Lecture 6 Flashcards
Describe the annual rainfall patterns in Australia.
High contrast between centre of Australia and its margins - central areas receive less than 200 mm per annum whereas coastal margins can receive up to 2000 +.
Average daily temperatures increase the further _____ in Australia you go. Roughly the upper third of the country has an average daily maximum of __ degrees C.
north; 27.
Many parts of Australia (mostly in the centre of the country) have maximum average daily temperatures of 40 degrees C + in the ______ months.
Summer.
Dry matter production (a measure of productivity) ______ when precipitation ______.
Increases; increases.
Less than _% of plant water use is in reactions of photosynthesis. There is a net ___ of water in photosynthesis.
1; use.
Gas exchange is regulated via _________. Gas exchange requires open ______.
stomata; stomata.
The pore size of stomata ________ when the turgor of the guard cells increases.
increases.
When turgor of guard cells decreases, the pore size of the stomate _______.
decreases.
Is there a big gradient between CO2 concentration inside C3 plants and CO2 concentration outside? How does this affect the rate of CO2 diffusion?
No. Thus CO2 diffusion is slow.
Is there a big gradient between H20 concentration inside plants and H20 concentration outside? How does this affect the rate of flow of H20 from the plant?
Yes. High humidity inside plant; relatively low humidity outside plant. Thus when stomata are open, flow of humid air from inside the plant to outside is rapid.
What key process drives the movement of water from the roots of a plant to the stems?
Transpiration.
List the three photosynthetic pathways in order of least to most water efficient.
C3, C4, CAM.
Are ‘drought avoidant’ plants necessarily more water efficient?
No.
What is the main way that drought avoidant plants survive during droughts?
Through maximising water supply.
Give some examples of drought avoidant plants and the way in which they exhibit this characteristic.
- River red gum (deep roots to access ground water)
- Sturt’s desert pea (reproduces quickly after rain)
- Annual/ephemeral plants (spend dry times as seeds and reproduce quickly after rain)
What is the other name for drought tolerant plants?
Xerophytes.
What are the two main types of xerophytes?
Succulents and sclerophylls.
Sclerophylls are ___-leaved plants.
Hard
Are succulents or sclerophylls more common?
Sclerophylls.
Which conditions favoured the evolution and dominance of sclerophylls in the Australian landscape?
- increased aridity and fire frequency
- weathering of soils
Sclerophylls contain lots of ______ tissue. They have ____, rigid leaves that do not wilt when water stressed.
structural; hard.
List three adaptations of sclerophylls.
- small leaf size, short internodes
- proportionally thick leaves
- reduced surface area/volume ratio (sometimes through leaf rolling/leaves circular in cross section).
List three groups of sclerophylls (including one type of grass).
- Acacia
- Ericaceae (southern heaths are sub-family Epacridoideae).
- Triodia (spinifex) grass
List 4 anatomical features of sclerophyll leaves.
1) THICK WALLED CELLS
Sclerophylls lay down additional layers of carbohydrates (lignin) inside the primary cellulose cell walls to form thick secondary cell walls in fibre and sclereid cells. The secondary walls become thicker and thicker as additonal layers are added and the space for living contents diminishes. The cells are actually non-living at maturity (functioning as structural support).
2) THICK CUTICLE AND WAXY COATING
Makes leaf water tight except for where stomata are.
3) SUNKEN STOMATA
Creates a pocket of humid air just outside of guard cells to reduce loss of water vapour to atmosphere. Lowers concentration difference of H20 between inside and outside of guard cells.
4) LEAF HAIRS/FORMATION OF ‘BOUNDARY LAYER’
Dense mat of short interlocking hairs on the undersurface of leaves to trap water vapour from nearby stomata and reduce evapotranspiration. Water vapour accumulates in the hairs and creates a ‘boundary layer’ of humid air just near the external surface of the leaf. (Reduces concentration difference of H20 inside and outside guard cells).
