Responding to Changes In Environment (Topic 6) Flashcards
What are plant growth factors and where
are they produced?
• Chemicals that regulate plant growth response
to directional stimuli.
• Produced in plant growing regions (apical
meristems).
• Diffuse from cell to cell/ phloem mass transport.
Explain why shoots show positive
phototropism.
- Indoleacetic acid (IAA) diffuses to shaded side of shoot tip.
- As IAA diffuses down shaded side, it causes active transport of
H
+
ions into cell wall. - Disruption to H-bonds between cellulose molecules & action of
expansins make cell more permeable to water. (acid growth
hypothesis). - Cells on shaded side elongate faster due to higher turgor
pressure. - Shoot bends towards light.
Explain why roots show positive
gravitropism.
- Gravity causes IAA to accumulate on lower
side of the root. - IAA inhibits elongation of root cells.
- Cells on the upper side of the root
elongate faster, so the root tip bends
downwards.
Contrast mammalian hormones and
plant growth factors. (CASTS)
CASTS- Concentration, Action, Synthesis, Transport, Speed
Mammalian hormones:
C- response not always based on concentration
A- bind to complimentary proteins in/on target cells
S- specialised glands
T- circulatory system
S- faster-acting (homeostasis)
Plant growth factors:
C- response proportional to concentration
A- can affect all cells
S- various tissues in growing regions
T- diffusion of phloem translocation
S- slower-acting (plant growth)
Define taxis and kinesis. State their
advantage.
•** Taxis: directional movement in response to
external stimulus.
• Kinesis**: non-directional response to presence
and intensity of external stimulus.
• Maintain mobile organism in optimum
environment e.g. to prevent dessication.
Many organisms respond to temperature
and humidity via kinesis rather than
taxis. Why?
Less directional stimuli; often no clear
gradient from one extreme to the other.
How could a student recognise kinesis in
an organism’s movement?
- Organism crosses sharp division between favourable &
unfavourable environment: turning increases
(return to the original favourable environment). - If organism moves considerable distance into
unfavourable environment: turning slowly decreases;
begins to move in long, straight lines; sharper turns
(lead organism to new environment).
Outline what happens in a simple reflex
arc.
receptor detects stimulus → sensory
neuron → relay neuron in CNS
coordinates response → motor neuron
→ response by effector
Give the advantages of a simple reflex
- Rapid response to potentially
dangerous stimuli since only 3
neurons involved - Instinctive
Suggest 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
What features are common to all sensory
receptors?
• Act as energy transducers which
establish a generator potential.
• Respond to specific stimuli.
Describe the basic structure of a
Pacinian corpuscle.
• Single nerve fibre surrounded by layers of
connective tissue which are separated by
viscous gel and contained by a capsule.
• Stretch-mediated Na+
channels on plasma
membrane.
• Capillary runs along base layer of tissue.
What stimulus does a Pacinian corpuscle
respond to? How?
-
Pressure deforms membrane, causing
stretch-mediated Na+
ion channels to open. - If influx of Na+
raises membrane to threshold
potential, a generator potential is produced. - Action potential moves along sensory neuron.
Name the 2 types of photoreceptor cell
located in the retina.
- Cone cells
- Rod cells
Where are rod and cone cells located in
the retina?
Rod: evenly distributed around periphery
but NOT in central fovea
Cone: mainly central fovea no
photoreceptors at blind spot
Compare and contrast rod and cone
cells. (PACL)
PACL = Pigment, Visual Activity, Colour sensitivity, Light sensitivity
Rod cells:
P- rhodopsin
A- low res: many rod cells synapse with one bipolar neuron
C- monochromatic: all wavelength of light detected
L- very sensitive: spacial summation of subthreshold impulses
Cone:
P- 3 types of iodopsin
A- high res: 1 cone cell synapses with 1 bipolar neuron = no retinal convergence
C- tricolour: red, green, blue wavelengths absorbed by different types of iodopsin
L- less sensitive: not involved in night vision
Outline the pathway of light from a
photoreceptor to the brain.
photoreceptor → bipolar neuron →
ganglion cell of optic nerve → brain
Define myogenic.
Contraction of heart is initiated within the
muscle itself rather than by nerve
impulses.
State the name and location of the 2
nodes involved in heart contraction.
• Sinoatrial node (SAN): within the wall of the
right atrium.
• Atrioventricular node (AVN): near lower end
of right atrium in the wall that separates the
2 atria.
Describe how heartbeats are initiated
and coordinated.
- SAN initiates wave of depolarisation (WOD).
- WOD spreads across both atria= atrial systole.
- Layer of fibrous, non-conducting tissue delays impulse
while ventricles fill & valves close. - AVN conveys WOD down septum via Bundle of His, which
branches into Purkinje fibres along ventricles. - Causes ventricles to contract from apex upwards.
State the formula for cardiac output
cardiac output (CO)
stroke volume (V) x heart rate (R)
What is the autonomic nervous system?
• System that controls involuntary
actions of glands and muscles.
• 2 subdivisions: sympathetic &
parasympathetic.
State the difference between the
sympathetic and parasympathetic
nervous system.
Sympathetic involved in ‘fight or flight’ response:
stimulates effectors to speed up activity.
Parasympathetic involved in normal resting
conditions: inhibits effectors to slow down
activity.
Name the receptors involved in changing
heart rate and state their location.
Baroreceptors (detect changes in blood
pressure): carotid body.
Chemoreceptors (detect changes in pH e.g.
due to increase in CO2
concentration): carotid
body & aortic body.
