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A Level Biology > Plant And Animal Responses > Flashcards

Plant And Animal Responses Flashcards

1
Q

What is abiotic stress

A

Non-living environment factor that could harm a plant e.g. mineral deficiency, drought, depleted oxygen supply, pollution

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2
Q

How does Mimosa pudica respond to being touched

A

Seismonasty (touch sensitivity) causes leaves to fold

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3
Q

How do plants respond to abiotic stress and herbivory

A

May produce antifreeze enzymes
May contain bitter-tasting tannins
May contain bitter-tasting nitrogen containing compounds called alkaloids
Release cell-signalling pheromones to trigger defensive responses in other organisms

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4
Q

What is a plant tropism

A

Directional growth response of plants

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5
Q

How is leaf loss in deciduous plants controlled

A
  1. As leaf ages, cytokinin and auxin levels lower, ethene level increases
  2. Triggers production of cellulase enzymes, which weaken leaves by breaking down cell walls in abscission layer
  3. Leaves break to form branch. Below abscission layer, suberin layer forms to prevent entry of pathogens
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6
Q

List the functions of giberellins

A

Stimulate:
- Germination
- Elongation at cell internodes
- Fruit growth
- Rapid growth / flowering

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7
Q

How is germination stimulated

A
  1. Seed absorbs water, activating embryo to secrete giberellins
  2. Gibberellins diffuse to aleurone layer, which produces amylase
  3. Amylase diffuses to endosperm layer to hydrolyse starch
  4. Hexose sugars act as respiratory substrate to produce ATP as ‘energy currency’
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8
Q

List the functions of auxins

A
  • Involved in trophic responses e.g. IAA
  • Control cell elongation
  • Suppress lateral buds to maintain apical dominance
  • Promote root growth e.g. in rooting powders
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9
Q

Explain why shoots show positive phototropism

A
  1. Indoleacetic acid (IAA) diffuses to shaded side of shoot tip
  2. As IAA diffuses down shaded side, it causes active transport of H+ ions into cell wall
  3. Disruption to H-bonds between cellulose molecules & action of expansins make cell more permeable to water. (Acid growth hypothesis)
  4. Cells on shaded side elongate faster due to higher turgor pressure
  5. Shoot bends towards light
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10
Q

Explain why roots show positive geotropism

A
  1. Gravity causes IAA to accumulate on lower side of the root
  2. IAA inhibits elongation of root cells
  3. Cells on the upper side of the root elongate faster, so the root tip bends downwards
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11
Q

How do hormones stimulate stomata to close

A
  1. Abscisic acid binds to complementary receptors on guard cell membrane, causing Ca2+ ion channels on tonoplast to open. Ca2+ ions diffuse from vacuole into cytosol
  2. Positive feedback triggers other ion channels to open. Other ions e.g. K+ diffuse out of guard cell
  3. Water potential of guard cell becomes more positive. Water diffuses out via osmosis
  4. Guard cells become flaccid so stomata close
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12
Q

What is apical dominance

A

Phenomenon where during the growth of the shoot, the growth of side shoots does not take place. Maintained by the action of auxin, abscisic acid and cytokinins

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13
Q

Explain the experimental evidence that auxins maintain apical dominance

A

Auxins production in apex maintains high levels of abscisic acid. Inhibits growth of side shoots.
When apex is removed:
a) Auxin levels drop, abscisic acid levels to drop
b) Cytokinins (initially concentrated near auxin reserve in bud) diffuse evenly to promote bud growth in other parts of the plant = lateral buds

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14
Q

Explain the experimental evidence that gibberellins control stem elongation and germination

A

Stem elongation: Tall plants have higher gibberellin concentration than dwarf plants
Germination: Mutant seeds with non-functional gibberellin gene do not germinate unless gibberellin is applied externally. Inhibitors of gibberellin production prevent germination

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15
Q

How are auxins and cytokinins used commercially

A

Auxins: Rooting powder, growing seedless fruit, herbicides, low concentrations to prevent leaf and fruit growth, high concentrations promote fruit drop
Cytokinins: Prevent yellowing of lettuce leaves promotes shoot growth

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16
Q

How are gibberellins used commercially

A

Gibberellins: delay senescence in citrus, elongation of apples and grape stalks, brewing beer for malt production, increase sugar cane yield, speed up seed formation in confiners, prevent lodging

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17
Q

Outline the gross structure of the mammalian nervous system

A

Peripheral —> voluntary
I__> autonomic —> sympathetic
I___> Parasympathetic
Central —> Spinal cord
I___> brain

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18
Q

Name the two main divisions of the nervous system

A

Structural organisation
Central nervous system (Comprised of brain and spinal cord. Specialised system of nerve cells processes stimuli and propagates impulses)
Peripheral nervous system (all neurons that are not part of the CNS)

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19
Q

Name the two main divisions of the autonomic nervous system

A

Sympathetic: Often stimulates effectors (fight-or-flight response), neurotransmitter noradrenaline, ganglia near CNS
Parasympathetic: often inhibits effectors (rest/ digest response), neurotransmitter acetylcholine, ganglia far from CNS
Act antagonistically to regulate response of effectors

20
Q

Describe the gross structure of the human brain

A

2 hemispheres joined by band of nerve fibres (corpus callosum) Divided in lobes:
Parietal lobe at the top of the brain: movement, orientation, memory, recognition
Occipital lobe at the back of the brain: visual cortex processes signals from the eye
Temporal lobe beneath the temples: processes auditory signals

21
Q

What is the function of the cerebellum

A

Controls execution (not initiation) of movement e.g. timing, balance, coordination, posture
Possible role in cognition e.g. attention and language

22
Q

Identify the function of the medulla oblongata

A

Controls a range of autonomous functions, including breathing and heartrate (location of cardioacceleratory / deceleratory centres)

23
Q

Identify the function of the cerebrum

A

Uppermost part of the brain is organised into lobes which control voluntary functions e.g. initiating movement, speech, thought,

24
Q

Identify the function of the hypothalamus

A

Includes anterior pituitary gland (secretes metabolic and reproductive hormones)
Involved in thermo and osmoregulation

25
Q

Outline what happens in a simple reflex arc

A

Receptor detects stimulus –> sensory neurone –> relay neuron in CNS coordinates response –> motor neuron –> response by effector
Survival benefit: rapid response to potentially dangerous stimuli since only 3 neurons involved, instinctive

26
Q

Describe the knee jerk reflex

A

Important for maintaining posture and balance
1. Tapping patellar tendon stimulates stretch-mediated receptors
2. Impulses travels sensory –> motor (no interneuron). Quadriceps contract. Inhibits antagonistic hamstring contraction
Diagnostically useful: multiple kicks = symptom of cerebellar disease, lack of reflex = nervous problems

27
Q

Describe the blinking reflex

A

Brain stem reflex. Consensual response: both eyelids close rapidly when just 1 cornea is stimulated by bright light/ touch
Sensory neuron of trigeminal nerve –> spinal nucleus of trigeminal nerve –> interneurons –> facial motor nerve –> effector muscle orbicularis oculi

28
Q

What is the fight or flight response

A

If brain perceives threat, it stimulates stress responses involving adrenaline
Triggers physiological changes to prepare body: pupil dilation, inhibition of digestive system, greater blood flow to brain for mental awareness, faster metabolic rate

29
Q

Use the secondary messenger model to explain how adrenaline works

A
  1. Adrenaline 1st messenger. Hormone-receptor complex forms
  2. Conformational change to receptor activates G-protein
  3. Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP)
  4. cAMP 2nd messenger. Activates protein kinase A pathway.
  5. Results in glycogenolysis
30
Q

Describe skeletal muscle

A

Striated skeletal muscle consisted of multinucleated cells. Antagonistic muscle pairs enable movement.

31
Q

Describe the gross structure of the skeletal muscle

A

Muscle cells are fused together to form bundles of parallel muscle fibres (Myofibrils)
Arrangement ensures there is no point of weakness between cells
Each bundle is surrounded by endomycium: loose connective tissue with many capillaries

32
Q

Describe the microscopic structure of the skeletal muscle

A

Myofibrils: site of contraction
Sarcoplasm: Shared nuclei and cytoplasm with lots of mitochondria and endoplasmic reticulum
Sarcolemma: folds inwards towards sarcoplasm to form transverse (T) tubules

33
Q

How is muscle contraction stimulated

A
  1. Neuromuscular junction: action potential = voltage-gated Ca2+ channels open
  2. Vesicles move towards and fuse with presynaptic membrane
  3. Exocytosis of acetylcholine (ACh), which diffuses across the synaptic cleft
  4. ACh binds to receptors on Na+ channel proteins on skeletal muscle cell membrane
  5. Influx of Na+ = depolarisation
34
Q

Explain the role of Ca2+ ions in muscle contraction

A
  1. Action potential moves through T-tubules in sarcoplasm = Ca2+ channels in sarcoplasm reticulum open
  2. Ca2+ binds to troponin, triggering conformational change in tropomyosin
  3. Exposes binding sites on actin filaments so actinomyosin bridges can form
35
Q

Outline sliding filament theory

A
  1. Myosin head with ADP attached forms cross bridge with actin
  2. Power stroke: myosin head changes shape and loses ADP pulling actin over myosin
  3. ATP attaches to myosin head, causing it to detach from actin
  4. ATPase hydrolyses ATP —> ADP (+Pi) so myosin head can return to original position
  5. Myosin head re-attaches to actin further along filament
36
Q

How does sliding filament action cause a myofibril to shorten

A

Myosin heads flex in opposite directions = actin filaments are pulled towards each other
Distance between adjacent sarcoma Z lines shortens
Sliding filament action occurs up to 100 times per second multiple sarcomeres

37
Q

Explain the role of creatine phosphate in muscle contraction

A

Phosphorylates ADP directly to ATP when oxygen for aerobic respiration is limited e.g. during vigorous exercise

38
Q

State the name and location of the nodes involved in heart contraction

A

Sinoatrial node (SAN): within the wall of the right atrium
Atrioventricular node (AVN): near lower end of right atrium in the wall that separates the 2 atria

39
Q

Name the receptors involved in changing heart rate and state their location

A

Baroreceptors (detect changes in blood pressure): carotid body
Chemoreceptors (detect changes in pH e.g. due to increase in CO2 concentration): carotid body and aortic body

40
Q

How does the body respond to an increase in blood pressure

A

Baroreceptors send more impulses to cardioinhibitory centre in the medulla oblongata
More impulses to SAN down vagus node via parasympathetic nervous system
Stimulates release of acetylcholine which decreases heart rate

41
Q

How does the body respond to a decrease in blood pressure

A

Baroreceptors send more impulses to cardacceleratory centre in the medulla oblongata
More impulses to SAN via sympathetic nervous system
Stimulates the release of noradrenaline which increases heart rate and strength of contraction

42
Q

How does the body respond to an increase in CO2 concentration

A

Chemoreceptors detect pH decrease and send more impulses to cardioacceleratory centre of medulla oblongata
More impulses to SAN via sympathetic nervous system
Heart rate increases so rate of blood flow to lungs increases = rate of gas exchange and ventilation rate increases

42
Q

Describe the structure of a neuromuscular junction

A

Synaptic cleft between a presynaptic motor neuron and a skeletal muscle cell
Acts as end of neural pathway and always stimulates an excitatory response

43
Q

Describe smooth / involuntary muscle

A

Smooth involuntary muscle enables walls of blood vessels and intestines to contract

44
Q

Describe cardiac muscle

A

Cardiac muscle consists of branches uninucleated cells Myogenic contraction = heartbeat

45
Q

How is ethene used commercially

A

Speeds up ripening, promotes lateral growth, promotes fruit drop

A Level Biology (25 decks)

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