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BLGY1124 > Land Plants > Flashcards

Land Plants Flashcards

1
Q

Monophyletic Group

Definition

A

a group that contains an ancestral species and all of its descendants

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2
Q

Archaeplastida

Evolutionary History

A
  • derived from primary endosymbiosis event
  • diversification of marine photosynthesis for 1-2by
  • c. 450mya move to land
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3
Q

Archaeplastida

A
  • red algae
  • green algae
  • land plants
  • glaucophytes
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4
Q

Origin of Land Plants

A

all extant land plants area thought to have a common origin from a common ancestor with charophycean green algae
evolution in water, tidal pools and ponds
since then, a vast diversity of land plants with distinct features have evolved

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5
Q

Key Features of All Land Plants

A
  • alternation of generations

- roots/leaves/flowers

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6
Q

Alternation of Generations

A
  • plants have a complex life cycle involving the alternation of multicellular haploid and diploid forms
  • there are variations in the dominance of the gametophyte (haploid) and sporophyte (diploid) forms
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7
Q

Heteromorphic

Definition

A

gametophyte and sporophyte look structurally different

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8
Q

Isomorphic

Definition

A

gametophyte and sporophyte look structurally similar

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9
Q

Types of Life Cycle

A
  • asexual

- sexual (3) - involve the fusion of gametes at some stage

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10
Q

What are the three types of sexual life cycle?

A

1) Meiosis, orgaism is diploid but produces haploid gametes that fuse
2) Alternation of generations, both haploid and diploid organisms in cycle
3) Zygote undergoes mitosis, zygote is the only diploid cell, all other cells in the organisms are haploid

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11
Q

Similarities Between Land Plants and Algae

A

-eukaryotic
-multicellular
-cell walls contain cellulose
-chloroplasts with chlorophyll A and B
-

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12
Q

Similarities Between Land Plants and Charophytes

A
  • cellulose synthase complexes arranged in complex rosettes
  • peroxisome enzymes that minimise photorespiration (loss of H2O)
  • structure of flagellated sperm
  • cytokinesis
  • nuclear and chloroplast genomes
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13
Q

The Transition to Land - Problems

A
  • for the first 3by the terrestrial surface was lifeless
  • at the time of colonisation the land was hostile; bare rock, no soil, no shade
  • availability and uptake of water and nutrients
  • variation in climate
  • lack of physical support
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14
Q

Advantages of the Transition to Land

A
  • unfiltered sun
  • more carbon dioxide
  • nutrient rich rocks and soil
  • few herbivores / pathogens
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15
Q

What did plants need to transition to land?

A
  • desiccation tolerance: formation of waxy cuticle layer with stomata
  • water uptake mechanism: first plants lacked true roots/leaves so formed symbiotic associations with mycorrhizae
  • structural support: cell walls thickened and lignin (a tough polymer) was used
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16
Q

Xerophytes

A

-plants that have adapted to survive in dry environments

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17
Q

Xerophytes

Strategies for Survival

A
  • timing of life cycle:
  • flowering restricted to short periods
  • reduced water loss:
  • stomatal closure
  • sunken stomata
  • hairs to trap water
  • thick cuticle
  • water storage
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18
Q

Cooksonia

A
  • now extinct group of very early land plants
  • first to show apical dichotomous branching
  • terminal sporangia
  • maximises offspring from single fertilisation
  • tallest plant at time~5cm
  • evidence of stomata
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19
Q

Devonian Vegetation at Rhine

A
  • rich source of fossils
  • volcanic deposits c. 375mya
  • fossils of reed like vegetation
  • preserved in minute detail
  • <30cm
  • horizontal and vertical stems
  • dichotomous branching
  • microphylls and rhizoids instead of tru roots and leaves
  • terminal sporangia on aerial stems
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20
Q

Non - Vascular Plants

A
  • Byrophytes
  • lack of complex vasculature, some have primitive conductive tissues
  • small
  • rely on capillary movement and diffusion of water
  • rhizoids, no true roots
  • microphylls, small ‘leaves’
  • usually dioecious (male and female plants)
  • ground hugging due to absence of cell wall strengthening lignin
  • movement of sperm/fertilisation requires moisture
  • gametophyte is dominant
  • sporophyte is parasitic on the gametophyte
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21
Q

Mosses - Gametophyte

A
  • haploid
  • dominant vegetative plant
  • independent
  • bears gametes
  • union of gametes
  • sexual reproduction
  • host of sporophyte
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22
Q

Mosses - Sporophyte

A
  • diploid
  • seta (stalk) & capsule
  • dependent on gametophyte
  • bears spores
  • meiosis
  • multiplication
  • dispersal
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23
Q

Bryophytes

A

Mosses
Liverworts
Hornworts

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24
Q

Liverworts

A
  • c. 9000 species
  • simple thalllus
  • more leafy
  • dominant gametophyte
  • reduced sporophyte
  • complex gamete bearing structures
  • some reproduce asexually
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25
Q

Hornworts

A
  • c. 100 species
  • gametophyte thallus
  • sporophyte has two ‘horns’
  • single large chloroplast per cell
  • symbiotic with nitrogen fixing cyanobacteria
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26
Q

Seedless Vascular Plants

A
  • first to grow tall
  • complex vasculature
  • dominant sporophyte independent of the gametophyte
  • much reduced gametophyte, a prothallus
  • leaves and roots
  • mostly homosporous
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27
Q

Homosporous

A

plants that produce 1 type of spore that develops into a bisexual gamete

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28
Q

Heterosporous

A

plants that produce 2 types of spores, megaspores that become female gametotypes and microspores that become male gametotypes

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29
Q

Vascular Tissue

A

Xylem - water conducting cells strengthened by lignin, also provides strong structural support for plant to grow taller
Phloem - living cells that distribute sugars, amino acids and other organic products

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30
Q

Roots

A

organs that anchor vascular plants

31
Q

Leaves

A

microphylls - single vein
megaphylls - many veins
the greater the surface area, the greater the light absorption for photosynthesis

32
Q

Pteridophytes

A
  • Ferns, horsetails and whisk ferns

- vascular, seedless

33
Q

Ferns

A
  • 12000 species
  • large pinnate leaves or fronds (megaphylls)
  • young leaves unfurl as croziers
  • spores are bourne in sporangia, on under surface of leaf
  • characteristic sporangia with annulus mechanism
  • stem often a rhizome
  • true roots
  • small gamtopohyte, dominant sporophyte
  • homosporous
34
Q

Sporophylls

A

modified leaved with sporangia

35
Q

Sori

A

clusters of sporangia on underside of sporophyte

36
Q

Strobili

A

cone like structures, groups of sporophylls

37
Q

dehiscence

A

release of spores

38
Q

Annulus

A
  • dead water filled cells
  • thin outer walls
  • water evaporation from annulus distorts outer wall
  • outer wall peals back and sporangium opens
  • as more water is lost, air comes out of solution
  • bubble forms in the centre of the annulus
  • spores are dislodged a few cm then picked up on air currents
39
Q

Whisk Ferns

A
  • 13 species
  • ‘living fossils’
  • simple structure
  • dichotomous branching
  • may be primitive or reduced
  • high chromosome number
  • saprophytic gametophyte
40
Q

Horsetails

A
  • 15 species
  • ‘living fossils’
  • modern plants are much smaller than carboniferous ancestors
  • jointed rib stems
  • silica rich
  • scale leaves in whorls at nodes
  • distinctive strobili/cones
  • spores have elators
  • homosporous
41
Q

Elators

A
  • ribbon like appendages attached to spores
  • curl up when moist and expand when dry
  • they catch in air currents aiding spore dispersal
42
Q

Lycophytes

A
  • club mosses, spike mosses, quillworts
  • 1000 species
  • microphylls
  • true roots
  • reproductive shoots on sporophytes
  • similar life cycle to ferns
  • some species are heterosporous
43
Q

Significance of Seedless Vascular Plants

A
  • ancestors of modern lycophytes
  • evolution of vascular tisssues, roots and leaves
  • increase in photosynthesis, led to a spike in oxygen levels and a reduction in carbon dioxide
  • global cooling at the end of the carboniferous
44
Q

When did see plants first evolve?

A

350 mya

45
Q

What is the difference between Gymnosperms and Angiosperms?

A
  • both are seed plants
  • gymnosperm seeds are exposed on modified leaves forming cones
  • angiosperm seeds are enclosed in fruits
46
Q

Why have seed plants become dominant?

A
  • embryo and food supply (endosperm) are surrounded by a protective coat
  • the seed can be transported away from the mother plant to more favourable conditions
  • seeds can retain viability for up to centuries
47
Q

Heterospory

Definition

A

plant has distinct male and female producing structures

48
Q

Seed Plants

Lifecycle Features

A
  • Gamtophyte reduced and protected (multicellular but not independent)
  • retention of female gametophyte on sporophyte
  • pollination
49
Q

Advantages of a Miniaturised Gametophyte

A
  • gametophyte develops within sporophyte
  • moist environment prevents dessication
  • protection from UV
  • nutrients supplied by sporophyte
50
Q

Seed vs Seedless Reproduction

Seedless

A 
FlagellatedSsperm
--require aqueous environment to move
--travel few cm
-sensitive to desiccation 
Spores
--can survive if environment is good
--single cells - susceptible to damage
--no nutrient supply
51
Q

Seed vs Seedless Reproduction

Seeds

A 
Unflagellated Sperm
--use wind/animals to move
--can survive for long periods of time
Seeds
--can survive for centuries
--multicellular with protective coat
--nutrient supply
52
Q

When did gymnosperms first evolve?

A

305 mya

53
Q

When did Angiosperms first evolve?

A

105 mya

54
Q

Gymnosperm Phyla

A
  • Ginkgophyta
  • Cycadophyta
  • Gynetophyta
  • Coniferophyta
55
Q

Gymnosperm Phyla

Ginkgophyta

A
  • separate male and female plants
  • one extant member
  • living fossils (no close living relatives)
  • female cone splits to reveal seeds
56
Q

Gymnosperm Phyla

Cycadophyta

A
  • c.100 species

- ancient plant group

57
Q

Gymnosperm Phyla

Gynetophyta

A
  • closest extant relatives of angiosperms

- 69 species

58
Q

Gymnosperm Phyla

Coniferophyta

A
  • 610 species

- tallest and longest lived organisms on earth

59
Q

Pine Life Cycle

A

fertilisation is usually more than a year after pollination

60
Q

Angiosperms

A
  • dominant plants on earth today
  • colour
  • increased transpiration
  • superior vascular system
  • pollination -> coevolution of birds and insects
  • animals/humans depend on fruit and seeds
61
Q

What are the main adaptations of angiosperms?

A
  • flowers
  • double fertilisation
  • fruit
62
Q

Flowewrs

Stamen

A
  • made up of filament and anther

- produces microspores which develop into pollen grains

63
Q

Flowers

Carpel

A
  • made up of stigma, style and ovary

- produces megaspores which develop into female gametes

64
Q

Double Fertilisation

A
  • pollen grain germinates after landing on stigma
  • pollen tube (with 2 nuclei) grows through the style towards the ovaries
  • pollen tube penetrates through the micropyle
  • pollen tube discharges 2 nuclei into female gametophyte (egg sac)
  • one fertilises the egg forming a diploid zygote
  • the other fuses with 2 polar nuclei present in the ovary forming a triploid cell that divides to form the endosperm
65
Q

Mechanisms Promoting Cross Pollination

A
  • self incompatibility, male and female parts of the plat mature at different times
  • male and female flowers on different plants
66
Q

Pollination Mechanisms

A
  • responsible for transferring pollen from one flower to another
  • insect attracting mechanisms: colour, shape, smell
  • pollen can also be transferred by mammals e.g. bats
  • wind pollinated plants have no flowers e.g. grasses
67
Q

What do seeds form from?

A

ovules

68
Q

What do fruits form from?

A

ovaries

69
Q

Seed Energy Storage

A

-found in endosperm or cotyledons/embryo

-

70
Q

Why is seed dormancy an advantage?

A
  • it increases the chance that germination will occur at a time and place most advantageous to the seedling
  • dormancy is broken in response to a change in the environmental conditions e.g. temperature
71
Q

Seed Dispersal

A 
By Wind
-parachute e.g. dandelion
-tumbleweed
By Animals
-barbed fruit
-'buried in caches
-carried to ant nest
-seeds in faeces
72
Q

Diversity of Angiosperms

A
  • terrestrial / aquatic
  • development and dispersal mechanisms
  • germination, branching, leaf shape
  • annuals, biennials, perenials
  • trees, shrubs, herbs
  • hot / cold
  • wet / dry
  • sun / shade
73
Q

Grasslands

A
  • ~20% of Earth’s surface area

- 10 000 species

74
Q

New Uses for Plants and Algae

A
  • phytopharmaceuticals
  • materials
  • biofuels
  • cell factories
  • ‘environmental managers’
  • biolubricants
  • biopolymers

BLGY1124 (8 decks)

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