Plant Life Cycles And Reproduction Flashcards
What are a plant’s three basic organs?
Root System
- Center tap root, lateral roots that absorb water and minerals through root hairs
Shoot System
- Stems that give leaves placement and used for food storage
- Leaves which are the main photosynthesis organ and have veins that carry water and nutrients
Reproductive Shoot
- For flowers and fruits
What is the angiosperm life cycle?
Gametophytes are reduced in size.
Wholly dependent on the sporophyte for nutrients
Most reduced of all plants, only a few cells!
Angiosperm Reproductive Structures?!
The flower is the sporophytic structure of angiosperms specialized for sexual reproduction.
Flower has petals, sepals, stamen, and carpels.
Flowers are determinate growth as in they stop growing after flowers and fruit are formed.
Carpels and stamens are sporophylls - modified leaves specialized for reproduction. Carpel contains a stigma, style, and ovary.
- Stigma is sticky structure that captures pollen
- Ovary is where the egg containing ovules develops, and if fertilized the ovules become seeds
Stamen consists of a stalk called the filament and a terminal structure called the anther. Anther are chambers called microsporangia (pollen sacs) that produce pollen.
Petals and sepals are sterile modified leaves. Petals are bright colored and used to advertise a fertile flower to pollinators. Sepals enclose and protect flower buds and resemble normal leaves.
A complete flower contains all four organs, incomplete flowers are missing one or more.
What’s up with pollination and flowers?
Plants which sexually reproduce require pollen to fertilize an ovule!
Plants require an outside force to move their pollen to the intended target!
Pollination by WIND. Grasses and many trees pollinate by wind by releasing massive quantities of smaller-size pollen.
Pollination by BEES. Bees can see the UV spectrum, so some flowers have evolved “bullseyes” that bees can see clearly. Flower that utilize bees have sweet odors to attract foragers to nectar.
Pollination by MOTHS and BUTTERFLIES. Usually sweet-smelling flowers. Butterflies attracted to many bright colors. Moth-pollinated flowers are typically white or yellow, to help stand out at night.
Pollination by FLIES. Flies use flowers as a nectar course and transmit pollen similarly to bees. Some flowers mimic the smell of decay to lure in fly pollinators.
Pollination by BATS. Much like moths, these flowers are usually white or yellow.
Pollination by BIRDS. Hummingbirds.
What is up with Co-evolution in Pollination?
Some plants have evolved partnerships with very specific pollinators.
Co-evolution: the joint evolution of two interacting species, each in response to selection imposed by the other.
Many plants have coevolved with a single species that can pollinate them.
FIG WASP COEVOLUTION
Figs have inverted flowers.
- Pollen-laden female wasps enter an unripe fig through an opening called ostiole.
- Once inside, she lays eggs inside some flowers, pollinating as she moves.
- Newly hatched wasps mate, then the males dig tunnels out of the fruit for the females.
- Males die inside the fruit.
Most fig species have evolved to be pollinated by a single wasp.
Tricking Pollinators: Corpse Flowers
Parasitic corpse flower looks and smells like rotting meat. It uses flies to pollinate, tricking them into laying eggs on its massive petals. Flies pick up pollen, but their eggs are doomed!!
Tricking Pollinators: Bee Orchid
Bee orchid petals mimic the appearance of a female bee, and it produces similar sex pheromones. Males bees will attempt to mate with the flower and in the process pollinates. But they get nothing out of this!!
Development of Female Gametophytes
Once pollen fertilizes egg.
As a carpel develops, one or more ovules form deep within the ovary.
Embryo sac: female gamete that forms inside each ovule
Megasporangium: tissue where each embryo sac develops; cells undergo meiosis to form 4 haploid megaspores (3 degenerate, only 1 survives) and surviving megaspore divides by mitosis three times without cytokinesis = one large cell with 8 haploid nuclei. This mass is then divided by membranes to form the embryo sac.
Ovule: consists of the embryo sac, enclosed by the megasporangium and two surrounding integuments. The structure will become a seed if pollinated.
Development of Male Gametophytes in Pollen Grains
- As the stamens are produced, each anther develops four microsporangia, also called pollen sacs. Within the microsporangia are many diploid cells called microsporocytes. These undergo meiosis, forming 4 haploid microspores, which rise to haploid male gametophyte.
Microspore undergoes mitosis once to produce a gametophyte made of 2 cells Generative cell and Tube cell.
Sperm Delivery by Pollen Tubes and Double Fertilizaton
- Pollen released, if contact with stigma, then pollination
- Pollen absorbs water and germinates by forming a pollen tube.
- Generative cell divides into 2 sperm cells. The sperm discharge from the tube into the embryo sac.
- Once sperm fertilizes the egg, forming the zygote.
- The other sperm combines with the two polar nuclei, forming a triploid (3n) nucleus in the center of the large central cell of the female gametophyte.
- This cell gives rise to endosperm, a food-storing tissue of the seed.
- The union of the two sperm cells with different nuclei of the female gametophyte is called double fertilization.
What is the purpose of double fertilization?
Double fertilization ensures that the endosperm develops only in ovules where the egg has been fertilized, thereby preventing angiosperms from squandering nutrients on infertile ovules.
Seed Development
After double fertilization, each ovule develops into a seed!! Meanwhile ovary develops into a fruit, which encloses the seeds and aids in their dispersal by wind or animals.
Fruits protect seeds and aids is dispersal!
Dispersal Methods
Wind: seeds developed gliding methods
Water: coconuts are buoyant and capable of floating until they reach a suitable germination spot
Animals: common carriers of seeds, some dry fruit are adapted to stick to animal’s bodies, some can pass through animal’s gut, others trick animals into dispersal
Elaiosomes Example
Some seeds have developed an edible “cap” called an Elaiosome. This cap is highly nutritious for ants. Ants will carry the seeds back to their nests, eat the elaiosome, and leave the seed intact. They carry the seed to their waste piles, which are rich in nutrients.
