Animal and Plant Responses to Environmental Stimuli

UBC bio 260 - midterm 2

Nervous System

Electrical signaling within neurons and chemical signaling at synapses.

Endocrine System

Hormonal signaling through the bloodstream to target cells.

Stress Response

Coordination between nervous and endocrine systems (e.g., sympathetic nervous system and HPA axis).

Acute Stress

Short-term stress response that can lead to effects such as memory loss and immune suppression.

Chronic Stress

Long-term stress response that can lead to effects such as memory loss and immune suppression.

Neuron Structure

Dendrites (receive signals), cell body, axon (conducts signals), synapse.

Graded Potentials

Occur in dendrites/cell body, vary in magnitude, short-distance travel.

Action Potentials

Occur in axons, 'all-or-none,' long-distance travel.

Membrane Potential

Difference in charge across the membrane, maintained by ion gradients (Na⁺, K⁺, Cl⁻, Ca²⁺).

Equilibrium Potential

Calculated using the Nernst equation; predicts ion movement.

Synaptic Transmission

Neurotransmitters released at synapses bind to receptors on postsynaptic cells.

Phototropins

Detect blue light for phototropism and stomatal opening.

Phytochromes

Detect red/far-red light for germination and flowering.

Stomatal Regulation

Blue light triggers H⁺-ATPase activation, leading to K⁺/Cl⁻ uptake and stomatal opening.

Auxin

Promotes cell elongation (acid growth hypothesis), phototropism, gravitropism.

Gibberellins (GA)

Promote seed germination by activating α-amylase.

Abscisic Acid (ABA)

Induces seed dormancy and stomatal closure under stress.

Ethylene

Triggers fruit ripening (climacteric fruits) and senescence.

Cytokinins

Delay leaf senescence.

Phototropism

Bending toward light via auxin redistribution.

Gravitropism

Roots grow downward, shoots grow upward, mediated by auxin.

Hypersensitive Response (HR)

Programmed cell death to limit pathogen spread.

Systemic Acquired Resistance (SAR)

Long-term defense activation.

Nernst Equation

Calculate equilibrium potential for ions (e.g., K⁺, Na⁺).

Goldman Equation

Predict membrane potential considering multiple ions.

Darwin's Phototropism Experiments

Demonstrated light sensing in coleoptile tips and auxin's role.

Lidocaine

Blocks voltage-gated Na⁺ channels, preventing action potentials.

Ethylene Gas

Accumulates in a closed bag, accelerating ripening (autocatalytic effect).

Stomata Under Blue Light

Opens stomata (H⁺-ATPase activation); ABA closes them (K⁺/Cl⁻ efflux).

FR:R Ratio

High R light (low FR:R) promotes germination by increasing active Pfr phytochrome.