Biology term 1

I am SO cooked, but not as cooked as I am for Chemistry!

Tolerance

Each species has an optimal range of abiotic factors (e.g., pH, temperature) for survival; organisms are only found where their tolerance range is met).

Homeostasis

The relatively constant physiological state of the body despite fluctuations in the environment.

Coordinating systems

The nervous system and the endocrine (hormonal) system work together to maintain homeostasis.

Stimulus-response mode

l 1. Stimulus detected by receptors; 2. Chemical message sent to brain/spinal cord (coordinating center); 3. Center determines if a change is needed; 4. Response triggered (e.g.

Negative feedback

Detects departures from a set point and restores balance. Examples: thermoregulation, blood sugar regulation, osmoregulation.

Positive feedback

Amplifies the change detected

Examples: childbirth, lactation, blood clotting, fever.

Mechanoreceptors

Respond to physical pressure (skin,muscles, inner ear)

Thermoreceptors

Detect skin temperature changes and send info to the hypothalamus.

Nociceptors

Detect painful/damaging stimuli (skin, organs).

Photoreceptors

Detect light, color, and movement (eyes).

Chemoreceptors

Detect chemicals (smell, taste, CO₂/O₂ levels in blood).

Central Nervous System (CNS)

Brain and spinal cord.

Peripheral Nervous System (PNS)

Cranial and spinal nerves outside the CNS.

Neuron

Tansmits signals via electrochemical changes.

Cell body (Soma)

Contains nucleus and organelles.

Dendrites

Receive messages.

Axon

Carries nerve impulses away from the cell body.

Axon terminals

Hair-like ends of the axon.

Myelin sheath

Fatty insulation around the axon (increases speed of impulse transmission).

Nodes of Ranvier

Gaps in the myelin sheath where action potentials occur.

Schwann’s cells

Produce myelin in the PNS.

Synaptic knobs

Release neurotransmitters into the synapse.

Synapse

Gap between neurons or a neuron and an effector cell.

Ganglia

Swelling where nerve cell bodies are grouped together.

Afferent (Sensory) neurons

Receive stimuli and send signals to the CNS.

Association (Interneurons)

Found only in the CNS; connect sensory and motor neurons.

Efferent (Motor) neurons

Send signals from the CNS to effectors (muscles or glands).

Reflex arc

Automatic response where the signal is processed by the spinal cord instead of the brain.

Nerve impulse

Movement of an action potential along a neuron due to changes in Na⁺ and K⁺ ion concentrations.

Excitatory synapse

Action potential continues (e.g., adrenaline).

Inhibitory synapse

Impulse stops (e.g., acetylcholine).

Endocrine system

System of endocrine glands that secrete hormones directly into the bloodstream.

Stimuli for hormonal release

Presence of a specific metabolite

Hypothalamus

Controls homeostasis; monitors hormone/chemical levels; sends signals to the pituitary gland.

Pituitary gland

Produces hormones regulating metabolism, growth, reproduction, and other vital functions; controlled by the hypothalamus.

Thyroid gland

Produces hormones essential for cell function (e.g., thyroxine (T4) and triiodothyronine (T3)); regulates heart rate, blood pressure, body temperature, growth, and metabolism; uses iodine.

Autocrine hormones

Bind to receptors on the same cell that produced them (e.g., IL-2 in T lymphocytes).

Paracrine hormones

Bind to receptors on neighboring cells (e.g., infected plant cells warning neighbors).

Endocrine hormones

Travel long distances through the blood to reach target cells.

Pheromones

Hormones that act at a distance to influence behavior or physiology (e.g., sex pheromones in insects).

Up-regulation

Increases receptors to enhance sensitivity (e.g., oxytocin receptors during pregnancy).

Down-regulation

Reduces receptors to decrease sensitivity (e.g., insulin receptors in high insulin levels).

Thermoregulation

The process by which organisms maintain or adjust their internal body temperature.

Thermoregulators

Maintain constant internal temperature (e.g., mammals, birds, reptiles).

Thermoconformers

Adopt environmental temperature (e.g., deep-sea fish).

Ectotherms

Gain heat from the environment and reduce heat loss; can be thermoregulators or thermoconformers.

Endotherms

Generate heat internally via metabolism; examples: birds, mammals, sacred lotus.

Heat exchange mechanisms

Conduction (direct contact); radiation (electromagnetic waves); evaporation (heat loss via water).

Homeostatic control of body temperature

Negative feedback loop where the hypothalamus detects temperature changes and triggers responses (e.g., releasing thyroxine to increase metabolic rate).

Osmoregulation

The process by which organisms regulate the concentrations of salts and water in their bodies.

Osmoregulators

Actively regulate internal salt concentration (e.g., shore crab).

Osmoconformers

Allow internal fluid concentration to fluctuate with the environment (e.g., spider crab).

Marine fish adaptations

Body fluids are hypotonic to seawater; drink seawater; low kidney filtration rate; salt excretion via gills.

Freshwater organisms adaptations

Live in a hypotonic environment; impermeable covering; high kidney filtration rate; active salt uptake via gills/intestines.

Terrestrial organisms adaptations

Must replace water lost; waterproof outer surface; reduced kidney filtration rate; behavioral modifications; metabolic water; tissues tolerant to water loss.

ADH (Antidiuretic Hormone)

Controls water reabsorption in the Loop of Henle and Collecting Duct; low water → more ADH → water retention; high water → less ADH → dilute urine.

Nephron

Three main functions: filter blood; reabsorb required molecules and water; secrete unwanted waste materials.

Filtration

Blood enters the glomerulus under high pressure; filtrate (water, ions, glucose, amino acids, urea) collected in Bowman’s capsule.)

Reabsorption

Proximal convoluted tubule reabsorbs glucose, amino acids, sodium, potassium, and water; distal convoluted tubule reabsorbs ions like sodium, potassium, and calcium.

Water balance in plants

Structural adaptations: cuticle; stomata & guard cells; vacuoles; homeostatic mechanisms: abscisic acid (ABA) signals stomatal closure during drought.