Unit 8 Plants

Where did all life originate?

in the ocean + evidence suggests that plants evolved onto land - 500 mya

What are plants used for?

• medicines

• reduction of green house gases

• food + water filtration

• habitats

Are land plants descended from modern charophytes

land plants are not descended from modern charophytes, but share a common ancestor w them

What are the homologous traits btwn charophytes + plants? (6)

1. cell wall containing cellulose

2. chloroplasts containing chlorophyll a + b

3. rosette shaped cellulose synthesizing complexes

4. molecular + biochem evidence → nuclear + chloroplasts gene homology

5. synthesis of sporopollenin (most durable organic polymer known) → prevents them from drying out

6. structure of flagellated sperm

Benefits of terrestrial life for plants

1. unfiltered sunlight

2. more CO2 in atmosphere

3. soil rich nutrients

4. few herbivores + pathogens at 1st

Challenges of terrestrial life for plants

1. scarcity of water

2. disiccation

3. structural support vs gravity

4. reproduction

What are derived traits in plants?

traits that separate land plants from algae ancestors

What are the 4 main challenges of newly land bound plants?

1. acquisition + transport of materials/nutrients

2. drying out

3. fertilization

4. development + dispersal of the embryo

Challenge #1- acquisition + transport of materials/nutrients

• most plants have vasculature- xylem + phloem

• vasculature led to the evolution of plant organs - leaves, stems, + roots

What is the function of xylem + phloem?

xylem= transports water + dissolved materials throughout plant

phloem= transports AA’s, sugars, + organics throughout plant

How do the 3 plant organs help the plant?

leaves= make food, increase surface area for photosynthesis, organize compound production, + enable gas exchange

stems= support

roots= anchor, absorb water + nutrients from soil

How did vascular tissues alter Earths landscape?

• supports taller plants

• taller plants get more sun + photosynthesis which mean CO2 levls decrease + O2 lvls increase

• spore from taller plants travel farther

• forests formed - 385 mya

Challenge #2- Drying Out

• plants had cuticle→ waxy covering that prevents water loss but this made gas exchange difficult

• plants developed stomata → special pores that open/close to allow for gas exchange to occur

Challenge #3- Fertilization

• in water sperm can swim easily to egg but on land this is not possible + is hard to bring 2 sex cells together→ plants evolved alternation of generations

What is alternation of generations?

multicellular forms that give rise to each other in turn

• muticell haploid (1n)= gametophyte that makes gametes

• multicell diploid (2n)= sporophyte that makes spores

• n= unique set of chromosomes

What are the steps of the plant life cycle?

sporophyte → mitosis → 1 spore cell from “mother” → meiosis → 4 spore → mitosis → gametophyte → mitosis → 2 gametes → fertilization → 1 zygote → mitosis ——> back to step 1 sporophyte

Gametophyte of ferns

• sperm are produced + released from the Antheridia (testes) w/in the gametophyte

• eggs are produced + fertilized in the Archegonia (ovaries) w/in the gametophyte

What does gametophyte mean?

the haploid stage in the life cycle of plants and some algae that produces gametes (sperm and eggs) through mitosis

• alternates w diploid sporophyte phase

What does sporophyte mean?

the diploid multicellular stage in the life cycle of plants and certain algae, which produces asexual spores

• alternates w gametophyte haploid phase