What are the 6 important necessities of plant life?
- 1. optimum hydration - avoid dehydration of the body
- 2. protection of gametes from dehydration
- 3. maintenance of physical structure and posture of the body
- 4. obtain sufficient water and nutrients from surrounding medium
- 5. carry out maximum photosynthesis
- 6. maximum body size possible
How do water plants fulfill the 6 important necessities?
- 1. for optimum hydration, they have no deficiency of water
- 2. for protection of gametes from dehydration, they need no special protection in water, they can just be released into the water
- 3. for maintaining physical structure, there's no issue since water provides buoyancy and organisms in water don't have to support their weight
- 4. for obtaining water and nutrients, they can just diffuse into the plant through to body surface with simple diffusion; no special organs or structures needed
- 5. photosynthesis is limited only by the depth in water as light intensity decreases
- 6. body size in general is limited
How do land plants fulfill the 6 important necessities?
- 1. for optimum hydration, water availability is a problem; evolve organs for absorption of water and minerals like roots and root hairs. Water conservation through controlled loss through stromata (first appear in mosses, and surface cuticle (all plants)
- 2. for protection of gametes from dehydration, protected by only making water available in preparation for fertilization and evolve seed habit resistant to dehydration
- 3. for maintaining physical structure, cell wall thickening in tissues to provide mechanical strength. evolution from homospory to heterospory for better differentiation of sexes.
- 4. for obtaining water and nutrients, evolve special pathways for distribution of water and minerals through long-distance transport (xylem, phloem)
- 5. for photosynthesis, leaves with large surface area evolved for maximum photosynthesis to benefit from higher light intensity
- 6. for body size, large sporophytic body evolved. evolution of the diploid sporophyte as the predominant body form to provide cushion against mutations as well as higher gene dosage to increase body size
Did all land plant adaptations arise at the same time?
No, their sequential evolution can be seen through the evolution of various land plants
What is the alternation of generations?
It is a phenomenon in sexually reproducing organisms when haploid gametophytes alternate with diploid gametophytes.
What is haploid?
Gametophyte with one set of chromosomes
What is diploid?
Sporophyte with 2 sets of chromosomes
What is a gametophyte?
In the life cycle of plants, the gamete-producing haploid phase, producing gametes that fuse to form zygote that develops into sporophyte
What is a sporophyte?
- Gametophyte fuse to form a zygote which develops into a sporophyte. It then forms haploid spores through meiosis. Each spore develops into a gametophyte.
What are the ancestors of plants?
- Advanced green algae like chara and coleochaete
- gametes already protected in these ancestors
What do all green algae have?
- Photosynthesis with chlorophyll a and b
- Cellulose cell walls
- Haploid dominant
Pair of advances green algae groups jointly had what which made them good ancestors for plants?
- multicellular thallus growth form
- antheridium and oogonium protect gametes
What are coleochaete-like alga?
could serve as ancestor of thallus-based plants like liverworts
What are chara-like alga?
Possess branching growth pattern and could serve as ancestor for most land plats with erect growth habit
What is a thallus?
- Flat, mat-like structure
- A thallus usually names the entire body of a multicellular non-moving organism in which there is no organization of the tissues into organs. Even though thalli do not have organized and distinct parts (leaves, roots, and stems) as do the vascular plants, they may have analogous structures that resemble their vascular "equivalents". The analogous structures have similar function or macroscopic structure, but different microscopic structure; for example, no thallus has vascular tissue.
What is an antheridium?
- An antheridium is a haploid structure or organ producing and containing male gametes.
- An antheridium typically consists of sterilecells and spermatogenous tissue. The sterile cells may form a central support structure or surround the spermatogenous tissue as a protective jacket.
What is an oogonium?
The oogonia of certain Thallophyte species are usually round or ovoid. Its contents are divieded into several uninucleate oospheres. This is in contrast to the male antheridia which is elongate and contains several nuclei.
What is isogamy?
When the 2 gametes are similar in appearance
What is asexual reproduction?
The multiplication of the haploid gametophytic phase
What is heterogamy?
- The 2 gametes are dissimilar in appearance and are protected in gametangia. It shows homospory.
- Each spore produces male or female thallus, one is motile and one is not
Which (gametophyte or sporophyte) is matrotrophic?
- In plant sciences, matrotrophy (maternal care) is considered a critical innovation preceding the origin of embryophytes and thus essential to the evolution of land plants
- matrotophic refers to ingestation of part of "mother"
What is important about the life cycle of a moss?
- Stomata appear for gaseous exchange
- 1. each archegonium (female) produces a single egg
- 2. each antheridium (male) produces millions of sperms (the traveling gamete)
- 3. stromata appear for the first time
- 4. sporophyte is matrotrophic
What is the stomata?
- a stoma is a pore, found in the leaf and stem epidermis that is used forgaseous exchange. The pore is bordered by a pair of specialized cells known as guard cells that are responsible for regulating the size of the opening.
- The term stomata is also used collectively to refer to an entire stomatal complex, both the pore itself and its accompanying guard cells.
- Air containing carbon dioxidea nd oxygen enters the plant through these openings where it is used in photosynthesis and respiration, respectively.
- Oxygen produced by photosynthesis exits through these same openings.
- Also, water vapor is released into the atmosphere through these pores in a process called transpiration.
- Stomata are present in thesporophyte generation of all land plant groups except liverworts.
When did heterospory first appear?
- In the earliest vascular plants - the Pteridophytes
- The club-mosses or lycopods, ferns, and horsetails
What are microphylls?
Simple leaves with a single vascular projection
What are macrophylls?
Expanded leaves with many vascular veins
Why did microphylls and macrophylls evolve?
To maximize size and light interception
Why are selaginella (a lyocopod) important to plant evolution?
- Ancestor of ferns
- Shows both heterospory and heterogamy
- Micropores give rise to male gameophyte, megaspores give rise to female gametophyte
- Microphylls appear
Why are ferns important to plant evolution?
- Ferns include both homosporous and heterosporous species
- Megaphylls appear
- Xylem and phloem appear
What is a xylem?
- Xylem is one of the two types of transport tissue in vascular plants (phloem is the other).
- Its basic function is to transport water, but it also transports some nutrients through the plant.
- Main function - upwards water transport
What is a phloem?
- In vascular plants, phloem is the living tissue that carries organic nutrients, in particular, sucrose to all parts of the plant where needed.
- The phloem is concerned mainly with the transport of soluble organic material made during photosynthesis. This is called translocation.
What is important about the gymnosperm life cycle?
- Sperms are not motile
- Still no flowers
- No xylem vessels
- Gametophyte is matrotrophic
- Sporophyte is ~300ft tall (tree)
- Same tree bears male strobili and female cones
- Naked ovule develops into a naked seed
- Show polyembryony
What is polyembryony?
Several embryos develop within one seed
What's important about the angiosperm life cycle?
- Flowers appear
- Xylem vessels appear
- Sperms not motile
- Gametophyte matrotrophic
- Male gametophyte: represented by mature pollen grain consisting of 2 cells
- Female gametophyte: represented by 8 celled embryo sac. One of those cells is the egg
- Double fertilization
- Only one embryo per seed
What makes up the higher plant vasculature?
- Tracheids (xylem)
- Vessels (xylem)
- Seive tubes (phloem)
- Companion cells (phloem)
How did the alternation of generations evolve?
- Gametophyte predominant and nourishes smaller sporophyte
- Gametophyte much smaller than sporophyte but both live independently
- Sporophyte predominant and nourishes the hidden and inconspicuous gametophyte
- (as sporophyte/gametophyte ratio increased over time, evolution went from the sporophyte being matrotrophic, to both living independently, to the microscopic gametophyte being nourished by the much larger sporophyte