Topic 10

Question 1

What are the key concepts of the evolution of seed plants?

Answer 1

seeds and pollen grains are key adaptations for life on land

gymnosperms bear “naked” seeds typically on cones

angiosperms have seeds encased in “fruit”

Question 2

What is the evolutionary advantage of seeds?

Answer 2

seeds provide some evolutionary advantages over spores

they may remain dormant for days to years, until conditions are favorable for germination

seeds have a supply of stored food

they may be transported long distances by wind or animals

Question 3

Why is the change from gametophyte to sporophyte dominant an improved adaptation for land plants?

Answer 3

need water: sporopollenin protects gametes (pollen) from desiccation, they are the ideal thing to have as the dispersal stage for fertilization as they do not depend upon water

protect developing embryo

diploid can be better: diploid cells can respond to varying environmental conditions more efficiently than haploid cells can

Question 4

What is a downside of embryo retention?

Answer 4

in ferns and horsetails, sporophytes have to live in the same place, as their parent gametophyte

seed plants overcome this limitation: embryo of seed plants are portable and can disperse to new location

Question 5

What are the characteristics of the evolution of pollen and seeds?

Answer 5

Gametophyte dependent on sporophyte: no longer free-living, gains: nourished and protected by sporophyte, losses: more stress on the sporophyte

Pollen: male gametophyte, gain: protected by pollen grain, water not necessary for fertilization, loss: need some mechanism to carry pollen (air, insects)

Ovule: female gametophyte, gain: protected by sporophyte (non-motile), loss: extra care for sporophyte

Seeds (fertilized ovule): contains next-generation sporophyte, gain: protection, dispersal, food storage, dormancy, loss: great energy cost to plant

Question 6

In addition to seeds, what features are common to all seed plants?

Answer 6

reduced gametophytes

heterospory (small and large spores)

pollen (small mobile “spores”)
ovules (large retained “spores”)

Question 7

What are male gametophytes?

Answer 7

within the pollen grain

microscope (1n) produced within microsporangium (2n), develops into male gametophytes (1n)

each pollen grain produces a pollen tube for delivering the sperm to the egg–> fertilization

Question 8

What are female gametophytes?

Answer 8

integuments + megasporangium + megaspore = ovule

megaspore (1n) produced within megasporangium (2n)

Question 9

What is pollen?

Answer 9

pollen grains coated with sporopollenin, making them tough

can withstand drying, UV, and physical damage

important since male gametophytes have to disperse to pollinate and then fertilize the ovule

Question 10

What is pollenation?

Answer 10

pollination represents another drastic change in evolutionary strategy

pollination: transfer of pollen to the part of a seed plant containing the ovules

in non-seed plants, single-celled sperm requires water to swim through (usually short distances)

in seed plants, entire male gametophyte carried inside pollen grain, wind or animals can transport pollen, can travel much greater distances, no need for a film of water

Question 11

What are seeds?

Answer 11

embryo is sporophyte tissue, along with its food supply (often gametophyte tissue), packaged in a protective coat = seed

range in size from minute orchid seed to gigantic coco-de-mer

main source of variation in seed size is amount of gametophyte-derived food

travel by air, water, in or on animals

seed often has tough coat

tiny embryo protected

Question 12

What is seed germination?

Answer 12

some seeds need special treatment to germinate (fire or smoke, overwintering, passage through digestive system of vertebrate)

large seeds with a lot of food can germinate and grow in low light

small seeds with little food need light to grow into strong seedlings

Question 13

What are the two main clades of seed plants?

Answer 13

gymnosperms: naked seeds
angiosperms: fruit covered seeds

Question 14

What are gymnosperms?

Answer 14

characterized by seed that is relatively “naked”

ovule and seed develops on surface of sporophylls

sporophylls normally in cones (strobila)

Question 15

What is the phylum ginkgophyta?

Answer 15

1 extant species, Ginkgo biloba

no wild individuals, all are associated with human habituations

common street tree because foliage attractive (yellow in autumn) and able to withstand harsh environment

Question 16

What is the phylum cycadophyta?

Answer 16

very diverse and dominant in Mesozoic (age of dinosaurs)

now only ~130 species in tropical areas

individuals have large cones and palm-like leaves

Question 17

What is the phylum gnetophyta?

Answer 17

some are tropical others live in deserts

morphologically diverse

grouping based on molecular evidence

Question 18

What are conifers?

Answer 18

shapes of leaves vary: scale-like leaves, long needles, flat leaves

dominant trees in boreal and alpine regions in Canada

most are evergreen

well-adapted to cold, dry habitats (thanks to waxy coat and leaf retention)

Question 19

What is the gymnosperm life cycle?

Answer 19

mature tree is 2n sporophyte

sporangia are located on scale-like leaves (sporophylls) in clusters (cones)

heterospory: megasporangia and microsporangia (on same tree or different trees)

pollination by wind (pollen has two hollow “air bladders”)

seed dispersal also by wind (seed is winged)

Question 20

What are angiosperms?

Answer 20

just one phylum: anthophyta

make up vast majority of seed plants

includes smallest and tallest seed plants

Question 21

What is the evolution of angiosperms?

Answer 21

gymnosperms dominant seed plants until middle Mesozoic

huge radiation of angiosperms, and decline of many gymnosperm groups in Cretaceous period

Darwin viewed sudden appearance and rise to dominance of flowering plants in the fossil record as a “mystery”

new fossil discoveries have allowed a plausible hypothesis of how flowering plants might have evolved from gymnosperm-like ancestors

Question 22

What is the angiosperm phylogeny?

Answer 22

angiosperms/gymnosperms likely diverged

angiosperms related to bennettitales (extinct seed plants with flowerlike structures)

Question 23

What was the angiosperm radiation?

Answer 23

the diversification of angiosperms is associated with three key adaptations: water-conducting vessels, flowers and fruits

these adaptations allow angiosperms to transport water, pollen, and seeds efficiently

Question 24

What are the two types of flowers?

Answer 24

monoecious: male and female flowers on same individual plant
dioecious: male and female flowers on different individual plants

Question 25

What is the angiosperm life cycle?

Answer 25

the female gametophyte, develops within an ovule (contained within an ovary)

a pollen grain on a stigma germinates and the pollen tube grows down to the ovary

double fertilization occurs when the pollen tube discharges two sperm into the female gametophyte within an ovule

one sperm fertilizes the egg

the other sperm initiates development of food-storing endosperm (sperm combines with two nuclei in the central cell of the female gametophyte)

the triploid (3n) endosperm nourishes the developing embryo

Question 26

What is the directed-pollination hypothesis?

Answer 26

natural selection favored structures that reward an animal for carrying pollen directly from one flower to another

flowers vary in size, structure, scent, and color in order to attract specific pollinators

Question 27

What is the co-evolution between plants and pollinators?

Answer 27

mutual evolutionary influence between two species, each of the species involved exerts selective pressure on the other, so they evolve together (co-evolve)

Question 28

What is the mutualistic relationship between plants and pollinators?

Answer 28

the plant expends less energy on pollen production and instead produces showy flowers, nectar, and/or odors

the pollinator gets a reward such as nectar and/or pollen for pollinating the plant

Question 29

What is the specific co-evolutionary relationship between flowering plants and their animal pollinators?

Answer 29

1. Plants evolve ever more elaborate methods to attract animal pollinators
2. Animals evolve ever more specialized body parts and behaviors to obtain the reward (nectar, pollen)

Question 30

What are the adaptive advantages to angiosperm-style fertilization?

Answer 30

1. Food store for seed (endosperm) develops only after fertilization, double fertilization (hence no resources are wasted if egg is unfertilized)
2. Female gametophyte reduced in size and hence cheaper to produce
3. Production of the small female gametophyte takes only a few days rather than months

Question 31

What are the key concepts angiosperms and the evolution of seed plants?

Answer 31

angiosperms have seeds encased in “fruit”

fertilization occurs twice = double fertilization (once for embryo and once for endosperm), hence no resources are wasted if egg is unfertilized

pollination is mainly by animals vs gymnosperms which are wind pollinated

co-evolution occurs between plant and pollinators