Biology II

Fall 2009

Chapter 23

Introduction to Plants

Section 1 Vocabulary

• Cuticle

• Spore

• Sporophyte

• Gametophyte

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What is a Plant? Let’s review..

• Most plants are autotrophs

– Which is….?

• Plants use photosynthesis

– Which is….?

– Where does photosynthesis occur?

– Requires energy from sun and carbon dioxide

to produce organic material (energy)

• Plants need sunlight, water, air, and

minerals to survive

Establishment of plants on land

• Dominant group of organisms on land based on

weight

• Plantae = Very diverse group

• Range from 2mm across to more than 100 m tall

• Most are photosynthetic

– Produce inorganic materials by photosynthesis

• Some are parasitic

• Probably evolved from multicellular aquatic green

algae that could not survive on land

Plants on Land

• THREE MAIN OBSTACLES….

– Absorbing nutrients

– Preventing water loss

– Dispersal on Land

Relationship between algae and

plants

Absorbing Nutrients

• Take nutrients from the water around them

• On land, most take nutrients from soil with their roots

• The first plants did not have roots

– Fossils show they lived underground and fungi lived on or within their parts

– Symbiotic relationship = what?

– Mycorhizae – symbiotic relationship between fungi and plant roots

• Today, 80% of all plants form mycorhizae

Preventing Water Loss

• Cuticle – waxy layer that covers the nonwoody

aboveground parts of most plants

– Before this, most plants lived near water where drying

out water not an issue

– PROHIBIT oxygen and carbon dioxide to pass

through

• Stomata – (singular =stoma) permit plants to

exchange oxygen and carbon dioxide

– Extend through the cuticle and the outer layer of cells

• Guard cells – border each stoma

Stomata and Guard Cells

Reproducing(Dispersal) on Land

• Aquatic algae reproduce sexually when

sperm swim through water

– The sperm of most plants, must be able to

move without water….

• Spores – unicellular reproductive cell that

is resistant to environmental conditions

– In seed plants, sperm is contained in POLLEN

• Pollen permits the sperm of plants to be carried by

wind or animals rather than water

Plant Life Cycles

• Plants have life cycles in which haploid gametophytes alternate with diploid sporophytes

• A life cycle in which a gametophyte alternates with a sporophyte is called alternation of generations.

• Unlike the green algae with alternation of generations, plants have gametophytes and sporophytes that look very different.

Quick Questions

• What structure produces gametophytes?

• Is a plant sporophyte diploid or haploid?

• End 23.1

23.2 Seedless Plants

• Archegonium

• Atheridium

• Sporangium

• Rhizome

• Frond

• sorus

2 types of seedless plants

•Nonvascular

•Vascular

Nonvascular

• Do not have a vascular system for

transporting water and nutrients

• Reproduce by spores

• Lack true roots, stems, and leaves,

although most have structures that

resemble them

Nonvascular, cont.

• Water transported by osmosis and

diffusion

– Moves materials short distances and very

slowly

• Limits the size of a nonvascular plant body

– Most are relatively small…

Kinds of Nonvascular Plants

• Mosses (phylum Bryophyta)

– The most familiar nonvascular plant

– “leafy” green plants you recognize as mosses

are gametophytes

• Sporophytes, which are not green, grow from the

tip of gametophyte

Example: Polytrichum

**Most have cuticle,

stomata, and simple

conducting cells

Nonvascular cont. • Liverworts (phylum Hepatophyta)

– Grow in mats of individuals, like mosses

– Gametophytes are green, flattened and have

lobes

– Sporophytes are very small and consist of a

short stalk topped by a spore capsule

Example: Marchantia

**Have no conducting

cells, cuticle, or

stomata

Nonvascular cont.

• Hornworts (phylum Anthocerophyta)

– Completely lack conducting cells

– Gametophyte is green and flattened

– Green hornlike sporophytes grow upward

from the gametophyte

• Have stomata and cuticle

Example: Anthoceros

Reproduction in Nonvascular

• Gametophyte is dominant generation

– Must be covered by film of water for

fertilization

– Produce gametes (eggs and sperm) in two

separate structures

• Archegonium – produces eggs

• Atheridium – produces sperm

• The sporophyte produce spores in

sporangium

– Grow on gametophytes

• Depend on them for nutrition

Life Cycle of a Moss • Spores form by meiosis inside spore capsule

– Spores are haploid

• Spore capsule opens when spores are

mature

– Spores are carried by wind or water

• When spore settles, it germinates and grows

into leafy green gametophyte

• Archegonia and antheridia form at tips of

haploid gametophytes

– Eggs and sperm form by mitosis inside

A&A

Seedless Vascular Plants

• Do not produce seeds

• Have horizontal underground stems, or

rhizomes

Key Features of seedless vascular

plants

• Vascular system – Can grow much larger due to vascular system

– Develop true roots, stems, and leaves

• Larger sporophyte – Small gametophtes develop on or below surface of

soil

– Size makes it easier for wind to carry spores

– Water is needed for fertilization • When enough water is present, sperm swim to eggs

Seedless vascular cont. • Club Mosses (phylum Lycophyta)

– Have roots, stems, and leaves unlike true

mosses

– Spores develop in sporangia that form on

specialized leaves

– In some species, spore-bearing leaves form a

structure called a cone

Example: Lycopodium

*Sometimes called

ground pines

Ferns and Fern Allies

• Phylum Monilophyta

• Most common seedless vascular

plants

• Most abundance in the tropics

• Plants recognized as ferns are

sporophytes

• Most are anchored by rhizomes and

have leaves called fronds

– Coiled fronds are called fiddleheads

Example: Sword Fern

Reproduction in Seedless

Vascular Plants • Like nonvascular plants, seedless vascular

plants can reproduce sexually only when a

film of water covers the gametophyte.

• Unlike nonvascular plants, seedless

vascular plants have sporophytes that are

much larger then their gamtophytes.

• Archegonia and antheridia develop on the

lower surfaces of the gametophytes

– Sperm and egg mostly produced by same

individual

Spores

• Haploid reproductive cell

• Produced by meiosis

– Capable of developing into adult without

fusing with another cell

• Have thickened walls that allow spores to

withstand tough environmental conditions

• Easily dispersed by wind

• Produced in sporangia of sporophytes

• Sorus – cluster of sporangia on a fern

frond

– Look like brown dots under leaves of ferns

23.3 Seed Plants

• Seed – a structure that contains the

embryo of a plant

– Embryo – an early stage in the development

of plants and animals

• Most plants today are seed plants –

vascular plants which produce seeds

• First seed was roughly 380 mya

Structure and Function of Seeds

Gymnosperms – Seed Plants

• Seed plants whose seeds do not develop

within a sealed contain (fruit)

• Word comes from Greek words “gymnos,”

meaning “naked,” and sperma, meaning

“seed.”

• Most seeds develop within a cone

Angiosperms – Seed Plants

• Flowering plants

• Produce seeds that develop enclosed

within a specialized structure called a fruit

• Word angiosperm comes from the Greek

words angeion, meaning “case,” and

sperma, meaning “seed.”

**Gymnosperms v.

Angiosperms • Key difference… unlike seeds of

angiosperms, seeds of gymnosperms do

not develop within a fruit…

Reproduction in Seed Plants

• Do not require water to reproduce sexually

• Have greatly reduced gametophyte and a

dominant sporophyte

• Produce 2 kinds of spores which develop

into gametophytes

– Female – eggs

– Male - sperm

Reproduction, cont.

• Female gametophyte develops inside

ovule

• Following fertilization, ovule and contents

develop into seed

• Male gametophyte develops inside a

pollen grain

Pollination and Fertilization

• Pollination is the transfer of pollen grains

from the male reproductive structure to the

female reproductive structure

• When pollen grained reaches compatable

female reproductive, a tube emerges

(pollen tube)

– Grows to female gametophyte

• Allows sperm to pass directly to egg

• Fusion of egg and sperm = fertilization

Seed Formation

• After fertilization, ovule is termed seed

– Contains embryo

• Outer layers harden to form seed coat

– Protects embryo from harsh environment and

mechanical damage

• Contains tissue that provides nutrients

• Some angiosperms have a nutritious

tissue called endosperm

Seed Dispersal

• Can prevent competition for water,

nutrients, light, and living space between

plants

• Many have structures that help wind,

water, or animals carry them away

Kinds of Gymnosperms

• Conifers (phylum coniferophyta)

– Most familiar and most successful

gymnosperms

– have needle-like or tiny scales for leaves

which help them limit water loss

– Some of the tallest and oldest trees in the

world

Example: Juniper

Gymnosperms, cont.

• Cycads (Phylum Cycadophyta)

– Have short stems and palmlike leaves

– Cones produce pollen and those that produce

seeds develop on different plants

Example: Encephalartos

Gymnosperms, cont.

• Gingko (Phylum Gingkophyta)

– Only 1 living species

– Fan-shaped leaves

– Male and female gametophytes of gingko

develop on separate trees

– Seeds do not develop within a cone

Example: maidenhair tree

Gymnosperms, cont.

• Gnetophytes (Phylum Gnetophyta)

– Diverse group of trees, shrubs, and vines that

produce pollen and seeds in cones that

resemble flowers

– Only one type is common in the Western US

(ephedra)

Example: Ephedra

Life Cycle of Conifer

• Characterized by dominant sporophyte,

wind pollination, and the development of

seeds in cone

• The gametophytes of most gymnosperms develop in cones, which consist of circles of modified leaves called scales.

• Many gymnosperms produce both female and male cones on the same plant.

Cones

• Gametophytes of most conifers develop in

cones

– Consist of whorls (circles) of modified leaves

called scales

• Male (pollen cones)

• Female cones (seed cones)

• Can produce male and female on same

plant

23.4 Flowering Plants • Aka angiosperms

• Most successful group of plants today

• Tiny herbs to giant trees

• Subgroups

– Monocots (CORN)

• One leaf, or cotyledon

• Long, narrow leaves with parallel veins

• Parts in multiples of 3

– Dicots (BEAN)

• Seeds have two seed leaves, two cotyledons

• Branching leaves with veins

• Parts in 4 or 5

Reproduction In Angiosperms

• Flower = specialized structure of

angiosperms

• Male and female gametophytes develop

within flower

– Promote pollination and fertilization more

efficiently than cones

• Does not require water

Structure of Flowers • Arranged in 4 concentric whorls, or circular

swirls

• Sepals – protect flower from damage while

a bud

• Petals – attract pollinators

• Stamens – produce pollen

• Pistils – produce ovules

– Ovules develop in ovary deep within pistil

• Ovules develop into seeds

– Style rises from ovary, pollen lands on stigma (top of

style)

Kinds of Flowers

• May or may not have all four basic flower

parts

• Complete – has all 4 parts

• Incomplete – lacking any one of the 4

parts

Pollination

• Some can fertilize the plant’s own ovules

– Self-fertilization

• Cross-fertilization – unable to fertilize own

ovules

• Flowers are intended to attract pollinators

– Insects and birds, etc.

• If pollinated by wind, flowers are usually

small and lack bright colors, strong odors,

or nectar.

Will transfer pollen

to the next flower it

visits = cross

pollination

**Attractive Orchids… Did you

know?!?!

• Orchids have highly elaborate ways of attracting pollinators

– One resembles a female wasp to attract male wasps…

• The wasps picked up pollen trying to mate with the modified petals

– One holds a small pool of water • When a bee tries to collect nectar it falls into the

pool of water and can only escape via small passageway through forces the bee to brush against pollen

Fruits

• Ovary of a pistil is called fruit after ovules

are fertilized

– Fruits develop from an ovary of a flower and

contains seeds

• Botanical fruit different than everyday

meaning of fruit

• Fruits do provide some protection for

seeds, but primarily function in seed

dispersal

Vegetative Reproduction

• Most plants are able to reproduce

asexually

– Genetically identical to parent plant

• Use stems, roots, and leaves to reproduce

asexually

• Typically faster than sexual reproduction

– Can spread quicker