Botany

(the Study of Plants)

General Plant Review All plants are:

Eukaryotic

Autotrophic

Multicellular

Cell Walls with cellulose

Chloroplasts w/ chlorophyll a, b, and carotenoids

May have waxy cuticle to prevent water loss.

Stomata allow gas exchange.

Plants probably evolved from green algae (charophytes) Chloroplast similarity

Biochemical similarities

Cell Wall similarities

Plant Reproduction

Alternation of Generations – plants grow a separate,

haploid organism to produce gametes; the same plant

exists in two different forms during its life, although

sometimes it’s hard to differentiate between the forms

Multicellular

Sporophyte – (2N)

Meiosis

Multicellular

Gametophyte (N)

Zygote (2N)

Unicellular

Spores (N)

Unicellular

Gametes (egg

& sperm)

fertilization

Mitosis

Evolutionary Trend – early plants displayed the gametophyte

(n) as the dominant structure, modern plants show the

sporophyte as dominant (2n) (Ex: Moss is HAPLOID, but Oak

Trees are DIPLOID)

zygote

GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

Classifying Plants

Plants can be divided into 2 major categories based on their characteristics: Nonvascular Plants

Do NOT have specialized tissues to transport water and nutrients

Instead, these plants transport water from cell-to-cell by osmosis

Vascular Plants Have specialized tissues to transport water and nutrients in

plants

Xylem – carries water upward from roots

Phloem – carries nutrients and carbohydrates produced by

photosynthesis

Nonvascular Plants (Bryophytes)

Short with no specialized tissues to transport water

Major types:

Mosses

Liverworts

Hornworts

Nonvascular Plants/

Bryophytes

Mosses

Have rhizoids that anchor

them to the ground

(instead of roots)

Depend on water for

fertilization

The sperm must swim to the

egg

Therefore, nonvascular

plants must live in MOIST

environments

Gametophyte is the dominant

phase of the life cycle

Moss/ Bryophyte Life Cycle

Zygote grows, develops into a sporophyte while still attached to gametophyte.

Fertilization

zygote

sperm-producing structure

egg-producing structure

Diploid Stage

Haploid Stage

mature sporophyte

Meiosis

Spores germinate.

male gametophyte

female gametophyte

Vascular Plants/Tracheophytes

Have specialized tissues to transport water

and nutrients in plants called Xylem & phloem

Vascular plants (tracheophytes) can be

divided into 2 categories:

Seedless vascular plants (spores)

Seed (vascular) plants

Seedless Vascular Plants

Ferns – A Close Up

Diploid sporophyte is the

dominant stage

Have rhizomes, which are

underground stems

Fronds: large “leaves”

where spores develop

Develop spores in

sporangia on underside

of fronds

Reproduce using spores

A sorus (plural: sori) is a

cluster of sporangia

Fern Life Cycle

Spores

are

released

Sporophyte still attached to gametophyte

zygote

fertilization Diploid Stage

Haploid Stage

egg

sperm

mature gametophyte

Spores develop

meiosis

Spore germinates

rhizome

sorus

Seed (Vascular) Plants

Have true roots, leaves, and stems

Have the ability to form seeds, which are used for reproduction

Seed plants are the most dominant group of photosynthetic organisms on land

There are 2 types of seed (vascular) plants:

1. gymnosperms (cones)

2. angiosperms (flowers)

Seed (Vascular) Plants Gymnosperms =

“cone bearers” “naked seeds” – not

enclosed in ovaries

Bear seeds directly on the surfaces of cones

Cones = sporophyte structures that produce

gametophytes (seeds)

Coniferous trees are the major example

Pines, junipers, spruces, etc.

section through one ovule

ovule

surface view of one cone scale (houses two ovules)

section through a pollen-producing sac

surface view of one cone scale (houses a pollen-producing sac)

meiosis fertilization

seed coat

embryo

zygote

mature sporophyte

seeding

pollen tube

sperm-producing cell

eggs

female gametophyte

pollination

microspores form

megaspores form

seed Diploid

Haploid

Pine Life Cycle

Seed (Vascular) Plants

Angiosperms = flowering plants

Seeds are enclosed by an ovary

Flowers are reproductive organs

Evolutionary advantage

attract pollinators

Flowering plants contain ovaries

Ovaries surround and protect

seeds

Ovary develops into a fruit after

pollination & helps with seed

dispersal when eaten

Examples:

Maple trees, tulips, grass

Flowering

Plant Life

Cycle Double fertilization Meiosis Meiosis

microspores

female gametophyte

pollination

mitosis

without

cytoplasmic

division

two

sperm

enter

ovule

Diploid

Haploid

sporophyte

Evolutionary Tree for Plants

green

algae zygophytes,

related

groups

charophytes bryophytes lycophytes horsetails cycads conifers

flowering

plants

seed plants

euphyllophytes

vascular plants

embryophytes (land plants)

(closely related groups)

ferns ginkgos gnetophytes

Nested monophyletic groups

Transport in Vascular

Plants

Transport Within Plants

Water and minerals

absorbed by roots are

drawn upward in the

xylem to the shoots

Sugar produced by

photosynthesis is

exported from leaves

to other organs via the

phloem

Transport can be

passive or active

Short- and Long-Distance

Transport in Plants

Water and sugars move differently in

plants, depending on whether they’re

going a short or a long distance

Ie. – walking down the street or taking an

airplane across the world

Short-Distance Transport 1. Simple diffusion/osmosis

substances in one cell move out of one cell, across the cell wall, and into another cell

2. Plasmodesmata

Plasmodesmata are connections between the cytoplasm of adjacent plant cells

Substances move between cells through these openings

Long-Distance Transport

Over long distances, these 3 processes

(simple diffusion, apoplast,& symplast) take

too long

Water and solutes move through xylem and

phloem by bulk flow, the movement of a fluid

driven by pressure

Transpiration

Transpiration is the evaporation of water from

leaves and other parts of the plant; it causes a pull

that brings more water up through the xylem

An average maple tree loses more than 200L of

water per hour during the summer!

Unless this water is replaced by water absorbed by

the roots, leaves will wilt and die

(Cohesion-Tension Theory) Transpiration works through a

combination of evaporation, water potential, adhesion, and cohesion to pull water up the xylem

The Photosynthesis-

Transpiration Compromise

Exposing leaves to the sun and opening stomata (cellular “holes” in the underside of the leaf) to allow for gas exchange helps photosynthesis, but causes transpiration to occur at a faster rate. Plants balance the loss by controlling when stomata are open.

Mechanism for Stomatal

Opening & Closing

Guard cells open and close

stomata by changing shape

using ion and hormone

signals based on plant

stress.

Plant Structure, Growth, &

Development

The Diversity of Angiosperms

Angiosperms

(flowering plants) can

be divided into 2

major categories:

Monocots –

have one seed leaf

(cotyledon)

Dicots –

have 2 seed leaves

(cotyledons)

Monocots

Monocots have only 1 cotyledon (seed leaf)

Examples of monocots:

Corn, wheat, lilies, orchids, palms

Dicots

Dicots have 2 cotyledons (seed leaves)

Examples of dicots:

Roses, clover, tomatoes, oaks, daisies

Woody vs. Herbaceous Plants

Angiosperms can also be subdivided into

woody (produce wood) and herbaceous (do

not produce wood) plants

Woody plants are made of cells with thick cell

walls that support the cell body

Examples: trees, shrubs, vines

Herbaceous plants do not produce wood as they

grow, and instead have smooth stems

Examples: dandelions, sunflowers

Plant Life Spans The lifespan of plants, however, is genetically

determined Annuals – complete their life cycle in 1 year

Examples: marigolds, cucumbers (lots of garden plants)

Biennials - complete their life cycle in 2 years

Year 1: germinate & grow roots

Year 2: grow stems & leaves, produce flowers & seeds

Examples: evening primrose, celery

Perennials – live for more than 2 years

Examples: Maple trees, grasses, palm trees

Plant Structure

Plants are made up of

a root system and a

shoot system

The Root System

What do roots do?

Anchor the plant in the soil

Absorb minerals and water

Store food

Types of root systems

Fibrous root system

Found mostly in monocots

Taproot system

Found mostly in dicots

How do roots grow?

Roots grow down from the tip in a region called the apical meristem, where the cells are dividing quickly

The Shoot System

The shoot system consists of: vegetative shoots (which

bear leaves)

floral shoots (which bear flowers)

Stems have 3 important functions: Producing leaves, flowers

(reproduction), branches

Holding leaves up to the sunlight for photosynthesis

Transporting substances between roots and leaves

How do stems grow? Primary growth

Increase in length

Occurs by cell divisions in

apical meristem (at top

of shoot)

Secondary growth

Increase in width

Occurs by cell divisions in

the lateral meristems

(outward growth)

The Shoot System: Leaves

Leaves are the primary

photosynthetic organs of

most vascular plants

Most leaves have a

flattened blade and a

petiole, which is the

stalk that attaches the

leaf to the stem

Tissues in Plants

All 3 plant organs (root/stem/leaf) have dermal, vascular, and ground tissue systems

Dermal Tissue System

Outer protective covering, similar to our skin

Protects the plant from water loss and disease

The cuticle is a waxy coating that helps to prevent water loss

Tissue Systems in Plants

Vascular Tissue System

Carries out long-distance transport of materials within the plant

Xylem and phloem are examples of vascular tissues

Ground Tissue System

Pith (inside vascular tissue) and cortex (outside vascular tissue) are examples of ground tissue

Inner cells specialized for storage, photosynthesis, and support

Flower Structure

Flowers are the reproductive structure of angiosperms

Sepals: Enclose the bud before

it opens

Protect flower while it’s developing

Petals: Usually brightly colored

to attract pollinators

Flower Structure

Stamens:

The male portion of a

flower

Made up of an anther

and a filament

The anther produces

haploid pollen grains by

meiosis

Most flowers have

multiple stamens

Flower Structure

Carpels/Pistils: The female portion of a

flower

Stigma:

Sticky – to trap pollen

Style:

Hollow tube which connects stigma and ovary

Ovary:

Produces female gametes (ovules)

Fruit grows from an expanded ovary

Seed Dormancy

Seed dormancy means that a seed will not

germinate, even if sown in a favorable place,

until a specific environmental cue causes

them to break dormancy

Seed dormancy increases the chances that

germination will occur at a time and place

most advantageous to the seedling

How did we break dormancy in our lab??

Stages of Seed Germination

(1) The seed absorbs water, causing it to expand and rupture its seed coat

(2) The embryo resumes growth, digesting the storage materials of the endosperm

(3) The radicle (embryonic root) emerges from the germinating seed

(4) The shoot tip breaks through the soil surface

Stages of Seed Germination

Plant Asexual Reproduction

When plant species clone

themselves by asexual

reproduction, it’s known

as vegetative

reproduction

Asexual Reproduction

Fragmentation is the

separation of a parent

plant into parts that re-

form whole plants

This type of asexual

reproduction is used to

produce clones from

cuttings (common with

houseplants)

Plant Responses to

Internal & External

Signals

Plant Hormones

REVIEW: Hormones are chemical signals

that coordinate the various parts of an

organism

A hormone is a compound produced in one part

of the body which is then transported to other

parts of the body, where it triggers responses in

target cells and tissues

Examples of human hormones:

Adrenaline, testosterone, estrogen, epinephrine…

Plant Hormones

There are 5 major classes of plant hormones:

Auxin -

Cytokinins

Gibberellins

Abscisic acid

Ethylene

Auxin

Stimulates stem elongation

Stimulates fruit development

Involved in phototropism (bending to light)

and gravitropism (growing UP)

Cytokinins

Stimulate cell division and growth

Stimulate cytokinesis

Stimulate germination and flowering

Gibberellins

Trigger seed and

bud germination

Promote stem

elongation and leaf

growth

Important in fruit

growth

Ethylene

Promotes fruit ripening

Senescence (aging) is a progression of irreversible change that eventually leads to death Caused, at least in part,

by ethylene

“One bad apple spoils the whole bunch”

Abscisic Acid

Induces seed dormancy

Anti-gibberellin

Inhibits cell growth

Anti-cytokinin

Inhibits fruit ripening

Anti-ethylene

Closes stomata during

water stress, allowing

many plants to survive

droughts

Tropisms

Tropisms are growth responses that result in curvatures of whole plant organs toward or away from a stimuli

There are three major stimuli that induce tropisms

Light (Phototropism)

Gravity (Gravitropism/Geotropism)

Touch (Thigmotropism)

Phototropism

Phototropism is the

growth of a shoot

towards light

This is primarily due to

the action of auxin

Auxin elongates the

cells on the non-light

side

Plant Defenses

Plants defend themselves against herbivores

in several ways

Physical defenses, such as thorns

Chemical defenses, such as

producing distasteful/toxic

compounds