Lecture 11: Mosses & Land

Question 1

What did land plants probably evolve from?

Answer 1

Green algae

Question 2

Define land plants

Answer 2

Land plants are multicellular photosynthetic autotrophic eukaryotes that can survive and reproduce on land.

Question 3

What two important innovations led to the plants moving to land?

Answer 3

1. Sexual reproduction on land: This was made possible by the embryophyte, which are organisms that nourish and protect the developing diploid embryo.
2. The ability to survive on land and in contact with air: This came from the waxy cuticle layer that helps retain moisture, the stomata that helped with gas exchange, and vascular tissue that transports water and nutrients throughout the plant body.

Question 4

What are the four main groups of land plants?

Answer 4

1. Non-vascular plants
2. Vascular plants
   - Named because of their possession of vascular tissue
3. Gymnosperms
   - “naked seeds”
4. Angiosperms
   - flowering plants

Question 5

What 3 innovations allow plants to survive in a non-aqueous environment and are common to all land plants?

Answer 5

1. Waxy cuticle layer: helps retain moisture in tissues
2. Stomata: found on leaves, allows exchange of gases with environment
3. Flavonoids: protect plants from UV rays

Question 6

What are non-vascular plants?

Answer 6

Non-vascular plants are embryophytes that have a waxy cuticle layer and some have stomata.
They DO NOT have vascular tissue, so are limited to very moist envrionments and do not grow tall.

Question 7

What are some features of the moss life cycle? (8)

Answer 7

1. It has alternation of generations
2. The gametophyte is dominant
3. Male and female gametophytes are independent; they have separate spores
4. Sperm develop in the antheridium, the male reproductive organ
5. The egg develops in the archegonium, a structure of sterile cells that shelters the egg
6. The zygote develops into an embryo in the archegonium when the sperm swims into it. The archegonium protects the embryo and is the defining feature of embryophytes.
7. In mosses, the sporophyte grows out of the archegonium and is dependent upon the gametophyte for water and nutrients
8. Fertilization still requires water, because sperm need water to reach the archegonium and fertilize the egg.