PLANTS

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PLANTS

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How Are Plants All Alike?

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Plant Characteristics Multicellular Autotrophic (photosynthesis) Chlorophylls a and b in thylakoid

membranes Surrounded by cell walls

containing cellulose (polysaccharide)

Store reserve food as amylose (starch)

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Plant Structure and Anatomy Roots, stems, and leaves

Roots anchor the plant and draw water and minerals from the soil

Stems support the body and carry water and nutrients

Leaves are the main photosynthetic organ

Plant tissue Three kinds of tissue in general

Dermal Outer covering Vascular Fluid-conducting system Ground Support and photosynthesis

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Plant Structure and Anatomy Plant cells

Cells within the dermal tissue need to protect the plant from transpiration yet allowing gas exchange to occur

Ground tissue contains mainly of parenchyma cell, which are thin-walled and form the bulk of tissue in roots, stems, and leaves. These cells are very active in photosynthesis. Collenchyma and sclerenchyma cells support the plant

Vascular tissue has the xylem and phloem, which carries water and nutrients, respectively.

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Roots A growing seedling first sends a

single primary root into the soil and as it grows bigger, secondary roots branch off the primary root

This enlarges the SA dramatically Epidermis

Outer covering of the root Has root hairs that make direct contact

with the soil The hairs are responsible for the large

SA

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Roots Cortex

The layer of spongy cells beneath the epidermis

Parenchyma cells of the cortex move water from the epidermis to the vascular tissue

Vascular cylinder The central region of xylem and phloem Carries water and nutrients between

roots and the rest of the plant

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Roots

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How Roots Work Osmosis!! Water moves out of damp soil into

root hairs, which contain high concentrations of dissolved salts and sugars

The water passes through the root hairs and eventually into the vascular cylinder

What would happen if a plant was placed inside salt water? Rapid water loss from roots is known as

“root burn”

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Roots Active transport

Minerals going through cell membrane This also brings in the water to the core

The Casparian strip Endodermis—inner boundary of cortex

that is very tight Separates cortex from vascular cylinder Known as the waxy layer that can

control the entry into the core

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Stems Connects roots with the leaves: water and

nutrients with photosynthesis Epidermal tissues on the edge but

different arrangement of ground and vascular tissue For later.

Wood As stem grows, new cells form between

vascular cells, thus pushing outward and increasing the diameter

Vascular cambium: layer of dividing cells, usually the xylem

Phloem cells don’t grow as much and thus can get ‘cracked’ Cork cambium produces cork that form the bark

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Stems Cambium produces

much more xylem in the summer than in colder weather

Historical information can be seen via annual tree rings

Nutrient transport and growth occurs within the thin layers of cells just under the bark very delicate and easily damaged

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Leaves Main site of photosynthesis Large SA with little mass efficient in collecting

solar energy Attached to the stem by a petiole

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Leaves Epidermis

Covered with waxy cuticle Stomata underneath for gas exchange

Guarded by two guard cells that open and close

Need to balance need for CO2 against need to conserve water

Mesophyll tissue Packed with chloroplasts Two types

Tall palisades on top Spongy ones on bottom—lots of air space

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Leaves Leaf veins—

vascular tissue Xylem and

osmosis Xylem and

phloem found as vascular bundles called ‘veins’

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Leaves

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Stomata Activity Closed

Photosynthesis halts Open

Photosynthesis can resume but too much transpiration could occur

Guard cells When water flows in, increase in pressure

causes a structural change that OPENS the stoma

When water flows out, decrease in pressure causes stoma to CLOSE

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Stomata Activity Several factors cause stomata to

close: Lack of water reshapes the guard cells High temperatures stimulates cellular

respiration, which can increase CO2 concentration within the air spaces

Other factors cause stomata to open: Depletion of CO2 within the air spaces of

the leaf, which occurs when photosynthesis begins

An increase in potassium ions (K+) into guard cells, which causes water to enter

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Xylem Water conducting system Consists of two types of cells

Tracheids: long, thin cells that overlap and are tapered at the ends; function to support the plant as well as to transport the water

Vessel elements: generally wider, shorter, thinner walled, and less tapered; aligned end to end and differ from tracheids in that the ends are perforated to allow free flow through vessel tubes

Makes up most of wood and dead upon functional maturity

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Phloem Sugar conducting system via active

transport Consist of chains of sieve tube

members/elements whose end walls contain sieve plates that facilitate the flow of fluid from one cell to the next

Alive at maturity, although they lack nuclei, ribosomes, and vacuoles

Connected to each sieve tube member is at least one companion cell that contain a full complement of cell organelles

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Xylem and Phloem

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Fluid Transport Xylem transport

Water gets transported against gravity but doesn’t require any energy From root to leaves

Fluid can be pushed up by root pressure via root pressure: Results from water flowing in to the roots from soil via osmosis; can push xylem sap upward only a few yards

The morning dew is due to root pressure Guttation Transpirational pull can carry fluid up the world’s

tallest tress. Transpiration causes a negative pressure (tension) to develop and thus pulls up the sap

Cohesion of water due to strong attraction between water molecules makes it possible to pull a column of water from above

Transpirational pull-cohesion tension theory

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Fluid Transport Phloem transport

Phloem sap carries sugar from leaves into root and often to developing fruits as well

Translocation: Sugar gets distributed from various sources to sinks

The source is where sugar is being produced and the sink is where sugar gets stored or consumed

Movement of sugar into phloem highway creates a driving force because it establishes a concentration gradient Causes water to come in and thus higher pressure occurs.

This pressure drives the movement of sugars and water through the phloem

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Plant Growth Tropisms: Derived from Greek and means

‘to turn’; plant responses to cues from their environment

Geotropism/Gravitropism Response to gravity Helps seedling grow toward sunlight Different directions for root and stem

Thigmotropism Response to touch

Phototropism Response to light First recognized by Darwin and his son (1880s)

Plant Hormones Hormone is a substance produced in one part of an

organism that affects activities in another part Plant hormones help coordinate growth,

development, and responses to environmental stimuli

Darwin’s experiment with phototropism: Figure 26-11 on p. 612

Auxin Indoleacetic acid (IAA) is a naturally occurring auxin; “To

increase”; first plant hormone discovered Stimulate cell growth and are produced by cells in the

apical meristem, the rapidly growing region near the tip of a root or stem; preferential growth upward rather than lateral

Also stimulates stem elongation and growth by softening the cell wall

Produces phototropism due to unequal distribution Mainly produced in the shoots and leaves

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Plant Hormones Cytokinins

Promotes cell division (cytokinesis, hence the name!) in lateral branches and leaf enlargement

Slows down the aging of leaves Ratio between auxin and cytokinin concentration

determines cell growth, rather than the level of either hormone by itself

However, can work antagonistically against auxins in relation to apical dominance

Produced in roots and travels upward in the plant Gibberellin

Promote stem and leaf elongation Work in concert with auxins to promote cell growth Induce bolting, the rapid growth of floral stalk

Ex. Broccoli entering the reproductive stage Sends up a tall shoot to ensure pollination and seed dispersal

Induction of growth in dormant seeds, buds, and flowers

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Plant Hormones Abscisic acid (ABA)

Inhibits growth! Enables plants to withstand drought Closes stomata

during times of water stress Promotes seed dormancy: Prevents seeds that have fallen

on the ground in the fall from sprouting until the spring when conditions are more favorable

Ethylene gas Small amount released when fruit tissues respond to

auxin; Large amount released when plant is going through time of stress

Promotes fruit ripening Aged flowers and leaves falling off Facilitates apoptosis

(programmed cell death) and promotes leaf abscission. Prior to death, cells break down many of their chemical components for the plant to salvage and reuse

Works in opposition to auxins

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Controlling Plant Life Cycles Annuals (marigolds, corn, peas), biennials

(carrots, sugar beets), and perennials (trees and shrubs)

Whatever category a plant may fall into, timing is very important to a plant.

Must time their reproductive cycles so their reproductive cells will be ready at the same time as those of other members of their species

The environmental stimulus a plant uses to detect the time of year is the photoperiod, the relative lengths of day and night.

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Controlling Plant Life Cycles

Circadian rhythm: The plant’s biological clock that is set to a 24-hour day Long-day plants = short-night plants Short-day plants = ?

Phytochrome is a pigment used by plants to detect day and night via changes in the length of light and dark periods each day There are two forms: Pr (red-light absorbing)

and Pfr (infrared light absorbing) Pr Pfr: when there is light present Pfr Pr: when it’s dark This conversion enables the plant to keep track

of time

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Plant Reproduction Asexual reproduction

Plants can clone themselves by vegetative propagation

A piece of the vegetative part (root, stem, or leaf) can produce an entirely new plant genetically identical to the parent plant

Naturally occurring example Figure 26-14

Agricultural use Grafting to combine wanted characteristics of two different plants; done during dormancy

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Plant Reproduction The sexual reproduction in flowering

plants is quite unusual Alternation of generations life cycle

Diploid (2n) sporophyte stage and haploid (n) gametophyte stage

Two haploid gametes combine to form diploid zygote (2n), which then divides mitotically to produce the diploid multicellular stage called SPOROPHYTE (2n)

The sporophyte undergoes meiosis to produce a haploid spore.

Mitotic division leads to the production of haploid multicellular organisms called GAMETOPHYTES (n)

The gametophyte undergoes mitosis to produce gametes, which combine to form diploid zygotes and so on.

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Alternation of Generations

2n Sporophyte

2n gametophyte

1n pollen

Ovary with 1n ovules (eggs)

2n seed with plant embryo

Sporophyte

Gametophyte

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For most plants, including ferns, conifers (cone producing plants), and angiosperms (flowering plants), the prominent generation is the sporophyte (2n)

For the moss (bryophyte), the prominent generation is the gametophyte (n)

The dominant sporophyte generation is considered more advanced evolutionarily than a dominant gametophyte generation

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Plant

Divisions

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Plant Classification Plants are

divided into two groups

Based on the presence or absence of an internal transport system for water and dissolved materials

Called Vascular System

Vascular Bundles

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Plant Classification Bryophytes Non-vascular plants

Ex) Mosses Tracheophytes Vascular plants

Seedless plants: Ferns (reproduction via spores)

Seed plants Gymnosperms: Cone bearing

Cedars, sequoias, redwoods, pines, yews, and junipers

Angiosperms: Flowering plants Roses, daisies, apples, and lemons Monocots and dicots

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Vascular System Xylem tissue carries water

and minerals upward from the roots

Phloem tissue carries sugars made by photosynthesis from the leaves to where they will be stored or used

Sap is the fluid carried inside the xylem or phloem

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Multicellular Algae Algae are photosynthetic aquatic

organisms that are actually classified as protists

Although most are unicellular, some are multicellular (seaweed) and their reproductive cycles are quite similar to that of plants

Think of them as ‘honorary’ plants!

All algae contain chlorophyll a

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Multicellular Algae Brown algae

Contain carotenoids and xanthophylls In the phylum Phaeophyta (dusky

plants) Giant kelps Can be as long as 100 m Common form is Fucus, which is found

almost everywhere on the eastern coast of the US and is sometimes known as rockweed for the way in which it attaches itself to rocks

Most are salt-water organisms Figure 24-2, p. 558

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Multicellular Algae Red algae

Get their color from a pigment called phycobilin and phycoerythrin

In the phylum Rhodophyta “red plants” Most live in the ocean within the deep waters Can absorb non-visible light via accessory

pigments Green algae

Most live in fresh water In the phylum Chlorophyta “green plants” Remarkably similar to green plants Contain cellulose cell walls, chlorophyll a and

b, and store food as starch

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Nonvascular Plants Do not have

vascular tissue for support or conduction of materials

Called Bryophytes

Require a constantly moist environment

Moss Gametophytes & Sporophytes

Sporophyte stage

Gametophyte Stage

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Nonvascular Plants Includes mosses (Bryophyta),

liverworts (Hepatophyta), and hornworts (Antherophyta)

Liverworts Hornworts

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Bryophytes Plants can’t grow as tall Lack of lignin-

fortified tissue No true roots, stems, or leaves Cells must be in direct contact with

moisture and thus live close to the ground

Materials move by diffusion cell-to-cell Sperm must swim to egg through water

droplets Contains flagella Exhibit alternation of generations

Gametophyte generation is dominant Partial adaptation to life away from

water Waxy covering

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Sporophytes

Gametophytes

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Bryophytes To a limited extent, bryophytes are able

to gather water from moist soil as they are anchored by rhizoids, which are thin filaments that absorb water and nutrients from the soil.

Mosses When a moss spore lands on wet soil, it

germinates and grows into a tangle of protonema

As the protonema gets larger, its filaments become more organized and starts growing upward

These moss plants are the gametophyte stage of the moss life cycle

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Moss Gamete formation and

fertilization Gametes produced from

gametophytes Must be in water for

sperm to swim Diploid zygote grows into

sporophyte, which becomes dependent on the gametophyte

Spore formation From capsule of

sporophyte Meiosis

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setae

Spore Capsule

• Sporophyte lacks chlorophyll & gets food from the gametophyte.• Sporophyte has a long, slender stalk (setae) topped with a spore producing capsule

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Hornworts and Liverworts

Liverworts: Name comes from the way in which the lobes of liverwort gametophytes resemble the lobes of liver

Both are dependent upon water and like the mosses, contain a waxy cuticle, rhizoids, and have alternation of generations.

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Main Parts of Vascular Plants

Shoots-Found above ground-Have leaves attached-Photosynthetic part of

plant Roots

-Found below ground-Absorb water & minerals-Anchors the plant

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Tracheophytes Characteristics include:

Xylem and phloem for transport Lignified transport vessels for support Roots to absorb water while also

anchoring and supporting the plant Leaves that increase the

photosynthetic surface Life cycle with a dominant sporophyte

generation Subdivided into two groups:

Seedless vascular plants and seed-bearing vascular plants

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Seedless Tracheophytes Includes club moss

(Lycophyta), horsetails (Sphenophyta), whisk ferns (Psilophyta), and ferns (Pterophyta)

HorsetailsWhisk ferns

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Tracheophytes Club mosses and horsetails

Believed to have formed the Earth’s first great forests and the largest land plants for more than 100 million years

Have large, independent sporophytes Ferns

Excellent vascular system but still need moist habitat

Well-developed underground stems Rhizomes Large leaves known as fronds Sporophyte: Produce haploid spores via meiosis.

They form on the undersides of the fronds in little chambers called sori, which bursts open when the spores are mature

Gametophyte: Independent and small. On the underside, gametes develop in tiny reproductive organs

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Club Moss Spores Contain chemicals

that explode & burn quickly

Yellowish powdery spores used in fireworks and explosives

Spore

Burning Lycopodium powder

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Club Moss Sporophylls

Strobili

Sporophylls

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Fronds

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Seed-Producing Vascular Plants

Includes two groups: Gymnosperms and Angiosperms

Gymnosperms have naked seeds in cones

Angiosperms have flowers that produce seeds to attract pollinators and produce seeds

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Seeds Ability to form seeds is important. Why? A seed is a reproductive package that

contains a plant embryo and a supply of stored food inside a protective covering

Resistant to drying Tougher and more resistant to hard

compared to spores Can grow just about anywhere and

reproduce at times of the year that are much too dry for ferns or mosses to reproduce

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Reproduction Cones and flowers

Gametophyte lives inside the sporophyte, specifically in the cones or flowers

Spores Heterosporous Produce two different forms

of spores, also known as mega and microspores

Megaspores develop into female gametophytes, which produce the eggs

Microspores develop into male gametophytes , which produce the sperm, usually contained within the pollen

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Gymnosperms Coniferophyta

are known as conifers

Includes pine, cedar, spruce, and fir

Cycadophyta – cycads

Ginkgophyta - ginkgo Ginkg

o

Cycad

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Gymnosperms

Contains the oldest living plant – Bristle cone pine

Contains the tallest living plant – Sequoia or redwood

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Gymnosperms: The Conifers

First seed plants to appear Seeds are ‘naked’ because they are

not enclosed inside a fruit. Instead, they are exposed on modified leaves that form cones

Better adapted for dry environments Needle-shaped leaves that have a

thick, protective cuticle and a small SA Depend on wind for pollination

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Gymnosperms: The Conifers Reproduction cycle p. 582

Most have two kinds of cones Male cones produce pollen Female cones produce eggs. Also called the

seed cones because they eventually contain the mature seeds

Process of fertilization and seed formation may take as long as a year After fertilization, can take up to a full year

before actual release of the seeds Embryo is 3n=Sporophyte (2n) surrounded

by food-storing tissues of the gametophyte (n); All this is enclosed in a seed coat as well

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Angiosperms Flowering plants Seeds are formed when

an egg or ovule is fertilized by pollen in the ovary Ovary is within a flower

Flower contains the male (stamen) and/or female (ovaries) parts of the plant

Fruits are frequently produced from these ripened ovaries and it protects the dormant seeds

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From Gymno to Angiosperms

Unlike naked seeds, angiosperms produce seeds encased in a protective tissue of the sporophyte known as the ovary

The combination of seed and ovary is known as a fruit

Method of reproduction independence from water and fast reproduction

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The Flower A typical flower Both male and female

gametophytes Exceptions: Corn (separate flowers on same

plant) and willows (separate flowers on different plants)

Formed from four types of specialized leaves Sepals and petals

Sepals enclose and protect developing flower; leaf-like Petals are brightly colored Attracts insects

Stamens and carpels Stamens are the male leaves Produce pollen; thin

filaments that contain anther sacs Carpels are the female leaves that includes the ovary with

one or more ovules

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The Seed Protective seed

coat Embryo

Hypocotyl Lower stem

Epicotyl Upper stem

Radicle Embryonic root; first organ to emerge

Cotyledon /Endosperm Food for the

growing embryo

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The Fruit In most plants, the

nutrients flow into the wall of an ovary, which surrounds the seeds, as well as ‘feeding’ the developing embryo. Gradually, the wall thickens and joins with other parts of the flower stem to form a fruit.

This is how the seed gets enclosed inside the walls of the ovary

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Angiosperm Reproduction

Pollination One pollen grain containing 3 monoploid nuclei, 1 tube nuclei, and 2 sperm nuclei, land on the sticky stigma of the flower

Pollen tube formation as it burrows down the style into the ovary

DOUBLE FERTILIZATION: 2 sperm nuclei travel down the tube and once inside the ovary, one sperm fertilizes the egg and becomes the embryo (2n). The other sperm fertilizes the two polar bodies and becomes a 3n endosperm, the food for the growing embryo

Ovule becomes the seed and the ripened ovary becomes the fruit

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Angiosperm Angiosperms are further classified into two

groups based on the number of cotyledons, the large seed leaves that contain food to nourish the plant embryos of seeds.

Monocot One cotyledon Grass, irises, and cattails

Dicot Two cotyledons Roses, clover, tomatoes, oaks, and daisies Also includes the flowering trees: maple, oak, elm,

apple, and dogwood

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Monocots Parallel

venation in leaves

Flower parts in multiples of 3

Vascular tissue scattered in cross section of stem

Figure 25-9a on p. 589

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Dicots Net venation in

leaves Flower parts in

multiples of 4 or 5

Vascular tissue in rings in cross section of stem

Figure 25-9b on p. 589

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Monocots vs. DicotsCharacteris-

ticMonocots Dicots

Cotyledons (seed leaves)

One Two

Vascular bun-dles in stem

Scattered In a ring

Leaf venation Parallel Netlike

Floral parts Usually in 3s Usually in 4s or 5s

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Types of Fruits Simplest fruits have a single seed enclosed by a single ovary

wall Grains: Wheat and corn Wall of the ovary is so thin that it actually fuses to the seed coat

Nuts Acorns and chestnuts Ovary wall hardens and forms a protective shell around the seed

Drupes (flesh) Peaches and cherries Ovary walls are soft and fleshy and encloses a single tough, stony

seed Legumes

Peas, beans, and even peanuts! Seeds are within a pod that splits open

Berries Grapes and tomato Soft ovary wall encloses many seeds

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Modes of Dispersal Dispersal by wind

Maple and ash trees have winged fruits that carry their seeds

Dandelions have a parasol of tiny filaments Dwarf mistletoes, a parasitic plant, produces sticky seeds

enclosed within a fluid-filled chamber. As the fruit matures, the fluid pressure builds up so it blows away the end of the fruit, pushing out the seeds

Dispersal by water Some fruits contain air pockets to keep the seeds afloat Coconut palm fruits are packed with corklike tissue and air

spaces Dispersal by animals

Some fruits have ‘bribes’ that entice the animals Edible flesh

The tough seeds can pass through the digestive system, totally unharmed

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PLANTS