Seed Plants - Ch. 26 Flashcards
(27 cards)
male gametophytes
pollen grains, dispersed by wind or pollinaters, no need for water
female gametophytes
develop within the ovule, enclosed within the diploid sporophyte tissue in angiosperms
gymnosperms
plants with “naked seeds”
all lack flowers and fruits of angiosperms, all have an exposed ovule
can be divided into 4 groups: coniferophytes, cycadophytes, gnetophytes, and ginkgophytes
conifers (phylum coniferophyta)
most familar gymnosperm phylum
includes: pines, spruces, firs, cedars, etc.
found in colder and drier regions
source of important products like timber, paper, resin, or taxol
pines (conifer)
more than 100 species in the N. hemisphere
produce tough needle like leaves in clusters, leaves have thick cuticles and recessed stomata to prevent water loss, leaves have canals with resin to deter insect and fungal attacks
pine reproduction
- male gametophytes (pollen grains) develop from microspores in male cones by meiosis.
- female pine cones form on the upper branches of the same tree. the female cones are larger and have woody scales, 2 ovules develop on each scale, each contains a megasporangium that will become a female gametophyte.
- female cones usually take 2 seasons or more to mature.
- during the first spring, pollen grains drift down between the open scales.
- a year later, female gametophyte matures and the pollen tube grows. the mature male gametophyte will have 2 sperms.
- 15 months after pollination, pollen tube reaches the archegonium and discharges contents to produce a zygote.
cycads (phylum cycadophyta)
slow growing gymnosperm of tropical and subtropical regions. sporophytes resemble palm trees, and has the largest sperm of all organisms, thrive in mild climates, can be pollinated by beetles or wind
gnetophytes (phylum gnetophyta)
only gymnosperm with vessels in their xylem, has three genera: welwitschia, ephedra, and gnetum
ginkgophytes (phylum ginkgophyta)
only one species remains: ginkgo biloba, has flagellated sperm, dioecious (male and female reproductive structures form on different trees)
angiosperms
flowering plants, ovules are enclosed in diploid tissues at the time of pollination, carpal, a modified leaf that covers seeds develop into fruit, fruits, in flowering plants, add a layer of protection to seeds that attract animals that assist in seed dispersal, expanding the potential range of species
originated 145-208 mya
flower morphology
modified stems bearing modified leaves, primordium develops into a bud at the end of stalk called the pedicel, the pedicel expands at the tip to form a receptacle, to which other parts attach. flower parts are organized in circles called whorls
flower whorls
outermost whorl = sepals second whorls = petals third whorls = stamens innermost whorl = gynoecium -consists of one or more carpels and house the female gametophyte
carpel
has three major regions:
- ovary = the swollen base containing ovules, later develops into a fruit
- stigma = tip where pollen lands
- style = neck or stalk
pollination
mechanical transfer of pollen from anther to stigma, may or may not be followed by fertilization, pollen grains develop a pollen tube that is guided to an embryo sac
advantages to life on land
sunlight is abundant, carbon dioxide is more readily available, and land plants evolved before land animals
advantages to seeds
have a protective coat, prevents desiccation and no need for constant water supply, seeds can remain in a state of dormancy
when did flowering plants first appear?
125 mya in the lower cretaceous period and diversified about 200 mya
what did angiosperms originate from?
no consensus, but may have originated from small, woody bushes or tropical grasses, not derived from gymnosperms, they are a sister clade
characteristics of gymnosperms
paraphyletic group (may not have derived from a single ancestor) naked seeds, separate male and female gametophytes, pollen cones and ovulate cones, pollination by wind or insects, tracheids, alternation of generation, heterosporous,
do gymnosperms have ovaries?
no, they are partially sheltered by modified leaves called sporophylls.
a layer of sporophyte tissue that surrounds the megasporangium and later the embryo
lifecycle of a conifer
- male and female develop on different strobili
- in male cones, the microsporophyte undergoes meiosis and give rise to male gametophytes (pollen)
- a pollen tube develops slowly and the pollen grain will produce 2 haploid sperm by mitosis
- at fertilization, the haploid sperm will unite with the egg cell
- female cones, contains two ovules per scale
- each ovule has a narrow passage that opens near the base of the sporophyll, which is where the pollen tube will grow
- the megaspore will undergo meiosis, and a single cell will become a female gametophyte
- as the female gametophyte develops, a sticky pollination drop traps pollen so a pollen tube will grow.
- the sperm and egg will fuse to make a zygote
lifecycle of an angiosperm
- inside the anther’s microsporangia, male sporophytes divide by mitosis to make pollen grains. There are two cells, one will divide to produce 2 sperm and the other will make the pollen tube
- the ovule, sheltered within the ovary, contains the megasporangium
- within the megasporangium, the megasporocyte undergoes meiosis to produce 4 haploid megaspores. there are 1 big and 3 smalls and only the big survives
- the large megaspore divdes 3x to produce 8 nuclei. 3 cells at one pole become an egg and 2 synergids. the three 3 cells at the opposite pole become antipodal cells. the remaining 2 will be at the center of the cell and become the endosperm.
- one sperm and egg will unite to form a diploid zygote
- the other sperm with fuse with the two cells to make an endosperm, which is the food source for the egg
- the zygote develops into an embryo with a radide (small root), and 1-2 cotyledons
what are the two categories of fruit?
fleshy (berries, peaches, apples, etc.) and dry (rice, wheat, nuts)
what are the three groups of angiosperms?
basal, monocots, and eudicots
