Plant structure & growth Flashcards
What are the 3 basic plant organs?
Roots
Stems
Leaves
What are the 3 basic plant organs organised into?
Root & shoot systems
What are the 3 functions of roots?
> anchoring plant
absorbing minerals & water
storing carbohydrates
What is the primary root?
The 1st root (& organ) to emerge from a germinating seed
Describe the root system of eudicots & gymnosperms
Taproot system:
> a taproot = main vertical root
> lateral roots = arise from taproot
Describe the root system of monocots
Fibrous root system:
> adventitious roots = arise from stems/leaves
> lateral roots = arise from adventitious roots
Where does absorption of water & minerals occur in most plants?
At or near root hairs
- increase SA
What are the examples of root adaptations w/ specialised functions?
> prop roots > buttress roots > 'strangling' aerial roots > pneumatophores > storage roots
What is the function of prop roots?
Support tall, top-heavy trees in sandy soils
e.g. Hala trees in south pacific
What is the function of buttress roots?
Prevent trees falling over which have v shallow root systems
e.g. in tropical forests w/ nutrient-poor soil
What is the function of ‘strangling’ aerial roots?
Why are they ‘strangling’?
Seeds can germinate in branches of tall trees
–> send aerial roots to the soil
Shading from leaves of new plant kills the host tree
What is the function of pneumatophores?
Obtain O2 from air as thick estuarine mud lacks O2
- negatively geotropic roots
e.g. Mangroves
What is the function of storage roots?
Store water & sugar
e.g. sugar beet
What do stems consist of?
Alternating system of nodes (= points where leaves attach)
& internodes (= segments between nodes)
What is an axillary bud?
A structure that has the potential to dorm a lateral shoot or branch
What is an apical bud?
(AKA terminal bud)
Located near shoot tip & causes elongation of a young shoot
What are the examples of modified stems?
> rhizome
stolons
tubers
bulbs
What are rhizomes?
Horizontal shoots that grow just below surface
e.g. Iris
What are stolons?
Horizontal shoots that grow along soil surface & allow asexual reproduction of platelets at nodules along stolon
E.g. strawberry plants
What are tubers?
Enlarged ends of rhizomes/stolons
Used for storing food
(the ‘eyes’ on potatoes are axillary buds)
What are bulbs?
Vertical underground shoots that store food
E.g. onion
What do leaves generally consist of?
A flattened blade & a petiole (=stalk)
- joins leaf to node of stem
How do monocots & eudicots differ in the arrangement of veins in leaves?
Monocots = parallel veins
Eudicots = branching veins
What are the 3 types of leaf shape?
Simple
Compound
Doubly compound
What are the examples of modified leaves?
> tendrils > spines > storage leaves > reproductive leaves > bracts
What are tendrils?
What is different about grapevine tendrils?
Leaves that support plants e.g. pea plants use to cling to objects
Once attached tendril coils & pulls plant closer to support
They’re modified stems NOT leaves
Give an example of spines
Spikes on a cactus
Photosynthesis carried out in fleshy green stem
Give an example of a storage leaf
In ice plants they store water
Give an example of reproductive leaves
In succulents they form adventitious platelets that fall off & take root in the soil
What are bracts?
Modified leaves surrounding flowers
- brightly coloured & attract pollinators
e. g. in poinsettia
What are the 3 types of tissue in each plant organ?
Dermal
Vascular
Ground
What is dermal tissue?
The protective layer
What is vascular tissue?
A continuous transport system arranged differently in each organ
What is ground tissue?
Where most metabolic functions take place
Describe dermal tissue systems in non-woody plants
Called the epidermis
Cuticle (=waxy coating) prevents water loss from epidermis
Describe dermal tissue systems in woody plants
Protective tissues called periderm replace epidermis in older regions of stems & roots
Trichomes = outgrowths of shoot epidermis & helps/ insect defence
What is the role of the vascular tissue system?
Carry out long-distance transport of materials between roots & shoots
What are the 2 vascular tissues?
Phloem - organic nutrients
Xylem - water & minerals
What is the vascular system of a stem/root collectively known as?
The steele
‘pilar’ in greek
Describe the arrangement of the ground tissue system
Pith = internal to vascular tissue
Cortex = external to vascular tissue
Includes cells specialised for storage, photosynthesis & support
What are the 5 major types of plant cells?
> parenchyma > collenchyma > sclerenchyma > water-conducting cells of xylem > sugar-conducting cells of phloem
What are the features of parenchyma cells?
> thin, flexible primary walls
NO secondary walls
least specialised
perform the most metabolic functions
retain ability to divide & differentiate
large central vacuole
can differentiate into other cells types e.g. wound repair
(entire plant can be grown from 1 parenchyma cell)
What is the difference between parenchyma cells in leaves vs stems & roots
> in leaves - have chloroplasts
> in stems & roots - have colourless plastids that store starch (=amyloplasts)
What are the features of collenchyma cells?
> grouped in strands & help support young parts of plant shoot
thicker & uneven cell walls
NO secondary walls
provide flexible support w/out restraining growth
What are the features of sclerenchyma cells?
> rigid due to thick secondary walls strengthened w/ lignin > dead at functional maturity > 2 types: - sclereids - fibres
What are the features of sclereids?
> Short & irregular in shape
Thick lignified secondary walls
Impact hardness to seed coats & nut shells
(texture of pear fruits)
What are the features of fibres?
> long & slender
> arranged in threads
What happens to water-conducting cells of the xylem at maturity?
Die
- cell components disintegrate leaving lignin-hardened cell wall
What are the 2 types of water-conducting cells of the xylem?
Where are they found?
Tracheids
- found in xylem of most vascular plants
Vessel elements
- in most angiosperms & few gymnosperms
What are vessel elements?
Wider, shorter, thinner walled & less tapered than tracheas
Movement of water between vessel elements is via perforated end walls
What are tracheids?
Long, thin w/ tapered ends
Movement of water between tracheids is via pits
What are sieve-tube elements like at maturity?
Alive
Lack nucleus, ribosomes, vacuole & cytoskeleton
What does the reduction in cell contents enable sieve-tube elements to do?
Conduct nutrients
What are sieve plates?
Porous end walls that allow fluid to flow between cells along the sieve tube
What does each sieve-tube element have?
A non-conducting companion cell whose nucleus & ribosomes serve both cells
What is the general function of meristems?
Generate cells for primary & secondary growth
What are the 2 types of growth in plants?
Indeterminate
- grow throughout life
Determinate
- organs that cease to grow at certain size
What are the 2 type of meristems?
Apical
Lateral
Where are apical meristems located?
Tips of roots & shoots
Axillary buds of shoots
What do apical meristems do?
Elongate roots & shoots = primary growth
What do lateral meristems do?
In woody plants - add thickness to shoots & roots
= secondary growth
What are the 2 lateral meristems?
Vascular cambium
- adds layers of vascular tissue
= secondary xylem & secondary phloem
Cork cambium
- replaces epidermis w/ periderm
= thicker & tougher
What is the root tip covered by?
Why?
A root cap
- protects apical meristem as root pushes through soil
What are the 3 zones of cells behind the root tip?
> zone of cell division
zone of elongation
zone of differentiation/maturation
Where do lateral roots arise from?
Within the pericycle
= outermost later in vascular cylinder
Describe a shoot apical meristem
Dome-shaped mass of dividing cells at shoot tip
Where do leaves develop from?
Leaf primordia along sides of apical meristem
Where do axillary buds develop from?
What do axillary buds give rise to?
Meristematic cells left at bases of leaf primordia
Lateral shoots
How is vascular tissue arranged in most eudicots?
Vascular bundles arranged in a ring
How is vascular tissue arranged in most monocot stems?
Vascular bundles scattered throughout ground tissue
What is the ground tissue in a leaf called?
What are the 2 layers can eudicots called?
Mesophyll
Palisade mesophyll
Spongy mesophyll
What is each vein/vascular bundle in leaves enclosed by?
What is the role of vascular bundles?
A protective bundle sheath
Support leaf shape
