Terms in this set (151)
Dermal tissue system
forms the epidermis of a plant and usually consists of a single cell layer. The stems and roots of woody plants develop dermal tissue called periderm.
Ground tissue system
Virtually all the tissue lying between the dermal tissue and the vascular tissue in both shoots and roots is part of the ground tissue system. Therefore the ground tissue makes up most of the plant body. The ground tissues function primarily in storage, support, and photosynthesis. There are three types of cells classified according to their cell wall structure: parenchyma, collenchyma, sclerenchyma
Most common cell type in plants. Have large vacuoles and thin walls consisting only of a primary wall and the shared middle lamella. Parenchyma cells play important roles in photosynthesis; proteins, starch, fats, or oils may be stored in parenchyma cells of the seeds and/or roots. Many retain the capacity to divide and give rise to new cells, as when a wound results in cell proliferation.
The middle lamella is a layer of pectin that cements adjacent plant cells together.
Resemble parenchyma cells that have been modified to provide flexible support. They are generally elongated, and their primary walls are characteristically thick at the corners of the cells. In these cells the primary wall thickens in part because of the deposition of pectins, but no secondary wall forms. Collenchyma cells provide support to leaf petioles, nonwoody stems, and growing organs. Tissue make of collenchyma is flexible, permitting stems and petioles to sway in the wind without snapping.
Sclerenchyma cells have thickened secondary walls that enable cells to perform their major function: support. Many sclerenchyma cells undergo programmed cell death after developing the lignified secondary walls, and thus perform their supporting function when dead. There are two types: fibers and sclereids.
Are sclerenchyma cells that are elongated. They are often organized into bundles and provided relatively rigid support to wood, bark, and other parts of the plant.
Sclereids may pack together densely, as in a nut's shell or in some seed coats. Isolated clumps of sclereids, called stone cells, occur in pears and some other fruits and give them their characteristic gritty texture.
Vascular Tissue System
The vascular tissue system is the plant's plumbing, or transport system. Its constituent tissues, the xylem and phloem, distribute minerals throughout the plant
Distributes water and mineral ions taken up by the roots to all the cells of the stems and leaves. It is unidirectional and can only transport nutrients from roots to shoots using negative pressure
Phloem performs a variety of functions, including transport, support, and storage. All the living cells of the plant body require a source of energy and chemical building blocks. The phloem meets these needs by transporting carbs away from the sites of production, called sources (primarily leaves). The carbs are transported to site of utilization or storage called sinks. Sinks include growing tissues, storage organs and developing flowers.
Can have a flow rate of up to 100cm an hour
Bidirectional (different sieve tube elements can move different directions)
Part of xylem tissue that have secondary cell walls and undergo apoptosis before assuming their function of transporting water and dissolved minerals. There are two types of tracheary elements: tracheids and vessel elements
Tracheids are spindle-shaped and are evolutionarily more ancient than vessel elements and are the major cell type in wood of gymnosperms. When tracheids die, their internal composition disintegrate and pits remain between the cells.
Pits are part of tracheids. They are cavities in the secondary walls spanned by porous structures that allow minerals to move between tracheids and thus through the xylem tissue.
Are in flowering plants. These cells are laid down end-to-end. They have pits in their cell walls, but their pits are generally larger in diameter than those in tracheids. Before they undergo apoptosis, the end walls of vessel elements partially break down, forming a continuous hollow tube that functions as an open pipeline for water conduction. They are shorter and wider then tracheids, and their end walls have become less oblique.
Sieve Tube Elements
Part of the phloem. Like vessel elements, these cells meet end-to-end. They form long sieve tubes, which transport carbohydrates and many other materials from their sources to tissues that consume or store them. The end walls for sieve tube elements contain plasmodesmata which enlarge to form pores. The end look and function like sieves and are called sieve plates. Although these cells remain alive, some of their components, including the nucleus, ribosomes, and vacuole, break down during development. So they need companion cells. They are connected to those by plasmodesmata.
Companion cells are specialized parenchyma cells that retain their organelles and function as "life support systems" for the sieve tube elements. They are connected to those by plasmodesmata.
Primary growth is characterized by cell division followed by cell enlargement. It results in the proliferation and lengthening of shoots and roots. All seed plants have a primary plant body, which consists of all the nonwoody parts of the plant. Many herbaceous plants consist entirely of a primary plant body
Secondary growth increases plant thickness. Woody plants, such as trees and shrubs, have secondary plant body consisting of wood and bark. As the tissues of the secondary plant body are laid down, the stems and roots thicken.
cells that perpetuate the meristems and are comparable to animal stem cells
Apical meristems in the root and shoot orchestrate primary growth, ultimately giving rise to every cell in the primary plant body.
When initials of apical meristems divide, some of their daughter cells differentiate into primary meristems. Three kinds exist and give rise to the three major tissue systems: Lateral, vegetative, and root
Lateral meristems (also called secondary meristems) orchestrate secondary growth. Two lateral meristems, vascular cambium and cork cambium, contribute to the secondary plant body
Also called shoot apical meristems supply the cells for new leaves and stems. In addition to the main stem of the plant, each branch has its own shoot apical meristem.
Root Apical Meristems
Supply the cells that extend roots, enabling the plant to penetrate and explore the soil for water and minerals. each type of root has its own root apical meristem.
From the outside to the inside of the shoot or root, the primary meristems are:
Protoderm, ground meristem, and the procambium. They give rise to, in oder: dermal tissue system, ground tissue system, vascular tissue system.
Protects the delicate growing region of the root as it pushes through the soil. Secretes a mucopolysaccharide (slime) that acts as a lubricant. Even so, the cells of the root cap are often damaged or scraped away and must therefore must be replaced
Quiescent center of root apical meristem
Place in which cell division is rate. However, can become more active when needed, like following an injury.
Zone of cell division
Part of apical and primary meristems which is the source of all the cells of the root's primary tissues.
Zone of elongation
Just above the zone of cell division where newly formed cells are elongating and thus pushing the root farther into the soil
Zone of maturation
Is where the cells are differentiating, taking on specialized forms and functions.
Produced from epidermal cells and vastly increase the surface area of the root allowing for absorption of mineral ions and water. Grow out into the soil particle, probing nooks and crannies and taking up water and minerals
Internal to the epidermis, ground tissue gives rise to a region of ground tissue that is many cells thick, called the cortex. The cells in the cortex are relatively unspecialized and often serve as storage depots. Innermost layer of the cortex is the endodermis
The innermost layer of the cortex and contain a waterproof substance called suberin in their primary cell walls. Suberin forms a cylindrical ring around the inside of the endodermis, which allows the endodermal cells to control the movement of water and dissolved mineral ions into and out of the vascular tissue system
Produced by the procambium and part of the endodermis. Contains three types of tissue, pericycle, xylem, phloem. Go to life10e.com/ac34.1 and Life10e.com/ac34.2
The pericycle consists of one or more layers of relatively undifferentiated cells. It has three important functions: 1. It is the tissue within which lateral roots arise 2. It can contribute to secondary growth by giving rise to lateral meristems that thicken root 3. Its cells contain membrane transport proteins that export nutrient ions into the cells of the xylem
A region of cells in monocots that lies in the center of the root, surrounded by xylem and phloem. Stores carb reserves and is also found in the stems of both eudicots and monocots.
The embryonic root which angiosperms develop from
The primary root which most radicles of eudicots develop into. It extends downward by tip growth and outward by initiating lateral roots.
Taproot and lateral root form this and can take on a variety of forms. For example the taproot often functions as a nutrient storage organ.
The roots of monocots and often form fibrous root systems composes of numerous thing roots that are all roughly equal in diameter. This root system clings to the soil very well and often when on steep hills prevent erosion
Adventitious roots that grow down from above the ground and function as props to help support the shoot
Shoot Apical Meristem
Where phytomers responsible for shoot growth come from. They are present in the terminal buds of each branch and the main stem. Like the root apical meristem, gives rise to protoderm, ground meristem, and procambium which in turn give rise to the three shoot tissue systems
Leaf primordia are bulges on the sides of the shoot apical meristem that occur at regular intervals that develop as the shoot grows and extends. They are made up of primary meristematic tissues, which go on to develop into the mature tissues of the leaf
Form on the base of the leaf primordia. They have the potential for becoming new apical meristems and initiate new shoots.
Vascular systems of root
Lie deep in the interior, with the xylem near or at the center
Vascular systems of stems
In a young stem is divided into discrete vascular bundles.
Vascular systems in in stems that contain both xylem and phloem. In eudicots the vascular bundles are generally form a cylinder, whereas in monocots they are scattered
Differences in Leaves vs. Stems
A highly simplified way to think of the development of leaves is that a leaf primordium is a flattened stem. However there are two differences:
1. Unlike the growth of stems, which is indeterminate, the growth of a leaf is determinate
2. Whereas the tissues of the stem are arranged in a radial pattern, the leaf, as a flat organ, has a distinct top and bottom
Photosynthetic parenchyma tissue in leaves. There are two zones, the upper layer of elongated cells called the palisade mesophyll, and a lower player of irregularly shaped cells called the spongy tissue. Within the mesophyll, there is a great deal of air space through which CO2 can diffuse to photosynthetic cells.
a cylindrical layer of tissue derived from secondary growth consisting predominately of elongated cells that divide frequently. It supplies the cells of the secondary xylem and the secondary phloem, which eventually become wood and bark. Only in plants that have secondary growth (aka eudicots, not monocots)
Derived from secondary growth and produces mainly waxy-walled protective cells. It supplies some of the cells that become bark.
How vascular cambium grows and produces secondary phloem and xylem
Initially it is a single layer of cells lying between the primary xylem and the primary phloem within vascular bundles. The root or stem system increases in diameter when the cells of the vascular cambium divide, producing secondary xylem cells towards the inside of the root or stem and producing secondary phloem cells toward the outside. It also produces vessel elements, tracheids, and supportive fibers in the secondary xylem; and the sieve tube elements, companion cells, fibers, and parenchyma cells in the secondary phloem.
In plants, there is a circular ring of vascular cambium. From that arises the secondary xylem. It is what becomes the wood of the plants.
Comes from the vascular cambium and contributes to the bark.
Is made up of the periderm and the secondary phloem, or all the layers external to the vascular cambium
Spongy regions of the periderm that allow for gas exchange because when periderm forms on the stems or roots, the underlying tissue needs to release CO2 and take up O2 for cellular respiration.
Also known as Ψ, is defined as the tendency for a solution to take up water from pure water across a membrane. The water potential of pure water is zero. A solution with a water potential less than zero has a tendency to take up water from surroundings, vice versa if higher. The lower the water potential, the greater the driving force for water movement across the membrane. Has two major components: Ψs and Ψp
Ψs and Ψp
Ψs: the solute potential. The Ψs of pure water is zero so any solution will create a negative solute potential. The greater the concentration of solute, the lower the water potential the and lower the solute potential. More solutes will take up more water
Ψp: the pressure potential. As plants take up water, they tend to swell. The cell wall provides resistance to swelling. The result is an increase in turgor pressure which decreases the tendency for the cell to take up more water. There the pressure potential within a plant cell is usually positive.
Ψ = Ψs + Ψp
The equation for water potential. If the overall equation, water will be taken up, if positive, will be released. It is measured in MPa
When a cell has significantly positive pressure potential
Gradient of Pressure Potential
Is what is responsible for water movement over long distances in unobstructed tubes such as xylem vessels and phloem sieve tubes. The water moves from higher pressure (at the bottom) to lower pressure (at the top)
The movement from high to low pressure. Bulk flow in xylem is between regions of differing negative pressure potentials (tension) and the bulk flow in phloem is between regions of different positive pressure potentials (turgor pressure)
Movement of materials across root cell plasma membrane
Impeded by two things:
1. The membrane is hydrophobic, whereas water and mineral ions are polar
2. Some mineral ions must be moved against their concentration gradients
1. Aquaporins which are located in the plasma membrane and the tonoplast of a cell and allow water to diffuse rapidly. They are passive proteins so can only move the water from higher potential to lower
2. Ion channels and pumps ions either by facilitated diffusion (with gradient) or active transport (against the gradient) which requires energy.
Proton pump in plants
Plants do not use sodium-potassium pumps like animals to drive active transport but rather use a proton pump which uses energy obtained from ATP to move protons out of the cell against a proton concentration gradient. This results in two things:
1. An electrical gradient is created, with region outside the cell more +
2. A proton concentration gradient is created, with more H+ outside
Since the inside of the cell is more negative than the outside, it allows cations to move into the cell by facilitated diffusion. The energy from the gradient can be harnesses to help in active transport of anions
Consists of the cell walls and the intercellular spaces that are common in many plant tissues. It is a continuous meshwork through which water and solutes can flow without having to cross a membrane and the movement of the materials is unregulated and rapid
Solutes and sugars move out of the mesophyll cells and then diffuse through the apoplast to the sieve tubes. Specific sugars and amino acids are then actively transported into the sieve tube elements
Is the continuous cytoplasm of the living cells, which are connected by plasmodesmata. The selectively permeable plasma membranes of root cells control access to the symplast so movement of water and solutes is tightly regulated.
solutes remain within the symplast and pass through plasmodesmata all the way from the mesophyll cells to the sieve tube cells. Since no membranes are crossed, the solutes are loaded into the phloem by mechanisms other than active transport
Is on the endodermis only. It is a waxy, Suberin-impregnated region of the endodermal cell wall that forms a hydrophobic belt around each endodermal cell where it is in contact with another endodermal cell. It acts as a seal that prevents water and ions from moving through the apoplastic spaces between endodermal cells. Means that water and ions must enter the symplast to cross endodermis into the stele which contains the vascular tissue of he root. These materials pass from the endodermal cells to cells in the stele via plasmodesmata
Accounts for xylem transport.
Transpiration of water molecules from the leaves by evaporation
Cohesion of water molecules in the xylem sap from the leaves to the roots
Tension in the xylem sap resulting from the
transpiration from the leaves
Water evaporates from the leaves of the plant and creates increased tension (or a negative pressure potential) and the cohesion between water molecules prevents the column of water from breaking
Part of the leaf where CO2 is let and often leads to heavy loss of water. They are usually on the bottom of the leaf to prevent water loss due to evaporation
Are around the stomatal openings and control when they open and close.
How guard cells control the opening and closing of stomatal cells
1. In light, a pigment in guard cells absorbs blue light, which activates proton pump that actively transports H+ out of the guard cell thus facilitating the entry of K+ and Cl-
2. Higher internal K+ and Cl- concentrations give guard cells a more negative water potential, causing them to take up water, increase pressure, and stretch, opening the stoma
3. In the absence of light, K+ and Cl- diffuse passively out of the guard cells and water follows by osmosis. The guard cells shrink and the stoma closes.
Additionally, stomata respond to water availability. On hot dry days the plants will close their stomata. The water potential in the mesophyll is the signal as when it is too dehydrated, its cells release the hormone ABA (abscisic acid) which causes the guard cells to close
The movement of carbs and other solutes through the phloem
The products of photosynthesis
Girlding a Tree
Phloem moves nutrients and it is part of the bark. By girdling the tree (removing a ring of bark from the trunk of tree) you can kill the tree because eliminate the ability to move sucrose and other nutrients. Additionally, the tree swells above the removed bark due to nutrient build up
Contents of Phloem
90% sucrose, but also contains hormones, small molecules such as amino acids mineral nutrients, and viruses
Pressure Flow Model of translocation in phloem
1. Transpiration pulls water up the xylem vessels
2. Source cells load sucrose into phloem sieve tubes, reducing their water potential...
3. so water is taken up from the xylem vessels by osmosis, raising the pressure potential in the sieve tubes.
4. Internal pressure differences (in this case higher at the top of the tube) drive the sap along the sieve tube to the sink cells
5. Sucrose is unloaded into the sink cells, increasing the water potential in the sieve tube...
6. ...and the water move back to xylem vessels
After arriving at the sink, the solutes are actively transported out of the sieve tube elements into the surrounding tissue which helps:
1. maintain the gradient of solute potential and hence of pressure potential in the sieve tube
2. it supplies carbs and amino acids to developing organs
3. helps build up high concentrations of proteins and carbs in storage organs
Mechanisms for sap flow in plant vascular tissues
Driving Force for bulk flow
Xylem: transpiration in leaves
Phloem: Active transport of sucrose at source and sink
Site of bulk flow:
Xylems: nonliving vessel elements and tracheids
Phloem: Living sieve tube elemts
Pressure potential in sap:
Xylem: Negative (pull from top; tension)
Phloem: Positive (push from source; pressure)
Needs concentrations of at least 1 gram per kg of plant dry matter
carbon, hydrogen, oxygen, nitrogen. Hydrogen comes mainly from water. Nitrogen enters most plants from the soil which can be aided by the activity of microorganisms that convert nitrogen into forms that can be used by the plants
Needs concentrations of less than 100 milligrams per kg plant dry matter
Iron, Chlorine, Manganese, Boron, Zinc, and others
What soil provides plants
1. Mechanical Support
2. Mineral nutrients and water from soil solution
3. O2 for root respiration
A Horizon: is the topsoil that supports the plant's nutrients needs. It contains most of the soil's living and dead organic matter
B Horizon: is the subsoil, which accumulates materials from the topsoil above it and from the parent rock below.
C Horizon: is the parent rock, also called the bedrock, that is in the process of breaking down to form soil
Soil that is the optimal mixture of sand, silt, and clay and thus has the sufficient levels of air, water, and available nutrients
created by microorganisms break down dead leaves and other plant organs on the ground. It is used as food source for microbes that break down complex molecules into the soil solution. It also helps provide air spaces that increase O2 availabilty
Cation Exchange of Soil
1. A clay particle, which is negatively charged, binds cations.
2. The cations are exchanged for hydrogen ions obtained from the root hair of plant or carbonic acid made from the CO2 released from the root
3. Mineral cations are released into soluton
Plants roots produce compounds called strigolactones that stimulate rapid growth of the fungal hyphae (the part of the fungus that grows) toward the root. In fungi then produce a signal that stimulate the expression of plant symbiosis-related genes. The product of some of this guides the fungal hyphae to grow into the cortex of the plant. Arbuscules are the places of nutrient exchange between fungus and plant which are in the root cortical cells.
The primary nutrient from the mycorrhizae is phosphorous. The fungus in turn for providing P gets every from the plant
Root nodules and rhizobia bacteria
In legumes, a form of symbiosis with soil bacteria can occur. The legume releases chemical signals that attract the rhizobia in the area. The signal also triggers the transcription of genes that makes nodulation factors. When these factors are secrete by the bacteria, it causes the cell root cortex to divide, and create a root nodule. The bacteria enter the root and become bacteroids -- a form of bacteria that can fix nitrogen
A plant produced protein in the cytoplasm of a nodule which is an O2 carrier. Transports enough oxygen to the nitrogen-fixing bacteria to support their respiration while keeping free O2 concentrations low enough to produce nitrogenase
the part of a parasite that invades the host and taps into the vascular tissue in the root or stem
Hemiparasites still photosynthesize but derive water and mineral nutrients from the host plant. Mistletoe is an example of this type of plant
Are completely parasitic and do not perform photosynthesis
Key factors in regulating plant growth and development
Environment cues, receptors, hormones, regulatory proteins and enyzmes
Suspended embryo development. Mechanisms for mainting dormancy:
Exclusion of water or oxygen from the embryo by impermeable seed coat.
Mechanical restraint of the embryo by a tough seed coat
Chemical inhibition of germination of growth regulators
Photodormancy: some plants need a period of light or dark before the can germinate
Themodormancy: some seeds need high or low temperatures to germinate
The uptake of water and is the first step of germination
Monocot seed germination
1. a coleoptile (a cylindrical sheath of cells) protects the early shoot as it grows to the soil surface
2. after the shot emerges from the soil, it continues to elongate and the leaves emerge
Eudicot seed germination
1. The shoot apex of most eudicots is protected by cotyledons as the upper part of the plants if pulled above the surface.
2. When the shoot elongates, the first foliage leaves emerge
Abscisic Acid (ABA)
hormone that maintains dormancy
Promote stem elongation, adventitious root initiation, and fruit growth
Inhibits axillary bud outgrowth, leaf abscission, and root elongation
Is responsible for phototropism, root initiation, leaf abscission, apical dominance, fruit development, cell expansion
Promote stem and pollen tube elongation and promote vascular tissue differentiation
Inhibit leaf senescence
promote cell division and axillary bud outgrowth, affect root growth
Promotes ripening and leaf abscission
Inhibits stem elongation and gravitropism
Promote seed germination, stem growth, and ovule and fruit development, break winter dormancy, mobilize nutrient reserves in grass seeds
Herbivores induce plant defense throughout plant when this hormone is transported in the phloem
detect changes in the quality and the direction of light as well as the timing of light availability. They are often proteins associated with pigments. Light acts directly on the photoreceptor which regulates the development processes that need to be responsive to light.
a response to light in which the plant stems bends toward the light source. It seems to from the tip of the shoot down the plant and across the plant (if you place an impermeable plate vertically in the plant tip, it will not bend)
Acid Growth Hypothesis
Explains how auxin-induced cell expansion works.
1. Protons are pumped from the cytoplasm into the cell wall, lowering the pH of the cell wall
2. This activates enzymes called expansins that catalyze changes in the cell wall structure that such as that the polysaccharides adhere to each other less strongly
3. This makes it easier for the plant to stretch
Auxin has two roles in this process:
1. increase the synthesis of the proton pumps
2 guide their insertion into the plasma membrane
How Gibberellins and Auxin Work
1. In the absence of the hormone, a repressor inhibits transcription of growth-stimulating genes
2. Hormone binds to a receptor protein, and the complex enters the nucleus
3. The hormone-receptor complex binds to the repressor
4. Binding stimulates the addition of ubiquitin to the repressor
5. The repressor is broken down in the proteasome. Growth stimulating genes are now transcribed
is the photoreceptor that turn red light to far red light
The plant we see in nature is sporophyte, and the male or female gametophytes are contained in the flowers.
Usually diploid. It is the zygote after fertilization, which turns into a multicellular sporophyte which undergoes meiosis to turn haploid
haploid, via mitosis it turns into a multicellular gametophyte and via mitosis turns into gametes
female sex organ of plants that contains the developing female gametophyte
Male sex organ of plants that contains the developing make gametophyte
have both male and female flowers on the same plant
species that have male and female flowers on different plants
embryo sac (angiosperm)
the female gametophyte (also called a megagametophyte) and it develops inside an ovule. One or more ovules are contained within the ovary
pollen grains (angiosperm)
the male gametophyte (also called the microgametophyte) which development inside the anther, on the stamen
Female gametophyte (angiosperm)
Of the four haploid megaspores resulting from meiosis, three undergo apoptosis. The remaining one undergoes 3 mitotic divisions without cytokinesis producing 8 haploid nuclei, all initially contained in one cell. Cell wall formation leads to a 7 cell 8 nuclei megagametophyte
the cells in the megagametophyte that participate in fertilization by attracting the pollen tubes. The pollen tube enters one of the synergids before the sperm cells are released for fertilization
Male gametophyte (angiosperm)
four haploid products of meiosis each develop a cell wall and undergo a single mitotic division producing four two-celled pollen grains.
After pollination the generative cell divides by mitosis to form two sperm cells that participate in fertilization
The tube cell forms the elongating pollen tube that delivers the sperm to the embryo sac
Sexual Reproduction in Angiosperms
1. The microspore undergoes mitosis, forming a tube cell and a generative cell
2. In the ovule, three of the four meiotic products degenerate
3. The embryo sac is the female gametophyte. After three mitotic divisions, it contains eight haploid nuclei
4. the pollen grain is transferred to the stigma (pollination)
5. the pollen tube grows the embryo sac
6. One sperm cell fuses with the egg cell
7. The second sperm cell fuses with the central cell, the the polar nuclei fuse with the sperm nucleus (end up with 2n zygote and the 3n endosperm nucleus)
8. the fruit is derived from the ovary wall and aids in seed dispersal
are triploid (from the second fertilization)
occurs in angiosperms. One pollen cell fertilizes the egg cell forming a 2n zygote, the other fuses with the central cell, forming a 3n nucleus
Meristem identity genes
LEAFY1 and APETALA1
Is the length of day (or rather night) that a plant needs in order to flower
Short day plants
Flower only when the day is shorter than the critical maximum. It needs the uninterrupted amount of dark
Long day plants
Flower only when the day is longer than the critical minimum. It needs the uninterrupted amount of dark
is a gene whose expression follows a circadian rhythm and encodes for the transcriptional regulator that controls for the expression of flowering genes.
1. photoperiodic stimulus at leaf companion cell stabilizes CO, which acts a transcription factor
2. FT is made and enters sieve tube element through plasmodesmata
3. FT is transported through the phloem up to the apical bud
4. FT combines with FD, and the complex acts as a transcription factor for AP1
5. AP1 is made and acts to initiate flowering
FT is a small protein that can travel through plasmodesmata. FT synthesized in the phloem companion cells of the leaf and then diffuses to the adjacent sieve tube elements. It then goes to the apical meristem. If the FT gene is coupled to an active promoter and expressed at high levels in the shoot meristem, flowering is induced even in the absence of an appropriate photoperiodic stimulus
encodes for a protein that binds to FT protein when it arrives in the apical meristem. FD when bound to FT activates promoters for meristem identity genes, such as APETALA1. The expression of FD primes meristem cells to change from a vegetative fate to a reproductive fate once FT arrives
Needing extended periods of cold to flower
Position gradient pathway
plants need to be a certain size to flower
pathogen defense that is always present in the plant
pathogen defense that is produced in reaction to damage or stress
Avirulence (Avr) genes
help prevent against pathogens.
1. If the host and pathogen have matching R and Avr genes, the plant will resist the pathogen.
2. but if either half is missing, the plant will be susceptible
Process of Alteration of Generations
1. gametophyte produces haploid gametes by mitosis
2. two games unite (fertilization) and form a diploid zygote
3. the zygote develops into a multicellular diploid sporophyte
4. the sporophyte produces unicellular haploid spores by meiosis
5. the spore develop into multicellular haploid gametophytes
are multicellular organs that produce spores. Within it, they have diploid cells called sporocytes or spore mother cells
is a pear shaped organ that produces a single nonmotile egg retained within the bulbous part of the organ. Not in angiosperms but in everything else
produce sperm and release them into the environemnt
are "naked seed" plants because their seeds are not enclosed in chambers.
MOSS IS AN EXAMPLE (and liverwort and hornwort)
Haploid gametophyte is the dominant stage of life cycle.
They require water is disperse spores.
Gametophores are the gamete-producing structure
No vascular system
Most gametophytes are bisexual
Life Cycle of Moss
1. the spores develop into threadlike protonemata
2. the haploid protonemata produce "buds" that divide and grow into gametophytes (either male or female) which have on them either the antheridia which produce the sperm or the archegonia that produce the eggs
3. Sperm must swim through film of moisture to reach the egg to fertilize
FERTILIZES within an archegonium to make a diploid zygote
4. the zygote develops into a sporophyte embryo
5. the sporophyte grows a long stake that emerges from the archegonium
6. Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte
7. meiosis occurs and haploid spores develop in the capsule. When the capsule is mature, its lid pops off, and the spores are released
Life cycle of a Fern
1. Sporangia releases spores. Most fern species produce a single type of spore that develops into a bisexual photosynthetic gametophyte
2. Each gametophyte develops antheridia and archegonia
3. Sperm use flagella to swim to eggs in the archegonia. An attractant secreted by archegonia helps direct the sperm
4. a zygote develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte.
5. grows into a fern
6. on the underside of the sporophyte's leaves are spots called sori. Each sorus is a cluster of sporangia
PS680 and PS700
Chlorophyll a pigment molecules that get excited during photosynthesis and excite electron to a higher energy state that then releases energy. The electron is transferred to a primary electron acceptor
Cyclic Electron Flow
In photosystem, photoexcited electrons are occasionally shunted back from ferredoxin (fd) to chlorophyll via the cytochrome complex (that happens btwn PS II and PS I). The supplements the supply of ATP (via chemiosmosis) but does not produce ATP. Basically, it recycles the energy back into itself