Survey of Plants and Plant Structure

Chapter 28

How Did Plants Evolve?

• Plants are extremely diverse and cover both land and many bodies of water around the Earth

• Plants that live in the water can absorb water easily through all layers

• When plants moved to land, however, they had to adapt to the drier environment:– Prevent water loss– Obtain nutrients from environment– Reproduce without water

Prevent Water Loss

• Moving to land meant more exposure to sunlight• Increased photosynthesis AND drying out• Plant leaves evolved cuticles to protect from

sunlight, prevent too much water loss and prevent loss of carbon dioxide

• Stomata – small openings in the surfaces of leaves that can open and close to exchange CO2 and O2

Absorb Nutrients

• Aquatic plants absorb nutrients readily from the water around them

• Terrestrial plants, however, evolved roots for stability and absorption of nutrients

• Some plants evolved vascular tissue to transport water and nutrients up and down the plant:– Xylem: carries water and inorganic nutrients in one

direction (root to stems and leaves)– Phloem: carries carbohydrates (sugar) in any direction

(leaves to roots or roots to leaves)

Reproduction

• Simple plants reproduce via spores (kind of like fungi), but more complex plants reproduce via seeds and spores

• Plant spores are haploid cells surrounded by a hard outer wall; they allowed for dispersal of early plants

• Plant seeds are embryos surrounded by a protected coat; seeds are more effective at dispersal than spores

Classification of Plants

• There are 12 Phyla under the Kingdom Plantae• These phyla can be divided into two groups: non-

vascular and vascular plants• Non-vascular plants DO NOT have a true vascular

system (xylem and phloem), nor do they have true roots, stems and leaves

• Vascular plants DO have xylem, phloem, roots, stems and leaves

• Among vascular plants, there are seed plants and non-see plants

Alternation of Generations

• All plants have a complex life cycle that involves two phases

• The diploid (2n) phase produces spores: this is called the sporophyte phase

• The haploid (n) phase produces eggs and sperm: this is called the gametophyte phase – Hint to remember: YOU produces GAMETES via

meiosis (n = haploid)• This is called alternation of generations

Non-Vascular Plants - Moss

• Phylum Bryophyta – This includes moss; these are the most simple and primitive plants

• They are seedless and mostly terrestrial• Reproduction via alternation of generations, BUT

they need water to reproduce sexually for sperm to swim

• Very small (less than 3 cm tall) and have rhizoids instead of roots

• Bryophytes are usually the first plants to grow in an area

Non-Vascular - Liverworts

• Phylum Hepatophyta – This includes liverworts; these grow in moist, shady areas

• The leaflike structures of liverworts are very thin and they also have rhizoids instead of roots

• ALL liveworts live close to the ground so they can absorb water easily

• Sperm also swim to the egg

Non-Vascular - Hornworts

• Phylum Anthocerophyta – This includes hornworts; these also grow in moist, shady areas

• Hornworts have long, thin, horn like sporophytes that grow out of the top of the plant

• No stems or leaves and they have rhizoids instead of roots

Vascular Plants

• Vascular plants have roots, leaves and stems• In their stems are xylem and phloem (RECALL)• These plants are more diverse and can live in

many different areas than non-vascular plants• Some vascular plants can grow very tall and

get more light than shorter plants

Seedless Plants

• Whisk Ferns – NOT ferns; no roots or leaves, but have branches with spores on the end– These were probably the first land plants– Some grow on other plants (epiphytes)

• Club Mosses – They look like mini pine trees– They produce small cones– Can survive without water– They will curl up when it is dry but can uncurl

within hours of getting more water

Seedless Plants Cont

• Horsetails – Have photosynthetic stems with scalelike leaves at the end– The vertical stems of horsetails are hollow– They are very tough and early Americans used them to

scrub pots and pans• Ferns – Are a very diverse group– Can grow in the arctic, the desert and in temperate

areas– Ferns have an underground stem (like roots) called a

rhizome, leaves and stems

Seed Plants - Gymnosperms

• Gymnosperms – produce “naked” seeds (most produce cones)

• Gymnosperms include FOUR phyla: – Cycads – Were around with dinos, only about 100

species left– Gingkoes – Deciduous (retain leaves year-round)– Conifers – Includes pines, cedar, redwood, fir, spruce,

juniper and cypress– Gnetophytes – resemble angiosperms, short stems

and leaves, can live in desert environments

Seed Plants – Angiosperms

• Phylum Anthophyta – The largest phylum of plants, includes ALL flowerd plants

• They are characterized by the presence of a flower and fruit

• FRUIT is defined as a ripened ovary that surrounds the seeds of angiosperms

• An ovary is the FEMALE part of the plant that encloses the egg(s)

Monocots vs Dicots

Plant Type Embryo Leaves Stems Flower Parts

Examples

Monocots ONE cotyledon

Parallel veins

Scattered Vascular Bundles

Usually occur in threes

Lilies, bananas, bamboo, coconut

Dicots TWO cotyledons

Net veins Ringed vascular arrangment

Usually occur in fours or fives

Beans, lettuce, maples, roses