Lecture 5

Question 1

Leaves

Answer 1

Photosynthetic organs with a manufacturing cost

Question 2

Leaf shape

Answer 2

A) Hight surface area for CO₂ absorption (H₂O loss) and light exposure, high SA:V

Question 3

Leaf Shape

Answer 3

B) lower SA:V , less photosynthesis but better H₂O conservation

Question 4

Leaf Shape

Answer 4

C) Lowest SA:V, little SA for gas exchange best H₂O conservation

Question 5

Leaf Shapes

Answer 5

D) High SA, no self shading, must be long to achieve volume = a

Question 6

Leaf Layer

Answer 6

-Chloroplasts are mainly located in mesophyll cells

Layer from top to bottom

• Cuticle
• Upper epidermis
• Pallsiade Mesophyll Cell
• Bundle Sheath Cell
• Xylem
• Phloem
• Lower Epidermis
• Spungy mesophyll Cells
• Guard cell
• Stoma
• Cuticle

Question 7

Leaf Fibers

Answer 7

• made from xylem and phloem cells bundled in leaves
• sisal and henequen come from leaves of Agave spp. *Agave sisalana *has sharp spoines that may also be used a needles, “needle and thread” plant
• ropes made from sisal in Africa - can make heavy duty rugs/mats
• has thorns on the side that would be used as a needle

Question 8

Surface area to volume relationship of different leaf shapes

Answer 8

A) High SA:V = High surface area for CO₂ absorption (H₂O loss) and light exposure (example: standard broad leaf)

B) Lower SA:V = less photosynthesis but better H₂O conservation

C) Lowest SA:V = little SA for gas exchange, best H₂O conservation

D) High SA = no self-shading, must be long to achieve volume = a (Example: needle plant)

Question 9

Chloroplast structure

Answer 9

Chloroplasts are mainly located in mesophyll cells

Question 10

Mesophyte

Answer 10

• Syringa vulgaris*
• plants that live in medium conditions

Example: lilacs

Question 11

Xerophyte

Answer 11

• Nerium oleander* (Oleander)
• plants that live in extremely dry conditions
• plants of dry areas
• multiple layers of endodermis with thick cuticle - prevents loss of water molecules
• stomatal crypts
• trichomes within crypts retain moisture near stomata

Question 12

Stomatal crypts

Answer 12

• where the stomata is sunken into the epidermis like a little cup
• can have trichomes - prevents water loss, creates drags
• reduce moisture loss
• found mostly in Xerophytes
• example: Oleander

Question 13

Trichomes

Answer 13

DEFINNEEEEE

Question 14

Hydrophyte

Answer 14

• Nypmphaea* (Water lily)
• stomata on upper surface, or lacking
• lots of air space to conduct O₂to submerged portions of plant
• less xylem tissue
• air spaces help move O₂ to parts of submerged portions of the plant so they can get oxygen as well
• pants that grow in wet areas, either mud or partially to wholly submerged in water*

Question 15

Monocot - Zea mays

Answer 15

• mesophyll does not have distinct layers
• conspicuous bundle sheath cells (AKA Kranz antomy) - surrounding vascular bundles, a wreath-like shape
• typical of monocots and grasses
• monocots tend to have parallel leaf veinnation

Question 16

xylem

Answer 16

water transport in plants

Question 17

bundle sheath and bulliform cells

Answer 17

• bundle sheath - one or more layers of parenchyma or sclerenchyma cells that surround the vascular bundles (veins) of some plants
• bulliform cells - open and close the “V” of a grass leaf, upon losing water cause the leaf to roll or fold up, large epidermal cells that occur in rows in grass leaves, and which are thought to play a role in leaf foldnig and unfolding
• turgid cells open the leaf
• folded leaf conserves water

Question 18

Cuticle

Answer 18

• this surface blocks much of the moisture loss

Question 19

aerenchyma

Answer 19

• tissue with large air spaces
• present on floating and emergent leaves that have blades and stalks
• helps in floatation as well as provides air passageways to the submerged roots for gas exchange

Question 20

Manila hemp

Answer 20

• grown extensivey in Phillipines, where pineapple cloth is also made (for ceremonial purposes)
• used for tectilse, cigarette filters, “Manila” envelopes, tea bags

Question 21

abscission zone

Answer 21

• forms across the base of the leaf stalk to facilitate leaf drop

Question 22

specialized guard cells

Answer 22

• guard cells of eudicots and many monocots are bean shaped
• when turgid they open and close when the lose turgid

Question 23

Stomatal opening

Answer 23

1. Zeaxanthin -pigment that is able to see blue light and activates proton pumps
2. Active transport - protons pumped out of guard cells, forming proton gradient
3. Facilitated diffusion - potassium ions enter guard cells through voltage-activated ion channels
4. Solute concentration increases - chloride ions also enter guard cells through ion channels
5. guard cells become turgid - water enters guard cells by osmosis, and stoma opens

Question 25

Transpiration

Answer 25

• the movement of water through the plant from roots, leaves, atmosphere
• leaves play critical role in transpiration

Question 26

Leaf senescence

Answer 26

• leaf death
• individual leaves don’t have a very long life span
• leaf life spans vary by species
• in temperate species abscission is cued by shortened day length (aka cued by change in daylight)
• starches and proteins broken down into simple sugars and amino acids that are reabsorbed by the plant
• some essentional minerals also recovered
• autumn in the temperate zone yields senescing leaves containing xanthophyll and carotenoid accessory pigments

Question 27

Leaf Abscission

Answer 27

• adaptive to winter “deserts” with little water available for photosynthesis
• leaves become a liability when they collect heavy snow causing branches and stems to snap
• ethylene (plant hormone) promotes abscission (leaf drop)
• protective layer of cork cells and suberin - leaf scar is made of this
• leaf scar is created when leaf falls*
• leaf abscission results in leaf scar

Question 28

leaf scar

Answer 28

• protective layer of cork cells & suberin
• created when leaf falls

Question 29

leaf modifications

Answer 29

• water storage, Aloe
• Epiphyte phyllotaxy (arrangement of leaves) stores rainwater (i.e. leaf cups to hold water, make pools of water to store its own water)
• protect floral and leaf buds
• showy
• food storage
• climbing tendrils (i.e. pea plant - allowed to climb)

Question 30

Phyllotaxy

Answer 30

• arrangment of the leaves in a plant

Question 31

leaves modified for defense

Answer 31

• spines are modified leaves (i.e. on a cacti)
• thorns are specialized stems (i.e. Honey locust thorn)
• prickles are extensions of epidermis or cortex (i.e. Rose prickle)

Question 32

leaves trap animals

Answer 32

• pitcher plants
• venus fly trap
• sundew

Question 33

Summary points

Answer 33

• leaves are arranged in distinct patterns on stems
• the epidermis provides structural support and retards water loss
• Mesophyll is the photosynthetic tissue of leaves
• xylem and phloem are the conducting tissues of leaf veins
• stomatal movements control transpiration
• autumn leaf abscission is preceded by a period of senescence
• leaf abscission is preceded by formation of an abscission zone
• some leaves are specialized for water or food storage (i.e. pitcher plant vs. plant phyllotaxy)
• leaves are modified for defense in some plants
• leaves capture animal prey in some plants