Lecture 2: The dermal system Flashcards
What are the 6 types of cells
parenchyma epidermis collenchyma scelerenchyma sieve tube elements vessel elements
What is the dermal system comprised of?
shoots: epidermis (derived from protoderm)
root: rhizodermis
How many layers are the parts of the dermal system?
single cell
Where is the dermal system derived from?
protoderm meristem
What is the purpose of the dermal system?
protects the inner part of the plant from water loss, gas exchange, herbivores, pathogens
What kind of dermis is the upper epidermis
adaxial epidermis
what kind of dermis is the lower epidermis
abaxial dermis
What 2 zones is the rhizodermis divided into?
zone of maturation (root hairs are; when root gets older)
zone of elongation
zone of cell division
how do epidermal cells divide?
anticlinally
define anticlinally
division of cells, 90 degrees to surface of plant (new cell wall is 90 degrees to surface of plant)
What is the main job of the epidermis?
protective barrier
what are the things the epidermis controls (5)
water loss gas exchange leaf temperature invading organisms compound exchange
How is the leaf temperature controlled?
-regulated by the amount of sun energy that
penetrates the leaf
- the amount of air movement that occurs around the leaf (influences water loss)
What are the 4 components of the epidermis
cuticle
epidermal cells
stomatal and subsidiary cells
trichomes
What is the cuticle made of?
epicuticular wax (smooth, glandular, ridged) cuticle proper ( cutins - fatty acids) pectin rich layer (polysaccharides; like a cement)
where is epicuticular wax not found
root hairs
What does the form and thickness of the epicuticular wax influence
- influences the amount of sun energy that comes into the leaf
- impacts on the ability of bacteria to penetrate the epidermal cells
- also affects the ability of insects to penetrate the epidermal cells
together what does the epicuticular wax, cuticle proper and pectin rich layer form?
strong barrier from the outside
What are examples of the uses of epicuticular wax when harvested?
lipstick car wax dental floss disposable cups floor polish
What is the purpose of the cuticle
absorbs UV-B light
reflects light
cools surface
conserves water
what are xerophytes?
grow in the desert
- xero meaning dry, phyte meaning plant
- control water loss & over absorption (the cuticle)
- cuticle is thick and has heavy wax layers
What are the properties of the cuticle?
water repellence
cooling
what damages the cuticle layer?
pollutants, wind
Where is cuticle not usually found?
roots
Describe the characteristics of epidermal cells
underneath the cuticle
elongated or isodiametric often have wavy outline (absorbs stresses) lack chlorophyll (except shade plants)
Describe stomata
the pores are bordered by GUARD CELLS
- aerial (most abundant on leaves) 500- 1000 mm^2 common
contain chloroplasts
What is the stomata organization in monocots
in rows
what is the stomata organization in dicots
stomata regularly placed
What are subsidiary cells?
- size and presence depends on species
flank stomata
may ASSIST in opening and closing
How is the stomata developed (2 steps)
- ) unequal division of guard cell mother cells
2. ) the smaller cell divides into two guard cells
What does the pore diameter of the stomata control?
- CO2 levels
- humidity
- water stress
- temperature
- wind
What is the function of the stomata
- ) control water loss via transpiration (allows the plant to pull the water from the roots)
- ) allow entry of CO2
- ) allow exit of CO2
When is a stomata open? turgid or flaccid?
turgid cells
When is the stomata closed?
flaccid cells
What are trichomes?
- hairs ( star shaped, branched, unbranched)
- scales
- root hairs facilitate water and mineral uptake
How do trichomes vary?
- single cell or multicellular
- glandular or non glandular
- functional when dead or alive
What are trichomes for?
- prevent dessication
- reflects solar radiation
- lower leaf temperature
- decrease water loss
- absorb water and minerals (on roots and leaves)
- secrete salt
- insect resistance
- exude compounds
What are trichomes made of?
contain cellulose +/- lignin, cutin; may have crystals
What is the role of invaginations on a plant?
increases the surface area ; also where compounds are secreted out
What are the protective functions of trichomes
decrease transpiration
reflect light and UVB
secrete chemicals
absorb water and minerals
what is the name given for the cultivated species of tomatoes? What is it susceptible to?
lycopersicon esculentum
- susceptible to aphid attacks
What is the name given for the wild species of tomatoes? What is it resistant to?
lycopersicon pennelli
- aphid attacks
Why is the wild tomato resistant to aphid attacks?
it secretes triacylglucose secreted from glandular trichomes
what does Dioecious mean?
has 2 genders
What kind of resin does Cannabis sativa produce?
THC (tetrahydrocannabinol) from its glandular trichomes
In which gender is the concentration of THC greater?
on female flowers
- especially from hot, dry areas (Colombia, Mexico, India)
Where is Cannabis sativa originally from?
from China; Dioecious annual
What are the properties of Cannabis sativa?
Smoked or ingested hallucinogen attributed medical benefits impairs short term memory fat soluble, so remains in body for days after inhalation
What are the medicinal uses of Cannabis sativa?
nausea and vomiting; particularly with chemotherapy
wasting and severe weight loss, in people with HIV/AIDS
asthma
epilepsy
glaucoma
appetite stimulant
pain relief
What are the effects of cannabis
sense of calmness
euphoria
perception of time and space distorted
