nodes and internodes


the main photosynthetic organ of vascular plants


(1) A leaflike structure of a seaweed that provides most of the surface area for photosynthesis. (2) The flattened portion of a typical leaf


the stalk of a leaf, which joins the leaf to a node of the stem


(1) In animals, a vessel that returns blood to the heart. (2) In plants, a vascular bundle in a leaf

tissue system

one or more tissues organized into a functional unit connecting the organs of a plant

dermal tissue system

the outer protective covering of plants


(1) The dermal tissue system of nonwoody plants, usually consisting of a single layer of tightly packed cells. (2) The outer covering of animals


the protective coat that replaces the epidermis in plants during secondary growth, formed of the cork and cork cambium


(1) A waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial plants. (2) The exoskeleton of an arthropod, consisting of layers of protein and chitin that are variously modified for different functions. (3) A tough coat that covers the body of a nematode

vascular tissue system

a system formed by xylem and phloem throughout a vascular plant, serving as a transport system for water and nutrients, respectively


vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from roots to the rest of the plant


vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant


the vascular tissue of a stem or root

vascular cylinder

the central cylinder of vascular tissue in a root

vascular bundle

a strand of vascular tissues (both xylem and phloem) in a stem or leaf

ground tissue system

plant tissues that are neither vascular nor dermal, fulfilling a variety of functions, such as storage, photosynthesis, and support


ground tissue that is internal to the vascular tissue in a stem; in many monocot roots, parenchyma cells that form the central core of the vascular cylinder


ground tissue that is between the vascular tissue and dermal tissue in a root or dicot stem


the contents of a plant cell exclusive of the cell wall

parenchyma cell

a relatively unspecialized plant cell type that carries out most of the metabolism, synthesizes and stores organic products, and develops into a more differentiated cell type

collenchyma cell

a flexible plant cell type that occurs in strands or cylinders that support young parts of the plant without restraining growth

sclerenchyma cell

a rigid, supportive plant cell type usually lacking protoplasts and possessing thick secondary walls strengthened by lignin at maturity


a short, irregular sclerenchyma cell in nutshells and seed coats and scattered through the parenchyma of some plants


a lignified cell type that reinforces the xylem of angiosperms and functions in mechanical support; a slender, tapered sclerenchyma cell that usually occurs in bundles


a long, tapered water-conducting cell that is dead at maturity and is found in the xylem of all vascular plants

vessel element

a short, wide, water-conducting cell found in the xylem of most angiosperms and a few nonflowering vascular plants. Dead at maturity, vessel elements are aligned end to end to form micropipes called vessels


a thinner region in the walls of tracheids and vessels where only primary wall is present


continuous water-conducting micropipes found in most angiosperms and a few nonflowering vascular plants

sieve-tube member

a living cell that conducts sugars and other organic nutrients in the phloem of angiosperms. They form chains called sieve tubes

sieve plate

an end wall in a sieve-tube member, which facilitates the flow of phloem sap in angiosperm sieve tubes

companion cell

a type of plant cell that is connected to a sieve-tube member by many plasmodesmata and whose nucleus and ribosomes may serve one or more adjacent sieve-tube members

indeterminate growth

a type of growth characteristic of plants, in which the organism continues to grow as long as it lives

determinate growth

a type of growth characteristic of most animals and some plant organs, in which growth stops after a certain size is reached


a flowering plant that completes its entire life cycle in a single year or growing season


a flowering plant that requires two years to complete its life cycle


a flowering plant that lives for many years


plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth

apical meristem

embryonic plant tissue in the tips of roots and in the buds of shoots that supplies cells for the plant to grow in length

primary growth

growth produced by apical meristems, lengthening stems and roots


referring to nonwoody plants

secondary growth

growth produced by lateral meristems, thickening the roots and shoots of woody plants

lateral meristem

a meristem that thickens the roots and shoots of woody plants. The vascular cambium and cork cambium are lateral meristems

vascular cambium

a cylinder of meristematic tissue in woody plants that adds layers of secondary vascular tissue called secondary xylem (wood) and secondary phloem

cork cambium

a cylinder of meristematic tissue in woody plants that replaces the epidermis with thicker, tougher cork cells


cells that remain within an apical meristem as sources of new cells


new cells that are displaced from an apical meristem and continue to divide until the cells they produce become specialized

primary plant body

the tissues produced by apical meristems, which lengthen stems and roots

root cap

a cone of cells at the tip of a plant root that protects the apical meristem

zone of cell division

the zone of primary growth in roots consisting of the root apical meristem and its derivatives. New root cells are produced in this region

zone of elongation

the zone of primary growth in roots where new cells elongate, sometimes up to ten times their original length

zone of maturation

the zone of primary growth in roots where cells complete their differentiation and become functionally mature


the innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the cortex and the vascular cylinder


the outermost layer of the vascular cylinder of a root, where lateral roots originate

leaf primordia

fingerlike projections along the flanks of a shoot apical meristem, from which leaves arise


a microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant

guard cells

the two cells that flank the stomatal pore and regulate the opening and closing of the pore


the ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis

palisade mesophyll

one or more layers of elongated photosynthetic cells on the upper part of a leaf; also called palisade parenchyma

spongy mesophyll

loosely arranged photosynthetic cells located below the palisade mesophyll cells in a leaf

leaf trace

a small vascular bundle that extends from the vascular tissue of the stem through the petiole and into a leaf

bundle sheath

a protective covering around a leaf vein, consisting of one or more cell layers, usually parenchyma

secondary plant body

the tissues produced by the vascular cambium and cork cambium, which thicken the stems and roots of woody plants

fusiform initials

cells within the vascular cambrium that produce elongated cells such as tracheids, vessel elements, fibers, and sieve-tube members

ray initials

cells within the vascular cambrium that produce xylem and phloem rays, radial files that consist mostly of parenchyma cells


older layers of secondary xylem, closer to the center of a stem or root, that no longer transport xylem sap


outer layers of secondary xylem that still transport xylem sap


small raised areas in the bark of stems and roots that enable gas exchange between living cells and the outside air


all tissues external to the vascular cambium, consisting mainly of the secondary phloem and layers of periderm


the development of body shape and organization

systems biology

an approach to studying biology that aims to model the dynamic behavior of whole biological systems

preprophase band

microtubules in the cortex (outer cytoplasm) of a cell that are concentrated into a ring

pattern formation

the ordering of cells into specific three-dimensional structures, an essential part of shaping an organism and its individual parts during development

positional information

signals to which genes regulating development respond, indicating a cell's location relative to other cells in an embryonic structure


a lack of symmetry. Structural differences in opposite ends of an organism or structure, such as the root end and shoot end of a plant

phase change

a shift from one developmental phase to another

meristem identity gene

a plant gene that promotes the switch from vegetative growth to flowering

organ identity genes

plant homeotic genes that use positional information to determine which emerging leaves develop into which types of floral organs

ABC model

a model of flower formation identifying three classes of organ identity genes that direct formation of the four types of floral organs.

active transport

the movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins

transport protein

a transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane

proton pump

an active transport mechanism in cell membranes that uses ATP to force hydrogen ions out of a cell, generating a membrane potential in the process

membrane potential

the charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances


the coupling of the downhilldiffusion of one substance to the uphilltransport of another against its own concentration gradient


an energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Most ATP synthesis in cells occurs by chemiosmosis


the diffusion of water across a selectively permeable membrane

water potential

the physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure

megapascal (MPa)

a unit of pressure equivalent to 10 atmospheres of pressure

solute potential (Ψs)

a component of water potential that is proportional to the number of dissolved solute molecules in a solution and measures the effect of solutes on the direction of water movement; also called osmotic potential, it can be either zero or negative

osmotic potential

a component of water potential that is proportional to the number of dissolved solute molecules in a solution and measures the effect of solutes on the direction of water movement; also called solute potential, it can be either zero or negative

pressure potential (Ψp)

a component of water potential that consists of the physical pressure on a solution, which can be positive, zero, or negative

turgor pressure

the force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis


limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter


to shrink and pull away from a cell wall, or when a plant cell protoplast pulls away from the cell wall as a result of water loss


very firm. A walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water


the drooping of leaves and stems as a result of plant cells becoming flaccid


a transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis)

vacuolar membrane

a membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap; also known as the tonoplast


a membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap; also known as the vacuolar membrane


in plants, the continuum of cytoplasm connected by plasmodesmata between cells


in plants, the continuum of cell walls plus the extracellular spaces

bulk flow

the movement of water due to a difference in pressure between two locations


mutualistic associations of plant roots and fungi


the innermost layer of the cortex in plant roots; a cylinder one cell thick that forms the boundary between the cortex and the vascular cylinder

Casparian strip

a water-impermeable ring of wax in the endodermal cells of plants that blocks the passive flow of water and solutes into the stele by way of cell walls


the evaporative loss of water from a plant

root pressure

the upward push of xylem sap in the vascular tissue of roots


the exudation of water droplets, caused by root pressure in certain plants

circadian rhythm

a physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues


a plant adapted to an arid climate


(1) An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome. (2) During protein synthesis, the third stage in the elongation cycle when the RNA carrying the growing polypeptide moves from the A site to the P site on the ribosome. (3) The transport of organic nutrients in the phloem of vascular plants

sugar source

a plant organ in which sugar is being produced by either photosynthesis or the breakdown of starch. Mature leaves are the primary sugar sources of plants

sugar sink

a plant organ that is a net consumer or storer of sugar. Growing roots, shoot tips, stems, and fruits are sugar sinks supplied by phloem

transfer cell

a companion cell with numerous ingrowths of its wall, increasing the cell's surface area and enhancing the transfer of solutes between apoplast and symplast

mineral nutrient

an essential chemical element absorbed from the soil in the form of inorganic ions

essential element

in plants, a chemical element that is required for the plant to grow from a seed and complete the life cycle, producing another generation of seeds


a chemical substance that an organism must obtain in relatively large amounts. See also micronutrient


an element that an organism needs in very small amounts and that functions as a component or cofactor of enzymes. See also macronutrient


a mixture of particles derived from rock, living organisms, and humus


decomposing organic material found in topsoil


a distinct layer of soil, such as topsoil


the most fertile of all soils, made up of roughly equal amounts of sand, silt, and clay

cation exchange

a process in which positively charged minerals are made available to a plant when hydrogen ions in the soil displace mineral ions from the clay particles

sustainable agriculture

long-term productive farming methods that are environmentally safe


an emerging nondestructive technology that seeks to cheaply reclaim contaminated areas by taking advantage of the remarkable ability of some plant species to extract heavy metals and other pollutants from the soil and to concentrate them in easily harvested portions of the plant

nitrogen-fixing bacteria

microorganisms that restock nitrogenous minerals in the soil by converting nitrogen to ammonia

nitrogen fixation

the assimilation of atmospheric nitrogen by certain prokaryotes into nitrogenous compounds that can be directly used by plants


an enzyme complex, unique to certain prokaryotes, that reduces N2 to NH3


a swelling on the root of a legume. Nodules are composed of plant cells that contain nitrogen-fixing bacteria of the genus Rhizobium


a form of Rhizobium contained within the vesicles formed by the root cells of a root nodule

crop rotation

the alternation of planting a nonlegume one year and a legume the next year to restore concentration of fixed nitrogen in the soil


mutualistic associations of plant roots and fungi


a type of mycorrhiza in which the mycelium forms a dense sheath, or mantle, over the surface of the root. Hyphae extend from the mantle into the soil, greatly increasing the surface area for water and mineral absorption


a type of mycorrhiza that, unlike ectomycorrhizae, does not have a dense mantle ensheathing the root. Instead, microscopic fungal hyphae extend from the root into the soil

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