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Response to stimuli
topic 15
| Question | Answer |
|---|---|
| What is tropism? | a response to stimulus in a plant |
| Outline four types of tropism | Geotropism - response to gravity Phototropism - response to light Hydrotropism - response to water Chemotropism - response to chemicals |
| What is the difference between positive tropism and negative tropism? | Positive tropism is growth towards a stimulus Negative tropism is growth away from a stimulus |
| Name a growth hormone in plants | IAA or Indoleacetic acid |
| What does IAA do? | Prevents elongation of cells in a plant |
| Where does IAA collect in the shoots? | It is positively phototropic in shoots so it moves toward, and collects, in the side of the stem facing the light |
| Where does IAA collect in the roots? | It is negatively phototropic in roots so it moves away from light, and collects in the side of the root further in the ground |
| What is taxis? | Taxis is the movement of an organism in direct response to a stimulus |
| What is kinesis? | Kinesis is the |
| What is a reflex arc? | An involuntary and instant response to a harmful stimulus to prevent harm. It bipasses the control center (brain and SC) |
| What is the process of a reflex arc? | Stimulus -> receptor -> sensory neuron -> intermediate neuron -> motor neuron -> effector -> response |
| Give the name of a receptor | Pacinian corpuscle |
| What type of stimulus does a Pacinian corpuscle respond to? | Pressure |
| What is a generator potential? | The electrical conversion of stimulus energy e.g. Pacinian corpuscle converts mechanical energy to electrical impulse |
| Explain the structure of the Pacinian corpuscle | Single neuron ending surrounded by multiple layers of lamellae which are separated by gel. Capsule of constructive tissue surrounding lamellae. //|\\ \\|// 0 | 0 | |
| How does the Pacinian corpuscle establish a generator potential? | -external pressure=PC deforms -shape changed -stretch-mediated Na+ ion channels open -ions diffuse into neurone down conc gradient -depolarisation+creates generator potential -greater pressure=more channels -reach threshold +action potential formed |
| Outline rod cells | -sensitive to low intensity light -distinguish light and dark in dim light -so sensitive can detect just one photon -rods cannot distinguish colour |
| Outline cone cells | -sensitive to different wavelengths so can distinguish colours -humans have three types of cone -red, blue, and green -combinations of cones stimulated mean range of visible spectrum can be seen |
| What is spatial summation? | when a combination of receptors contribute to reach threshold for an action potential (rod cells) |
| Outline the autonomic nervous system | sympathetic NS - responsible for stimulation of effectors and speeds up activity in response to stressful stimuli parasympathetic NS - responsible for inhibition of effectors to conserve energy and replenish body''s reserves |
| Explain the first part of the initiation of a heart beat | -electrical waves generated in and sent out from sinoatrial node (pacemaker) -initiates heart beat and determines heart rate -SAN send out wave of electrical activity across walls of atrium -contraction of atrium walls |
| What is the atrioventricular septum | fibrous non-conductive tissue between atria and ventricles |
| What does the atrioventricular septum do? | prevents the electrical signal from crossing the ventricles |
| Explain the second part of the initiation of a heart beat | -impulses from atria detected by AVN -short delay allows atria to finish contracting before - impulses sent down Bundle of His to Purkinje fibres -electrical impulses from apex up ventricular walls -causes simultaneous contraction of ventricular walls |
| Why is it important ventricles contract from apex upwards? | -if heart contracted top downwards then blood would pool at apex |
Created by:
Ziggyisweird
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