Plant Origins Flashcards
(65 cards)
1
Q
Endosymbiosis
A
Engulfing without digestion
2
Q
Primary Endosymbiosis
A
- resulted in the retention of: Mitochondrion = Alpha Proteobacterium, and Plastid/chloroplast = Cyanobacterium
3
Q
Plastids within the eukaryotic cell allowed for photoautotrophs (algae)
A
- Reduces requirement for phagocytosis
- Increases need for cellular water
4
Q
Secondary Endosymbiosis occurred across:
A
various lineages of aquatic algae
5
Q
Secondary Endosymbiosis
A
Subsequent uptake of a red and/or green alga by other non-photosynthetic eukaryotes gave rise to several aquatic algal lineages and phytoplankton
6
Q
Chloroplasts
A
- utilize the energy from light to break H2O molecules into O2 and H+ ions
- H+ ions are used to generate ATP by pumping through an ATP synthase on the thylakoid membrane into the stroma
- An electron transport chain caused by the splitting of the water molecules allows for the reduction of NADP to NADPH
- The high energy compounds ATP and NADPH aid in the fixation of CO2 into polysaccharides through the Calvin Cycle starting with Rubisco in the stroma
7
Q
Heterotrophic Plants – Alternative Nutrition
A
- Some plants have lost the ability to photosynthesize in favour of alternative nutrient acquisition strategies
- These are and represent <1% of all plant species – All ancestral lineages were photoautotrophs
8
Q
Mycoheterotrophs
A
– obtain carbon source from fungal associations with other plants
9
Q
Parasitic plants/heterotrophs
A
obtain carbon source directly from other plants
10
Q
Plant Cell Walls
A
- Reduced requirement for phagocytosis allows for the development of cell walls
- quite porous and allows for nutrients and water to pass-through
11
Q
Primary Plant Cell Walls
A
- Provide support and protection but allow for flexibility
- Rigidity is highly dependent on turgor pressure, which is dictated by the surrounding environment and maintained by vacuole
- Deposited outside of the plasma membrane
- Composition is largely the same among all plants
12
Q
Cellulose
A
- The most abundantbiopolymer in the world/known universe
- Long, unbranched microfibrils made up of β1-4 glucose linkages
- major component of dietary fibre (hard to digest)
13
Q
Osmotic Pressure
A
- Vacuoles have higher solute concentration and the osmotic flow of water occurs from outside the cell (lower solute concentrations) to into the vacuoles
- The turgidity of the vacuole pushes the plasma membrane outwards and this pushes against the cell wall
14
Q
Turgid State
A
The ideal state for plant cells, helps maintain the structure of the plant and maintains osmotic balance
15
Q
Effects of Osmotic Pressure
A
- Rapid and concerted movements of solutes can quickly divert water from the cell and force some cells to contract
- Pressure sensors or mechanosensors can activate ion channels that change the osmotic potential of the cell
- Actually causes an action potential similar to animal cells and can trigger coordinated events in nearby tissues or organs
15
Q
Effects of Osmotic Pressure
A
- Rapid and concerted movements of solutes can quickly divert water from the cell and force some cells to contract
- Pressure sensors or mechanosensors can activate ion channels that change the osmotic potential of the cell
- Actually causes an action potential similar to animal cells and can trigger coordinated events in nearby tissues or organs
16
Q
Multicellularity in Eukaryotic Algae
A
- True multicellularity involves the specialization of cells to perform different functions
- Allows for coordinated behaviour of different tissues to aid in the fitness of the organism as a whole
17
Q
We know that all land plants are descended from the same clade of Eukaryotic Green Algae because:
A
- Multicellularity arose multiple times in algal lineages, completely separate from the animal/fungal ancestral lineage
- End products are similar but the processes are unique and can be used to distinguish evolutionary trends
18
Q
All land plants display:
A
multicellularity
19
Q
Plant Cell Multicellularity – Cell Division
A
- Critical importance to the multicellularity of Land Plants
- Land plant cell division progresses through the production of the Phragmoplast
- This arrangement of the microtubules allows for cell wall deposition between the two separated nuclei prior to the complete division of the cytoplasm
- Deposition of the cell wall materials also involves the fusion of vesicles from the ER and Golgi to form the new plasma membranes
20
Q
Plasmodesmata
A
- are intercellular connections between plant cells
- These connections are formed cell division
- Secondary plasmodesmata can develop through the degradation of the cell wall but do not occur in all cells
- Analogous to the gap junctions seen in animal cells
- These connections allow for easier cell-to-cell transport of cytoplasmic contents
21
Q
Passage of materials through the plasmodesmata is regulated by:
A
the ER within the cavity (desmotubule)
22
Q
Defining Characteristics of Land Plants
A
- Are sessile
- Are photoautotrophic (vast majority)
- Have primary cell walls (largely composed of cellulose and hemicellulose)
- Are multicellular
- Have Cuticles
- Have Stomata for gas exchange
- Have an alternation of generations -> Diphasic life-cycle
23
Q
True colonization began with
A
fungi, early embryophytes (~475mya), and then animals (arthropods first)
24
Vascular plants develop:
Around 425mya and proceed to dominate to the end of the Carboniferous (~300mya)
25
Tetrapods arise
~400mya, first to come on land ~360-380mya
26
Seed plants arise
~300mya, arthropods and amphibians dominant animals on land, reptiles begin to radiate, last common ancestor between reptiles and mammals ~285mya
27
Why Move Out of the Water?
- NO competition
- Unlimited and untapped mineral resources
- Unlimited space for establishment and growth
- Full access to light
- No predators
- Any organisms that could become accustomed to life on land had room to radiate
28
Freshwater algal mats would have been the first to:
begin photosynthesizing on land, would have to withstand wet-dry cycles but were still largely aquatic.
- Likely formed symbiotic relationships with fungi -> established the first soils and allowed for further diversification
29
First truly terrestrial plants were the first of the:
Embryophytes -> Bryophytes (475mya)
30
Plants established habitable regions, acting as the:
primary producers
31
Challenges with Life on Land
- Desiccation
- Respiration
- Reproduction
- Locomotion and support
- Nutrients
- Senses
32
Desiccation Challenges
- Protection from drying out (resistant coat or skin to prevent body fluids from evaporating) and dealing with scarce water
33
Respiration Challenges
- In water, dissolved oxygen and carbon dioxide are exchanged.
- Organisms had to deal with the exchange of atmospheric gases. (e.g. Stomata, Lungs)
34
Reproduction Challenges
- In water, eggs and sperm could be released into the water or broadcast
- Land organisms had to develop successful reproductive strategies under desiccating conditions. (i.e. tighter control over the dispersal of “soft” propagules/gametes) (e.g. alteration of generations in plants, the evolution of amniotes in animals)
35
Locomotion and Support Challenges
- No more propulsion through a viscous medium, no more support or buoyancy from the water
- Now require new locomotive systems and supports (e.g. Limbs/appendages, types of joints, reinforced tissues)
36
Nutrient Challenges
- Mineral nutrients and ions are diffused in the water and are readily taken up through diffusion and maintaining osmotic balance.
- On land, mineral nutrients are held in the substrate.
37
Senses Challenges
Organisms on land had to adapt to the changes in light, sound, and smell which were perceived very differently in water.
38
Major Early Adaptions of Land Plants
1. Waxy Cuticles
2. Stomata
3. Alternation of generations
39
Waxy Cuticle
- is a waxy layer that prevents water loss from stems and leaves
- Protects the plants from drying out and also from pathogen attack
- Wax is deposited outwards by the epidermal cell layers (upper and lower)
- Thickness varies depending on the perception of heat and light
- Wax is not easily permeable to gases
40
Stomata
- are pores that allow the exchange of gases across photosynthetic surfaces
- Opening and closing of the pore is controlled by specialized cells called Guard cells
- The guard cells themselves are still covered by the cuticle but create a pore when they swell and pull apart
- Regulation of the release of gases only when water is plentiful greatly reduces unnecessary water loss
41
Jigsaw puzzle growth pattern of epidermal layers allows for
complete and intricate seals between neighbouring cells regardless of swelling/contracting
42
The guard cells are able to swell and contract quickly in response to:
- the accumulation of solutes -> changes their osmotic potential:
- Water moves in (plentiful) -> swell to sausage shape -> pore opens
- Water moves out (lacking) -> contract to flaccid straight-sided shape -> pore closes
43
Alternation of Generations
- Instead of one “body”, the plant life cycle progresses through two multicellular growth forms:
- Diploid (2n) Phase = Sporophyte -> makes spores (n) through meiosis
- Haploid (n) Phase = Gametophyte -> makes gametes (n) through mitosis
44
Sporophyte
- Diploid (2n)
- multicellular body/form
- produces spores (n) through meiosis
45
Spores
- Haploid
| - Unicellular but will germinate to produce Gametophyte (n) through mitosis
46
Gametophyte
- Haploid
- multicellular body/form
- produces haploid, unicellular gametes (n) through mitosis
47
Gametes
Sperm and egg cells fuse (fertilization) to form a unicellular zygote (2n) that will quickly develop into an embryo through mitosis
48
Embryo
- Diploid (2n)
- multicellular
- will develop into a sporophyte through mitosis
49
The embryo of land plants is retained on the
Female gametophyte
50
Why Alternate Generations?
Amplifies of gametes and their chances of successful fertilization events and offspring
51
Algae reproduction was entirely water-mediated
- Long gametophyte phase
- Zygote immediately undergoes meiosis to produce spores
- Haploid spores give rise to gametophytes which produce haploid gametes through mitosis (very difficult on land)
52
Alternation of generations (Embryophytes)
- Retention of the zygote on the female gametophyte and allowing it to develop into an embryo -> Diploid Sporophyte
- Localized dispersal of gametes for greater certainty
- Allows for greater production of spores (“hard” propagules) for dispersal and amplification of offspring from a single fertilization event
53
In the simplest form, the land plants are separated by the presence of 2 features alone:
1. Presence of Vasculature
| 2. Presence of Seeds
54
Plant Vasculature
- No muscles or moving pumps are involved in moving the solutes
- Vascular tissues are commonly grouped together in either 1 or several bundles (xylem, phloem, parenchyma, fibre (sclerenchyma))
- Complex network that connects the entire plant from root/anchoring system to the photosynthetic surface
- Allows for the transfer of water and nutrients throughout the plant
- Contributes to the overall structure and support of the plant
55
Xylem cells transport:
Water and dissolved nutrients
56
Phloem cells transport:
Sugars and other nutrients
57
Secondary Cell Walls
- Not present in all plant cells
- Develop in areas that require additional support and in the vasculature
- Composed of cellulose, hemicellulose, and pectin BUT all the gaps are filled in with Lignin
58
Lignified parenchyma =
Sclerenchyma (fibre cells)
59
Xylem cells also develop from lignified parenchyma but are
dead at maturity
60
Lignin
- A highly complex phenolic polymer that covalently binds the cellulose and hemicellulose and is extremely resistant to degradation
- Creates a hydrophobic and impermeable barrier to water
- Rigidity of cell is reliant on lignin
61
Xylem Tissue
- The pits that develop along the xylem cells are not blocked by secondary cell walls
- Pits of vessels even lack primary cell walls
- Water can transit through xylem cells from bottom to top and into the next or exit the xylem into the surrounding tissue
62
Vasculature – Transport
- The taller plants grow = more room with less competition for light but are further from their resources
- Becomes harder to distribute those products throughout the plant and they become top-heavy
- Require long-distance transport mechanisms: xylem + phloem
- Require substantial supportive tissues: xylem + sclerenchyma
63
Seeds
- Seeds are housings for the young embryo
- Comprised of maternal sporophytic tissue and female gametophytic tissue
- A derived feature shared by the Gymnosperms (conifers and others) and the Angiosperms (flowering plants)
64
Extant diversity:
- Bryophytes: ~19,000 species
- Pterophytes: ~10,000 species
- Gymnosperms: ~1000 species
- Angiosperms: ~260,000 species
