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Questions and Answers

What is the primary function of fruit in plants?

To provide nutrients to the plant

To attract pests for pollination

To store water for the plant

To facilitate the dispersal of seeds (correct)

Which type of fruit is formed from a single flower with multiple carpels?

Multiple fruit

Accessory fruit

Simple fruit

Aggregate fruit (correct)

What adaptation is typically associated with seed dispersal by wind?

Brightly colored edible fruit

Winged or feather-like structures (correct)

Heavy, fleshy fruit

Spiny hard shells

What term describes an organism that contains a gene from another species?

Transgenic organism Signup and view all the answers

Which hormone is primarily responsible for promoting cell elongation?

Gibberellins Signup and view all the answers

How does auxin typically influence plant growth?

By promoting apical dominance Signup and view all the answers

What physiological response occurs due to high levels of abscisic acid (ABA) in seeds?

Seed dormancy Signup and view all the answers

What is the 'triple response' in plants subjected to mechanical stress?

Stem elongation, thickening, and curvature Signup and view all the answers

What is the primary function of blue light photoreceptors in plants?

Triggering phototropism and de-etiolation Signup and view all the answers

Which of the following is NOT a way that plants can respond to water deficit?

Producing more chlorophyll for photosynthesis Signup and view all the answers

What role do phytochromes play in seed germination?

They influence germination by detecting light wavelengths Signup and view all the answers

Which phenomenon involves the response of plants to mechanical stress such as wind?

Thigmomorphogenesis Signup and view all the answers

What is the critical night length concept in relation to plants?

It refers to the total number of hours of darkness a plant experiences in a day. Signup and view all the answers

What is the primary difference between macronutrients and micronutrients?

Macronutrients are needed in larger quantities than micronutrients. Signup and view all the answers

Which of the following is NOT considered an essential macronutrient for plants?

Copper Signup and view all the answers

What are the three main elements commonly found in chemical fertilizers?

Nitrogen, Phosphorus, Potassium Signup and view all the answers

In which part of the plant do mineral nutrients mainly need to be for effective root uptake?

In the soil solution Signup and view all the answers

Which ion is crucial for establishing the membrane potential in plants?

H+ Signup and view all the answers

What is the primary driving force for water transport in plants according to the cohesion-tension hypothesis?

Transpiration from leaves Signup and view all the answers

What phenomenon occurs when the solute concentration increases in an area?

The number of free water molecules decreases. Signup and view all the answers

What usually causes guard cells to open stomata in the morning?

Increased light intensity Signup and view all the answers

Which of the following are examples of a sugar sink in plants?

Flowers Signup and view all the answers

What mechanism drives the transport of nutrients from the source phloem to the sink in plants?

Pressure flow mechanism Signup and view all the answers

What distinguishes a gametophyte from a sporophyte in the plant life cycle?

Gametophytes are haploid, sporophytes are diploid. Signup and view all the answers

Which of the following describes the term heterospory?

Producing two types of spores: microspores and megaspores. Signup and view all the answers

What is a major evolutionary advantage of having seeds?

Seeds protect the embryo and help in dispersal. Signup and view all the answers

In seedless vascular plants, what distinguishes the gametophyte-sporophyte relationships compared to bryophytes?

Sporophytes are always dominant in seedless vascular plants. Signup and view all the answers

How many cotyledons does a typical eudicot seed possess?

Two Signup and view all the answers

What develops inside the ovules during female gametophyte formation?

Megaspores Signup and view all the answers

Study Notes

Macronutrients and Micronutrients

Macronutrients: Elements plants need in relatively large amounts.
Micronutrients: Elements plants need in smaller amounts.

Essential Macronutrients

Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Phosphorus (P)
Potassium (K)
Calcium (Ca)
Magnesium (Mg)
Sulfur (S)

Chemical Fertilizer: The Big Three

Nitrogen (N): Found as ammonium (NH₄⁺) or nitrate (NO₃⁻).
Phosphorus (P): Found as phosphate (PO₄³⁻).
Potassium (K): Found as potassium ions (K⁺).

Other Nutrient Sources

Organic fertilizers: Compost, manure.
Nitrogen-fixing bacteria: Convert atmospheric nitrogen into usable forms.

Acidic Soil Preference

Most plants prefer slightly acidic soils (pH 6.0 to 6.5) for optimal mineral uptake.
Acid conditions make nutrients more readily available.

Mineral Nutrient Availability

Minerals need to be dissolved in the soil solution to be absorbed by roots.

Cation Exchange

Negatively charged soil particles (clay and humus) bind to positively charged mineral ions (cations).
This process makes minerals available in the soil solution, replenishing them as they are taken up by roots.

Long Distance Transport in Plants

Xylem: Transports water and dissolved minerals from roots to leaves.
Phloem: Transports sugars and other organic products throughout the plant.

Plant Parts and Resource Acquisition

Roots: Absorb water and minerals from soil.
Stems: Support the plant and transport water and nutrients.
Leaves: Photosynthesis for food production; gas exchange.

Apoplast and Symplast

Apoplast: The space outside the plasma membranes of plant cells, including cell walls and intercellular spaces.
Symplast: The continuous network of cytoplasm connected by plasmodesmata, allowing the movement of substances through the cell interiors.

Routes of Transport

Apoplastic Route: Substances move through cell walls and intercellular spaces, bypassing the plasma membrane.
Symplastic Route: Substances move through plasmodesmata, traversing plasma membranes only once.
Transmembrane Route: Substances move across multiple plasma membranes between adjacent cells.

Membranes Potential in Plants

Potassium ions (K⁺) establish the membrane potential in plants.
Hydrogen ions (H⁺): Drive co-transport with other substances, moving them against their concentration gradients.

Water Potential and Water Movement

Water Potential (Ψ): The tendency of water to move from one area to another.
Water moves from areas of higher water potential to areas of lower water potential.
Solute Potential: The negative pressure or tension generated by the presence of solutes; drives water movement.
Solutes within plant cells: Sugars, salts, and organic acids.
Increasing solute concentration: Reduces the number of free water molecules.

Wilting

When a plant loses more water than it absorbs, its turgor pressure decreases, causing the plant to wilt.

Bulk Flow

Bulk Flow: The mass movement of a fluid driven by pressure gradients, facilitated by differences in water potential.

Endodermis Barrier

The Casparian strip, a waterproof band within the endodermis, forces water and minerals to move through the plasma membranes of endodermal cells, preventing apoplastic movement, ensuring a controlled passage.

Cohesion-Tension Hypothesis

Cohesion: Water molecules stick to each other due to hydrogen bonding.
Tension: Transpiration pulls water up through the xylem.

Transpiration

Transpiration: The process by which water vapor is lost from the leaves of plants through stomata.

Cohesion and Water Transport

The cohesion of water molecules allows the continuous column of water to be pulled upward through the xylem, creating the transpiration stream.

Stomata Opening and Closing

Opening: Increased guard cell turgor pressure caused by an influx of water, due to active potassium ion pump.
Closing: Decreased guard cell turgor pressure caused by the loss of water.

Stomata Opening Cues

Light: Blue light and red light activate stomata opening.
Carbon Dioxide Concentration: Low CO₂ levels promote opening. -Internal Clock: Stomata open in the morning, even in the dark, controlled by circadian rhythms.

Sugar Source and Sink

Source: Tissues where sugars are produced, e.g., leaves during photosynthesis.
Sink: Tissues where sugars are used or stored, e.g., roots, flowers, and fruits.

Phloem Transport

Pressure Flow Hypothesis: Sugars are loaded into the phloem at the source, creating a high turgor pressure. This drives the movement towards the sink, where sugars are unloaded, reducing pressure.

Charophyceae and Land Plant Similarities

Cell Wall Structure: Cellulose synthesis in both.
Chloroplast Structure: Similar chloroplast and chlorophyll.
Peroxisome Enzymes: Similar enzymes for photorespiration.
Flagellated Sperm: Both produce sperm with whiplike flagella.

Derived Key Traits of Land Plants

Alternation of Generations: Life cycle with a multicellular haploid gametophyte and multicellular diploid sporophyte.
Apical Meristem: Localized regions of active cell division at shoot (terminal bud) and root tips.
Multicellular Dependent Embryo: Embryo develops within tissues of parent plant.
Sporopollenin: A durable polymer that coats spores and pollen grains, protecting them from desiccation, decay and UV radiation.
Cuticle: Waxy layer on the outer surface of the plant, preventing desiccation.
Stomata: Pores on leaves that allow gas exchange.

Gametophyte and Sporophyte

Gametophyte: The haploid, multicellular generation that produces gametes.
Sporophyte: The diploid, multicellular generation that produces spores.

Bryophyte Phyla

Liverworts (Hepatophyta)
Hornworts (Anthocerophyta)
Mosses (Bryophyta)

Gametophyte-Sporophyte Relationship: Bryophytes vs. Ferns

Bryophytes: The dominant generation is the gametophyte; sporophyte is smaller and dependent on gametophyte.
Ferns: The dominant generation is the sporophyte; the gametophyte is smaller and independent.

Seedless Vascular Plants

Key Developmental Features: Vascular tissues (xylem and phloem), true roots, and leaves.
Phyla:
- Lycophytes (Lycopodiophyta): Club mosses, spike mosses, and quillworts.
- Pterophytes (Pteridophyta): Ferns, horsetails, and whisk ferns.

Heterospory

Heterospory: The production of two types of spores: megaspores (female) and microspores (male).

Ovule

Ovule: A structure that contains a female gametophyte and is enclosed in the sporophyte tissue.

Advantages of Reduced Gametophytes

Protection: Reduced gametophytes are protected from desiccation and environmental stresses within the sporophyte tissues.
Efficient Reproduction: Reduced gametophytes allow for faster reproduction and more efficient fertilization.

Evolutionary Advantages of a Seed

Dispersal: Seeds can be transported by wind, water, or animals, allowing long-distance dispersal.
Dormancy: Seeds can remain dormant for long periods, ensuring survival in harsh conditions.
Nutrition: Seeds contain a food supply for the developing embryo, enabling it to grow and establish itself independently.

Sporophyte Dominance in Higher Plants

Lower Land Plants (Bryophytes): The sporophyte is dependent on the gametophyte for nutrition and survival.
Higher Land Plants (Gymnosperms, Angiosperms): The sporophyte generation is dominant and independent, producing seeds that can disperse to new locations.

Female Reproductive Structure

Pistil: The female reproductive structure consists of:
- Stigma: The sticky top part of the pistil that receives pollen.
- Style: The stalk that connects the stigma to the ovary.
- Ovary: The swollen base that houses the ovules.

Male Reproductive Structure

Stamen: The male reproductive structure consists of:
- Anther: The pollen-producing sac.
- Filament: The stalk that supports the anther.

Inside the Ovary

Ovules: Contain the megasporangium (structure that produces megaspores).

Female Gametophyte Formation

Megaspores: Develop inside the ovule's megasporangium.
Megaspore Development: One megaspore survives and undergoes mitosis to form a multicellular female gametophyte (embryo sac) with:
- Egg cell: The female gamete (1 cell).
- Two synergids: Assist in fertilization.
- Three antipodal cells: Function is unclear.
- Central cell: Contains two polar nuclei.

Synergid Cells

Synergids: Assist in fertilization by guiding the pollen tube to the egg cell and releasing signaling molecules.

Pollen Sac

Microsporangium: The pollen sac inside the anther of a stamen, where microspores are produced.

Mature Seed Contents

Embryo: The young sporophyte.
Endosperm: A food-storing tissue that nourishes the developing embryo.
Seed Coat: Protective outer covering of the seed.

Endosperm Function

Stored Food: Provides nutrients to the developing embryo.

Eudicot Seed Structure

Eudicots: Have two cotyledons (seed leaves).

Germination Steps

Imbibition: The absorption of water by the seed.
Radicle: The embryonic root emerges first.
Shoot: The embryonic shoot emerges second.
Cotyledons: Seed leaves open and photosynthesize, providing nutrition to the seedling.

Fruit

Fruit: A mature ovary, usually containing seeds, which develops after fertilization.
Function: Protects and disperses the seeds.

Fruit Types

Simple Fruit: Develops from a single ovary (e.g., apple, cherry, pea).
Aggregate Fruit: Develops from multiple ovaries of a single flower (e.g., raspberry, strawberry).
Multiple Fruit: Develops from multiple ovaries of a cluster of flowers (e.g., pineapple, fig).
Accessory Fruit: Develops mainly from tissues other than the ovary, often with a small ovary encased within (e.g., apple, pear).

Fruit Dispersal Adaptation

Water Dispersal: Fruits with buoyant or waterproof features (e.g., coconut).
Wind Dispersal: Fruits with wings, hairs, or lightweight structures (e.g., dandelion).
Sharp Spines: Attach to animal fur for dispersal.
Edible Fruits: Animals eat the fruit and disperse the seeds in their droppings.

Plant Biotechnology

Plant Breeding: Selectively crossing plants with desirable traits.
Genetic Engineering: Directly altering a plant's DNA to introduce new traits.
Transgenic: An organism whose DNA has been altered through genetic engineering.

Plant Biotechnology Advantages

Improved Yield: Increased crop production (resistance to pests, diseases, and herbicides).
Enhanced Nutrition: Increased nutrient content in food.
Pest and Disease Resistance: Developing crops that are less susceptible to pests and diseases, reducing the need for pesticides and fungicides.
Herbicide Resistance: Creating crops that can tolerate herbicides, allowing for more effective weed control.
Increased Stress Tolerance: Developing crops that can withstand harsh environmental conditions, such as drought or salinity.

Plant Biotechnology Risks

Unintended Consequences: Unforeseen effects on other organisms, ecosystems, and human health.
Gene Flow: The transfer of genes from genetically modified crops to wild relatives, with potential impacts on biodiversity.
Monoculture: Increased dependence on a few genetically similar crops, reducing genetic diversity and making crops more vulnerable to pests and diseases.
Ethical Concerns: Concerns about the safety and long-term effects of genetically modified foods.

Hormones: Plant Growth Regulators

Hormones: Chemical messengers produced within a plant that influence growth, development, and other responses.
Multiple Effects: The specific response to a hormone can depend on the hormone concentration, the plant tissue, and the developmental stage.

Phototropism: Shoot and Root Responses

Shoot: Bends towards light, due to auxin accumulation on the shaded side.
Root: Bends away from light, due to auxin inhibiting root growth on the lighted side.

Plant Hormone Pioneers

Charles Darwin and Francis Darwin: Demonstrated that the tip of a coleoptile (protective sheath of a grass seedling) is responsible for phototropic bending.
Frits Went: Isolated auxin (chemical messenger) produced by the coleoptile tip.
Kenneth Thimann: Identified the chemical structure of indoleacetic acid, a major form of auxin.

Auxin Effects

Cell elongation: Promotes cell elongation in stems and roots.
Apical Dominance: Inhibits the growth of lateral buds, promoting vertical growth.
Fruit Development: Promotes fruit development and ripening.

Auxin Polar Transport

Polar Transport: Auxin moves unidirectionally from the tip of the shoot to the base, not influenced by gravity.
Mechanism: Auxin is actively transported across membranes by specialized proteins.

Auxin and Cell Growth

Stimulated by Auxin: Cell wall loosening: Increased cell wall extensibility.
Low Cell Wall pH: Activates expansins, enzymes that break down bonds in cell walls.
Expansin Activity: Loosens cell walls, allowing for expansion.
Increased Turgor Pressure: Water influxes into cells, increasing pressure against cell walls.

Auxin and Apical Dominance

Reduced Auxin Flow: From the apical bud, weakens lateral buds and weakens their growth (apical dominance).
Apical Bud Removal: Results in increased growth of lateral buds.

Cytokinin Functions

Cell division: Promotes cell division in roots, shoots, and other tissues.
Lateral Bud Development: Stimulates lateral bud development and shoot branching.
Production: Primarily in roots.

Callus Differentiation Control

High Cytokinin/Low Auxin Ratio: Promotes shoot formation.
Low Cytokinin/High Auxin Ratio: Promotes root formation.

Apical Dominance Control

Auxin: The apical bud produces auxin that inhibits lateral bud growth.
Cytokinins: Produced by the roots, counteract auxin's effects, promoting lateral bud growth.

Gibberellin Effects

Stem Elongation: Promotes stem elongation and leaf growth.
Seed Germination: Triggers seed germination by stimulating the breakdown of food reserves.
Fruit Development: Promotes fruit growth and development.
Flowering: Can induce flowering in some plants.

Gibberellins and Seed Germination

Environmental Cues: Water uptake and warmer temperatures initiate the release of gibberellins within the seed.
Gibberellin Action: Promotes synthesis of enzymes (amylases) that break down starch into sugars, providing energy for growth.

Abscisic Acid Actions

Dormancy: Promotes seed dormancy and bud dormancy.
Stress Response: Helps in stress response, including drought tolerance and response to cold temperatures.
Differentiation: Helps to control leaf formation and growth.

ABA in Seed Dormancy

High ABA Levels: Maintains seed dormancy by preventing germination until conditions are favorable.

ABA and Wilt Response

Wilt: ABA accumulates in leaves experiencing water stress, closing stomata, reducing transpiration.

Ethylene Effects

Triple Response (Mechanical Stress): Inhibits stem elongation, promotes lateral swelling, and promotes curvature of the stem in response to mechanical stress (e.g., pushing a seedling through soil).
Fruit Ripening: Promotes fruit ripening by stimulating the production of enzymes that soften fruits and break down cell walls.
Senescence: Promotes senescence (aging) of leaves, flowers, and fruits.
Leaf Abscission: Promotes leaf abscission (shedding) in autumn.

Ethylene in Fruit Ripening

Storage in Paper Bag: Promotes ethylene production, triggering ripening.

Photomorphogenesis

Photomorphogenesis: The development of a plant in response to light.

De-etiolation (Green up)

Light Triggers: Seedlings grown in darkness exhibit etiolated growth (elongated stems, small leaves, and pale color).
Light Triggers: De-etiolation, plant growth responds to light: stems thicken, leaves expand, and chlorophyll production increases.

Photoreceptors

Photoreceptors: Light-sensitive pigment proteins that absorb specific wavelengths of light.

Blue Light Photoreceptors

Blue Light: Controls phototropism, stomatal opening, and hypocotyl elongation.

Phytochromes and Seed Germination

Red Light: Stimulates germination in many seeds.
Far Red Light: Inhibits germination.

Phytochrome Toggle Switch

Pr (inactive form): Absorbs red light (660 nm).
Pfr (active form): Absorbs far red light (730 nm).
Interconversion: Pr and Pfr are interconvertible.
Red Light: Converts Pr to Pfr.
Far Red Light: Converts Pfr to Pr.

Shade Avoidance

Shade Trees: Allow more far-red light to pass through, increasing the Pr/Pfr ratio in plants underneath the shade tree.
Shade Avoidance Response: Plants growing under shade trees grow taller, producing longer petioles and thinner leaves to reach more sunlight.

Circadian Rhythm

Circadian Rhythm: Internally regulated, daily fluctuations in plant processes, such as opening and closing of stomata, leaf movement, and flower opening.

Photoperiodism

Photoperiodism: The response of plants to the relative lengths of day and night.
Controls:
- Flowering: Induction of flowering.
- Tuber Formation: Formation of underground storage organs.
- Leaf Abscission: Shedding of leaves.
- Dormancy: Entering a dormant state during winter.
Environmental Stimulus: Day length (night length) is the primary environmental cue.

Photoperiodism: Plant Types

Short-Day Plants: Flower when the night length is longer than a critical period (e.g., poinsettia).
Long-Day Plants: Flower when the night length is shorter than a critical period (e.g., lettuce).
Critical Night Length: The specific length of darkness that determines whether a plant will flower or not.

Gravitropism

Gravitropism: The growth response of plants in response to gravity.
Roots: Grow downwards (positive gravitropism).
Shoots: Grow upwards (negative gravitropism).

Statioliths

Statioliths: Dense starch-filled plastids found in root cap cells.
Gravity Sensing: They settle to the bottom of cells, providing a signal for gravity sensing.

Thigmomorphogenesis

Thigmomorphogenesis: The changes in plant growth and development in response to mechanical stimuli (touch or wind).

Thigmotropism

Thigmotropism: Directional growth response to touch (e.g., vine tendrils wrapping around a support).

Plant Responses to Water Deficit

Stomata Closure: Reduces transpiration.
Leaf Rolling: Reduces surface area exposed to the sun, minimizing water loss.
Root Growth: Increases root growth to access deeper sources of water.
Hormonal Changes: Production of ABA stimulates stomatal closure and root growth.

Overwatering Damage

Overwatering: Reduces oxygen availability in the soil, leading to root suffocation and death.

Salt Damage

Osmotic Stress: High salt concentration draws water out of plant cells, leading to dehydration.
Toxicity: High levels of salt ions can be toxic to plant cells.

Heat Stress

Heat Harm: High temperatures damage proteins and enzymes, leading to cellular dysfunction.
Heat Shock Proteins: Protect proteins from damage caused by high temperatures.

Cold Stress

Cold Harm: Low temperatures damage membranes and can lead to freezing damage.
Coping Mechanisms:
- Increased Levels of Unsaturated Fatty Acids: Increase membrane fluidity, improving resistance to cold.
- Production of Antifreezes: Protect cells from freezing.

Herbivore Defense Mechanisms

Physical Defenses:
- Thorns: Sharp, pointed structures (e.g., rose).
- Spines: Modified leaves with sharp points (e.g., cactus).
- Trichomes: Hair-like structures that can irritate or deter herbivores.
- Tough Leaves: Difficult to chew or digest.
Chemical Defenses:
- Toxic Compounds: Poisons that deter herbivores.
- Digestive Inhibitors: Interfere with herbivores' digestive systems.
- Attractants: Attract predators or parasites of the herbivore.
- Alarm Signals: Chemicals released by damaged plants that warn other plants or attract natural enemies of the herbivore.

Plant Alarm Signals

Lima Bean Plants: When attacked by spider mites, they release volatile compounds, signaling to neighbors to increase their defenses.

Effector-Triggered Immunity

Effector-Triggered Immunity: A plant's immune response to specific molecules (effectors) produced by pathogens.

Hypersensitive Response

Hypersensitive Response: A plant's localized defense response to pathogens, involving programmed cell death of infected cells.
Mechanism: Confines the infection, preventing its spread.

Salicylic Acid for Defense

Salicylic Acid: A plant hormone that activates systemic acquired resistance (SAR).
SAR Activation: Induces a long-lasting, broad-spectrum resistance in the plant to future pathogens, making the plant primed for future infection.

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