Chapter 30

Question 1

Seed plant evolution

Answer 1

Evolved from progymnosperms (spore-bearing). Gymnosperm and progymnosperms are similar with vascular tissue (including secondary xylem to increase girth), leaves, grew tall and produced wood. Progymnosperms produce spores.
Evolved 350 MYA (305-465 MYA)
Rapid diversification around 309 MYA. Whole genome duplications (4n) occurred at origin of both gymnosperm and angiosperm. Genes have evolutionary pressures: Mutations (Pseudogenes no proteins produced), novel functions (resistance), reinforce existing functions.

Question 2

Seed plant characteristics

Answer 2

Seeds
Sporophyte is dominant generation (protects small gametophyte generation). Male and female gametophytes are highly reduced - (protected from UV radiation and desiccation).
Vascular tissues - wood =secondary xylem
Water not required to move male gametophyte
Heterosporous - 2 morphology types Microspores (male) and megaspores/macrospores (female)

Question 3

Microspores vs Macrospores/Megaspores

Answer 3

Microspores - Male, generally smaller, diversity in shape and size. Don’t need water for movement. Pollen grains. Microsporocyte.
Microspore mother cell (2n) to microspore (1n) to microgametophyte

Macrospores/Megaspores - Female, larger. Develop within ovules and remain attached to the sporophyte. Immature female cone holds megaspore, surrounded mostly by integument but allows a gap for male sperm to enter.
Megaspore mother cell (2n) to megaspore (1n) to megagametophyte

Question 4

Seed plant anatomy

Answer 4

Embryo, food for embryo and seed coat.
Allows “clock to be stopped” to survive harsh periods. Spores have to grow immediately, seeds can wait.
Naked seeds (Gymnosperms) first, then later development of fruits to enhance dispersal.
1 seed coat - Integument (gymnosperms). Can withstand harsh conditions.
2 Embryo - (2n) baby plant, sustained by nutritive tissue for energy found inside seed
3 Similar structures in angiosperms as well, theses allow for dormant stages, Opens up larger range of habitats.

Question 5

Pollination vs Fertilization

Answer 5

Pollination is sperm getting into pollen tube (female parts) but has not meet the egg.
Fertilization is sperm and egg being fused.

Question 6

5 Phyla of existing seed plants

Answer 6

Coniferophyta - gymnosperms
Cycadophyta - gymnosperms
Gnetophyta - gymnosperms
Ginkgophyta - gymnosperms
Anthophyta - Angiosperm, seeds enclosed within carpel (tissue)

Gymnosperm-naked seeds, ovules not enclosed by an ovary but exposed. Lack flowers, fruit. Ovule exposed on a scale (thick cone)

Question 7

Conifers phylum

Answer 7

Coniferophyta
Most diverse and familiar gymnosperm. Pines, spruces, firs, cedars, yews, and others. Found in colder and sometimes dry regions. Conifers are source of important products. (Timber, paper, resin, taxol (yew anti-cancer chemical)).

Question 8

Pines

Answer 8

100 spp. in All in northern hemisphere. Produce tough needlelike leaves in clusters. Leaves have thick cuticle and recessed stomata to retard water loss. Leaves have canals with resin to deter insect and fungal attacks.

Question 9

Pine Reproduction

Answer 9

Male gametophytes (pollen grains in male cones) develop microspores by meiosis, lower branches, smaller. Pollen releases 2 sperm, only one reaches egg. Female cones (ovules) form on the upper branches of same tree. Have woody scales, larger, two ovules develop on each scale and contain megasporangium, each will become female gametophyte.

Question 10

Seed and maturing

Answer 10

Female cones usually take 2 or more seasons to mature. During the first spring pollen grains drift down between open scales, drawn into micropyle (opening on seeds). Scales then close. 1 year later female gametophyte matures. 15 months after pollination, pollen tube reaches archegonium and discharges contents. One sperm unites with egg to form zygote, other degenerates.

Question 11

Cycads (Cycadophyta)

Answer 11

300ish spp. Slow growing gymnosperm of tropical or subtropical regions. Sporophytes resemble palm trees. Female cones can weigh 45 kg. Have largest sperm cell of all organisms.
Sago palm

Question 12

Gnetophytes (Gnetophyta)

Answer 12

Only gymnosperms with vessels in their xylem. Additional vessels for drawing in water. Desert, arid, semiarid. Usually smaller, not tall
Contain 3 genera Welwitschia (SW Africa), Ephedra (SW US and Mex)(Treats respiratory illness)(Large leafy shrub), Gnetum (vines & tropical trees) (Taproots, shallow cupped stem)

Question 13

Ginkgophytes (Ginkgophyta)

Answer 13

1 living spp Ginkgo biloba. Flagellated sperm, uses pollen or wind. Dioecious, usually vegetative propagation.

Question 14

Angiosperms
Carpels

Answer 14

Flowering plants. Ovules contain eggs, and become seeds after egg fertilization.
Carpels- A modified leaf that covers seeds, develops into fruit. Sporophyte tissue (Fruit tissue) covering gametophyte. Holds the seed.
As early as 145-208 MYA. Oldest known angiosperm is fossil Archaefructus. Diversified rapidly.

Question 15

Flower morphology

Answer 15

All flower parts have evolved from either stems or leaves. Primordium that develops into bud at end of stalk.
Flower parts are organized in circles called whorls.
Flower = modified stems bearing modified leaves.

Question 16

Flower parts and whorls

Answer 16

Outermost whorl - sepal (green 3-5)
Second whorl - petals (colorful to attract pollinators. 3-5. Could be missing fused or seperate)
Third whorl - stamens (androecium) (pollen is male gametophyte) each stamen has an anther (where pollen is) and a filament (stalk)
Forth whorl (center) - gynoecium (Female gametophyte) Consists of one or more carpels

Question 17

Carpel 3 major regions

Answer 17

Ovary - contains the ovules. Later develops into fruit and ovules inside becomes the seeds.
Stigma - Tip where pollen lands
Style - neck or stalk

Question 18

Pollination

Answer 18

Mechanical transfer of pollen from anther to stigma, mostly between different flowers/plants.
May or may not be followed by fertilization
Pollen grains develop a pollen tube that is guided to the embryo sac.
The generative cell divides to produce two sperm cells. No flagella on angiosperm sperm

Question 19

Double fertilization

Answer 19

One sperm unites with egg to form the diploid zygote (New sporophyte embryo).
Other sperm unites with 2 polar nuclei to form the triploid endosperm (3n). Provides nutrients to new sporophyte embryo and surrounds embryo.
Seed may remain dormant for many years. Germinate (Grow by mitosis) when conditions are favorable.

Question 20

Seeds in angiosperms

Answer 20

Development of embryo stops soon after meristems and cotyledons differentiate. Integuments develop into a relatively impermeable seed coat. Encloses the seed with its dormant embryo and stored food.
Once seed coat forms most of the embryo’s metabolic activities cease/greatly reduced. Germination cannot take place until water and oxygen reach the embryo.

Question 21

4 important adaptations of seeds

Answer 21

1 Maintain dormancy under unfavorable conditions.
2 They protect the young plant when it is most vulnerable.
3 Provide food fort the embryo until it can produce its own food (Leaves and roots, perform photosynthesis)
4 They facilitate dispersal of the embryo (Pass through digestive system, wind blown)

Question 22

Fruits

Answer 22

Most are simply define as mature ovaries (carpels) Ovary’s develop into fruit. At the same time seeds are forming the flower ovary begins to develop into a fruit. (It is possible for fruits to develop without seed development).

Question 23

Types of fruits

Answer 23

True berries
Legumes
Drupes
Samaras
Aggregate fruits
Multiple fruits

Question 24

True berries

Answer 24

Multiple seeds in 1 or more ovaries. Tomatos

Question 25

Legumes

Answer 25

2 carpel edges with seeds attached to edges. Dry out and then pop open.
Pea and beans

Question 26

Drupes

Answer 26

Single seed in hard pit. Pericarp 3 layers - Exocarp (Skin), Mesocarp (fruit), endocarp (pit)
Peach, plum, cherry

Question 27

Samaras

Answer 27

Seed attaches to pericarp wing
Maple, elm, ash

Question 28

Aggregate fruits

Answer 28

Ovaries of single flower with multiple lobes. Ovary not fused.
Blackberry, strawberry, raspberry.

Question 29

Multiple fruits

Answer 29

Individual flower forms fruit around single stem. Fruit fused together.
Pineapple pericarp fuse together.

Question 30

Fruit Dispersal

Answer 30

Occurs through a wide array of methods and allows to colonize large areas.
Ingestions and transportation by birds or other vertebrates. Consume fruit, seed survives guts.
Hitching a ride with hooked spines or birds and mammals
Burial in caches by herbivores.
Wind blown
Floating and drifting on water.