Survival and Response

Survival and Response

1. Stimulus - detectable change in internal/external environment of an organism that produces a response

2. Tropism - a plant's growth response to an external, directional stimulus

3. Plant growth regulators (not hormones): stimulate or inhibit growth e.g. auxin

4. IAA - produced by the tip of the shoot, diffusing to other parts of the plant and causes uneven distribution of IAA, causing uneven growth

   • Positive phototropism in shoots (towards light)
   • Negative phototropism in roots (away from light)

5. A taxis is a simple, directional response to a stimulus

6. A kinesis is a non-directional response to a stimulus, rate of movement or rate of change in direction linked to intensity of stimulus

7. Nerve cells (neurones) secrete neurotransmitters onto target cells, resulting in rapid, short-lived and localised responses

8. Reflex Arc

   • Sensory neurones carries impulse from receptors to CNS
   • Motor neurones carries impulse from CNS to an effector (e.g. muscle/gland)
   • Some are just monosynaptic, very fast, only sensory & motor neurones
   • Most spinal reflexes are linked by a relay neurone, within spinal cord called the grey matter

9. Sympathetic (noradrenhaline) & parasympathetic (acetylcholine)

   • Medulla oblongata controls the cardiac centre in the brain
     • Chemoreceptors in the walls of the carotid arteries detect increase in CO2 levels in the blood as pH decreases, responding by increasing frequency of impulses to sympathetic nerve, increasing heart rate
     • Baroreceptors detects changes in blood pressure in the aorta e.g. increase changes in blood pressure, increase impulses in sympathetic nerve and noradrenhaline released
   • More frequent impulses in the sympathetic nerve/fewer in the parasympathetic results in a faster heart rate
   • More frequent impulses in the parasympathetic nerve/fewer in the sympathetic results in a faster heart rate

Images and files in the map