Concepts 19,20 Flashcards
(146 cards)
1
Q
What features do all multicellular organisms have? 4
A
1) Macroscopic - visible to the naked eye
2) Cell specialisation –> division of labour, increase efficiency
3 ) Same organisation:
Cells > tissues > organs > organ systems
4) Communication between cells
2
Q
What is the organisation of cells?
A
Cells → tissues → organs → organ systems
3
Q
What may specialised cells be involved in?
A
Sensing predators
Movement
Absorption of digested food
Secrete digestive molecules
Secrete communication molecules
Secrete
Sensing gravity
4
Q
Plant and animal lineage?
A
- Sequence of species that follow one another over time
For example, plant lineage = evolutionary path from common ancestor to modern plants
5
Q
What is a common ancestor?
A
STARTING ORGANISM BEFORE ORGANISM SPLITS INTO 2 SPECIES
- Start with a common ancestor
- Due to MUTATION → individuals can no longer reproduce (SPECIATION)
- Results in the formation of 2 DIFFERENT SPECIES
6
Q
How do scientists estimate when multicellularity evolved? 2 ways
A
1) Molecular clock
2) Fossil record
7
Q
Molecular clock? - what method?
A
Uses the mutation rate of DNA
8
Q
Molecular clock? - what is it used to find?
A
Used to find time in history when a common ancestor speciated, formed 2 species!
9
Q
Are both molecular clock calculators and fossil records needed to accurately estimate the time when distant evolutionary events occurred?
A
YES
- Fossil records are poor for DISTANT evolutionary events
- So both must be combined for more accurate predictions
10
Q
Fossil record/molecular clock - cons?
A
FOSSIL RECORD
- Gaps in fossil record → unable to know diversification of eukaryotes + origin of multicellularity
MOLECULAR CLOCK
- Can’t confirm whether plants and animals share a unicellular or multicellular ancestor
11
Q
Multicellular lineages other than plant+animal lineages?
A
Red/brown algae
Oomycetes
Different types of fungi
12
Q
EXPLAIN how the evolution of multicellularity arose? Ie. UNICELLULAR → MULTICELLULAR 5
A
UNICELLULAR → Start with unicellular (1 cell) organism
1) CLUSTER → Cells aggregate into a cluster of cells
2) COMMUNICATION → Intercellular communication + coordination within the cluster
3) SPECIALISATION → Some clusters will contain specialised cells (COOPERATION)
4) TISSUE → Specialised cells arranged into groups called TISSUES
5) Most cells cannot survive if separated
13
Q
With reference to Volvocine green algae DESCRIBE the hypothesis that scientists have for evolution of multicellularity in this group. 2
- tip= same for all organisms regardless of green algae!
A
KEY IDEA 1 = STEPS
- Hypothesised that green algae will have a STEPWISE ACQUISITION of multicellularity
KEY IDEA 2 = INCREASING COMPLEXITY
1) as the steps progress, the green algae will INCREASE IN COMPLEXITY
2) Hence different members of green algae will have DIFFERENT DEGREES of multicellularity
3) Hence different members of green algae will have VARYING DEGREES of SPECIALISED CELLS + DEVELOPMENTAL CYCLES
14
Q
What is the result/impacts of turning into a multicellular organism?
A
CANNOT SURVIVE INDEPENDENTLY!!!
- TOTALLY DEPENDENT on other cells of the organism to DIVIDE
- Rely on intercellular communication + coordination of activities
15
Q
Pros of multicellularity? 3
A
1) Larger size
- Provides protection from predators - can’t be eaten anymore
2) Cells work in unison
- eg. cells work tgth to beat the flagella VS one cell beating the flagella alone
- multicellular would be better at a job than unicellular
3) Cells focus on one job (specialization)
- Cells dedicate energy to ONE task rather than multiple tasks
- Increases EFFICIENCY
16
Q
Does multicellular organisms evolving many times tell us that they are more successful that single-celled organisms?
A
NO
It tells us that they evolved INDEPENDENTLY
17
Q
Diffusion
A
- passive movement down a concentration gradient
- Doesn’t require energy
- Rate of movement depends on hydrophobic/hydrophilic qualities
18
Q
When does diffusion stop taking place?
A
- DIFFUSION NEVER STOPS TAKING PLACE!!!
- It just no NET movement when net equilibrium is reached
19
Q
Hypotonic
A
- High water potential outside of the cell
- Water ENTERS the vacuole via OSMOSIS
- Cell membrane pushes against the cell
- Creates TURGOR PRESSURE on all sides (pushes into the cell wall)
- BUT won’t burst due to the cell wall
- Increases TURGIDITY → plant remains upright
20
Q
Hypertonic
A
- Low water potential outside of the cell
- Water LEAVES the cell
- Vacuole decreases in size
- Plasma membrane detaches from the cell wall + cytoplasm shrinks
- PLASMOLYSIS
- Plants will wilt
21
Q
Isotonic
A
No net movement
Cell becomes FLACCID - plant starts to droop
22
Q
Osmosis
A
- Diffusion of water through a selectively permeable membrane of a region to high to low water potential
- PASSIVE PROCESS
23
Q
Water potential definition
A
Tendency of a solution + solutes in it to take up water from across a membrane
24
Q
Turgor pressure - definition
A
- Pressure caused by…
- Water inside a cell causes vacuole to swell
- This will PUSH against the plant’s cell membrane / cell wall
25
Low osmolarity
Just another word for HIGHER WATER POTENTIAL
26
Solute potential - when solute is added? - explanation
WHEN solute is added
HIGHER TENDENCY for solution + solutes in it to TAKE UP water
MORE NEGATIVE/LOWER WATER POTENTIAL
SO…SOLUTE ADDED = LOWER/MORE NEGATIVE SOLUTE POTENTIAL
27
Pressure potential - when water is added? - explanation
WATER ADDED = MORE POSITIVE PRESSURE POTENTIAL
Water is added to a fix component (eg. a cell/beaker)
Increase in internal pressure → TENDENCY to take up water DECREASES
MORE POSITIVE WATER POTENTIAL
So WATER ADDED = HIGHER PRESSURE POTENTIAL
28
Solute potential + pressure potential - what value do these USUALLY take in plant cells?
Solute potential = normally NEGATIVE
Because solute inside of the cell
Pressure potential = normally POSITIVE
Because plants tend to have some turgor pressure + turgid
29
Rate of diffusion of O2 through water is time = distance^2 / 2D. Diffusion rate D = 0.00001 cm^2/sec. Find the time taken for a single celled organism to take in oxygen if its 0.1mm.
1) Write formulas but in terms of units.
Seconds = (cm)^2 / cm^2/sec
2) Convert all values into the correct units
0.1mm = 0.01cm
3) Sub in values
Time = (0.01)^2 / 2x0.00001 = 5 seconds
30
What are the 3 exchange needs?
1) Gas exchange o2 IN, co2 OUT
2) Nutrients IN
3) Waste OUT
31
List two (2) examples of molecules/substances that need to reach many cells in a multicellular organism.
Glucose → Metabolic activity
Oxygen
32
Gas exchange
Movement of gases (o2 and co2) in opposite directions during cellular respiration
33
How does exchange occur?
DIFFUSION
** regardless of uni or multi, just the way it is done differs
Unicellular - relies on diffusion alone from environment to one cell (DIRECT EXCHANGE w/ the environment)
Multicellular - relies on special transport systems, where diffusion occurs (INDIRECT EXCHANGE w/ the environment)
34
How are exchange needs met in unicellular organisms?
By DIFFUSION alone
-As they only have one cell, the nutrients can go from surface to the inner parts of the cell
35
Exchange surfaces - definition
- Group of cells SPECIALISED
- Substances from the environment will be PASSED THROUGH THIS to get into the organism's cells
- Acts like an INTERMEDIATE
EG.
- alveoli wall in the lungs, NOT the blood capillaries
- villi
- water channels in sponges
36
Examples of gas exchange surfaces
Body surface
Trachea
Gills in fish
Lungs in animals
Stomata in plants (photosynthesis)
37
What is an issue with multicellular organisms?
- As an object gets larger, the Sa:vol ratio DECREASES
- Ie. lower surface area, higher volume
- PROBLEMS OF LOW SA:VOL EXPLAINED BELOW
38
Multicellular organisms - issues with large sa:vol? 3
1) SURFACE ISSUE
Less surface area → less CONTACT with the environment → less EXCHANGE of gases, waste, nutrients
2) VOLUME ISSUE
- Diffusion only efficient over short distances
- Diffusion only occurs on the surface of the organism → internal cells do not exchange with the environment
- SO...Diffusion is not sufficient for ALL CELLS to exchange with the environment
3) TIME ISSUE
- Diffusion takes LONGER over greater distances
39
Explain the limitations of diffusion in multicellular organisms - EXAM Q MARK SCHEME 3 marks
(ie. why can’t it rely on just pure diffusion?)
1) As an object gets larger, the Sa:vol ratio DECREASES
- ALWAYS MENTION THIS POINT
2) Think through SA:vol ratio problems, but only limited to diffusion
- VOLUME ISSUE:
- Diffusion is not sufficient for ALL CELLS to exchange with the environment
Eg. cells deep inside won’t get materials
3) SO…multicellular organisms have TRANSPORT SYSTEMS to ensure all cells get nutrients and exchange waste!!
40
Partial pressure - definition
- Imagine we have 3 gases in a container
- Partial pressure is the pressure of ONE of these gases alone
- This is proportional to the concentration of the gas
41
DALTON’S LAW
Total partial pressure = adding up partial pressure of all gases
42
Diffusion coefficient - what is it?
Solubility of a gas in a liquid + air
- Depends on medium + gas itself
43
How is co2 taken in by the stomata of plants for photosynthesis?
- Spongy mesophyll has a wet layer on its surface
- Co2 diffuses into the water
- This allows it to be TAKEN IN by the cell
44
Diffusion distance - definition
Distance the SUBSTANCE OF INTEREST, FROM THE OUTSIDE has to diffuse across the exchange surface to the target cells / cells of the organism
45
Fick’s law of diffusion - what does is state
4 factors influencing the RATE OF DIFFUSION
1) Surface area
2) Partial pressure gradient
3) Diffusion coefficient
4) Diffusion distance
46
Fick’s law of diffusion - formula
Rate of diffusion = surface area x partial pressure gradient x diffusion coefficient / diffusion distance
47
How do mutlicellular organism solve the SA:VOL issue? Examples
MAKE ADJUSTMENTS BASED ON FICKS LAW TO MAXIMISE RATE OF DIFFUSION!!!
1) Maximise SURFACE AREA
- lungs with highly BRANCHED structure, FOLDING
2) Maximise PARTIAL PRESSURE GRADIENT
- Circulatory system - constantly pumping oxygenated blood, always high o2 conc outside of body cells
- Respiratory system - ventilation (breathing) means HIGH o2 in the alveoli, heart pumps deoxygenated blood to the lung so LOW O2 in the blood vessels
3) DIFFUSION COEFFICIENT
4) Minimise DIFFUSION DISTANCE
- Alveoli of the lungs have lots of surfaces, close to human blood vessels
- Extracellular fluid right outside cells containing substances
- Gastrovascular system
++ Volume - small size/thin organism means minimise volume issue
48
How does the lungs maximise diffusion (ie. exchange)? EXAM Q APPLICATION
THINK OF FICK’S LAW
1) MAXIMISE SA:
- Achieved by branching
2) SMALL DIFFUSION DISTANCE:
- Walls of the air sacs are close to the walls of the blood capillaries
3) MAXIMISE PARTIAL PRESSURE GRADIENT
- HIGH O2 IN THE ALVEOLI - ventilation (breathing)
- LOW O2 IN THE BLOOD VESSELS - heart pumps deoxygenated blood to the lung
4) HIGH DIFFUSION COEFFICIENT
- Aqueous layer inside air sacs is thin
- Minimise diffusion through the liquid
- Because respiratory gases is more soluble in air compared to liquid
49
FISH - what is their exchange surface?
- Gills have finger like structures
- EACH finger contains blood capillaries
- Water spreads on the fin
- Water contains oxygen gas etc, which can be diffused into the blood capillaries
50
Explain how the features/properties of external gills in an axolotl facilitate gas exchange (O2 and CO2), making sure to refer to Fick’s Law in your answer.
“REFER TO FICK’S LAW” - means you have to make direct reference to the FORMULA
- Exchange surface = finger like projections (INTERMEDIATE)
1) HIGH SA
- Finger-like structures
- Means MORE CONTACT, EXCHANGE with the environment
- This will increase numerator → increase diffusion rate
2) SHORT DIFFUSION DISTANCE
- Cells on the gills are thin
- This will decrease denominator → increase diffusion rate
3) PARTIAL PRESSURE GRADIENT
- High o2 in environment, low o2 in blood vessels
- This is maximised by having deoxygenated blood CONSTANTLY moving through the gills
- Greater the numerator → greater diffusion rate
51
Fick’s law + the sponge’s exchange surface
- exam q
1) MAXIMISE SURFACE AREA
- A lot of water channels + branching
2) SHORTER DIFFUSION DISTANCE
- Many water channels → ensures that each cell is no more than 1mm away from seawater in the water channels
3) MAINTAINING PARTIAL PRESSURE GRADIENT
- high o2 in water, low o2 inside
- Continual movement of water through water channels → always freshly oxygenated water into the sponge.
52
What are some exmaples of transport systems of multicellular organisms to help with the sa:vol issue? 3
1) circulatory
2) respiratory
3) gastrovascular
53
What is bulk flow? How is it done?
CIRCULATORY SYSTEM
- Movement of LARGE VOLUMES of blood to reach every cell of the body
- Pressure is built up
54
What do circulatory systems need? 2
1) Branching to reach every cell (eg. different vessels)
2) Pressure for bulk flow
Animals → uses PUMPS (active processes) for bulk flow
Plants → transpiration, passive process
55
Gastrovascular systems
- central cavity = water channels (branches w/ water circulating)
- this means water containing gases/food from the surrounds will PERMEATE into the sponge
56
Homeostasis definition
Maintaining a constant internal environment
57
Set point
Physiological value around which the normal range fluctuates
Eg. 37 degrees in humans
58
Control centres
- INSIDE the brain/other organs of the body
- They monitor + respond to deviations for homeostasis
- USING negative/positive feedback
59
Explain the importance of homeostatic mechanisms in multicellular organisms - 2 marks
1) Cellular structures and biochemical reactions have OPTIMUM CONDITIONS for activity and efficiency
2) SO…Maintaining a constant internal environment will contribute to the survival of the organism
60
Homeostasis pathway - summarised 2 parts
1) RESPONSE = Stimulus (deviation from set point) → skin receptors → control centre (brain) → effectors
2) FINISHED, BACK TO SET POINT = receptors → control center
61
Homeostasis pathway - 6 steps
1) Stimulus = body temperature becomes too high
2) Detected by skin receptors
3) Information goes to the control centre in the brain
4) Once there is deviation from the set point, the brain sends impulses to effectors
5) Once we are back to the set point, receptors detect this
6) Goes to control centre, which will reduce sweat production
62
Negative feedback loop vs positive feedback loop
NEGATIVE FEEDBACK LOOP
- When there is change from the set point (eg. too much/too little), it acts in OPPOSITION
- So…MAINTAINS homeostasis
POSITIVE FEEDBACK LOOP
- When there is change from the set point (eg. too much/too little), it acts in the SAME DIRECTION
- So…Pushes organisms FURTHER AWAY from homeostasis
63
Negative + positive feedback loop - example
NEGATIVE:
- Let’s say there is a pathway of reactions
- The final product will INHIBIT one of the earlier reactions in the pathway
POSITIVE:
- Let’s say there is a pathway of reactions
- The final product will STIMULATE one of the earlier reactions in the pathway
64
Positive feedback loop - example in real life
BLOOD CLOTTING
- Stimulus = cut in the blood vessel walls
- Triggers platelets to release nearby signals
- Activates clotting factors, attracts more platelets to the site of injury
- Platelets release more signals to attract more platelets to the site
PRODUCT IN THIS CASE IS PLATELETS, STIMULATES MORE PLATELETS!!
65
Negative feedback loop - example in real life
When blood glucose is too high/low
Glucagon / insulin is released
66
Intercellular vs intracellular cell signalling?
INTERCELLULAR = communication BETWEEN different cells
INTRACELLULAR = communication WITHIN a cell
67
Contact-dependent signalling
Communication between physically linked cells
ANIMALS = gap junctions
PLANTS = plasmodesmata
68
Plasmodesmata vs gap junctions - structure
Basically direct channels between 2 neighbouring cells
GAP JUNCTIONS = protein channel which connects adjacent cells
PLASMODESMATA = tunnels through the cell wall. Connects one cell directly to the other cell’s cytoplasm
69
Plasmodesmata vs gap junctions - importance?
Allows for communication between cells to occur QUICKLY + EFFICIENTLY
Very important in multicellular organisms
70
Types of cell signalling?
- Intercellular, intracellular
- Autocrine, paracrine
- Contact dependent
- Endocrine
- Synaptic
Basically different TYPES/WAYS OF COMMUNICATION
71
Endocrine signalling
Communication between different parts of an organism
Eg. ligand released from the brain, into the blood, travels to target organ like the kidney
72
Synaptic signaling
- This is how nerve cells communicate with each other
- Neurotransmitters released through SYNAPTIC CLEFT
73
Blood glucose levels - set point?
Kept within 4-8 mmol/L
74
What happens if blood glucose levels are too low?
HYPOGLYCAEMIA
- Affects the nervous system
Eg. seizures, loss of consciousness
75
What happens if blood glucose levels are too high?
HYPERGLYCAEMIA
- Damage cells
- Increases risk of heart + kidney disease
- Increases risk of stroke
- Occasionally nervous system impacted through vision impairment
76
Insulin + glucagon - start + end cell?
- STARTS WITH THE PANCREAS
- ENDS WITH THE LIVER
77
Insulin + glucagon role
INSULIN
- detects high blood glucose levels
GLUCAGON
- detects low blood glucose levels
78
What releases insulin + glucagon?
PANCREAS
- Beta islet cells = insulin
- Alpha islet cells = glucagon
79
What happens when blood glucose levels are too high?
- High blood glucose levels detected by the BETA ISLET cells, PANCREAS
- Cells will release INSULIN in the blood
- Insulin binds to an insulin receptor on the LIVER cell membrane (tyrosine kinase)
- Phosphorylation occurs → attaches a phosphate to one of the amino acids of the receptor
- Initiates a signalling pathway
80
Insulin + signalling pathway - what is the result? 3
PURPOSE = DECREASE blood glucose levels
- Take glucose in
- OR stop glucose going out
1) GLUCOSE TRANSPORTERS
- this will INCREASE on the liver membrane
- increases FACILITATED DIFFUSION of glucose into the cell
2) CONVERT GLUCOSE TO GLYCOGEN
- insulin activates an enzyme (glycogen synthase)
- glycogen is a hydrophilic molecule, can’t diffuse out of the membrane
3) PHOSPHATE STUCK ONTO GLUCOSE
- Limits activity of glucose phosphatase
- phosphate from glucose can no longer be removed
- too big, can’t diffuse out
81
How is blood glucose example of negative feedback loop?
Negative feedback prevents excessive hormone production once set point has been reached
eg. INSULIN - stop release of insulin once blood glucose levels decrease
82
What happens when blood glucose levels are too low?
- High blood glucose levels detected by the ALPHA ISLET cells, PANCREAS
- Cells will release GLUCAGON in the blood
- Glucagon binds to a glucagon receptor on the LIVER cell membrane
- Activates a g-protein coupled receptor pathway
- THIS DOES 2 THINGS
83
Insulin + pathway - results summarised 2
- BREAK DOWN GLYCOGEN INTO GLUCOSE
- high conc of glucose causes diffusion into the blood
1) activate enzyme GLYCOGEN PHOSPHORYLASE
2) Inactivation of GLYCOGEN SYNTHASE
84
Two symptoms of type II diabetes include insulin insensitivity and poor glucose tolerance (slow clearance of glucose from the blood). Using your knowledge of blood glucose homeostasis explain the likely causes of these symptoms. - 2 mark exam q
NOT BETA CELLS - this detects high blood glucose levels, NOT insulin
- Insulin is detected by RECEPTORS on the liver!!
- Insulin insensitivity occurs since they have FEWER INSULIN RECEPTORS than those who are non-diabetic
- Hence they do not respond to insulin → do not increase uptake of glucose into cells → so… they have a slower clearance of glucose from the blood
85
Stimuli in plants
EXTERNAL
Light
Day length
Temp
Gravity
Nutrients
Water
INTERNAL
Developmental
86
Plant response to external stimulus 4
1) Shoot growth
2) Tropism (bending)
3) Flowering
4) Root growth
87
Plant response to internal stimulus 2
1) Cell fate
2) Specialisation
88
Plant hormones - how are they similar to animal hormones? 3
1) Can have effects at very low concentrations
2) Can act at a distance
3) Hormones are distributed throughout the plant
89
Plants vs animal hormones
2
1) LOCATION OF PRODUCTION
Animals = hormones produced by specific glands / made by specialised cells
Plants = hormones produced in many locations / diff types of cells
2) FUNCTION
Animals = hormones have specific effects
Plants = one hormone can have many roles / overlap in function
3) CATEGORIES
Animals = either hydrophillic or lipophillic
Plants = 6 main categories
90
Plant hormones - 3 key characteristics
1) Hormones can OVERLAP IN FUNCTION
- Eg. auxin + gibberellin both promote stem growth
2) Hormones can work SYNERGISTICALLY or ANTAGONISTICALLY
- Eg. abscisic acid promotes seed dormancy vs gibberellins promote seed germination
3) Respond to VARIOUS stimuli (external + internal)
91
Animal hormones - the 2 types of categories
1) Hydrophilic (water soluble) or lipophilic (lipid soluble)
2) Transported through the blood
3) Hydrophilic = act on extracellular receptors
4) Lipophilic = act on intracellular receptors (ie. inside the cell)
92
How many main types of plant hormones?
SIX MAIN TYPES
Abscisic acid
Cytokinins
Auxins
Ethylene
Brassinosteroids
Gibberellins
93
Functions of plant hormones 4
1) Growth and development
2) Seed dormancy
3) Defence against herbivores
4) Stress responses (Eg. water shortage)
94
What plant hormone is the most similar to animal hormones
All very different except BRASSINOSTEROIDS
Similar to animal steroid hormones (eg. sex hormones)
95
Cell communications via hormones vs chemical communication - 2 differences
HORMONES
- Slower
- But longer lasting
96
Where is the stomata located?
- There is a layer of epidermal cells
- Amongst this will be specialised guard cells
- Guard cells move to open or close the stomata
97
What is transpiration?
- Loss of water in a plant through the STOMATA when it is open
- because INSIDE = high WP (water vapour) // OUTSIDE = low WP
98
How does a windy day impact transpiration rates?
- Wind blows away humid air
- Less water vapour outside the cell
- SO...Faster transpiration rates
99
How does temp impact transpiration rates?
- accelerates water evaporation INSIDE the leaf
- faster diffusion through the stomata
100
Does the plant have a lot of water loss?
YES
Up to 95% of water taken up by the plant through the soil is lost through transpiration
101
What happens when the stomata is open? 2 Always a PRO and CON when the stomata opens
1) PRO = CO2 IN for photosynthesis
2) CON = WATER VAPOUR OUT = water loss
- this is balanced based on environmental situation
102
Why does the stomata have to open?
PHOTOSYNTHESIS!
- even though transpiration...
- Stomata needs to be open for uptake of co2 gas (co2 IN)
- Once inside, Co2 will dissolve in the layer of moisture surrounding the spongy mesophyll cells
103
What is the cue for stomatal opening and closing? 4
BALANCING BETWEEN WATER LOSS + PHOTOSYNTHESIS EFFICIENCY
1) CO2 CONCENTRATION
- Low co2 inside the plant → stomata open for photosynthesis
2) LIGHT
- Stomata only opens when there is light
- photosynthesis can only occur when there is light
3) AIR HUMIDITY
- Low humidity means transpiration rate increases -> stomata closes
4) WATER AVAILABILITY
- due to transpiration
- Tree loses lots of water to the environment via transpiration → INSIDE of the plant has low water availability -> stomata closes
104
How does the stomata open SCIENTIFICALLY?
GUARD CELLS!
- When the guard cells SWELL they are filled w/ water
- We call this TURGID
105
Where is ABA produced in a plant cell?
Root + leaf cells
106
When is ABA produced?
WHEN IS IT PRODUCED?
- Drought
- Water deficiency
- Low water potential
OR
- High temperatures + wind speed INCREASES transpiration rates
- Plants lose water faster
WHAT DOES THIS MEAN?
- Detrimental → plant becomes dehydrated + damaged!
SO...
- we want to CLOSE the stomata
ABA WILL HELP WITH THIS!
107
How does ABA get to the guard cells (target)?
Moved through the plant through the XYLEM
Xylem = vascular tissue, part of veins?
108
How does ABA close the stomata? - summarised 3
1) ABA BINDS TO RECEPTOR, SIGNAL TRANSDUCTION PATHWAY
2) HIGHER WP INSIDE THE GUARD CELL:
so...ANIONS MOVE OUT → K+ MOVES OUT
3) WATER MOVES OUT OF THE CELL
109
How does ABA close the stomata? 3
POINT 1
- ABA binds to ABA receptors in guard cells
- Binding triggers a SIGNAL TRANSDUCTION PATHWAY
- Secondary messenger molecules activate ion channels on the guard cell
POINT 2
- ACTIVATES potassium efflux channels
- K+ LEAVES the guard cells
- This LOWERS K+ concentration -> HIGHER WATER POTENTIAL inside the guard cell
POINT 3
- Water will move OUT of the guard cells into the SURROUNDING CELLS via OSMOSIS + aquaporins
- TURGOR PRESSURE of the guard cell decreases
- Become FLACCID, stomata closes, stops transpiration/water loss
110
What does ABA do? - simple
CLOSE THE STOMATA
111
Explain what would happen to a plant if an inhibitor of ABA (abscisic acid) synthesis was sprayed on it and the plant was subsequently exposed to drought conditions (4 marks)
1) Plant will no longer produce ABA, even if drought conditions occur
2) ABA is a SIGNAL produced in leaf and root cells when drought/low environmental water potential is detected
3) ABA targets receptors on the guard cell.
- This will ACTIVATE potassium channels, so K+ leaves the cell.
- K+ concentration decreases, water leaves the cell via osmosis.
- Guard cell turgor decreases. This causes the stomata to close.
4) SO…transpiration rate will continue to be high - water will be lost - plant will wilt
112
Other issues with water stress/prolonged drought?
- other than water loss + dehydration 2
1) Membrane integrity reduced
2) Clumping of proteins in the cytoplasm, becomes inactive
113
What are the responses of a plant to prolonged ABA exposure? Ie. long times of drought
- ABA binding to receptor triggers a signalling pathway
- This will activate 2 types of genes
GENE 1 = drought response genes
GENE 2 = gene coding for hydrophobic proteins
114
Drought response genes - what do they do?
Promotes long term response to drought by...
Will reduce shoot growth + increase root growth → plant will extract more water from the soil
115
Significance of gene coding for hydrophobic proteins
- Hydrophobic proteins bind to membrane + cellular proteins to stabilise them
- Prevents them from clumping and maintains their activity
116
How is ABA an example of homeostasis + negative feedback loop?
- When there is water stress, ABA levels INCREASE
- When there is no water stress, ABA levels DECREASE
- This will allow for restoration of original water potential levels, prevent too much hormone (KEEP AT A SET POINT)
117
Why are neural circuits important
Chemical signals are too slow
-> Sometimes we need autonomic, quick responses
118
Neural circuit example -
Bright light will make our pupil constrict
Reduces light entering the eye so we are not blind
119
Neural circuit pathway
- Photoreceptors detect light when it enters the eye
- Sudden light changes activate an electrical signal
- Electrical signal transmitted through optic nerve, then other neurons to the brain
- Brain will send a signal through the motor neuron
- Signal reaches muscles so that it constricts
120
Neural circuit pathway - how does it show a strength of multicellular organisms?
It makes use of different specialised cell types
Eg. receptor, neuron, brain, effector
121
Neurons
Nerve cells
Transmit electrical impulses
122
Key features of neurons 4
1)Soma → contains the nucleus
2) Dendrites → goes TO the soma
3_ Axon → goes AWAY from the soma
4) Axon terminals
Presynaptic neuron
Postsynaptic neuron
123
How does the axon help with faster transmission of electrical signals?
Axon has NODES OF RANVIER + myelin sheath
- Action potential is generated at the NODES OF RANVIER
- Action potential jumps over each myelin sheath, allows for faster transmission
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All or none law
- Action potential either happens or it doesn’t → all the same magnitude
- Stimulus must be strong enough to reach the action potential THRESHOLD
- If the stimulus is too weak, no action potential will be generated
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Importance of the refractory period?
1) Ensures the action potential travels ONLY FORWARDS
- ZOOM OUT
- Since the previous part of the axon is hyperpolarized and can’t fire, the action potential has no choice but to move forward
2) Limits frequency of firing
- If no hyperpolarisation, the neuron will fire immediately after the last action potential
- If this happens, the action potentials won’t be separate + clear
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What can we infer about the neuron membrane?
- Selectively permeable
- Ions like Na+ and k+ cannot diffuse across the membrane, only through the voltage-gated ION channels
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How do electrical impulses travel from one neuron to another? - LOCATION/STRUCTURE 3
1) First neuron = PRESYNAPTIC NEURON
2) Synaptic cleft = gap in between neurons, via neurotransmitters
3) Second neuron = POSTSYNAPTIC NEURON
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Why are neurotransmitters needed?
- Action potentials cannot travel through the synaptic cleft
- SO…these signals are converted to neurotransmitters
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How do electrical impulses travel from one neuron to another?
ORIGINAL STATE:
- Neurotransmitters are held in VESICLES
- Action potential reaches the end of the presynaptic terminal
TRIGGERS:
- Voltage gated Ca2+ channels OPEN
- Ca2+ rushes INTO the cell
- TRIGGERS vesicles to FUSE with the presynaptic terminal membrane
- neurotransmitters RELEASED into the synaptic cleft
TRAVELLING:
- Neurotransmitters bind to receptors on the postsynaptic neuron
- This changes the likelihood of an action potential being generated in the postsynaptic neuron
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Reuptake proteins?
Neurotransmitters are still floating in the synaptic cleft!
- Reuptake proteins on the presynaptic neuron take them back into the neuron + vesicles
- so RECYCLE neurotransmitters
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Function of the soma?
- 1 neuron can have 1000s of synapses
SO...
- These signals are combined in the soma of the POSTSYNAPTIC neuron
- It will decide whether the pass the message forward or not
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How do we know that glucagon + insulin are hydrophillic hormones?
- because receptors are on the LIVER cell membrane and not found inside the cell
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Difference between positive and negative feedback mechanisms
- Stimulus causes a change away from set point
Negative feedback
- OPPOSES this change + bring back to desired set point
- eg. glucose levels lower than normal is increased
Positive feedback ACT IN THE SAME DIRECTION + move further away from the set point
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Explain why positive feedback would not be effective at maintaining steady glucose levels
Increase in glucose = positive feedback loop will keep INCREASING the glucose levels
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Membrane potential
Relative difference in electrical charge/voltage between the inside and outside of a cell membrane
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Action potentials
- Electrochemical signal propagated along the axon
- These signals result in the release of neurotransmitters at axon terminals → synapse
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3 types of membrane potential
FROM LOWEST TO HIGHEST
1) Resting potential = -70mV
2) Threshold for action potential = point where an action potential is triggered
3) Peak of action potential = 40mV
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What would a membrane potential of -70mV mean?
More negative INSIDE the neuron
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3 types of polarisation
1) Depolarise = more POSITIVE
2) Repolarise = more NEGATIVE
3) Hyperpolarization = LOWER than the resting potential
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Action potential graph - 4 steps summarised
1) Resting potential
2) Depolarisation
- Action potential threshold → Action potential peak
3) Repolarisation
4) Hyperpolarization (refractory period)
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Polarisation - channels involved?
RESTING POTENTIAL
- maintained via sodium potassium pump
(3Na+ out, 2K+ in)
DEPOLARISATION
- become more positive
- Na+ voltage gated channels OPEN - Na+ enter the cell
REPOLARISATION
- become more negative
- Na+ voltage gated channels CLOSE
- K+ voltage gated channels OPEN
- K+ leaves the cell
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STEP 1 - Resting potential? How is it maintained?
BASICALLY WHAT IS THE STATE OF THE NEURON BEFORE AN ACTION POTENTIAL IS GENERATED?
- 70mV - more negative inside!!!
2 STRUCTURES INVOLVED:
1) Sodium potassium pump open
- 3Na+ out, 2K+ in
- Higher Na+ OUTSIDE, higher K+ INSIDE the neuron
2) K+ channels OPEN
K+ moves OUT of the cell (LESS SO, IGNORE)
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STEP 2 - Depolarisation
- Action potential threshold → Action potential peak
DEPOLARISATION!!! - BECOME MORE POSITIVE
- Signal triggers Voltage gated Na+ channels to OPEN
- (As more Na+ outside)
- Na+ diffuses INTO the neuron DOWN its concentration gradient
- Membrane is DEPOLARISED - more POSITIVE
- BUT only when it reaches the threshold, it will further depolarise + reach the peak of action potential
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STEP 3 - Repolarisation
BECOME MORE NEGATIVE
- Voltage-gated Na+ channels CLOSE
- Na+ can no longer dififuse in
- Voltage-gated k+ channels OPEN
- K+ rushes OUT of the neuron DOWN its concentration gradient
- Reduces membrane potential
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STEP 4 - hyperpolarisation
- When it reduces below resting potential = HYPERPOLARIZATION = REFRACTORY PERIOD
- Reduces the chance of a new action potential
- Resting potential will be restored
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Black mamba snakes produce a presynaptic neurotoxin that blocks voltage-gated potassium channels in neurons, leading to muscular convulsions in those bitten. Describe how this toxin might act on the neuronal action potential, and the effect this has on acetylcholine (Ach) release in the synaptic cleft. 2 marks
POTASSIUM CHANNEL MAIN ROLE = when the action potential peak is reached
1) Potassium channels can’t open → K+ cannot LEAVE → will PREVENT REPOLARISATION (ie. cannot become more negative)
2) result in more acetylcholine being released
