5.1.5 Plant And Animal Responses Flashcards
1
Q
What is a tropism
A
Directional growth in response to stimuli
2
Q
Types of plant hormones
A
Auxins, gibberellins, ABA, ethene
3
Q
Roles of auxins
A
- control cell elongation
- prevent abscission
- maintain apical dominance
- tropisms
- stimulate release of ethene
- fruit ripening
4
Q
Roles of gibberellin
A
- stem elongation
- mobilisation of food stores in a seed at germination
- stimulate pollen tube growth in fertilisation
5
Q
Roles of ethene
A
- fruit ripening
- promotes abscission in deciduous trees
6
Q
Roles of ABA
A
- maintains dormancy of seeds and buds
- stimulates cold protective responses (antifreeze production)
- stimulates stomata closing
7
Q
How is germination controlled
A
- seed absorbs water, embryo activated and begins to produce gibberellins
- gibberellins stimulate production of enzymes that break down food stores in the seed (cotyledons in dicot seeds, endosperm in monocot seeds)
- food stores produce ATP for building materials so it can grow and break out of seed coat
- gibberellins switch on genes that code for amylases and proteases
- ABA acts as an antagonist to gibberellins, relative levels of both hormones determine when a seed will germinate
8
Q
Evidence supporting role of gibberellins in germination of seeds
A
- mutant varieties of seeds bred which lack the gene that enable them to make gibberellins, seeds do not germinate and if gibberellins were applied externally, they germinate normally
- if gibberellin biosynthesis inhibitors are applied to seeds, they don’t germinate as they can’t make gibberellins to break dormancy, when inhibition is removed/gibberellins applied, seeds germinate
9
Q
What are auxins
A
Growth stimulants, made in cells at tip of roots/shoots and in meristems
Move down the stem and up the roots
Effect depends on concentration
10
Q
How are auxins used to stimulate growth of the apical shoot
A
- affect plasticity of the cell wall, presence of auxins means the cell wall stretches more easily
- bind to specific receptor sites in plant cell membrane, pH falls to about 5 (optimum pH for enzymes needed to keep walls flexible and plastic)
- as cells mature, auxin destroyed, pH rises, enzymes become inactive, wall becomes more rigid and fixes, cells cant expand and grow
11
Q
How do auxins affect growth of lateral shoots
A
- high concentrations suppress growth
- apical dominance, main shoot grows quickly and lateral shoots inhibited by hormone that diffuses down the stem so do not grow
- further down the stem, auxin concentration is lower so lateral shoots grow more strongly
12
Q
Evidence for role of auxins in lateral shoot growth
A
- apical shoot is removed, auxin-producing cells removed so no auxin
- lateral shoots grow faster
- auxin applied artificially to cut apical shoot, apical dominance reasserted and lateral shoot growth is suppressed
13
Q
Role of auxins in root growth
A
- low concentrations promote root growth
- up to given concentration, more auxin reaching roots, more they grow
- high concentrations inhibit root growth
14
Q
Evidence for role of auxins in root growth
A
- if apical shoot removed, auxin reaching roots is reduced, root growth slows and stops
- if auxin is replaced artificially at cut apical shoot, growth of roots is restored
15
Q
Role of gibberellins in elongation of stems
A
affect length of internodes, gibberellins make the plant have longer and thinner stems
16
Q
Evidence for role of gibberellins in stem elongation
A
- scientists found fungus that affects rise, infected seedlings grew tall and thin
- gibberellins where the chemicals that did this
- scientists have bred dwarf varieties of plants where gibberellin synthesis pathway is interrupted
17
Q
How to investigate effect of hormones on plant growth
A
- grow seedlings in serial dilutions of different hormones
- apply different concentrations of hormones to cut ends of stems or roots
18
Q
What is synergism
A
Different hormones working together, complementing eachother and giving greater response than on their own
19
Q
What is antagonism
A
Hormones having different effects, balance between them will determine the response
20
Q
Examples of abiotic stressors
A
- Changes in day length
- temperature
- lack/excess of water
- high winds
- changes in salinity
21
Q
Why do deciduous plants need to lose their leaves
A
- If the amount of glucose required for respiration to maintain leaves and produce chemicals from chlorophyll (to protect against freezing) is greater than glucose produced by photosynthesis
- more likely to be damaged/blown over by wind in winter
22
Q
How are plants sensitive to day length
A
Light-sensitive pigment: phytochrome
Exists in Pr and Pfr
- each absorbs different type of light, ratio changed depending on levels of light
23
Q
How does abcission occur
A
- falling light levels results in falling auxin concentration which triggers ethene production
- abscission zone is at the base of the leaf stalk and is made up of 2 layers of cells sensitive to ethene
- ethene initiates gene switching in these cells, new enzymes produced
- enzymes digest and weaken cell walls in outer layer of abscission zone (separation layer)
- vascular bundles sealed off and fatty material is deposited in cells on stem side of separation layer, protective waterproof scar formed when leaf falls which prevents pathogen entry
- cells in separation zone respond to hormones, retain water and swell, puts pressure on weakened outer layer
- abiotic factors seperate layer from plant
24
Q
How is freezing prevented in plants
A
- cytoplasm in plant cells and sap in vacuoles contain solutes which lower freezing point
- some plants produce sugars, polysaccharides, amino acids, and proteins which act as antifreeze (protect from damage or freezing)
- genes suppressed and activated in response to sustained fall in temperature and reduced day length
25
How is stomata closure controlled
- leaf cells release ABA under abiotic stress, causes stomatal closure
- plant roots produce ABA which is transported to leaves where it binds to receptors on plasma membrane of stomatal guard cells, water potential reduced and turgor of cells, guard cells close as a result
26
What is herbivory
Process by which herbivores eat plants
27
Physical defences to herbivory
- Thorns
- barbs
- spikes
- spiny leaves
- fibrous and inedible tissue
- hairy leaves
- stings
28
Examples of chemical defences to herbivory
Tannins
Alkaloids
Terpenoids
Pheromones
29
How do alkaloids act as a chemical defences to herbivory
Alkaloids: group of bitter tasting, nitrogenous compounds found in plants
- many act as drugs, affect metabolism of animals that take them in, sometimes poison them
e.g. caffeine, nicotine, morphine, cocaine
Caffeine: toxic to fungi and insects, spreads in soil and prevents germination of seeds of other plants
Nicotine: toxin produced in roots and stored in vacuoles in leaves to be released when leaf is eaten
30
How do pheromones act as chemical defences to herbivory
Pheromone: chemical made by organism that affects social behaviour of other members of the same species
- plants aren’t social, dont rely a lot on pheromones
- if maple tree is attacked by insects, released pheromone absorbed by leaves on other branches, leaves make chemicals (callose) to protect if they’re attacked, leaves on branches of nearby trees do this too
- chemicals produced in root systems, one plant tells a neighbour it is under water stress
31
How do VOCs act as a chemical defence to herbivory
Volatile organic compounds: act like pheromones, diffuse through air in/around the plant
- cabbages attacked by caterpillars, produce chemical signal which attracts parasitic wasp, lays eggs in caterpillar which are then eaten alive, plant is protected, deters other butterflies from lasting eggs
- cabbage attacked by greenfly, sends out different signal for a different wasp to attack the greenfly
- apple trees attacked by spider mites, VOCs produced, predatory mites attracted
- wheat seedling produces VOCs when attacked by aphids, repels other aphids
32
Why do plants fold in response to touch
Frightens off larger herbivores, dislodges small insects that have landed on the leaves
Happens in mimosa pudica
33
Types of tropism
Phototropism
Geotropism
Chemotropims
Thigmotropism
34
What is phototropism
Growth in response to light
If plants are grown in bright all-round light, they grow upwards
In low light, plants grow up, faster and taller
If light is unilateral, shoots grow towards the light and roots will grow away
35
Experiments for phototropism
- If shoot tip is removed or covered, no photo tropic response
- if a thin, impermeable barrier of mica is on the light side, shoot bends towards the light
- if a barrier of mica is on the dark side, no phototropic response
- if the shoot tip is removed and replaced with a gelatin block in between, shoot bends towards the light
- orginally thought auxin was destroyed by light but experiments show levels of auxin in shoots are similar in dark and unilateral illumination
36
How do phototropic responses happen
- light causes auxin to move laterally across the shoot, greater concentration on the unilluminated side
- stimulates cell elongation and growth on the dark side so the shoot grows towards the light
- when the shoot is growing directly towards the light, transport of auxin stops and shoot grows towards lights
37
Why do shoots grow faster in the dark
- known as etiolation, thin and pale plants produced
- biological imperative to grow upwards rapidly to reach the light to photosynthesise
- first to break through will not have to compete with other seedlings for light
- gibberellins are responsible for extreme growth in the dark
- slow growth in light allows resources to be used for strengthening stems/ synthesising leaves/ overall growth
38
What is geotropism
Growth in response to gravity
- shoots are negatively geotropic
- roots are positively geotropic
39
Experiments for geotropism
- Use rotating drum, known as clinostat
Slowly rotating so gravitational stimulus is applied evenly, root and shoot grow straight (in the dark)
- seeds can be placed in Petri dishes stuck to wall of the lab, dishes rotated 90º at intervals as the seedlings grow
40
How is ripening controlled commercially
Ethene is involved in ripening of fruit, peak of ethene production triggers chemical reactions such as increased respiration rate
Fruits are harvested when they’re formed but before they’re ripe, cooled stored and transported
When fruit is needed for sale, exposed to ethene under controlled conditions, ensures ripening happens at the same rate, all at the same stage for shelving for sale
Prevents wastage of fruit during transport, increases time available for sale
41
How can plant hormones be used for micropropagation
Application of auxin to cut shoots stimulates production of roots
Cut stems are dipped into hormone rooting powder before being placed into soil
Increases chances of roots forming, means micropropagation can happen on a large scale
42
How are plant hormones used as weed killers
Synthetic auxins have been developed by scientists
Incorrect balance of hormones can interrupt metabolism of the whole plant
Specialised auxins taken up by weeds, growth rate increases which becomes unsustainable so the weeds die whereas the plants can continue to grow as normal
Simple and cheap to produce, low toxicity to mammals, are selective
43
Other uses of plant hormones
- auxins used for production of seedless fruit
- ethene used to promote fruit dropping in plants
- cytokinins used to prevent aging of ripened fruit and in micropropagation to control tissue development
- gibberellins used to delay ripening and ageing in fruit, improve size/shape of fruits and to speed up malting process in beer brewing
44
How is the nervous system split structurally
Central nervous system: brain and spinal chord
Peripheral nervous system: neurones that connect the CNS to the rest of the body (sensory and motor)
45
How is the nervous system split functionally
Somatic nervous system: system under conscious control, used for voluntary actions, carried impulses to body’s muscles
Autonomic nervous system: works constantly, subconsciously controlled, involuntary, e.g. heart beating or food digesting, carries impulses to glands/ smooth muscle/ cardiac muscle
46
How is the autonomic nervous system split
Sympathetic: generally, increases activity, ‘fight or flight’, noradrenaline
Parasympathetic: generally, decreases activity, ‘rest and digest’, acetylcholine
47
Main components of the brain
Cerebrum
Cerebellum
Medulla oblongata
Hypothalamus
Pituitary gland
48
Function of the cerebrum
Controls voluntary actions: learning, memory, personality, conscious thought
- receives sensory information and sends impulses along motor neurones to effectors to produce a response
Cerebral cortex = reasoning and decision-making
49
Function of the cerebellum
Controls unconscious functions: posture, balance, non-voluntary movement
Coordinates movement, doesn’t initiate it
50
Function of the medulla oblongata
Use in autonomic control, e.g. heart rate and breathing rate
Controls swallowing, peristalsis, coughing
51
Function of the hypothalamus
Regulatory centre for temperature and water balance
- controls complex patterns of behaviour
- produces hormones, endocrine gland
- monitors composition of blood plasma
52
Function of the pituitary gland
Stores and releases hormones that regulate many body functions
Controls most of the glands
53
Structure of the hypothalamus
2 centres: one for parasympathetic and one for sympathetic
54
Structure of the cerebrum
Split into cerebral hemispheres: each half controls one half of the body
Outer layer = cerebral cortex
55
Structure of the pituitary gland
At the base of the hypothalamus
Divided into 2 sections:
- anterior: produces FSH and 5 other hormones involved in reproduction and growth hormones
- posterior: stores and releases hormones produced by hypothalamus e.g. ADH
56
What is the reflex arc
Receptor: detects stimulus and creates action potential in sensory neurone
Sensory neurone: carries impulse to CNS
Relay neurone: connects sensory neurone to motor neurones within spinal chord or brain
Motor neurone: carries impulse to effector
Effector: carries out a response
57
Structure of the spinal cord
Grey matter: cell bodies / unmyelinated axons
White matter: myelinated axons
58
Describe the knee-jerk reflex
- leg is tapped below the kneecap, patellar tendon is stretched = stimulus
- stimulus initiates reflex arc that causes extensor muscle on top of the thigh to contract, relay neurone inhibits the motor neurone of the flexor muscle, causing it to relax
- contraction, coordinated with the relaxation causes the leg to kick
- used to maintain posture and balance
59
Why are reflexes important
Reflexes increase chances of survival
-brain can deal with more complex responses, prevents brain being overloaded with situations where response is the same
- don’t need to be learnt
- fast and short reflex arc, involves one or two synapses
- everyday actions
60
Types of muscles
Skeletal muscle
Cardiac muscle
Involuntary muscle (smooth)
61
What is skeletal muscle
Make up bulk of body muscle tissue
Cells responsible for movement, e.g. triceps/biceps
62
What is cardiac muscle
Found in the heart
Myogenic, contract without need for nervous stimuli
Causes heart to beat in regular rhythm
63
What is involuntary muscle
Found in walls of hollow organs (stomach/bladder)
Found in walls of blood vessels and digestive tract (move food along the gut through peristalsis)
64
Features of skeletal muscle
Striated
Voluntary control
Regularly arranged so muscle contracts in one direction
Rapid, short contraction
Tubular and multinucleated fibres
65
Features of cardiac muscle
Specialised striated
Involuntary
Cells branch and interconnect, simultaneous contraction
Intermediate contraction speed and length
Branched and uninucleated fibres
66
Features of involuntary muscle
Non-striated
Involuntary
No regular arrangement, different cells contract in different directions
Slow contraction speed but relatively long contraction length
Spindle shaped, uninucleated fibres
67
Structure of skeletal muscle
- Fibres enclosed within sarcolemma (plasma membrane)
- parts of the sarcoplasm fold inwards (T tubules) to spread electrical impulses throughout the sarcoplasm, all of the fibres receive impulse to contract at the same time
- Fibres are longer than normal cells, formed from many embryonic muscle cells fusing together, makes them stronger
- Cytoplasm of a muscle fibre = sarcoplasm
- many mitochondria, provide ATP for contraction
- sarcoplasmic reticulum = extends throughout muscle fibre, with Ca2+ for contraction
- each fibre contains many myofibrils
68
Structure of myofibrils
Long cylindrical organelles made of protein
Lined up in parallel to provide maximum force when they all contract together
Made up of:
- actin: thinner filament, 2 strands twisted around eachother
- myosin: thicker filament, long rod-shaped fibres with bulbous head that project to one side
69
Features of myofibrils
- Light bands: where actin and myosin do not overlap, only actin (I bands)
- dark bands: where myosin is (A bands)
- Z-line: line at centre of each light band, distance between each is the sarcomere
- H-zone: lighter coloured region at the centre of dark bands as only myosin is present, decreases when muscle contracts
- sarcomere: functional unit of the myofibril, shortens when muscle contracts
70
What are the properties of slow-twitch fibres
- contract slowly
- less powerful contractions, over a longer period
- used for endurance activities, don’t tire easily
- gain energy from aerobic respiration
- rich in myoglobin (red protein which stores oxygen, makes fibres appear red)
- rich supply of blood vessels/ mitochondria
71
Where are slow-twitch fibres found
In large proportions in muscles that help to maintain posture (in back and calf muscles, contract continuously)
72
Properties of fast-twitch fibres
- contract quickly
- powerful contractions, short periods
- used for short bursts of speed/power, tire easily
-energy from anaerobic respiration
- pale coloured, low levels of myoglobin and blood vessels
- more, thicker myosin filaments
- store creatine phosphate (rapidly generates ATP from ADP in anaerobic conditions)
73
Where are fast-twitch fibres
Found in high proportions in muscles which need short bursts of intense activity (e.g. biceps and eyes)
74
Describe the structure of myosin
Filaments have globular heads, binding site on the myosin head, for actin and ATP
Myosin tails align together to form filament
75
Describe the structure of actin
Have binding sites for myosin heads (actin-myosin binding sites)
Sites blocked by presence of protein called tropomyosin, held in place by protein troponin
76
Changes in the muscle filaments during contraction
Myosin filaments pull actin filaments inwards towards centre of sarcomere
- light band becomes narrower
- Z lines move closer together, sarcomere shortens
- H-zone becomes narrower
77
How does muscle contraction occur
When an action potential arrives at a neuromuscular junction (motor neurone and skeletal muscle meet)
Many junctions along a muscle to ensure the fibres contract simultaneously (contraction is then more powerful and faster)
All fibres supplied by single motor neurone are a motor unit
78
Actions at a neuromuscular junction
- action potential reaches junction, voltage-gated Ca2+ channels open, Ca2+ diffuses into synaptic knob
- causes vesicles to fuse with presynaptic membrane, acetylcholine is released into synaptic cleft by exocytosis, diffuses across synapse
- binds to receptors on postsynaptic membrane (sarcolemma), Na+ channels open and depolarisation occurs
- acetylcholine broken down by acetylcholinesterase into choline and ethanoic acid, diffuse back into neurone, recombined into acetylcholine using ATP
79
What events take place in the sarcoplasm after depolarisation of the sarcolemma
- depolarisation spreads through T tubules, in contact with sarcoplasmic reticulum which contains Ca2+ that are actively absorbed from sarcoplasm
- when action potential reaches SR, Ca2+ channels open, diffuse out down concentration gradient into sarcoplasm
- Ca2+ bind to troponin, changes shape, pulls on tropomysosin so binding sites are exposed
- myosin heads bind to actin filaments, cross-bridges form
- myosin head flexes which pulls actin filament along, ADP bound to myosin head is released
- ATP binds to myosin head, head detaches from actin filament
- Ca2+ activates ATPase activity of the myosin, ATP hydrolysed which releases energy, myosin head returns to original position
- myosin can now attach to binding site further along the filament, cycle continues as long as muscle is stimulated
80
How is energy supplied for muscle contraction: aerobic respiration
Most is regenerated from ADP during oxidative phosphorylation, inside mitochondria, plentiful in muscle
Only occurs in presence of O2, used for long periods of low-intensity excercise
81
How is energy supplied for muscle contraction: anaerobic respiration
In active muscle O2 used up more quickly than blood supply can replace it
ATP has to be generated anaerobically, made by glycolysis
Pyruvate is converted into lactate, builds up in muscles, resulting in muscle fatigue, used for short periods of high-intensity excercise
82
How is energy supplied for muscle contraction: creatine phosphate
Stored in muscle
Acts as reserve supply of phosphate, available immediately to combine with ADP
Generates it quickly but stores are used up quickly
Used for short bursts of vigorous excercise
When muscle is relaxed, creatine phosphate store replenished with phosphate from ATP
83
What is the fight-or-flight response
Instinct when potentially dangerous situation is detected, automatic series of physical responses
- once a threat is detected by autonomic nervous system, hypothalamus communicates with sympathetic nervous system and adrenal-cortical system
- both hormones and neuronal pathways used to respond
- sympathetic nervous system: sends out impulses to glands and smooth muscles, tells adrenal medulla to release adrenaline and noradrenaline
84
Examples of fight-or-flight responses
- heart rate increases: to pump more oxygenated blood around the body
- pupils dilate: to take in more light for vision
- arterioles constrict: more blood to major muscle groups, brain, heart, muscles of ventilation
- blood glucose levels increase: increase respiration for muscle contraction
- smooth muscle of airways relaxes: allows more oxygen into lungs
- non-essential systems shut down (e.g. digestion): focus resources on emergency functions
- difficulty focusing on small tasks: brain focused on threat
85
86
Role of adrenaline in the fight-or-flight response
Triggers liver cells to undergo glycogenolysis, so glucose is released into the bloodstream, respiration increases and more energy is available for muscle contraction
87
Describe the action of adrenaline
Hydrophilic so cannot pass through cell membranes, binds with receptors on surface of liver cell membrane, triggers chain reaction inside cell
Known as second messenger model, cAMP is second messenger
- adrenaline binds to receptor, enzyme adenylyl cyclise is activated
- triggers conversion of ATP into cAMP on inner surface of cell membrane in cytoplasm
- increase in cAMP levels activates protein kinases which phosphorylate and activate other enzymes for conversion of glycogen to glucose
88
How is the heart rate controlled
By autonomic nervous system
Medulla oblongata in the brain controls it, 2 centres which are linked to the SAN by motor neurones
- one centre increases heart rate through the sympathetic nervous system, transmitted by accelerator nerve
- one centre decreases heart rate through parasympathetic nervous system, transmitted by vagus nerve
89
How are changes in heart rate detected
- baroreceptors: detect change in blood pressure, present in aorta, vena cava, and carotid arteries
- chemoreceptors: detect change in level of chemicals in the blood, located in aorta, carotid artery, medulla
90
How do chemoreceptors work
Sensitive to changes in pH levels of the blood
- if there’s increase metabolic activity, more CO2 will be produced
- blood pH will be lower due to more carbonic acid being produced
- centre in medulla oblongata that speed up heart rate increases frequency of impulses to SAN via sympathetic nervous system
- SAN increases heart rate, increases blood flow so CO2 is removed faster
- CO2 level returns to normal
91
How do baroreceptors work
Detect changes in pressure
- if blood pressure is too high, impulses sent to medulla oblongata centre which decreases heart rate
- impulses sent along parasympathetic neurones to SAN, decreases heart rate
- blood pressure returns to normal
Opposite happens in blood pressure is too low, impulses sent along sympathetic neurones
92
How is heart rate controlled by hormones
Adrenaline and noradrenaline are released in times of stress, affect pacemaker region of the heart, speed up rate by increasing frequency of impulses by SAN
93
How can heart rate be monitored
Taking a pulse, per minute, equal to how many times your heart beats per minute
