Bis 2C MT 2

What is a plant?

What is a plant?

Autotrophic eukaryotic organism capable of converting light energy (solar radiation) into chemical energy (carbs) via the process of photosynthesis in the presence of chlorophyll inside chloroplasts.

gametophyte

haploid gamete plant that produces gametes by mitosis in gametangia

gametangia

multicellular organs of gametophyte that produces gametes by mitosis

archegonia

produce female gametes (egg cells)

antheridia

produce male gametes (sperm cells)

homosporous

1. individual hermaphroditic plant makes both male and female gametes.

2. only one type of sporangium in one sporophyte that produces one type of spore

heterosporous

1. male and female gametangia occur on separate unisexual plants

2. two types of sporangia on the sporophyte that produce two types of spores that give rise to 2 types of unisexual gametophytes

megagametophyte

female gametophyte haploid (n) plant that produces female gametes (eggs) in archegonia

megagametophyte in flowering plant

reduced to embryo sac (7 cells, 8 nuclei), no archegonium

microgametophyte

male gametophyte haploid (n) plant that produces male gametes (sperm) in antheridia

microgametophyte in seed plants

reduced to pollen grain, 4-8 cells, no antheridium

microgametophyte in flowering plants

reduced to pollen grain with 2 cells, tube and generative, no antheridium

gametes

fuse at fertilization to produce a single-celled diploid zygote that gives rise to multicellular diploid sporophyte

sporophyte

multicellular diploid spore plant that produces spores by meiosis in sporangia

sporangia

multicellular organs of sporophyte that produces spores by meiosis

megasporangia

contain diploid (2n) megasporocyte cells that divide by meiosis to produce halpoid (n) megaspores that give rise to female multicellular haploid (n) megagametophyte

in seed plants, surrounded by integument

ovule

in seed plants, the intefument and enclosed megasporangium

microsporangia

contain diploid (2n) microsporocyte cells that divide by meiosis to produce haploid (n) microspores that give rise to male haploid (n) microgametophyte

spores

single haploid cells that undergo mitotic cell division after germination to give rise to the multicellular haploid gametophyte, coated in sporopollenin

1st cell of haploid stage

sporopollenin

Most robust organic compound (polymer), protects pollen from desiccation and allows it to last for a very long time

protected embryo

where the zygote develops while embedded in gametophyte tissue

What plants have homosporous lifecycle?

All land plants EXCEPT spike moss, leptosporangium ferns, or seed plants (gymo/angiosperms)

diagnostic features of plants

-possession of chloroplasts via primary endosymbiosis of cyanobacteria

-photopigment “chlorophyll a”

Challenges to life on land

1. desiccation

2. water transport

3. structural support against gravity, wind

4. intense UV radiation

5. dispersal of gametes & progeny

Benefits of living on land

1. increased access to sun for photosynth

2. increased access to gases (oxygen, CO2) for photosynthesis

3. decreased competition with other plants and herbivores initially

Algal plants…

1. store products of photosynthesis as starch inside chloroplasts

2. photopigment “chlorophyll b”

3. retention of egg on parent plant

4. encasement of egg on parent plant (enclosed by parent tissue)

When did chlorophyll b evolve?

On the branch to chlorophytes/after red algae

When did starch as storage evolve/what doesn’t use it?

Evolved on the branch to chlorophytes

red algae don’t use it

charales

Sister group to land plants, occur in near-shore habitats.

How do unicellular and multicellular organisms reproduce?

1. Unicellular: asexually

2. Multicellular: sexually by haplontic lifecycle (multicell haploid stage)

Meiosis

Cell division with reduction of ploidy in daughter cells

mitosis

cell division that results in no ploidy level change in daughter cells

gametes

sexual haploid cells (sperm/egg)

fertilization

fusion of n gamete nuclei to form single celled 2n zygote

Diplontic lifecycle

multicellular diploid phase (animals, humans)

Haplontic Lifecycle

multicellular haploid phase (fungi and algal gorups)

Sporic lifecycle, Alternation-of-generations

Both multicellular and haploid generations, innovation of land plants

cuticle

waxy coating to prevent desiccation

Bryophytes (non-vascular land plants)

Restricted to cool, damp habitats because

1. lack true vascular system, true stems, leaves, and roots

2. poorly developed cuticle

3. rely on water for reproduction, swimming sperm requires water, limits ability to disperse and timing of reprod.

What are bryophyte bodies reliant on for support?

Lack a true vascular system, rely on capillary action (osmosis causing cell turgor) and nutrient transport relies on diffusion of water through cell membranes.

Bryophytes include

1. liverworts

2. mosses

3. hornworts

rhiniophytes

extinct sister group to vascular plants, had 2 major innovations

1. branched sporophyte with apical sporangia

2. vascular tissue that lacked tracheid cells

branched sporophyte

allowed production of more apical sporangia and spores per plant

vascular system allows..

for more efficient water and nutrient transport in the plant

In vascular plants…

the sporophyte is nutritionally independent of the gametophyte at maturity

tracheid

cells with lignified walls that provide structural support and comprise the xylem

xylem

conducts water and minerals from roots to aerial parts of the plant by passive transipration-cohesion-tension system. Tissue comprised of tracheid cells that are dead at functional maturity and have cell walls fortified with lignin.

phloem

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

Tissue comprised of sieve-tube elements and companion cells (nurture sieve tube elements)

Adaptive value of vascular system to plants

1. more efficient water and nutrient transport

2. rigid structure allows plant to grow taller, better competitor for sunlight and spore dispersal

lateral sporangia

1. sometimes clustered in apical “cones” called strobili

2. solution to increase number of sporangia on sporophyte

microphyllous leaves

relatively simple leaves with singular vascular strand derived from sterile lateral sporangia

simple roots

dichotomously branch underground stems with rootlets that evolved from microphyll leaves

dichotomous branching

present in rhiniophytes, the division of the apical meristem into two independently functioning axes

overtopping growth

1. sporophyte has dominant axis and side branches

2. asymmetric division of apical meristem

ALLOWS:

1. taller growth and better sunlight competitor

2. enhances spore dispersal

3. allowed elaboration of novel organs from side branches (like megaphyllous leaves)

megaphyllous leaves

“true” leaves with more complex vascularization that evolved from side branches, ramified vascular tissue derived from modified side branches

complex roots

with complex branching and root hairs that evolved from the dermis

apical meristem

1. region of continuously dividing cells that give rise to plant body (in stem and roots)

2. meristematic (undifferentiated) cells that give rise to many tissues

3. all root/shoot cells descended from these.

What are the different branching plants can have?

1. Lycophytes divide asymmetrically, sporophyte branches dichotomously

2. Euphyllophytes divide asymmetrically with overtopping growth: sporophytes have main axis with side branches

leaves

composed of photosynthetic organs emerging laterally from a stem/branch possessing vascular tissue

Seed plants

comprised of gymnosperms and angiosperms, with 2 extinct groups called progymnosperms and seed ferns

progymnosperms

-trees that exhibited secondary growth (wood) but lacked seeds, NOT progenitor of gymnosperms

-have wood, no seeds

seed ferns

-trees with fern-like leaves that bore seeds, distantly related to ferns

-have wood and seeds

primary growth

the ability to increase the length of the plant by means of apical meristems in roots and shoots.

secondary growth

the ability to increase the girth/width of a plant by means of vascular cambium

vascular cambium

innovation of seed plants, comprised of ring of meritematic cells between 1° xylem and 1° phloem.

bifacial vascular cambium

→2° xylem to the inside of the plant that gives rise to wood,

→2° phloem to the outside of the plant that gives rise to bark

Significance of secondary growth

1. allows taller growth of sporophyte, better sunlight competitor

2. taller growth facilitates efficient dispersal of pollen/seeds

3. constant rejuvenation of xylem and phloem, gets clogged with resins over time

4. formation of bark prevents water loss and protects against pathogens

evolved independently in lycophytes with unifacial vascular cambium

unifacial vascular cambium

in lycophytes (quillworts). Produces 2° xylem but not 2° phloem. In quillworts, girth increase is limited because the phloem gets squeezed

Where does nutritive haploid tissue come from in gymnosperm seeds?

megagametophyte

where does the diploid seed coat come from in gymnosperm seeds?

the integument

Benefits of seed innovation

1. Facilitates efficient dispersal of next sporophyte generation

2. provides protection of developing sporophyte

3. allows for prolonged dormancy of embryo so that development can resume when conditions are favorable, contains nutrients for when plant germinates and grows

pollen/pollen grain

highly reduced male gametophyte (microgametophyte) of seed plants.

1. comprised of 4-8 cells, 2 of which are sperm cells/male gametes

2. lacks multicellular male gametangia (antheridia)

3. enclosed in sporopollenin

Benefits of pollen

1. efficient dispersal of sperm over great distances

2. delivery of sperm to megagametophytes without water!

dioecious

Male and female reproductive organisms on separate individuals

monoecious

having male and female reproductive organisms on the same individual

cycads

1. Dioecious cone-bearing palm-like plants, pollen make swimming sperm

2. deliver sperm via pollen grain, sperm swim within megagametophyte to fertilize egg after pollination

ginko

1. single species of dioecious plants.

2. Pollen have swimming sperm

3. ovules borne in pairs surrounded by fleshy integument, fertilized ovule has fleshy swelling of integument tissue that smells bad

gnetophytes

1. Dioecious and monoecious plants with opposite leaves and non-motile sperm (non-swimming).

2. Have vessel elements in xylem and exhibit double fertilization, 2 sperm fertilizing one egg

conifers

1. dioecious and monecious cone-bearing plants with needle-like leaves and non-motile sperm.

2. pollen cones have scales that are modified leaves

3. scales of seed cone are modified branches

4. half of the species have fleshy, fruit-like swelling around fertilized ovule (juniper “berries”)

Angiosperms have long phylogenetic stem

dominant terrestrial plants for the past 90 million years.

speciation event that gave rise to mrca of gymnosperms and mrca of flowering plants occured 370 mya.

Long stem has 2 important consequences

1. Difficult to locate position of root of flowering plants. Closest relative (gymnosperms) separated by a long time span. Identified root at “ANITA” grade of plants.

2. provided opportunity for many angiosperm innovations to accumulate, most related to reproduction

flower

reproductive structure of flowering plants

carpel

enclosed megasporangia

fruit

expanded ovary

double fertilization

one sperm gives rise to diploid zygote, other to triploid endosperm

endosperm

triploid tissue that nourishes developing embryo

embryo sac

1. highly reduced female megagametophyte, usually 7 cells and 8 nuclei.

Angiosperms have new vascular cell types

vessel elements and fiber cells in xylem

Xylem in flowering plants has 2 new cell types

1. Vessel elements: increase efficiency of h2o and mineral transport

2. fiber cells are structural elements that aid in supporting plant body

perfect flower

both stamens and carpels

imperfect flower

either stamens or carpels, bot both

inflorescence

group of flowers borne on a branch

umbel

flowers stemming from short stalks (pedicels) that radiate from a common point. Onions

compound umbel

cluster of umbels stemming from stalks (rays) that radiate from common point. Carrots

spike

cluster of flowers along unbranched axis. Grass

head

outer ring of sterile ray florets and central cluster of disc florets. Sunflowers

fruit

develops by elaboration of the ovary after fertilization surrounding the seed.

1. provides additional embryo protection

2. facilitates dispersal of seed

drupe

simple fruit that is derived from single flower, contains one ovule

berry

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

aggregate fruit

derived from single flower with multiple separate ovaries, glomming together fruitlets from each of the separate ovaries in a single flower.

multiple fruits

develops from many separate florets: pineapples