8: Leaf Anatomy & Organ Modifications Flashcards
What are the two outer layers of a dicot leaf called?
Upper epidermis and lower epidermis
What are the tissues within the two epidermal layers of a dicot leaf called?
Mesophyll tissues:
- Palisade mesophyll
- Spongy mesophyll
Describe the palisade mesophyll tissue and where it is located
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
Describe the spongy mesophyll tissue and where it is located
- parenchyma cells
- near the lower epidermis of a dicot leaf
- shorter, wider cells that are loosely packed with lots of air spaces
- contain chloroplast
Describe the upper epidermis in dicot leaves
- transparent cells
- covered by waxy cuticle
- does not usually contain stomata
- no chloroplasts
Describe the lower epidermis in dicot leaves
- transparent
- waxy cuticle covers it
- guard cells located here which contain chloroplast
Describe guard cells
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
Describe stoma
- The opening in the waxy cuticle of the epidermis
- surrounded by guard cells
- the site of gas exchange
Describe leaf veins
the vascular bundles that contain xylem on the top and phloem on the bottom
Describe bundle sheath
The ring of cells that surround the vascular bundles in the leaf
Describe air spaces
The space between cells throughout the leaf where gas exchange occurs
What is the main vein called in a dicot leaf with netted venation?
Midrib
How are the minor veins of a dicot leaf with netted venation arranged?
They branch off the main vein/midrib throughout the leaf tissue
What are 4 leaf adaptations for hot, sunny, arid conditions?
- thick waxy cuticle for water retention
- two full layers of palisade mesophyll with lots of chloroplasts
- leaf is thick
- sunken stomata
- hypodermis protects from UV damage
What are 4 leaf adaptations for shady conditions?
- wider, thinner leaves for larger surface area for sun collection
- one layer of palisade mesophyll that’s not super tightly packed
- spongy mesophyll very loosely packed - lots of air space
- mesophyll tissues have less chloroplasts
Describe leaf gap
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
Describe abscission and the steps
The process of leaves dropping from deciduous trees (ex. in temperate climates in the fall)
- 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
- on the stem side, suberin gets pumped into the cells to seal them and form the leaf scar
- 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
During abscission, what is the layer of cells called that is on the stem side of the plant?
Protection layer
it secretes suberin to coat and protect the exposed cells while the petiole is breaking away and prevent water loss
During abscission, what is the layer of cells called that is on the petiole side of the plant?
Separation layer
In a monocot leaf, where are the upper and lower epidermis located?
Upper epidermis is on the inside of the V
Lower epidermis is on the underside of the V
T or F: Monocot leaves have both palisade and spongy mesophyll tissues
FALSE. Only contain spongy mesophyll leaves
Describe bulliform cells
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
T or F: Stomata can occur on the upper and lower epidermis of a monocot leaf?
TRUE
Describe bundle sheath extensions
Common in monocot leaves
- cells that run right from the sheath to the epidermal surface to help stiffen the plant in upward growth
What environmental conditions trigger a stoma to open/guard cells to become turgid?
Daylight triggers the stoma to open as water will flow into the guard cells and make them turgid
also moisture
What environmental conditions trigger a stoma to close/guard cells to become flaccid?
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
Describe trichomes
Leaf hairs that aid in water loss as they interrupt the air flow on the leaf surface
T or F: the conifer needle is an adapted leaf for living in dry or arid conditions
True
What 3 adaptations does the conifer needle have?
- Thick cuticle to prevent water loss
- Sunken stomata
- Hypodermis layer and an endodermis containing suberin
Describe hypodermis. Which leaves have this adaptation?
A layer of thick collenchyma cells beneath the epidermis that protects from UV damage.
Conifer needles have this
Describe resin ducts. which leaves have this adaptation?
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
What is the purpose of a sunken stomata?
Stomata (guard cells and stoma) are recessed into the epidermal surface to create a boundary layer to protect excess water loss
T or F: Conifer needles have an endodermis that contains suberin surrounding the vascular tissues?
TRUE
What are the 10 stem modifications?
- cladophyll
- prickle
- stolon/runner
- succulent stem
- climbing
- thorn
- bulb
- corm
- rhizome
- tuber
Describe cladophyll, provide the function, and give an example
A stem modification
Flattened stems to photosynthesize instead of leaves
Function: photosynthesis/nutrient capturing
ex. Christmas cactus
Describe prickles, provide the function, and give an example
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.
Describe stolons/runners, provide the function, and give an example
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
Describe succulent stems, provide the function, and give an example
stem mod
store water and can take over the role of photosynthesis
function: photosynthesis/storage/nutrient capturing
ex. succulents
Describe the two climbing stems, provide the function, and give an example
modified stem
two kinds:
- twining stems: stem twists around an object to climb upwards
ex. wisteria - Tendrils: coils around something and tightens grip to climb
ex. hops, quinquefolia
Describe thorns, provide the function, and give an example
Modified stem
appears ONLY at the nodes and is not superficial like prickles
ex. hawthorns
Describe bulbs, provide the function, and give an example
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
Describe corms, provide the function, and give an example
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
Describe rhizomes, provide the function, and give an example
Modified horizontal storage stem.
Thick, fleshy rhizomes used for storage and propagation (asexual reproduction). The rhizomes can have nodes
ex. ferns, iris
Describe tubers, provide the function, and give an example
Modified underground storage stem
structure: rounded with ‘eyes’ or nodes and internodes. Filled with parenchyma cells
function: Storage and reproduction
Ex. potatoes
What are the 6 leaf medications?
- carnivorous leaves
- bracts
- spines
- spiny stipules
- succulent leaves
- tendrils
Describe carnivorous leaves, provide the function, and give an example
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
Describe bracts, provide the function, and give an example
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
Describe spines, provide the function, and give an example
Leaf modification
spiky modified leaves found on cacti for protection
ex. Cacti
Describe spiny stipules, provide the function, and give an example
Leaf modification
a pointy appendage at the base of the petiole
function: protection
ex. barberry
Describe succulent leaves, provide the function, and give an example
Leaf modification
thick, water-filled leaves that are modified for a specific kind of photosynthesis
function: water storage supports drought tolerance; nutrient capturing (photosynthesis)
Describe tendrils, provide the function, and give an example
Leaf modification
grow off the compound leaves and will wrap around objects with which they come in contact
function: climbing
ex. peas
