AP Bio Plants Quiz study guide is written in the frame work of the College Boards’ “Four Big
Ideas”. Pay close attention to the information in red for the quiz. Don’t forget the essays – they
are at the end of the study guide.
Study Guide: Plants
Big Idea 2: Biological systems utilize energy and molecular building blocks to grow, to
reproduce, and to maintain homeostasis
Organisms use various metabolic and reproductive strategies to maximize free energy changes and
minimize disruptions to the population size and to the ecosystem.
Based on its life cycle, a plant is classified as an annual, biennial, or perennial
Annual – germination, flowering and death all occur within one growing season
Biennial – the entire life cycle takes two years; first year includes growth of leaves, stems and
roots and the second year includes growth of the flower
Perennial – grow and bloom every year; require specialized structures for reproduction and
dormancy
In the life cycle of all flowering plants:
 The sporophyte is diploid
 The sporophyte produces heterospores.
 The male gametophyte is the pollen grain.
 The female gametophyte is retained within the body of the sporophyte parent generation.
Growth, reproduction and homeostasis require that cells create and maintain internal environments
that are different from their external environments
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Cell membranes are selectively permeable
Growth and homeostasis are maintained by constant movement of molecules across
membranes
Plasma membranes are selectively permeable and cellular energy or concentration gradients can be
used to drive transport * (for plants as it relates to movement of water and substances through
vascular tissue
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The plasma membrane of plant cells actively transports some mineral ions into the cell.
Guttation - Describes forcing water out of the plant at the edges of its leaves.
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Plasma membranes are semipermeable to regulate what molecules move across the plasma
membrane
Small, nonpolar or uncharged molecules can often move across the lipid bilayer of the plasma
membrane. Large polar molecules and ions need embedded channel and transport proteins to
aid the transport across the membrane.
Molecules can move from high concentration to low concentration through the process of
diffusion.
When ions or polar molecules move from high concentration to low, they pass through a
membrane-bound integral protein in a process of facilitated diffusion.
Osmosis involves the movement of water from high water concentration to low water
concentration or from high water potential to low water potential.
Aquaporins are proteins in the plasma membrane that increase the rate or water transport
across the membrane.
When the water concentration is the same on both sides of a membrane, the two environments
are isotonic.
An environment is hypotonic when it has a higher water concentration or higher water potential
and lower solute concentration.
An environment is hypertonic when it has a lower water concentration or lower water potential
and a higher solute concentration,
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Transpiration - force most responsible for moving water up to the tops of the tallest trees; the
central causative agent of the cohesion-tension model of xylem transport.
 Root pressure – force that pushes water into the xylem as osmosis moves water into the
roots
 Pressure-flow model of phloem transport:
o Phloem sap can move up or down a plant.
o Pressure is created in the phloem by the buildup of water and sugar.
o Sugar produced by photosynthesis is actively transported into phloem cells.
o Sugar is actively transported out of the phloem at a sink area such as the root.
Can you:
Describe the following transport processes: Diffusion, osmosis, and discuss when and where they are
present in plants.
Describe transpiration, root pressure and the pressure-flow model of phloem transport.
Organisms use feedback mechanisms to regulate growth and reproduction, and to maintain
homeostasis.
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Organisms use specific feedback mechanisms to respond to environmental changes.
Positive Feedback is when the cellular processes increase the rate of a chemical reaction or cellular
process and its occurrence further increases the rate. This often leads to a greater degree of instability.
Example: Fruit ripening – a ripe apple releases a hormone (ethylene) to stimulate a variety of enzymes
which converts starch and acids of the unripe fruit to sugars and softens the fruit by breaking down
pectins in the cell wall. Exposure to ethylene stimulates the synthesis of more ethylene creating a
positive feedback loop.
Organisms use cellular mechanisms to respond to environmental changes through behavioral and
physiological mechanisms.
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The effect of length of day and night on plant growth is called photoperiodism. Some plants
require differing lengths of uninterrupted light and/or night.
o Photoperiodism:
 A short-day plant flowers when the day length is shorter than some critical
length.
 A long-day plant will flower even when the day period is not long enough if
there is a short period of light during the dark period.
 A day-neutral plant flowers according to some form of regulation other than
photoperiodism.
o physiological changes related to photoperiodism
 seed germination
 breaking bud dormancy
 some flowering
 onset of senescence
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The direction of plant growth as determined by the direction of the light sources is called
phototropism
Circadian rhythms repeat once a day, persist without specific cues, can be adjusted to match
local time differences and maintain the same clock regardless of temperature. Biological clocks
are present in plants and animals.
circadian rhythms:
o tend to persist even in the absence of daily light cues.
o example is the opening of stomata in the morning and their closing at night.
o The primary usefulness of circadian rhythms seems to be to measure day-length
changes so plants respond appropriately to seasonal environmental changes.
o Example: a plant folds up its leaves each night in accordance with a circadian rhythm.
If a plant were moved to a region that day and night were opposite of where it was
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originally from then the plant could slowly adjust to synchronize with the new daynight cycle.
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gravitropism.
o positive gravitropism the response of roots growing downward
All of the following pertain to movement of plants
o seismonastic movements
o sleep movements
o phototropism
o gravitropism
Organisms have a variety of mechanism to exchange nutrients and wastes with the environment.
Aquatic and terrestrial plants exchange gas with the environment in unique ways. In terrestrial plants,
gas exchange occurs through pores called stomata in the epidermis of the leaf. The stomata are
surrounded by guard cells that regulate the opening and closing of the stomata. In totally submerged
aquatic plants, nutrients and dissolved gases diffuse through the epidermal cells which do not contain
any cuticle. In plants that float above water, stomata may be located on the surface of the leaf, instead
of the underside to maximize gas exchange.
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Leaf stomata allow gaseous carbon dioxide into the leaf, yet preserve the plant's supply of water
o Stomata close on a windy or hot day to prevent too much water loss.
o Tree leaves that orient flat and present the top side to the sun have most of their stomata
on the bottom of the leaf.
o Corn, oats, rice, and wheat—all monocots—have relative upright blades with sunlight
hitting both sides and have stomata distributed fairly evenly on both sides.
o Stomata close at night
Essential to mineral uptake by plant roots are:
o mycorrhizae
o root hairs
o process of active transport
Root adaptations in plants include:
o Some plants, including orchids, require the presence of fungal symbionts to survive.
o Parasitic plants have root adaptations called haustoria that draw nutrients from the host.
o Bacteria of the genus Rhizobium live in root nodules in legumes, producing available
nitrogen that the plant uses.
o Some plants have very poorly developed roots or none at all.
Stomata and guard cells:
o As guard cells become turgid, the stomata open.
o There are two guard cells around each stoma.
o Guard cells take up potassium ions and water enters the guard cells.
o Stomata open and close on a daily basis, even if kept in the dark, on a circadian rhythm.
o carbon dioxide concentration
o blue light of sun light absorbed by flavin pigment causes them to open
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Homeostatic mechanisms support the theory of a common ancestor.
Osmoregulation in terrestrial plants:
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In terrestrial plants, the stomata are critical in regulating water loss through transpiration. The
large central vacuole regulates the concentration of solutes in the cytoplasm of the cell.
Hormones (abscisic acid) regulate stomatal opening and closing to conserve water. Plants have
many adaptations to conserve water including leaf modification, sunken stomata, waxy cuticles,
and stomata location.
Biological systems utilize a variety of mechanism to adjust to disruptions to equilibrium
Plants respond to pathogens and toxins:
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Plants use systemic responses to pathogen defense and have a chemical response system to
destroy infected cells
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Mechanisms by which plants protect themselves against invading bacteria and fungi include
o producing strong protective chemicals.
o maintaining a waxy nonliving cuticle surface.
o building up and replacing an outer layer of dead cork (bark).
o having guard cells open to expose the soft juicy mesophyll of a leaf only when gas
exchange is needed.
Many biological processes involved in growth, reproduction and homeostasis include temporal
regulation and coordination.
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Timing and coordination of specific events are necessary for the normal development of an
organism.
Timing and coordination of physiological events are regulated by multiple mechanisms.
o During seed germination, hormones (gibberillin, abscisic acid, and ethylene) are involved
in negative feedback loops. The production of these hormones is regulated by
additional regulatory genes and transcription factors.
o Plant hormones
 Include at least one form that is a gas.
 Each naturally occurring hormone has a specific chemical structure.
 Are among the principal internal regulators of plant growth.
 Responses to plant hormones may be observed in nearly any part of a plant.
Can you:
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Discuss how plant hormones affect seed germination?
Describe the transduction pathway plants may utilize in their defense against herbivores.
Describe the difference between negative feedback and positive inhibition?
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Big Idea 3: Living systems store, retrieve, transmit, and respond to information essential to life
processes.
Cells communicate by generating, transmitting and receiving chemical signals.
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Cell communication processes share common features that reflect a shared evolutionary
history.
Cells communicate with each other through direct contact with other cells or from a distance via
chemical signaling.
Signal transduction pathways link signal reception with cellular response.
Changes in signal transduction pathways can alter cellular response.
The general sequence by which a plant responds to stimuli is:
o reception-transduction-response.
Cell to cell communication can occur by cell to cell contact, as well as at the local or long distance level
at the cellular, organismal or ecosystem level.
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Cells must communicate to coordinate their activities
Cells communicate by direct contact through cellular junctions or by the signal molecule
dissolving in the cytoplasm.
o Autocrine signaling – a cell signals other cells at a distance by secreting hormones
(endocrine factors) or chemical messengers that bind to autocrine receptors on a cell
leading to changes in that cell.
o Paracrine Signaling – form of cell communication in which a cell produces a signal to
induce changes in nearby cells, altering the behavior or differentiation of nearby cells.
Signaling molecules known as paracrine factors diffuse over a relatively short distance
(local action) as opposed to endocrine factors.
Plasmodesmata are specialized cellular structures for communication in plants. Phloem loading
(transduction) may occur via plasmodesmata.
Plants use cell communication to respond to pathogens and insects.
o Plants do not produce antibodies or T-cell responses
o Plants secrete chemical compounds to make them less attractive
o Some plant parts are disposable so this is an option for plant immune system response
o Receptors on plant cells identify pathogens and trigger elicitors which trigger apoptosis
in some plant cells
Can you:
Describe how plants and animals communicate differently?
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Transmission of information results in changes within and between biological systems
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Organisms can act on information and communicate it to others.
Organisms can detect external and internal signals, transmit and integrate information, and
produce responses.
Transcription factors affect gene expression.
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Temperature, as well as water and oxygen availability, affects seed germination in plants.
Germination is the process where a plant emerges from a seed. Seeds often have an optimum
temperature range. This range can be cool (28-40 F) or warm (76-90 F). Seeds will not
germinate while dormant even if conditions are favorable.
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Depending on the species of plant, germination of the seeds may require:
o oxygen for increased metabolism.
o adequate temperature.
o adequate water.
o exposure to light.
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Plant species/populations can "migrate," due to seed dispersal
Seeds contain
o an embryo sporophyte.
o stored food.
o Integuments - the protective layer around an ovule that becomes the seed coat
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Fertilization occurs when the pollen grain germinates.
Some plants seeds "know" when it is day and night, and when to germinate because:
o Phytochromes cycle between red and far-red absorption and light levels can inhibit or
promote germination.
Gene expression can be modified by other factors
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Internal molecular signals in plants include phototropism and photoperiodism.
o Phototropism occurs when plants grow in a direction determined by light. It can also
occur in fungi. Phototropism is directed by photosensitive receptors called
phototropins and phytochromes or cryptochromes. Specific sections of plants react
differently to light e.g. stems, roots)
o Plant hormones are responsible for the activation of enzymes to reduce rigidity of cell
walls that can cause cell walls to swell.
o Photoperiodism occurs when plants have seasonal changes in photoperiod to flower.
This is also dependent upon photoreceptor proteins.
o Photoperiodic plants are classified as long day plants or short day plants. This is
regulated by the hours of darkness.
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Can you:
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Describe germination?
Discuss the difference between long day and short day plants?
Explain how phototropisms work?
Describe a signal transduction pathway?
Big Idea 4: Biological systems interact, and these interactions possess complex properties
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Competition and cooperation are important aspects of biological systems
Interactions between molecules affect their structures and function.
Cooperative interactions within organisms promote efficiency in the use of energy and matter.
Efficient functioning of organisms is often due to interactions within organisms.
Compartmentalization is a technique that organisms use to ensure that tasks are completed efficiently.
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For multicellular organisms, at the organismal level, organs work together in organ systems to
complete a specific function. This collection of tissues is unique for specific organs.
o In plants, gases pass through pores called stomata in the cuticle and epidermis of the
terrestrial plant. In aquatic plants, water passes through the tissues and the gases
diffuse into the liquid.
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In leaves:
o The epidermis is covered by a waxy layer of cuticle that reduces water loss.
o Gas exchange occurs through tiny openings in the leaf surface called stomata.
o Regulation of gas exchange through the leaf is the responsibility of the guard cells.
o Vascular tissue is arranged in a net pattern in dicots and a parallel pattern in
monocots.
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Phloem - Vascular tissue that transports organic nutrients from the leaves to the roots is
Naturally occurring diversity among and between components within biological systems affects
interactions with the environment
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Variation in molecular units provides cells with a wider range of functions.
Environmental factors influence the expression of the genotype in an organism.
Organisms adapt to their local environment based upon pressures.
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There are timing alterations in flowering due to climate changes.
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Essays:
Organisms evolved in a world in which they were both constrained by and subject to the laws of
physics and chemistry. Explain how plants manage to utilize the principles of physics and chemistry
for the process of transpiration (movement of water) and translocation (movement of carbohydrates).
It has been suggested that stomata are controlled by the action of a flavin pigment which absorbs
blue light and activates proton pumps and ultimately leads to stomatal opening.
a. Explain how the action of the proton pumps leads to the opening of the stomata.
b. State a hypothesis that can be tested to examine the possibility that blue light may be
activating a flavin pigment leading to the opening of the stomata. Then design an experiment
to test that hypothesis.
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