6.1.1 survival and response Flashcards
What is a stimulus?
A detectable change in the internal and external environment of an organism that leads to a response in the organism.
How do organisms increase their chance of survival?
By responding to changes in their environment via different response mechanisms.
What detects stimuli?
Receptors (cells).
What is the structure of the response to survival?
Stimulus → Receptor → Coordinator → Effector → Response.
What is taxis?
A simple response in which an organism moves its entire body towards a favorable stimulus or away from an unfavorable stimulus.
What is the result of a taxis?
A motile organism responds directly to environmental changes by moving its whole body either towards a favorable stimulus or away from an unfavorable one.
What is positive taxis?
Moving towards a stimulus.
What is negative taxis?
Moving away from a stimulus.
What is negative phototaxis?
Moving away from light.
What is positive chemotaxis?
Moving towards certain chemicals to aid survival.
What is kinesis?
When an organism changes the speed of movement and the rate it changes direction.
What is the response of an organism moving from an area with beneficial stimuli to an area of harmful stimuli?
To increase the rate it changes direction to return to favorable conditions.
What happens if an organism is surrounded by negative stimuli?
The rate of turning decreases to keep it moving in a relatively straight line.
to increase the chance of finding new location with favourable conditions
What is the kinesis response of woodlice crossing from a damp to a dry area?
To turn rapidly to increase the probability that it will end up back in the damp area.
What happens if woodlice are in a fully dry area?
The turning rate would decrease so that it would move in a straight line to increase the chance of finding a new damp area.
What is tropism?
When a plant responds via growth to directional stimuli.
What is positive tropism?
Growing towards stimuli.
What is negative tropism?
Growing away from stimuli.
What do plants respond to?
Light, gravity, and water.
What controls tropisms?
Specific growth factors, e.g., indoleacetic acid (IAA).
What is IAA?
A type of auxin that controls cell elongation in shoots and inhibits growth of cells in roots.
Where is IAA made?
At the tip of roots and shoots, and it diffuses to other cells.
Why do shoots need light?
For light-dependent reactions (LDR) in photosynthesis; they bend towards light controlled by IAA.
What happens in positive phototropism in shoots?
IAA is produced in the shoot tip
IAA diffuses uniformly down the shoot
IAA builds up on the shady side if unilateral light
higher conc of IAA on shady side of shot
IAA stimulates shoot cell elongation the cell on the shady side elongate more
The shoot grows towards the light
roots
dont photosynthesise
dont require light
anchor plant if they are Depp in the soil away from light
What is negative phototropism in roots?
a higher conc of IAA inhibits cell elongation
roots cells enlongate more on lighter side
roots bend away from light
What is negative gravitropism in shoots?
IAA diffuses from upper to lower side of shoot
the greater concentration of IAA on the lower side
increases cell elongation
causes this side to elongate more than the upper side..
What is positive gravitropism in roots?
IAA diffuses from the upper side to the lower side of the root
IAA inhibits the elongation of root cells so the lower side elongates less than the upper side.
This causes the root to bend downwards
as there is a greater elongation of cells on the upper side.
Anchors the plant
What tropisms do roots show?
Roots grow away from light (negative phototropism), towards gravity (positive gravitropism), and towards water (positive hydrotropism).
What is the adaptive value of positive gravitropism in roots and positive phototropism in shoots?
Positioning for light energy for photosynthesis and anchoring roots in soil for water search.
How does IAA affect the plasticity of the cell wall?
It increases the plasticity of the cell walls of young cells.
As the plant cells mature, they develop rigidity so older parts will not be able to respond.
How does IAA work?
IAA binds to cell surface receptor of the plant cell Receptor is bound to a H+ pump which is activated H+ ions are pumped into the cell membrane space This disrupts the H-bonds in the cellulose causing the microfibirls to slide past each other with ease Water now moves into plant cell via osmosis The cell now expands and elongates - increases in plasticity The auxin eventually breaks down. The pump becomes inactivated pH returns to normal Cellulose reforms H- bonds and becomes rigid
Where is IAA produced in flowering plants?
Cells in the tip produce IAA, which is transported down the shoot.
Initially transported throughout the shoot evenly.
Where is IAA produced in plant roots?
Cells in the tip of the root produce IAA, which is then transported along the root.
It is initially transported evenly.
Suggest two advantages to a plant of having roots that respond togravity by growing in the direction of its force.
esponse ensures that roots grow down into the soil, anchoring the plant firmly and bringing them closer to water (needed for photosynthesis).
What are auxins?
Plant hormones that are growth factors.
What are plant growth factors?
Hormones that affect growth and are made by cells, e.g., indoleacetic acid (IAA).
What is indoleacetic acid (IAA)?
An auxin produced in the tips of shoots and roots.
What tropisms do plant shoots show?
Shoots grow towards light (positive phototropism) and away from gravity (negative gravitropism).
Why do many organisms respond to temperature and humidity via kinesis rather than taxis?
Because kinesis is less directional; often there is no clear gradient from one extreme to the other.
How could a student recognize kinesis in an organism’s movement?
- Organism crosses sharp division between favorable and unfavorable environment: turning increases. 2. If organism moves into unfavorable environment: turning decreases; begins to move in long, straight lines.
Why do shoots show positive phototropism?
IAA diffuses to the shaded side of the shoot tip, causing cells on the shaded side to elongate faster.
Why did the student remove the shoot tip from each seedling?
tips produce IAA
Affects conc of IAA
affects shoots length/ elongation
Mitosis occurs in shoot tips
Affects length/ elongation
What are the two parts of the nervous system?
Central nervous system (CNS) and peripheral nervous system (PNS).
What is the central nervous system made up of?
The brain and spinal cord.
What does the peripheral nervous system consist of?
Pairs of nerves that originate from either the brain or the spinal cord.
What are the divisions of the peripheral nervous system?
Sensory neuron and motor neuron.
What does a sensory neuron do?
Carries nerve impulses from receptors towards the central nervous system.
What does a motor neuron do?
Carries nerve impulses away from the central nervous system to effectors (muscles or glands).
What are the divisions of the motor neuron?
Voluntary nervous system and autonomic nervous system.
What does the voluntary nervous system do?
Carries nerve impulses to body muscles and is under voluntary control.
What does the autonomic nervous system do?
Carries nerve impulses to glands, smooth muscle, and cardiac muscle involuntarily.
What happens in a simple reflex arc?
Receptor detects stimulus → sensory neuron → relay neuron in CNS coordinates response → motor neuron → response by effector.
What are the advantages of a simple reflex?
- Only 3 neurons. 2. Rapid. 3. Protect against damage to body tissues. 4. Don’t have to be learned. 5. Help escape from predators. 6. Enable homeostatic control.
What is a reflex?
A response to a sensory stimulus.
example of reflex arc process
What is a reflex arc?
The pathway along which impulses are transmitted from a receptor to an effector without involving conscious regions of the brain.
What is a relay neuron?
Found in the CNS, it connects sensory and motor neurons.
What is a suitable statistical test to determine whether a factor has a significant effect on the movement of an animal in a choice chamber?
Chi squared.
Describe a suitable procedure the student could follow to investigate the effect of different conc of GA on the growth of stem segments (5)
