2.5 Leaves Flashcards
What is the primary function of a leaf?
Photosynthesis
What is the petiole?
Stalk (midrib minus the tissue!)
What is the lamina?
Simple leaf blade
Describe the veins?
Midrib is central vein, and secondary veins branch off that.
What is the midrib?
The central vein in a leaf
Simple leaf shapes? (4)
Lanceolate (spearhead shape)
Ovate (egg shape)
Linear (grasses)
Palmate (acers etc)
How does leaf colour vary?
Varies according to pigment in leaves
Chlorophyll breaks down over time - light green goes to darker, and then red/browns etc.
Variegated leaves are mixture of yellow (non-photosynthetic) and green (photosynthetic)
Some have red undersides - reflects sun’s rays back into leaf. Good for forest floor plants!
Leaf arrangements on stems? (3)
Alternate
Opposite
Whorled
How are leaves adapted to form other functions? (8)
Optimal photosynthesis
Climbing
Preventing water loss
Encouraging water loss
Defence
Storage
Reproduction
Carnivory
What does the mesophyll layer in a leaf do?
The palisade mesophyll is the main site of photosynthesis.
The spongy mesophyll is also site of photosynthesis. Air spaces facilitate gas exchange and store CO2. Cells may also store starch.
What are compound leaf shapes? (2 examples)
These are simple leaves divided into “leaflets”
Pinnate compound - leaflets are arranged along a midrib
Palmate compound - leaflets are attached at a common point.
How do leaves adapt for optimal photosynthesis?
Arranged in patterns to catch maximum sunlight
Lamina tracks the sun via pulvinus at base of petiole
Pulvinus allows Oxalis leaves to collapse at night
How do leaves adapt for climbing?
Leaves wrap around supports or other plants
Tendrils cling to surroundings
How do leaves adapt for reproduction?
Some species produce tiny plantlets on leaf margins
How do leaves adapt to prevent water loss?
Mediterranean/coastal/”cold” deserts etc:
Thick, silky hairs on leaf surface catch moisture
Thick, waxy coatings prevent evaporation
Needle-like leaves roll in to reduce surface area to drying winds
Pores are on underside of leaf (so inside rolled “needle”)
How do leaves adapt to encourage water loss?
Attenuate leaves channel water off leaves (drip tips) - tropical rainforests etc.
(this prevents water logging to allow efficient photosynthesis, and prevent fungal infection)
How do leaves adapt for defence?
Spiny leaves
Stinging hairs
Variegation (camouflage)
Strong colour on midrib and veins (to mimic toxic ferns)
How do leaves adapt for storage?
Bulbs are modified, underground leaves - swell up and store nutrients. (Plants survive harsh conditions underground)
Outer leaves dry off and act as protection (onion)
Vegetative reproduction (bulblets form underground)
How do leaves adapt for carnivory?
In low nitrogen areas this is a backup!
Modified leaves that catch insects for protein
Pitcher plants have a soup of enzymes
Sundews and butterworts have sticky, sugary leaves
What is the function of stomata?
Site of entry of carbon dioxide and release of oxygen (gas exchange) and transpirational water vapour loss.
What is the function of the cuticle?
Waterproofing waxy layer which reduces water loss and protects from pest and disease damage.
What is the function of guard cells?
Control the opening and closing of the stoma and control water loss.
Describe FOUR leaf adaptations:
Leaf spine - for defence or protection
Succulent or fleshy leaves - to store water
Bulb - starch storage or perennation
Needles - to reduce water loss
