chapter 2 Flashcards
What are the most dominant group of plants living today?
Seed plants(gymnosperms and angiosperms)
From where did seed plants appear to have evolved from?
spore-bearing plants known as progymnosperms(extinct).
Progymnosperms
seedless plants that have simple reproduction
What features do progymnosperms share with gymnosperms?
having secondary vascular tissues (2ndary xylem and 2ndary phloem which allow the plant to increase in width/girdth)
Gymnosperms and angiosperms features
-Vascular plants (with more efficient food and water conducting systems)
-Sporophyte generation is dominant and independent
-Gametophyte is greatly reduced to a few tissues or cells within the sporophyte.
-Heterosporous
Gymnosperms and angiosperms advanced features
-Have seeds(embryo is protected within sporophyte tissues)
-Most adapted to live on land
-No need of water for fertilization to occur
All seed plants are heterosporous or homosporous?
Heterosporous
What was the precursor for seed development?
Heterospory
Define heterospory. Explain
It is the production of 2 types of spores and it results in the production of 2 types of gametophytes.
A microspore germinates into a male gametophyte which produce antheridia. Each antheridium produces many sperm
In seed plants, what is the male gametophyte?
there are no antheridia; the male gametophyte is called the pollen grain.
How are pollen grains transferred for fertilization?
Pollen grains are dispersed by wind or pollinators →no need of water for fertilization(most adapted to live on land).
In seed plants, what is the female gametophyte?
In seed plants, the female sporangium is called megasporangium/ovule.
During the whole process of fertilization, what happens within the ovule/megasporangium?
-Within the ovule (megasporangium), megasporocytes undergo meiosis to produce (N) megaspores.
-Each megaspore divides by mitosis/germinates into a female (N) gametophyte, which is reduced to a few tissues within the sporophyte.
-The gametophyte forms (N) archegonia; each archegonium produces a single (N) egg/female gamete.
After fertilization, what happens to the ovule?
After fertilization, the diploid egg (zygote) becomes the embryo, which is enclosed withing a seed (the ovule becomes the seed)
List the advantages of seeds. 5
1-A seed is covered by a seed coat (integument is made of 1 or 2 layers of sporophyte tissue that hardens into a seed coat)
2-The seed coat protects the embryo
3-A seed contains nutrients for embryo to give energy during germination.
4-A seed becomes dormant under unfavorable conditions (like spores)
5-The seed is easily dispersed.
stored food
endosperm
seed coat
integument
integument
integument is made of 1 or 2 layers of sporophyte tissue that hardens into a seed coat.
How many divisions and phyla do the seed plants consist of?
Seed plants consist of 2 divisions and 5 phyla
What are the 2 divisions of the seed plants?
Gymnosperms and Angiosperms
What are the 5 phyla of the seed plants?
—For the gymnosperms:
1)Coniferophyta/sometimes called Pinophyta: conifers
2)Cycadophyta: cycads
3)Gnetophyta: gnetophytes
4)Ginkgophyta: ginkgo trees
—For the angiosperms:
5)Anthophyta: flowering plants or angiosperms
Coniferophyta/sometimes called Pinophyta: conifers, pines, spruces, firs, yews, redwoods… 6
-largest phylum of gymnosperms; It includes some of world record trees
-Sperm not motile; accesses the egg by a pollen tube.
-Leaves mostly needle-like.
-con bearing trees or shrubs
-found in cold, temperate and dry regions
-sources of important products:
Timber, paper, resin, and taxol (anti-cancer).
Cycadophyta: cycads
-Sperm flagellated and motile but confined within a pollen tube that grows to the vicinity of the egg.
-Water is NOT needed for fertilization to occur.
-slow-growing
-Found in tropical and subtropical regions
-The tree are dioecious = male or female trees: making either pollen-bearing or ovule-bearing cones (respectively), but not both.
-Female cones are huge.
Male cones produce pollen grains, which are usually carried by wind (or by beetles
-Palm-like plants with pinnate leaves.
-Secondary growth slow compared with that of the conifers.
-Seeds in cones
Gnetophyta: gnetophytes
-Sperm not motile; accesses the egg by a pollen tube.
-The only gymnosperms with vessels in their vasculature.
-Trees, shrubs, vines. Three very diverse genera (Ephedra, Gnetum, Welwitschia).
Ginkgophyta: ginkgo trees
-Sperm flagellated and motile but accesses the egg by a pollen tube.
-Only one living species remains: Ginkgo biloba
-Dioecious = male and female reproductive structures form on different trees.
-Female trees produce seeds on fleshy structures.
-Trees are resistant to pollution and frequently planted as ornamental trees in cities.
-Deciduous tree with fan-shaped leaves.
-Trees are either male or female.
-Seeds resemble a small plum with fleshy, foul-smelling outer covering.
-One genus
Anthophyta: flowering plants or angiosperms
-Sperm not motile; accesses the egg by a pollen tube.
-Seeds enclosed within a fruit.
-Leaves greatly varied in size and form.
-Herbs, vines, shrubs, trees.
-Most significant foods consumed by humans and animals.
-About 14,000 genera
General characteristics of gymnosperms
1-They are plants with “naked seeds”
2-They consist of 4 groups or lineages of seed plants.
3-All have ovule exposed on a scale:
In gymnosperms, the ovule (which becomes a seed) rests exposed on a scale (modified leaf or shoot)→ It is not completely enclosed by sporophyte tissues at the time of pollination.
4-They have no flowers and no fruits
What are pines’ leaves like?
-tough needle-like leaves in clusters.
-thick cuticle and recessed (hidden) stomata to minimize water loss when the soil freezes in winter.
-have canals with resin to deter insect and fungal attacks
What is the function of the thick cuticle and hidden stomata in pines’ leaves?
minimize water loss when the soil freezes in winter
What is the function of having canals with resin in pines’ leaves?
to deter insect and fungal attacks
Is pines’ wood soft or hard? why?
Soft; it lacks some of the more rigid cell types.
Is pines’ bark thick or thin? why?
Thick; an adaptation to survive fire and low temperature.
Pine tree sporophyte/gametophyte
The pine tree is a sporophyte.
It has tiny gametophyte in its cones
Is the pine tree homosporous or heterosporous?
it is heterosporous, it produces micro-and megaspores in separate cones.
What do the male cones look like? and where do they develop?
-The male cones are small and green. It has leaf-like papery scales, arranged in a spiral.
-It develops at the tip of lower branches.
-A pair of microsporangia are found on each scale.
During the pine life cycle, what happens inside the microsporangia?
-There are many microspore mother cells (2N), which undergo meiosis, and give rise to (N) microspores.
-Each microspore develops into a male gametophyte (N), called the pollen grain.
What does the pollen grain consist of? And how is it dispersed?
-The pollen grain; male gametophyte; consists of 4 cells, including 2 air sacs for buoyancy (to make it light).
-Pollen grains are dispersed by air (wind).
What do the female cones look like? and where do they develop?
-larger and woody (brown). woody scales. Two ovules develop at the base of each scale.
-found on upper branches.
How many ovules develop at the base of each scale in the female cone?
2 ovules
What does each ovule in the female cone consist of?
-Each ovule contains a megasporangium called nucellus which is surrounded by a thick layer of cells, the integument, which has a small opening :the micropyle = opening for sperm entry.
-One of the layers of the integument will become the seed coat.
Nucellus
Megasporangium in the female cone’s ovule which is surrounded by the integument.
Integument
Thick layer of cells which has the micropyle.
One of its layers becomes the seed coat.
micropyle
small opening in the integument for sperm entry
small opening in the integument for sperm entry
micropyle
What happens inside the megasporangium?
-Only one megaspore mother cell (2N) undergoes meiosis to produce 4 (N) megaspores.
-3 megapores breakdown
-1 megaspore survives and develops into a female gametophyte: producing 1 (N) egg per archegonium.
How is the pollen carried to the female cone?
Wind brings pollen on female cones. The pollen grain sticks on the micropyle.
When does the female cone become mature?
The female cones take 2 or more seasons to mature.
So, when pollination occurs, the female cone is still immature.
What happens during pollination?
-The pollen grain slowly produces a pollen tube that travels slowly down the nucellus to reach the egg (still developing).
-One of the pollen grain’s 4 cells, the generative cell, divides by mitosis resulting in two (N) cells:
—2 non-mobile (non-flagellated) sperm
-1 sperm degenerates
-1 fuses with the (N) egg to produce a (2N) zygote/the pine embryo.
-The embryo is within the seed, surrounded by a seed coat.
Life cycle of a typical pine
-Male cones are small and green.
-The male gametophyte is the pollen grain.
-Pollen is dispersed by wind.
-Pollination involves the germination of a pollen tube (from generative cell).
-Female cones are woody and contain 2 ovules per bract.
Which is more effective in conducting water in tracheids? xylum or vessels
vessels are more-efficient water conducting cells than tracheids in xylem
deciduous tree
a tree that is shedding its
leaves annually
Dioecious
can have either male or female gametangia, but not both
monoecious
can have both male and female gametangia simultaneously
What are some unique and advanced features of angiosperms?
-Flowers evolved to attract pollinators and enhance reproduction
-Seeds are enclosed within a fruit
-Life cycle with double fertilization
What are the 2 main differences between angiosperms and gymnosperms?
Angiosperms have :
-ovules that are enclosed in diploid tissue at the time of pollination.
-Carpel, a modified leaf that encapsulates seeds, and develops into a fruit
Carpel
Angiosperms have it; it’s a modified leaf that encapsulates seeds, and develops into a fruit.
What is the ovule surrounded by?
Ovule is surrounded by sporophyte tissues derived from leaves. (Carpel; it then develops into a fruit)
How many classes does the phylum anthophyta consist of?
2 classes; monocots and dicots
monocots
-Leaves with parallel venation
-Floral parts (petals) in 3 or multiple of 3
-Seed with 1 cotyledon (embryonic seed leaf)
-Endosperm (food) present in mature seeds
-In x section of herbaceous stem: veins are scattered
-Lateral meristems usually absent
-Roots fibrous (shallow and thin)
( grasses/ rice, corn, wheat; onion…)
dicots
-Leaves with netted/branched veins
-Floral parts in multiple of 4 or 5
-Seed with 2 cotyledons
-No endosperm in mature seeds.
-In x-section of herbaceous stem: veins are in a circle.
-Lateral meristems present (stem can become woody/increase in width)
-Roots: tap root (thicker and deeper)
(peas, roses, sunflowers, tomatoes, fruit trees…; more numerous)
What is the structure of the flower?
-A flower is a modified stem bearing 4 groups of modified leaves(attached in circles called whorls):
sepals, petals, stamens, carpels (gynoecium)
-A flower originates as a primordium that develops into a bud at the end of a stalk called pedicel.
Sepals/calyx
outermost whorl; green; protect young bud
Petals/corolla
colored; attract pollinators
Stamens/androecium
-male reproductive unit
-Each stamen consists of a stalk called filament and a sac-like anther bearing pollen.
-The anther is where meiosis occurs, and pollen (=male gametophytes) are produced
anther
sac-like structure bearing pollen. The anther is where meiosis occurs, and pollen (=male gametophytes) are produced.
pistil/carpel/gynoecium
-female gametophyte/reproductive unit.
-The pistil consists of 1 or more units called carpels.
-Each carpel contains:
-an ovary bearing one or more ovules
-a stalk called the style
-a stigma(at tip): sticky or feathery; where the pollen grains land and adhere.
stalk
style
stigma
at tip; where pollen grains land and adhere
What is one way that flowers can attract pollinators?
many flowers have nectaries (nectar secreting glands at the base of the ovary; nectar contains sugars, amino acids and other molecules to attract pollinators (birds, insects…).
Nectaries
Nectar secreting glands at the base of the ovary used to attract birds/insects…
In the life cycle of angiosperms, what does the ovule contain?
Megasporangium
In the life cycle of angiosperms, what happens in the megasporangium/ovule?
-Only 1 megaspore mother cell (2N) undergoes meiosis to give 4 (N) megaspores.
3 break down
1 survives
-The nucleus of the surviving (N) megaspore divides 3 times by mitosis to produce the female gametophyte.
-The 3 mitotic divisions result in the production of 8 (N) nuclei arranged into 2 groups.
-One nucleus from each of group moves to the center.
-A cell wall forms around the 2 central nuclei called polar nuclei; so that they are both enclosed inside one cell.
polar nuclei
the cell wall that forms around the 2 central nuclei so that they are both enclosed in one cell.
How many nuclei does the female gametophyte consist of?
The female gametophyte consists of 8 (N) nuclei found in 7 cells
embryo sac
female gametophyte
female gametophyte is also called
embryo sac
What does the embryo sac consist of?
-3 antipodals, at the upper pole. These are cells with no apparent function; they soon disintegrate.
-2 polar nuclei, at the center
-2 synergids and 1 egg, at the pole next to the micropyle (= opening for sperm entry).
antipodals
cells with no apparent function, as they soon integrate.
synergids
cells next to the egg next to the micropyle.
What is the embryo sac surrounded by?
2 layers of the ovule, the integuments, which also have the micropyle.
anther
pollen sac
What does the anther contain
microsporangia and nutritive tissues.
What happens inside the microsporangia?
-Within microsporangia, microspore mother cells (2N) undergo meiosis Each diploid microspore mother cell gives rise to 4 haploid microspores.
-At first, the 4 (N) microspores remain together as a quartet, called tetrad.
-Then the microspores (in each tetrad) separate and develop into pollen grains.
-A 2-layered wall develops around each microspore.
-The nucleus in each pollen grain undergoes mitosis to form 2 haploid nuclei:
the tube nucleus and generative nucleus.
What does the immature pollen grain consist of?
binucleate microspore.
What is the mature pollen grain formed of?
The mature pollen grain is formed of 2-cells:
-a small generative cell found inside
the large pollen tube cell.
-the tube nucleus
What is the pollen grain surrounded by?
a pollen grain wall which is usually sculptured and contains:
1-Chemicals to react with the stigma:
to signal whether or not to germinate
2-Pores called apertures, through which the pollen tube emerges
What is the function of the chemicals in the pollen grain?
react with the stigma:
to signal whether or not to germinate
What is the function of the pores/apertures in the pollen grain?
It is through which the pollen tube emerges.
What is pollination?
Pollination is the mechanical transfer of the pollen from the anther to the sticky stigma
How could pollination happen? by what?
It could happen via wind, gravity, water, or pollinators.
Self-fertilization/Selfing
If pollen falls on the stigma of the same flower -
Cross fertilization
If pollen falls on the stigma of a different flowers on same plant or different plant
What happens if the stigma is receptive and compatible?
the pollen grain germinates: it grows a pollen tube down the style until it reaches the micropyle.
What makes the stigma receptive and compatible?
interactions of chemicals between stigma and pollen
How fast is pollen tube growth in angiosperms? And is it faster or slower than in gymnosperms?
pollen tube growth is more rapid in angiosperms than gymnosperms; it takes about 2 days.
What happens after the pollen grain reaches the micropyle?
the generative nucleus (which was lagging behind) divides by mitosis, giving rise to two haploid sperm nuclei(or sperm cells or male gametes), which do not have flagella.
What happens as the pollen tube enters the embryo sac?
-it destroys the synergids, then discharges the 2 sperm nuclei.
-Both sperm nuclei are functional and both are involved in double fertilization, which is unique to angiosperms:
-1 sperm nucleus fuses with the egg to produce a (2N) zygote, which becomes the embryo sporophyte plant.
-The other sperm nucleus fuses with the 2 polar nuclei giving (3N) endosperm: stored food/nutritive tissue for the embryo (during its germination).
-The integuments (outer 2 layers of the ovule) develop into a seed coat.
-The embryo stops developing and becomes dormant.
What does it mean when the embryo becomes dormant?
it germinates when conditions are favorable/temporarily inactive
List the major functions of seeds.
a)They maintain dormancy under unfavorable conditions and postpone development until better conditions arise.
b)They afford protection of the young plant when it is in a vulnerable developmental stage.
c)They provide food for the embryo until it can produce its own food
d)They facilitate dispersal of the embryo into new habitats.
What happens when the seed coat forms?
-most of the embryo’s metabolic activities stop.
-the seed and embryonic plant are very stable
-Germination cannot take place until water and oxygen reach the embryo
-Seeds of some plants have been known to remain viable for thousands of years
How much water does a mature seed contain?
5-20% water
What are the specific adaptations that plants have to ensure that their seeds will germinate only under suitable conditions?
1)Seeds of some pine trees lie within tough cones that do not open until exposed to fire (heat).
This way the seeds will germinate in an open, fire-cleared habitat (after a fire; and the soil will be rich with nutrients).
2)Seeds of desert plants germinate only when inhibitory chemicals leach (washed out) from their seed coats by rain or water.
This way they will germinate when there is enough water in the soil.
3)Seeds of some plants must pass through the intestines of birds or mammals to weaken the seed coat before germinating
Is there any way that extinct plant seeds can germinate again?
Seeds of plants thought to be extinct may germinate under improved environmental conditions.
In angiosperms life cycle, what happens after fertilization?
the ovules become the seeds and the ovary develops into a fruit
What are fruits?
-Fruits are mature ovaries.
-Fruits are adapted for dispersal (disperse the seeds).
BUT it is possible to have fruits without seed development, like bananas which are propagated asexually.
What does the ovary wall of the fruit called? And what does it consist of?
Pericarp
It consists of 3 layers
a. Exocarp(outer skin)
b. Mesocarp(usually fleshy)
c. Endocarp(inner pit/surrounding the seed)
How many genotypes does a fruit consist of in 1 package?
1.Fruits and seed coat from prior sporophyte generation.
2.Embryo represents next sporophyte generation.
3.The endosperm is a transient, triploid product of fertilization.
1—Simple fruits
most diverse.
They develop from a single pistil containing 1 carpel (with many seeds) or with several united carpels.
When mature, what can simple fruits be?
a)fleshy: berry or drupe
b)dry: dehiscent (follicle, legume, capsule) or
indehiscent (grain, achene, samara)
Dehiscent
open spontaneously to release seeds/pollen
Indehiscent
not opening to release seeds
Simple Freshy fruit: Berry
-a fruit with soft tissues.
-The entire pericarp (ovary wall) is fleshy.
-It has a thin skin.
Ex. Tomato, grape, blueberry, cranberry
Simple Fleshy fruit: Drupr
-fruit with hard, stony pit surrounding one seed.
-The mesocarp is fleshy.
-The endocarp is hard and forms a pit.
Ex. Peach, cherry, plum, prune, apricot, avocado, olive.
Simple dry fruit; Dehiscent
At maturity:
-The entire pericarp is dry.
-The dry dehiscent fruit splits open along lines (sutures) to release the seeds.
Example:
-follicle(opens along 1 line): ex milkweed
-legume(opens along 2 lines): ex pea pods
-capsule(opens along many lines): ex. cotton
Simple dry fruit; Indehiscent
At maturity, the indehiscent dry fruit does not open.
It contains one seed per fruit.
Example
-GRAIN: seed coat is fused to fruit wall. Ex. Rice, corn , wheat
-ACHENE: seed coat is not fused to fruit wall. Ex. Sunflower seeds.
-SAMARA: pericarp forms a wing. Ex. Mapple seed.
2—-Aggregate fruit
-It forms from 1 flower with many, separate ovaries (or many separate carpels).
-As ovaries of different carpels enlarge, they fuse to form one fruit.
Ex. Raspberry, blackberry, strawberry
3—-Multiple fruit
-It develops from ovaries of many flowers, found close together on a common stalk.
-As ovaries of different flowers expand, they fuse to form one fruit.
Ex. Pineapple
What are the 3 different methods of fruit dispersal?
via animals, wind, or water
via animals
–Fruits with fleshy covering (often shiny black, blue or red) are ingested and transported by birds or other vertebrates.
–Fruits with hooked spines (ex burr grass) are dispersed by mammals as they get attached to fur or clothing.
–Nuts and acorns are buried (and sometimes forgotten) by herbivores like squirrels
via wind
-Fruits with wings (maples, ashes, elms) are carried by wind.
-Minute, dust-like seeds of orchids are blown by wind.
-Seeds with feather (dandelion) are light and blown by wind
via water
-coconuts (and other plants found near beaches) have fruits that can float on water and spread to new regions. This is how coconuts colonized Hawaiian islands.
