Lecture 9: Leaf Flashcards
What is the stipule
protective leaf-like appendage at the base of the leaf
What is the petiole
the stalk of a leaf. When there is no petiole, the leaf is SESSILE
What do you call a leaf with no petiole
sessile
What is the lamina?
leaf blade
What is a simple leaf?
an undivided leaf lamina (may be deeply lobed)
What is a compound leaf?
lamina is divided into leaflets
What are the two types of simple leaf?
entire margin
lobed margin
What are the two types of compound leaf?
pinnate
palmate
Define pinnate
leaflets borne on central rachis
What does rachis mean?
stem of plant
Define palmate
leaflets borne on top of petiole
What are the differences between leaflets and leaves?
- buds are found at the axils of leaves; but not on leaflets
- leaves extend from stem in various plants; leaflets lie on the same plane
What kind of venation do dicot leaves have?
netted venation
What kind of venation do monocot leaves have?
parallel venation
true or false; monocot leaves have a sheath surrounding the stem
true
What does phyllotaxis mean?
arrangement of leaves around a stem
how many types of phyllotaxis are there; and name them all
5 spiral alternate opposite decussate whorled
What does spiral phyllotaxis mean?
- most common arrangement
- leaves are 137.5 degrees apart (2.6 leaves/360 degrees)
- this is the ideal angle
Why is the spiral arrangement more beneficial than other plants?
maximizes light interception, minimizes self- shading
Describe alternate phyllotaxis
successive leaves are 180 degrees apart
Describe opposite phyllotaxis
a pair of opposite leaves is formed at each node
Describe Decussate
successive pairs of leaves are 90 degrees apart eg. mint
Describe whorled
three or more leaves formed at each node
Where is the leaf primordia initiated from
the shoot apical meristem
What are the two zones of shoot apical meristem (SAM)
tunica
corpus
What does tunica mean
(outer layer) - cells usually divide anticlinally
What does corpus mean
(inner layers)- cells divide in all direction
Where are leaves derived from?
the founder cells in the peripheral zone
When does cell division in a leaf stop?
when the leaf is very small eg. 10% final length
Where does the leaf stop divided first
- the tip first
- the base last
true or false; the tip of the leaf differentiates before the base
true
What is the structure of a typical leaf; from adaxial to abaxial
upper epidermis
palisade mesophyll
spongy mesophyll
lower epidermis
What are mesophytes
plants that require a weather that is neither too hot nor too dry
Describe the epidermis
- on upper and lower sides
- lack chlorophyll
- trichomes
- stomata especially on the lower surface
Describe the palisade mesophyll
- long, narrow cells
- sometimes branched
- near upper surface of leaf (adaxial)
- rich in chlorophyll
- specializes in photosynthesis
Describe spongy mesophyll
- first leaf cells to stop dividing
- irregular shapes
- large air spaces
- chlorophyll
What are vascular bundles
- xylem above phloem
- collenchyma and/or sclerenchyma may provide support
What is used in garlic
bublets
What is used in mustard
seed
What is used in celery
fruit
What is used in cumin
leaves and fruits
What is used in bay leaves
leaves
What is used in basil
leaves
What is the effect of variation in leaf structure
- enhance their competitive performance
What are the benefits of coiled organs?
they coil rapidly in response to contact stimuli
What are the characteristics of shade plants
- thin leaves
- chloroplasts in epidermis
- poorly developed palisade mesophyll
- low chlorphyll a:b ratio (more b)
- undulated epidermal cells
- anthocyanins on undersurfaces
Describe the features of xerophytes
- thick cuticle
- hairs
- recessed stomata
- hypodermis
- well developed palisade mesophyll
- inclined leaves
- solar tracking
purpose of thick cuticle of x
reflects sunlight
purpose of hairs of x
reduce water loss
recessed stomata purpose of x
reduce transpiration
purpose of hypodermia of x
reduce wilting injury
purpose of well developed palisade mesophyll of x
optimise light use
purpose of inclined leaves of x
lower temperature
purpose of solar tracking of x
avoid intense sunlight
What does rubisco do?
evolved under low o2 conditions
binds both CO2 and O2
photorespiration (if O2 is bound)
How much O2 in atm
21%
how much N2 in atm
78%
how much CO2 in atm
0.036%
What is photorespiration
- O2 substitutes for CO2 in the active site of the enzyme rubisco
- the photosynthetic rate is reduced
What happens to plants on hot, dry, days
plants close their stomata
- conserving water but limiting access to CO2
- causing oxygen to build up
What is the alternative carbon fixation in hot, arid climates
- by incorporating CO2 into four carbon compounds in mesophyll cells
- these four carbon compounds are exported to bundle sheath cells, where they release CO2 used in the Calvin Cycle
What happens in C4 plants; spatial separation
in C4 plants carbon fixation and the Calvin cycle occur in different types of cells
What happens in CAM plants
carbon fixation and the calvin cycle occur at the same cells at different times
