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Concept Check: Eukaryotes and Examples

• Eukaryotes can be unicellular.
• Example: Protists.

Exam Preparation Topics

Dimensions of Diversity

• Understand:
  • Land plants, seed plants, and angiosperms.
  • Fungal body structures, fungal "friends" & "foes."
  • Protists.
• Major characteristics of plants: structure and development.
• Mechanisms of plant interaction with surroundings.
• Diagram relationships between major plant groups & reproductive modes.
• Plant responses to stimuli and human exploitation of these responses.

Biodiversity II: Protists

Key Concepts You Should Know

1) Eukarya as a third domain of life.
2) Protists are a non-monophyletic group of diverse eukaryotes.
3) Endosymbiosis contributed to protist diversity.
4) Overview of eukaryote "supergroups."
5) Ecological roles of protists.

Definition: Eukaryotes

• Organisms with a nucleus and other membrane-bound organelles.

Examples of Eukaryotes

• Animals, plants, fungi, protists.

Review of Endosymbiosis

• Description:
  • A larger prokaryotic cell (likely an archaeal host) engulfed smaller free-living bacteria forming a symbiotic relationship without digesting them.
• Engulfing of aerobic heterotrophic bacterium → Common ancestor of heterotrophic eukaryotes (mitochondria).
• Engulfing of photosynthetic bacterium → Common ancestor of photoautotrophic eukaryotes (chloroplasts).

Definition: Protists

• A eukaryote that is not a plant, animal, or fungus.

Characteristics of Protists

• Mostly unicellular.
• Nutritional diversity:
  • Photoautotrophs: Produce own food through photosynthesis.
  • Heterotrophs: Obtain food from other organisms.
  • Mixotrophs: Combine photosynthetic and heterotrophic nutrition.

Unicellular vs. Multicellular

• Multicellular: Cells are specialized for different functions.
• Unicellular: A single cell performs all functions of life.

Autotroph Evolution Among Protists

• A heterotrophic eukaryote engulfed a cyanobacterium, which then evolved into a chloroplast.

Large Subgroups of Protists

• Protists do not form a single natural (monophyletic) group:

1. Excavata

• Includes parasites, predators, producers.

2. SAR (Stramenopiles, Alveolates, Rhizarians)

• Example: Kelp (brown algae)
  • Photosynthetic and multicellular.
  • Has root-like "holdfast" and leaf-like floating "blades."
  • Important ecologically (e.g., kelp forests).

3. Archaeplastida

• Includes red and green algae.
  • Red Algae: Possesses photosynthetic pigments.
  • Green Algae: Closely related to plants.

4. Unikonta

• Example: Plasmodial slime molds.
  • Not multicellular! A single mass of cytoplasm with many nuclei.
  • Feeds on decaying organic matter and forms a fruiting body for reproduction, similar to fungi.

Ecological Roles of Protists

1. Photosynthesize.
2. Provide food as primary producers.
3. Engage in symbiotic relationships (e.g., gut symbionts).
4. Act as pathogens.

Biodiversity III: Fungi

Key Concepts You Should Know

1) Overview of fungi body structure, function, and life cycle.
2) Types of symbiotic relationships.
3) Overview of fungal diversity and example groups.
4) Human dependence on fungi.

Definition: Fungi

• Crucial for terrestrial ecosystems.
• Roles include organic material decomposition and nutrient recycling.
• Mostly multicellular; heterotrophs that feed by absorption.
• Most exhibit cell walls containing chitin.
• Propagate by producing spores and include decomposers, parasites, and mutualists.

Types of Symbiotic Relationships

Symbiosis Definition

• Occurs when two species live in close contact.

Types:

1. Mutualism: Both organisms benefit.
   • Example: Bees and flowers.
2. Commensalism: One organism benefits; the other neither helped nor harmed.
   • Example: Barnacles on whales.
3. Parasitism: One organism benefits while the other is harmed.
   • Example: Mosquito feeding on blood.
   • Pathogens: symbiont causes disease to host (e.g., Malaria).

Fungal Body Structure and Function

Heterotrophic Fungi

• Digest organic matter by secreting enzymes and absorbing nutrients.

Specialized Hyphae Examples

1. Trapping and Killing Prey:
   • Hyphae in soil trap nematodes and digest tissues.
2. Arbuscules:
   • Hyphae specialized to extract nutrients from living plant cells.

Types of Mycorrhizae

1. Ectomycorrhizae

• Fungi surround the outside of roots (e.g., in trees like pine and oak).
• Do not penetrate root cells.

2. Arbuscular Mycorrhizae

• Fungi penetrate root cells, forming arbuscules inside cells.
• Most common type (found in many crops and grasses).

Mycorrhizal Fungi: Mutualistic Symbiosis with Plants

Benefits to Fungus

• Receives sugars (glucose and carbohydrates) produced by plants.

Benefits to Plant

• Increased water absorption.
• Enhanced uptake of minerals, especially phosphorus.
• Improved resistance to drought and pathogens.

The Fungi Life Cycle

Stages of the Life Cycle

1. First Stage:
   • Fungi usually begin as haploid spores (n).
   • Spores germinate and develop into hyphae, forming a mycelium (the fungus's main body).
2. Plasmogamy (Fusion of Cytoplasm):
   • Compatible haploid mycelia fuse, merging cytoplasm but keeping nuclei separate.
   • Creates a dikaryotic (n + n) stage.
3. Karyogamy (Fusion of Nuclei):
   • The two haploid nuclei fuse to form a diploid (2n) zygote.
   • This stage is typically short.
4. Meiosis:
   • The diploid cell undergoes meiosis to produce new haploid spores (n), which disperse, continuing the cycle.

Quick Vocabulary

• Asexual Reproduction in Fungi:
  • Common for many species, involving asexual spores (via mitosis), budding (in yeast), and fragmentation of hyphae.
  • Allows rapid population growth.
  • Hyphae: threadlike filaments; Mycelium: network of hyphae.
  • Plasmogamy: fusion of cytoplasm; Karyogamy: fusion of nuclei; Dikaryotic stage (n + n): two nuclei per cell.

Fungi Phylogeny

Groups of Fungi

1. Microsporidians:
   • All unicellular parasites of protists and animals with resistant spores.
   • Example: Nosema infects the gut, linked to colony collapse disorder.
2. Chytrids:
   • Common in lakes and soil; play roles as decomposers, parasites, and mutualists.
   • Flagellated spores called zoospores.
   • Amphibian Declines:
     • Infect amphibian skin, causing fatal disruptions.
3. Ascomycetes:
   • Approximately 90,000 species; spores produced in sacs called asci.
   • Highly diverse including pathogens, mutualistic symbionts, and decomposers.
   • Example: Lichens (symbiosis between photosynthetic organisms and fungi).
4. Basidiomycetes:
   • Approximately 50,000 species; characterized by large fruiting bodies (basidiocarps) that produce sexual spores (basidia).
   • Life cycle parts:
   • Begin with haploid basidiospores released, forming haploid mycelia.
   • Appear as a dikaryotic mycelium (n + n) after plasmogamy, maturing into a basidiocarp (mushroom).

Quick Vocabulary for Life Cycles

• Karyogamy occurs in specialized cells called basidia.
• Two haploid nuclei form a diploid (2n) nucleus; this stage is short.
• Meiosis produces four haploid basidiospores, which disperse, completing the cycle.

Plant Structure and Development

Key Concepts You Should Know

1) Differentiation of plant cells, tissues, and structures.
2) Different structures fulfill distinct functions.
3) Different meristems cause primary (length) versus secondary (width) growth.

Plant Organs

• Stems: Support and elevate.
• Leaves: Provide surface area.
• Roots: Anchor and absorb.

Monocot vs. Eudicot

Characteristics

Monocots (Approx. 25% of Angiosperms):

• Characteristics:
  • One cotyledon.
  • Leaf venation usually parallel.
  • Vascular tissue scattered.
  • Fibrous root system (no main root).
  • Pollen grain with one opening.
  • Floral organs usually in multiples of three.
  • Examples: Orchids, palms, grasses (maize, rice, wheat).

Eudicots (Approx. 70% of Angiosperms):

• Characteristics:
  • Two cotyledons.
  • Leaf venation usually net-like.
  • Vascular tissue usually arranged in a ring.
  • Taproot (main root) usually present.
  • Pollen grain with three openings.
  • Floral organs typically in multiples of four or five.
  • Examples: Legumes, roses, apples, oaks, maples.

Concept Check: Comparison Chart

• Draw a comparison chart contrasting eudicot and monocot. List examples of each.

Plant Structure and Function

Root and Shoot Systems

1. Shoot System:
   • Shoot apical meristem includes leaves and stems (upper part of plant).
2. Root System:
   • Root apical meristem (lower part of plant).

Root System Types

1. Taproot and Lateral Roots (eudicots and gymnosperms)

• Functions:
  • Absorb water and minerals.
  • Anchors plant.
  • Stores carbohydrates.

2. Fibrous Root System (angiosperm monocots)

• Functions:
  • Absorb water and minerals.
  • Anchors plant.
  • Grows in shallow soils; useful for erosion control.

3. Modified Roots:

• Storage: Stores carbohydrates and water.
• Support:
  • Prop roots support top-heavy plants.
  • Aerial roots (epiphytes) grow on other plants.
• Pneumatophores: Facilitate gas exchange.

Root Hairs

• Increase surface area for absorption near root tips; projections from single cell which are constantly replaced.

Shoot System: Stems

1. Nodes: Points on stem where leaves attach, where new growth occurs.
2. Internodes: Stem segments between nodes; primary location for elongation.
3. Apical Buds: Located at the tip of the stem; contain the apical meristem causing upward growth.
4. Axillary Buds: Form branches but are inhibited by apical dominance.

Concept of Apical Dominance

• Apical dominance occurs when the apical bud at the stem's tip prevents side branch growth.
• The apical bud produces the hormone auxin, inhibiting axillary (side) bud growth, allowing for taller rather than bushier growth.

Concept Check: Apical Bud Removal

• If the apical bud is removed, the source of auxin is cut off, leading to the growth of axillary buds, making the plant bushier.

Stem Functions

• Elevates reproductive structures and disperses pollen and fruit.
• Functions in food storage (e.g., rhizomes) and asexual reproduction (e.g., bulbs can split).

Shoot System: Leaves

1. Petiole: Stalk attaching leaf to stem.
2. Blade: Broad flat part; main site of photosynthesis.
3. Flowers: Reproductive structures developed from modified leaves and buds. Function in sexual reproduction.

Types of Leaves

• Compound Leaf: Blade divided into multiple leaflets; all attach to one petiole.
• Double Compound Leaf: Leaflets further divided into smaller leaflets, highly branched.
• Simple Leaf: One undivided blade with one petiole.

Leaf Functions and Modifications

1. Photosynthesis: Production of sugar.
2. Support.
3. Protection.
4. Storage.
5. Reproduction.

Plant Tissue Systems

1. Ground Tissue System: Storage, photosynthesis, and support.
   • Pith: Internal to vascular tissue.
   • Cortex: External to vascular tissue.
2. Vascular Tissue System: Conductive.
   • Xylem: Conducts water from roots to shoots (think straw).
   • Phloem: Conducts sugars from shoots to roots (think trap doors).
3. Dermal Tissue System: Protective.
   • Epidermis: Outer cell layer.
   • Cuticle: Waxy outer layer reducing water loss.

Leaf Anatomy

Dermal Tissue

• Guard Cells: Regulate pore openings, controlling gas exchange and water loss.
• Epidermis: Secretes cuticle; leaf skin.
• Stomata: Pores for gas exchange: CO₂ in, O₂ out, H₂O vapor out (transpiration).
• Cuticle: Waxy waterproof outer layer secreted by epidermis, reducing water loss.

Ground Tissue

• Mesophyll: Middle layer of leaf; main site for photosynthesis, containing chloroplasts.

Vascular Tissue

• Xylem: Transports water up.
• Phloem: Moves food down.
• Veins: Bundles of xylem and phloem inside leaves, providing support and transport.

Phenotypic Plasticity

• Definition:
• Plant’s capacity to modify traits in response to environmental changes, despite stable DNA.

Meristems

Definition

• Plant stem cells involved in growth:

1. Primary Growth: Growth in length (occurs at apical meristem).
2. Secondary Growth: Growth in thickness (occurs at lateral meristem).

Effects of Environmental Conditions on Growth

• Warm and wet: trees grow more.
• Cold and dry: trees grow less.

Tree Rings

• Provide age of the tree and information about historical climates.

Plant Life Cycle

Types of Plants by Life Cycle

• Annuals: Life cycle ≤ 1 year (e.g., grains, legumes, wildflowers).
• Biennials: Life cycle spans 2 years (flowers in 2nd year; e.g., beets, carrots).
• Perennials: Life cycles last many years (e.g., trees, shrubs, some grasses, wildflowers).

Lecture: Plant Resource Acquisition

Key Concepts You Should Know

1) Three mechanisms of plant transport.
2) How vascular plants pull water and minerals up through xylem.
3) How vascular plants push sugars from sources to sinks using phloem.

Mechanisms of Plant Transport

Three Mechanisms

1) Short-distance transport within plants:

• Routes: Symplastic and apoplastic.
• Selectively permeable plasma membranes involved.
  2) Transport in/out of plants:
• Increases surface area: root hairs and transport mechanisms.
• Osmosis: Diffusion of water.
• Stomata: Key for gas exchange. 3) Long-Distance (Bulk) Transport within plants:
  • Xylem and phloem.

Short Distance Mechanisms

1. Water and solutes can move through cells via the symplastic route (connected cytosol through plasmodesmata) or through cell walls via the apoplastic route.
2. There is selective permeability across the plasma membrane:
   a. Membrane potential: ATP-driven (H+ out of cell creates pH gradient driving solute transport).
   b. Co-transport: Neutral solutes (sugars) or ions move into cells alongside H+ ions.
   c. Ion channels: Responsive to voltage, membrane stretching, and chemical signals.

Transport in and out of Plant

1. Plants maximize surface area for efficient gas/water/nutrient exchange via root hairs.
2. Osmosis: Water flow determined by water potential:
   • Solute/osmotic potential: water moves toward solutes binding water.
   • Pressure potential: physical pressure on a solution.
   • Conditions: Hypotonic, Isotonic, and Hypertonic conditions impact flow.
3. Stomata: Participate in gas exchange crucial for photosynthesis/respiration:
   • Water exits through stomata, air being drier outside than inside the leaf.
   • Spongy mesophyll cells enhance evaporation surface area.
   • Guard cells regulate stomatal openings via potassium ion movement, controlled by plant hormones.
   • Opening Triggers: Light, CO₂ depletion, circadian rhythms.
   • Closing Triggers: Water deficiency, high temperatures.

Long-Distance (Bulk) Transport Within Plant

Xylem Mechanisms

1. Facilitates the bulk flow of water and minerals:
   • Movement occurs via bulk flow transpiration, predominantly driven by pressure potential.
   • Xylem structures (dead cells, hollow tubes) lack internal resistance.
   • Roots actively pump minerals, leading water to follow due to osmosis.
   • Water loss from leaves creates low pressure at the plant top, drawing water upward (cohesion and adhesion roles).
   • Cohesion: Water molecules attract each other upwards.
   • Adhesion: Water’s hydrogen bonds with xylem walls help resist gravity.
   • Main force for water movement: PULL.

Phloem Mechanisms

1. Facilitates the bulk flow of nutrients:
   • Active loading of sugars from photosynthesis (along with hormones, minerals, etc.) at source sites to unloading at sink sites.
   • Dynamic sources/sinks change as tissues produce and consume sugars.
   • Sources are where concentrations are high; sinks are where concentrations are low.
   • Phloem utilizes positive pressure carried out by living cells (sieve tubes).
   • Sieve Plates: Cell end walls with perforations facilitate nutrient passage.

Plant Nutrition

Key Concepts You Should Know

1) Soil contains a living, complex ecosystem.
2) Plants acquire essential nutrients from soil with organismal assistance:
a) Nitrogen-fixing bacteria.
b) Mycorrhizal fungi.
3) Sustainable farming practices maintain soil health.

Soil Composition

• Physical Properties: Texture and composition classified by particle size: sand > silt < clay.

Effects of Soil Composition

• Too Much Gravel/Sand: Low water retention, inadequate moisture for turgidity.
• Too Much Clay: High water retention, risks drowning plants.
• Loam: Optimal mix of sand, silt, and clay.

Nutritional Relationships in Soil

• Bacteria's Role:
  1. Decomposing dead organic matter.
  2. Fixing atmospheric nitrogen, making it accessible for plants (mutualistic relationship).
• Example of Nitrogen Fixation:
  • Roots of legumes (beans) house nitrogen-fixing bacteria in nodules.
  • Bacteria convert N₂ into ammonium, accessible for plant use.
• Farming Techniques:
  • Employ cover crops and crop rotations to enable nitrogen fixation (e.g., planting alfalfa as cover crops increases soil nitrogen and reduces erosion).

Mycorrhizal Fungi:

1. Ectomycorrhizae: Mycelium forms sheath over roots.
2. Arbuscular Mycorrhizae: Hyphae form arbuscules in root cells, enhancing absorption surface.
3. Mutual benefits:
   • Increases root water/nutrient absorption; fungi receive sugars from plants.

Nutritional Adaptations in Plants

1. Epiphytes: Produce and gather nutrients via leaves.
2. Parasitic Plants: Absorb water, minerals, and sometimes sugars from host plants.
3. Carnivorous Plants: Photosynthetic but capture insects for nutrients (e.g., Venus flytrap).

Plant Reproduction

Key Concepts You Should Know

1) Review of the angiosperm life cycle.
2) The three F’s: Flowers, double fertilization, and fruit.
3) Human use and modification of the angiosperm life cycle.

Alteration of Generations in Plants

1. Alternation occurs between:
   • Sporophyte (2n): Diploid, produces spores by meiosis.
   • Gametophyte (n): Haploid, produces gametes by mitosis.
2. Fertilization: Restores diploid state (2n).

Step by Step in Angiosperm Life Cycle

1. Sporophyte (2n):
   • Inside the flower: Microsporangia (male) and Megasporangia (female).
2. Meiosis occurs in Microsporangia (2n):
   • Produces microspores (n).
3. Meiosis occurs in Megasporangia (2n):
   • Produces megaspores (n).
4. Gametophyte formation (Mitosis):
   • Male (microspore to pollen grain).
   • Female (megasporocyte to embryo sac).
5. Gametogenesis (Mitosis):
   • Male gametophyte: forms sperm (n).
   • Female gametophyte: forms ovule (egg, n).
6. Pollination: Transfer of pollen lands on stigma; pollen tube grows.
7. Double Fertilization: Two sperm enter:
   • First sperm fertilizes egg (forms zygote, 2n = embryo).
   • Second sperm fertilizes two polar nuclei (forms endosperm, 3n).
8. Seed Formation: Contains:
   1. Embryo (2n).
   2. Endosperm (3n).
   3. Seed coat (2n, from parent tissue).

• Seed germinates to develop a new sporophyte (2n).

Concept Check: Definitions

• Haploid (n):
  • Microspore, Megaspore, Pollen grain, Egg.
• Diploid (2n):
  • Sporophyte plant, Microsporangia, Megasporangia, Zygote, Seed coat.
• Triploid (3n):
  • Endosperm.

Angiosperm Life Cycle Overview

1. Seed: Contains embryo and food supply in protective coat; initially dormant until suitable conditions.
   • Germination factors include water, light/temp, and fire.
   • Eudicots have dual “leaves”; monocots have one foliage leaf first.
2. Flower: Specialized for sexual reproduction.
   • Stamen: Anther plus filament (pollen produced).
   • Carpels: Ovary, style, stigma (egg produced in ovule).
   • Fruit: Develops from the mature ovary of a flower.
   • Pollination: Pollen transfers to ovule structure.
   • Double Fertilization: Two sperm fertilize cells in the ovary:
     • First sperm forms zygote (2n); second sperm forms endosperm (3n).
   • Seed: Develops from ovary tissue; aids in dispersal and co-evolution with animals (e.g., acorns cached by squirrels).
3. Asexual Reproduction in Angiosperms:
   • Fragmentation: Part of the plant develops into a new whole.
   • Root systems allow cloning through modified stems (stolons, rhizomes, bulbs).

Human Benefits of Angiosperm Life Cycle Modification

1. Many plants are modified through artificial selection (e.g., cotton and maize).
   • Cotton: Domesticated multiple times for fiber.
   • Maize: Selective breeding for larger flower heads, more caloric endosperm, and stable seed retention.
2. GMOs (Genetically Modified Organisms): Genes from one species introduced into another via biotechnology, rather than traditional breeding methods.
   • Flavr-Savr Tomato: Extended shelf-life, ripens on the vine.
   • Crops: Soy beans, corn, cassava, and various modified organisms enhance nutritional value or growth rates (e.g., rice enriched with beta-carotene).

Conclusion on GMOs

• GMOs may reduce incidences of mineral deficiency.
• Aim to decrease chemical fertilizer, herbicide, and pesticide use while improving nutritional content (e.g., increased iron).
• Discussion on the benefits and drawbacks remains ongoing and complex for various stakeholders.