Botany Lecture Final Exam Coverage | Lecture notes Botany and Agronomy

Botany Lecture Finals

Plant Hormones

Five major types of hormones regulate plant

growth and development

- Hormone is chemical signal that is

produced in one part of the body and

transported to another, where it

triggers responses in target cells

- Binding of hormones to specific

cellular receptors triggers a signal

transduction pathway

- Tiny amounts of hormone can have a

big effect

Auxin stimulates the elongation of cells in

young shoots

- Indoleacetic acid (IAA) ~ naturally

occurring auxin that promotes

seeding elongation

- Produced in shoot apical meristems

and transported downward through a

plant

- Concentration of auxin and site of

activity are important to auxin’s

effects

- In moderate concentration, auxin

promotes cell elongation in stems

- In high concentrations, auxin reduces

cell elongation in stems

- Affects cell elongation in roots at

lower concentration

Cytokinins stimulate cell division

- Promote cytokinesis or cell division

- Are produced in actively growing

organs such as roots, embryos, and

fruits

- Produced in roots then move upward

through the plant

- Retard aging in leaves and flowers

Gibberellins affect stem elongation and have

numerous other effects

- Promote stem elongation by

increasing cell division and

elongation

- Also promote fruit development and

seed germination

- Act antagonistically against another

plant hormone called abscisic acid

Abscisic acid inhibits many plant processes

- Inhibits growth

- High concentration ~ promote seed

dormancy

- ABA must be removed for

germination to occur

- The ratio of ABA to gibberellins

controls germination

- Influences plant water relations

- Accumulation of ABA in

wilted leaves promotes

stomatal closure

- ABA produced in roots can

signal low soil moisture

conditions and triggers plans

to conserve water by closing

stomata

Ethylene triggers fruit ripening and other

aging processes

- Is a gaseous by product of natural

gas combustion and a naturally

occurring plant hormone

- Plants produce ethylene in response

to stresses such as mechanical

pressure, injury, infection, and

drought or flood

Responses to stimuli

Tropisms orient plant growth toward or

away from environmental stimuli

Tropism ~ responses that causes plants to

grow in response to environmental stimuli

- Positive tropism cause plants to grow

toward a stimulus

- Negative tropism cause plants to

grow away from a stimulus

Plants respond to various environmental

stimuli

- Phototropism ~ response to light

- Gravitropism ~ response to gravity

- Thigmotropism ~ response to touch

Plants have internal clocks

-Circadian rhythms are innate

biological cycles of approx. 24 hours

- Both plants and animals have

circadian rhythms

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Plant Hormones Five major types of hormones regulate plant growth and development

Hormone is chemical signal that is produced in one part of the body and transported to another, where it triggers responses in target cells
Binding of hormones to specific cellular receptors triggers a signal transduction pathway
Tiny amounts of hormone can have a big effect Auxin stimulates the elongation of cells in young shoots
Indoleacetic acid (IAA) ~ naturally occurring auxin that promotes seeding elongation
Produced in shoot apical meristems and transported downward through a plant
Concentration of auxin and site of activity are important to auxin’s effects
In moderate concentration, auxin promotes cell elongation in stems
In high concentrations, auxin reduces cell elongation in stems
Affects cell elongation in roots at lower concentration Cytokinins stimulate cell division
Promote cytokinesis or cell division
Are produced in actively growing organs such as roots, embryos, and fruits
Produced in roots then move upward through the plant
Retard aging in leaves and flowers Gibberellins affect stem elongation and have numerous other effects
Promote stem elongation by increasing cell division and elongation
Also promote fruit development and seed germination
Act antagonistically against another plant hormone called abscisic acid Abscisic acid inhibits many plant processes
Inhibits growth
High concentration ~ promote seed dormancy
ABA must be removed for germination to occur
The ratio of ABA to gibberellins controls germination
Influences plant water relations
Accumulation of ABA in wilted leaves promotes stomatal closure
ABA produced in roots can signal low soil moisture conditions and triggers plans to conserve water by closing stomata Ethylene triggers fruit ripening and other aging processes
Is a gaseous by product of natural gas combustion and a naturally occurring plant hormone
Plants produce ethylene in response to stresses such as mechanical pressure, injury, infection, and drought or flood Responses to stimuli Tropisms orient plant growth toward or away from environmental stimuli Tropism ~ responses that causes plants to grow in response to environmental stimuli
Positive tropism cause plants to grow toward a stimulus
Negative tropism cause plants to grow away from a stimulus Plants respond to various environmental stimuli
Phototropism ~ response to light
Gravitropism ~ response to gravity
Thigmotropism ~ response to touch Plants have internal clocks
Circadian rhythms are innate biological cycles of approx. 24 hours
Both plants and animals have circadian rhythms

Circadian rhythms are influenced by environmental cues such as light, but they are controlled by biological clocks
The biological clocks of plants are likely the result of rhythmic production of proteins that influence gene expression Plants mark the seasons by measuring photoperiod
Flowering, seed germination, and dormancy are all seasonal phenomena in plants
Detect season by measuring photoperiod, the relative lengths of day and night
Plant flowering signals are determined by night length
Short day plants flower when the dark period is greater than some critical length
Long day plants flower when dark period is shorter than some critical length
Experiments that altered light and dark periods were used to determine that it is night length and not day length that cues plants to flower Phytochrome is a light detector that may help set the biological clock
Phys constitute a large receptor family sensitive to red and far red light occur implants, (cyano)bacteria and fungi
Pr is naturally produced during dark hours, while Pfr is broken down
The relative amounts of Pr and Pfr present in a plant change as day length changes Water Transport in Plants Molecular movement Molecules and ions are constantly random motion
Diffusion (passive)
Solutes from higher concentration to lower concentration
Maintain equilibrium
Osmosis (passive)
Solvent movement from higher to lower
Active transport
Solutes from low to high concentration
Assisted by proteins/pumps that require energy (ATP) to open
Turgor
Have enough water inside the central vacuole
Maintain the size and shape of the cell
Plasmolysis
Loss of water through osmosis, accompanied by the shrinkage of protoplasm away from the cell wall
Imbibition

The stomata regulate transpiration and gas exchange
Changes in turgor pressures in the guard cells, which contain chloroplasts, occur when they are exposed to changes in light intensity, carbon dioxide concentration, or water concentrations
Stomata are open during the day and closed at night, but water is conserved in a number of desert plants whose stomata open only at night when there is less water stress on plants (CAM photosynthesis)
High humidity reduces transpiration and low humidity accelerates it
If a cool night follows a warm humid day, water droplets may be produced through hydathodes at the tips of veins of the leaf ~ guttation Plant Metabolism Autotrophs are the producers of the biosphere
Able to make own food without organic molecules derived from any other living thing
Photoautotroph ~light
Lithoautotroph
Chemoautotroph Photosynthesis
Takes place in chloroplasts and other parts of green organisms
Light energy is stored in simple sugar molecule
Chloroplasts
consisting of photosynthetic pigments, enzymes, and other molecules grouped together in membranes
Concentrated in the cells of the mesophyll, the green tissue in the interior of the leaf
Two membranes encloses the stroma, the dense fluid within the chloroplast
A system of interconnected membranous sacs called thylakoids segregates the stroma from another compartment, the thylakoid space
Thylakoids are concentrated in stacks called grana
Chlorophyll resides in the thylakoid membranes The principal components of photosynthesis Water
Less than 1% is absorbed and used
Source of oxygen
Limiting factor in photosynthesis Light
Exhibits properties of both waves and particles
About 40% of radiant energy we receive is in the form of visible light Chlorophyll
Most plants have two kinds
𝛼 ~ bluish green C35H72MgN4O
𝛽 ~ yellowish green C55H70MgN4O
𝛼 is three times more than 𝛽 usually
Other pigments
Carotenoids ~ yellow to orange
Phycobillins ~ blue or red
Chlorophyll a, d, e Photosynthesis is a redox process Two major steps in photosynthesis
Light reaction and calvin cycle Light reaction
Light energy converted in the thylakoid membranes to chemical energy and O
Water is split to provide O2 as well as electrons
H+ ions reduce NADP+ to NADPH

Each pigment has its own distinctive pattern of light absorption Pigment absorption spectrum

Pigment absorbs light
Energy levels of some of the pigments electrons are raised
Emitted also in light Each pigment has its own distinctive pattern of light absorption

Pigments, molecules that absorb light are built into the thylakoid membrane
Chloroplasts contain several different pigments and all absorb light of different wavelengths
Chlorophyll a absorbs blue violet and red light and reflects green
Chlorophyll b absorbs blue and orange and reflects yellow-green
The carotenoids absorb mainly blue-green light and reflect yellow and orange Photosystems
The energy released could be lost as heat or light, but rather it is conserved as it is passed from one molecule to another molecule Photosystems capture solar power
All of the components to accomplish this are organized in thylakoid membranes in clusters called photosystems
Photosystems are light harvesting complexes surrounding a reaction center complex
Pigment absorbs photons and pass the energy to the reaction center
Each photosynthetic unit of Photosystem I consists of chlorophyll a and b, carotenoid and a pair of special reaction-center molecule of chlorophyll P
Each photosynthetic unit of Photosystem II consists of chlorophyll a and b, B-carotene and reaction-center molecule of chlorophyll P Overview of the two stages of photosynthesis in a chloroplast Electron flow in the light reactions

A pigment molecule in a light-harvesting complex absorbs a photon of light. The energy is passed on until it reaches the reaction center of Photosystem II to excite electron of chlorophyll P
The electron is captured in the primary electron acceptor
Water is split, its electron electrons are supplied one by one to P680,

A cladogram depicts patterns of shared characteristics among taxa
A clade is a group of species that includes an ancestral species and all its descendants
Cladistics studies resemblances among clades
A shared derived character (apomorphies) is an evolutionary novelty unique to a particular clade Importance of naming plants and classifying them
To impart information about the plant
Necessary for communication
Common names
Native names
International names Division Bryophyta: Mosses
Gametophyte typically consists of small leaflike structures (not true leaves) arranged spirally or alternately around a stem-like axis
The axis is anchored to its substrate by means of rhizoids
Leaves are the only one cell thick (except at the midrib), lack vascular strands and stomata and are haploid Division of Anthocerophyta: Hornworts
Found in tropical forests, along streamsides, and in disturbed fields around the world
The group’s common name “hornwort” refers to the tall narrow sporophytes which are embedded in the top of the plant (gametophyte) Division Hepaticophyta: Liverwort
“Wyrt” means plant
“Liver plant” because flattened gametophyte resembles the liver
Stomata fixed open
Gametophyte stage is dominant stage in both liverworts and hornworts
Viewed as the plants most closely related to the ancestor that moved to land Division Lycopodiophyta: Club mosses, Spike mosses, Quillworts
Plants with true leaves, roots, and stems
Leaves are, without exception, microphylls (one single, unbranched leaf vein) and this is a defining feature of the group
Roots are adventitious

Division Psilophyta: Whisk ferns

The only living vascular plants to lack both roots and leaves
Stem lacks roots, it is anchored instead by a horizontally creeping stem called a rhizome
The erect position of the stem bears paired enations, outgrowths which looks like miniature leaves but unlike true leaves, the enations have no vascular tissue Division Equisetophyta: Horsetail
With a single extant family
Whorled microphylls and hollow, jointed, green stems
Some species have numerous small branches and bear a slight resemblance to a horse’s tail Division Polypodiophyta: Ferns
A group of non seed plants
With true leaves, roots, and stems Gymnosperms and Angiosperms Gymnosperms Cone-bearing
“naked seeds”
Separate male and female gametes
Pollination by wind
With vascular system
Seeds not enclosed in ovary but enclosed in cones or modified leaves
Classified into four divisions
Coniferophyta (same pattern of seed development and with secondary cambium)
Cycadophyta (same pattern of seed development and with secondary cambium)
Ginkgophyta(same pattern of seed development and with secondary cambium)
Gnetophyta (produced true xylem tissue) Gymnosperm Life Cycle
Involves alternation of generation with a dominant sporophyte in which the female gametophyte resides
Male and female reproductive organs can form cones
Male cones (staminate) give rise to pollen grains by meiosis
Pollen grain houses two sperm cells
Yellow pollen is released and carried by the wind during spring
Some gametophytes will land on female cone
One sperm will unite with egg
Upon fertilization, diploid egg will give rise to embryo Coniferophyta/Pinophyta
Dominant group of gymnosperms
Most variety of species
Typically tall trees that usually bear scale-like or needle-like leaves (adaptation)
Predominant at high altitudes and cold climates
Many coniferous trees are harvested for paper, pulp and timber
“softwood” – contains tracheids but no vessel elements Cycadophyta
Thrive in mild climates
Often mistaken for palms
Large cones commonly pollinated by beetles rather than wind (unusual for gymnosperm)
Some face possible extinction
Often used as ornamental plants
Rarely branched trunks with soft pithy wood Ginkgophyta
Fan-shaped leaves
Male and female organs are produced on separate plants
Deciduous
Leaves alternate and simple
“Living fossil” with no close relatives
Single surviving species: Maidenhair tree G. biloba Gnetophyta
Closest relative to modern angiosperm
Includes three orders with one genera each (~70 sp.): Ephedra, Gnetum and Welwitschia
Broad leaves
Vines or small shrubs in subtropical regions
Posses vessel elements in their xylem

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