BIOL10005 Lecture Notes - Lecture 30: Cork Cambium, Vascular Cambium, Secondary Growth
LECTURE 30
SEED PLANTS
CHAPTER
WHAT YOU SHOULD KNOW
•Seed plant life cycle
•Why are the seed plants better adapted to life on the land than the more primitive mosses and
ferns? Evolutionary novelties.
•How is the distribution of extant Southern Conifers influenced by Gondwana and continental
drift?
•Features that might account for angiosperm biodiversity and dominance:
•Flowers, double fertilization,
endosperm production
SEED PLANTS
•Seed plants include Cycads, conifers
and angiosperms (flowering plants).
•Seeds are one of the most important
innovations in land plant evolution.
•A seed is an embryonic plant
encased within a protective coating,
typically resourced with stored food.
•Conifers reproduce in cones and are
very diverse.
•250,000 species of flowering plants.
•100s of species of conifers.
•10s of species of cycads.
CYCADS, CONIFERS & ANGIOSPERMS
•Four main derived features: major events in land plant evolution;
•1. Development of secondary growth - produces woody tissues.
•2. Produce two types of spores (Heterospory): megaspores (in ovules – female) and microspores
(pollen - males). In conifers both are born on cones. Modifying the life cycle.
•3. Reproduce by seeds - female gametophyte & embryo enclosed within an ovule, which is
nourished and protected by a covering on the parent plant. Thus the next generation embryo can
be nourished.
•4. Male gametes transported in pollen.
SECONDARY GROWTH
•The vascular cambium is a meristem that produces additional vascular tissue (xylem on the inside
and phloem on the outside).
•Secondary growth increases the girth of a stem by producing cork cambium; adding wood and
bark.
•Secondary growth is essential for
development of shrubs and trees.
Lecture 30 - Friday 7 September 2016
BIOL10005 - GENETICS & THE EVOLUTION OF LIFE
FERN LIFE CYCLE
•(below right). The sporophyte is the dominant generation (same in seed plants). Clusters of
sporangia on the bottom of leaves. Meiosis occurs in the sporangium sac to create haploid spores,
which germinate into the other generation; the heart shaped gametophyte.
LAND PLANTS: ALTERNATION OF GENERATIONS
•(below left).
HETEROSPOROUS ALTERNATION OF
GENERATIONS
•(right, below).
•Alternation between haploid part of the life
cycle and the diploid (sporophyte) part.
•The yellow sporophyte is the plant we see. It
produces 2 types of spores, microspores
(pollen) and megaspores (seed).
•Because these are the products of meiosis and
undergo cell division, we call the products of
these structures the mega and micro
gametophytes.
•Microgametophyte; germinating pollen grain.
•Egg and sperm come together to form a
zygote which becomes the new zygotic
generation.
REPRODUCTIVE BIOLOGY: SEEDS
•Seeds develop from fertilized ovules, which are
borne in pine trees/cones.
•An ovule is a sporangium (or container) surrounded by a protective covering (integument).
•This is the main difference between seed plants and ferns in terms of
sporangium.
•The ovule contains only one functional spore, which is retained on the
parent plant.
•Reproductive biology of conifers occurs in cones.
•Pinus ovule and pollen cones at time of pollination.
LIFE CYCLE OF A PINE TREE
•(below).
Lecture 30 - Friday 7 September 2016
BIOL10005 - GENETICS & THE EVOLUTION OF LIFE
micropyle
integument
Functional
megaspore
microsporangium
Document Summary
Evolutionary novelties. drift: flowers, double fertilization, endosperm production. Cycads, conifers & angiosperms: four main derived features: major events in land plant evolution, 1. Development of secondary growth - produces woody tissues: 2. Produce two types of spores (heterospory): megaspores (in ovules female) and microspores (pollen - males). Reproduce by seeds - female gametophyte & embryo enclosed within an ovule, which is nourished and protected by a covering on the parent plant. Thus the next generation embryo can be nourished: 4. The sporophyte is the dominant generation (same in seed plants). Clusters of sporangia on the bottom of leaves. Meiosis occurs in the sporangium sac to create haploid spores, which germinate into the other generation; the heart shaped gametophyte. Generations: (right, below), alternation between haploid part of the life cycle and the diploid (sporophyte) part, the yellow sporophyte is the plant we see.
