Plants are multicellular eukaryotes that are photosynthetic autotrophs Cell walls are made of cellulose

General characteristics of plants

1. Plants are multicellular eukaryotes that are photosynthetic autotrophs

2. Cell walls are made of cellulose

3. Carbohydrates are stored as starch

4. Alternation of Generations

   1. Sporophyte

      1. Diploid plant

   2. Gametophyte

      1. Haploid plant

   3. Sporangium

      1. Where meiosis occurs to form haploid spores

   4. Gametangia

      1. Where gametes are formed

A case for green algae as plant ancestors (400 million years ago)

1. Fungi may have accompanied them

   1. Thus explaining the intimate relationship of fungi and algae (lichens) and fungi and plants (mycorrhizae)

2. Some evidence includes

   1. Both have the same photosynthetic pigments

   2. Chloroplast structure similar

   3. Cell walls of both are made of cellulose

   4. Both store carbohydrates as starch

   5. Cell division similar

3. The specific green algae that colonized land are unknown

   1. There is little fossil evidence since green algae thalli are soft

4. During the Silurian period, land was subjected to flooding and draining

   1. Thus, natural selection would favor algae that could survive when not submerge

   2. Cuticles and jacketed reproductive organs evolved

5. Terrestrial frontier offered unfiltered sunlight and, initially, the absence of herbivores (predators of plants)

In the plants kingdom, "phylum" is replaced with "division"

The text recognizes 12 divisions

Know there general characteristic, variation in life style, and how each is more adapted for land

1. Nonvascular Plants

   1. Division Bryophyta

      1. Mosses

      2. 16,000 species

   2. Division Hepatophyta

      1. Liverworts

   3. Division Anthocerophyta

      1. hornworts

2. Vascular Seedless Plants

   1. Division Psilophyta

      1. Whisk ferns

      2. 10 to 13 species

   2. Division Lycophyta

      1. Club mosses

      2. 1,000 species

   3. Division Sphenophyta

      1. Horsetails

      2. 15 species

   4. Division Pterophyta

      1. Ferns

      2. 12,000 species

3. Vascular Seed Plants

   1. Division Coniferophyta

      1. Conifers

      2. 550 species

   2. Division Cycadophyta

      1. Cycads

      2. 100 species

   3. Division Ginkgophyta

      1. Ginkgo

      2. 1 species

   4. Division Gnetophyta

      1. Gnetae

      2. 70 species

   5. Division Anthophyta

      1. Flowering Plants

      2. 235,000 species

Non-vascular plants

1. Adaptations

   1. Waxy cuticle

   2. Protected gamatangia

      1. Sperm is produced in antheridium

      2. Egg is produced in archegonium

      3. Embryo develops in protective jacket of female reproductive organ

2. Dependence on water

   1. Sperm

   2. No vascular tissue (acts like sponge)

3. Bryophyta (Mosses)

   1. Be familiar with life cycle

4. Hepatophyta (liverworts)

   1. Gametophyte liver-shaped

5. Anthocerophyta (hornworts)

   1. Sporophyte shaped like a horn

   2. Contains 1 single large chloroplast

Vascular-seedless plants

1. Adaptations

   1. Subterranean roots that absorbs water and minerals, and an aerial shoot system of stems and leaves to make food (on land, the necessary resources were spatially separated)

   2. Lignin

      1. A material embedded in the plant cell walls that provides support (unnecessary in aquatic habitats since plants are essentially weightless there)

   3. A continuos vascular system transports material from roots to shoots, and vice versa

      1. Xylem

         1. Dead, tube-shaped cells that carry water and minerals from roots to aerial parts of the plant

      2. Phloem

         1. Living cells that distribute sugars throughout the plant

   4. Diploid dominant

      1. If UV light destroys an essential gene, it has a backup

   5. Still have flagellated sperm

2. Psilophyta

   1. Whisk ferns

      1. Not a true fern

   2. Sporophyte stage is dominant

3. Lycophyta

   1. Club mosses or ground pines

      1. Not a moss nor a pine

      2. Sporophyte dominant

   2. Many are epiphytes

      1. Plants that use another organism for substrate, but not parasitic

   3. Gametophyte

      1. Non-photosynthetic

      2. Lives underground (up to 10 years) nurtured by fungi

      3. Each gametophyte contains an archegonium and anthredium

4. Sphenophyta

   1. Horsetails

   2. Sporophyte dominant

   3. Gametophyte free-living and photosynthetic

5. Pterophyta

6. Ferns

   1. Most common seedless plants

   2. Know life cycle

   3. Sporophyte dominant

      1. Sori

         1. Contain sporangia

Three life cycle modification contributed to seed plant success

1. Gametophytes became reduced and retained in the moist reproductive tissue of the sporophyte generation (not independent)

   1. Protected against desiccation and UV radiation

2. Pollination evolve

   1. Since no flagellated sperm, not confined to damp soil

3. The evolution of the seed (approximately 360 million years ago)

   1. Seed

      1. Zygote develops into an embryo packaged with a food supply within a protective covering

   2. Seeds replace spores as main means of dispersal

GYMNOSPERMS (naked seed)

1. Introduction

   1. Encompass 3 small divisions (Cycadophyta, Ginkgophyta, and Gnetophyta) and one large division, Coniferophyta

   2. Were the first seed plants to evolve (before angiosperms)

   3. Lack an enclosed chamber in which seeds develop

2. Division Coniferophyta

   1. Introduction

      1. Contains the pines, firs, yews, redwoods, cedars, junipers, spruce, larches and cypresses

      2. Most are evergreens

      3. Coniferous trees are among the tallest, largest, and oldest organisms on Earth

   2. Conifers are heterosporous

      1. Male and female gametophytes develop from different types of spores produced by two types of cones:

         1. The smaller pollen cones where the male gametophytes (pollen) develop

         2. The larger ovulate cones where the female gametophytes develop

   3. Life cycle

      1. Fertilization occurs one year after pollination

      2. Winged seeds are dispersed by wind

Introduction

1. A radiation of flowering plants occurred approximately 130 million years ago

   1. The flower has protective ovaries, unlike the naked seeds of gymnosperms

   2. The vast majority of contemporary plants are angiosperms (flowering plants)

2. Taxonomy

   1. Flowering plants are the most widespread and diverse

   2. Has only one division, Anthophyta

      1. Contains two classes

         1. Monocotyledons (monocots) and Dicotyledones (dicots)

3. Dependency on animals

   1. Most use insects and animals for transferring pollen, and, therefore, are less dependent on wind and have less random pollination

      1. Those that don't use wind dispersal usually have drab colored flowers (i.e., grasses)

   2. Seeds are dispersed from the source plant when fruits are moved about by the wind or animals

Life cycle of an angiosperm (Summary)

1. Seeds deposited in soil of the proper conditions (moisture, nutrients) will germinate

2. The embryo starts growing and develops into a new sporophyte

3. After flowers are produced by the sporophyte, a new generation of gametophytes develop

4. The gamete of the male gametophyte (pollen) will fuse with the egg of the female gametophyte to produce a zygote that will develop into a seed, and the life cycle continues

The angiosperm life cycle (Overview)

1. Includes an alternation of generations

   1. An alternation between a haploid form (gametophyte) and diploid form (sporophyte) in the life cycle of a plant

2. The sporophyte is the recognizable "plant" most familiar to us

   1. It produces haploid spores by meiosis in sporangia

3. Spores undergo mitotic division and develop into multicellular male & female gametophytes

4. Gametophytes produces gametes (sperm and egg) by mitosis

   1. The gametes fuse to form a zygote which develops into a multicellular sporophyte

5. The sporophyte is dominant in the angiosperm life cycle with the gametophyte stages reduced to a few cells being totally dependent on the sporophyte

The flower

1. Introduction

   1. Flowers are the reproductive structure of an angiosperm

      1. Male gametophytes develop in the stamen sporangia

      2. Female gametophytes develop in the carpel sporangia

2. Parts of the flower

   1. Sepals

      1. Enclose the bud (usually green)

   2. Petals - aid in attracting pollinators

   3. Stamen

      1. Male reproductive structure

      2. Filament

         1. Structure to which the anther is attached

      3. Anther

         1. Produces the male gametophytes (pollen)

   4. Carpel

      1. Female reproductive structure

      2. Stigma

         1. Part of the carpel that receives the pollen

      3. Style

         1. Tube from stigma to ovary

      4. Ovary

         1. Part of the carpel that protects the ovules (female gametophyte)

The fruit

1. A ripened ovary that protects dormant seeds and aids in their dispersal

   1. Seeds are within fruits that act as kites or propellers to aid in wind dispersal

   2. Fruits are modified as burrs that cling to animal fur

   3. Fruits are edible and seeds pass through the digestive tract of herbivores unharmed, dispersing seeds miles away

2. Fruit classification

   1. Simple fruits

      1. Fruit derived from a single ovary

      2. For example, cherry (fleshy) or soybean (dry)

   2. Aggregate fruits

      1. Fruit derived from a single flower with several separate carpels

      2. For example, strawberry

   3. Multiple fruits

      1. Fruit derived from an inflorescence or separate tightly clustered flowers

      2. For example, pineapple

Pollen

1. Pollen grain

   1. The immature male gametophyte that develops within the anthers of stamens in an angiosperm

2. Formation of a pollen grain

   1. Within the sporangial chamber of an anther, diploid microsporocytes undergo meiosis to form four haploid microspores

   2. The haploid microspore nucleus undergoes mitotic division to give rise to a generative cell and a tube cell

   3. The wall of the microspore then thickens and becomes sculptured into a species-specific pattern

   4. These two cells and the thickened wall are the pollen grain, an immature male gametophyte

Ovules

1. Ovules

   1. Structures which form within the chambers of the plant ovary and contains the female gametophyte

2. Development

   1. A megasporocyte in the sporangium of each ovule goes through meiosis to form 4 haploid megaspores (only one survives)

   2. The remaining megaspore's nucleus undergoes 3 mitotic divisions, forming 1 large cell with 8 haploid nuclei

   3. Membranes partition this into a multicellular embryo sac

      1. The egg cell is located at one end

      2. 2 cells (synergids) flank the egg cell

      3. At the opposite end are 3 antipodal cells

      4. The other 2 nuclei (polar nuclei) share the cytoplasm of the large central cell

Pollination and fertilization

1. Pollination

   1. The placement of pollen onto the stigma of a carpel

      1. Some plants use wind to disperse pollen

      2. Other plants have relationships with animals that transfer pollen directly between flowers

   2. Some plants self-pollinate, but most have mechanisms that make self-pollination difficult or prevent self-pollination, ensuring genetic variety

   3. Most monoecious angiosperms have mechanisms to prevent self-pollination

      1. Dioecious plants do not have to worry about self pollination

      2. These mechanisms thus contribute to genetic variations in the species by ensuring sperm and eggs are from different plants

      3. The stamens and carpels mature at different times in some species

      4. Structural arrangement of the flower in many species pollinated by animals reduces the chance that pollinators will transfer pollen from anthers to the stigma of the same flower

      5. Other species are self-incompatible, a single-gene-based mechanism

         1. A biochemical block prevents the pollen grain from developing and fertilizing the egg

2. Angiosperms undergo double fertilization

   1. After adhering to a stigma, the pollen grain germinates and extends a pollen tube between the cells of the style toward the ovary

   2. The generative cell divides (mitosis) to form two sperm

      1. Pollen grain with tube enclosing two sperm

         1. Mature male gametophyte

   3. The pollen tube enters the ovule and discharges its two sperm nuclei into the embryo sac

   4. One sperm unites with the egg to form the zygote

   5. The other sperm combines with the two polar nuclei to form a 3N nucleus in the large central cell of the embryo sac

      1. This central cell will give rise to the endosperm which is a food storing tissue

   6. After fertilization is completed, each ovule will develop into a seed and the ovary will develop into a fruit surrounding the seed(s)

The seed

1. The triploid nucleus divides to form a milky, multinucleated "supercell"

   1. The endosperm undergoes cytokinesis to form membranes and cell walls between the nuclei

      1. Endosperm is rich in nutrients, which it provides to the developing embryo

         1. In many dicots, food reserves of the endosperm are restocked in cotyledons, thus mature seeds have no endosperm

Breaking Dormancy

1. Conditions for breaking dormancy vary

   1. A desert plant may not germinate unless there has been heavy rainfall (not a drizzle)

   2. In chaparral regions where brush-fires are common, seeds may not germinate unless exposed to intense heat, after a fire has cleared away old, competing vegetation

   3. Other seeds may require exposure to cold, sunlight, or passage through an animal's digestive system before germination will occur

More about flowers

1. Complete flower

   1. A flower with sepals, petals, stamens, and carpels

2. Incomplete flower

   1. A flower that is missing one or more of the parts listed for a complete flower

      1. Most grasses do not have petals on their flowers

3. Perfect flower

   1. A flower having both stamens and carpels

      1. May be incomplete by lacking either sepals or petals

4. Imperfect flower

   1. A flower that is either staminate (having stamens but no carpels) or carpellate (having carpels but no stamens) - a unisex flower

5. Monoecious

   1. Plants having both staminate flowers and carpellate flowers on the same individual plant

6. Dioecious

   1. Having staminate flowers & carpellate flowers on separate plants of the species

Plant morphology

1. The study of the external structure of plants (arrangement of the parts of a flower

General

1. A plant can be divided into two basic systems, a subterranean root system and an arial stem system (stems, leaves, flowers)

   1. This two system arrangement reflects the evolutionary history of plants as terrestrial organisms

      1. Unlike the algal ancestors which are completely surrounded by nutrient rich water, terrestrial plants face a divided habitat

         1. Air is the source of CO₂ for photosynthesis and sunlight cannot penetrate into the soil; soil provides water and dissolved minerals to the plant

      2. Each system depends on the other for survival of the whole plant

         1. Roots depend on shoots for sugar and other organic nutrients

         2. Shoots depend on roots for minerals, water, and for support

      3. Xylem conveys water and dissolved minerals to the shoots

      4. Phloem conveys food from shoots to roots and other non-photosynthetic parts, and from storage roots to actively growing shoots

The root system

1. Roots anchor plants, absorb and conduct water and minerals and store food

2. There are two major types of root systems

   1. Taproot system

      1. One large, vertical root (the taproot) produces many smaller secondary roots

      2. Seen in many dicots

      3. Provides firm anchorage

      4. Some taproots such as carrots, turnips, and sweet potatoes, are modified to store a large amount of reserve food

   2. Fibrous root system

      1. Mat of thread-like roots spread out below the soil surface

      2. Provides extensive exposure to soil water and minerals

      3. Roots are concentrated in the upper few centimeters of soil, preventing soil erosion

      4. Mostly seen in monocots

      5. Absorption of water is greatly increased by root hairs, which increase the surface area of the root

         1. Roothairs are normally most numerous near the root tip

   3. Adventitious roots

      1. Roots arising above ground from stems or leaves

      2. Some, such as prop roots of corn, help support the plant stem

The shoot system

1. Shoot systems are comprised of vegetative shoots and floral shoots

   1. Vegetative shoots consist of a stem and attached leaves; may be the main shoot or branch

   2. Floral shoots terminate in flowers

2. Stems

   1. Nodes are the points at which leaves are attached to stems

   2. Internodes are the stem segments between the nodes

3. Leaves

   1. Introduction

      1. Leaves are the main photosynthetic organs of a plant

      2. Usually in the shape of a flattened blade

      3. Petioles join the leaf to the node of a stem (Most monocots lack petioles; instead, the leaf base forms a sheath enclosing the stem.)

      4. Monocot leaves have parallel major veins running the length of the blade

      5. Dicot leaves have a multi-branched network of major vein Can be palmate or pinnate

      6. All leaves have numerous minor cross-veins

   2. Classification of leaf arrangement on stem

      1. Opposite

         1. 2 leaves at each node 180 apart.

      2. Alternate

         1. Each node has one leaf and leaves at adjacent nodes point in opposite directions

      3. Whorled

         1. A node has 3 or more leaves attached

      4. Simple leaf

         1. One undivided blade

      5. Compound leaf

         1. Divided into several leaflets

   3. Classification by leaf shape

      1. Can be lanceolate, oval, cordate (heart-shaped) or triangular

   4. Classification by leaf margin

      1. Can be entire (smooth), undulate, serrate, or lobed

   5. Leaf adaptations

      1. Tendrils are modified leaflets that cling to supports

      2. Spines of cacti function in protection

      3. Many succulents have leaves modified for storing water

      4. Some plants have brightly colored leaves that help attract pollinators to the flower

Plant anatomy

1. The study of the internal structure of the plant

   1. Arrangement of the cells and tissues in a leaf

Types of plant cells

1. Parenchyma cells

   1. Parenchyma cells are relatively unspecialized

   2. Structure

      1. Primary walls are thin and flexible

      2. Lack secondary walls

      3. The protoplast usually has a large central vacuole

   3. Function in synthesizing and storing organic products

      1. Some in stems and roots have colorless plastids that store starch

      2. Most mature cells do not divide, but retain the ability to divide and differentiate into other cell types under special conditions (repair and replacement after injury)

2. Collenchyma cells

   1. Collenchyma cells have protoplasts and usually lack secondary walls

   2. Structure

      1. Primary walls are unevenly thickened

   3. Function

      1. Are usually grouped in strands or cylinders to support young parts of plants without restraining growth

      2. Elongate as the young stems and leaves they support grow

3. Sclerenchyma cells

   1. Function

      1. Sclerenchyma cells function in support

   2. Structure

      1. Have very rigid, thick secondary walls strengthened by lignin

      2. So specialized for support that many lack protoplasts at functional maturity

      3. At maturity, cannot elongate and may be dead, functioning only as support

4. Tracheids and vessel elements

   1. Water-conducting cells

      1. Xylem consists of two cell types, both dead at functional maturity

   2. Tracheids are long, thin tapered cells having lignin-hardened secondary walls with pits (thinner regions where only primary walls are present)

      1. Water flows from cell to cell through pits

      2. Also functions in support

   3. Vessel elements are wider, shorter, thinner-walled, and less tapered

      1. End walls are perforated for free flow of water through long chains of vessel elements called xylem vessels

      2. More efficient as water conductors than tracheids

      3. Evolved from tracheids

5. Sieve-tube members

   1. Food-conducting cells

      1. Sieve-tube members transport sucrose, other organic compounds, and some minerals

   2. Chains of cells are collectively called phloem

      1. Are alive at functional maturity

      2. Protoplast lack a nucleus, ribosomes and a distinct vacuole

         1. A companion cell is connected to each sieve-tube member by many plasmodesmata

         2. The companion's nucleus and ribosomes may also serve the sieve-tube member

   3. Sieve plates

      1. Porous end-walls between cells of angiosperms

Plant tissues

1. Each of the three systems is continuos throughout the plant

2. Dermal tissue system or epidermis

   1. Single layer of tightly packed cells covering the young parts of the plants

   2. Functions in protection and has special characteristics consistent with the functions of the organs it covers

      1. For example, root hairs specialized for water and mineral absorption are extensions of epidermal cells near root tips

      2. The waxy cuticle is secreted by epidermal cells of leaves and most stems

3. Vascular tissue system

   1. The xylem and phloem that functions in transport and support

4. Ground tissue system

   1. Predominantly parenchyma that fills the space between dermal and vascular tissue systems

ASCENT OF WATER UP THE XYLEM

1. Capillary action

   1. Cohesion and adhesion, due to hydrogen bonding

   2. Cohesion is the attraction of water molecules to itself

   3. Adhesion is the attraction of water to the hydrophilic walls of xylem cells

   4. The small diameter of vessels and tracheids is important to the adhesion effect

   5. The upward pull of water causes tension (negative pressure) in xylem, which decreases the water potential and allows passive flow of water from soil into the roots

2. Root pressure

   1. Ions are pumped into the roots, which increases water flow into the

   2. This uptake increases pressure which forces fluid up the phloem

3. Transpirational pull (transpiration)

   1. Water in leaves evaporate into the drier atmosphere through the stomata

   2. This causes a negative pressure which pulls water from the xylem

   3. Guard cells flank the stomata and control the stomatal diameter by changing shape

   4. Stomata are mostly located on the underside of the leaf to prevent over evaporation

   5. Function in carbon dioxide uptake and in cooling

General

1. Plants require nitrogen to produce proteins, nucleic acids, and other organic molecules

   1. The nitrogen cannot be in gaseous form for plant use, but must be in the form of ammonium or nitrate

Nitrogen fixation

1. The process of converting atmospheric nitrogen (gaseous state) to nitrogenous compounds that can be directly used by plants (ammonia or nitrate)

2. This process is catalyzed by the enzyme nitrogenase

   1. N₂ + 8e^- + 8H⁺ + 16 ATP 2NH₃ + H₂ + 16 ADP + 16 P_i

   2. Some soil bacteria possess nitrogenase

      1. Very energy consuming process

   3. Plants absorb the water and it is incorporated into organic compounds

Parasitic plants

1. Some are photosynthetic, but supplement nutrition by using haustoria to obtain sap from its host plant (mistletoe)

2. Some have ceased photosynthesis entirely, drawing all nutrients from the host plant (dodder)

Carnivorous plants

1. Live in habitats with poor soil conditions (usually nitrogen deficient)

2. Are photosynthetic, but obtain some nitrogen and minerals by killing and digesting insects

3. Most insect traps evolved by modification of leaves and usually are equipped with glands that secrete digestive juices

Mycorrhizae

1. Symbiotic associations (mutualistic) between plant roots and fungi

   1. Helps the plant absorb water

   2. Absorbs minerals and may secrete acid that increases mineral solubility and converts minerals to forms easily used by the plant

   3. May help protect the plant against certain soil pathogens

   4. The plant nourishes the fungus with photosynthetic products

2. Almost all plants are capable of forming mycorrhizae if exposed to the proper species of fungi

   1. Plants grow better when mycorrhizae are present

3. Mycorrhizae may have permitted early plants to colonize land

   1. Fossils indicate the earliest land plants possessed mycorrhizae

   2. This early mutualistic association may have allowed the early plants to obtain enough nutrients to survive colonization

Tropism

1. Growth responses that result in curvatures of whole plant organs toward or away from stimuli

2. Mechanism is a differential rate of cell elongation on opposite sides of the organ

3. There are 3 primary stimuli which result in tropism

   1. Phototropism is caused by light

   2. Gravitropism is a response to gravity

   3. Thigmotropism is a response to touch