lecture 10 Flashcards
1
Q
mosses
A
- mosses are gametophyte dominant
- the cushiony green growth that we associate with moss is the gametophyte
2
Q
five stages of the moss life cycle
A
- gametes develop in male and female gametangia
- these are usually located on seperate plants
- flagellated sperm swim through a water film to reach the egg in the female gametangium - after fertilization the zygote remains in the gametangium
- in the gametangium the zygote divides by mitosis
- develops into a sporophyte embryo and then a mature sporophyte
- sporophyte remains attached to the gametophtye - meiosis occurs in the aporangia, at the tips of the sporophyte stalks
- following meiosis, the haploid spores are released from the sporangium - spores undergo mitosis and develop into gametophyte plants
3
Q
ferns
A
these plants are sporophyte dominant
- gametophyte is very small
- often have a distinct heart- like shape
- flagellated sperm requiring mositure to reach the egg - zygote remians on the gametophyte
- the zygote develops into an independant sporophyte
- within the clusters or sporangia cells undergo meiosis producing haploid spores which are then released
- spores develop into gametophytes by mitosis
4
Q
all seed plants have a special structure within the sporophyte where all stages of reproduction occur
A
- spores
- egg
- sperm
- zygote
- embryo
5
Q
in gynosperms the specialized structure where reproduction occurs is called
A
- cone
- each scale of the cone contains sporangia which produce spores by meiosis
- these spores are not released but give rise to gametophytes within the cone structure
- the gametophyte go on to produce gametes which then unite and form a new sporophyte
6
Q
pine trees have two types of cones which produce spores
A
- smaller cones called pollen cones and produce male gametophytes
- these contain many sporangia which produce many haploid spores by meiosis
- male pollen grains (gametophytes) develop from these spores
- mature pollen cones release millions of micoscopic pollen grains in clouds
- these pollen grains care carried by wind
- they contain cells that will develop into sperm if they land on a cone containing a female gametophyte
7
Q
gymnosperms
A
- the ovulate cone, producing the female gametophyte is larger than a pollen cone
- each of the cones stiff scales contains a pair of ovules
- each ovule contains a sporangium covered by a protective called the integument
8
Q
pollination occurs in gymnosperms when
A
a pollen grain lands on an ovulate scale and eneters an avule
- following pollinantion the scales grow together, sealing the cone until the seeds mature
- now meiosis occurs in a spore mother cell within the ovule
9
Q
development of gymnosperms
A
- over the course of months one surviving haploid spore will develop into the female gametophyte
- this gametophyte will produce eggs
- a tiny tube grows out of the pollen grain
- this tube digests its way through the ovule
- eventually sperm is released near an egg
- fertilization usually occurs more than a year after pollination
- all eggs in an ovule are usually fertilized
- only one of these zygotes will fully develop into a sporophyte embryo
- the ovule will mature into a seed
- the seed contains the embryo’s food supply and tough seed coat
- the food supply is the remains of the female gametophyte
- the seed coat is the ovules integument
- typically seeds are shed two years after pollination
- the seed is dispersed by wind
- under favorable conditions the seed will germinate and its embryo will develop into a pine seeding
10
Q
differences and similarities between angiosperms: flowering plants and gymnosperms
A
- flowers are the site of pollination and ferilization
- much like pine cones:
- flowers house sperate male and female sporangia and gametophytes
- mechansims of sexual reproduction (pollination and fertilization) are similar also
- differ from pine cones:
- each structure of the flower is highly specialized for very different functions
11
Q
angiosperms: structure
A
- floral structures are attached in a circle to a receptacle at the base of the flower
- the outer layer of the circle contains seapals which are usually green
- these enclose the flower before it opens
- the next layer, after the sepals are removed are the petals
- these are very noticeable and attract pollinators
- these showy petals are key to the success of angiosperms
- removal of the flower petals reveals the stamen filaments
- at the top of each of these filaments is the anther
- the anther is a sac containing the male sporangia
- this will eventually release pollen
- the carpel is the structure located at the center of the flower
- this is the female reproductive structure, including the ovary
- this is the unique angiosperm adaptation which encloses the ovules
- each ovule contains sporangium that will produce a female gametophyte and eventually become a seed
- the ovary will mature into a fruit which aids in seed dispersal
12
Q
angiosperms: fertilization
A
- this group of plants is sporophyte dominant
- the gametophyte generation is produced within its body
- meiosis occurs within the anther of the flower
- this produces haploid spores which undergo mitosis
- these will form the make gametophyte (pollen grains)
- meiosis in the ovule produces a haploid spore that under goes mitosis
- this forms the few cells of the female gametophyte
- one of these cells is destined to become an egg
- pollination occurs when a pollen grain lands on the stigma
- the pollen grain is carried by wither wind or an animal
- a tube grows from the pollen grain to the ovule and a sperm fertilizes the egg (same as in the gymnosperms)
- this forms a zygote
13
Q
angiosperms: reproduction
A
- a seed develops from each ovule
- each seed consists of an embryo surrounded by a seed coat and a food supply
- the embryo is a new sporophyte
- as the seed develops the ovaries wall thickens
- this forms the fruit that encloses the seeds
- when conditions are favorable the seed germinates
- as the embryo grows it uses the food supply from the seed until it can begin photosynthesis
- eventually it develops into a mature sporophtye completing the life cycle
- flowers attract animals which carry pollen more reliably than wind
- a key adaptation of angiosperms
- they are also able to produce very rapidly
- fertilization occurs in just 12 hours after pollination
14
Q
fruit structure
A
- fruits are the ripened ovary of the flower
- aids is seed dispersal
- some angiosperms rely on the wind for seed dispersal
- many angiosperms produce fleshy, ediable fruits which attract animals-food source
- during development the fruits remain green and thus camoflaged against their backdrop
- when ripe fruits become brightly colored advertising their presence to animals such as birds and mammals
- when the fruit is eaten most of the seeds which are tough pass unharmed through the digestive tract of the animal
- the animal may then deposit the seeds, along with fertilizer some distance away from where it initially found the fruit
15
Q
animal pollination and angiosperm evolution
A
- not all flowers have colorful accessories and sweet scents
- red maple has many anthers but not petals
- relies on wind for pollination: not fool proof
- massive amounts of pollen must be produced to ensure that some makes it to another plant and fertilization takes place
- the columbine has an elaborate flower: vibrantly colored
- this is associated with high energy cost
- this investment pays off when a pollinator carries the plant’s pollen to another flower
- the pollinator is attracted to the vibrant color
- estimated that 90% of anigosperms use animals for pollination
- animals visit the flowers in search of a meal
- flowers provide meal in form of nectar which is a high energy fluid
- the colorful petals and strong fragrance mark the plant as a food source
