← Responses of plants and animals to their external environment

1 Reading the notation

Learn these word-for-word. In Biology, marks are routinely lost for vague definitions. Examiners want the precise term.

⭐ The answer chain every Excellence response follows

1. Stimulus — name the environmental cue (light direction, day length, temperature, tide, touch).
2. Response — name the mechanism precisely (auxin migrates to the shaded side and promotes cell elongation).
3. Immediate benefit — what the organism gains right now (more light captured, less heat lost, predator avoided).
4. Reproductive success — finish here: “…so the organism survives longer / has more energy to invest in offspring, which increases its reproductive success.”

⚠

Do not stop at step 3

Stopping at “so it gets more light” is a Merit answer. The 2021–2025 schedules use the phrase reproductive success 28 times across all five years — it is the wording that closes an Excellence answer. Timing questions are marked the same way: “…ensuring flowering coincides with when the bumblebee pollinators are active, ensuring pollination and therefore kōwhai reproductive success.”

📖 Required terms the specification names (and this page used to skip)

6 terms

All listed in the NZQA 2026 assessment specification for 91603.

Phytochrome: The light-sensitive pigment in plants that detects day length. It switches between an inactive form (P_r) and an active form (P_fr) depending on the light received. This is the actual receptor behind photoperiodic responses like flowering — name it when asked HOW a plant measures day length.
Phytohormones: Plant hormones that coordinate growth and responses. Auxin (cell elongation, tropisms) and abscisic acid (closes stomata under water stress, maintains dormancy) are the two named in the specification. Abscisic acid is the “stress and shut-down” hormone; auxin is the “grow toward it” hormone.
Photoperiodic behaviour: A response triggered by day length rather than temperature or food — in plants (flowering) and animals (migration, breeding, moulting) alike. Day length is used because it is the one cue that is identical every year.
Actogram: A chart plotting an animal’s activity against time across many days, each day drawn on its own row. Read it for the free-running period: under constant conditions the activity band drifts diagonally, which proves the rhythm is endogenous.
Activity period: When in the daily cycle an animal is active — diurnal (day), nocturnal (night), crepuscular (dawn and dusk). Explain the choice by food availability, predator avoidance, or temperature — then link to reproductive success.
Navigation: Finding the way to a specific distant destination, using cues such as the sun, star patterns, the Earth’s magnetic field, landmarks and smell. Distinguish from simple orientation (taxis/kinesis), which does not require knowing where you are going.

📖 Key definitions: Responses (91603)

19 terms

Every bolded term below has appeared in past papers. Cover the right column and recite.

Stimulus: A detectable change in the environment that produces a response in an organism.
Response: The reaction of an organism to a stimulus.
Tropism: A directional growth response of a plant, where the direction is determined by the direction of the stimulus. Positive = grows toward; negative = grows away.
Nastic response: A non-directional plant response. The direction of movement is independent of the direction of the stimulus. e.g. thigmonasty (Venus flytrap), nyctinasty (day/night leaf folding).
Auxin: A plant hormone that promotes cell elongation; it accumulates on the shaded side of a shoot, causing it to bend toward light.
Kinesis: A non-directional animal response in which the rate of movement or turning changes with the intensity of a stimulus. The animal ends up in a favourable area by chance, not by steering.
Taxis: A directional animal response, movement directly toward (positive) or away from (negative) a stimulus.
Innate behaviour: Inherited, instinctive behaviour that is present without learning and is the same across all members of a species.
Learned behaviour: Behaviour that is modified as a result of experience.
Habituation: A simple form of learning in which an animal stops responding to a repeated, harmless stimulus. Survival value: saves energy.
Imprinting: Rapid learning that occurs during a limited critical period early in life and is generally irreversible.
Classical conditioning: Learning to associate a neutral stimulus with a significant one, producing the same response (Pavlov’s dogs).
Operant conditioning: Learning through the consequences of behaviour: reinforced (rewarded) behaviours increase, punished ones decrease.
Circadian rhythm: A biological rhythm with a cycle of approximately 24 hours.
Endogenous rhythm: A rhythm generated by an internal biological clock, which continues even in the absence of external cues.
Exogenous rhythm: A rhythm driven directly by an external environmental cue.
Zeitgeber: An external cue (e.g. light, temperature, tides) that entrains, resets, an endogenous biological clock.
Entrainment: The process by which an endogenous rhythm is synchronised to an environmental cycle by a zeitgeber.
Survival value: The way a response or behaviour increases an organism’s chance of surviving and reproducing. ⚠ Every Excellence answer in this standard must state this explicitly.

Related elsewhere

Study skills: NZQA command words Biology grades hinge on the command word: “describe” wants what happens, “explain” wants why, and “discuss/evaluate” wants a judgement. A precise definition plus the right depth for the verb is most of the difference between Achieved and Excellence here.