Biology 152: Unit 2
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Why are plants important to humans?
Plants are important resources for humans and are major model organisms for studying biology.
What are some major discoveries made using plants as model organisms?
Genes and transposons.
When did the invasion of land by plants begin?
About 475 million years ago.
What were the three major challenges of moving onto land?
Maintaining water, physical support, and sexual reproduction.
What was a major advantage of moving onto land?
Less competition for light.
What are embryophytes?
Land plants.
Which algal group is most closely related to embryophytes?
Charophytes.
Why are charophytes not considered the ancestors of modern land plants?
Modern charophytes and land plants share a common ancestor; modern charophytes did not directly become land plants.
What is a homologous trait?
A trait shared because it was inherited from a common ancestor.
What homologous traits do green algae share with land plants?
Cellulose cell walls, chlorophyll a and b, and sperm with two anterior flagella.
Why were freshwater charophytes likely preadapted for life on land?
They often lived near pond edges where changing water levels created selection for surviving dry periods.
What charophyte traits may have helped the transition to land? (4)
Freshwater adaptations, spores, sporopollenin, and associations with mycorrhizal fungi.
What does sporopollenin do? (3)
It protects against dehydration, decay, and UV radiation.
How could mycorrhizal fungi help early land plants?
They helped plants acquire nutrients when soils were not yet well developed.
When did the first multicellular land plants appear?
About 475 million years ago.
What did the earliest land plants likely resemble?
Liverwort thalli.
How did land plants transform Earth’s surface?
They helped create soil by breaking up rocks and adding organic material when they died.
How did soil formation affect aquatic environments?
Soil helped create rivers, which carried nutrients into the oceans.
What traits did the charophyte–land plant common ancestor likely have? (4)
Freshwater habitat, spores, sporopollenin-covered spores, and mycorrhizal associations.
What major problem does the cuticle solve for land plants?
It reduces water loss.
What problem does the cuticle create?
It inhibits gas exchange.
How do land plants maintain gas exchange despite having a cuticle?
Through pores or stomata.
What three major adaptations are shared by all land plants?
Cuticle, pores or stomata, and an embryo.
Why are land plants called embryophytes?
They produce an embryo that develops into a young sporophyte.
What are gametes?
Haploid reproductive cells, such as eggs and sperm.
What is a zygote?
The diploid cell formed when egg and sperm fuse during fertilization.
What does diploid (2n) mean?
Having two sets of chromosomes.
What does haploid (n) mean?
Having one set of chromosomes.
What does meiosis do in the plant life cycle?
Produces haploid spores from diploid cells.
What does mitosis do in the plant life cycle?
Allows growth without changing chromosome number.
What are the two generations in alternation of generations?
The haploid gametophyte and diploid sporophyte.
What does the gametophyte produce?
Gametes by mitosis.
What does the sporophyte produce?
Spores by meiosis.
What is the basic sequence of alternation of generations? (8 steps)
Gametophyte → gametes → fertilization → zygote → sporophyte → meiosis → spores → gametophyte.
What is an embryo in the plant life cycle?
A young sporophyte nourished by maternal tissue.
Why is alternation of generations beneficial for reproduction on land?
One fertilization can produce a sporophyte that makes many spores, increasing dispersal and reproductive output.
What three groups are called “bryophytes”?
Liverworts, mosses, and hornworts.
What characteristics do bryophytes share? (3)
They are short, usually live in moist habitats, and have a dominant gametophyte generation.
In bryophytes, how does the sporophyte depend on the gametophyte?
The sporophyte lives on the gametophyte and depends on it for nourishment.
What distinguishes liverworts from the other bryophytes?
They have pores instead of stomata.
What distinguishes mosses from liverworts?
Mosses have stomata.
What distinguishes hornworts?
Their sporophyte is longer-lived than the sporophyte of mosses and liverworts.
What is the main benefit of vascular tissue in land plants?
It allows plants to transport water and sugars throughout the body.
Why was vascular tissue important for plants becoming taller?
Tall plants need to move water up to leaves and sugars from leaves to roots and stems.
How did vascular tissue help plants colonize terrestrial environments?
It allowed plants to grow taller, compete better for light, and live farther from constant surface moisture.
Which generation has vascular tissue in vascular plants?
The sporophyte generation.
What does xylem transport?
Water.
What does phloem transport?
Sugars made by photosynthesis.
Why did taller growth provide an advantage?
Being taller than competitors improves access to light.
What does it mean for a plant to be gametophyte dominant?
The gametophyte is the larger, longer-lived, and more independent life stage.
Which plants are gametophyte dominant?
Bryophytes: liverworts, mosses, and hornworts.
How is the bryophyte sporophyte related to the gametophyte?
It grows on the gametophyte and depends on it for nourishment.
What does it mean for a plant to be sporophyte dominant?
The sporophyte is the larger, longer-lived, and more independent life stage.
Which major plant groups are sporophyte dominant?
Vascular plants, including ferns, gymnosperms, and angiosperms.
Why did sporophyte dominance become advantageous?
Larger, branched sporophytes can make more spores and disperse them farther.
Why are gametophytes more limited on land?
They require water for reproduction and lack vascular tissue.
How do fern gametophytes and sporophytes differ from bryophytes?
In ferns, both generations can live independently. postedlecture 3_bryos & vasc pl…
What major plant groups should you know in order on the phylogenetic tree?
Liverworts → mosses → hornworts → ferns → gymnosperms → angiosperms.
What traits evolved at the base of all land plants?
Land habit, embryo, alternation of generations, and cuticle.
What trait evolved after liverworts?
Stomata.
What trait evolved before vascular plants?
A long-lived sporophyte.
What traits define vascular plants on the tree?
A branched sporophyte and vascular system.
What trait evolved in the common ancestor of gymnosperms and angiosperms?
Seeds.
What trait is unique to angiosperms on this tree?
Flowers.
What is the correct evolutionary order of the major adaptations emphasized in this lecture?
Cuticle → vascular tissue → seeds → flowers.
What is the overall evolutionary trend from bryophytes to seed plants?
The sporophyte becomes larger and dominant, while the gametophyte becomes smaller and more dependent.
Why does increased plant height improve spore dispersal?
Spores released from greater heights can be carried farther by wind.
Why can a larger, branched sporophyte increase reproductive success?
It can produce more spores from a single fertilization event.
How does the gametophyte change across land plant evolution?
It becomes progressively smaller and more dependent on the sporophyte.
What are gametophytes like in seed plants?
They are greatly reduced, usually microscopic, and depend on sporophyte tissue for nutrition.
What are the major evolutionary changes in the sporophyte across land plant evolution?
It becomes longer-lived, branched, vascular, larger, and eventually the dominant generation.
What is a seed?
A fertilized ovule containing an embryo, food supply, and protective coat.
What is a fruit?
A structure derived from the ovary.
What is the main difference between a seed and a fruit?
A seed develops from a fertilized ovule, while a fruit develops from ovary tissue.
How do seeds differ from spores?
Seeds contain an embryo, stored food, and a protective coat, while spores are single reproductive cells without those features.
Why are seeds advantageous for reproduction on land?
They protect the embryo, provide stored food, and can remain dormant until conditions are favorable.
How do seeds help gymnosperms and angiosperms reproduce successfully?
They protect and nourish the embryo and allow dispersal away from the parent plant.
What happens to the ovule after fertilization?
It develops into a seed.
What happens to the ovary after fertilization in angiosperms?
It develops into the fruit.
Where is the female gametophyte produced in angiosperms?
Inside the ovule, which is located in the ovary.
What structures make up a carpel? (3)
Ovary, style, and stigma.
What is a pistil?
One or more carpels.
What is the starting cell for female gametophyte development?
The diploid megaspore mother cell.
What does the megaspore mother cell produce by meiosis?
Haploid female spores.
What happens to the surviving female spore?
It undergoes mitosis to form the female gametophyte.
What important structures are found in the female gametophyte?
An egg and two polar nuclei.
What is the ploidy of the egg?
Haploid, n.
What is the ploidy of each polar nucleus?
Haploid, n.
Where is the male gametophyte produced?
In the anther.
What structures make up the stamen?
Anther and filament.
What is pollen?
The male gametophyte.
What is the starting cell for male gametophyte development?
The diploid microspore mother cell.
What does the microspore mother cell produce by meiosis?
Four haploid male spores.
What happens to each male spore?
It undergoes mitosis to form the male gametophyte inside a pollen grain.
What are the two important cells/nuclei in the male gametophyte?
A generative cell and a tube cell nucleus.
What does the generative cell eventually produce?
Two sperm cells.
What is pollination?
Transfer of pollen from a stamen to a stigma.
What happens when pollen lands on an appropriate stigma?
It produces a pollen tube.
Where does the pollen tube grow?
Down the style toward the ovule and egg.
Why is angiosperm fertilization called double fertilization?
Two sperm participate in two separate fusion events.