2.5 Leaves

Question 1

What is the primary function of a leaf?

Answer 1

Photosynthesis

Question 2

What is the petiole?

Answer 2

Stalk (midrib minus the tissue!)

Question 3

What is the lamina?

Answer 3

Simple leaf blade

Question 4

Describe the veins?

Answer 4

Midrib is central vein, and secondary veins branch off that.

Question 5

What is the midrib?

Answer 5

The central vein in a leaf

Question 6

Simple leaf shapes? (4)

Answer 6

Lanceolate (spearhead shape)

Ovate (egg shape)

Linear (grasses)

Palmate (acers etc)

Question 7

How does leaf colour vary?

Answer 7

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!

Question 8

Leaf arrangements on stems? (3)

Answer 8

Alternate

Opposite

Whorled

Question 9

How are leaves adapted to form other functions? (8)

Answer 9

Optimal photosynthesis

Climbing

Preventing water loss

Encouraging water loss

Defence

Storage

Reproduction

Carnivory

Question 10

What does the mesophyll layer in a leaf do?

Answer 10

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.

Question 11

What are compound leaf shapes? (2 examples)

Answer 11

These are simple leaves divided into “leaflets”

Pinnate compound - leaflets are arranged along a midrib

Palmate compound - leaflets are attached at a common point.

Question 12

How do leaves adapt for optimal photosynthesis?

Answer 12

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

Question 13

How do leaves adapt for climbing?

Answer 13

Leaves wrap around supports or other plants

Tendrils cling to surroundings

Question 14

How do leaves adapt for reproduction?

Answer 14

Some species produce tiny plantlets on leaf margins

Question 15

How do leaves adapt to prevent water loss?

Answer 15

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”)

Question 16

How do leaves adapt to encourage water loss?

Answer 16

Attenuate leaves channel water off leaves (drip tips) - tropical rainforests etc.

(this prevents water logging to allow efficient photosynthesis, and prevent fungal infection)

Question 17

How do leaves adapt for defence?

Answer 17

Spiny leaves

Stinging hairs

Variegation (camouflage)

Strong colour on midrib and veins (to mimic toxic ferns)

Question 18

How do leaves adapt for storage?

Answer 18

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)

Question 19

How do leaves adapt for carnivory?

Answer 19

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

Question 20

What is the function of stomata?

Answer 20

Site of entry of carbon dioxide and release of oxygen (gas exchange) and transpirational water vapour loss.

Question 21

What is the function of the cuticle?

Answer 21

Waterproofing waxy layer which reduces water loss and protects from pest and disease damage.

Question 22

What is the function of guard cells?

Answer 22

Control the opening and closing of the stoma and control water loss.

Question 23

Describe FOUR leaf adaptations:

Answer 23

Leaf spine - for defence or protection

Succulent or fleshy leaves - to store water

Bulb - starch storage or perennation

Needles - to reduce water loss