8: Leaf Anatomy & Organ Modifications

Question 1

What are the two outer layers of a dicot leaf called?

Answer 1

Upper epidermis and lower epidermis

Question 2

What are the tissues within the two epidermal layers of a dicot leaf called?

Answer 2

Mesophyll tissues:

1. Palisade mesophyll
2. Spongy mesophyll

Question 3

Describe the palisade mesophyll tissue and where it is located

Answer 3

thin walled, long parenchyma cells tightly arranged like a palisade (fence/stakes) in one or two layers nearest to the upper epidermis of dicot leaves
- contain chloroplast

Question 4

Describe the spongy mesophyll tissue and where it is located

Answer 4

• parenchyma cells
• near the lower epidermis of a dicot leaf
• shorter, wider cells that are loosely packed with lots of air spaces
• contain chloroplast

Question 5

Describe the upper epidermis in dicot leaves

Answer 5

• transparent cells
• covered by waxy cuticle
• does not usually contain stomata
• no chloroplasts

Question 6

Describe the lower epidermis in dicot leaves

Answer 6

• transparent
• waxy cuticle covers it
• guard cells located here which contain chloroplast

Question 7

Describe guard cells

Answer 7

Part of the collective term: stomata

• contain chloroplasts to generate energy
• swell up or shrink to open/close the stoma depending on water flow
• found in the lower epidermis of dicot leaves and both epidermal layers in monocot leaves

Question 8

Describe stoma

Answer 8

• The opening in the waxy cuticle of the epidermis
• surrounded by guard cells
• the site of gas exchange

Question 9

Describe leaf veins

Answer 9

the vascular bundles that contain xylem on the top and phloem on the bottom

Question 10

Describe bundle sheath

Answer 10

The ring of cells that surround the vascular bundles in the leaf

Question 11

Describe air spaces

Answer 11

The space between cells throughout the leaf where gas exchange occurs

Question 12

What is the main vein called in a dicot leaf with netted venation?

Answer 12

Midrib

Question 13

How are the minor veins of a dicot leaf with netted venation arranged?

Answer 13

They branch off the main vein/midrib throughout the leaf tissue

Question 14

What are 4 leaf adaptations for hot, sunny, arid conditions?

Answer 14

1. thick waxy cuticle for water retention
2. two full layers of palisade mesophyll with lots of chloroplasts
3. leaf is thick
4. sunken stomata
5. hypodermis protects from UV damage

Question 15

What are 4 leaf adaptations for shady conditions?

Answer 15

1. wider, thinner leaves for larger surface area for sun collection
2. one layer of palisade mesophyll that’s not super tightly packed
3. spongy mesophyll very loosely packed - lots of air space
4. mesophyll tissues have less chloroplasts

Question 16

Describe leaf gap

Answer 16

When the continuity of the vascular bundle going vertically up the stem is broken by the growth of a leaf petiole a gap forms so the vascular bundle can go into the leaf

• this also occurs with buds and is called bud gaps

Question 17

Describe abscission and the steps

Answer 17

The process of leaves dropping from deciduous trees (ex. in temperate climates in the fall)

1. after the chloroplast has been taken back into the stem, a gap will open up between the petiole cells and the main stem of the plan as the cells break away
2. on the stem side, suberin gets pumped into the cells to seal them and form the leaf scar
3. vascular tissues are the last part of the leaf holding it to the stem and eventually the wind will blow it off leaving a leaf scar that will be protected and sealed by suberin

Question 18

During abscission, what is the layer of cells called that is on the stem side of the plant?

Answer 18

Protection layer

it secretes suberin to coat and protect the exposed cells while the petiole is breaking away and prevent water loss

Question 19

During abscission, what is the layer of cells called that is on the petiole side of the plant?

Answer 19

Separation layer

Question 20

In a monocot leaf, where are the upper and lower epidermis located?

Answer 20

Upper epidermis is on the inside of the V

Lower epidermis is on the underside of the V

Question 21

T or F: Monocot leaves have both palisade and spongy mesophyll tissues

Answer 21

FALSE. Only contain spongy mesophyll leaves

Question 22

Describe bulliform cells

Answer 22

cells specific to monocot leaves that are located near the midrib

structure is like an accordion that swells up with water and pushes the grass blade open to create a flatter surface and will pull the blades in closer and curl up when dry

Question 23

T or F: Stomata can occur on the upper and lower epidermis of a monocot leaf?

Answer 23

TRUE

Question 24

Describe bundle sheath extensions

Answer 24

Common in monocot leaves

- cells that run right from the sheath to the epidermal surface to help stiffen the plant in upward growth

Question 25

What environmental conditions trigger a stoma to open/guard cells to become turgid?

Answer 25

Daylight triggers the stoma to open as water will flow into the guard cells and make them turgid also moisture

Question 26

What environmental conditions trigger a stoma to close/guard cells to become flaccid?

Answer 26

Darkness will trigger the stoma to close as water will leave the guard cells and they will become flaccid and close the stoma also drought

Question 27

Describe trichomes

Answer 27

Leaf hairs that aid in water loss as they interrupt the air flow on the leaf surface

Question 28

T or F: the conifer needle is an adapted leaf for living in dry or arid conditions

Answer 28

True

Question 29

What 3 adaptations does the conifer needle have?

Answer 29

1. Thick cuticle to prevent water loss 2. Sunken stomata 3. Hypodermis layer and an endodermis containing suberin

Question 30

Describe hypodermis. Which leaves have this adaptation?

Answer 30

A layer of thick collenchyma cells beneath the epidermis that protects from UV damage. Conifer needles have this

Question 31

Describe resin ducts. which leaves have this adaptation?

Answer 31

Resin is a defensive compound to repair or coat a wound if a plant gets injured. It is also a feeding deterrent conifer needles have this

Question 32

What is the purpose of a sunken stomata?

Answer 32

Stomata (guard cells and stoma) are recessed into the epidermal surface to create a boundary layer to protect excess water loss

Question 33

T or F: Conifer needles have an endodermis that contains suberin surrounding the vascular tissues?

Answer 33

TRUE

Question 34

What are the 10 stem modifications?

Answer 34

1. cladophyll 2. prickle 3. stolon/runner 4. succulent stem 5. climbing 6. thorn 7. bulb 8. corm 9. rhizome 10. tuber

Question 35

Describe cladophyll, provide the function, and give an example

Answer 35

A stem modification Flattened stems to photosynthesize instead of leaves Function: photosynthesis/nutrient capturing ex. Christmas cactus

Question 36

Describe prickles, provide the function, and give an example

Answer 36

A stem modification Found randomly on the stem, petioles, and leaves of some plants. Superficially embedded on the stem Function: protection ex. roses, salmon berries, etc.

Question 37

Describe stolons/runners, provide the function, and give an example

Answer 37

stem modification an elongates stem that stays above the ground and will root and grow a new plant when a node touches the ground function: reproduction/propagation ex. Strawberries, spider plants

Question 38

Describe succulent stems, provide the function, and give an example

Answer 38

stem mod store water and can take over the role of photosynthesis function: photosynthesis/storage/nutrient capturing ex. succulents

Question 39

Describe the two climbing stems, provide the function, and give an example

Answer 39

modified stem two kinds: 1. twining stems: stem twists around an object to climb upwards ex. wisteria 2. Tendrils: coils around something and tightens grip to climb ex. hops, quinquefolia

Question 40

Describe thorns, provide the function, and give an example

Answer 40

Modified stem appears ONLY at the nodes and is not superficial like prickles ex. hawthorns

Question 41

Describe bulbs, provide the function, and give an example

Answer 41

modified underground storage stem The bulb is a bunch of fleshy leaves pushed together the stem is at the very bottom of the bulb where the roots emerge ex. tulips, onions

Question 42

Describe corms, provide the function, and give an example

Answer 42

Modified vertical underground stem. Structure: papery leaves surround the vertical storage stem that is hard and in the centre. The previous year's corm can be found at the bottom of the structure and is very dense and roots grow. Function: storage Ex. Crocus

Question 43

Describe rhizomes, provide the function, and give an example

Answer 43

Modified horizontal storage stem. Thick, fleshy rhizomes used for storage and propagation (asexual reproduction). The rhizomes can have nodes ex. ferns, iris

Question 44

Describe tubers, provide the function, and give an example

Answer 44

Modified underground storage stem structure: rounded with 'eyes' or nodes and internodes. Filled with parenchyma cells function: Storage and reproduction Ex. potatoes

Question 45

What are the 6 leaf medications?

Answer 45

1. carnivorous leaves 2. bracts 3. spines 4. spiny stipules 5. succulent leaves 6. tendrils

Question 46

Describe carnivorous leaves, provide the function, and give an example

Answer 46

Leaf modification Cells will lose water rapidly to contract leaves and trap insects inside then secrete a substance to digest the insect function: captures nutrients ex. Venus fly trap

Question 47

Describe bracts, provide the function, and give an example

Answer 47

Leaf modification structure: leaf-like appendages found under a flower function: can be for attracting pollinators ex. poinsettia (the red is actually the bracts), lilies

Question 48

Describe spines, provide the function, and give an example

Answer 48

Leaf modification spiky modified leaves found on cacti for protection ex. Cacti

Question 49

Describe spiny stipules, provide the function, and give an example

Answer 49

Leaf modification a pointy appendage at the base of the petiole function: protection ex. barberry

Question 50

Describe succulent leaves, provide the function, and give an example

Answer 50

Leaf modification thick, water-filled leaves that are modified for a specific kind of photosynthesis function: water storage supports drought tolerance; nutrient capturing (photosynthesis)

Question 51

Describe tendrils, provide the function, and give an example

Answer 51

Leaf modification grow off the compound leaves and will wrap around objects with which they come in contact function: climbing ex. peas