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a. Advantage of seed plants over non-seed
i. Have protection and food from parent tissue
ii. Can lie dormant and have a long viability
iii. Independence from water
b. Difference between seed plants and non-seed plants
i. Seed plants produce by seeds, which can lie dormant and the non-seed produce by spores, which die quickly
- ii. Independence from water versus water required to allow sperm to fertilize egg
- 1. Allows for expansion of environment
iii. The archegonium of seed plants does not have a long neck as the non-seed do
c. Requirements for Evolution of Seed Plants
i. Heterospory (essentially, having male and female plants)
ii. Endosporal development
iii. The megaspore remains inside
iv. Megasporangium itself is surrounded by parental tissue
v. Continuous supply of food
vi. Ability to lie dormant
vii. Independence from water
True or False: Selaginella is an ancestor
False because it meets some requirements, but not all. For example, it does produce an embryo early in development, as well as has endosporal development where the meiospores remain inside. It is also heterosporous. However, what it lacks is the independence from water, a seed coat, a continuous food supply, and the ability to lie dormant.
Parts of a Seed
seed coat, endosperm (food), and embryo
Structure of the ovule
i. Around the outside: integuments that develop into the seed coat
ii. To the inside of the integuments is the female megasporangium, called the nucellus
iii. Inside the nucellus is the female gametophyte, which eventually becomes the stored food
iv. In the center of the ovule are the archegonia, which have the egg and are oriented closer to the micropyle
Development of the Ovule
i. Homospory developed into heterospory with microspores and megaspores.
From there, the megasporangium forms; and, it carries out meiosis to produce four megaspores, three of which disintegrate to give one functional megaspore.
The tissues then grow around the megaspore, protecting it and nourishing it.
The megasporangium becomes the nucellus and the tissue on the megasporophyte becomes the integuments.