Bio80H Midterm 2

Evidence of Algal Ancestry in Plants

• Multicellular

• Eukaryotic

• Photosynthesis

• Cellulose Walls

• Certain chlorophyll

Closest relative: Charophytes (Have circular protein rings that synthesize cellulose)

Sporopollenin

Layer of durable polymer that prevents drying, can be found in plant spores

Pros and Cons of Colonizing Land

Pros:

• Unfiltered sunlight

• CO2 abundance in the air vs in water

• Mineral rich soil

Cons:

• Lack of water on surface

• Lack of structural support to combat gravity

Unique Plant Traits (Distinguishes from Charophytes)

• Alternation of generations

• Multicellular, dependent embryos

• Walled spores made in sporangia

• Apical meristem

Alternation of Generations

A life cycle that alternates between the diploid sporophyte and haploid gametophyte generation. Found in all plants

Gametophyte

Production by mitosis of haploid gametes

Sporophytes

Haploid gametes fuse and mitotically divide

Spores

Haploid, produced by meiosis in a sporophyte from the sporangium, mitotically divides to form a gametophyte

Placental Transfer Cells

Increase transfer rate of nutrients by increasing surface area via ingrowth of walls, found in developing reproductive organs.

Embryophytes

Common name given to plants for their multicellular, dependent embryos

Explain “Walled spores produced in sporangia”

Sporocytes divide via meiosis in the sporangia to produce spores, which are protected by sporopollenin

Apical Meristem

Localized regions of cell division at the tips of roots and shoots

Plant epidermis

Single-tissue layer covering leaves, stems, roots, flowers, etc to protect from sunlight, water, dehydration, and pathogens

Cuticle

Wax and polymer based layer secreted by the epidermis, helps retention of water and protection

Stomata

Pores on plants that help with the exchange of O2 and CO2, helps in photosynthesis and water evaporation

Bryophytes

Nonvascular plants, consists of:

• Phylum Heptophyta (Liverworts)

• Phylum Bryophyta (Mosses)

• Phylum Anthocerophyta (Hornworts)

Seedless Vascular Plants

• Phylum Lycophyta (Lycophytes)

• Phylum Monilophyta (Monilophytes)

Gymnosperms

Seeds not enclosed in chambers, consists of:

• Phylum Ginkophyta (Ginkgo)

• Phylum Cycadophyta (Cycads)

• Phylum Gnetophyta (Gnetophytes)

• Phylum Coniferophyta (Conifers)

Angiosperms

Flowering plants, consists of:

• Phylum Anthophyta (Flowering plants)

Vascular tissue

Specialized cells joined into tubes to transport water and nutrients from the roots to various parts of the plant

Bryophyte Life Cycle

1. Spore becomes a protonema

2. Protonema grows “buds“ that divide mitotically to form the gametophytes (Antheridia and Archegonia)

3. After the antheridia releases the flagellated sperm, they travel via chemotaxis to the archegonium in water

4. Embryo stays inside the archegonia while placental cells bring nutrients

5. Sporophyte remains attached to the gametophyte as it grows, being feed sugars, amino acids, minerals, and waters (despite plastids)

6. The peristome opens in dry conditions and closes in wet conditions so the spores discharge gradually through the wind

Protonema

One-cell branched thick filament that increases water absorption

Rhizoid

Root-like structures that anchor the gametophytes to the ground, do not absorb water or minerals

Gametangia

Multicellular structures on the gametophyte that produce gametes mitotically

Antheridia

Male gametangia, produces many sperm

Archegonia

Female gametangia, produces one egg

Chemotaxis

Process in which archegonia release chemicals to guide sperm to the egg

Parts of a Sporophyte

• Foot

• Seta (Stalk)

• Capsule (Sporangium)

  • Peristome

Foot

Absorbs nutrients from gametophyte

Seta (stalk)

Conducts materials to sporangium, can elongate to improve elevation level

Capsule (sporangium)

Produces spores via meiosis

Peristome

Upper part of capsule with interlocked structures

Peat

Decayed matter of sphagnum, slow decaying helps preserve corpses and has low temp, pH, and O2 levels. Used as fuel source or soil conditioner occasionally.

Main characteristics of vascular plants

• Dominant Sporophyte

• Transport through Xylem and Phloem

  • Well developed leaves and roots, including sporophylls

Xylem

Conducts water and minerals from roots up

Tracheids

Tube-shaped cells carrying minerals up the roots, xylem of all vascular plants

Lignin

Strengthens cell was via lignification of water-conducting cells (dead at functional maturity)

Phloem

Cells arranged in a tube to distribute amino acids, sugars, and other organic products (alive at functional maturity)

Vascular Seedless Plant Life Cycles

1. Spore released that will, in most of this group, produce a bisexual photosynthetic gametophyte

2. Each gametophyte creates antheridia and archegonia structures (Each mature at different times to prevent self-pollination)

3. Flagellated sperm swim to egg via chemotaxis

4. Zygotę grows out of archegonium and develops into sporophyte

5. Sporophyte creates sporophylls, which have sori on the underside, with each sorus have several sporangia

   1. Sporangia undergoes meiosis and produces spores

Homosporous

1 type of sporophyll, 1 sporangium, creates a bisexual gametophyte with both sperm and egg

Heterosporous

2 type of sporophyte which create different sporangium, create different gametophytes with one having egg and one having sperm

Megaspore

Spores from heterosporous plants that become female gametophytes from a megasporangium on a megasporophyll

Microspore

Spores from heterosporous plants that become male gametophytes from a microsporangium on a microsporophyll

Sporophylls

Genetically modified leaves for sexual reproduction

Sporangia

Capsule that produces spores via meiosis of sporocytes

Sori

Clusters of sporangia on the underside of sporophylls

Strobili

Clusters of sporophylls forming a cone-like structure

Roots

Organs that absorb water and nutrients from the soil and anchor plants

Microphylls

Small, spine-shaped structure supported by a singular strand of vascular tissue (Lycophytes only)

Megaphyllls

Heavily branched, more photosynthetic product

Epiphytes

Plants that use other plants as substrate but not parasitic (Done by lycophytes)

Seedless vascular plant importance

Early forests lead to large CO2 drops, which are now deposited in the ocean. Also lead to the creation of coal

Seed plant reductions

• Gametophyte size

  • Can now grow in spores, preventing environmental stressors and letting sporophyte feed it

• Heterospory

• Ovules

• Pollen

Lead to better cope with drought, UV, and water-dependency

Integument

Sporophyte produced, protects megasporangium. Eventually transforms into seed coat.

Ovule

Megasporanguim, megaspore, and integument.

Pollen grain

Microspore develops into a gametophyte, which is surrounded by the pollen wall produced by the sporophyte

Pollination

Pollen to ovule

Seed formation process in gymnosperm

1. The unfertilized ovule is surrounded by fleshy megasporangium and hard integument, with an opening known as the micropyle where the pollen grain enters

2. Ovule becomes a female gametophyte, by which time the pollen grain has formed a pollen tube to connect the pollen grain and transfer the sperm

3. Fertilization occurs and zygote is formed, with gametophyte tissue being the nutrient package for the zygote, the spore wall being megasporangium remnant, and the seed coat forming from the integument

Advantages of seeds and pollen

Pollen:

• Can spread on dry land

Seeds:

• Can remain dormant until favorable conditions are met

• Have food to germinate

Gymnosperm lifecycle

1. Conifers (most gymnosperms) are heterosporous, thus producing microsporangium and megasporangium

2. Microsporocytes in the microsporangium are divided by meiosis to be placed in the pollen grain and released via the wind

3. Pollen reaches ovule and begins pollen tube development

4. Megasporocyte undergoes meiosis, 1 of the 4 daughter cells becomes a megaspore

5. The megaspore produces 2-3 archegonium

6. Once eggs have matured fertilization occurs, with only one egg turning into a zygote

Conifers

Cone-bearing plants (most gymnosperms)

Gymnosperm rise

As climates dried, lycophytes died and gumnosperms took over, with large SA leaves and thick cuticles

Parts of a flower

Stamen (male sexual reproductive organ (microsporophyll))

• Filament: Stalk heightening the anther

• Anther: Site of meiosis to produce microspores and pollen

Carpel (female sexual reproductive organ (megasporophyll))

• Stigma: Sticky site of landing for pollen

• Style: Tube connecting stigma and ovary

• Ovary: Site of ovules who become female

Sterile organs

• Petals: Used to attract pollinators

• Sepal: Protect flower prior to bloom

Simple pistol

1 carpel

Compound pistil

2+ fused carpel

Fruit

Ovary wall thickens and matures, creating pericarp protecting the seed(s)

Pericarp

Ripened wall of plant ovary protecting the seed

Methods of Dispersal

• Parachutes via wind

• Water

• Animals (digestible or clings to fur)

Angiosperm lifecycle

1. After meiosis in each ovule of the megasporocyte, 1 megaspore will survive

2. This megaspore will undergo 3 mitotic divisions and be sectioned into 7 parts (3 antipodal cells, 2 synergic cells, 1 egg cell, and 1 dikaryotic polar nuclei) which make up the embryo sac (female gametophyte)

3. Microsporocyte divides to form 4 microspores

4. Microspores become pollen grain with gametophytes generative cell breaking into two sperm

5. Pollen grain connects to stigma,

   tube cell then produces pollen tube which is fed by the ovule through the style to ovule where both sperm are discharged at the micropyle

6. Double fertilization occurs to the central cell (now endosperm) and the egg cell (now a zygote) while the synergid and antipodal cells disintegrate

7. Egg forms zygote and central cell forms endosperm

Antipodal cells

Provide nourishment for embryo sac

Polar nuclei

Eukaryotic central cell

Synergid cell

Guides pollen tube to the egg

Egg cell

Cell that will be fertilized

Tube cell

Pollen grain produces this to guide sperm to egg

Endosperm

Tissue rich in starch and food to nourish embryo (3n)

Cotyledon

Seed leaves on embryo, has some food and depending on dicot/eudicot will help breakdown endosperm or absorb it

Bilateral symmetry

Symmetry down only one line

Radial Symmetry

Any line drawn through the middle is symmetrical

Monocots

Only have 1 cotyledon

Dicots

Have 2 cotyledon, but are a paraphyletic group so they are broken into three groups:

• Eudicots: True dicots

• Basal angiosperms

• Magnolids

Monocot vs Dicot

Tissue

Group of 1 or more cells doing a specialized function

Organ

Several types of tissue that carry out a function

Vascular Plant Organs

Roots, leaves, stems

Basic Plant Structure

Primary Root

First root to form

Lateral Roots

Branching from primary

Taproot

Main vertical root, common in tall plants, mostly does anchorage while lateral shoots absorb nutrients. Can be used for food storage.

Fibrous Root System

Used by smaller vascular plants to make many roots with the death of primary root. Good at preventing soil erosion

Root hairs

Extensions of epidermal cells that increase surface area for absorption

Types of Specialized Roots

• Prop roots: Help tall, top-heavy roots

• Storage roots: Store nutrients

• Pneumatophores: Projects above low tides to obtain O2 which is unavailable in waterlogged soil

• Buttress roots: Large and shallow above ground to help stability

• Strangling aerial roots: Grow down to the ground, wrap around host to get it’s nutrients and kill the tree

Stem

Plant organ bearing leaves and buds, elongates and orients to help photosynthesis and elevate reproductive structures

Parts of the Stem

• Nodes: Points where leaves are attached

• Internodes: Stem between nodes

• Apical buds: Growing shoot tip where growth is concentrated

• Axillary bud: Grows in the upper nook of the node, can become lateran branch or thorn/flower

Specialized Types of Roots

• Rhizomes: Below surface

• Stolons: Horizontally across surface, enable asexual reproduction via axillary buds

• Tuber: Englargened ends of rhizomes for food storage

Leaves

Main photosynthetic organ in most plants, CO2 exchange, dissipate heat, defense

Flattened Blade

Leaf

Petiole

Joins leaf to stem

Veins

Vascular tissue

Simple leaf

Single undivided leaf

Compound leaf

Multiple leaflets