Botany: Chapter 22 Flashcards
What is a plant?
- multicellular eukaryotes with cell walls made of cellulose
- organisms that develop from multicellular embryos and carry out photosynthesis using the green pigment chlorophyll
- most are photoautrophs (produce their own food)
Alternation of Generations
life cycle in which a haploid gamete-producing plant (the gametophyte) alternates with a diploid spore-producing plant (the sporophyte)
- the gametophyte (n) produces haploid gametes by mitosis
- the male and female gametes unite in the process called fertilization
- the resulting zygote is diploid, and it develops into the embryo which eventually becomes the 2n sporophyte plant
- the sporophyte (2n) produces haploid spores by meiosis
- the spores germinate and develop into the gametophyte as a result of the mitotic division
* the sporophyte is the dominant generation in all plant groups except the bryophytes
Evolution of life on land
ancestry: a freshwater green alga is the ancestor of modern day land plants
Solving problems that come with a terristrial lifestyle
- problem: standing upright against gravity and transporting materials; solution: vascular tissue- adapted to transport materials througout the plant and support it
- problem: reducing evaporation/dehydration; solution: cuticle - waxy, waterproofing layer seen in vascular plants
Byrophytes (division byrophyta)
- primitive
- lack vascular tissue
consequences:
1. lack of vascular tissue means minimal support neded to attain taller heights
2. true roots lacking, thus water must be absorbed from the environment
3. lack of vascular tissue means internal transport must be achieved by other means- diffusion and osmosis - a true root, stem, or leaf is one that contains vascular tissue; so true stems and leaves are also lacking; the gametophyte is dominant*
Evolution of Vascular plants
- When: about 4.2 mya
- Key innovation: vascular tissuehas made this the most suffessful group of plants today (some 250,000 species currently exist)
- Examples: seedless vascular plants: club mosses, horsetails; seed producers: naked seed plants, flowering plants
The fern sporophyte
2n; the dominant generation
Frond
a large divided leave (ex. those possessed by ferns in their sporophyte stage)
Sori
reproductive structures on the underside of some fern leaves; contain sporangia
Sporangia
structures that produce haploid spores by meiosis
Rhizome
underground stem of many ferns; tree ferns lack rhizomes
Roots
ferns contain strong root systems
The fern gametophyte
- reduced, tiny, heart-shaped
- n
Antheridia
male reproductive structure that produces motile sperm by mitosis
*also seen in the gametophytes of byrophytes
Archegonia
female reproductive structure that produces ovaries by mitosis
*also seen in the gametophytes of bryophytes
Moisture is absolutely required for:
- sperm to egg transport
- spore germination
Key characteristics of the seed plants
vascular; water is not necessary for sperm to egg transfer
Adaptations accounting for the success of seed plants
(such adaptations allowed these plants to successfully expolit drier habitats)
- woody tissue: not seen in all; if lacking, the plant is regerred to as herbaceous
- more complex vascular tissue: for more efficient support and transport
- seeds: develop from fertilized egg and associated parts
- means of sperm to egg transfer without using water
Pollen
- means by which spern is carried to the egg in seed plants
- produced by cones or flowers
The naked seed plants
ovules, which become the seeds are not surrounded by an ovary
Gymnosperms
- many (the conifers) produce seeds in cones
- ginko biloba: a popular ornamental tree used to decorate streets in some cities (NYC) because they are tolerant of population
- the oldest (5,000 yr. old bristlecone pine) and tallest (giant sequoia260 ft) planys are gymnosperms
- seed dispersal is by wind; the structural adaptation in many spcies are wings
Angiosperms
- the most recent addition to the plant kingdom
- the most successful group because they are very diverse and the largest group of plants today
Characteristics of Angiosperms
- Flowers: secual structures that help ensure gamete transfer
- Fruits: ripened ovaries; structures that enclose, protect, and help disperse the seeds
Dormancy
- period of rest and inavticity
- occurs if conditions are infavorable for germination
Germination
the beginning of frowth of a seed, spore, or other reproductive body, usually following a period of dormancy
