Lecture 17

Created by agauvin 

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What are the four major groups of plants? Be able to give some little bit of detail on each.

Bryophytes - mosses

Seedless vascular plants - ferns

Gymnosperms - cone-bearing and others

Angiosperms - flowering plants

Why are mosses, liverworts and hornworts limited to moist habitats?

Because they produce motile sperm, so they need to be moist for sperm to transport. They have no developed a vascular system - rely on diffusion

What major advancements (name 2) do ferns and their relatives display that mosses and their relatives do not? What advantages do these major advancements confer?

Evolution of the vascular system and at least three additional morphological features - roots, stems, and leaves. These allow the plants to grow large on land by transporting nutrients and water efficiently.

What is a seed? What two major groups of plants have evolved seeds? How are the seeds of these two groups different?

A seed contains a developing embryo. It has a tough casing and contains food to nourish the embryo.

Gymnosperms and Angiosperms have evolved seeds. Gymnosperms produce seeds that are exposed to the environment and pollen. Pollen contain sperm and are transported through the air to the eggs (do not need to swim through water). Angiosperms have flowers that produce the gametes (pollen and egg). Some have separate male and female flowers, in which they attract animals for pollination.

What is double fertilization, and how might it be adaptive in angiosperms?

Double fertilization refers to a process in which two sperm cells fertilize cells in the ovary. If a pollen grain germinates, a pollen tube grows down the style toward the ovary. The pollen tube discharges two sperm into the female gametophyte (embryo sac) within an ovule. One sperm fertilizes the egg, forming the zygote. The other sperm combines with the two polar nuclei of the embryo sac's large central cell, forming a triploid cell that develops into the nutritive tissue called endosperm.

Gymnosperms have non-motile (no flagella) sperm encased in a tough pollen grain, so that they can survive when the wind carries them to a female cone. This mechanism of pollination requires mass quantities of pollen. How have some angiosperms evolved to reduce the amount of pollen they produce?

Angiosperms rely on animals to pollinate them which is much more direct and requires the plant to produce less pollen and uses less energy.

How do flowers aid in plant reproduction? How does the phenomenon of co- evolution figure into plant reproduction? Give some examples!

The flower is the structure that produces the gametes (pollen and egg). Flowers often attract animals for pollination, thus there has been substantial co-evolution between flowering plants and their animal pollinators. Insect and angiosperm diversification is especially tightly-linked, probably due to herbivory and pollination. E.g. pollen covered honeybee on a dandelion.

Fruits help plants to disperse their (often heavy) seeds. Discuss several mechanisms that plants have evolved to disperse their fruit.

Many fruits are eaten and digested, but the tough seeds are deposited with feces elsewhere; Burrs attach themselves to animals; maple "helicopters" assist in wind dispersal - plants stay in one place, produce food, hold water.

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