Stability and Change Flashcards

A forest ecosystem experiences a severe wildfire. Afterward, some areas are colonized by fast-growing grasses, while others see the slow regrowth of fire-resistant trees. Which statement best distinguishes between ecological resistance and resilience in this scenario?

Answer: The ability of the fire-resistant trees to survive the fire with little change is resistance; the process of grasses colonizing and starting a new growth cycle is resilience.

Resistance is an ecosystem's ability to withstand a disturbance without significant change. The trees that survived the fire exemplify this. Resilience is the ability of an ecosystem to recover and re-organize after a disturbance. The colonization by new grasses, initiating a process of succession and recovery, is a perfect example of resilience.

In the context of evolutionary biology, the theory of punctuated equilibrium proposes that species remain stable for long periods, with evolutionary changes occurring in rapid bursts. How does this concept relate to the crosscutting concept of 'Stability and Change'?

Answer: It demonstrates that a system can experience long periods of stability (stasis) that are 'punctuated' by short periods of rapid, significant change (speciation events).

Punctuated equilibrium is an excellent advanced example of Stability and Change. It describes a pattern where a system (a species) maintains a stable state for an extended time, followed by a quick and fundamental change, before settling into a new stable state. This contrasts with gradualism, where change is slow and constant.

A biochemist is studying a reversible reaction in a closed system that has reached dynamic equilibrium. If a catalyst is introduced into the system, what is the expected outcome?

Answer: The position of the equilibrium will not change, but the system will reach equilibrium faster.

A catalyst affects the rate of both the forward and reverse reactions equally. It provides an alternative reaction pathway with lower activation energy. Therefore, it does not change the concentrations of reactants and products at equilibrium (the position of equilibrium), but it does decrease the time required to reach that equilibrium.

Which of the following describes a system moving from an unstable state to a more stable one without continuous energy input?

Answer: A ball balanced carefully on the peak of a hill beginning to roll down one side.

A ball at the top of a hill is in an unstable equilibrium; any small disturbance will cause it to change state. It will then roll down to the bottom, releasing potential energy and settling into a more stable state. This process happens spontaneously without needing a continuous input of energy. The other examples represent stable cycles or states maintained by energy or balanced forces.

In climate science, the melting of arctic sea ice is often cited as a positive feedback loop. Why is this considered a 'positive' feedback loop in the context of stability and change?

Answer: Because the initial change (warming and melting) is amplified by the consequences (less reflective surface, more heat absorption), leading to further change in the same direction.

In systems thinking, a 'positive' feedback loop is one that reinforces or amplifies the initial change, pushing the system further from its stable state. White ice is highly reflective (high albedo), bouncing solar radiation back into space. When it melts, it exposes the darker ocean, which absorbs more solar radiation, leading to more warming and more melting. This amplification makes it a positive feedback loop, which causes instability.

Homeostasis, the maintenance of a stable internal environment, occurs at multiple scales in biological systems. Which of the following is an example of homeostasis at the cellular level, rather than the organismal or ecosystem level?

Answer: Maintaining a specific pH and ion concentration inside a cell through the action of membrane proteins.

While all options relate to stability and change, only the regulation of internal pH and ion concentration occurs specifically at the cellular scale. This process involves the cell membrane actively managing what enters and leaves to keep the internal environment stable for biochemical reactions, a direct example of cellular homeostasis. The other options describe homeostasis or responses to maintain stability at the level of the whole organism or ecosystem.