Plant Diversity I - How Plants Colonized the Earth

Question 1

what ancestor did all land plants derive from?

Answer 1

green algae

Question 2

what characteristics do land plants share with green algae?

Answer 2

-photosynthetic, multicellular
-cellulose cell wall, eukaryotic
-food stored as starch

Question 3

what are the four key characteristics of land plants?

Answer 3

1. alteration of generations
2. spores in sporangia
3. multicellular gametangia
4. meristem

Question 4

what is alteration of generations?

Answer 4

a form of reproduction in plants where the organism alternates between two stages - a gametophyte (n) and a sporophyte (2n)

sporophyte undergoes meiosis and releases spores, spores become gametophytes which release gametes through mitosis, which get fertilized, which become a zygote which becomes a sporophyte, repeat

Question 5

what is sporopollenin?

Answer 5

an organic compound that protects fragile plant spores from external dangers in the environment

Question 6

what reasons did plants have for moving onto land?

Answer 6

-unfiltered sunlight
-more CO2
-more nutrients in the soil
-initially, less predators and pathogens

Question 7

what problems did plants face when moving to land?

Answer 7

-desiccation [loss of water]
-trouble getting nutrients
-trouble having reproductive cells get together to fertilize
-no more water to support them -> need to grow against gravity

Question 8

what are the four main plant groups?

Answer 8

bryophytes
pterophytes
gymnosperms
angiosperms

Question 9

what plants make up the bryophyte group?

Answer 9

-earliest ancestors of terrestrial plants

phylum hepatophyta - liverworts
phylum anthocerophyta - hornworts
phylum bryophyta - mosses

Question 10

what are the characteristics of the bryophyte group?

Answer 10

-no true roots - only short ones called rhizoids
-no transport system for water & no lignin for support = small size & need to be near water
-need water for reproduction

Question 11

broadly, how do bryophytes reproduce?

Answer 11

-gametophyte dominant

haploid
spores produce male & female gametophytes -> males have antheridia which make sperm, females have archegonia which makes eggs -> these two fertilize in the archegonium

diploid

fertilization forms a zygote - forms an embryo - develops into a dominant gametophyte - produces sporophytes on top which release spores

Question 12

why are mosses important?

Answer 12

-mosses can form deposits of organic material called peat moss -> stores carbon and is harvested for fuel as well as soil conditioning

Question 13

what types of seedless vascular plants / pterophytes are there?

Answer 13

phylum lycuophyta - club mosses
phylum pterophyta - ferns and horsetails

Question 14

what are the characteristics of seedless vascular plants / pterophytes?

Answer 14

-sporophyte dominant
-vascular tissue: xylem and phloem
-lignin for support
-roots to anchor and absorb nutrients
-leaves for photosynthesis

Question 15

how do ferns reproduce?

Answer 15

haploid:
-sporangia releases spores, producing a bisexual gametophyte
-fern spore develops into a gametophyte
-gametophyte releases gametes: antheridium and archegonium, which fertilize

diploid:
-zygote develops and gives rise to a sporophyte, growing from the archegonium
-the underside of each sporophyte leaf has a spot called a “sori”, and each sori is a cluster of sporangia, which release spores

Question 16

what is the difference between homosporous and heterosporous plants?

Answer 16

homosporous: spore develops into a bisexual gametophyte that produces male & female gametes

heterosporous: plant has two types of spores, one that develops into its respective sex