Comprehensive Biology Midterm Study Guide: Scientific Method, Prokaryotes, Evolution, Protists, and Plant Biology

Plagiarism, Scientific Method, and Microscopy

Academic Integrity and Plagiarism

Plagiarism Definition: The practice of taking someone else's work or ideas and passing them off as one's own.
Internal Citation: Allows the writer to give immediate acknowledgement of sources of information used in a research paper as they are used, presented in an abbreviated format.
Works Cited Page: A list of works that were referenced in the body of a paper.
Common Knowledge: Information that needs no internal citation in a paper. Common knowledge includes information considered a well-established fact verifiable in five or more sources, common sayings and proverbs (such as "look before you leap"), and historical dates, places, and events.
Unique Phrase: Does not need an internal citation. A unique phrase is one coined by an author and used commonly by other authors in a specific genre or discipline, but is not necessarily a common fact or phrase used by everyone.

The Scientific Method

Define the Problem: Identify the specific question that you are trying to answer.
Form the Hypothesis: Formulate an educated guess to address the problem identified.
Research and Collect Data: Gather relevant observations and facts.
Experiment: Conduct tests to collect experimental data.
Conclusion: Restate the hypothesis, present the results discovered in the experiment, and explain what was learned.

Defining and Formulating a Hypothesis

Definition: A suggested solution for an experiment or event, formulated without a pre-determined outcome.
Formulation Rules:
- State the problem clearly to define the topic and focus of the experiment.
- Write the hypothesis as an "if-then" statement.
- Explicitly define the experimental variables.
Hypothesis vs. Theory:
- Hypothesis: An assumption made prior to completing research, established for testing purposes.
- Theory: A principle set to explain a phenomenon that is already supported by experimental data.

Microscopy and Magnification

Microscope Types:
- Dissecting Microscope
- Compound Microscope
Calculating Magnification:
- Total magnification is calculated using the formula: $\text{Total Magnification} = \text{Objective Lens} \times \text{Ocular Lens}$
- Specific Magnification Calculations (using a $10\times$ ocular lens):
- $4\times \text{ Objective} \times 10\times \text{ Ocular} = 40\times \text{ Total Magnification}$
- $10\times \text{ Objective} \times 10\times \text{ Ocular} = 100\times \text{ Total Magnification}$
- $40\times \text{ Objective} \times 10\times \text{ Ocular} = 400\times \text{ Total Magnification}$
- $100\times \text{ Objective} \times 10\times \text{ Ocular} = 1000\times \text{ Total Magnification}$

Prokaryotes

General Characteristics and Structure

Abundance and Distribution: Prokaryotes are the most abundant organisms on Earth, inhabiting every environment.
Extremophiles: Organisms that live in extreme environments hostile to most life forms.
Taxonomic Domains: Encompass two of the three domains of life: Bacteria and Archaea.
Cellular Structure: Lack membrane-bound organelles.
Phylogenetic Diversity: Highly diverse phylogenetically; the exact number of species remains unknown, and many species cannot be cultured in laboratory settings.
Metabolic Diversity: Capable of diverse metabolic pathways that drive fundamental biogeochemical cycles on Earth.
Cell Wall Composition:
- Bacteria: Cell walls are composed of peptidoglycan, which surrounds the cytoplasmic membrane and maintains cell shape.
- Archaea: Cell walls do not contain peptidoglycan.

Gram Staining Process and Bacterial Classification

Gram-Positive Bacteria:
- Possess a thick peptidoglycan layer that traps Crystal Violet stain.
- Appear purple at the completion of the staining process.
Gram-Negative Bacteria:
- Possess a thin peptidoglycan layer that cannot retain Crystal Violet stain.
- Must be counter-stained with Safranin, appearing pink at the end of the staining process.
Decolorization Agent: Ethyl alcohol is used as the decolorizing agent during the staining procedure.

Ecological Roles and Specific Bacterial Genera

Ecological Importance of Cyanobacteria:
- Produce oxygen through photosynthesis.
- Fix atmospheric carbon dioxide ( $CO_2$ ) and nitrogen ( $N_2$ ).
- Serve as a primary food source for invertebrates, cycling carbon and nitrogen up the food chain.
- Serve as indicators of water quality; high nutrient levels trigger cyanobacterial blooms that release toxins and reduce water quality.
- Habitat distribution includes freshwater, saltwater, hot springs, and topsoil.
Representative Cyanobacteria and Bacteria Genera:
- Anabaena:
- Forms symbiotic relationships with aquatic plants and organisms.
- Contains heterocysts—specialized cells produced during periods of nitrogen limitation.
- Heterocysts carry out nitrogen fixation, converting $N_2$ gas into usable nitrogen compounds.
- Oscillatoria:
- Filamentous cyanobacteria found in freshwater, saltwater, and hot springs.
- Named after its oscillating movement, where colonies slide back and forth against each other to position themselves relative to light sources.
- Merismopedia:
- Inhabits diverse aquatic environments and freshwater sediments.
- Forms symbiotic relationships with zooplankton.
- Forms grid-like sheet colonies resulting from cell division occurring in only two directions, bound together by a mucilaginous sheath.
- Rhodospirillum rubrum:
- Gram-negative proteobacterium.
- Appears pinkish/purple under anaerobic (oxygen-free) conditions due to the production of pigmented photosynthetic structures.
- Performs nitrogen fixation, converting $N_2$ gas into ammonia ( $NH_3$ ) usable by cells.

Phylogeny and Evolution

Phylogenetic Trees

Phylogenetic Tree Topology:
- Monophyletic: Refers to a taxonomic group consisting of a common ancestor and all of its descendants.
- Paraphyletic: Refers to a group containing a common ancestor and some, but not all, of its descendants (for example, reptiles excluding birds).
- Polyphyletic: Refers to a group containing taxa with different ancestors while excluding their most recent common ancestor (for example, protists).

Mechanisms of Evolution: Natural Selection and Genetic Drift

Natural Selection:
- Theory stating that organisms with traits better adapted to their environment have a higher probability of survival and reproduction.
- Key Principle: Individuals do not evolve; populations evolve.
- Observation #1: Inherited traits vary among individuals within a population (later understood as dominant and recessive traits).
- Observation #2: Species produce more offspring than the environment can support, leading to resource competition and mortality.
- Inference #1: Organisms with specific favorable traits that survive in their environment are more likely to reproduce and leave offspring.
- Inference #2: As organisms with non-favorable traits die, they remove those traits from the population, causing favorable traits to persist and accumulate.
Genetic Drift:
- Alters allelic frequency in a population due to random chance events unrelated to organismal fitness.

Patterns of Evolutionary Change

Convergent Evolution:
- Occurs when two distinct species from different lineages evolve similar physical or functional traits because they occupy similar environmental niches.
- Species independently evolve similar solutions to comparable environmental challenges.
- Example: The giant anteater and the echidna both independently evolved long snouts and long tongues to feed on ants.
Divergent Evolution:
- Occurs when two groups of the same species or common lineage diverge and evolve different traits in response to differing environmental and social pressures.
Distinguishing Summary: Convergent evolution involves two species with distinct ancestral origins developing similar characteristics, whereas divergent evolution involves two species branching from a common ancestor to develop different characteristics.

Protists

Key Characteristics of Protist Supergroups

Supergroup Excavata:
- Defined by a specialized feeding groove.
- Includes both autotrophic and heterotrophic species.
- Some members are photosynthetic as a result of secondary endosymbiosis (evidenced by multiple chloroplast membranes).
- Features a distinctive cytoskeleton, unique flagellar structures, and modified mitochondria.
Supergroup "SAR" (Stramenopiles, Alveolates, Rhizarians):
- Highly diverse group categorized on the basis of DNA sequence similarities.
- Stramenopiles: Characterized by straw-like hairs on their flagella that enhance swimming efficiency.
- Alveolates: Characterized by membrane-bound sac-like vesicles called alveoli beneath the plasma membrane.
- Rhizarians: Possess narrow, thread-like pseudopodia (referred to as axopodia).
Supergroup Archaeplastida:
- Contains plastids (photosynthetic organelles) derived from primary endosymbiosis of an engulfed cyanobacterium.
Supergroup Unikonta (Amoebozoans):
- Heterotrophic feeding via phagocytosis.
- Locomotion achieved through cytoplasmic streaming.
- Extends pseudopods around prey to encapsulate and ingest food.

Ecological Importance of Protists

Diatoms:
- Fix and cycle approximately $25\%$ of Earth's carbon.
- Supply substantial amounts of atmospheric oxygen.
- Serve as a major food source for aquatic organisms.
Brown Algae (Phaeophyta):
- Produce oxygen and synthesize organic compounds in marine environments.
- Form dense underwater kelp forests that provide habitat and shelter from predators.
Dinoflagellates:
- Serve as essential marine primary producers.
- Act as endosymbionts inside reef-building corals.
- Produce potent neurotoxins during algal bloom events.
Red Algae (Rhodophyta):
- Serve as a critical primary food source in aquatic ecosystems.
- Play a key structural role in the formation and growth of tropical coral reefs.

Taxonomic Survey and Functional Morphology of Protists

Volvox:
- Domain: Eukarya | Supergroup: Archaeplastida
- Spherical colonies made of numerous connected cells. Synchronous beating of two flagella per cell drives a spinning motion through water. Undergoes asexual reproduction to produce internal daughter colonies.
Pandorina:
- Domain: Eukarya | Supergroup: Archaeplastida
- Colonial green alga composed of grouped flagellated cells.
Spirogyra:
- Domain: Eukarya | Supergroup: Archaeplastida
- Filamentous green alga forming long, unbranched chains of identical cells attached end-to-end. Characterized by distinctive spiral chloroplasts.
Chlamydomonas:
- Domain: Eukarya | Supergroup: Archaeplastida
- Unicellular green alga featuring two flagella and a light-detecting stigma (eyespot).
Caulerpa:
- Domain: Eukarya | Supergroup: Archaeplastida
- Benthic green alga found attached to substrate beds and frequently washed ashore.
Ulva:
- Domain: Eukarya | Supergroup: Archaeplastida
- Multicellular marine green alga commonly known as sea lettuce.
Rhodophyta (Red Algae):
- Domain: Eukarya | Supergroup: Archaeplastida
- Red algae that owe their characteristic pigmentation to the accessory photosynthetic pigment phycoerythrin.
Phylum Mycetozoa (Slime Molds):
- Domain: Eukarya | Supergroup: Unikonta (Amoebozoans) | Phylum: Mycetozoa
- Amoeboid organisms that ingest food particles by phagocytosis and digest them intracellularly.
- Plasmodial Slime Molds: Multi-nucleated supercells composed of a continuous mass of cytoplasm uninterrupted by cell membranes.
- Cellular Slime Molds: Exist as independent solitary cells when food is abundant; aggregate into a multicellular slug-like structure when food becomes depleted.
Amoeba:
- Domain: Eukarya | Supergroup: Unikonta (Amoebozoans)
- Moves via pseudopodia. Utilizes a contractile vacuole to collect and expel excess water to maintain osmoregulation.
Foraminifera:
- Domain: Eukarya | Supergroup: SAR / Rhizaria
- Planktonic heterotrophs with shells composed of calcium carbonate ( $CaCO_3$ ). Narrow pseudopodia project through microscopic pores in the shell.
Radiolarians:
- Domain: Eukarya | Supergroup: SAR / Rhizaria
- Planktonic heterotrophs with intricate skeletons made of silica ( $SiO_2$ ) and thin pseudopodia supported by internal microtubules.
Dinoflagellates:
- Domain: Eukarya | Supergroup: SAR / Alveolata
- Unicellular protists protected by interlocking cellulose plates. Feature two perpendicular flagella causing a characteristic whirling swimming motion. Overgrowths cause toxic "red tides."
Stentor:
- Domain: Eukarya | Supergroup: SAR / Alveolata
- Large horn-shaped ciliate featuring a prominent ciliated corona used for feeding and locomotion.
Paramecium:
- Domain: Eukarya | Supergroup: SAR / Alveolata
- Ciliated protist exhibiting taxis (directional movement in response to environmental stimuli like light or chemicals).
Diatoms:
- Domain: Eukarya | Supergroup: SAR / Stramenopila
- Unicellular photosynthetic algae containing chlorophyll a and c. Glass-like cell wall composed of silicon dioxide ( $SiO_2$ ). Flagellated stages feature straw-like hairs.
Brown Algae / Giant Seaweed (Phylum Phaeophyta):
- Domain: Eukarya | Supergroup: SAR / Stramenopila | Phylum: Phaeophyta
- Large multicellular marine algae. Anatomical structures include:
- Fronds: Leaf-like photosynthetic structures.
- Stipe: Stem-like stalk supporting the fronds.
- Holdfast: Root-like structure anchoring the alga to benthic substrates.
- Air bladders: Gas-filled bladders providing buoyancy to hold fronds near the water surface.
Euglena:
- Domain: Eukarya | Supergroup: Excavata
- Mixotrophic protist (capable of autotrophy and heterotrophy). Moves via a flagellum and senses light using a pigmented stigma (eyespot) at the base of the flagellum.
Trypanosoma:
- Domain: Eukarya | Supergroup: Excavata
- Parasitic kinetoplastid found in blood plasma that causes African sleeping sickness. Equipped with an undulating membrane (a membrane fold incorporating the flagellum and cell body wall) enabling movement through thick fluid like blood.
Giardia lamblia:
- Domain: Eukarya | Supergroup: Excavata
- Parasitic protist transmitted through feces-contaminated water that causes giardiasis.

Seedless and Seed Plants

Plant Group Classification and Dominant Generations

Nonvascular Seedless Plants (Bryophytes):
- Dominant Generation: Gametophyte (haploid, $N$ ).
- Taxonomic Phyla:
- Marchantiophyta: Liverworts
- Bryophyta: Mosses
- Anthocerophyta: Hornworts
Seedless Vascular Plants:
- Dominant Generation: Sporophyte (diploid, $2N$ ).
- Taxonomic Phyla:
- Monilophyta: Ferns and horsetails
- Lycophyta: Club mosses and spike mosses
Gymnosperms (Vascular Seed Plants):
- Dominant Generation: Sporophyte (diploid, $2N$ )—forms the main photosynthetic body.
- Gametophyte Generation: Reduced, haploid ( $N$ ), and dependent on the sporophyte (contained within cones).
- Taxonomic Phyla:
- Coniferophyta
- Ginkgophyta
- Cycadophyta
- Gnetophyta
Angiosperms (Vascular Flowering / Seed Plants):
- Dominant Generation: Sporophyte (diploid, $2N$ ).
- Gametophyte Generation: Reduced, haploid ( $N$ ), and dependent on the sporophyte (contained within flowers).
- Taxonomic Phylum:
- Anthophyta

Generation Dynamics in Mosses

In mosses, the green leafy structure constitutes the dominant haploid gametophyte ( $N$ ) situated at the plant base.
The diploid sporophyte ( $2N$ ) is reduced in size, physically attached to and dependent on the gametophyte, and consists of a stalk terminating in a capsule where haploid spores ( $N$ ) are produced via meiosis.

Alternation of Generations Life Cycle

Cycle Mechanics:
1. The diploid Sporophyte Generation ( $2N$ ) undergoes meiosis to produce haploid Spores ( $N$ ).
2. Spores undergo germination and mitosis to form the haploid Gametophyte Generation ( $N$ ).
3. The gametophyte produces haploid Gametes (sperm and ova) via mitosis.
4. Fertilization fuses sperm and egg to yield a diploid zygote that grows via mitosis into the Sporophyte Generation ( $2N$ ).

Alternation of generations diagram comparing nonvascular and vascular plants

Reproductive Structures in Plants

Female Reproductive Organs:
- Archegonia: Multicellular female gametangia producing eggs in nonvascular and seedless vascular plants.
- Pistil (Carpel): Female reproductive structure of flowers, comprising:
- Stigma: Receptive sticky surface for pollen capture.
- Style: Elongated tube connecting stigma to ovary.
- Ovary: Basal structure housing ovules.
- Megasporangium: Sporangium producing megaspores that develop into female gametophytes.
Male Reproductive Organs:
- Antheridia: Multicellular male gametangia producing sperm in nonvascular and seedless vascular plants.
- Stamen: Male reproductive organ of flowers, comprising:
- Anther: Terminal sac producing pollen grains.
- Filament: Stalk elevating the anther.
- Microsporangium: Sporangium producing microspores that develop into male gametophytes.
- Pollen: Protective structure housing male gametophytes.

Plant Energetics and Vascular Transport

Photosynthesis:
- Primary pathway by which plants synthesize cellular energy.
- In horsetails, photosynthetic activity takes place in stems and leaves (primarily within the stem due to reduced leaves).
- In seed-bearing plants, photosynthesis occurs within the sporophyte, which represents the photosynthetic body.
Transport and Photosynthetic Structures:
- Chloroplasts: Organelles responsible for photosynthesis; leaves serve as the primary photosynthetic organs.
- Xylem: Vascular tissue specialized for transporting water and mineral nutrients upward from roots.
- Phloem: Vascular tissue specialized for transporting sugars and metabolic products throughout the plant.
- Vascular Bundle: Organized strand combining xylem and phloem tissue.

Terrestrial Adaptations

Rhizoids and Roots: Provide structural anchorage in soil and facilitate absorption of water and minerals.
Vascular Tissue (Xylem and Phloem): Enables systemic transport of fluids, dissolved nutrients, and sugars throughout tall land plants.
Gametangia (Antheridia and Archegonia): Protective multicellular structures that prevent gametes and developing embryos from desiccating.
Cuticle: Waxy hydrophobic layer covering outer epidermal surfaces to prevent desiccation and water loss in dry aerial environments.