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Unit V - Plants Anatomy and Physiology

Ch 13.6 - Control of Plant Growth and Development

Plant growth regulator: a chemical produced by plant cells that regulates growth and differentiation

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Plants can modify their growth and differentiation through plant growth regulator

act by signaling plant cells to undergo particular changes
auxins, gibberellins, cytokinin, ethylene, and abscisic acid
can be categorized in tropism and nastic movement

Tropisms and Plant Growth Regulators

Tropism

Tropism: a directional change in growth/ movement in response to a stimulus and occurs slowly / not noticeable
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Phototropism: a change in direction of a growing plant in response to light
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Gravitropism: a directional change in growth pattern in response to gravity
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Thigmotropism: a directional change in growth pattern in response to touch

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Tropism is a change in the direction of growth/movements of a plant in response to a stimulus

controlled by plant growth regulators

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Phototropism: a change in direction of growth of a plant in response to light

plant can bend towards areas of higher light in an attempt to maximize the amount of light they received
positive phototropism: towards the light
negative phototropism: away from the light

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Gravitropism: a change in the direction of growth in response to gravity

regardless of the orientation of the plant, the root will always grow downwards - positive gravitropism
regardless of the orientation of the plant, the stem will always grow upwards - negative gravitropism
also known as “ geotropism”

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Thigmotropism: a change in the direction of growth in response to contact

slow responses to touch/pressure
eg. vines have positive thigmotropism

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Chemotropism: a change in the direction of growth in response to chemicals

eg. root grow towards useful minerals but away from acids

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Hydrotropism: a change in the direction of growth in response to water

eg. root exhibit positive hydrotropism

Nastic movements

Turgor response/nastic movements: quick responses to stimuli

does not depend on the direction of the stimulus
movement is reversible
turgid cells filled with water quickly lose water and pressure
eg. venus fly traps, Mimosa plants

Hormones

Hormone: a chemical that affects how organism functions, causing the organisms to respond in various ways to the chemical signal

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The growth and development of many plants and development of plants are regulated by the activity of plant hormones

auxin, cytokinin, gibberellins, abscisic acid, ethylene

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Auxin: promotes cell elongation and suppresses the growth of lateral branches and leaves drop in spring

shoot apical meristem is the main site of auxin synthesis
diffuse down from the shoot tip to cells on its shaded side → stimulate cells elongation by loosening up cellulose → causing the shoot to bend towards the light
stimulate cell division in the vascular cambium and promotes the formation of new lateral meristems and new root apical meristems
eg.1 - synthetic auxins may also be applied to fruits to induce cell elongation
eg.2 - spraying auxins on orchard can artificially synchronize the ripening in all plants → reduce the cost of harvesting the fruits as most of the fruits can be picked at one time

Apical Dominance: the condition in which most shoot growth from apical bud and not lateral buds

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Apical dominance is an example of auxin inhibiting cell division

cell division occurs in the apical bud but is inhibited in the lateral buds
caused by the high level of auxin released in the apical meristem
grower can cause a plant to produce more flowers, fruits/leaves by removing the apical bud
eg.1 - basil plants can be made bushier by removing the apical bud

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Gibberellins: promotes cell division and cell elongation

produced by the young tissues of shoots and by developing seed, but from leaves and young roots as well
help make the stored carbohydrate reserve available to the growing embryo
eg.1 - grapes are sometimes sprayed with gibberellins to induce fruit production → cause fruit stem to elongate → give each grape more space to grow → grape grows larger → make the grape bunch look larger and more appealing

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Cytokinins: promote cell division and differentiation through mitosis

found in tissues that are actively diving, such as meristems, young leaves, and growing seeds
stimulate adventitious buds
slow cell aging by inhibiting protein breakdown and stimulating protein synthesis
eg.1 - synthetic cytokinins are sprayed on lettuce and mushrooms to keep them from spoiling

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Ethylene: “plant stress hormone” as it induces changes that protect a plant against environmental stress

Senescence: developmental events in a plant tissue/organ from maturity to death

regulates the growth of roots and shoots around obstacles → causes the roots to grow sideways → no longer produced when root cells no longer touch the stone
stimulate fruit ripening, shoot and root growth and differentiation, and flower opening
stimulate fruit drop and flower and leaf senescence, losing leaves in drought conditions
release ethylene as fruits ripen, which induces further ripening and eventually spoilage
eg.1 - an increase in ozone leads to the increase of ethylene production in plants → reduces crop yield
eg.2 - producers ship fruits in well-ventilated trucks that contain ethylene-absorbing filters or shipped separately to make sure all products all ripen at the same time → helps the product sell more steadily

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Abscisic Acid: respond to changes in temperatures and light, maintains dormancy in leaf buds and seeds

reason why deciduous trees are dormant over winter and grass, becomes dormant and turns brown during hot, dry periods as dormant plants are less vulnerable to damage
control the closing of stomata → Abscisic Acid diffuses to the guard cells of the stomata and induces them to close → leaves can conserve their internal water
eg.1 - Abscisic Acid is applied to plants before they are shipped from nurseries to garden centers so they can be less vulnerable to damage

Ch 12.5 - Transport in Vascular Plants

Phloem: transport of sugars
Xylem: transport of water and nutrients

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Basic Overview of transportation:

Water and dissolved nutrients from soil enter plant roots by passive active transport through the plasma membrane of root hairs → Water and dissolved nutrients travel from root hairs into xylem vessels by passing through/between cells → Vascular tissue distributes substances throughout the plant, sometimes over great distances → Cells load and unload sugars into and out of the phloem

Transport in the Roots

Water enters the root by osmosis, but nutrients enter by active transport
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Osmosis: the diffusion of water molecules across a selectively permeable membrane, from an area of high concentration to an area of lower concentration
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The key role of the Casparian strip is to prevent substances from leaking back into the cortex

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The cytoplasm of plant cells has a lower concentration of water molecules than soil water, and the cell membrane allows water molecules to cross freely → water molecules enter cells in the plant roots by osmosis → water flows through the epidermal cells, cortex → water molecules move towards the vascular cylinder

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The concentration of nutrients in the cytoplasm of a plant cell is higher than the concentration of nutrients in the soil water → must use active transport to move nutrients from the soil to roots cells → moved through the cells of the cortex towards the endodermis

movement is made easier since the adjacent plant cells have interconnecting stands of cytoplasm

→ once nutrients/water enter a root cell, they would not need to cross another cell membrane until they reach the vascular cylinder

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Water molecules and nutrients reach the endodermis → pass directly through the endodermal cell → nutrients are actively pumped across cell membranes into the xylem once they’re inside the vascular cylinder

Transport into the Stem

Root pressure: the osmotic force pushing xylem sap upwards in root vascular tissue
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Capillary action: the tendency of a liquid to rise/fall because of attractive forces between the liquid molecules

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Water molecules and dissolved nutrients cross the Casparian strip → form xylem sap → create root pressure and help push the xylem sap upwards as concentration increases and water molecules follow by osmosis

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Capillary action: the tendency of a liquid in a narrow tube to rise and fall

Adhesion - a column of liquid is held together by weak attractive forces between molecules and rises because of attractive forces between the liquid and the side of the tube

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Cohesive-tension: Attractive forces occur between water molecules and molecules in the cell walls

water molecule in xylem sap stick to each other and are drawn up from the sides of the xylem tubes → water column moves upward → xylem sap move from one xylem tube to another through pits in the cell wall/move out of the xylem through pits into the surrounding tissue

→ ensure all cells in the plant body receive water and nutrients

Transport to the leaves

Transpiration: evaporation of water through the stomata of plant leaves
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The main driving force of transport up the xylem is Cohesion-tension (transpiration)
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Turgor: pressure caused by the fluid contents of central vacuole, which pushes against the wall of a plant cell

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Plants release water vapor through stomata during transpiration → water evaporates through the stomata when they are open → water molecule moves up the xylem column → pulls neighboring water molecules with them and etc.

due to the attractive force between water molecules, one is able to pull another up

Water and dissolved nutrients enter the root by osmosis and active transport → 2) Release of water molecules through transpiration in the leaves drives the uptake of replacement water molecules from soil → 3) Transpiration continues to pull the column of water up the xylem tubes w/ root pressure and capillary action → 4) Transpiration pulls the column of water up through the xylem tubes and evaporates

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A plant cell stores water and dissolved substances in its central vacuole → exerts pressure against the cell wall when it’s full → Turgor

help support the plant
water moves out of the vacuole when the plant is unable to take up water from soil → plant wilt

Transport of Sugar

Source: plant cell with a high concentration of sugars and other solutes
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Sink: plant cells with a low concentration of sugar → may be converted to starch for storage/used for energy/building blocks for carbohydrates
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Angiosperm - companion cells transport sugar from source cells to the sieve tube elements
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Gymnosperm - sugars are transported from source cells directly into sieve cells

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Sugar can move bi-directional

depends on the location of source cells relatives to sink cells
generally, sugars are transported from a source to a sink, which is connected by columns of phloem cells

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Eg.1 - the location of sink and source cells in plants often changes in seasons

winter: many plants are dormant → do not grow or photosynthesize
spring: plants depend on carbohydrates stored in roots and stems → plant breaks down starch as sugar
spring: root and stem cells are sources, and sink is mainly the leaves → phloem moves up
summer: leaves produce sugar → sources, and the roots and stem cells are the sinks → phloem moves down

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The produced sugar transport to the phloem involves active transport → concentration of sugar in the phloem sap increase → water are drawn from the xylem cells into the phloem cells by osmosis → increase the turgor of phloem cells

concentration of sugars in phloem cells is generally higher than the concentration in the source cell

Translocation

Translocation: long-distance transport of substances through the phloem, particularly glucose

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Phloem tubes are not hollow, substances in the phloem sap have to move between living cells

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It is suggested that translocation is driven by the difference in turgor between the phloem cells near source cells and the turgor of phloem cells near sink cells

differences in turgor push the phloem sap towards the direction of sink cells

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Sugar molecules leave the phloem once they reach a sink cell → sugar moves from the phloem to the sink by passive transport → sieve tube elements have a lower concentration of sugar → water returns to the xylem from the phloem

maintains the relatively low turgor of phloem cells near the sink
recirculates the water back into the xylem

Ch 12.4 - Roots

The main role of plant roots: is to anchor the plant and keep it upright, to absorb water and nutrients other than carbohydrates
→ some roots store water and carbohydrates for the plant

Types of Root Systems

Taproot system: a root system composed of a large, thick, root; can have smaller lateral roots → Eudicot
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Fibrous root system: a root system made up of many small, branching roots → Monocot
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Lateral root: a smaller root that branches from a larger root
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Root hair: a microscopic extension of the epidermal cells of the root

General Structure of Roots

Root cap: the mass of cells that form a productive covering for the meristem at the root tip
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Root cortex: a region of parenchyma cells under the epidermis of a root
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Endodermis: the innermost layer of cells in the cortex of the root
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Casparian strip: the wax-like strip that runs through the cell wall of an endodermis cell
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Vascular Cylinder: the central portion of a root that contains the xylem and the phloem

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The tip of the root contains the root cap and a meristem. and behind the apical meristem is the region of elongation followed by the region of maturity

root cap produces a slippery substance that helps the root to penetrate the soil → minimize the damage to the root cells
meristem produces new cells to increase the length of the root

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The Root hairs are found above the root tip, projecting outward from the epidermis

increase the surface area of the epidermis → the root can absorb water and dissolve nutrients more efficiently

The root cortex is a region of parenchyma cells beneath the epidermis

store carbohydrates and help transport water from the epidermis to the xylem
ends at the endodermis → walls are wrapped with a wax-like substance which forms the Caparian strip

The vascular tissues of roots are contained in the vascular cylinder

gymnosperms and eudicot - in the center of the root, forming an X/star shape
Monocot - the center of the root contains parenchyma cells, surrounded by a ring of xylem and a ring of phloem cells

Root specialization

Tuberous Root: a lateral root specialized in storing carbohydrates
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Adventitious Root: a root that develops from somewhere other than the root apical meristem that emerges from the seed

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Root specialization may help roots to

more efficiently absorb water and nutrients
anchor the plant
store carbohydrates
help protect the roots from being eaten

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Almost all plants have relationships with other organisms

The roots of over 80% of plants have a mutualistic relationship with Mycorrhizal - the fungi can get into smaller spaces and are able to release digestive enzymes that break down organic matter → receive carbohydrate
some root species and nitrogen-fixing bacteria - the bacteria take nitrogen from the air and convert it into a form that plants can use → receive carbohydrates and live within the nodules
strangler fig and other organisms - the fig will obtain water and nutrients from the host tree and the roots will prevent the host’s trunk from growing outwards → host tree dies and loses its leaves, and leave behind a large hollow space within the strangler fig → strangler fig engulf the trunk of the host and becomes the host
humans and plants - most roots eaten by organisms are specialized for carbohydrates storage (eg. carrots and beets → taproot, Yams, cassava and sweet potatoes → tuberous roots)

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Some roots produce chemicals to avoid the risk of being eaten by other organisms

eg.1 - bitter roots - the bear root taste so horrible that few animals would eat them
eg.2 - Cassava roots produce a deadly toxin to protect them
eg.3 - black walnut root secretes a toxin that inhibits the growth of other plants
eg.4 - common reed releases a corrosive acid that breaks down the roots of the neighboring plants

Human Uses of Roots

We use roots for food, for ourselves and our livestock

food - parsnip, turnips, beets, taro, and sweet potato
Ourselves - licorice roots can be used in candies, roots can be used for beverages
livestock - Cassava, turnips, yams, rutabaga, and other roots
chemicals - can be used to dye textiles (eg. beet/madder for red, and dandelion for brown), pesticides (eg. Rotenone)
Medicine - Ipecac (induce vomiting and prevent further absorption of poison), Kava kava (eg. reduce anxiety)

Erosion Control

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Roots are useful in controlling erosion

fibrous roots can form a mat that holds the upper soil layers in place during heavy rain, snow/wind
trees can be planted to control erosion → often done after an area of the forest has been clear-cut since it exposes the soil surface which makes it vulnerable to erosion

Ch 12.3 - Stems

Roots connect the vascular tissue in the leaves to the vascular tissue in the root → allowing water and dissolved substances to be transported throughout the plant body
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Roots also raise and support the leaves and reproductive organs
→ maximize their exposure to sunlight so they are able to photosynthesize more efficiently
→ place the organs in an ideal position to photosynthesize more effectively
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Some can store water/carbohydrates, and to protect the plant from injuries and herbivores

Stem Structure

Herbaceous: describes plants with stems that do not have wood
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Woody: describes plants with stems that contain wood

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Herbaceous plants’ stems are relatively pliable, carry out photosynthesis and have a thin epidermis

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Woody plants’ stems are relatively hard, have bark, and do not usually carry out photosynthesis

all gymnosperms/eudicots have woody stems

Anatomy of Herbaceous Stems

Vascular Bundle: arrangement of vascular tissue that consists of xylem and phloem

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Vascular bundles run continuously from the roots to the leaves

xylem is always close to the center while phloem is always closer to the outside of the stem
vascular bundles are scattered throughout the parenchyma - monocot
vascular bundles are arranged in a ring around the margin of the stem and occupied by pith - dicot

Anatomy of Woody stems

Vascular Cambium: the meristematic cell layer in vascular tissue
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Bark: the protective outermost layer of the stems and roots of woody plants; consists of phloem, cork cambium and cork
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Cork cambium: the meristematic layer in a woody plant that produces cork

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Vascular cambium is a layer of meristematic cells in the vascular tissues that divide to form new xylem and phloem cells

secondary xylem grows to the inside of the vascular cambium, and secondary phloem to the outside → increase the width of the plant

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Sapwood is the younger xylem through which water and minerals are transported to the leaves → older xylem layers fills up with resins and oils and no longer conduct water → form heartwood

heartwood helps support the tree

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Bark consist of phloem, cork cambium, and cork

phloem transport sugars made in leaves throughout the plant
protect plants from herbivores and low-temperature fires (eg. Ontario’s red and white pine)

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Cork cambium is a layer of meristematic tissue that produce cork

cork prevents water loss from the stem

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The apical meristem is embedded in the tip of the stem within the Terminal bud

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Along the side of the stem are lateral buds that forms new branches and twigs → leaves unfold at intervals as terminal bud moves up

leaves attached at points - nodes
spaces between nodes - internodes
openings - lenticels → permit gas exchange between stem and surrounding air

Spring wood - the vascular cambium grows rapidly in spring, producing large xylem cells that have thin walls → wood is less dense and in light color

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Summer wood - fewer xylem cells are produced and have thicker cell wall → wood is more dense and in dark color

Cell Types in Vascular Tissues

Xylem: thick walled and dead at maturity, cell walls are rich in lignin
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Phloem: contain cytoplasm, living at maturity
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Tracheid: elongated, tapered xylem with thick cell walls containing small pits, that overlap one another to form continuous tubes from root to shoot
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Vessel element: a shorter blunt-ended xylem cell with thick cell walls containing small pits, stack end to end to form vessel tubes that run from root to shoot
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Perforation plate: perforated end wall of a vessel element
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Sieve cell: phloem cell with pores in its cell walls, contains all necessary cell organelles
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Sieve tube element: a phloem cell with pores in its side cell walls, lack organelles and depend on associated companion cell
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Sieve plate: the perforated end wall of a sieve tube element
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Companion cell: a small nucleated phloem cell that is always associated with a sieve tube element
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Xylem

Tracheid all have pits → allow water and solutes to pass up or across to neighboring xylem cells
Vessel element is shorter and wider and have less tapered end
Perforation plates are end walls with one/more openings → allow water and solutes to pass through
→ gymnosperm: tracheid
→ angiosperm: tracheid and vessel elements

Phloem

Sieve cells have narrow pores, organelles including a nucleus
Sieve tube element have cytoplasm but lack cell organelles
Sieve plates are perforated → allow sugars solution to pass to neighboring phloem cell
Companion cell have a nucleus and organelles
→ gymnosperm: sieve cells
→ angiosperm: sieve tube element and companion cell

Stem Specialization

stolons are modified stems that grow along the soil instead of upright
spider plants produce new plants on the ends of stolons
vines take advantage of other objects to raise and support their leaves

Human Uses of Stems

Fuel

ethanol
wood

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Food

sugar canes
potato
yams
maple syrup
asparagus

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Textiles

flax - manufacture linen
hemp - produce textiles
bamboo - make clothing w/ other natural fibers such as cotton

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Dyes

indigo - dye jeans
hematoxylin - stain used to prepare microscope slides

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Chemicals

tannin - wood stains
turpentine - solvent
latex rubber - gloves, tubing and erases

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Medicine

salicylic acid - pain reliever made from willow bark
taxol - anti-cancer drug from bark and needles of yew trees

Ch 12.2 Leaves

Functions of Leaves

Chloroplast: organelle found in large numbers in many plant cells, site of photosynthesis within a plant cell
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Photopigment: a pigment that undergoes a physical/chemical change in presence of light
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Leaves are the primary site of photosynthesis
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The plant used glucose as a building material and as an energy source for cellular processes

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Leaf absorb energy from sunlight in a chloroplast → which contains various photopigments

photopigments are chemicals that absorb particular wavelengths in the light
chloroplasts also
eg.1 - chlorophyll absorbs light at the red and blue ends of visible lights → gives leaves their green color

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Leaves carry out the gas exchange between the interior of the plant and its environment

epidermis contains many pores → allow for gas to pass in and out
photosynthesis (use CO2 and release O2) and cellular respiration (use O2 and produce CO2) requires gas exchange

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Leaves may offer protection from herbivores

protect themselves with surface hair w/ irritating compounds → make leaves unpalatable
produce toxins or bad-tasting chemicals → deter herbivores
eg.1 - leaves in cacti are reduced to sharp spines → protect photosynthetic stem

Structures of Leaves

Blade: the flat part of a leaf
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Petiole: stalk that attached the leaf blade to the plant stem

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Venation: the arrangement of veins within a leaf

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Monocots

have parallel venations
have narrow leaves

Dicot

have branching venation
have broad leaves

Internal Structures of Leaf

Mesophyll: the photosynthetic middle layer of cells in the lead of a terrestrial plant
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Palisade mesophyll: the later of elongated photosynthetic cells arranged in columns under the upper surface of a leaf on a terrestrial plant, part of mesophyll
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Spongy mesophyll: the latter of loosely packed photosynthetic cells with large air spaces between them under the lower surface of a leaf on a terrestrial plant, part of the mesophyll
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Stoma: opening in leaves through which gases pass in and out of leaves
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Guard cells: one of two kidney-shaped cells that control the opening and closing of a stoma

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The epidermal cells are tightly packed in a single layer and covered by a waxy coating called the cuticle

cuticle prevents water loss → provides a physical barrier against bacteria, molds, and insects
transparent → so light can pass through to the cells within → does not carry out photosynthesis

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Mesophyll

Palisade mesophyll are elongated and closely packed, and contain many chloroplasts → maximizing amount of light collected and use for photosynthesis
Spongy mesophyll are loosely packed and have large air spaces → allowing for gas exchange between the mesophyll cells and the atmosphere through stomata

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Stomata

an opening in the epidermis, through which gases pass in and out
regulates the rate of gas exchange

Guard cells

are thicker on their inner side → when swollen with water, they bow outwards → open stomata
turgor pressure - the pressure exerted on the guard cell to open
low concentration of CO2 and an accumulation of potassium ion + environmental conditions (i.e. temperature) → instigate the opening

Aerenchyma

tissue composed of loosely packed parenchyma with large pores
help leaves float on the surface of the water for aquatic plants

Leaf Specialization

Leaves have a specialization that protects the plants

produce chemicals in their leaves to repel herbivores
→ eg.1 - tobacco plants produce nicotine
deters herbivores from structural specialization
→ eg.2 - cacti have spines that protect the stem from being eaten
plants will lose their leaves in fall → help conserve water and nutrients during winter
Gymnosperm have small leaves, a thick epidermis, and cuticle, and stomata are recessed below the epidermis, and chemicals that prevent them from freezing → prevent water loss
→ conifers (i.e. spruce and pines) have needle-shaped leaves → allow shedding snow more readily

Human Uses of Leaves

Dark green leafy vegetable (spinach)

contain calcium, potassium, iron, magnesium, vitamins B, C, E, and K,
provide nutrients that protect our cells from damage such as beta-carotene, lutein, and zeaxanthin
contain a small amount of omega-3 essential for brain and heart function

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Cuticles

wax produced by carnauba palm leaves is used to make car and furniture polishes, surfboard wax, coating for candies, and ingredient in chocolate
Candelilla produced by Euphorbia Cerifera is used to make lipstick

Leaves

leaves of sweet grass plants are used in NA Aboriginal people’s religious ceremony
braided sweet grass is burnt at the start of ceremonies to purify spirits by the Cree and Anishinaabe Algonquian people
palm leaves are used to make thatched roofs

Leaves and Chemicals

Many species protect themselves by synthesizing toxic chemicals in their leaves

eg.1 - hydrangea leaves can cause vomiting, diarrhea, or even coma
eg.2 - leaf blades of rhubarb plant can cause vomiting, nausea, or even kidney damage

Some plant poisons can be beneficial in cancer treatments → used to kill the rapidly dividing cancer cells

eg. 1 - vincristine → treat childhood leukemia and vinblastine → treat Hodgkin’s disease produced by rosy periwinkle

Psychotropic drugs

Psychotropic drugs: mind-altering

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some plants produce chemicals that alter perception, emotion/behavior

eg.1 - marijuana produce psychotropic compound tetrahydrocannabinol → increases appetite and reduces nausea and may reduce muscle spasms, reduce internal pressure in the eye → useful in treating glaucoma
eg.2 - coco plants produced cocaine→ that suppresses hunger, pain, and fatigue. and help lessen the symptoms of altitude sickness; produce euphoria, talkativeness, and alertness, and produce paranoia, irritability, and nervousness