BIS 2C Midterm 2

What is a plant?

autotrophic eukaryote that converts light energy into chemical energy via photosynthesis in the presence of chlorophyll inside the chloroplast

Are plants monophyletic?

yes

How did plants acquire chloroplasts?

primary endosymbiosis of a cyanobacterium

What specific photopigment is a diagnostic feature of plants?

chlorophyll a

what did benefits did life on land offer to plants?

• increased access to sunlight

• increased access to gasses for photosynthesis

• decreased competition with other plants and herbivores (initially)

how were plants restricted initially?

they were only aquatic

meiosis

cell division that results in 4 daughter cells with reduced ploidy level

mitosis

cell division that results in 2 daughter cells with unchanged ploidy level

gametes

sexual haploid cells, typically eggs and sperm

fertilization

fusion of haploid gamete nuclei to form a single diploid cell, the zygote

diplontic life cycle

multicellular diploid phase (seen in all animals)

haplontic

multicellular haploid phase (seen in some fungi and algal groups)

Sporic

both multicellular haploid and diploid generations, characterized by an alteration of generations (innovation of land plants)

vegetative innovations of land plants

• waxy cuticle

• pigments

• microrrhizae

reproductive innovations of land plants

sporic life cycle

what does the sporic life cycle involve?

sporophyte, sporangia, spores, gametophyte, protected embryo

what is a sporophyte?

multicellular diploid plant

what is sporangia?

multicellular organ of the sporophyte that produced spores

what is a gametophyte?

a multicellular haploid plant that makes gametes in the gametangia organ

what is the antheridia?

the gametangium that produces male gametes

what is the archegonia?

the gametangium that produces female gametes

what is a protected embryo?

a zygote that develops while embedded in gametophyte tissue

bryophyte traits

• lack vascular system: water transported by capillary action, nutrient transport through diffusion.

• lack true leaves, stems, and roots.

• poorly developed cuticle.

• largely rely on water to have the sperm fertilize the egg, limits dispersal and reproductive timing.

bryophyte examples

• liverworts

• mosses

• hornworts

what were the major innovations of rhyniophytes (first vascular plants)?

• branched sporophyte with apical sporangia (at the tips) allowed for more spores per plant

• vascular tissue (lacked tracheid cells) allowed a more efficient transport of water and nutrients.

what are the diagnostic features of vascular plants?

• sporophyte is nutritionally independent of the gametophyte at maturity.

• Tracheid cells provide structural support and comprise the xylem.

what does the xylem do?

conducts water and minerals from the roots by passive transpiration-cohesion-tension system.

what does the phloem do?

conducts phloem sap (products of photosynthesis) from the source to the sink regions of the plant via the pressure flow model.

what are the adaptive values of the vascular system to plants

• more efficient transport of water and nutrients, allowing plants to colonize more land.

• Rigid structural support allows plants to grow taller to compete for sunlight and more effectively disperse spores.

what does the evolution of vascular plants involve?

homoplasy

which innovations were evolved independently?

• leaves: microphylls and megaphylls

• roots: simple and complex

• heterospory in lycophytes, monilophytes, and MRCA of seed plants.

what are microphylls?

leaves with a single vascular strand that evolved from sterile lateral sporangia in lycophytes

what are megaphylls?

leaves with many branched vascular strands that evolved from modified side branches in euphyllophytes

what are simple roots?

roots comprised of dichotomously branching rhizome (underground stem) with rootlets derived from microphyllous leaves evolved in lycophytes

what are complex roots?

roots with complex branching and root hairs derived from the dermis evolved in euphyllophytes

what is homosporous in gametophytes?

male and female gametangia may occur on a single individual plant

what is heterosporous in gametophytes?

male or female gametangia occur on separate individual plants

what is a megagametophyte?

female haploid plant that produces female gametes

what is a microgametophyte?

male haploid plant produce male gametes

what is homosporous in sporophytes?

only one type of sporangium on the sporophyte that produces one type of spore that gives rise to one type of hermaphroditic gametophyte

what is hetersporous in sporophytes?

two types of sporangia on the sporophyte that prodice two types of spores that give rise to two types of unisexual gametophytes

what are megasporangium?

contain megasporocytes that divide by meiosis to produce megaspores that become the multicellular female megagametophyte

what are microsporangium?

contain microsporocytes that divide by meiosis to produce microspores that become the multicellular male microgametophyte

what are the adaptive values of heterospory?

• genetic diversity: separate male and female gametophytes reduce the probability of self fertilization, which maintains genetics diversity in the population via outcrossing

• separate gametophytes facilitates evolution

what are the two main groups of seedless vascular plants?

• lycophytes

• monilophytes

what are the diagnostic features of lycophytes?

• lateral sporangia

• microphyll leaves

• simple roots

what are diagnostic features of euphyllophytes (monilophytes + seed plants)?

• overtopping growth

• megaphyll leaves

• complex roots

what is overtopping growth and what are the adaptive values?

asymmetric division of the apical meristem, so that the sporophyte has a main stem/axis and side branches.

• taller growth

• enhances dispersal of spores

• elaboration of novel organs from side branches (megaphyllous leaves and complex roots)

what are the two main seed plant groups?

• gymnosperms

• angiosperms

what are the four main innovations that arose from the MRCA of seed plants?

• secondary growth

• reduced

• dependent megagametophyte

• seed

• pollen

what is primary growth?

the ability to increase the length of the plant by means of apical (shoot and root) meristems

what is secondary growth?

the ability to increase the girth of the growing plant by means of vascular cambium

what is the vascular cambium?

a ring of meristematic cells between the primary xylem and primary phloem

what does the bifacial vascular cambium do?

produces secondary xylem to the inside of the plant (giving rise to wood) and secondary phloem to the outside of the plant (giving rise to bark).

what is the adaptive significance of secondary growth?

• allows taller growth of the sporophyte which enhances photosynthesis.

• increased efficiency of pollen and seed dispersal.

• allows for constant rejuvenation of the xylem and phloem.

• bark prevents water loss, infection, and protects against disease

what innovation enabled the evolution of the seed?

the megagametophyte was greatly reduced and embedded within and nutritionally dependent upon the sporophyte

what are the three nested components of the gymnosperm seed?

• innermost component: diploid embryo (baby sporophyte)

• middle component: haploid nutritive tissue (megagametophyte)

• outer component: diploid seed coat (integument)

what is the adaptive significance of seeds?

• facilitates efficient dispersal of the next sporophyte generation,

• provides protection for the developing sporophyte plant,

• allows for prolonged dormancy of the embryo so development can resume when conditions are favorable.

• Provisioned with nutrients to facilitate growth when development resumes.

what is pollen?

the highly reduced microgametophyte

what are the characteristics of pollen?

• it is comprised of just 4-8 cells

• lacks an antheridia (multicellular male gametangia)

• includes two sperm cells

• enclosed in sporopollenin to protect the pollen from desiccation.

what is the adaptive significance of pollen?

• facilitates efficient dispersal of sperm over great distances to pollenate megagametophytes which then promotes outcrossing and enhances genetic diversity

• delivery of sperm to megagametophytes without water

what is a flowering plant?

a megagametophyte reduced to an embryo sac (7 cells, 8 nuclei), with no archegonium

what is a seed plant?

a microgametophyte reduced to pollen grain (with 4-8 cells) with no antheridium

what makes up an ovule?

integument + enclosed megasporangium

what are the innovations of angiosperms?

• flower: reproductive structure that houses the micro- and megasporangia

• carpel: enclosed megasporangia

• fruit: expanded ovary

• double fertilization: one sperm gives rise to diploid zygote, the other to triploid endosperm

• endosperm: triploid tissue of the angiosperm seed that nourishes the developing embryo

• highly reduced megagametophyte: embryo sac

• new vascular cell types: vessel elements and fiber cells in xylem

what are traits of the flower?

• they are comprised of four concentric whorls of modified leaves

• houses the sporangia

• heterosporous— where both the microsporangia and megasporangia are located

what are features of the two outermost whorls?

• sterile (do not bare spores)

• comprise the perianth: outer whorl of sepals (calyx) and inner whorl of petals (corolla)

what are features of the two innermost whorls?

• spore-bearing leaves (sporophylls)

• outer of stamens: including a basal shaft (filament) and apical microsporangia (anthers)

• anthers contain microsporocytes which eventually give rise to pollen

• the pollen grain is comprised of two cells: an outer tube cell that contains the second, generative cell.

• carpels are located in these whorls, which include an apical stigma (“landing pad” for pollen), the style (connects the stigma to the ovary), and a basal ovary.

how are angiosperms pollinated?

by animals

what is the function of the flower?

to attract animal pollinators, either by offering a reward (nectar) or by tricking them (mimicking sexually receptive pollinators)

what are the three main components of the angiosperm seed?

• the diploid embryo (product of first fertilization)

• the triploid endosperm (product of the second fertilization)

• the diploid seed coat (derived from the diploid integument)

what is the difference between gymnosperm and angiosperm seeds?

the nutritive tissue in gymnosperms is haploid and triploid in angiosperms.

what are the two new cell types from xylem in flowering plants?

• vessel elements: increase efficiency of water and energy transport

• fiber cells: structural elements that aid in supporting the plant body

what is a perfect flower?

has both stamens and carpels

what is an imperfect flower?

either has only stamens (staminate flower) or only carpels (carpellate flower)

what is monoeicious?

a single plant that has both separate imperfect staminate and carpellate flowers

what is dioecious?

a single plant that either has imperfect staminate flowers or imperfect carpellate flowers (not both)

what is an inflorescence?

a group of flowers borne on a branch

what is an umbel?

an inflorescence comprised of flowers stemming from short stalks (pedicels) that radiate from a common point. ex: onions

what is a compound umbel?

an inflorescence comprised of a cluster of umbels stemming from stalks (rays) that radiate from a common point. example: carrots

what is a spike?

an inflorescence comprised of a cluster of flowers along an unbranched axis. ex: bunny grass

what is a head?

an inflorescence comprised of an outer ring of sterile ray florets and a central cluster of disk florets. ex: sunflowers

what develops by elaboration of the ovary after fertilization?

fruit

how is fruit adaptive?

• provides additional protection for the embryo

• facilitates dispersal of the seed (by biotic or abiotic vectors)

what is a drupe?

a simple fruit that is derived from a single flower with one ovary that contains one ovule

ex: cherries, plums

what is a berry?

a fleshy fruit that is derived from a single flower with one ovary that contains multiple ovules

ex: tomato

what is an aggregate fruit?

derived from a single flower with multiple, separate ovaries. the fruit forms by glomming together the fruitlets from each of the separate ovaries in a single flower. as they ripen, the ovaries aggregate (fuse) together

ex: blackberries, currants

what is a multiple fruit?

develop from the many separate florets of an inflorescence

ex: pineapples

what is an accessory fruit?

develop from parts of the plant other than carpels and seeds

ex: strawberries

what is a legume?

non-fleshy fruits that develop from one carpel with many ovules, where the fruit splits lengthwise into two halves; each ovule is a bean

ex: green beans, peanuts

what is an achene?

dry fruits that contain a single seed

ex: sunflower seeds

what is a samara?

an achene with wings

ex: hops, maple “helicopter”

what are features of eudicots?

• two cotyledons

• star shaped root vasculature

• reticulate (net like) leaf venation

• three (tricolpate) pollen grooves

what are features of monocots?

• one cotyledon

• ring shaped root vasculature

• parallel leaf venation

• one (monocolpate) pollen groove