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Alevel Biology OCR > 5.1.5- Plant and animal responses > Flashcards

5.1.5- Plant and animal responses Flashcards

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1
Q

What is abiotic stress?

A

non-living factors that can have harmful effects on plants

eg. water shortage

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2
Q

Why do plants need to respond to their environment?

A
  • to avoid abiotic stress
  • to cope with changing conditions
  • to maximise photosynthesis
  • to avoid herbivory grazing
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3
Q

What is a tropism?

A

a directional growth response of a plant where the direction of the response is determined by the direction of the external stimulus

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4
Q

What is a positive tropism?

A

growth towards the stimulus

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5
Q

What is a negative tropism?

A

growth away from the stimulus

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6
Q

What is phototrophism?

A

plant growth in response to light

  • shoots are positively phototrophic (grow towards light -to increase rate of photosynthesis)
  • roots are negatively phototrophic (grow away from light)
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7
Q

What is geotropism?

A

plant growth in response to gravity

  • shoots are negatively geotropic (grow upwards, away from gravity)
  • roots are positively geotropic (grow downwards, towards gravity)
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8
Q

What is chemotropism?

A

plant growth in response to chemicals

eg. pollen tubes grow towards chemicals given off by flower’s ovary

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9
Q

What is thigmotropism?

A

plant growth in response to touch/contact with something else

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10
Q

What is hydrotropism?

A

plant growth in response to water

-roots are positively hydrotropic (grow towards water)

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11
Q

What is thermotropism?

A

plant growth in response to temperature

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12
Q

What experiment could be carried out to investigate phototrophisms?

A

-plant seedlings
-cover the tips of some of the seedlings with a foil cap, wrap foil around the base of some shoots and leave some seedlings without any foil
-leave the plants in a light source and after a few days check which direction the shoots have grown in
RESULTS:
-plants with exposed tips and with foil around base grew towards light whereas the ones with covered tips did not

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13
Q

What experiment could be carried out to investigate geotrophism?

A

-plant cress seeds into petri dishes with moist cotton wool
-wrap each dish and lid with foil (to prevent light affecting results)
-prop different petri dishes at different angles (horizontal, vertical, etc) and leave for a few days before checking their growth
RESULTS:
-shoots should have all grow upwards/away from gravity whatever their angle and roots should have all grown downwards/towards gravity

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14
Q

Why are seedlings used for investigating tropisms?

A

they are easier to manipulate and observe

  • are still growing and responding rapidly to changes
  • have a relatively simple plant system
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15
Q

What defences do plants have to avoid herbivory (being eaten by animals)?

A
  • produce chemicals (tannins, alkaloids and pheromones)

- folding in response to touch (eg. Mimosa pudica)

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16
Q

What chemicals do plants produce as a defence to herbivory?

A
  • tannins
  • alkaloids
  • pheromones
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17
Q

What are tannins?

A

bitter-tasting chemicals which in some herbivores (eg. cattle) can bind to proteins in the gut to make the plant hard to digest

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18
Q

What are alkaloids?

A

chemicals with bitter tastes, noxious smells or poisonous characteristics which deter or kill herbivores
eg. tobacco plants produce nicotine (poisonous to some insects)

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19
Q

What are pheromones?

A

signalling chemicals which are released into the air in response to herbivores grazing which cause nearby plants that detect them to start chemical defences (eg. producing tannins)

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20
Q

What plant hormones are there?

A
  • auxins
  • gibberellin
  • ethene
  • ABA (abscisic acid)
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21
Q

What are the roles of auxins?

A
  • controls cell elongation
  • prevent abscission (leaf fall)
  • maintains apical dominance
  • involved in fruit ripening
  • stimulates release of ethene
  • involved in tropisms
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22
Q

What are the roles of auxins?

A
  • controls cell elongation
  • prevent abscission (leaf fall)
  • maintains apical dominance
  • involved in fruit ripening
  • stimulates release of ethene
  • involved in tropisms
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23
Q

What is abscission?

A

leaf loss

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24
Q

What are the roles of gibberellin?

A
  • causes stem elongation
  • stimulates growth of pollen tube
  • triggers mobilisation of good stores in seed (during germination)
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25
Q

What are the roles of ethene?

A
  • causes fruit ripening

- promotes abscission in deciduous trees

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26
Q

What are the roles of ABA (abscisic acid)?

A
  • stimulates cold protective responses (eg. antifreeze production)
  • maintains dormancy (alive but not growing) of seeds and buds
  • stimulates stomata closing
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27
Q

What happens in seed germination?

A
  • when the seed absorbs water, embryo is activated and gibberellins are produced
  • the gibberellins stimulate the production of enzymes (eg. amylases and proteases) that break down the seed’s food stores, which is used to produce ATP
  • ABA interferes with the action of gibberellins to control when the seed germinates
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28
Q

What experimental evidence is there for seed germination?

A
  • mutant seed varieties that do not have the gene which controls gibberellin production do not germinate (but when gibberellin is applied to them externally, they do germinate)
  • when gibberellin biosynthesis inhibitors are applied to seeds, they can not produce gibberellins and can’t germinate (but if the inhibitor is removed or the gibberellins are applied externally, they do germinate)
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29
Q

Why is apical dominance important?

A
  • main shoot grows upwards more, towards sunlight

- having more light increases the rate of photosynthesis

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30
Q

How do auxins control apical dominance?

A

high concs of auxins suppress lateral shoots from growing
growth in main shoot is stimulated by auxins produced at the tip so grows quickly whereas growth of lateral shoots is inhibited
…
-auxins are synthesised in and released from the meristem cells
-auxin diffuses away from the top and binds to receptors (on cell surface membranes)
-vacuoles form
-H+ are pumped into the cell, which decreases pH, causing the cell wall to become more flexible
-cells absorb water and expand as they do so
-vacuoles get bigger and cell walls stretch
-one large vacuole is formed and cell wall becomes rigid when auxins are broken down by enzymes

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31
Q

How can the role of auxins in apical dominance be investigated?

A

-plant 30 plants and count the number of side shoots growing from each of them
-for 10 plants, remove the tip of the shoot and apply a paste containing auxins
-for another 10 plants, remove the tip and apply a paste without any auxins
-for the other 10 plants, leave them as they are (as controls)
-leave them in the same conditions and after a week, count the number of side shoots from each plant
RESULTS:
-removing tips caused extra side shoots to grow but when auxins were applied the extra side shoots did not grow
-auxins inhibit growth of side shoots so are involved in apical dominance

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32
Q

How can plant hormones be used commercially?

A
  • to control ripening (ethene)
  • in rooting powders (auxins)
  • in weed killers (auxins)
  • to produce seedless fruit (auxins)
  • to promote food dropping (ethene)
  • to prevent ripened fruit aging (cytokinins and gibberellins)
  • to delay ripening (gibberellins)
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33
Q

How are plant hormones used commercially to control fruit ripening?

A
  • fruits are picked before they are ripe and are stored in cool conditions
  • when they are needed to be sold, they are exposed to ethene, causing the batch to ripen at the same rate and be ready to be sold
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34
Q

How are plant hormones used commercially in rooting powders?

A
  • cuttings are placed in soil and grow roots to form a new plant
  • dipping the cutting in a hormone rooting powder (containing auxins) increases the chance of root formation
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35
Q

How are plant hormones used commercially in hormone weed killers?

A
  • most staple foods (like rice and wheat) are monocots whereas weeds are dicots
  • this means if synthetic dicot auxins are applied, they are absorbed by dicot plants (aka weeds) and cause them to grow too quickly, causing them to be unsustainable and die
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36
Q

How is stomatal closure controlled by hormones?

A
  • abscisic acid (ABA) is able to trigger stomatal closure by binding to receptors on guard cell membranes, causing calcium ion channels to open
  • calcium ions enter the cytoplasm from the vacuole
  • the increased conc of calcium ions in the cytoplasm causes potassium ion channels to open, so that K+ leave the cell, increasing the cell’s water potential
  • this causes water to leave the guard cells by osmosis
  • the guard cells become flaccid and the stomata close
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37
Q

Why is abscission (leaf loss) important?

A

helps plants conserve water during cold parts of year

  • when it is difficult to absorb water from soil (if water is frozen)
  • when there is less light for photosynthesis
38
Q

How is abscission (leaf loss) controlled by plant hormones?

A
  • auxin concs decrease, causing leaf loss
  • ethene produced, which stimulated cells in abscission layer (layer of cells where leaf joins stem) to expand/produce enzymes, causing their cell walls to weaken and break so that leaves fall off
39
Q

What are the two main systems of the nervous system?

A
  • central nervous system (CNS)

- peripheral nervous system

40
Q

What is the central nervous system made up of?

A
  • brain

- spinal cord

41
Q

What is the peripheral nervous system made up of?

A
  • sensory pathway (from receptors)

- motor pathway (to effectors)

42
Q

What are the subsections of the motor pathway in the peripheral nervous system?

A
  • autonomic nervous system (unconscious)

- somatic nervous system (conscious)

43
Q

What are the subsections of the autonomic nervous system in the peripheral nervous system?

A
  • sympathetic (fight or flight)

- parasympathetic (relax)

44
Q

How is heart rate controlled by an autonomic nervous system?

A
  • to increase heart rate, the medulla oblongata sends a signal down the accelerator nerve (SYMPATHETIC PATHWAY)
  • to decrease heart rate, the medulla oblongata sends a signal down the vagus nerve (PARASYMPATHETIC PATHWAY)
45
Q

Which neurotransmitters do the sympathetic neurones release?

A

noradrenaline

46
Q

Which neurotransmitters do the parasympathetic neurones release?

A

acetylcholine

47
Q

What structures are inside the human brain?

A
  • cerebrum
  • cerebral cortex
  • cerebellum
  • medulla oblongata
  • hypothalamus
  • pituitary gland
48
Q

What is the function of the cerebrum?

A
  • intelligence
  • conscious thought
  • memory
49
Q

What is the function of the cerebellum?

A
  • balance
  • muscle coordination
  • posture
50
Q

What is the function of the medulla oblongata?

A
  • controls heart rate and breathing rate

- controls non-skeletal muscles

51
Q

What is the function of the hypothalamus?

A

-controls homeostasis

52
Q

What is the function of the pituitary gland?

A

-controls hormone release

53
Q

What is the function of the corpus callosum?

A

-connects right and left side of the brain

54
Q

What is the cerebrum?

A

largest part of brain split into 2 hemispheres

55
Q

What is the cerebral cortex?

A

highly folded outer layer of the cerebrum made of nerve cell bodies

56
Q

What is the function of the motor area of the cerebral cortex?

A

sends impulses to effectors

57
Q

What is the function of the sensory area of the cerebral cortex?

A

receives impulses from receptors

58
Q

What is the function of the association area of the cerebral cortex?

A

compares input with previous experiences to put reasoning on a new situation and judge a response

59
Q

Where is the medulla oblongata?

A

at the top of the spinal cord

60
Q

Where is the hypothalamus?

A

in the brain just above the pituitary gland

61
Q

What is a reflex?

A

an unconscious response to a stimulus
-only spinal cord involved (sensory and association areas in brain aren’t required) except with the eye when the brain is involved

62
Q

What are the typical stages in a reflex arc?

A
  • receptor detects stimulus and creates an action potential
  • sensory neurone carries impulse to spinal cord
  • relay neurone connects sensory neurone to spinal cord
  • motor neurone carries impulse to effector
63
Q

What happens in the knee jerk reflex?

A
  • when leg is tapped just below the kneecap (patella), the patellar tendon is stretched (this acts as a stimulus)
  • stretch receptors detect that muscle is being stretched
  • reflex arc causes the extensor muscle (top of thigh) to contract and flexor muscle to relax
  • causes leg to kick (lower leg moves forward)
64
Q

What could the absence of the knee jerk reflex suggest?

A
  • nervous problems

- cerebellar diseases

65
Q

What happens in the blinking reflex?

A
  • cornea is stimulated (eg. by touch or a high pitch sound or very bright light is detected)
  • this stimulus triggers an impulse along a sensory neurone (fifth cranial nerve), along a relay neurone in the lower brain stem and finally along a motor neurone (seventh cranial nerve)
  • this causes blinking to occur
66
Q

What makes the blinking reflex a cranial reflex?

A

occurs in the brain not the spinal cord

67
Q

What could the absence of the blinking reflex suggest?

A

patient is brain-dead (lower brain stem is not functioning)

68
Q

What is the corneal reflex?

A

blinking reflex caused by cornea being stimulated by touch

-keeps cornea safe from damage from foreign substances, like dust

69
Q

What is the optical reflex?

A

blinking reflex as a reaction to very bright light

-protects lens and retina

70
Q

Why are reflexes important for survival?

A

they avoid body being harmed

71
Q

How do reflexes increase your chance of survival?

A
  • they are extremely fast
  • they don’t have to be learnt (present from birth)
  • they are involuntary responses (decision-making regions of brain not involved so brain can deal with more complex responses)
72
Q

What happens when adrenaline binds to a receptor (cell signalling)?

A
  • adrenaline binding to receptor activates adenylyl cyclase
  • adenylyl cyclase converts ATP to cAMP
  • cAMP acts as a second messenger by activating other enzymes inside the cell
73
Q

What are the three types of muscles?

A
  • skeletal muscle (aka voluntary muscle)
  • involuntary muscle (aka non-skeletal muscle)
  • cardiac muscle
74
Q

What are the three types of muscles?

A
  • skeletal muscle (aka voluntary muscle)
  • involuntary muscle (aka smooth muscle)
  • cardiac muscle
75
Q

Describe the structure of skeletal/voluntary muscle

A
  • striated
  • regular arrangement (so muscle contracts in one direction)
  • cells form multinucleated fibres containing myofibrils which are made up of sarcomeres (contractile units) made of actin and myosin
76
Q

Describe the structure of smooth/involuntary muscle

A
  • non-striated
  • no regular arrangement
  • fibres are spindle shaped and uninucleated (one nucleus per cell)
77
Q

Describe the structure of cardiac muscle

A
  • appears striated
  • cells are branched
  • cells have intercalated disks so they interconnect (causing simultaneous contraction as electrical impulses can pass through)
78
Q

What is the function of skeletal muscle?

A

voluntary/conscious movements

79
Q

What is the function of involuntary muscle?

A

involuntary movement

eg. movement of materials along gut, autonomic reflexes in eye (pupil dilation/constriction), etc.

80
Q

What is the function of cardiac muscle?

A

pumps blood around body

81
Q

What are myofibrils made up of?

A
  • actin (thinner filament which has tropomyosin wrapped around it)
  • myosin (thicker filament which has heads)
82
Q

Describe the sliding filament model

A

sarcomere is made up of I-band, A-band and I-band (where I-band is the area containing only actin and A-band is the length of myosin)
Z-line is the end of sarcomere
H-zone is the gap between each actin molecule

83
Q

Describe how the sliding filament model changes as muscle contracts

A

H-zone (gap between actin) becomes smaller

Z-lines become closer together

84
Q

What is the I-band in the sliding filament model?

A

area containing only actin

-aka light bands (light because actin and myosin don’t overlap)

85
Q

What is the A-band in the sliding filament model?

A

areas containing myosin (and at edges overlapping actin)

-aka dark bands (because myosin is thick and appears dark)

86
Q

What is the Z-line in the sliding filament model?

A

end of the sarcomere

87
Q

What is the H-zone in the sliding filament model?

A

gap between each actin (only myosin present)

88
Q

What happens at a neuromuscular junction?

A
  • action potential arrives at pre-synoptic knob and causes voltage-gated Ca2+ channels to open
  • Ca2+ diffuse in and cause vesicles (containing acetyl choline) to move
  • exocytosis occurs + Ach is released
  • Ach diffuses across synapse and binds to receptors on the sarcolemma, causing Na+ channels to open
  • Na+ diffuse into the muscle and depolarise T-tubules (make them more +ve)
  • depolarised T-tubules stimulate the sarcoplasmic reticulum, which releases Ca2+
  • Ca2+ cause a contraction
89
Q

What causes muscles to contract?

A
  • Ca2+ bind to troponin, which changes its shape
  • this moves tropomyosin, which exposes actin’s binding site
  • myosin head binds to actin’s binding site, creating a crossbridge (and releasing ADP and Pi)
  • myosin head pivots, moving the actin filament along
  • ATP molecule binds to myosin head, causing it to detach from the actin filament (breaking crossbridge)
  • ATP is hydrolysed to ADP, causing myosin head to return to its original position
  • cycle repeats
90
Q

How is the supply of ATP maintained during muscle contraction?

A
  • in aerobic respiration oxidative phosphorylation produces most ATP (suited to long periods of low intensity exercise when there is oxygen)
  • anaerobic respiration rapidly makes ATP in glycolysis but lactate fermentation of pyruvate causes lactate to build up in muscles/muscle fatigue (suited for short periods of hard exercise)
  • creatine phosphate (CP) is stored inside cells and can generate ATP very quickly by donating a phosphate to bind to ADP (used during short bursts of vigorous exercise as CP runs out very quickly)
91
Q

What happens in the ATP-CP system?

A

creatine phosphate’s phosphate group is taken and used to phosphorylate ADP to produce ATP

  • generated ATP quickly
  • CP runs out quickly so is used in short, vigorous exercise
  • is anaerobic
  • is alactic (doesn’t form any lactate)

Alevel Biology OCR (26 decks)

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