Plant Origin & Classification All Materials © Cmassengale

Overview of Plants:

• All plants are multicellular & contain chlorophyll inside of chloroplasts
• Plants (also called autotrophs or producers) trap energy from the sun by photosynthesis & store it in organic compounds
• Heterotrophs or consumers get their energy directly or indirectly from plants
• Plants also release oxygen needed by consumers
• All plants are multicellular, eukaryotic organisms that reproduce sexually
• Many medicines are produced by plants
• Plants are very diverse & may be terrestrial or aquatic
• Vary in size from 1 mm in width to more than 328 feet
• May live a few weeks or some over 5000 years
• Kingdom Plantae is divided into 12 phyla or Divisions
• More than 270,000 plant species identified, but new species still unidentified in tropical rain forests

Terrestrial Adaptations:

• Plants probably evolved from green algae

• Both algae & plants have chlorophyll a & b, have cell walls made of cellulose, and store energy as starch

• First land plants had to develop adaptations to scarcity of water & climate changes (air temperature changes more rapidly than water temperature)

• Moving onto land allowed more sunlight, nutrients,  & CO₂ for photosynthesis

• A support adaptation included a compound called lignin (a hard substance that strengthens cell walls so they can support additional weight)

• The origin of vascular tissue (specialized tissue for carrying food , water, & minerals) was an evolutionary breakthrough in the colonization of land

• Plants with vascular tissue are known as Tracheophytes

• Two types of vascular tissue developed --- xylem & phloem

• Xylem carries water & inorganic nutrients from the roots to the stem & leaves

• Phloem carries carbohydrates made by the plants to wherever they're needed or stored in the plant

Copyright Holt, Rinehart, & Winston

• Some plants formed woody tissue from xylem for extra support, while others kept a flexible, non-woody stem (herbaceous plants)
• Greater amount of water lost by evaporation (transpiration) on land
• A waxy covering or cuticle developed on all plant parts exposed to air which slowed transpiration (water loss)

• Gases (carbon dioxide & oxygen) had to be able to move into & out of the plant
• Openings in the cuticle called stomata allowed movement of gases
• Two guard cells on each side of a stoma helped open & close the opening

Copyright Holt, Rinehart, & Winston

• When guard cells lose water & shrink, the stoma closes (prevents water loss in the hotter times of the day)

• When guard cells swell with water, the stoma opens for gas exchange 

copyright McGraw-Hill

• Other structural adaptations to land included roots for absorption of water and minerals leaves for gas exchange and photosynthesis

Reproductive Adaptations:

• To be successful on land, plants had to develop protective seeds for their embryos with stored food or endoderm

Copyright Holt, Rinehart, & Winston

• Seeds are better at dispersal than spores

Classification of Plants:

• They're are 12 Divisions of plants divided into two main groups based on the presence of vascular tissue
• Nonvascular plants lack vascular tissue and do not have true roots, stems, or leaves (mosses, liverworts, & hornworts)
• Most plants have vascular tissue with true roots, stems, & leaves, but may or may not produce seeds

Copyright Holt, Rinehart, & Winston

• Ferns, horsetails, & club mosses are seedless vascular plants that reproduce by spores

• Plants that reproduce by seeds are divided into 2 groups --- gymnosperms & angiosperms

• Gymnosperms have "naked" seeds usually protected by cones & includes pines, cedars, spruce, fir ...

• Angiosperms are flowering plants whose seeds are produced & protected within the fruit

Plant Life Cycles:

• Plants have 2 phases in their life cycle called alternation of generation
• The haploid gametophyte stage produces eggs & sperm, while the diploid sporophyte stage produces spores 

Copyright Holt, Rinehart, & Winston

• Plant gametes are not directly produced by meiosis but rather by mitosis from the haploid multicellular stage
• Meiosis instead produced specialized haploid cells called spores
• These spores are released by most Seedless plants, but are retained by Seed plants
• In nonvascular plants, the Gametophyte stage is dominant (mosses)

• In vascular plants, the Sporophyte stage is dominant

• Seedless vascular plants usually have a separate, small gametophyte plant

• Sexual reproduction in plants ensures that there will be genetic recombination

Seed-Bearing, Vascular Plants:

• The development of seeds with their protected embryo & stored food supply increased the reproductive success of seed plants
• Seeds remain dormant or inactive when conditions aren't favorable
• Moisture & warmer temperature cause seeds to germinate or sprout
• Young plant embryos use their endosperm as energy for early growth

• Seeds plants are divided into 2 groups based on  the type of seed they produce

Gymnosperms:

• Gymnosperms  produce seeds that not protected within an ovary
• The seeds are exposed on the upper surfaces of a spore producing structure (e.g. cone scales in conifers)
• Called "naked" seeds
• Gymnosperms do not produce flowers or fruit
• The four phyla of gymnosperms alive today include the cycads (Cycadophyta), the ginkgo (Gingkophyta), the gnetophytes (Gnetophyta), and the conifers (Coniferophyta)

• All gymnosperms have vascular tissue to conduct food, water & minerals and produce woody tissue
• Two types of cones are made by gymnosperms --- pollen cones & seed cones
• Pollen cones are small & produce pollen containing the male gametophyte which is spread by wind or insects to the female gametophyte
• Seed cones are larger and contain eggs on scales that form seeds when they are fertilized

Division Cycadophyta:

• Dominated earth when dinosaurs lived, but only about 100 species are alive today & are endangered

• Most are slow growing, palm-like plants found mostly in tropical areas

• All cycads bear cones, which are made up of seed bearing leaves (sporophylls)

• They have large compound leaves, a short thick trunk, and are dioecious (either male or female plant)

• Cycads bear naked seeds

Zamia (native to Georgia)

Division Gingkophyta:

• Ginkgoes were common in the Mesozoic period,  but today only one species of ginkgo remains (Ginkgo biloba)
• Gingko trees have distinctive fan shaped leaves & are dioecious (each tree is either male or female but not both)
• Commonly planted as an ornamental tree
• Gingkoes are not native to North America (they are found growing wild only in China)
• Deciduous tree (loses leaves in fall) with plum-shaped, fleshy seeds with a foul odor

Division Coniferophyta:

• Largest group of gymnosperms
• Called conifers 
• Found in abundance in temperate zones
• Include cedars, pines, spruce, fir, juniper, & bald cypress trees
• Their leaves are characteristically needle-like, but may be scale-like
• Usually trees or shrubs
• Evergreens (don't lose their leaves in the fall)
• Almost all conifers are monoecious, producing both male and female cones on the same tree
• Female cones are larger than male cones with woody scales containing the seeds

Pollen Cone	Seed Cone

• Conifers are dependent on the wind for pollination
• Pollen grain has air bladders to help it stay aloft in the wind
• Important source of wood, paper, turpentine, ornamental plants, Christmas trees
• Redwoods and Giant Sequoia trees are the largest living organism on earth
• Bristlecone pines are the oldest living organism on earth

Redwood Tree	Bristlecone pine Tree

Division Gnetophyta:

• The phylum Gnetophyta consists of 3 genera that are not very closely related
• Ephedra is the largest genus and consists of plants that resemble horsetails & grow in deserts
• Welwitshcia is found only in the desert area of south western Africa and has 2 single, long leaves

Welwitshcia	Ephedra

Division Anthophyta (Angiosperms):

• Flowering plants are the most successful group of plants today
• They live in almost all possible habitats
• All flowering plants produce both flowers & fruit

• Fruit is a ripened ovary with its seeds (acorns, apples, dandelion seeds, etc)

• Flowering plants co-evolved with their insect pollinators
• May be herbaceous (grasses & snapdragons or woody (oaks & grape vines)
• Rafflesia, the stinking corpse lily, is the world's largest flower

•  Flowering plants have diverse lifestyles (Sundew is carnivorous on insects; Spanish moss is an epiphyte living on another host plant; some orchids are saprophytes living on soil fungi)
• Subdivided into 2 classes based on the number of seed leaves or cotyledons in the plant embryo --- Monocotyledons & Dicotyledons
• Monocots have a single seed leaf, leaves with parallel venation, vascular tissue scattered in bundles throughout the stem, and flower parts in 3's or multiples of 3

• Dicots have a 2 seed leaf, leaves with net-veined venation, vascular tissue in rings in the stem, and flower parts in 4's or 5's multiples of 4 or 5

• Monocots are usually herbaceous, while dicots often produce wood