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Higher'Plants'

Gymnosperms'&'Angiosperms'''

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Gametophytes/Sporophyte Evolution

Most%seedless%vascular%plants%are%homosporous%as%they%have%iden4cal%spores%(moss,%ferns)%Some%plants%are%heterosporous%as%they%have%two%types%of%spores.%

Homosporous%

Sporophyte% Single%type%of%spore%

Bisexual%gametophyte%(with%archegonia%and%antheridia)%

Eggs%&%sperm%

Heterosporous%

Sporophyte%Microspore%

Megaspore%

Male%gametophyte%

Sperm%

Female%gametophyte%(inside%the%spore)%

Eggs%

The%heterosporous%life%cycle%was%important%in%the%evolu4on%of%the%seed.%%In%fact,%all%seed%plants%are%heterosporous.%

Phylum Tracheophyta: vascular plants from ferns to higher plants

Completed their evolution to land by:

1. Protective cuticle to prevent desiccation (drying out)

2. Evolved tissues to conduct and support

a)  Xylem: thick rigid tubes that conduct water and minerals from the

soil (from roots) to all parts of the plant. Also provides support

(like a skeleton).

b)  Phloem: thin walled tubes that conduct the products of

photosynthesis (food) to all of the non-photosynthetic parts of the

plant (ie: fruit, roots).

XYLEM

Moves water from soil to plant

Moves food from leaf to roots… PHLOEM

3. True roots: their roots contain xylem & phloem, and can be much

longer (no longer rely on diffusion).

4. Developed leaves: do photosynthesis ONLY

5.  Specialized sex organs.

6.  Don�t require water to distribute offspring (except for ferns).

KINGDOM PLANTAE Vascular Plants

Phylum Tracheophyta

Seeds

Subphylum Spermopsida

Seeds �naked�

Seeds enclosed

Class Gymnospermidia

Sub Class Liliopsida

MONOCOTS

Sub Class Magnoliopsida

DICOTS

Class Angiospermidia

GYMNOSPERMS%•  Belong'to'the'Phylum'Tracheophyta'(“windpipe”'plants)'

•  Introduc@on'–'Gymnosperm'means'�naked'seed�'''(From'the'Greek:'gymnos'='naked;'sperm'='seed)''

•  More'advanced'than'ferns'–'do'not'have'spores,'they'have'seeds.'

•  The'seeds'of'the'gymnosperms'lack'a'protec@ve'enclosure'(unlike'flowering'plants'which'have'flowers'and'fruit).'

•  Examples'of'gymnosperms:''–  Conifers'(pine'trees),'cycads,''ginkgo,'Welwitschia'

Evolu@on'of'Gymnosperms'

•  Gymnosperms'evolved'from'fernQlike'ancestors'

•  Advancements'of'gymnosperms'over'ferns:'1.'Seeds'(plant'embryo,'food'storage'@ssue,'and'seed'coat)''2.''Gymnosperms'do'not'depend'on'water'for'fer@liza@on'(have'airQborne'pollen)'3.''Have'a'more'dominant'sporophyte'genera@on'4.''Have'a'vascular'system'

Subphylum Spermosida (seed bearing plants)

•  True roots (with vascular tissue)

•  Reproduction WITHOUT water (evolved flower)

•  Protective covering around embryo (seed) – can survive winter

•  Improved conducting tissue: thicker and stronger xylem. Became taller.

Class Gymnospermidia Characteristics

1. Evolved in the early Mesozoic in cooler, isolated areas.

2. Adapted to cool, dry climates; dominant type of tree type in Canada.

3.  Leaves = Needles. Don�t freeze and carry sap; This allows conifers to continue on with photosynthesis in the winter.

(Covered by resins – for protection from predators, fire, etc.)

4. Superior (very thick) xylem; allows for tall growth

Sequoia Tree Redwood Trees

5. Cones for reproduction; protects the seeds through the winter. Airborne pollen eventually pollinates the egg.

6. The seed develops scales and when mature, the scales open and the seed is distributed by the wind.

FEMALE CONE: Ovulate Cones

With ovules (X)

MALE CONES:

Staminate Cones

(with pollen X)

Gymnosperm'life'cycle'•  Exhibits'alterna@on'of'genera@ons'•  Sporophyte'genera@on'(2N'or'diploid)'is'dominant'

•  Gametophyte'genera@on'(N'or'haploid)'is'contained'in'and'dependent'on'the'sporophyte'genera@on'(see'handout')'

Pine'life'cycle'''

Sporophyte'Genera@on'•  Sporophyte'produces'two'types'of'spores'(heterosporous)'

•  Megasporangium'–'undergoes''meiosis'to'produce'haploid'megaspores'which'form'eggs'or'ova'(the'female'gametophyte)'

•  Microsporangium'–'undergoes''meiosis'to'produce'haploid'microspores'which'form'pollen'(male'gametophyte)''

•  Many'gymnosperms'use'wind''for'pollina@on'and'seed'dispersal'

Figure%30.2%%The%development%of%a%seed%from%an%unfer4lized%ovule.

The three most important new adaptations to land found in the seed plants are all shown in this diagram:

1.  Very small gametophytes that are nourished by and protected inside the parental sporophyte

2.  Pollen grains, which provide protection and dispersal for the male gametophyte

3.  The seed, which protects and disperses the new sporophyte embryo

Figure%30.3%%Winged%seed%of%a%White%Pine%(Pinus(strobus),%a%gymnosperm.%Wood'produced'by'gymnosperms'

•  Gymnosperms'have'a'very'efficient'and'effec@ve'vascular'system'

•  Usually'woody'plants'•  Xylem'!'wood'of'a'tree'

•  Phloem'!'bark'of'the'tree'

•  Wood'is'formed'''from'secondary'growth'

Annual'rings'•  Annual%rings'–'xylem'formed'by'the'vascular'cambium'during'one'growth'season'

•  Early%Spring%wood'–'vessel'diameter'is'large,'xylem'walls'are'thinner'

•  Late%Summer%wood'–'vessel'diameter'is'small,'walls'are'thicker'

•  Tropical'trees:'have'no'annual''rings,'because''seasons'are'so''similar'

Conifers'–'an'important'group''•  Conifers'–'cone'bearers'•  Conifers'adapted'to'temperate'to'cold'regions'

•  Narrow'leaves'(needles)'help'to'conserve'water'

•  Covered'by'resins'–'for'protec@on'from'predators,'fire,'etc.'

• The cone is made up of a very short branch with many small, rounded, leaf-like structures (scales) attached to a central stem.

• A female cone lives and grows for several years, becoming much larger than a male cone.

• An ovule develops on each scale of a female cone. Inside the ovule, an egg is produced.

• If fertilization occurs, an embryo grows inside the ovule. The ovule hardens, becoming a seed.

• Eventually the scales spread, allowing the seeds to fall. If conditions are favourable where it falls, the embryo inside the pine seed will grow into a new tree.

Adult sporophyte (2N)

Seedling sporophyte (2N)

Gametophytes

Other'Gymnosperms'

•  Cycads'–'short'shrubs,'na@ve'to'tropical'regions''(look'like'palms)'

•  Ginkgo'biloba'–''a'�living'fossil�,''male'and'female'tree,'used'as'a'medicinal'plant'

Cycads(

Figure%30.5a%%The%only%surviving%species%in%Phylum%Ginkgophyta:%Ginkgo(biloba.(Ginkgo’s%nice%traits%include%that%it%is%very%tolerant%of%urban%pollu4on,%and%turns%a%beau4ful%gold%color%in%fall.%%A%notVsoVnice%trait%is%that%the%seeds,%when%they%decompose,%smell%like%vomit,%or%worse.%%Ginkgos%are%also%dioecious,%meaning%they%lose%their%leaves%in%the%Fall.%If%you%want%to%play%a%bad%hor4cultural%joke%on%someone,%plant%a%female%Ginkgo%in%their%yard.%

Ginkgo'is'a'�living'fossil�'

Leaves'of'living'plants'are'iden@cal'to'fossils'which'are'millions'of'years'old.'

A'cast'of''ginkgo'fossil'

Ginkgo%sperm%is%flagellated!%%Conifers%have%nonVflagellated%sperm,%as%do%all%the%Angiosperms%or%flowering%plants.%

Other'gymnosperms:'Phylum(Gnetales(

•  Welwitschia'–'a'bizarre'gymnosperm'plant'that'grows'in'Namib'desert'of'South'Africa.''

•  Live'up'to'2000'years'in'these'extreme'condi@ons!'

•  Only'makes'two'leaves'throughout'its'life.'It'takes'water'from'sea'mist'and'fog!'

Significance'of'Gymnosperms'

Ecological'importance:'– Provide'food'and'habitat'for'wildlife'– Forests'prevent'soil'erosion'– Help'control'flooding'by'absorbing'rainwater'– Reduce'greenhouseQeffect'gasses'(remove'CO2'and'add'O2'to'atmosphere)''

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Economic'and'commercial'importance:'– Lumber'for'wood,'paper,'etc.'

– Resins'–'wood,'furniture,'etc.'– Ornamental'plants'(trees,'landscaping)'

– Food'–'pine'nuts'(pesto,'etc.)'