Plant Biology - Tissues - Quick Guides | Biology

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Study GuidePlant Biology–Tissues1. Growth and DevelopmentThe wordsgrowthanddevelopmentare often used as if they mean the same thing. In botany,however, they describedifferent but closely related processesthat help shape a plant as itmatures.1.1What Is Development?Developmentrefers to the overall process by which a plant becomes mature. For example, when afertilized egg slowly turns into a fully grown tree, development is taking place.Development includes three main processes:•Growth–an increase in size•Morphogenesis–the formation of shape and structure•Differentiation–the specialization of cellsPlant development is controlled bygenetic instructionsinherited by the cells and byenvironmentalfactorssuch as light, water, and nutrients. Together, these determine how the plant forms its tissuesand organs.1.2What Is Growth?Growthis anirreversible increase in sizeof cells or plant organs. This happens in two main ways:1.Cell division–new cells are produced2.Cell enlargement–cells become biggerCell enlargement occurs because:•Thecell wall becomes more elastic•Thevacuole increases in size and water contentGrowth can occur in two patterns:•Determinate growth–growth stops after reaching a certain size•Indeterminate growth–growth continues for an unlimited timeMost plants showindeterminate growth, meaning they can keep growing throughout their lives.

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Study Guide1.3Differentiation: How Cells Become SpecializedDifferentiationis the process by which unspecialized (generalized) cells becomespecialized cellswith specific structures and functions.Although all cells formed in meristems have thesame genetic makeup, they become differentbecause:•Certain genes areturned on (expressed)•Other genes areturned off (repressed)A cell’slocationalso matters. For example:•Root cells do not form in flowers•Petals do not grow on rootsSo, both gene activity and position determine what type of cell develops.1.4Dedifferentiation: When Cells Change BackUnder special conditions,mature plant cells can reverse their specialization. This process iscalleddedifferentiation.Dedifferentiation usually happens when a plant is injured, such as:•Broken branches•Leaves damaged by insectsTo repair itself, the plant causes nearbyparenchyma cellsto dedifferentiate and then divide. Thesecells form new tissues that replace the damaged ones or perform similar functions.1.5How Plant Growth Is Different from Animal GrowthPlants and animals grow in very different ways.•Animalsgrow until they reach a genetically fixed adult size. After that, growth stops.•Plantscontinue growingthroughout their entire lives, but only in certain regions.

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Study GuidePlant growth occurs mainly inmeristematic tissues, which leads to:•Two types of tissues:primaryandsecondary•Two body forms:primary plant bodyandsecondary plant body•Two types of meristems:apicalandlateral1.6Apical Meristems and Primary GrowthApical meristemsare regions of active cell division found at thetips of roots and stems.Their main function is to:•Increase thelengthof the plant•Produceprimary tissuesAs these new cells grow:•Their vacuoles enlarge•Stems and roots increase ingirth(thickness) up to a limitOnce the maximum girth is reached (based on cell wall elasticity), the plant can still growlonger, butnot thicker.Plants that have only primary tissues—such as mostherbaceous plants—remain relatively small.1.7Lateral Meristems and Secondary GrowthWoody plantscan grow very large because they havelateral meristems.Lateral meristems:•Develop around the outer edges of roots and stems•Producesecondary tissues•Add strength and protectionThese tissues form thesecondary plant body, allowing trees and shrubs to grow thick, strong, andtall over many years.

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