Bio112 exam 2

What makes a plant a plant? (Characteristics all plants share?)

Plants are multicellular organisms that have chlorophyll, allowing them to perform photosynthesis to produce their own food. They also have cell walls made of cellulose, and their life cycle includes an alternation of generations (sporophyte and gametophyte). Plants are eukaryotic and have specialized structures for reproduction, transport, and growth (roots, stems, leaves).

Basic Structures and Functions of a Plant Cell:

• Cell Wall: Provides structure and support to the cell. Made of cellulose.

• Chloroplasts: Contain chlorophyll for photosynthesis.

• Central Vacuole: Stores water, nutrients, and waste products, helps maintain turgor pressure.

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Powerhouse of the cell, provides energy.

• Plasmodesmata: Channels between plant cells for communication and transport.

Basic Structures and Functions of Angiosperm Root and Shoot Systems:

• Root System: Anchors the plant and absorbs water and nutrients.

  • Primary Root (taproot) - main root, grows downward.

  • Lateral Roots - branch off the primary root to increase surface area for absorption.

• Shoot System: Includes stems, leaves, and reproductive structures (flowers).

  • Stems: Support leaves and flowers, transport water, nutrients, and sugars.

  • Leaves: Perform photosynthesis.

Modified Roots, Stems, and Leaves:

• Modified Roots:

  • Adventitious roots: Grow from unusual places like stems or leaves (e.g., ivy).

  • Storage roots: Store nutrients, e.g., carrot, sweet potato.

• Modified Stems:

  • Rhizomes: Underground stems, e.g., ginger.

  • Stolons: Horizontal stems, e.g., strawberries.

  • Tubers: Underground storage stems, e.g., potatoes.

• Modified Leaves:

  • Tendrils: Support structures, e.g., pea plants.

  • Spines: Protect against herbivory, e.g., cactus.

  • Bracts: Modified leaves that attract pollinators, e.g., poinsettias.

Monocots vs. Eudicots (3 Ways They Differ):

1. Number of Cotyledons:

   • Monocots: 1 cotyledon.

   • Eudicots: 2 cotyledons.

2. Leaf Venation:

   • Monocots: Parallel veins.

   • Eudicots: Reticulate (branching) veins.

3. Vascular Bundles:

   • Monocots: Scattered vascular bundles.

   • Eudicots: Vascular bundles in a ring.

Parenchyma, Collenchyma, and Sclerenchyma:

• Parenchyma: Thin-walled, flexible cells responsible for photosynthesis, storage, and wound healing. Found in leaves, stems, roots.

• Collenchyma: Cells with unevenly thickened walls that provide structural support to growing parts of the plant. Found in petioles, stems.

• Sclerenchyma: Thick, lignified cell walls, providing rigid support. Includes fibers and sclereids. Found in mature tissues like wood and seed coats.

Ground, Vascular, and Dermal Tissue:

• Ground Tissue: Includes parenchyma, collenchyma, and sclerenchyma. Functions in photosynthesis, storage, and support.

• Vascular Tissue: Includes xylem (transports water and minerals) and phloem (transports sugars). Responsible for long-distance transport.

• Dermal Tissue: The outer protective layer. Includes epidermis, cuticle, guard cells, and trichomes.

Anatomy of a Leaf:

1. Epidermis: Protective outer layer.

2. Mesophyll: Includes palisade parenchyma (photosynthesis) and spongy parenchyma (gas exchange).

3. Vascular Bundles: Contain xylem and phloem for transport.

Tissues from Primary Growth:

• Shoot Primary Growth: Produces epidermis, primary xylem and phloem, and ground tissue.

• Root Primary Growth: Forms epidermis, root cortex, and vascular tissue.

Why Do Plants Grow from Their Tips?

Growth occurs at apical meristems (tip of roots and shoots), which produce new cells for elongation.

Why Do Plant Bodies Grow Continuously?

Plants have indeterminate growth, meaning they can grow continuously throughout their life due to the activity of meristems.

Parts of Plants with Indeterminate Growth:

• Apical meristems: At tips of roots and shoots.

• Lateral meristems: In the cambium, allowing secondary growth.

Roots Adapted for Growing Through Abrasive Soil:

Roots have a root cap that protects the growing tip from damage, and they produce mucilage to lubricate the passage through the soil.

Forces that Force Roots Downward:

• Gravity (gravitropism) directs roots to grow downward.

• Root pressure (osmotic pressure) helps push water into roots.

Xylem and Phloem Cells:

• Xylem: Includes tracheids and vessel elements (unique to angiosperms). They are hollow cells that conduct water and minerals.

• Phloem: Includes sieve tube members and companion cells, which transport sugars.

Secondary Growth and Annual Growth Rings:

• Secondary growth occurs in lateral meristems (vascular cambium).

• Annual growth rings form due to the varying growth rates in different seasons (e.g., wider in spring, narrower in winter).

Cells Produced by the Vascular Cambium:

• Xylem cells (secondary xylem) and phloem cells (secondary phloem).

What is Bark?

Bark is made up of the periderm (cork cambium and cork) and secondary phloem. It serves as protection and prevents water loss.

Cells Produced by the Cork Cambium:

• Cork (protective layer) and phelloderm (inner layer).

Why Does Girdling a Tree Kill It?

Girdling removes the phloem layer, disrupting nutrient transport, which can starve the tree.

Vocabulary (with definitions):

• Indeterminate Growth: Growth that continues throughout life.

• Determinate Growth: Growth that stops after reaching a certain size.

• Root System: The underground part of the plant.

• Shoot System: The above-ground part of the plant.

• Taproot: Main root from which lateral roots arise.

• Lateral Roots: Branches of the primary root.

• Axillary (Lateral) Buds: Buds that form at the angle between the leaf and stem.

• Apical Bud: The tip of the stem or root.

• Meristem: A region of undifferentiated cells capable of division.

• Rhizome: Horizontal underground stem.

• Tuber: Underground storage stem, e.g., potato.

• Petiole: Stalk that attaches a leaf to the stem.

• Stomata: Pores on leaves for gas exchange.

• Guard Cells: Control the opening and closing of stomata.

• Vascular Cambium: Lateral meristem that produces secondary xylem and phloem.

• Periderm: Outer protective tissue formed during secondary growth.

• Bark: Outer covering of the tree, made from periderm and phloem.

• Tracheids: Water-conducting cells in xylem.

• Sieve Tube Members: Cells in phloem that conduct sugars.

• Heartwood: Inner, non-functioning xylem.

• Sapwood: Outer, functional xylemthat actively conducts water and nutrients within the plant.

1. What Factors Affect Water Potential Within a Plant? (Think Weather)

• Water potential is the potential energy of water in a system, influencing its movement.

• Factors that affect water potential in plants include:

  • Solute concentration: The more solutes dissolved in water (e.g., sugars, salts), the lower (more negative) the water potential.

  • Pressure potential: The physical pressure exerted on the water. For instance, turgor pressure inside cells increases pressure potential.

  • Temperature: Higher temperatures can reduce water potential because they can increase the movement of water molecules.

  • Humidity: The drier the environment, the lower the water potential in the atmosphere compared to inside the plant, which drives water loss.

2. Be Able to Calculate Water Potential from Solute and Pressure Potential

• Water potential (Ψ) is calculated as the sum of solute potential (Ψs) and pressure potential (Ψp):

  Ψ=Ψs+ΨpΨ=Ψs​+Ψp​

  • Solute potential (Ψs): A negative value, related to the concentration of solutes. The more solutes, the more negative the solute potential.

  • Pressure potential (Ψp): Positive in living cells due to turgor pressure. For xylem, it can be negative due to tension created by transpiration.

Example:

• If solute potential is -0.5 MPa and pressure potential is 0.3 MPa, then water potential is:Ψ=−0.5+0.3=−0.2 MPaΨ=−0.5+0.3=−0.2MPa

3. Be Able to Determine Water Movement by Comparing the Water Potential Between Two Areas

• Water always moves from areas of higher (less negative) water potential to areas of lower (more negative) water potential.

  • For example, if the water potential in the soil is -0.3 MPa and in the leaf is -0.5 MPa, water will move from the soil (higher water potential) to the leaf (lower water potential).

4. Why/When Do Plants Wilt?

• Wilting occurs when a plant's turgor pressure is lost, often due to water loss. This happens when the water potential inside the plant is too low.

• Turgor pressure is what keeps plant cells rigid. Without sufficient water, the cell’s vacuoles lose water, causing the plant to lose its shape and become limp.

5. What is the Controlling Force that Drives Water and Minerals Up a Plant During the Day?

• Transpiration: The evaporation of water from the plant’s leaves creates a negative pressure, which pulls water and minerals up through the plant’s vascular system (mainly xylem).

• Cohesion and adhesion of water molecules also help maintain the flow. Water molecules stick to each other (cohesion) and to the walls of xylem vessels (adhesion).

6. What Plant Structure Regulates Transpiration?

• Stomata: Small pores on the leaf surface that regulate water loss by controlling gas exchange. Guard cellssurrounding the stomata control their opening and closing.

7. How is K+ Involved in Opening/Closing Stomata?

• Potassium ions (K+) are involved in the opening and closing of stomata:

  • When K+ ions enter guard cells, water follows, causing the guard cells to swell and open the stomata.

  • When K+ ions exit, water follows, and the guard cells shrink, closing the stomata and reducing transpiration.

8. Distinguish Between Symplastic and Apoplastic Transport as Water Moves Laterally Into the Vascular Tissue of a Root

• Symplastic transport: Water moves through the cytoplasm of cells via plasmodesmata (channels connecting plant cells).

• Apoplastic transport: Water moves through the cell walls and the spaces between cells, bypassing the cell membrane.

9. What is the Role of the Casparian Strip? Where is It Located?

• The Casparian strip is a band of suberin (waxy substance) found in the endodermis of the root.

• It blocks the apoplastic pathway, forcing water to enter cells through the symplastic pathway, ensuring selective uptake of minerals and preventing toxins from entering the vascular system.

10. How Does the Polarity of Water Contribute to the Flow of Water Through Plant Xylem?

• Cohesion: Water molecules are attracted to each other, which helps maintain the column of water in the xylem vessels.

• Adhesion: Water molecules also stick to the walls of xylem vessels, helping to counteract gravity and maintain the upward flow.

11. Distinguish Between a Source and a Sink. Can a Structure Ever Be Both? Explain

• Source: Any part of the plant that produces or releases sugars (e.g., leaves where photosynthesis occurs).

• Sink: Any part of the plant that consumes or stores sugars (e.g., roots or fruits).

• Yes, a structure can be both depending on the time of year or phase of the plant’s life cycle. For example, during photosynthesis, leaves are sources, but during the night when they consume sugars for respiration, they can act as sinks.

12. What Drives Flow in the Phloem?

• Pressure-flow hypothesis: Sugar (mainly sucrose) is actively transported into the phloem at the source, which causes water to enter, creating a high pressure. This pressure drives the flow of sap (sugar solution) from source to sink.

13. How is Sugar Moved from a Source to a Sink?

• At the source (e.g., leaves), sucrose is actively loaded into the phloem.

• The influx of sucrose causes water to enter the phloem by osmosis, increasing pressure and pushing the sugar solution towards the sink (e.g., roots, fruits).

• At the sink, sugar is unloaded, and water exits the phloem, maintaining the pressure gradient.

14. What Did Aphids Teach Researchers About Phloem Function?

• Aphids have specialized mouthparts to feed on the sugary sap of phloem. By piercing the phloem and studying the sap flow, researchers confirmed that pressure-flow is the mechanism that drives sap movement in the phloem.

Vocabulary Definitions

• Water potential (Ψ): The potential energy of water in a system, influencing its movement. Water moves from areas of higher to lower water potential.

• Solute potential (Ψs): The component of water potential caused by solute concentration. It’s always negative because solutes reduce water potential.

• Pressure potential (Ψp): The physical pressure exerted on the water, usually positive in plant cells due to turgor pressure.

• Hypotonic: A solution with lower solute concentration than another solution, leading to water entering the cell.

• Hypertonic: A solution with higher solute concentration, causing water to exit the cell.

• Isotonic: A solution with equal solute concentration to another solution, resulting in no net movement of water.

• Osmosis: The movement of water from a region of lower solute concentration to a region of higher solute concentration through a semipermeable membrane.

• Turgor pressure: The pressure exerted by the vacuole against the cell wall in plant cells, which helps maintain cell structure.

• Megapascal (MPa): Unit of pressure used to measure water potential.

• Root hairs: Extensions of root epidermal cells that increase surface area for water and nutrient absorption.

• Casparian strip: A waxy barrier in the endodermis that controls the flow of water into the vascular tissue of the root.

• Apoplastic: Water movement through the cell walls and intercellular spaces.

• Symplastic: Water movement through the cytoplasm and plasmodesmata between cells.

• Root pressure: The pressure generated in roots as water is absorbed, pushing water upward.

• Adhesion: The attraction between water molecules and surfaces like the walls of xylem vessels.

• Cohesion: The attraction between water molecules that helps pull water up through the plant.

• Transpiration: The process of water evaporation from leaves, creating a pull that moves water and minerals through the plant.

• Translocation: The movement of sugars through the phloem from source to sink.

• Source: Part of the plant that produces or releases sugars (e.g., leaves).

• Sink: Part of the plant that consumes or stores sugars (e.g., roots, fruits).

• Pressure-flow: The mechanism by which sugars are transported through the phloem from source to sink driven by pressure differences.

1. What Are the Key Macronutrients that Plants Require? (Think, Don’t Memorize)

The key macronutrients that plants require for growth and development are:

• Carbon (C): From CO₂ in the atmosphere, used in photosynthesis to make sugars.

• Hydrogen (H): From water (H₂O), used in many cellular processes.

• Oxygen (O): Also from CO₂ and H₂O, used in cellular respiration.

• Nitrogen (N): Found in soil as nitrate (NO₃⁻) or ammonium (NH₄⁺), used to make proteins and nucleic acids.

• Phosphorus (P): From phosphate ions (PO₄³⁻) in soil, important for energy transfer (ATP) and nucleic acids.

• Potassium (K): Helps in water regulation, enzyme activation, and overall plant metabolism.

• Calcium (Ca): Important for cell wall structure, and as a secondary messenger in signaling.

• Magnesium (Mg): A core component of chlorophyll, essential for photosynthesis.

2. Where Do Plants Get These Key Nutrients?

• Carbon (C): From carbon dioxide (CO₂) in the atmosphere, absorbed through the stomata.

• Hydrogen (H): From water (H₂O) absorbed by the roots from the soil.

• Oxygen (O): From water (H₂O) and CO₂.

• Nitrogen (N): Primarily from the soil, in the form of nitrate (NO₃⁻), ammonium (NH₄⁺), or through the process of nitrogen fixation by soil bacteria.

• Phosphorus (P): From phosphate ions (PO₄³⁻) in the soil, often derived from weathered rock.

• Potassium (K): From soil minerals and organic matter, often dissolved in soil water.

• Calcium (Ca): From calcium ions (Ca²⁺) in the soil.

• Magnesium (Mg): From magnesium ions (Mg²⁺) in the soil.

3. Why Do Plants Require These Macronutrients?

• Carbon, Hydrogen, Oxygen: These elements are essential for making the organic molecules that make up the plant. They are involved in photosynthesis, respiration, and the synthesis of sugars, lipids, and proteins.

• Nitrogen: Required for synthesizing amino acids (the building blocks of proteins), nucleic acids (DNA and RNA), and chlorophyll.

• Phosphorus: A critical component of ATP (the energy currency of the cell) and nucleic acids (DNA, RNA).

• Potassium: Essential for regulating water balance, activating enzymes, and facilitating photosynthesis.

• Calcium: Helps with cell wall structure and acts as a signaling molecule in response to stress.

• Magnesium: Central to chlorophyll, which is essential for photosynthesis.

4. Carnivory in Plants is an Adaptation to What Conditions?

• Carnivory in plants is an adaptation to nutrient-poor soils, particularly in terms of nitrogen. In these environments, plants may not be able to access enough nitrogen from the soil, so they turn to consuming insects or other small organisms to get the nitrogen they need.

• Common examples of carnivorous plants include Venus flytraps, pitcher plants, and sundews.

5. What Role Do Soil Bacteria Play in the Nitrogen Cycle and Nitrogen Uptake in Plants?

• Soil bacteria are essential for converting nitrogen in the atmosphere into a usable form for plants, through a process called nitrogen fixation.

• Groups of soil bacteria involved:

  • Nitrogen-fixing bacteria (e.g., Rhizobium) break the triple bond of N₂ in the atmosphere, converting it into ammonia (NH₃), which is then converted into ammonium (NH₄⁺).

  • Nitrifying bacteria (e.g., Nitrosomonas, Nitrobacter) convert ammonium (NH₄⁺) into nitrate (NO₃⁻), a form that plants can readily absorb.

  • Decomposing bacteria break down organic matter, releasing ammonia and other nitrogen compounds back into the soil.

  • Denitrifying bacteria (e.g., Pseudomonas) convert nitrate (NO₃⁻) back into N₂ (atmospheric nitrogen), completing the nitrogen cycle.

6. Which Group of Plants Have Mutualistic Nitrogen-Fixing Bacteria Within Their Root Nodules?

• Legumes (e.g., beans, peas, soybeans) have a mutualistic relationship with nitrogen-fixing bacteria (like Rhizobium) within specialized structures in their roots called root nodules.

7. What Do the Bacteria in Root Nodules Gain in the Symbiosis? The Plant?

• Bacteria (Rhizobium): Gain carbohydrates (energy) from the plant, which they need for growth.

• Plant: Gains nitrogen in a usable form, such as ammonium (NH₄⁺) or nitrate (NO₃⁻), which is essential for protein and nucleic acid synthesis.

8. Why Is It Important to Rotate Crops and Plant Legumes Periodically?

• Crop rotation is important because it helps maintain soil fertility. Legumes, through their symbiotic relationship with nitrogen-fixing bacteria, add nitrogen to the soil, reducing the need for synthetic fertilizers. This practice prevents nutrient depletion and promotes healthy soil ecosystems.

9. Mycorrhizae Form a Mutualistic Relationship with Plant Roots – What Do the Fungi Gain? What Do the Plants Gain?

• Fungi (Mycorrhizae): Gain carbohydrates from the plant (e.g., sugars produced through photosynthesis).

• Plants: Gain nutrients like phosphorus, minerals, and water through the fungal hyphae, which can extend far beyond the plant's root system, allowing access to nutrients in hard-to-reach areas.

10. What is Topsoil?

• Topsoil is the uppermost layer of soil, rich in organic matter, minerals, and nutrients. It is the most fertile layer of soil and is where most plant roots are located for nutrient absorption.

11. Give an Example of a Practice That Increases the Sustainability of Agriculture

• Organic farming practices, such as using compost, crop rotation, and no-till farming, increase soil health and reduce dependency on chemical fertilizers and pesticides. These practices help maintain a balance in the soil ecosystem and improve sustainability.

Vocabulary Definitions

• Macronutrient: Essential elements that plants require in large quantities for growth (e.g., nitrogen, phosphorus, potassium).

• Micronutrient: Essential elements required by plants in small amounts (e.g., iron, manganese, copper).

• Topsoil: The upper layer of soil, rich in organic material and nutrients, ideal for plant growth.

• Mycorrhizae: Fungi that form a mutualistic relationship with plant roots, aiding in nutrient and water uptake.

• Symbiosis: A relationship between two organisms of different species that live together, often to their mutual benefit.

• Mutualism: A type of symbiosis where both organisms benefit from the relationship.

• Legumes: A family of plants (e.g., beans, peas) that form mutualistic relationships with nitrogen-fixing bacteria in their root nodules.

• Root nodules: Swellings on plant roots that house nitrogen-fixing bacteria.

• Nitrogen fixation: The process by which nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into a form usable by plants (ammonium or nitrate).

• Ammonia (NH₃): A form of nitrogen that can be converted into ammonium (NH₄⁺) by bacteria or taken up directly by plants.

• Ammonium (NH₄⁺): A form of nitrogen that plants can use to make amino acids and proteins.

• Nitrate (NO₃⁻): A form of nitrogen that is highly available for plant uptake, often produced by nitrifying bacteria

1. What Hormone Causes Shoots to Bend Towards Blue Light?

• The hormone responsible for phototropism (the bending of plant shoots toward light) in response to blue light is auxin.

• Auxin accumulates on the side of the stem away from the light, causing cells on that side to elongate and the plant to bend toward the light source.

2. How Is Asymmetrical Cell Elongation Responsible for Phototropism?

• Asymmetrical cell elongation occurs when auxin is distributed unevenly across the plant tissue.

• When a plant is exposed to light, auxin is transported to the shaded side of the shoot. This causes cells on the shaded side to elongate more than those on the illuminated side, resulting in the bending of the plant toward the light source.

3. Why Would Sensing and Growing Toward Blue Light Benefit Plants?

• Blue light is important because it is the most efficient light for photosynthesis. By growing toward blue light, plants can optimize their exposure to light, enhancing photosynthesis and maximizing energy production for growth and reproduction.

4. Discuss the Role of Amyloplasts (AKA Statoliths) in Root Caps in the Gravitropic Response.

• Amyloplasts (also called statoliths) are specialized organelles that store starch grains. They play a key role in gravitropism (growth in response to gravity).

• In the root cap, amyloplasts sink due to gravity, providing a signal that helps the plant detect the direction of gravity. This helps the plant orient its roots to grow downward (positive gravitropism) and shoots to grow upward (negative gravitropism).

5. What Hormone is Involved in Gravitropism? Do Roots Bend Toward Gravity Primarily Due to Cell Division or Elongation?

• The hormone involved in gravitropism is auxin.

• Roots bend toward gravity because auxin accumulates on the lower side of the root, inhibiting cell elongation on that side and causing the upper side to elongate more.

• Roots bend due to elongation, not division, as the cells on the upper side of the root elongate more than those on the lower side.

6. Give an Example of a Plant Structure that is Positively Thigmotropic.

• An example of a plant structure that exhibits positive thigmotropism (growth toward touch) is the tendril of a vine. Tendrils will coil around objects they come into contact with, allowing the plant to secure itself to a support for climbing.

7. How Do Plants Respond to Wind?

• Plants respond to wind through thigmomorphogenesis, where they adjust their growth patterns.

• In windy conditions, plants often develop shorter, thicker stems with increased lignin production, making them more resistant to mechanical stress.

8. How Do Auxin and Cytokinins Interact in Apical Dominance and Lateral Bud Suppression?

• Auxin produced in the apical bud suppresses the growth of lateral buds through a process known as apical dominance.

• Cytokinins, which promote cell division, are produced in the roots and move upward. If the apical bud is removed, the lower levels of auxin decrease, allowing cytokinin levels to promote lateral bud growth, leading to branching.

9. Why Are Branches Typically Longer/More Developed at the Base of the Tree When Compared to the Top or Tip?

• This is due to the influence of apical dominance. The apical bud (located at the tip) produces auxin, which inhibits the growth of lateral buds lower down on the plant. As a result, branches lower on the tree are less affected by auxin and grow longer and more developed than those near the top of the tree.

10. How Do Gibberellins and Abscisic Acid Interact in Keeping or Breaking Seed Dormancy?

• Gibberellins promote seed germination by breaking dormancy and stimulating growth. They help in the breakdown of stored food reserves in seeds.

• Abscisic acid (ABA) promotes seed dormancy by inhibiting growth and preventing premature germination under unfavorable conditions.

• These two hormones work in opposition to each other, with gibberellins promoting germination and ABA keeping seeds dormant until conditions are right.

11. Why Will Placing Green Tomatoes in a Box with a Ripe Apple Cause the Tomatoes to Ripen? What Hormone Is Involved?

• The hormone involved in this process is ethylene.

• Ethylene is a gaseous plant hormone that triggers fruit ripening. A ripe apple produces ethylene, which causes the green tomatoes in the box to ripen as well.

12. Give an Example of a Plant Response to Herbivory.

• An example of a plant response to herbivory is the production of volatile organic compounds (VOCs) that attract predators of the herbivores, such as parasitoid wasps. These compounds act as a signal for the natural enemies of the herbivores to help control the damage done by the herbivores.

Vocabulary Definitions

• Hormone: A signaling molecule produced by plants that regulates growth, development, and responses to stimuli.

• Signal Transduction: The process by which a plant cell responds to a signal (like a hormone) through a series of molecular events that lead to a cellular response.

• Phototropism: The growth of a plant toward or away from light, influenced by light receptors and hormones like auxin.

• Auxin: A plant hormone that promotes cell elongation, is involved in phototropism and gravitropism, and regulates other aspects of growth.

• Gravitropism: The directional growth of plant roots and shoots in response to gravity.

• Statolith/Amyloplast: Organelles that store starch and act as gravity sensors in plant cells, particularly in the root cap.

• Thigmotropism: A plant's response to touch or physical contact, such as the coiling of tendrils around a support.

• Apical Dominance: The phenomenon where the growth of lateral buds is inhibited by the presence of a dominant apical bud.

• Cytokinins: Plant hormones that promote cell division and shoot formation, often working in opposition to auxin in apical dominance.

• Dormancy: A period during which a seed or bud is inactive or in a resting state, typically until environmental conditions are favorable for growth.

• Gibberellins: Plant hormones that promote seed germination, stem elongation, and flowering.

• Abscisic Acid (ABA): A plant hormone that induces dormancy, inhibits growth, and helps plants respond to stress, especially water stress.

• Brassinosteroids: A class of plant hormones that regulate growth and stress responses, often working in concert with auxins and gibberellins.

• Ethylene: A gaseous plant hormone that promotes fruit ripening, leaf abscission, and responses to stress

1. Generalized Alternation of Generations Life Cycle

• Alternation of generations refers to the life cycle of plants, which includes two distinct phases: the sporophyteand the gametophyte.

Sporophyte Generation (Diploid - 2n)

• The sporophyte is the diploid (2n) stage of the plant life cycle, where the plant produces spores by meiosis.

• Spores are haploid (1n) cells that will develop into the gametophyte.

Gametophyte Generation (Haploid - 1n)

• The gametophyte is the haploid (1n) stage of the plant life cycle, which produces gametes (eggs and sperm) by mitosis.

• The egg and sperm fuse during fertilization to form a zygote.

Where Mitosis and Meiosis Occur:

• Meiosis occurs in the sporophyte to produce haploid spores.

• Mitosis occurs in both the gametophyte and in the production of gametes.

Diagram Summary:

1. Sporophyte (2n) → Meiosis → Spore (1n)

2. Spore (1n) → Mitosis → Gametophyte (1n)

3. Gametophyte (1n) → Mitosis → Gametes (1n)

4. Gametes (1n) → Fertilization → Zygote (2n)

5. Zygote (2n) → Mitosis → Sporophyte (2n)

2. What Is a Good Definition of a Sporophyte?

• The sporophyte is the diploid (2n) phase of a plant's life cycle that produces spores through meiosis. It is typically the dominant or visible stage in many plants, including angiosperms.

3. What Is a Gametophyte?

• The gametophyte is the haploid (1n) phase of a plant's life cycle that produces gametes (eggs and sperm) through mitosis. The gametophyte is often small and less visible in angiosperms compared to the sporophyte.

4. Which Structures Are Haploid? Which Are Diploid?

• Haploid (1n): Gametes (egg and sperm), spores, gametophyte.

• Diploid (2n): Sporophyte, zygote (the fertilized egg).

5. What Does the Zygote Grow Into?

• The zygote (2n) undergoes mitosis and develops into the sporophyte (2n) through a series of stages of growth and development.

6. What Are the Major Innovations That Have Allowed Angiosperms to Become the Dominant Plant Species on Earth?

• Angiosperms (flowering plants) became dominant due to several key innovations:

  1. Flowers for efficient reproduction and pollination.

  2. Fruits that protect seeds and aid in dispersal.

  3. Double fertilization (producing both a zygote and endosperm).

  4. The ability to produce seeds that are resistant to harsh conditions.

  5. Co-evolution with pollinators that increases reproductive success.

7. How and Where Are Plant Gametes Made in Angiosperms?

• In angiosperms, gametes are made in the flower:

  • Male gametes (sperm) are produced in the anther (part of the stamen) via meiosis, producing pollen.

  • Female gametes (egg) are produced in the ovule within the ovary (part of the carpel), also via meiosis.

8. Give an Example of Coevolution Between Flowering Angiosperms and Their Pollinator

• An example of coevolution is the relationship between hummingbirds and tubular flowers like those of trumpet vines. Hummingbirds are adapted to feed on the nectar of tubular flowers, and the flowers are adapted to attract the birds for pollination.

9. How Do Flowering Angiosperms Prevent Self-Fertilization? When Is Self-Fertilization a Good Strategy?

• Self-fertilization is prevented in many angiosperms through mechanisms like self-incompatibility (where the plant rejects its own pollen) and separate male and female organs in the same flower (i.e., dioecy).

• Self-fertilization can be beneficial in low-pollinator environments or when plants are isolated, as it ensures reproduction even in the absence of external pollinators.

10. What Is the Difference Between Pollination and Fertilization?

• Pollination is the process of transferring pollen (containing sperm) from the anther to the stigma of a flower.

• Fertilization is the fusion of the sperm (from the pollen) with the egg (in the ovule), resulting in the formation of a zygote.

11. Where Are Angiosperm Sperm and Eggs Located?

• Sperm are located in the pollen (which is produced in the anther).

• Eggs are located in the ovule, which is contained within the ovary of the carpel.

12. How Does Fertilization Take Place in Angiosperms?

• Fertilization in angiosperms involves double fertilization:

  1. The pollen grain lands on the stigma and forms a pollen tube.

  2. The pollen tube grows down through the style into the ovary, carrying sperm cells.

  3. One sperm cell fertilizes the egg (forming a zygote).

  4. The other sperm cell fuses with two polar nuclei to form the endosperm (3n).

13. How Does Endosperm Originate? What Is Its Role?

• Endosperm originates from the fusion of a sperm cell with two polar nuclei in the embryo sac during double fertilization.

• Endosperm provides nutrients to the developing embryo within the seed.

14. Where Does the Zygote Form?

• The zygote forms inside the ovule of the flower after fertilization (when the sperm fuses with the egg).

15. What Structures Form the Seed?

• The seed is formed from:

  1. The zygote, which develops into the embryo.

  2. The endosperm, which provides nutrients for the embryo.

  3. The seed coat, which forms from the outer layers of the ovule and protects the seed.

16. What Is the Purpose of the Seed?

• The seed's purpose is to:

  1. Protect the embryo.

  2. Provide nutrients for the embryo during its early stages of growth.

  3. Facilitate dispersal to new locations for germination.

17. What Structures Form the Fruit?

• The fruit forms from the ovary of the flower. After fertilization, the ovary matures into the fruit, which may contain the seeds.

18. What Is the Purpose of the Fruit?

• The fruit's purpose is to:

  1. Protect the developing seeds.

  2. Aid in seed dispersal, often through mechanisms like wind, animals, or water.

Vocabulary Definitions

• Alternation of Generations: The life cycle of plants, alternating between a sporophyte (diploid) and a gametophyte (haploid).

• Mitosis: Cell division that results in two identical daughter cells, important in the production of gametes.

• Meiosis: Cell division that reduces the chromosome number by half, creating haploid spores from the sporophyte.

• Egg: Female gamete produced in the ovule.

• Sperm: Male gamete produced in the pollen.

• Gamete: A haploid cell (egg or sperm) involved in sexual reproduction.

• Spore: A haploid reproductive cell that develops into the gametophyte.

• Gametophyte: The haploid phase of the plant life cycle that produces gametes.

• Sporophyte: The diploid phase of the plant life cycle that produces spores through meiosis.

• Zygote: The fertilized egg (diploid) formed from the fusion of sperm and egg.

• Diploid (2n): Cells that have two sets of chromosomes (one from each parent).

• Haploid (1n): Cells that have one set of chromosomes (such as gametes).

• Flower: The reproductive structure in angiosperms.

• Fruit: The mature ovary that protects and disperses seeds.

• Seed: A structure containing an embryo, endosperm, and seed coat.

• Ovary: The part of the flower that contains the ovules, which develop into seeds after fertilization.

• Style: The stalk that connects the stigma to the ovary.

• Stigma: The part of the flower that receives pollen.

• Carpel: The female reproductive organ of a flower, consisting of the ovary, style, and stigma.

• Ovule: The structure in the ovary that contains the egg.

• Megasporocyte: The diploid cell that undergoes meiosis to produce megaspore.

• Megaspore: The haploid cell that develops into the female gametophyte.

• Embryo Sac: The female gametophyte in the ovule.

• Filament: The stalk of the stamen that supports the anther.

• Anther: The part of the stamen that produces pollen.

• Microsporocyte: The diploid cell that undergoes meiosis to form microspores.

• Microspore: The haploid cell that develops into the male gametophyte.

• Pollen: The male gametophyte in seed plants.

• Pollen Tube: A tube formed by the pollen grain that carries sperm to the ovule.

• Seed Dormancy: A state in which a seed is not actively growing but can germinate under favorable conditions.

• Germination: The process by which a seed grows into a new plant.