exam stuff: BIOL123 plant bio

L17 onwards

Define fungi

Heterotrophic eukaryotes that absorb their food from the environment (by releasing digestive enzymes into enviro). Nature’s recyclers.

Outline the ecological importance of fungi

Some are decomposers (saprotrophs), some are pathogens (live off or kill other organisms and their resources), some are symbionts (symbiotic positive relationship with plants, e.g. help roots absorb nutrients).

Pathogens and symbionts can overlap depending on what species the fungi is acting on.

Role of decomposers on Earth

Break down organisms, return carbon to the atmosphere and nitrogen to the soil. Nutrients recycled into plants and eventually animals. Decomposition essential to all life on Earth.

Enzymes can break down lignin, cellulose, many other substrates (e.g. leather).

Principal decomposers on Earth

Fungi and heterotrophic bacteria

How many tonnes of fungi and bacteria are there per hectare in 20 cm topsoil?

5 tonnes

What bad things does decomposition by fungi contribute to (+ example)

Postharvest storage loss of fruit and veges, reduce palatability and nutritional value of food, produce mycotoxins (e.g. alfatoxins in peanuts, carcinogenic).

Main cause of post-harvest storage loss of lemons in NZ

Penicillium digitatum (fungi)

Role of penicillium roquefortii

Used in the production of cheeses like blue-vein, gorgonzola, roquefort and stilton.

The blue/green colour is due to pigmented spores (conidia).

Breaks down lipids in cheeses, gives strong flavours.

list 2 examples of fungi as a pathogen

Armillaria

Rust fungi

Outline armillaria (fungi as a pathogen)

root-rot fungus, parasitises living trees. Once tree dies, same fungus acts as a decomposer.

Outline rust fungi (fungi as a pathogen) + example

causes huge economic losses, many rusts have alternative hosts (can move between).

Black stem rust of wheat has alternate host barberry (asexual reproduction on wheat, sexual reproduction on barberry) - eradication of barberry can reduce infection of wheat.

Define symbioses

associations between fungi and other organisms, where both partners benefit (mutualistic).

4 examples of symbiotic fungi

• Mycorrhiza: fungus-root 

• Lichen: fungusalga/cyanobacterium 

• Endophyte: fungus-leaf

• Ant- and termite-cultivating fungi (ants feed with leaves then eat fungi)

(important) Outline characteristics/composition of fungi

• Mostly terrestrial—100,000 species including ~ 500 marine species

• Most fungi are filamentous

• Filaments = hyphae (singular: hypha)

• A mass of hyphae = a mycelium (plural: mycelia)

• Hyphae may be divided by cross-walls (septa, divided into separate cells) or not (aseptate, all hyphae one cell, can have hundreds of nuclei in it)

• Cell walls made of chitin

Outline hyphae

Filaments of fungi. Grow by extension of the tip (like pollen tubes) - cell wall very thin at tips, pushed out by hydrostatic/osmotic pressure.

A mycelium is composed of hyphae (singular: hypha).

Outline mycelium

Fungi form a mycelium - comprised of hyphae.

Outline cell division in fungi

Occurs by invagination of cell wall (not a “cell plate” as in plants). Plasma membrane pulled in by an actin ring (like in animal cells) - pinched off from restriction of actin ring.

Outline fungal cell walls

Composed of chitin (polysaccharide consisting of β-1,4-linked Nacetylglucosamine units).

• Similar linkages exist in cellulose (plant walls: β-1,4-linked D-glucose), and peptidoglycan (bacterial walls: β-1,4- linked alternating acetylglucosamine and N-acetylmuramic acid)

Walls in fungi similar to plants, but have different sugar - chemically different but structurally similar. Alternating sugars linked by glycolytic bonds.

Outline yeasts

Single-celled fungi.

Most reproduce by budding, some by fission.

Some fungi are dimorphic (alternate between yeast and filamentous growth depending on conditions).

80 genera, ~600 species.

Most are in phylum Ascomycota, 25% in phylum Basidiomycota.

Different species used in fermentation of different bread, beers, etc.

Outline asexual reproduction of fungi

Some fungi reproduce asexually by haploid spores enclosed in sporangia (singular: sporangium, spore containing vessel).

• Many sporangium-producing fungi are in phylum Mucoromycota

Other fungi reproduce asexually by conidia (conidiospores)

• In Penicillium, conidia (spores) are produced by cells called phialides, borne on a conidiophore (stalk)

• Conidia are not enclosed in a sporangium (cells produced externally)

• Many conidium-producing fungi are in the Phylum Ascomycota

Outline mycorrhizas (define + types)

Symbiotic association between a fungus and the root of a plant

2 types:

1. Endomycorrhizas (endo = inside, grow inside root) (e.g., arbuscular mycorrhizas formed by fungi in the Phylum Glomeromycota, in ~ 72% of all plant species)

   • Form arbuscles in root cells (site of nutrient transfer)

2. Ectomycorrhizas (ecto = outside), in 2% of plant species, but many important forest trees.

Most plants don’t have roots, they have mycorrhizas

Outline arbuscular mycorrhizal fungi (role + scientific study stuff)

Forms arbuscules in root cells (sites of nutrients transfer), takes up nutrients from soil and passes to plant, and absorbs sugars from plant root for fungi growth.

Can’t be cultured without a host plant (e.g. leek, onion, or chive roots). Spores or root segments can be extracted from soil. Permits tissue culture of root-only plant tissue (e.g. split-plate cultures), in-vitro cultivation means can be used experimentally (physiological, ecological, anatomical studies possible).

When can arbuscular mycorrhiza be grown on carrot roots?

When the carrot roots are transformed with Agrobacterium rhizogenes (which causes hairy root disease).

When did arbuscular mycorrhizae evolve?

450 Mya - found in very early fossils. Ancient symbiosis.

Outline 2 types of organisms that act as root endosymbioses

• Arbuscular mycorrhizas 

• Rhizobia 

  • N2-fixing bacteria 

    • Legumes 

    • Gram-negative rhizobia

  • All share some genetic machinery - same genes permit symbiosis in AM and nodules

Outline what ectomycorrhizaes form with

• Form with certain trees and shrubs, e.g:

  • Birch family

  • Oak and beech families

  • Willow family

  • Pine family

  • Some myrtles: including Eucalyptus, and mānuka and kānuka in NZ

• Coniferous forests in northern hemisphere 

• Southern beech forests in NZ 

• Plantation forests (e.g. Eucalyptus)

What part of the root do ectomycorrhizal fungi infect?

Only the root tip

(important) Outline key structures in ectomycorrhizal fungi

Hartig net - site of nutrient transfer (fungus grows between epidermal and sometimes cortical cells) - equivalent of arbuscules

Extrametrical mycelium (often extension, outside of root)

Sheat or mantle - outside the root

Outline evolution of ectomycorrhizal symbiosis

Has evolved many times in many different plant families (including pines, birches, tropical trees, eucalyptus, and willows)

How do mycorrhizas (including AM and ecto) most often benefit plants, and vice versa?

By increasing phosphate nutrition (especially in seedlings and low nutrient soils - soil phosphate generally low).

Mycorrhizal fungi increase surface area for nutrient uptake, can secrete enzymes that break down organic nutrients unavailable directly to plant roots.

Plants provide mycorrhizal fungi with carbon

Where are many of NZ’s ectomycorrhizal species found?

In native Nothofagus (southern beech) forests (incredible biodiversity of fungi).

Outline general gametic meiosis

Occurs in animals, some protists and algae.

Organism starts diploid life as zygote (after fertilisation), grows by mitosis (cells remain 2n, double set of chormosomes) into multicellular individual. Specialised cells undergo meiosis, produce gametes (sex cells, sperm/eggs) - recombination of parent chormosomes, results in haploid cells (n, single set of chromosomes).

Sperm fertilises egg, forms zygote (2n)

Outline sporic meiosis, aka alternation of generations

Occurs in plants and many algae.

Zygotes (2n) following fertilisation divide by mitosis into sporophytes (diploid, 2n, multicellular), cells of sporophyte undergo meiosis into spores (haploid, n, potentially spread by wind), which divide by mitosis into gametophytes (haploid, n), which produce gametes (n, sperm/egg), sperm can fertilise egg (often with assistance of water) to form zygote.

Called alternation of generations due to alternation between haploid and diploid stage.

Overview of moss (Phylum Bryophyta) reproductive cycle

All moss spores look the same (can give rise of male, female, or bisexual gameophytes) = homosporous.

Life cycle divided into haploid and diploid stages. Starts with spores (sporic meiosis, n), sporing occurs in capsule-structure (peristome), go on to germinate and produce gametophytes etc.

Outline moss gametophytes

Have rhizoids to anchor plant to substrate. Leaves usually 1 cell thick with no vascular tissue. Haploid, produce gametes.

Some gametophytes can grow very tall (e.g. Dawsonia superba, NZ native, up to 50 cm high).

Male gametophytes need water to move sperm, can splash onto female plant (specialised sacs on top of male gametophyte = antheridia, contains sperm, can rupture and spread sperm).

Female gametophytes have archegonia, long thin structure with canal with egg at the bottom. When egg ready to receive sperm (mature), neck canal opens (cells degrade) and sperm swims down to fertilise egg (relies on water), forms zygote.

Sperm require water to swim, so moss sexual reproduction reliant on water.

(important) Outline hydroids and leptoids of mosses

Central core of water and (sometimes) sugar-conducting cells. Conducting cells important for land plants.

Water conducting cells = hydroids, food-conducting cells = leptoids.

In more advanced plants, equivalent is xylem and phloem.

Hydroids not lignified, so mosses “non-vascular". Hydroids similar to xylem of vascular plants, leptoids similar to phloem.

(important) Outline moss gametangia (singular = gametangium)

Gametangia = sex organ/cells in which gametes are produced, in moss gametophytes.

Male gametangium = antheridium, has paraphyses (hairs that help to hold water, assist rupturing and spread of sperm), sterile jacket (surrounds sperm), and contains sperm.

Female gametangium = archegonium, has elongated “neck” with neck canal (opens when egg is ready), base is the venter and contains the egg (ovum), nestled in tissue that nourishes zygote after fertilisation.

Outline role of splash cups in moss reproduction

Splash cups = cup-shaped heads containing clusters of antheridia (male gametangium)

Aids sperm dispersal by maximising splashing of sperm when raindrop hits gametangium.

Outline the diploid part of moss life cycle

Fertilisation of egg by sperm forms zygote (2n), first cell of sporophyte generation (protected and nourished by gametophyte, haploid mother plant, = matrotrophy).

Embryo develops into long stalks, sporophytes (not free-living for mosses, attached to mother plant). Developing sporophyte surrounded by remnants of archegonial neck (now called the calpytra, cap/sheath).

Sporophyte continues to be nourished by the gametophyte via the “foot”.

Why is matrotrophy significant for land plants?

Major evolutionary innovation that allowed land plants to succeed (nourishment of zygote by mother plant).

Outline foot of moss gametophytes

Interface between gametophyte mother plant and developing sporophyte - enables matrotrophy.

Sporophyte connected to the parent gametophyte via the foot. Nourishment from the parent is transferred via the foot to the sporophyte.

Outline moss sporophyte development

Sporophyte stalk = seta. Sporangium (capsule) forms on top of seta.

Calyptra important for capsule development (eventually falls off).

Young sporophytes photosynthetic, turn brown and stop photosynthesising as they get older (semi-parasitic on mother moss plant).

Meiosis occurs in sporogenous tissues (2n) of the capsule, produces spores (n).

Operculum (lid on opening of capsule) falls off, spores released via the peristome (ring of teeth that open when dry).

Spores encased in sporopollenin (tough biopolymer that adds strength, prevents desiccation, UV protection). Adaptation to land. All plants have sporopollenin in spores or pollen.

Outline peristome teeth of moss sporophytes

Allow release of spores when weather is dry (adaptation to wind dispersal) by curling backwards. Closed when wet (prevents spores from being washed away directly into ground).

This feature seen in later plants, first evolved in mosses.

Outline explosive spore discharge in Sphagnum (type of moss)

Alternate form of spore release to peristome teeth. Capsule (containing spores) shrinks as dries out, eventually top (operculum) is blown off and spores are shot out.

Do ferns have alternation of generations?

Yes (like all land plants)

Outline fern reproductive life cycle (holy yap warning, just good to get it down)

Most fern spores look the same (give rise to bisexual gametophytes) = homosporous

Have haploid (gametophyte) and diploid (sporophyte) life stages.

Spores dispersed by wind, germinate, produce small groups of cells that develop into heart-shaped structure - gametophyte plant aka prothallus (know what prothallus is), rooted to substrate using rhizoids.

Prothallus matures and differentiates into organs that produce sperm (antheridium) and eggs (archegonium). Gametophytes are bisexual, produce both sperm and eggs.

Antheridia and archegonia mature at different times to minimise self-fertilisation (encourage genetic diversity)

Rhizoids anchor prothallus to ground.

Sperm bursts out when mature, needs water to swim, swims to archegonium which opens its neck once mature, sperm swims down canal and fertilises egg.

Fertilisation → zygote (first cell of diploid generation) in underside on prothallus, dependent on mother gametophyte for first part of life.

Zygote grows and divides and becomes embryo - Differentiates, have a little root and a leaf in sporophyte form

Proliferation of cells to form foot region, through which nourishment comes from gametophyte plant into developing sporophyte (matrotrophy).

With ferns, sometimes prothallus will die off after reproducing, but some ferns’ prothallus will continue producing gametes (like moss ones)

Fern sporophyte can break free from mother plant and become free living, becomes shoot with leaves/fronds with root, which gets water and nutrients from gound, leaf photosynthesises - independent of gametophyte plant eventually (unlike moss)

Then form sporangium with spores

Outline fern gametophytes

Aka prothallus. Produce gametes. Haploid (n).

Heart or ribbon-shaped.

Differentiation into male (antheridia) and female (archegonia) sex organs - gametangia, container of gametes.

Gametangia on underside as moisture/water needed for more movement of sperm.

Outline fern gametangia

Contained on gametophyte plants, house the gametes.

Archegonium = female (eggs), eggs at bottom of tubes that sperm need to swim down once egg has matured.

Antheridia = male (sperm), has a sterile jacket that houses sperm.

Leaf morphology of ferns

Fern leaves = fronds, prominent part of sporophytes.

Have multiple vascular traces so are called “megaphylls” (as are conifer and flowering plant leaves)

Stalk of leaf = stipe, central part = rachis, divided parts = pinna/leaflet. Leaflets can be further divided.

Simple, pinnate, bi-pinnate, and tri-pinnate leaf structures.

Are ferns vascular plants? + Justify

Yes

Have water-conducting xylem with lignin in cell walls (strengthens) and sugar-conducting phloem (like conifers and flowering plants).

(important) Outline fern spores - where they’re produced

Fern spores are produced in sporangia, which are in clusters of sporangia (called sori, plural sorus) on the underside of the fronds.

(exam question about this)

(important) Outline dehiscence (splitting) of sporangium in ferns

Ring of cells around outside of sporangium = annulus cells, which are unevenly thickened. Section of sporangium is the lip cells.

1. Lip cells have weak walls (easily broken).

2. Annulus cells dry out and annulus pulls back slowly (like a spring), carrying the stores.

3. Surface tension breaks and annulus springs back, spores catapulted out

List 2 types of ferns

Leptosporangiate ferns and eusporangiate ferns

(important) Outline leptosporangiate ferns what type of ferns most ferns are

What type of ferns most ferns are. Have leptosporangium.

lepto = drying, have sporangia that release spores through drying out.

The leptosporangium develops from a single initial cell, and contains relatively few spores

Outline eusporangiate ferns

Have eusporangium.

Develops from a row of initials. Contain many more spores. Sporangium wall 2 cells thick.

More rare in ferns but this type of sporangium occurs in all other vascular plants.

List 2 examples of fern sporophyte species

Psilotum nudum sporophyte, Tmesipteris sporophyte

Outline Psilotum nudum sporophyte (fern)

A eusporangiate fern with scale leaves and no roots

Previously thought to be a very primitive plant but that was wrong

The subterranean gametophyte is nourished by arbuscular mycorrhizal fungi

Outline Tmesipteris sporophyte (fern)

Often grows on tree fern trunks

Species native to NZ, Australia, New Caledonia, South Pacific

(important) Homospory vs heterspory (ferns)

Most ferns are homosporous - spores all the same

The “water ferns” are heterosporous (spores differentiate, male/female structures on separate plants)

(important) Outline spore types in heterospory (ferns) + where produced

Male spores are microspores produced in microsporangia

Female spores are megaspores produced in megasporangia

(important) Flowering plants vs water ferns in relation to heterosport

All flowering plants (angiosperms) are heterosporous, as are water ferns, but evolved separately - this sexual evolution has occurred more than once in land plants.

Pollen is a microspore (flowering plants)

Structures of water ferns

Produce bean-shaped resting structures called sporocarps, which unfold in water

Resting structures that contain mega and microspore structures, can fold up and withstand dry period

Outline Marsilea (water clover, type of water fern) spores

Water ferns are heterosporous

Both spore types are released. Megaspores develop an archegonium (egg at bottom) and are fertilised by sperm that develop in the microspores (doesn’t develop into free-living gametophyte plant).

Megaspore contains gametophyte tissue that nourishes developing sporophyte plant after fertilisation

Gametophytes in homosporous vs heterosporous plants

• In homosporous plants (mosses and most ferns)

  • Gametophyte is relatively large and free living (haploid plant)

  • E.g., leafy moss plants 

  • E.g., the fern prothallus

• In heterosporous plants (like water ferns):

  • Gametophyte is reduced and often enclosed in the spore (microspore and megaspore)

    • E.g., antheridium enclosed in the water fern microspore (sperm containing) 

    • E.g., archegonium in the water fern megaspore (egg containing) 

  • Megaspore often contains nourishing tissues for developing sporophyte

  • We’ve seen evolution of heterospory in the water ferns.

    • Heterospory has evolved several times (e.g. some lycophytes and in the seed plants)

Photo of moss vs fern sporophyte and gametophyte

Outline early vascular plants

Phylum Rhyniophyta, existed from 380-425 mya.

No differentiation into roots, stems, leaves (stalk plants). Homosporous. Dichotomous branches (forked), sporangium on top.

Examples of early vascular plants

Rhynia gwynne-vaughanii: short lateral branches with sporangia, dichotomously branching, rhizomes (underground stems). Marsh plant.

Cooksonia: oldest known vascular plant. Dichotomously branches axes.

When did early land plants first increase atmospheric oxygen levels to present day levels? + how were O2 levels kept stable

By 400 Mya (after initial increase in oxygen which drove evolution of respiration)

O2 levels kept stable by fire-mediated feedback (more oxygen = more fires, consumes oxygen)

3 categories of early vascular plants + what 2 of them are ancestors of

• Zosterophyllophytae downwards forks suggested to be early attempt to develop roots 

• Centripetal xylem differentiation = youngest xylem in center (can see by sizes)

• Trimerophyte = fossils tend to be larger, and opposite xylem arrangement (youngest xylem on outside, centrifugal differentiation)

• Seed plants = conifers, flowering plants, few other groups

vascular tissue diversity of early vascular plants

(important) What is stele (early vascular plants)

Primary xylem, primary phloem, and pith (tissue in centre of plant stems and roots, if present)

Outline phylum Lycopodiophyta

Mostly have sporangia aggregated into cones (or strobilli)

e.g. club moss, spike moss, quillwort.

Extinct members included shrubs and large trees - woody species extinct by 248 mya.

Present-day species non-woody, harbaceous.

All have microphylls (leaves with single vascular trave) and are eusporangiate (sporangium develop from groups of cells).

Dominant trees in the coal-forming forests of the Carboniferous (362–290 mya) period.

(important) What phylum were the dominant trees in the coal-forming forests of the Carboniferous (362–290 mya) period?

Phylum Lycopodiophyta

Outline lycopodium (early vascular plants)

All species are homosporous.

Have strobilis = cones

Each sporangium is borne in the axil of a fertile microphyll called a sporophyll.

Outline reproduction/sporing of lycopodium (early vascular plants)

Mother cells in sporangium split into 4 daughter cells, which stick together for early development (spore tetrads).

Young gametophyte germinates into asymmetrical gametophyte, produces gametes in archegonia and antheridia (sex organs, on top for exposure to water to move sperm)

Sperm develops inside antheridium, eggs at base of archegonium, long neck canal, neck region will break down when egg is mature to let sperm in

Sperm swims down neck canal, fertilises egg, forms 2n zygote

Zygote nourished and supported by parent gametophyte

Zygote divides to form embryo

Embryo forms connected to gametophyte via foot, transfer of nutrients

Group of cells called suspensor, doesn’t seem to do much in Lycopodium, but does in other plants

Sporophyte plants become independent of gametophyte, emerge out of ground as free-living plant, spread spores

Connected to roots of gametophyte but also develops own roots

Outline reproduction/ spores + structure of selaginella (spike mosses, early vascular plants)

Heterosporous; female spores = megaspores, male = microspores.

Differentiation, some sporangia have megaspores (female, egg usually at bottom of cone), some have microspores (sperm, male)

Leaf linked to megasporangium = megasporophyll

Independent evolution of mega and microspore differentiation - evolved a number of times (important, exam question about this)

Gametophytes aren’t free-living (unlike lycopodium etc). Entire gametophyte generation enclosed in mega- and microspores

Megaspore has tough outer layer, breaks open, female sexual organs develop on top after breakage, have familiar structures of egg at bottom, shorter neck regions of a few cells, which breaks open when egg is mature so sperm can swim in, forms zygote

Suspensor pushes embryo into megagametophyte tissue (provides nourishment)

sporophyte becomes independent

(important) Identify structures of selaginella (spike mosses, early vascular plants) from a diagram

(Important) Was the evolution of mega and microspores in early land plants independent?

Yes - evolved a number of times

What does the suspensor do in selaginella (spike mosses, early vascular plants)

Pushes embryo into the megagametophyte tissue which nourishes it

Summary of moss, fern, lycopodium (club moss), and selaginella (spike moss) reproduction: gametophyte habit, sporophyte habit, number of spore types

Note: club mosses and spikes mosses aren’t true moss, hence different.

Outline history of land plants

• Major increase in plant diversity c.400-450 million years ago (MYA) in Devonian

  • evolution of early vascular plants e.g. ferns and lycopods = first trees and forests

    • Male gametes still needed water to disperse

• Major increase in plant diversity c.300 MYA in Carboniferous

  • evolution of pollen and seeds

    • enabled colonisation of dry habitats

  • appearance of the “non-flowering Seed plants” (conifers, cycads, gingko - gymnosperms)

Diagram/tree of seed plants

Unique features of the seed plants

• Sporophyte (diploid) the dominant phase, like ferns:

  • Gametophytes (haploid) highly reduced, not free living (attached to sporophyte)

  • Pollen

  • Ovule

  • Seed

  • Fertilisation internal on sporophyte

Seed pollen, ovules, and seeds of seed plants

Pollen = resilient package containing 2-3 celled male gametophyte in sporophyte tissue

Ovule = highly reduced female gametophyte retained on sporophyte

Seed = resilient dispersal package containing embryo & food reserve

Outline gymnosperms

Four phyla (cyadophyta, gingkophyta, gnetophyta, coniferophyta).

All either dioecious (separate sexed plants) or monoecious (separate sexed cones (pollen and seed producing) on same plant)

Almost all are long-lived trees or shrubs

Summary of the 4 phyla of gymnosperms

Outline the cyads (gymnosperm phyla)

Appeared in Triassic (190 mya)

Palm-like

Cones with fleshy fruit

Separate male and female plants (dioecious)

Outline gingko biloba - maidenhair tree (gymnosperm)

One species, native to China.

Triassic/Jurassic age (250-150 mya roundabout)

Used in traditional medicine

Fleshy fruits (stinky to attract dispersal animals)

Separate male and female plants (dioecious)

Outline the gnetophytes (gymnosperms)

3 genera of woody plants (1 species of Welwitschia, > 30 Gnetum species, > 50 Ephedra species)

Cretaceous origin

Dioecious (separate male and female plants)

Many uses in traditional medicine

Outline the conifers (gymnosperms) examples

Pinaceae (pines, firs, spruces) - Podocarpaceae (e.g. rimu), Araucariaceae (e.g. Kauri)

Outline conifer reproduction (gymnosperms) - cone and pollen structure

• Usually have male cones and pollen

Mature pollen contains a 2-3 celled male gametophyte

• larger tube cell forms pollen tube (delivery of sperm to female gametophyte)

• generative cell divides to form 2 sperm

Outer wall of pollen grain = exine (made of sporopollenin, high resistant biopolymner)

Inner wall = intine

Fertilisation independent of surface water (sperm delivered in packages - pollen)

Outline role of sporopllenin (makes up exine (outer wall) of gymnosperm pollen grains

• protected male gametes from desiccation

• allows exine to persist for millions of years in sediment

• can be identified to species

• used in palynology and paleoclimatology (identify past distribution of plants and therefore weather etc(

Outline female cones and ovules of conifers (gymnosperms)

Ovules contains female gametophyte surrounded by sporophytic tissue, matures to become the seed after fertilisation.

Ovules sit on fertile scales of female cones (also have sterile scales).

Female cones (pinecones) persist on conifers unlike male cones which usually drop off after serving purpose

Outline female cone scale of Pinus (pine, conifer) (type of gymnosperm)

Ovule fitting on scale of cone - “naked”, exposed to enviro via whole, where pollen can deliver sperm

Outline pollination in conifers

Wind-dispersed pollen caught in pollination drop on ovule cone scape, drawn into micropyla (to female gametophyte).

Female gametophyte starts dividing after pollen drawn in

Megaspore mother cell meiosis, produces female gametophyte which divides by mitosis to form 2000+ cells

Forms 2-3 archegonia containing egg cells

Pollen tube digests its way through female gametophyte tissue (fertilisation can take a long time)

Generative cell divides into 2 sperm cells

Egg + sperm → embryo (Fertilisation can occur up to 15 months after pollen arrival)

Outline structure of female gametophyte of Pinus (conifer, gymnosperm)

2n = diploid

• Inside, where meiosis happens, gametophyte has half number of chromosomes than sporophyte (n), has gametophytic tissue, creates 2-3 egg cells/archegonia

• Pollination droplet exuded out micropyle, pulls pollen grains in, digest their way through gametophyte tissue to get to archegonia, internal fertilisation

• Tube delivers sperm cells to female gametophyte, both gametophytes surrounded by sporophytic tissue, fertilisation internal

What does the egg + sperm, female gametopjyte, integument, and overall ovule of gymnosperms form?

Egg + sperm → embryo

Female gametophyte → food reserve

Integument → seed coast (testa)

Ovule → seed

Diagram of structure of a conifer seed

Shows what each tissue/part of ovule becomes

• Sporophyte tissue = mother 2n 

  • Integument becomes seed testa

  • Nucleus remains as thin layer in seed

• Female gametophyte remains as seed reserve, digested by embryo as seed develops

• Embryo is product of fertilisation 

  • Forms root, shoot apex, cotyledons

Example of gymnosperm families with dry seeds - Araucariaceae

Gondwanian.

E.g., NZ kauri, Pacific “kauri” (da'ua, dakua, makadre in Fiji; duro in the Solomon Islands)

Has male and female cones (male cones produce pollen, female cones have scales with ovules/seeds)

Example of gymnosperm family that has fleshy seeds

Seeds with fleshy structure have multiple origins (interaction with animals etc).

E.g. Podocarpaceae, Gondwanan family - fleshy aril (modified stem - kahikatea) or cone scale (miro)