General Biology Collaborative Exam Study Guide: Genetics, Plant Biology, and Physiology

Genetics and Molecular Biology

DNA Structure and Function

The structure of DNA is fundamental to its role in heredity and cellular function. DNA consists of two antiparallel strands forming a double helix, with complementary base pairing between nucleotides.

• Complementary Base Pairing: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).

• Antiparallel Strands: The two strands run in opposite directions (5' to 3' and 3' to 5').

• Double Helix: The helical structure provides stability and allows for efficient replication and repair.

• Example: If one DNA strand has the sequence 5'-ATCG-3', the complementary strand will be 3'-TAGC-5'.

Additional info: The backbone of DNA is composed of alternating sugar and phosphate groups.

Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information from DNA to RNA to protein.

• Transcription: DNA is transcribed into messenger RNA (mRNA).

• Translation: mRNA is translated into a polypeptide (protein) at the ribosome.

• Codons: Each set of three nucleotides in mRNA (codon) specifies an amino acid.

• Example: The DNA coding sequence 5'-ATG-3' is transcribed to mRNA as 5'-AUG-3', which codes for methionine.

Gene Expression and Regulation

Gene expression is regulated at multiple levels, including transcription, mRNA processing, and translation.

• mRNA Processing: Addition of a 5' cap, poly-A tail, and splicing of introns.

• Regulation: Genes can be turned on or off in response to environmental or developmental signals.

• Example: During transcription, only exons are retained in mature mRNA, while introns are removed.

Plant Structure, Growth, and Development

Plant Tissues and Organs

Plants are composed of various tissues and organs that perform specialized functions.

• Vascular Bundles: Arranged in rings in dicots, scattered in monocots.

• Meristems: Regions of active cell division, such as the root and shoot apical meristems.

• Example: In celery, vascular bundles are visible as strings in the stalk.

Resource Acquisition and Transport

Plants acquire water and nutrients from the soil and transport them through specialized tissues.

• Xylem: Transports water and minerals from roots to shoots.

• Phloem: Transports sugars and other organic molecules throughout the plant.

• Water Potential ($\Psi$): Determines the direction of water movement. Water moves from regions of higher to lower water potential.

• Equation: $\Psi = \Psi_s + \Psi_p$ (where $\Psi_s$ is solute potential and $\Psi_p$ is pressure potential)

• Example: Placing a plant cell in a solution with lower solute concentration than the cytoplasm causes water to enter the cell.

Plant Growth Responses

Plants respond to environmental stimuli through growth and movement.

• Tropisms: Directional growth responses to stimuli such as light (phototropism) and gravity (gravitropism).

• Hormones: Auxins promote cell elongation, especially on the shaded side of a plant, causing bending toward light.

• Example: A root placed horizontally bends downward due to differential growth rates on upper and lower sides.

Plant Reproduction and Adaptation

Modes of Reproduction

Plants reproduce sexually and asexually, with each mode offering distinct advantages.

• Asexual Reproduction: Involves structures like rhizomes, producing genetically identical offspring.

• Sexual Reproduction: Involves pollination and fertilization, increasing genetic diversity.

• Example: Plant X reproduces by rhizomes (asexual), while Plant Y reproduces by seeds (sexual).

Adaptations to Environment

Plants exhibit various adaptations to survive in different environments.

• Drought Resistance: Some plants have deep roots or waxy leaves to reduce water loss.

• Competition: Plants may grow taller or spread horizontally to outcompete neighbors for light and nutrients.

• Example: In a crowded field, plants with rapid vertical growth may outcompete others for sunlight.

Animal Physiology and Feedback Mechanisms

Homeostasis and Feedback Loops

Animals maintain internal stability through homeostasis, often regulated by feedback mechanisms.

• Negative Feedback: A change in a physiological variable triggers a response that counteracts the initial change.

• Positive Feedback: A change triggers a response that amplifies the initial change.

• Example: Thermoregulation involves negative feedback to maintain body temperature.

Hormonal Regulation

Hormones coordinate physiological processes and responses to environmental changes.

• Auxins: Plant hormones that regulate growth and development.

• Animal Hormones: Regulate processes such as hunger, satiety, and stress responses.

• Example: In humans, hunger signals from the brain increase salivation, while satiety signals decrease it.

Data Analysis and Experimental Design

Interpreting Graphs and Experimental Results

Scientific experiments often involve collecting and analyzing data to draw conclusions.

• Stomatal Density: The number of stomata per unit area on a leaf affects gas exchange and water loss.

• Experimental Variables: Manipulating environmental factors (e.g., distance from highway) can affect plant traits.

• Example: Ivy sampled at various distances from a highway shows variation in stomatal density, which may influence CO2 uptake.

Distance from Highway	Stomatal Density
Close (A)	Lower
Far (D)	Higher

Additional info: Higher stomatal density can increase CO2 uptake but may also increase water loss.

Summary Table: Key Concepts

Concept	Definition	Example/Application
DNA Structure	Double helix with complementary base pairing	Genetic inheritance
Central Dogma	Flow of information: DNA → RNA → Protein	Gene expression
Water Potential ($\Psi$)	Determines water movement in plants	Osmosis in plant cells
Negative Feedback	Counteracts changes to maintain stability	Thermoregulation
Positive Feedback	Amplifies changes	Labor contractions