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Biology > Plant Behaviour > Flashcards

Plant Behaviour Flashcards

1
Q

What must all living organisms be able to do?

A

» Organise biological molecules on a higher level
» Access and use energy
» Grow
» Respond to their environment
» Make more of themselves
- In order to stay alive, plants and animals must be able to detect and respond to changes in their external environment

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2
Q

Define behavior

A

» The way in which an organism responds to an external stimulus
» In general terms, animals respond with movement, plants with growth

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3
Q

What are the effects that determine the way a plant grows

A
  • All plants grow and move in response to environmental information
    » Stem and leaves towards the sun
    » Foraging roots towards nutrients in the ground
    » Root elongation slows down and root hairs spread out in areas of high nutrients
    » Slow, so we generally don’t see it
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4
Q

How do plants behave?

A
  • Plants can detect a variety of external stimuli, and respond appropriately
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5
Q

How do plants detect light and environmental factors?

A 
- Photoreceptors:
» Light
- Mechanical stimulation
» Wind, herbivory
» Physical environment (eg, support structures)
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6
Q

How do plants detect nutrients and physical forces of nature like temperature?

A
  • Physical environment
    » Gravity, temperature, soil water, salt, CO2
  • Chemical receptors:
    » Nutrients
    » Scents (eg, dodder vine can detect tomato smell)
    » Chemical messages from other plants (eg, smell of freshly cut grass )
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7
Q

Why is light an especially important environmental factor for plants

A

» Required for photosynthesis
» Triggers key events in plant development (“photomorphogenesis”)
» Allows plants to measure the passage of days and seasons

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8
Q

What about light can plants detect?

A

» Presence/absence of light, but also
» Direction
» Intensity
» Wavelength (especially blue and red)

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9
Q

How is blue light received in plants and what is it used for?

A
  • Blue light receptors (cryptochromes)
  • Blue light initiates a range of responses in plants:
    » Phototropism (growth towards light)
    » Light-induced opening of stomata
    » Light-induced slowing of elongation of the juvenile shoot (hypocotyl) after it breaks ground
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10
Q

How is red light received in plants and what is it used for?

A
  • Red light receptors (phytochromes)
  • Plants use red light as a measure of light quality (and competition)
    » Measure ratio of far red (730 nm, NOT absorbed by overhanging leaves) to red (660 nm, absorbed by overhanging leaves)
    » This occurs because phytochromes change shape depending on the presence of red, far red, or no light
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11
Q

What are the responses t red light?

A 
- Seed germination
» Seeds have limited food reserves, so many seeds germinate only when light environment (and other conditions) are optimal (eg, death of a shading tree)
- Shade avoidance
» Stimulates branching
» Inhibits vertical growth
- Setting of internal clock
- Flowering
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12
Q

What are biological clocks?

A
  • Biological systems (plants and animals) exhibit cyclic activity patterns (“circadian rhythms”)
    » circa- = approximately, -dies = day
    » Opening and closing of stomata, sleep (orientation of leaves in legumes)
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13
Q

How does light effect biological clocks?

A
  • Biological clocks are internal
    » Still being researched, but appear controlled by alternating feedback loops of transcription of “clock genes”
  • But those internal clocks are not perfectly aligned to 24h (vary between 21-27h) … to avoid desynchronisation, they are constantly re-set by light cues (both red and blue)
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14
Q

How does photoperiod effect plants?

A
  • Plants also use the changing of the length of day (“photoperiod”) over a year to adapt to different seasons
    » Eg, to avoid producing leaves in winter (for deciduous trees)
  • The photoperiod is a critical determinant of flowering → ensure flowers are produced when the right pollinators are present
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15
Q

What are long-day plants?

A
  • “Long-day plants” (spinach, lettuce, irises …) flower only when the photoperiod is more than 14h, ie in spring/summer
    » Measure is very accurate (just a minute can make the difference!)
    » Actually controlled by length of darkness rather than day length )
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16
Q

What are short-day plants?

A
  • “Short-day plants” (chrysanthenums, soybeans …) flower only when the photoperiod is less than a specific number of hours, ie in autumn/winter
    » Measure is very accurate (just a minute can make the difference!)
    » Actually controlled by length of darkness rather than day length)
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17
Q

How does gravity effect plants?

A
  • Shoots grow upwards, roots grow downwards even in the absence of light because plants can detect gravity
18
Q

What are Statoliths?

A
  • Statoliths: dense components within the cytoplasm of sensor cells that settle at the bottom of the cell, with gravity (≈ balance in animals)
19
Q

What are the types of Environmental stresses plants face?

A
  • Environmental stresses can be biotic (living, eg herbivores) and abiotic (non living, eg water, temperature) - plants respond to both
20
Q

What are the types of water stress?

A
  • Drought

- Flooding

21
Q

What are the effects of a drought?

A

» Water is needed for photosynthesis …
» Water deficit causes stomata to close → greatly reduces transpiration
» Other responses within different species
• Grass roll into tubelike shape to reduce exposure to dry air
• Other shed leaves in response to seasonal drought
» All reduce photosynthesis, but at least the plant survives

22
Q

What are the effects of flooding?

A

» Flooded soils have no air space (thus less oxygen for cellular respiration)
» Some have adapted specialized aerial roots (eg mangroves)
» Others produce ethylene in response to flooding, which kills some cells in the root cortex, creating an air tube (≈ snorkel)

23
Q

What are the effects of salt on plants?

A
  • Salt stress affects plants for two reasons:
    » Excess soil sodium decreases water potential of the soil, thus causing a deficit in net movement of water to the plant
    » Sodium is toxic to plants at high concentrations
  • Some plants can produce organic compounds to counter-act these negative effects (to a certain extent …)
24
Q

What are the types of temperature stress

A
  • heat

- cold

25
Q

What are the effects of the heat temperature stress?

A

» Heat denatures proteins
» Transpiration helps plants cool down (by evaporative cooling)
» But if it is also dry, plants close their stomata, which stops this cooling, so plants also synthesize heat-shock proteins (HSPs; ≈ animals), which acts as scaffolds around proteins to help maintain their shape

26
Q

What are the effects of the cold temperature stress?

A

» Cold decreases membrane fluidity, altering transport across the cell membrane → plants increase proportion of unsaturated fat in membrane when exposed to low temps (which helps maintain fluidity)
» Plants in cold climates also secrete extra sugar to protect against frost

27
Q

How do plants respond to mechanical stimulation?

A
  • Plants respond to touch » Plants that are touched grow more slowly
    » Vines coil rapidly around support, to climb upwards towards a forest canopy
  • Most plant responses are mediated by hormones (chemical messengers of the endocrine system), but a few are similar to an action potential in the nervous system
28
Q

How do animal and plant communication systems differ?

A
  • Plants do not have a nervous system, but they use chemical communication to coordinate their multicellular activity
  • Endocrine communication in plants
29
Q

How does the endocrine system in plants work?

A
  • Plant hormones regulate virtually all aspects of growth and development
    » Plant hormones can have different effects in different tissues and the developmental stage of the plant
    » Multiple hormones often interact to control growth and development
30
Q

What are signal transduction pathways

A
  • The chains of molecules that relay signals inside a cell
31
Q

What are the steps of signal trasnduction?

A

1) Reception
2) Transduction
3) Response

32
Q

Draw and label the diagram of signal transduction

A

Google Doc

https://docs.google.com/document/d/1BpabtfqIj5MGsWdBTMRokVNMhJZjMkFjHpc7UqK5cCk/edit?usp=sharing

33
Q

Provide examples for four types of plants hormones

A
  • Auxin
  • Cytokinins
  • Giberellins
  • Ethylene
34
Q

What is Auxin and what is it used for?

A 
- Chemical messenger produced mainly by shoot, involved in
» Cell elongation (increases cell size)
» Stem elongation
» Enhances apical dominance
» Formation of lateral and adventitious roots
» Regulates development of fruit
» Phototropism (response to light)
» Gravitropism (response to gravity)
35
Q

Where is synthetic Auxin used?

A
  • Uses of synthetic auxins
    » Useful in vegetative propagation of plants by cuttings (stimulates formation of adventitious roots)
    » Monocots can rapidly degrade auxins, but eudicots cannot … application of synthetic auxins (eg, herbicide 2,4-D) kills eudicots by hormonaloverdose
36
Q

What is Cytokinins?

A
  • Chemical messenger produced mainly in roots, involved in
    » Cell division (thus works in concert with auxin for elongation)
    » Antagonises the apical dominance action of auxin
37
Q

What is Giberellins?

A
  • Chemical messenger
  • Also involved in stem elongation
  • With auxin, involved in fruit development
    » Use of synthetic giberellin sprays to make fruit bigger
  • When combined with water, triggers seed germination
38
Q

What is Ethylene?

A
  • When tip of growing seedling meets obstacle, ethylene is produced → “triple response” (enables the shoot to avoid the obstacle):
    » Slowing of stem elongation
    » Thickening of the stem (makes it stronger)
    » Curvature (causes the stem to grow horizontally)
39
Q

What are some function that Ethylene is used for?

A

» Senescence (programmed cell death)
» Leaf abscission (loss of leaves from deciduous trees)
» Fruit ripening: initiates enzymatic breakdown of cell wall and conversion of acids and starches to sugars to make the fruit sweet and attract animals
• Commonly used in commercial fruit production

40
Q

What is the first piece of evidence that proves plants have intelligence?

A
  • Plants communicate with other lifeforms
    » Other plants
    » Animals (eg, plants attacked by herbivorous insects release “help” chemicals that attract carnivorous insects)
41
Q

What is the second piece of evidence that proves plants have intelligence?

A
  • Just like animals, plants interact and compete with each other to capture sunlight and nutrients
    » “Pushing and shoving” towards the sun
    » Some even release of toxins and conduct chemical warfare underground
42
Q

What is the 3rd piece of evidence that proves plants have intelligence?

A
  • Plants also collaborate …
    » Can recognise relatives (by chemical signatures), and reduce root growth when near siblings to reduce competition
    » In forests, trees are connected underground by huge mycorrhizal network through this network, trees share carbon with fungi and with each other!
    • Expose one tree to 14CO2, and a few days later you’ll find that 14C in seedlings around it → seedling are being nurtured by larger plants
    • Dying trees can send food (and alarm signals) to neighbours from a different species

Biology (27 decks)

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