Response to stimuli Flashcards
(20 cards)
Why must organisms respond to changes in their environment?
To survive by finding favorable conditions, securing food, and avoiding predators.
What detects environmental changes in organisms?
Receptor cells that respond to stimuli by producing nerve impulses or secreting substances.
What happens after a stimulus is detected by receptors?
Nerve impulses travel to a coordinator (brain or spinal cord), which sends signals to an effector to produce a response.
What is the purpose of a reflex action?
To produce a rapid response to a stimulus that aids survival, often bypassing conscious brain regions.
How do plants respond to environmental stimuli like light and gravity?
Through tropisms, where growth direction changes due to uneven growth on different sides of the plant.
What is a tropism?
A growth response in plants toward (positive) or away from (negative) a stimulus such as light (phototropism) or gravity (gravitropism).
What chemical substances regulate plant growth in response to stimuli?
Specific growth factors, similar to hormones in animals, control plant growth and response.
What is Indoleacetic Acid (IAA), and where is it synthesized?
IAA is a growth factor in plants synthesized at the tips of roots and shoots, affecting cell elongation.
How does IAA promote cell elongation?
IAA lowers the pH, loosens cell walls, and allows cells to stretch when they absorb water.
How does IAA cause positive phototropism in shoots?
IAA moves to the shaded side of the shoot, causing cells there to elongate more, bending the plant toward the light.
How does IAA affect root gravitropism?
In roots, IAA inhibits cell elongation, causing the root to bend downwards toward gravity (positive gravitropism).
What is taxis?
A directional movement of an organism toward or away from a stimulus, such as phototaxis (movement toward light).
What is kinesis?
A non-directional response where the movement rate of an organism changes in response to the intensity of a stimulus.
How do planarians respond to light when exposed?
They move randomly until they find a darker, favorable environment.
What is a reflex arc?
A neural pathway that controls a reflex, involving sensory, relay, and motor neurons.
What do sensory neurons do in a reflex arc?
They carry impulses from receptors to the central nervous system (CNS).
Where are relay neurons located, and what is their function?
Relay neurons are located in the CNS and connect sensory and motor neurons.
What is the role of motor neurons in a reflex action?
Motor neurons carry impulses from the CNS to effectors (muscles or glands), triggering a response.
Give an example of a reflex action.
Withdrawing a hand from a sharp object is a reflex action mediated by sensory, relay, and motor neurons.
How are reflexes adapted for flexibility in responses?
After an initial rapid reflex response, organisms can control their reaction, allowing more complex behavior.
