•Between 260,000 and 300,000 plant specieshave been discovered and identified.
•Without plants,most life onEarth as weknow it wouldnot be possible.
What is a plant?
An Overview of Plants
An Overview of Plants
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•Plants are important food sources to humansand other
consumers.
•Plants range in sizefrom microscopicwater ferns to giantsequoia trees thatare sometimesmore than 100 min height.
•Most have roots or rootlike structures.
Plant Characteristics
An Overview of Plants
An Overview of Plants
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•Plants are adapted to nearly every environmenton Earth.
•All plants need water.
Plant Characteristics
An Overview of Plants
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•A plant cell has a cell membrane, a nucleus,and other cellular structures.
•In addition, plant cells have cell walls thatprovide structure and protection.
Plant Cells
An Overview of Plants
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•Many plant cells contain the green pigmentchlorophyll (KLOR uh fihl) so most plantsare green.
•Chlorophyll isfound in a cellstructure calleda chloroplast.
Plant Cells
An Overview of Plants
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•This structureplays an importantrole in regulatingthe water contentof the cell.
Plant Cells
An Overview of Plants
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•Most plant cells have a large, membrane-bound structure called the central vacuole thattakes up most of the
space inside of thecell.
•The first plantsthat lived on landprobably couldsurvive only indamp areas.
•Their ancestorswere probablyancient greenalgae that lived inthe sea.
Origin and Evolution of Plants
An Overview of Plants
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•Today, plants and green algae have the sametypes of chlorophyll and carotenoids (kuhRAH tun oydz) in their cells.
•These facts lead scientists to think that plantsand green algae have a common ancestor.
Origin and Evolution of Plants
An Overview of Plants
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•Most animals have bones or other hard partsthat can fossilize.
•Plants usually decay before they becomefossilized.
Fossil Record
An Overview of Plants
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•The oldest fossil plants are about 420 millionyears old.
•Cone-bearing plants, such as pines, probablyevolved from a group of plants that grewabout 350 million years ago.
•It is estimated that flowering plants did notexist until about 120 million years ago.
Fossil Record
An Overview of Plants
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•However, the exact origin of flowering plantsis not known.
•More sunlight and carbon dioxide, needed forphotosynthesis, are available on land than inwater.
•During photosynthesis, plants give off oxygen.
Life on Land
An Overview of Plants
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•Long ago, as more and more plants adapted tolife on land, the amount of oxygen in Earth'satmosphere increased.
Adaptations to Land - Protectionand Support
An Overview of Plants
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•The cuticle slowsthe loss of water.
•Covering the stems, leaves, and flowers ofmany plants is a cuticle (KYEW tih kul) - awaxy, protective
layer secreted bycells onto thesurface of theplant.
•Like all cells, plants cells have cellmembranes, but they also have rigidcell walls outside the membrane.
Adaptations to Land - Protectionand Support
An Overview of Plants
An Overview of Plants
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•Cell walls contain cellulose (SEL yuh lohs),which is a chemical compound that plants canmake out of sugar.
•Long chains of cellulose molecules formtangled fibers in plant cell walls. These fibersprovide structure and support.
Other Cell Wall Substances
An Overview of Plants
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•Through adaptations,structures developed inmany plants thatdistribute water,nutrients, and food toall plant cells.
•The presence of water-resistant sporeshelped some plants reproduce successfully.
Reproduction
An Overview of Plants
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•Other plants adapted by producing water-resistant seeds in cones or in flowers thatdeveloped into fruits.
•The plant kingdom is classified into majorgroups called divisions.
Classification of Plants
An Overview of Plants
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•A division is the same as a phylum in otherkingdoms.
•Another way to group plants is as vascular(VAS kyuh lur) or nonvascular plants.
•Vascular plants havetubelike structures thatcarry water, nutrients,and other substancesthroughout the plant.
Classification of Plants
An Overview of Plants
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•Nonvascular plants donot have these tubelikestructures and use otherways to move water andsubstances.
•In the third century B.C., most plants weregrouped as trees, shrubs, or herbs and placedinto smaller groups by leaf characteristics.
Naming Plants
An Overview of Plants
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•This simple system survived until late in theeighteenth century.
•Carolus Linnaeus developed a way to nameplants called binomial nomenclature (bi NOHmee ul · NOH mun klay chur).
•His new system used many characteristics toclassify a plant.