Bio 2 Seedless Plants

Aquatic Plants

• all terrestrial plants are descended from aquatic plants (mostly green algae)

• aquatic plant have it easy

no treat of desiccation, no need for structural support, water protects from UV rays, gametes are transported through water

How did aquatic plants colonize terrestrial environments?

• had to adapt to living outside of water, dry conditions, UV rays

Disadvantages of colonizing terrestrial environments

• threat of desiccation (a threat to terrestrial plants that involves water loss)

• UV rays

• need structural support

• plant reproduction is water- dependent

• zygote is water- dependent

Advantages of colonizing terrestrial environments

• sunlight is abundant

• carbon dioxide is abundant

• no competitors for resources

• no predators

First terrestrial plant strategies

• bryophytes or mosses

• live near water and/ or colonize humid environments

• develop tolerance to desiccation

• stay small

• develop mechanism to protect against UV rays

Time

• Natural selection will act on genetic variation and select for beneficial traits

Adaptations to terrestrial life

1. Sporopollenin

• protects spores/ pollen from desiccation

2. Alternation of generations life cycle

• Two life stages in the same individual: Sporophyte stage that produces sores and a gametophyte stage that produces gametes

3. Apical meristem in roots and shoots

• allows vertical growth

4. Waxy cuticle on leaves and stem

• prevents desiccation

5. Lignin in vascular tissues (only present in vascular plants)

• Structural support

Sporopollenin

• Spores have thick cell walls made of sporopollenin

• Sporopollenin is organic molecules that are similar to fatty acids, and carotenoids

• Very resistant to desiccation and degradation

• This is an adaptation to protect spores

Alternation of Generations

• All sexually reproducing organisms have diploid and haploid stages

• Plants’ diploid stage amnd haploid stage are both multicellular

• Alternation of generations describes the life cycle of organism that have multicellular diploid and haploid

General life cycle of seedless plants

1. The haploid gametophyte stage produces haploid gametes through mitosis

• The sperm of one plant fertilized the egg of a separate plant to create a new individual plant, the diploid sporophyte

2. The diploid sporophyte stage produces haploid spores through meiosis

• Spores germinate into new gametophyte plants

Sporangia in Seedless Plants

• In seedless plants, the sporophyte is the diploid (2n) stage (the sporophyte is the result of gamete fusion aka fertilization)

• In nonvascular seedless plants, the sporophyte stage is dependent on gametophyte (n) stage

• The sporophyte produces sporangia

the sporangium structure is made of cells called sporocytes

sporocyte cells produce haploid spores through meiosis

• Spores are released from the sporangia, disperse, and then germinate into a new haploid gametophyte plants

What is the sporangium structure made of?

cells called sporocytes

sporocyte cells produce haploid spores through what?

meiosis

What are the two types of spores?

Homosporous and Heterosporous

Homosporous

• Sporohytes that produce only one type of spore are called homosporous (“same spore”)

• These pores typically germinate into a monoecious gametophyte

Monoecious: both male and female on same plant

• Most, but not all, seedless plants are homosporous