Responses to Stimuli in Organisms and
Homeostasis Questions and Answers
Stimuli - ✅✅a change in the internal or external environment
Organisms' Response to Stimuli - ✅✅for survival (predator/prey awareness, homeostasis)
Taxis - ✅✅directional response to a stimuli (towards or away from)
Kinesis - ✅✅non-directional movement from an unfavourable area to a favourable area
Kinesis (continued) - ✅✅organism moves rapidly and randomly in unfavourable area until they reach
favourable area where they move slowly and less randomly
Kinesis (continued) - ✅✅so spends more time in favourable area, less time in unfavourable area
Tropism - ✅✅directional growth in plants in response to a stimuli
Positive Tropism - ✅✅towards a stimulus
Negative Tropism - ✅✅away from a stimulus
Types of Tropism - ✅✅light = photo, water = hydro, gravity = geo
Positive Phototropism - ✅✅shoot shows positive phototropism and negative geotropism
Positive Geotropism - ✅✅root shows positive geotropism and positive hydrotropism
, Plant Growth Factor - ✅✅equivalent to animal hormones
Plant Growth Factor (continued) - ✅✅difference: made by cells throughout the plant, only affects
cells locally, affects growth
Effects of IAA - ✅✅promotes growth in the shoot, inhibits growth in the root
Positive Phototropism Mechanism - ✅✅shoot tip produces IAA, sending it down both sides causing
the shoot to grow forwards
Positive Phototropism Mechanism (continued) - ✅✅if light is present on one side, the IAA
redistributes to the opposite side (shaded side)
Positive Phototropism Mechanism (continued) - ✅✅this causes the opposite side to grow faster, so
the shoot bends towards the light
Negative Geotropism Mechanism - ✅✅if gravity is present on one side, the IAA redistributes to the
same side
Negative Geotropism Mechanism (continued) - ✅✅this causes the same side to grow faster, so the
shoot bends away from gravity towards the light
Positive Geotropism/Hydrotropism Mechanism - ✅✅if gravity/water is present on one side, the IAA
redistributes to the same side
Positive Geotropism/Hydrotropism Mechanism (continued) - ✅✅this causes the same side to grow
slowly, so the opposite side grows faster, so the root bends towards the gravity/water
Evidence for Tropism - ✅✅removing or covering shoot tip prevents tropism [tip causes tropism]
Homeostasis Questions and Answers
Stimuli - ✅✅a change in the internal or external environment
Organisms' Response to Stimuli - ✅✅for survival (predator/prey awareness, homeostasis)
Taxis - ✅✅directional response to a stimuli (towards or away from)
Kinesis - ✅✅non-directional movement from an unfavourable area to a favourable area
Kinesis (continued) - ✅✅organism moves rapidly and randomly in unfavourable area until they reach
favourable area where they move slowly and less randomly
Kinesis (continued) - ✅✅so spends more time in favourable area, less time in unfavourable area
Tropism - ✅✅directional growth in plants in response to a stimuli
Positive Tropism - ✅✅towards a stimulus
Negative Tropism - ✅✅away from a stimulus
Types of Tropism - ✅✅light = photo, water = hydro, gravity = geo
Positive Phototropism - ✅✅shoot shows positive phototropism and negative geotropism
Positive Geotropism - ✅✅root shows positive geotropism and positive hydrotropism
, Plant Growth Factor - ✅✅equivalent to animal hormones
Plant Growth Factor (continued) - ✅✅difference: made by cells throughout the plant, only affects
cells locally, affects growth
Effects of IAA - ✅✅promotes growth in the shoot, inhibits growth in the root
Positive Phototropism Mechanism - ✅✅shoot tip produces IAA, sending it down both sides causing
the shoot to grow forwards
Positive Phototropism Mechanism (continued) - ✅✅if light is present on one side, the IAA
redistributes to the opposite side (shaded side)
Positive Phototropism Mechanism (continued) - ✅✅this causes the opposite side to grow faster, so
the shoot bends towards the light
Negative Geotropism Mechanism - ✅✅if gravity is present on one side, the IAA redistributes to the
same side
Negative Geotropism Mechanism (continued) - ✅✅this causes the same side to grow faster, so the
shoot bends away from gravity towards the light
Positive Geotropism/Hydrotropism Mechanism - ✅✅if gravity/water is present on one side, the IAA
redistributes to the same side
Positive Geotropism/Hydrotropism Mechanism (continued) - ✅✅this causes the same side to grow
slowly, so the opposite side grows faster, so the root bends towards the gravity/water
Evidence for Tropism - ✅✅removing or covering shoot tip prevents tropism [tip causes tropism]
