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Biology of Australian Flora and Fauna > Lecture 7 > Flashcards

Lecture 7 Flashcards

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1
Q

What is the name of the insect that ultimately controlled the Prickly Pear outbreak?

A

Cactoblastis cactorum (stem boring moth)

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2
Q

How did the stem boring moth control the Prickly Pear outbreak?

A

Adult females would oviposit on the Prickly Pear and the larvae would eat their way through the tissue of the cactus.

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3
Q

Why was Prickly Pear so successful?

A
  • low area/volume ratio to reduce water loss
  • extensive, shallow root system with the ability to maximise water uptake during showers
  • lots of water storage sites in their stems (cortex and pith)
  • CAM photosynthesis
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4
Q

What does CAM stand for?

A

Crassulacean Acid Metabolism.

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5
Q

In which plant family was CAM photosynthesis first observed?

A

Crassulaceae.

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6
Q

List the Australian plants that exhibit CAM mentioned in your lecture.

A

Most are epiphytes:

  • orchids
  • ferns
  • Myrmecodia

also:

  • isoetes (aquatic plant)
  • and a desert CAM plant!
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7
Q

List some common CAM plants (not specific to Australia).

A
  • Pineapple
  • Aloe
  • Orchids
  • Ferns
  • Air Plants
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8
Q

List the key features of CAM photosynthesis.

A
  • CAM plants have stomata
  • when stomata are open to let CO2 in, H20 escapes.
  • CAM plants open stomata at night (when rate of water loss is lower) and keep them closed during the day.
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9
Q

What do CAM plants do at night?

A

Stomata open. CO2 is pumped into storage at night via PEP carboxylase. CO2 is stored in the vacuole as malic acid.

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10
Q

What do CAM plants do during the day?

A

Stomata closed. Stored CO2 from the night before is released from the vacuole and is used in photosynthesis. As CO2 is still concentrated in the plant, it makes photosynthesis more efficient (photorespiration is inhibited) as CO2 is more abundant than O2&raquo_space; dictates which reaction rubisco catalyses.

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11
Q

In CAM plants, photosynthesis is _________ during the day, while photorespiration is __________.

A

stimulated; inhibited.

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12
Q

Key steps of photosynthesis (Calvin Cycle).

A

CO2 enters plant.
Rubisco catalyses carbon fixation of RuBP by adding CO2 to it.
In the cycle/reactions, sugars are released. (carbohydrate energy source for the plant).

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13
Q

During photorespiration, rubisco catalyses the _________ of RuBP.

A

oxygenation.

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14
Q

During photosynthesis, rubisco catalyses _______ ______ to RuBP.

A

carbon fixation.

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15
Q

Key steps of photorespiration.

A

O2 enters plant. Rubisco catalyses oxygenation of RuBP. Output is CO2. Plant doesn’t really get anything out of it e.g. sugar.

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16
Q

Roughly how much of the energy produced in photosynthesis can be lost through photorespiration?

A

25%.

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17
Q

Break down the name ‘photorespiration’.

A

Takes in O2, produces CO2 (just like regular respiration). ‘Photo’ because it happens in the presence of light.

18
Q

Which two factors dictate the balance between photosynthesis and photorespiration? I.e. what factors influence which reaction rubisco will catalyse?

A
  • Relative concentration of O2 and CO2 (that which is in higher concentration will be used by rubisco).
  • The temperature (rate of photorespiration increases as temperature increases)
19
Q

Name the location of each of the main events in photosynthesis in CAM plants.

A
  • CO2 enters and initial fixation reactions occur in the cytoplasm of the mesophyll cells.
  • CO2 stored overnight in the vacuole as malic acid
  • during the day, the malate is released from the vacuole and main photosynthesis reactions occur in the chloroplast
20
Q

What did Jean White (Unimelb alumni) discover about the effectiveness of arsenic pentoxide in containing the prickly pear outbreak? Based on what you have learned about CAM plants, why might this be?

A

She discovered that arsenic pentoxide was more effective at killing prickly pear if the spray was administered at night.

Must be because stomata are open at night and thus the poison could penetrate the plant much more effectively.

21
Q

What anatomical feature did the Cactoblastis cactorum moths have that enabled them to detect CO2 concentration?

A

Labial palps located on either side of their proboscis.

22
Q

Why did the Cactoblastis cactorum moths preferentially oviposit on the Prickly Pear plants?

A

Because they could sense a lower CO2 concentration on the pads of the Prickly Pear at night time compared with the surrounding vegetation.

23
Q

What are the 2 ways in which you can ‘spot’ a CAM plant?

A
  • Taste test (CAM plants will taste sour at night due to increased malic acid content and sweeter by day)
  • Isotope comparison using mass spectrometry
    (CAM plants will have a higher percentage of CO2^13 than C3 plants as PEP carboxylase doesn’t discriminate between isotopes as much as rubisco).
24
Q

Can sports officials look at carbon isotope ratios in athletes bodies to determine if they are using steroids? If so, why?

A

Yes. Because many steroids are of plant origin (phytosteroids), this will be reflected in the carbon isotope ratios in their testosterone.

25
Q

What does it mean if plants are ‘obligate’ (or constitutive) CAM plants?

A

They always perform CAM, regardless of conditions.

26
Q

What does it mean if plants are ‘facultative’ CAM plants?

A

They perform CAM when prompted by developmental/environmental cues.

27
Q

Is Prickly Pear (Opuntia) an obligate or facultative CAM plant?

A

Obligate.

28
Q

List a couple of examples of facultative CAM plants.

A

Pineapple and other bromeliads.

29
Q

What happens during CAM idling? When do plants turn to CAM idling?

A
  • Stomata always closed
  • no net CO2 uptake
  • CO2 from night time photorespiration stored as malic acid
  • same CO2 released during the day and used in photosynthesis
  • Plants turn to CAM idling when they are under extreme stress - the plant will not grow and is essentially at a stand still (imagine a car stopped in traffic with the engine on)
30
Q

What happens during CAM cycling? What is the biggest benefit of CAM cycling?

A
  • Stomata CLOSED at night instead of open like in regular CAM
  • CO2 from night time respiration stored as malic acid
  • CO2 released from storage during the day so that stomata do not need to open as much (thus less water is lost)
  • Plants use CAM cycling to save water!
31
Q

Are all succulents CAM plants?

A

No!

32
Q

Are most CAM plants succulents?

A

Yes!

33
Q

Why does Isoetes have such a big advantage by utilising CAM photosynthesis?

A

Because its competitors are all photosynthesizing during the day, it uses CAM to fix carbon at night time, thus avoiding the ‘traffic jam’.

34
Q

Is caustic vine an Australian terrestrial CAM plant?

A

Yes, one of the first known!

35
Q

Calandrinia polyandra (family Montiaceae) was Australia’s first identified succulent ______ CAM plant.

A

desert.

36
Q

Calandrinia are facultative CAM plants. When they are well watered they take up their CO2 during the _____.

A

day.

37
Q

Calandrinia are facultative CAM plants. When they are drought stressed they take up their CO2 during the _____.

A

night.

38
Q

Calandrinia hasn’t got the standard signature of CAM plants in its carbon isotope ratios due to the way it changes when it fixes carbon throughout the year. True or false?

A

True.

39
Q

Where is Calandrinia found in Australia?

A

All over Australia!

40
Q

Where in Australia are C4 plants most prevalent? Why?

A

In the north of Australia as C4 photosynthesis is a big advantage in hot environments where photorespiration would otherwise be favoured.

Biology of Australian Flora and Fauna (9 decks)

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