Biology Key Concepts: Homeostasis, Gas Exchange, Evolution, Ecology, and Speciation

What is homeostasis?

Maintaining stable internal conditions via negative feedback

What is negative feedback?

A response that reverses a change (e.g., sweating when hot)

Why does surface area-to-volume ratio matter?

Limits diffusion, heat exchange, and metabolism

Why can't large organisms rely on diffusion alone?

Diffusion is too slow over long distances

3 factors that increase gas exchange efficiency?

High surface area, thin barrier, strong gradient

5 steps of gas exchange?

Ventilation → diffusion (lungs) → transport → diffusion (tissues) → respiration

Why must respiratory surfaces be moist?

Gases dissolve in water before diffusing

Countercurrent exchange advantage?

Maintains gradient → maximizes oxygen uptake

Open vs closed circulatory system?

Open = low pressure, less efficient Closed = high pressure, efficient

Heart evolution trend?

2 → 3 → 4 chambers (increasing efficiency)

Why is a 4-chambered heart best?

No mixing → max oxygen delivery

endotherm vs ectotherm?

Endo = generates heat (high energy) Ecto = relies on environment (low energy)

What is ecology?

Study of interactions between organisms + environment

Biotic vs abiotic?

Biotic = living

Abiotic = non-living

What is a trophic level?

Position in food chain

10% rule?

Only ~10% energy transfers to next level

Exponential vs logistic growth?

Exponential = unlimited

Logistic = limited (levels off)

Carrying capacity?

Max population environment can support

Density-dependent factor?

Depends on population (disease, competition)

Density-independent factor?

Independent (weather, fire)

Keystone species?

Species with disproportionately large impact

What is a trophic cascade?

Changes at top, affect entire ecosystem

What is speciation?

Formation of new species

What prevents speciation?

Gene flow

What causes speciation?

Reproductive isolation

prezygotic barrier?

prevents mating/fertilization

Postzygotic barrier?

Offspring fail (die/sterile)

Allopatric speciation?

Physical separation

Sympatric speciation?

Same area

Parapatric speciation?

Adjacent populations

Gradualism vs punctuated equilibrium?

Slow vs rapid bursts

What does HIPPO stand for?

Habitat loss

Invasivespecies

Pollution

Populationgrowth

Overexploitation

Biggest driver of biodiversity loss?

Habitat destruction

Why are invasive species dangerous?

Outcompete natives

Why is climate change important?

Amplifies all threats

Behaviour pathway?

Stimulus → processing → response

Innate vs learned behaviour?

Innate = genetic

Learned = experience

Fixed action pattern?

Automatic sequence triggered by stimulus

What is kinesis?

Random movement

What is taxis?

Directed movement

What is altruism?

Behavior benefiting others at cost to self

Inclusive fitness?

Helping relatives → pass shared genes

Sexual selection trade-off?

Survival vs attracting mates

What is a trade-off example involving giraffes?

Long neck vs high blood pressure

What is a trade-off example involving endothermy?

Stable temperature vs high energy cost

What should you consider if a question feels vague?

Answer = trade-off

Two frogs live in the same pond but breed in different seasons. What barrier?

Prezygotic (temporal isolation) Why: They never mate → no fertilization occurs

Two insects try to mate but their reproductive structures don't fit.

Prezygotic (mechanical isolation) Why: Physical incompatibility prevents mating

Two species mate but the embryo dies early.

Postzygotic (hybrid inviability) Why: Fertilization occurs but offspring cannot develop

A horse and donkey produce a mule that cannot reproduce.

Postzygotic (hybrid sterility) Why: Offspring exists but gene flow still blocked

Wolves are removed → deer population increases → plants decrease. What is this?

Trophic cascade Why: Top predator controls entire food web (top-down control)

Sea otters decline → sea urchins increase → kelp forests disappear.

Trophic cascade Why: Removing predator disrupts ecosystem balance

A baby suckles milk immediately after birth.

Innate behaviour Why: Pre-programmed, no learning required

A dog learns to sit when given a treat.

Learned behaviour (operant conditioning) Why: Behavior changes based on experience

A bird learns to recognize its parent shortly after birth.

Learned (imprinting) Why: Requires experience during critical period

Blood glucose rises → insulin released → glucose decreases.

Negative feedback Why: Maintains homeostasis

Countercurrent exchange

two fluids flow in opposite directions to maximize the transfer of a substance (Fish gills, water flows one way, blood flows the opposite way)

Sunlight affecting plant growth.

Abiotic factor Why: Non-living environmental factor

Predators hunting prey.

Biotic factor Why: Interaction between living organisms

Drought reduces plant population.

Abiotic → biotic impact Why: Non-living factor affects living organisms

Circulation fails

oxygen delivery fails

Diffusion distance increases

efficiency drops

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