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Dr Bhavsar's A level Biology (OCR, A) > Module 5 Plant and animal responses essential notes > Flashcards

Module 5 Plant and animal responses essential notes Flashcards

1
Q

State the range of plant responses

A
  1. Responses to abiotic stress
    a. water levels
    b. Daylight
    c. temperature
  2. Herbivory
    a. chemical defences
    b. folding in response to touch
  3. Tropisms (specific growth in response to):
    a. Light
    b. Gravity
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2
Q

Describe the ways in which plants can defend

against herbivory with chemical

responses

A
  1. Tannins: phenolic compounds which taste bitter to animals and are toxic to insects
  2. Alkaloids: bitter tasting nitrogenous compounds, some of which act as poisons
  3. Terpenoids: oily substances acting as toxins to insects that may feed on the plants (inhibiting the functioning of their nervous system)
  4. Pheromones are chemicals that affect the behaviour of other members of the same species. Examples of this are:

a. Pheromones that cause the leaves of nearby trees to make callose
b. Volatile organic compounds (VOCs) produced when

a plant is attacked by a pest that alter gene expression via cell signalling, altering behaviour in another species which may deter the pest. For example, production of VOCs may attract a predator of the pest attacking the plant.

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3
Q

Explain how plants can defend against herbivory by folding in response to touch

A

Some plants such as Mimosa pudica will fold down leaves in response to touch

This may reduce accessibility by the herbivore, or scare them away, or dislodge any attacking insects

  1. Touching the leaves causes movement of potassium ions into specialised cells on the top and out of cells at the bottom parts of the base of the leaf
    a. So water enters the cells at the top of the ‘joint’, and water leaves the cells at the bottom
    b. Flexible cell walls allows these tissues to expand at the top, and contract at the bottom
    c. Causing the leaf to fold downward
    d. In the absence of further stimulus, ion concentrations return to normal and the leaf rises back
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4
Q

Explain why tropisms are important responses for the survival of a plant

A
  1. Tropisms are growth-related movements of plants in response to directional environmental stimuli such as light and gravity
  2. This is best exemplified by the emerging shoot and root during germination
  3. Where the shoot grows upward in the direction of light (and opposite to the direction of gravitational pull) to maximise the energy it has to photosynthesise (positive phototropism, negative geotropism)
  4. And the root(s) grow downward into the soil to maximise water and mineral uptake , and provide better support for the rest of the plant (negative phototropism, positive geotropism)
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5
Q

Describe the practical investigations into phototropism

A
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6
Q

Describe the practical investigations into geotropism

A
  1. Gravitational stimulus can be controlled/varied by the use a clinostat
  2. The rotating drum can be controlled to observe the effect of direction of gravitational stimulus on the growth of shoots and roots.
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7
Q

Explain how shoots are able to make positive phototropic responses

A
  1. Unilateral light (light of a particular direction) causes the plant hormone auxin to redistribute/move laterally in the shoot
  2. It accumulates on the opposite side to that facing the light source (auxin moves away from the light)
  3. Auxin causes cell elongation (in shoots) on the side not facing the light, causing the shoot to bend towards the light.
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8
Q

Explain how shoots are able to make negative geotropic responses

A
  1. light causes auxins to accumulate on the lower side of the root
  2. Recall that varying auxin concentrations affect different parts of the plant in different ways
  3. At the concentrations present in the root, auxin inhibits cell elongation
  4. At the concentrations present in the root, auxin inhibits cell elongation
  5. Therefore, roots bend away from the light source
  6. Positive geotropism
  7. gravity causes auxins to accumulate on the lower side of the root
  8. Recall that varying auxin concentrations affect different parts of the plant in different ways
  9. At the concentrations present in the root, auxin inhibits cell elongation
  10. Therefore, roots bend towards the direction of the gravitational stimulus
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9
Q

Explain how hormones allow plants to make responses to environmental factors

A
  1. Plants do not have a nervous system that allows fast responses
  2. But plants can respond to the environment with hormones
  3. (not to be mistaken for an endocrine system)
  4. Where a chemical produced by cells in one part of the plant Move to a different part of the plant from cell to cell, or via plant transport mechanisms
  5. And cause changes in behaviour in other cells and tissues (via cell signalling )
  6. Often affecting cell growth
  7. As a result these responses are usually relatively slow compared to that of animals
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10
Q

Give examples of plant hormones

A
  1. Auxins
  2. Gibberellins
  3. Abscisic acid (ABA)
  4. Ethene
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11
Q

Describe the effects of auxins

A
  1. Cell elongation
  2. Prevent leaf fall (abscission)
  3. Promote apical dominance
  4. Affects root and shoot growth
  5. Stimulates release of ethene (fruit ripening)
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12
Q

Describe the effects of gibberellins

A
  1. Stem elongation
  2. Mobilisation of energy storage carbohydrate during germination
  3. Stimulate pollen tube growth during fertilisation
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13
Q

Describe the effects of ethene

A
  1. Fruit ripening
  2. Promotes abscission in deciduous trees
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14
Q

Describe the effects of Abscisic acid (ABA) on plants

A
  1. Maintains dormancy of seeds and buds
  2. Stimulates cold protective responses (antifreeze production)
  3. Stimulates stomatal closing
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15
Q

Describe the role of gibberellins in seed germination

A
  1. Dormant seed absorbs water which activates the embryo
  2. Activated embryo produces the hormone gibberellin
  3. Gibberellin results in cell signalling that causes genes for amylases and proteases to be switched on
  4. Starch and protein are hydrolysed to glucose/maltose and amino acids respectively
  5. Providing the cells of embryo with respiratory fuel and material for biosynthesis of new cells
  6. ABA acts antagonistically to this process, which is initiated when gibberellin levels are higher than ABA
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16
Q

Describe the role of ethene in leaf fall (abscission)

A
  1. Deciduous trees lose their leaves in winter to conserve energy (less light for photosynthesis in the winter) and reduce the risk of being blown over by wind
  2. In response to reduced light levels, auxin levels fall
  3. Auxin levels falling cause an increase in the production of ethene
  4. Cell signaling is triggered that causes genes for enzymes that weaken the cell wall to be switched on.
  5. Vascular bundles (xylem and phloem) transporting materials to the leaf are sealed off
  6. Without a supply of water and nutrients the leaf dies, and falls away
  7. Fatty material is deposited on the stem side of the abscission zone, producing a waterproof scar that also prevents the entry of pathogens.
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17
Q

Explain how auxins such as (indoleacetic acid) IAA affect the growth of apical shoots

A
  1. Auxins are produced and released by meristem cells at the shoot tip in the zone of cell division
  2. Auxins diffuse down the shoot tip and bind to cells in the zone of elongation
  3. Cell signalling is triggered that results in hydrogen ions to be pumped out of cells, lowering the pH in the cell walls
  4. This lower pH (5) activates enzymes in the cell wall that maintain its plasticity
  5. When water enters these cells due to osmosis, the cells elongate (as the cell wall is somewhat stretchable)
  6. Mature cells further down the shoot break down auxin, in these areas the pH is higher, and cell walls are more rigid, and less able to elongate.
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18
Q

Describe the evidence for the role of auxin in apical dominance

A
  1. Shoot tips produce high levels of auxin and are the fastest growing parts
  2. While the apical bud is attached, the high levels of auxin suppress the growth of the lateral buds
  3. When the apical bud is removed, the lateral buds grow faster
  4. As the there are no longer high levels of auxin from the apical buds and the apical dominance has been removed
  5. When the apical bud is removed, and auxin is applied the apical dominance returns
  6. When the apical bud is removed, auxin is applied but not allowed to move down the stem, the apical dominance is removed.
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19
Q

Describe the experimental evidence for the role of gibberellins in stem elongation

A
  1. Seedlings infected with the fungus Gibberella grow very tall and thin, because the fungus produces gibberellins Plants that have short stems produce no, or very little gibberellins
  2. Plants modified to disrupt gibberellin synthesis are dwarf varieties
20
Q

Describe the experimental evidence for the role of

gibberellins in seed germination

A
  1. Mutant varieties of seeds, bred to have alleles which cause a lack of production of gibberellins do not germinate. When gibberellins are externally applied, germination occurs normally
  2. Gibberellin synthesis can be disrupted with inhibitor compounds. Inhibitor-treated seeds do not germinate. When gibberellins are applied, they germinate normally.
21
Q

Describe the use of plant hormones to control ripening of fruits and vegetables

A
  1. Ethene promotes climacteric fruit ripening
  2. This allows less ripe fruit to be picked and transported (less likely to be damaged)
  3. Ethene is then used to ripen the fruit
  4. There is a more uniformly ripe product available to the public
22
Q

Describe the use of plant hormones in rooting powders

A
  1. Auxin can be applied to cut stems (cuttings) to promote the growth of roots.
  2. This can increase the success of propagation of plants through cuttings.
  3. Plant hormones are also used in micropropagation, ensuring that the growth media contain the right hormones and hormones concentrations increases the differentiation and growth of calluses into plants.
23
Q

Describe the use of plant hormones as weedkillers

A
24
Q

Describe the function of the autonomic nervous system

A
  1. The autonomic nervous system is part o f the peripheral nervous system
  2. It consists of parasympathetic and sympathetic sensory and motor neurones
  3. The parasympthatic motor neurones stimulate rest and digest responses
  4. The sympathetic motor neurones stimulate fight and flight responses
25
Q

Explain how sympathetic and parasympathetic motor neurones are able to have different effects on their target organs

A
  1. Control centres in the CNS such as hypothalamus or medulla oblongata send impulses along either parasympathetic or sympathetic neurones
  2. Impulses result in the secretion of neurotransmitter which stimulates or inhibits the target
  3. Sympathetic neurones release noradrenaline
  4. Parasympathetic neurones release acteylcholine
  5. Different neurotransmitters cause different and opposite responses in target cells
26
Q

Describe the structure of the brain

A
  1. The brain has two hemispheres (left and right)
  2. The outer part of the brain is the cortex
  3. Much of the cortex is made up by the cerebrum (forebrain)
  4. The posterior region of the brain is the cerebellum (hindbrain)
  5. The diencephalon region of the brain (just above the brainstem) contains the hypothalamus and pituitary glands
  6. The brainstem contains the medulla oblongata
27
Q

State the functions of the main parts of the brain

A
28
Q

Describe the advantages of reflex responses

A
  1. Reflexes are fast responses to intense stimuli
  2. They are involuntary as they do involve the brain
  3. They do not require learning
  4. prevent serious harm to the organism
  5. Increasing the chance of survival
29
Q

Describe the knee-jerk reflex

A
  1. Spinal reflex (relay neurones are in the spinal cord) Stretch receptors in the ligaments are stimulated
  2. Impulses pass along sensory neurons to CNS
  3. Sensory dendrite synapses directly with extensor motor neuron (excitatory synapse)
  4. The relay neurone synapses with the flexor motor neurone (inhibitory synapse)
  5. The extensor contracts and the flexor relaxes
30
Q

Describe the blink reflex

A
  1. Cranial reflex (relay neurones are in the brain not spinal cord)
  2. Pressure on the cornea stimulates sensory neurons (blue)
  3. Impulses reach the relay neurons in the CNS
  4. This results in motor neurone impulses (red, green)
  5. Muscles in the eyelid contract to cause the blinking response
31
Q

Describe the key features of the fight or flight responses of mammals

A
  1. increase heart rate to maintain oxygen supply/CO2 removal increase blood glucose levels widen bronchioles (smooth muscle) reduce blood flow to/suppress ‘rest-and-digest’ systems, skin (smooth muscle)
  2. pupil dilation
32
Q

Describe the hormonal response to stress / fight-or flight

A
  1. collection of sensory information perceived by the brain as stressful nerve impulses to hypothalamus cause release of corticotropin releasing hormone
  2. this causes pituitary gland to release adrenocorticotropic hormone into blood
  3. This stimulates the adrenal cortex
  4. this causes adrenal cortex cells to release cortisol into blood
33
Q

Describe the effects of cortisol in the fight or flight response

A
  1. cortisol is a glucocorticoid affects blood glucose levels increases protein hydrolysis to amino acids in skeletal muscle
  2. amino acids carried in blood to liver
  3. increases activity of gluconeogenic enzymes in liver
  4. increases blood glucose
  5. Suppression of the immune system
34
Q

Describe the neuronal response to stress

A
  1. stress perceived in the brain
  2. causes nerve impulses along sympathetic motor neurones these stimulate cells of the adrenal medulla
  3. adrenal medulla releases adrenaline and noradrenaline into bloodstream
35
Q

Describe the effects of catecholamines (adrenaline and noradrenaline) during the fight or flight response

A
  1. adrenaline must bind a cell surface receptor protein this activates intracellular second messenger production (cAMP)
  2. In liver this causes glycogenolysis
  3. Increases heart rate
  4. Dilation of bronchioles
36
Q

Using the liver as an example, explain how hormones such as adrenaline cause cellular responses

A
  1. Adrenaline causes the liver to raise blood glucose levels Adrenaline is water soluble so it binds a complementary cell surface receptor
  2. This activates the enzyme adenylate cyclase which converts ATP to cyclic AMP
  3. The second messenger cAMP activates the enzyme glycogen phosphorylase (glycogen hydrolysis)
  4. It also inactivates the enzyme glycogen synthase (glycogen synthesis)
  5. Overall, this increases blood glucose levels
37
Q

Describe how neuronal mechanisms regulate the heart rate

A
  1. Sensors in arteries detect blood pressure (baroreceptors) or blood pH (chemoreceptors) impulses are sent along sensory neurones to the cardiovascular control centre of the medulla oblongata (brain)
  2. Accordingly, impulses are sent along sympathetic or parasympathetic motor neurones to the SAN of the heart
  3. noradrenaline increases frequency of SAN depolarisations, acetylcholine reduces them
  4. response acts to reverse the initial detection
38
Q

Explain how hormones and neurotransmitters affect the depolarisation rate of the SAN

A
  1. Noradrenaline (neurotransmitter) and adrenaline (hormone)
  2. bind to receptors that activate adenylate cyclase Acetylcholine (neurotransmitter) binds to receptors that inhibit adenylate cyclase
  3. Cyclic AMP causes sodium channels to open
  4. So, noradrenaline and adrenaline result in more frequent depolarisation of the SAN
  5. And acetylcholine results in less frequent depolarisation of the SAN
39
Q

Describe the features of skeletal muscle

A
  1. Has a striped (striated) appearance
  2. Parallel bundles of multinucleate cells, so direction of contraction is the same
  3. Under voluntary control (somatic motor neurones)
  4. Responsible for movement responses
40
Q

Describe the key features of cardiac muscle

A
  1. Specialized form of striated muscle
  2. Cells are interconnected but uninucleate (one nucleus per cell)
  3. which allows more synchronized contraction
  4. The cardiac muscle cells of the sinoatrial node are myogenic, which means they contract regularly without a stimulus
  5. But the rate of the SAN contraction can be affected by neurotransmitter of autonomic neurones and hormones
41
Q

Describe the key features of smooth muscle

A
  1. Found in the walls of digestive organs, airways and blood vessels
  2. Non-striated, spindle shaped, arranged in rings
  3. Cells are not interconnected or multinucleate
  4. So the timing or direction of contraction is not as unified as cardiac and skeletal muscle respectively
  5. Stimulated by the autonomic neurones
42
Q

Describe the structure and function of skeletal muscle

A
  1. Muscle tissue is composed of bundles of many muscle cells called muscle fibres
  2. Each muscle fibre has many nuclei
  3. And many myofibrils in it’s sarcoplasm (cytoplasm)
  4. It is the myofibrils that act as the contractile ‘machinery’.
  5. The sarcomere is composed of actin and myosin filaments
  6. contraction of the myofibrils result in the contraction of the muscle as a whole.
43
Q

Summarise the way in which sarcomeres shorten

A
  1. The sarcomere is made of myosin (thick) and actin (thin) filaments
  2. The myosin head proteins can bind to the actin filaments When attached, they change shape, pulling on the actin filaments
  3. This causes the filaments to slide over each other, increasing overlap, and shortening the sarcomere
44
Q

Describe how the binding of ADP or ATP results in progression through the crossbridge cycle

A
  1. the myosin heads (+ADP) b ind actin forming cross-bridges Release of ADP causes a change in protein shape, pulling the actin fibre along (power stroke)
  2. The binding of ATP causes the myosin head to detach from actin and return to its original position
  3. Hydrolysis of ATP (energy-releasing step) changes the the shape again so that it can bind actin again, and the cycle repeats.
45
Q

Describe the role of calcium ions in sarcomere shortening

A
  1. Neuronal stimulation of muscles causes release of calcium from the sarcoplasmic reticulum (SER of the muscle fibre) Calcium ions bind to troponin in the actin filament
  2. This causes tropomyosin to move exposing myosin-binding sites
  3. Myosin heads can now bind the actin filament and the crossbridge cycle can proceed, resulting in sarcomere shortening
46
Q

Describe the events at a neuromuscular junction which result in muscle contraction

A
  1. Nerve impulses cause neurotransmitter to be released into the synaptic cleft
  2. Neurotransmitter binds to receptors on the muscle fiber cell membrane
  3. This causes depolarisation of the muscle fiber cell membrane
  4. Depolarisation of the muscle fibre causes calcium ion channels in the sarcoplasmic reticulum to open
  5. Calcium ions diffuse into the sarcoplasm and bind to troponin resulting in myofibril contraction

Dr Bhavsar's A level Biology (OCR, A) (20 decks)

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