unit 6 Flashcards
What are plant growth factors and where
are they produced? 3
● 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 5
1.IAA diffuses to shaded side of shoot tip.
2. IAA diffuses down shaded side =causes active transport of H+ ions into cell wall.
3. Disruption to H-bonds between cellulose molecules & action of expansins make cell more permeable to water.
4. Cells on shaded side elongate faster due to higher turgor
pressure.
5. Shoot bends towards light
Explain why roots show positive
gravitropism3
- 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.
Define taxis
- directional movement in response to external stimulus
-responses genetically programmed)
-● Maintain mobile organism in optimum environment e.g. to prevent dessication
Define kinesis. State their advantage
●non-directional movement in response to a stimulus
-the size of the stimulus affects the speed of movement and rate of turning
favourable=rate for turning increases= chance of survival
● 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
Outline what happens in a simple reflex
arc.
SR(CNS)ME
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
define
-stimulus
-receptor
-sensory neurone 3
stim= a change that can bring about a response
receptor= changes energy from one form to another and are specfic (receptors in the eye only detect light)
sens= Specialised cell carries nerve impulses from receptors to coordinator
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,
-Mechanoreceptors- detect mechanical stimuli (pressure and vibrations)
-found in the skin
-ends in sensory neurones wrapped in lots of lamellae
● 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? 4
- 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. - This channels open which allows sodium ions to diffuse into the neurone
4 Action potential moves along sensory neuron.
What does a larger pressure cause to happen to the sodium channels and membrane (pacinian corpuscle)
-Causes a bigger generator potential
-If the generator potential reaches threshold potential it triggers an action potential
-action potential moves along sensory neurone to CNS
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
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
State the formula for cardiac output.
cardiac output (CO)
stroke volume (V) x heart rate (R)
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
how baroreceptors detect and respond to an increase in blood pressure
- Baroreceptors detect rise in blood pressure
- Increases the frequency of impulses to (cardioinhibitory centre) the medulla oblongata
- Increases the frequency of impulses to the SAN via the parasympathetic nervous system
- Decreases the rate of production of electrical waves by the SAN; therefore decreases heart rate
how baroreceptors detect and respond to fall in blood pressure(bp)
- baroreceptors detect a fall in blood pressure
2.increased frequency of impulses to medulla oblongata
3.increases the frequency of impulses to the SAN via the sympathetic nervous system - this increases rate of electrical waves produced by the SAN; increasing heart rate
How does the body respond to an
increase in CO2 concentration?
- Chemoreceptors in carotid arteries detect rise in CO2 / acidity / fall in pH
- Increases frequency of impulses to medulla oblongata
- Increases frequency of impulses to the SAN via the sympathetic nervous system
- Increases rate of electrical wave production by the SAN; increases heart rate
Describe the general structure of a motor neuron.
Cell body: contains organelles & high proportion of RER. (ribosomes)
Dendrons: branch into dendrites which carry
impulses towards cell body.
Axon: long, unbranched fibre carries nerve impulses away from cell body
Describe the additional features of a
myelinated motor neuron.
● Schwann cells: wrap around axon many times.
● Myelin sheath: made from myelin-rich membranes of Schwann cells.
● Nodes of Ranvier: very short gaps between
neighbouring Schwann cells where there is no myelin sheath.
Name 3 processes Schwann cells are involved in.
● electrical insulation
● phagocytosis
● nerve regeneration
How does an action potential pass along an
non-myelinated neuron?
- Stimulus leads to influx of Na+ ions. First section of membrane depolarises.
- electrical currents cause sodium voltage-gated
channels further along membrane to open.
Meanwhile, the section behind begins to repolarise.
3. Sequential wave of depolarisation.
Explain why myelinated axons conduct impulses
faster than unmyelinated axons
Saltatory conduction:
-Impulse ‘jumps’ from one node of Ranvier to another.
- Depolarisation cannot occur where myelin sheath acts as electrical insulator.
-So impulse does not travel along whole axon length
How is resting potential established?
- Membrane is more permeable to K+
than Na+ - Sodium-potassium pump actively transports
3Na+ out of cell & 2K+ into cell. - Establishes electrochemical gradient so membrane is more positive outside the axon
What happens during repolarisation?
- Voltage-gated Na+ channels close and
voltage-gated K+ channels open. - Facilitated diffusion of K+ ions out of cell
down their electrochemical gradient. - p.d. across membrane becomes more
negative
What happens during hyperpolarisation?
- ‘Overshoot’ when K+ ions diffuse out = p.d.
becomes more negative than resting potential. - Refractory period: no stimulus is large enough to raise membrane potential to threshold.
- Voltage-gated K+ channels close & sodium-potassium pump re-establishes resting potential
Explain the importance of the refractory period.
No action potential can be generated in
hyperpolarised sections of membrane:
● Ensures unidirectional impulse
● Ensures discrete impulses
● Limits frequency of impulse transmission
Name the factors that affect the speed of
conductance.
Myelin sheath
● Axon diameter
● Temperature
How does axon diameter affect the
speed of conductance?
greater diameter = faster
● Less resistance to flow of ions
(depolarisation & repolarisation).
● Less ‘leakage’ of ions (easier to maintain
membrane potential)
How does temperature affect speed of conductance?
Higher temperature = faster
● Faster rate of diffusion (depolarisation & repolarisation).
● Faster rate of respiration (enzyme-controlled) = more ATP for active transport to re-establish resting potential.
Temperature too high = membrane proteins denature.
How can an organism detect the strength
of a stimulus?
Larger stimulus raises membrane to
threshold potential more quickly after
hyperpolarisation = greater frequency of
impulses
What happens when blood glucose concentration falls? (4)
- Alpha cells in the Islets of Langerhans secrete glucagon
- Glucagon binds to receptors on liver cells.
- Activates enzymes that catalyse the conversion of stored glycogen to glucose (glycogenolysis)
- Activates other enzymes that convert amino acids into glucose (gluconeogenesis)
What happens when blood glucose concentration rises?
- Glucose enters the beta cells my facilitated diffusion
- Beta cells in Islets of Langerhan act as receptors and secrete insulin
- Glucose stimulates vesicles containing insulin to move and fuse with the plasma membrane
- Insulin binds to specific receptors on the cell surface membrane of liver and muscle cells.
- This causes more glucose channel proteins to be added to the membrane
- Activates the enzyme to cause glycogenesis. Increases the rate of respiration
Describe the Second Messenger Model
- Adrenaline or glucagon bind to receptors on the cell surface membrane of liver cells.
- Changes the shape of the protein that spans the membrane.
- Activates adenylate cyclase which catalyses the conversion of ATP into cyclic AMP (the 2nd messenger)
- cAMP activates enzyme protein kinase A in the cytoplasm
- Protein kinase A activates a cascade that breaks down glycogen into glucose (glycogenolysis)
Explain the effect of high glucose concentration on the water potential of the blood
- decreases WP of the blood (more solutes -> more concentrated)
- water in cells move down WP gradient by osmosis into the blood plasma or tissue fluid
- the cell would shrink/ crenate and not be able to carry out its function
What is homeostasis and some of the physiological control systems?
The maintenance of a constant internal environment within restricted limits
- stable core temperature
- stable blood pH
- stable blood glucose concentration of the blood
- blood plasma water potential
