Biology Review and Vocabulary Part 11

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

Adventitious- A term describing any plant organ that grows in an atypical location, such as roots growing from stems.

Annuals- A flowering plant that completes its entire life cycle in a single year or growing season.

apical dominance- Concentration of growth at the tip of a plant shoot, where a terminal bud partially inhibits axillary bud growth.

apical meristems- Embryonic plant tissue in the tips of roots and in the buds of shoots that supplies cells for the plant to grow in length.

asymmetrical cell division-

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.

Bark- All tissues external to the vascular cambium, consisting mainly of the secondary phloem and layers of periderm.

biennials- A flowering plant that requires two years to complete its life cycle.

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

bundle sheath- A protective covering around a leaf vein, consisting of one or more cell layers, usually parenchyma.

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.

cork cambium- A cylinder of meristematic tissue in woody plants that replaces the epidermis with thicker, tougher cork cells.

cortex- Ground tissue that is between the vascular tissue and dermal tissue in a root or dicot stem.

cuticle- (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.

deriviatives- New cells that are displaced from an apical meristem and continue to divide until the cells they produce become specialized.

dermal tissue system- The outer protective covering of plants.

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

endothermic- Referring to organisms with bodies that are warmed by heat generated by metabolism. This heat is usually used to maintain a relatively stable body temperature higher than that of the external environment.

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

fibers- 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.

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

fusiform initials- Cells within the vascular cambrium that produce elongated cells such as trocheids, vessel elements, fibers, and sieve-tube members.

ground tissue systems- Plant tissues that are neither vascular nor dermal, fulfilling a variety of functions, such as storage, photosynthesis, and support.

guard cells- The two cells that flank the stomatal pore and regulate the opening and closing of the pore.

heartwood- Older layers of secondary xylem, closer to the center of a stem or root, that no longer transport xylem sap.

herbaceous- Referring to nonwoody plants.

indeterminate growth- A type of growth characteristic of plants, in which the organism continues to grow as long as it lives.

initials- Cells that remain within an apical meristem as sources of new cells.

Internodes- A segment of a plant stem between the points where leaves are attached.

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

lateral roots- A root that arises from the outermost layer of the pericycle of an established root.

leaf- The main photosynthetic organ of vascular plants.

leaf primordial- Fingerlike projections along the flanks of a shoot apical meristem, from which leaves arise.

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

lenticels- Small raised areas in the bark of stems and roots that enable gas exchange between living cells and the outside air.

meristem identity genes- A plant gene that promotes the switch from vegetative growth to flowering.

Meristems- Plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth.

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

morphogenesis- The development of body shape and organization.

nodes- A point along the stem of a plant at which leaves are attached.

organ- A specialized center of body function composed of several different types of tissues.

organ identity genes- Plant homeotic genes that use positional information to determine which emerging leaves develop into which types of floral organs.

palisade mesophyll- One or more layers of elongated photosynthetic cells on the upper part of a leaf; also called palisade parenchyma.

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

pericycle- The outermost layer of the vascular cylinder of a root, where lateral roots originate.

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

perennials- A flowering plant that lives for many years.

petiole- The stalk of a leaf, which joins the leaf to a node of the stem.

phloem- Vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant.

pith- 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.

plasticity- An organism’s ability to alter or molditself in response to local environmental conditions.

polarity phase changes-

positional information- Signals to which genes regulating development respond, indicating a cell’s location relative to other cells in an embryonic structure.

preprophase band- Microtubules in the cortex (outer cytoplasm) of a cell that are concentrated into a ring.

primary growth- Microtubules in the cortex (outer cytoplasm) of a cell that are concentrated into a ring.

primary plant body- The tissues produced by apical meristems, which lengthen stems and roots.

protoplast- The contents of a plant cell exclusive of the cell wall.

ray initials- Cells within the vascular cambrium that produce xylem and phloem rays, radial files that consist mostly of parenchyma cells.

root- An organ in vascular plants that anchors the plant and enables it to absorb water and nutrients from the soil.

root cap- A cone of cells at the tip of a plant root that protects the apical meristem.

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.

root system- All of a plant’s roots that anchor it in the soil, absorb and transport minerals and water, and store food.

sapwood- Outer layers of secondary xylem that still transport xylem sap.

Sclereids- A short, irregular sclerenchyma cell in nutshells and seed coats and scattered through the parenchyma of some plants.

sclerenchyma cells- A rigid, supportive plant cell type usually lacking protoplasts and possessing thick secondary walls strengthened by lignin at maturity.

secondary growth- Growth produced by lateral meristems, which thickens the roots and shoots of woody plants.

secondary plant body- The tissues produced by the vascular cambium and cork cambium, which thicken the stems and roots of woody plants.

shoot system- The aerial portion of a plant body, consisting of stems, leaves, and (in angiosperms) flowers.

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

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

spongy mesophylll- Loosely arranged photosynthetic cells located below the palisade mesophyll cells in a leaf.

stele- The vascular tissue of a stem or root.

stem- A vascular plant organ consisting of an alternating system of nodes and internodes that support the leaves and reproductive structures.

stomata- 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.

systems biology- An approach to studying biology that aims to model the dynamic behavior of whole biological systems.

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

terminal bud- Embryonic tissue at the tip of a shoot, made up of developing leaves and a compact series of nodes and internodes.

Tissue- An integrated group of cells with a common function, structure, or both.

tissue system- One or more tissues organized into a functional unit connecting the organs of a plant.

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

vascular bundles- A strand of vascular tissues (both xylem and phloem) in a stem or leaf.

vascular cylinder- The central cylinder of vascular tissue in a root.

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

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

vessel elements- 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.

vessels- Continuous water-conducting micropipes found in most angiosperms and a few nonflowering vascular plants.

xylem- 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.

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.

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.

apoplast- In plants, the continuum of cell walls plus the extracellular spaces.

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

bulk flow- The movement of water due to a difference in pressure between two locations.

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.

chemiosmosis- 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.

circadian rhythms- A physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues.

cotransport- The coupling of the downhilldiffusion of one substance to the uphilltransport of another against its own concentration gradient.

endodermis- 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.

guttation- The exudation of water droplets, caused by root pressure in certain plants.

megapascals- A unit of pressure equivalent to 10 atmospheres of pressure.

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.

mycorrrhizae- Mutualistic associations of plant roots and fungi.

osmosis- The diffusion of water across a selectively permeable membrane.

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.

passive transport- The diffusion of a substance across a biological membrane.

plasmolyze- 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.

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

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.

root pressure- The upward push of xylem sap in the vascular tissue of roots.

solute 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 osmotic potential, it can be either zero or negative.

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.

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.

symplast- In plants, the continuum of cytoplasm connected by plasmodesmata between cells.

tonoplasts- 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.

transfer cells- 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.

transpiration- The evaporative loss of water from a plant.

transport proteins- A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

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

turgur pressure- The force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis.

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

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

wilting- The drooping of leaves and stems as a result of plant cells becoming flaccid.

xerophytes- A plant adapted to an arid climate.

Bacteroids- A form of Rhizobium contained within the vesicles formed by the root cells of a root nodule.

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.

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.

ectomycorrhizae- 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.

endomycorrizhae- 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.

essential elements- 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.

horizons- A distinct layer of soil, such as topsoil.

humus- Decomposing organic material found in topsoil.

hydroponic culture- A method in which plants are grown without soil by using mineral solutions.

loams- The most fertile of all soils, made up of roughly equal amounts of sand, silt, and clay.

macronutrients- A chemical substance that an organism must obtain in relatively large amounts. See also micronutrient.

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

mineral nutrients- An essential chemical element absorbed from the soil in the form of inorganic ions.

mycorrhizae- Mutualistic associations of plant roots and fungi.

nitrogenase- An enzyme complex, unique to certain prokaryotes, that reduces N₂ to NH₃.

nitrogen fixation- The assimilation of atmospheric nitrogen by certain prokaryotes into nitrogenous compounds that can be directly used by plants.

nitrogen fixing bacteria- Microorganisms that restock nitrogenous minerals in the soil by converting nitrogen to ammonia.

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

phytoremediation- 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.

sustainable agriculture- Long-term productive farming methods that are environmentally safe.

topsoil- A mixture of particles derived from rock, living organisms, and humus.

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