Plant Science

9.1 PLANT STRUCTURE AND GROWTH9.2 TRANSPORT IN ANGIOSPERMOPHYTES

9.3 REPRODUCTION IN ANGIOSPERMOPHYTES

Plant Science

Remember…

Plant cell!

Plant Evolution

Plants originated from green algae that lived in ponds that occasionally dried out.

Angiosperms

Angiosperms have dominated the land for over 100 million years.

Known as “flowering plants”There are about 250,000 known species of

flowering plants living today.Most of our food comes from flowering plants

Roots, such as beets and carrots Fruits of trees and vines, such as apples, nuts, berries,

and squashes Fruits and seeds of legumes, such as peas and beans; Grains, such as rice, wheat, and corn

Angiosperms

Divided into two groups: Names refer to the first leaves that appear on the

plant embryo. Embryonic leaves are called seed leaves, or

cotyledons: Monocots (embryo has one seed leaf) Dicots (embryo has two seed leaves)

Angiosperms

Monocots: Orchids, bamboos, palms, and lilies, as well as grains

and other grasses Leaves have parallel veins Stems have vascular tissues arranged in a complex

array of bundles. Flowers have petals and other parts in multiples of

three. Roots form a fibrous system (a mat of threads) that

spread out below the soil surface. Make excellent ground cover that reduces erosion.

Angiosperms

Angiosperms

Dicots: True dicots include most shrubs and trees (except for

conifers), as well as many food crops. Leaves have a multibranched network of veins Stems have vascular bundles arranged in a ring. Flower usually has petals and other parts in multiples

of four or five. Large, vertical root (called a taproot) goes deep into

the soil You can see this if you try to pull up a dandelion

Angiosperms

Plant Body

Composed of organs with various tissues reflective of their evolutionary history as land-dwelling organisms.

Must draw resources from two environments: Water and minerals from soil CO2 and light from air

Plant Body

Plant body is divided up to two main parts: Subterranean part root Aerial part shoot

Plant Body

Root system: Anchors in the soil, absorbs and transports minerals

and water, and stores food. Monocots Fibrous root system consists of a mat of

generally thin roots spread out shallowly in the soil Dicots have one main vertical taproot with many

small secondary lateral roots growing outward. Both Monocots and Dicots have tiny projectsions

called root hairs: Enormously increase the root surface area for absorption

of water and minerals.

Plant Body

Shoot system: Made up of stems, leaves, and adaptations for

reproduction (flowers) Stems are parts of the plant that are generally above

ground and support the leaves and flowers. Composed of: Nodes

Points at which leaves are attached Internodes

Portions of the stem between nodes Leaves are the main photosynthetic organs in most

plants (green stems also perform photosynthesis) Consist of a flattened blade and a stalk, or petiole, which

joins the leaf to a node of the stem.

Plant Body

Shoot system (continued): Two types of buds that are undeveloped shoots: Terminal bud

Found at the apex (tip) of the stem, has developing leaves and a compact series of nodes and internodes

Axillary bud one of each of the angles formed by a leaf and the stem,

are usually dormant.

Plant Body

Apical dominance Results from the terminal bud producing hormones

that inhibit growth of the axillary buds. By concentrating resources on growing taller, apical

dominance is an evolutionary adaptation that increases the plant’s exposure to light

Important where vegetation is dense. Removing the terminal buds usually stimulates growth

of the axillary buds. Branching is important for increasing exposure the

environment

Modified Roots, Stems, and Leaves

Modified roots: Some plants have unusually large taproots that store

food in carbohydrates such as startch: Carrots, turnips, sugar beets, and sweet potatoes

Sugar Beet


Modified Stems: Stolon

“runner”; has a horizontal stem that grows along the ground surface

Plantlets form at nodes along their length, enabling a plant to grow asexually

Example: strawberry Rhizomes

Look like large, brownish, rootlike structures Horizontal stems that grown just below or along the soil surface Store food, and having buds, can also spread and form new

plants Potato plant has enlarged structures specialized for storage

called tubers (the potatoes we eat)


Modified stems (continued) Bulbs

Modified stems that are also used for underground food storage (onions)


Modified Leaves: Tendrils

Tips coil around a stem, help plants climb Examples: grapevines, peas

Tendril- Pea Plant

Plant Tissues in Stems and Leaves

Each plant organ- root, stem, or leaf- is made up of three tissue systems: Dermal Vascular Ground tissues


Dermal Tissue Forms an outer protective covering. Acts as first line of defense against physical damage

and infectious organisms. Consists of a single layer of tightly packed cells called

the epidermis: Epidermis of leaves and most stems is covered with a

waxy layer called cuticle, which helps prevent water loss. Typical dicot leaf also has pores on its epidermis called

stomata which allow CO2 exchange between the surrounding air

and the photosynthetic cells inside the leaf. Surrounded by guard cells:

• Regulate the size of the stoma


Plant Leaf

Plant Tissues in Stems and LeavesVascular Tissue:

Made up of: Xylem

type of vascular tissue that is made up of cells that transport water and dissolved ions from the roots to the leaves

Phloem type of vascular tissue that is made up of cells that

transport sugars from leaves or storage tissues to other parts of the plant


Vascular Tissue (continued): In the stem..

Vascular tissue forms vascular bundles Dicots arranged in a circle

Plant Tissues in Stems and LeavesVascular Tissue (continued):

In the leaf… Vascular tissue form network of veins In the veins, the xylem and phloem are continuous with

the vascular bundles of the stem. Allows them to be in close contact with photosynthetic

tissues, ensuring water and mineral nutrients from the soil are supplied, and that sugars made in the leaves are transported throughout the plant


Ground Tissue (continued): Accounts for the bulk of a young plant, by filling in

spaces between the epidermis and vascular tissue. Functions include photosynthesis, storage, and

support. Ground tissue inside vascular tissue is called pith Ground tissue external to vascular tissue is called

cortex

Dicot Stem

Plant Tissue in Stems and Leaves

Ground Tissue (continued): Ground tissue of dicot stems…

consists of both a cortex region and pith region Ground tissue of the leaf…

Is called Mesophyll : Sandwiched between the upper and lower epidermis Consists mainly of photosynthesis cells Loosely arranged to provide air spaces which CO2 and

O2 can circulate Main location of photosynthesis

Plant Growth

Growth in plants is made possible by tissues called meristems. A meristem consists of cells that divide frequently,

generating additional cells. Some products of this division remain in the meristem

and produce still more cells, while others differentiate and are incorporated into tissues and organs of the growing plant.

Plant Growth

Apical Meristems Meristems at the tips of roots and in the buds of shoots Cell division in the apical meristems produces the new

cells that enable a plant cell to grow in length primary growth

Enables roots to push through the soil and allows shoots to increase exposure to light and CO2.

Growth occurs behind the root tip in three zones of primary growth:

Zone of cell division, zone of elongation, and zone of maturation

Zone of maturation brings about the three tissue systems (dermal, ground, and vascular)

Plant Growth

Primary Growth of a Root

Plant Growth

Lateral meristems Associated with the increase in thickness of stems and

roots secondary growth Caused by the activity of two cylinders of dividing

cells that extend along the length of roots and stems: Vascular cambium

Secondary growth adds layers of vascular tissue on both sides of the vascular cambium wood

Cork cambium Outer cambium that forms the secondary growth of the

epidermis cork

Control of Plant Growth

Auxin is a term used for any chemical substance that promotes seedling elongation. Apical meristem at the tip of a shoot is a major site of

auxin synthesis. As auxin moves downward, it stimulates growth of the

stem by making cells elongate. Concentration of auxin determines its effect

Too low to stimulate shoot cells will cause root cells to elongate

High conc. stimulates shoots cell and inhibits root cell elongation.

Stimulates stem elongation and root growth, differentiation, and branching.


Auxins also play a part in phototropism, an occurrence that involves plants bending or moving away from light. The shoot tip is responsible for directional

movement by the plant in response to sunlight, as this is the area where auxins can be found.

Sunlight eradicates auxin, meaning that the part of the shoot tip of the plant which is receiving direct sunlight will have the least amount of auxin.

The extra auxin present on the shaded side promotes more cell division and elongation, causing the plant to bend towards the sunlight after this lop-sided growth.


Cells on the darker side are larger and have elongated faster; causes the shoot to bend towards the light.

If a plant receives sunlight uniformly from all sides or is kept in the dark, the cells all elongate at a similar rate.

Effect of Auxin on Phototropism

Transport in Plants

Several factors necessary for plant growth: CO2 from airabsorbed by leaves O2 from air or soilabsorbed by leaves or roots H2O from soil absorbed by the roots Minerals from the soil absorbed by the roots

Sugars are made in the leaves from the absorbed molecules and ions and used to build the plant’s body and provide energy

Solute Uptake From The RootsMineral ions from the soil can get into the root

of plants by three different ways: 1. Diffusion

If the concentration of certain ions is lower inside of the root hair cells, they can simply diffuse into the root hair cells from the soil

2. Fungal hyphae Some plants live in a symbiotic relationship with fungi and

use fungal hyphae to increase the surface of the root even more. The combination of plant root and fungal fibers are called mycorrhiza. The fungus benefit from a constant supply of sugar while the plant benefit from the increased surface area that the fungal hyphae provide, they also excrete growth factors and antibiotics

3. Mass flow of water into the root can also carry ions passively in dissolved form

Solute Uptake From the Roots

Roots hairs are extensions of epidermal cells that cover the root and form a huge surface area Allows the plant to absorb the water and minerals it

needs for growth Watery solution has to be transported from the soil to

epidermal cells to cortex of the root to the xylem (water-conducting vascular tissue)

Plasma membrane of the xylem cells are selectively permeable, which helps regulate the mineral composition of a plant’s vascular system.


Two possible routes to the xylem: Intracellular route Extracellular route

Solute Uptake From the RootsIntracellular route:

A.k.a. Symplatic route Cells within roots are connected via plasmodesmata

(channels through the walls of adjacent cells) which allows for a continuum of living cytoplasm among the root cells

Once inside epidermal cells, solution can move inward from cell to cell without crossing membranes


Extracellular route: Solution moves inward within the hydrophillic walls and

extracellular spaces of the root cells but does not enter the cytoplasm of the epidermis or cortex cells.

Solution passes through no plasma membranes, and there is no selection of solutes until they reach the endodermis.

Endodermis has a waxy barrier called the Casparian strip which stops water and solutes from entering the xylem.

Water and ions are forced to cross a plasma membrane into an endodermal cells, then are discharged into the xylem.

Solute Uptake in the Roots

In a real plant… Water and solutes rarely follow just the two kinds of

routes May take a combination of these routes, and may pass

through numerous plasma membranes and cell walls en route to the xylem.

All water and solutes must cross a plasma membrane at some point.

Transpiration

Why transpiration? As a plant grows upward toward sunlight, it needs to

get water and minerals from the soil. Must be able to transport resources from the roots to

thrive.

Transpiration

Xylem tissue is made of two types of conducting cells: tracheids and vessel elements. When mature, but types of cells are dead, consisting

only of cell walls, and both are in the form of very thin tubes that are arranged end to end.

Because the cells have openings in their ends, a solution of water and inorganic nutrients, called xylem sap, can flow through these tubes.

Xylem sap flows all the way up from the plant’s roots through the shoot system to the tips of the leaves.

Transpiration

TranspirationForces that push xylem sap against gravity are:

Root pressure Root cells actively pump inorganic ions into the xylem, and

the root’s endodermis holds the ions there As ions accumulate in the xylem, water tends to enter by

osmosis, pushing xylem sap upward ahead of it. Can push sap up a few meters For the most part, however, xylem sap is not pushed from

below by root pressure by pulled upward by the leaves. Transpiration

The pulling force caused by the loss of water from the leaves and other aerial parts of a plant.

Water molecules leave the plant through the stoma of the leaf by diffusion. When the stoma is open, water concentration is higher in

the plant cells than in the surrounding atmosphere.

Transpiration

Properties of water stimulate transpiration: Cohesion

Sticking together of molecules of the same kind. Because water is polar, they are attracted to each other

by hydrogen bonds Water molecules form continuous strings in xylem tubes,

extending all the way from the leaves down to the roots. Adhesion

Sticking together of molecules of a different kind. Water molecules tend to adhere via hydrogen bonds to

hydrophillic cellulose molecules in the walls of xylem cells.

Transpiration

Transpiration-Cohesion-Tension Mechanism: Before a water molecule can leave the leaf, it must break off from the

end of the string It is pulled off a steep diffusion gradient between the moist interior of

the leaf and the drier surrounding air. Cohesion resists the pulling force of the diffusion gradient, but it is

not strong enough to overcome it. The molecule breaks off, and the opposing forces of cohesion and

transpiration put tension on the remainder of the string of water molecules.

As long as transpiration continues, the string is kept tense and is pulled upward as one molecule exits the leaf and the one right behind it is tugged up into its place.

Adhesion pulls the remaining water molecules upwards from the root against the downward pull of gravity.

Process does not require energy from the plant, they are all extended by physical properties of water and the surrounding molecules.

Transpiration

Summary of Transpiration-Cohesion-Tension Mechanism: Transpiration exerts a pull that is relayed downward

along a string of water molecules held together by cohesion and helped upward by adhesion.

Transpiration is an efficient means of moving large volumes of water upward from roots to shoots.

http://www.phschool.com/science/biology_place/labbench/lab9/transpull.html

Guard Cells

PROBLEM! Photosynthesis requires large leaf surfaces Results in constant transpiration and water loss If soil dries out, plants wilt and eventually die

SOLUTION! Leaf stomata can open and close via the control of guard cells. Guard cells control the opening of a stoma by

changing shape, widening or narrowing the gap between the two cells.

Abscisic Acid

Absicisic acid causes the closing of stomata. ABA crucial for plants to withstand drought. When the plant starts to wilt, ABA accumulates in the

leaves and causes stomata to close.

Abiotic Factors that Affect Transpiration

Light intensityTemperatureWindHumidity

**We will perform a lab to see how these factors affect Transpiration!

Adaptations of Xerophytes Plants adapted to dry conditions are called xerophytes. Adaptations include:

thick, waxy cuticles reduces water loss through the cuticle Prickly pear , ivy, sea holly

Reduced number of stomata reduces the number of pores through which water loss can occur Prickly pear, Nerium

Stomata sunken in pits, grooves, or depressions, leaf surfaces covered with fine hairs, massing of leaves into a rosette ground level moist air is trapped close to the area of water loss, reducing the diffusion gradient and therefore the rate of water loss Sunken stomata: Pinus sp, Hakea sp. Hairy leaves: lamb’s ear Leaf rosettes: dandelion, daisy

Adaptations of Xerophytes

Prickly PearLamb’s Ear

Hakea

Daisy

Adaptations of Xerophytes Adaptations include:

Stomata closed during the light, open at night CAM metabolism: CO2 is fixed during the night, water loss in the day is minimized. CAM plants, American aloe, pineapple, Kalanchoe, Yucca

When the weather is hot and dry, keeps its stomata closed most of the time, conserving water. At the same time, it continues making sugars by photosynthesis .Have an enzyme (very high affinity of CO2) that fixes carbon into a four-carbon compound, which acts as a shuttle to transfer CO2 around the leaf. a C4 plant; corn and sugar cane

Leaves reduced to scales, stem photosynthetic, leaves curled, rolled, or folded when flaccid reduction in surface area from which transpiration can occur Leaf scales: broom; Rolled Leaf: marram grass

Fleshy or succulent stems; Fleshy or succulent leaves when readily available, water is stored in the tissues for times of low availability Fleshy stems: candle plant; Freshly leaves: Bryophyllum

Deep root system below the water tableRoots tap into the lower water table Acacias, oleander

Shallow root system absorbing surface moisture roots absorb overnight condensation Most cacti

Adaptations of Xerophytes

Broom

Bryophyllum

Phloem transport

Main function of phloem is to transport the products of photosynthesis.

Phloem contains cells called sieve-tube members arranged end to end as tubes, with sieve-tube plates in between

Phloem sap (sugary solution may contain inorganic ions, amino acids, hormones, and mostly sucrose) moves freely from one cell to the next

Example: Maple syrup!

Phloem Transport

Phloem sap moves through the plant in various directions, in contrast to the xylem sap which only flows upward from the roots.

Sieve tubes always carry sugars from a sugar source (organ that is the net producer of sugar, mostly the mature leaf) to a sugar sink (an organ that is net consumer or storer of sugar; examples include growing roots, buds, stems and fruits, also tubers or bulbs )

Phloem Transport

Phloem Transport

Each food-conducting tube in phloem tissue has a source end and sink end, but these may change with the season or the developmental stage of the plant A storage organ, such as a tuber or bulb, may be a

source or sink depending on the season. When stockpiling carbohydrates in the summer, it is a

sugar sink. After breaking dormancy in spring, it is a source as its starch is broken down to sugar, which is carried to the growing tips of the plant.

Phloem Transport

The phloem sap moves by pressure flow mechanism:

1.At the sugar source, sugar is loaded into a phloem tube by active transport. Sugar loading at the source end raises the solute concentration inside the phloem tube.

2.The high solute concentration draws water into the tube by osmosis. The inward flow of water raises the water pressure at the source end of the tube.

3.At the sugar sink (a beet root, for example), both sugar and water leave the phloem tube. The exit of sugar lowers the sugar concentration in the sink end; the exit of water lowers the hydrostatic pressure in the tube.

4.The lower water pressure and sugar concentration causes the phloem sap to move toward the sugar sink.

Phloem TransportThe pressure flow mechanism explains why

phloem sap always flows from a sugar source to sugar sink, regardless of their locations in the plant.

Sexual Life Cycle of a Flowering Plant

From an evolutionary viewpoint, all the structures and functions of a plant can be interpreted as mechanisms contributing to reproduction. An oak tree is merely an acorn’s way of making more

acorns.

Reproductive Structures of Angiosperms

Flowers are the reproductive shoots of angiosperms.

Four types of modified leaves called floral organs: Sepals: enclose and protect the flower bud, usually

green and more leaf-like than the other floral organs. Petals: often colorful and advertise the flower to

pollinators Stamens: reproductive organ containing sperm Carpels: reproductive organ containing egg


Stamen Consists of a stalk (filament) tipped by an anther

Anther Contain sacs in which meiosis occurs and in which

pollen is produced. Pollen grains house the cells that develop into sperm.

Carpel Has a long slender neck (style) with a sticky stigma at

its tipStigma

Landing platform for pollen


Ovary Base of the carpel, contain ovules. Develops into a fruit, which protects the seed and aids

in dispersing.Ovules

Found within ovary, contain a developing egg and supporting cells.

Where fertilization occurs, which develops into a seed containing the embryo.

Seed germinates (begins to grow) in a suitable habitat; the embryo develops into a seedling; and the seedling grows into a mature plant.


Pollination

Pollination the first step to fertilization transfer of pollen from anther to stigma utilize wind, insects, birds, or other animals

Fertilization

After pollination, double fertilization occurs: 1. the pollen grain germinates on the stigma 2. Pollen tube forms and grows downward into ovary. 3. Pollen tube then reaches ovule and discharges two

sperm near the embryo sac. 4. One sperm fertilizes the egg, forming the zygote. 5. Another contributes its haploid nucleus to the large

diploid central cell of the embryo sac, forming a triploid (3n) nucleus. This gives rise to a food-storing tissue called endopserm.

Fertilization

Seed Dispersal After fertilization, the ovule, containing the triploid central cell and

the zygote, begins developing into a seed. The results of embryonic development in the ovule is a mature

seed. Flowering plants have evolved many ways to

ensure their seeds are dispersed. In some cases the seed itself is the agent of dispersal, but

often it is the fruit. Chief agents of seed dispersal are wind, water, and animals.

Wind: such seeds have wing-like or feathery structures that catch the air currents and carry the seeds long distances.

Water: many seeds, including those that lack special buoyancy mechanisms

Animals: seeds have hooks or barbs that catch animal hair, sticky secretions that adhere to skin or hair, or fleshy fruits that are eaten leaving the seed deposited in feces

Seed DispersalWind

Wind

Animals

Water

After fertilization, ovule with triploid central cell and zygote, develops into a seed. Endosperm is used to nourish embryo

Results of embryo development is a mature seedA seed is an entire reproductive unit, housing the

embryonic plant in a state of dormancy.

Dicot Seed StructureExternal Structures:

Testa, or tough, protective seed coat that encases the embryo and its food supply

Internal Structures: Embryo is an elongated structure with two fleshy cotelydons. Embryonic root develops just below the point at which the

cotyledons are attached to the rest of the embryo. Embryonic shoot, develops just above the point of attachment,

with embryonic leaves Micropyle: A minute opening in the ovule of a seed plant through

which the pollen tube usually enters. Seed contains no endosperm because it’s been absorbed by cotyledons

during seed formation. Nutrients pass from cotyledons to embryo during germination

Dicot Seed Structure

Seed Germination

The germination of a seed is commonly used to symbolize the beginning of life, but as you now know, the seed already contains a miniature plant, complete with embryonic root and shoot. …think about that the next time you make popcorn!

Thus, at germination, the plant does not begin life but rather resumes the growth and development that was temporarily suspended during seed dormancy.

Seed GerminationBegins when…

1.seed takes up water 2.hydrated seed expands, rupturing its coat. 3.inflow of water triggers metabolic changes in

embryo that make it start growing again 4.A hormone called gibberllin forms in the embryo’s

cotelydon. This stimulates the production of amylase, which catalyses the breakdown of starch to maltose. This subsequently diffuses to the embryo for energy release and growth.

Seed Germination

Seed Germination

Conditions needed seed germination: oxygen, moisture, temperature, and sometimes

Oxygen, which increases respiration, and correct temperature settings are needed to activate growth enzymes.

Providing the right amount of moisture to the growing medium is important in that if there is too much water, and oxygen is limited, it will prevent the normal germination process

Although most seeds do not need light to germinate, a few do such as lettuce and begonias.

Flowering in long-day and short-day plants

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Plant Science