1. Plant Diversity: How Plants Colonized Land
Chapter 29
Plant Diversity: How Plants Colonized Land

2. Plant Evolution
1.) The 1st land plants (& any other signs of life on land) appear in the fossil record about 500 mya.
2.) Plants’ closest living relative = green algae. This suggests that land plants evolved from an algal ancestor.

3. Plant Evolution 3.) Evidence of relationship b/w plants & green algae:
Both have…
a.) Cell walls made of cellulose
b.) Chloroplasts with chlorophyll a and b.
c.) Rosette cellulose synthesizing complexes: rose shaped protein complexes that make the cellulose fibers of the cell wall.
d.) Peroxisome enzymes
e.) Structure of flagellated sperm is similar (in land plants that produce them).
f.) Formation of phragmoplast: part of cell wall that forms during cell division.

4. Plant Evolution
4.) Based on this evidence it is likely that an ancestor of both today’s green algae & plants had adaptations that allowed it to make the move to land which gave rise to land plants.

5. Traits of Land Plants
1.) Apical meristems: regions of cell division at the tips of roots & shoots that can differentiate into various tissues throughout a plants life time.
2.) Alternation of generations life cycle: plants alternate b/w 2 different multicellular bodies. There are multicellular diploid AND multicellular haploid stages.

6. Traits of Land Plants
a.) Gametophyte generation: multicellular haploid that produces haploid sperm & egg cells.
b.) Sperm & egg cells fuse together to form a diploid zygote which then grows into a multicellular diploid organism – called the sporophyte generation.
c.) Sporophytes undergo meiosis to produce haploid spores.
d.) Spores can grow (through cell division, without fusing with another cell) into a multicellular haploid organism = gametophyte…and the cycle starts over.

10. Traits of Land Plants 3.) Walled spores produced in sporangia
a.) Sporangia: multicellular plant organs that undergo meiosis to produce spores (which can grow into a multicellular gametophyte).

11. Traits of Land Plants
4.) Multicellular gametangia: multicellular organs that produce eggs & sperm. They have names…
a.) archegonia: produce eggs
b.) antheridia: produce sperm
5.) Multicellular, dependent embryos: plant embryos are retained within the tissues of the female plant and derive nutrients from it.

12. Traits of Land Plants
6.) Many plants have cuticles: waxy covering on leaves that prevents water loss
7.) Many land plants also produce secondary compounds: chemicals that protect against herbivores & parasites.
a.) We derive chemicals & medicines from many secondary compounds.

13. Categories of Land Plants
Plants are divided into 2 main groups based on the presence of vascular tissue.
Vascular tissue: cells joined into tubes that are used to transport water & nutrients.

14. Categories of Land Plants
1.) Nonvascular plants – also called byrophytes
a.) Consists of mosses, liverworts & hornworts
2.) Vascular plants (can be divided further…)
a.) Seedless vascular plants: ferns
b.) Seed plants:
i.) Gymnosperms: “naked seeds” – seeds are not enclosed in chambers (conifers/evergreens)
ii.) Angiosperms: “contained seeds” – all flowering plants (where seeds develop inside ovaries, which are in flowers AND mature into fruits).

16. Bryophytes 1.) No vascular tissues (nonvascular)
2.) Consists of mosses, liverworts & hornworts

21. Bryophytes
3.) Gametophyte generation is larger & lives longer than sporophyte generation (this is the opposite of all vascular plants).
a.) Gametophytes produce flagellated sperm that swim through films of water to female gametophytes.
4.) Sporophyte is dependent on & grows out of the gametophyte. Also, much smaller.
a.) This is unique to bryophytes.

22. The stalks are the sporophytes which are rising out of the gametophytes.

24. Bryophytes
5.) Since bryophytes don’t have vascular tissues to transport water & nutrients, they typically grow low to the ground and they may only be a few cells thick.

25. Vascular Plants
1.) In all vascular plants, the sporophyte generation is the dominant generation – larger & more complex
2.) Have 2 types of vascular tissue:
a.) Xylem: transports water & dissolved minerals
b.) Phloem: transports sugars, amino acids & other organic products (FOOD).

26. Vascular Plants
3.) All have roots: anchor the plants, absorb water & nutrients from soil
4.) All have leaves to increase surface area = increase in photosynthesis

27. Vascular Plants
5.) Have sporophylls: modified leaves that have sporangia (meaning they produce spores).
a.) Homosporous (most seedless vascular plants): produce one type of spore that grows into a gametophyte producing both sperm & eggs.
b.) Heterosporous (all seed plants): produce 2 types of spores. One grows into female gametophyte (which produces eggs) and one grows into male gametophyte (produces sperm).

28. Seedless Vascular Plants
1.) Consists of ferns, horsetails, club mosses (not an actual moss).
2.) Still have flagellated sperm which is why they live in moist environments (so sperm can swim).

30. Fern gametophyte. Very small – live on ground or just under soil. Weird!