Lecture 4- Plant Structure; Cell Types and Primary Growth Flashcards
There are two systems in vascular plants
Shoot system: above ground, consists of shoot with nodes, depends on water and minerals
Root system: below ground, depends on photosynthates
Root
an organ that anchors a vascular plant in the soil
absorbs minerals and water
stores carbohydrates
Primary root
The first root (and organ) to emerge from a germinating seed
Originates in the embryo
Branches to form lateral roots
Lateral root
Greatly enhances the ability of the root system to anchor the plant and acquire water and minerals from soil
Taproot
One main vertical root
Develops from the primary root
Prevents the plant from toppling
Allows plant to be tall
Stem
An organ that raises and separates leaves, exposing them to sunlight
Raise reproductive structures, facilitates the dispersal of pollen and fruit
Consists of nodes: points at which leaves are attached
internodes: the stem segments between nodes
Axillary bud
Structure that can form a lateral shoot, called a branch
Young ones grow very slowly
Apical bud
Also called terminal bud
Composed of developing leaves, nodes, and internodes
The shoot tip, where most of the growth of a young shoot is
Leaf
The main photosynthetic organ
Consist of a blade and a petiole
Blade
Hard, flat part of leaf
Petiole
The stalk that joins the leaf to the stem at a node, the soft part
Cell Walls
Extracellular- outside the membrane and is made by the membrane
Composed mostly of cellulose: polysaccharide of glucose units
Made of cellulose microfibrils: adjacent, parallel cellulose molecules
There are two kinds of cell walls in land plants:
primary and secondary
primary cell wall
Primary wall
Thin
In all plant cells
Made first
secondary cell wall
Secondary wall Thicker than primary wall, made for strength In some plant cells Made on the inside Made seconds Provides support and protection
Functions of the Plant Cell Wall
Determines and maintains cell shape
Provides support and mechanical strength
allows plants to get tall, hold out thin leaves to obtain light
3) Prevents the cell membrane from bursting
resists water pressure
4) Controls the rate and direction of cell growth and regulates cell volume
5) Ultimately responsible for the plant architectural design
6) Physical barrier to a) pathogens and b) water in suberized (waxy) cells. However, remember that the wall is very porous and allows the free passage of small molecules
7) Carbohydrate storage
the components of the wall can be reused in other metabolic processes (especially in seeds)
The cell wall is composed of 3 polysaccharides:
cellulose, hemicellulose, pectin
cellulose
Polymer (chain) of up to 25,000 glucose molecules
approx 36 chains bond to make microfibril
made up of cellulose microfibrils
hemicellulose
Cross-linking glycans bond with cellulose
pectin
Jellylike, acts as the glue
Holds everything together
why do cells stick together
middle lamella: pectic substances
types of plant cells
6: Schlerenchyma Parenchyma Epidermal Collenchyma Trachieds and vessel elements Sieve elements
Schlerenchyma
-thick secondary wall: strong and woody two types: fibres that unite into strands, schlerieds that don't unite -dead and hard function: support, strength -ex: rope, clothing
Parenchyma
-Simple cells that have generalized functions
Least specialized
Usually lack secondary wall
Can often divide and differentiate at maturity
most abundant, can perform all kinds of functions based on their location
Function:
General
Most metabolic processes (photosynthesis, storage, secretion)
ex: fruit flesh, pith, and cortex of stems and roots
Epidermal
Epidermal Outermost cells of all land plants Single layer Function: Waterproofing: keeps water out and in Protection from bacteria, fungi, viruses Can be highly specialized: make hairs (trichomes) , nectar, guard cells- gas exchange Cuticle Formed by the epidermal cells Outermost part is wax Waxy coating on the epidermal surface, helps prevent water loss, pathogens, and UV radiation
Collenchyma
Thick, uneven primary wall No secondary wall Often occur in strands Alive at maturity: can elongate Function: Support, especially of young and growing organs
ex: celery leaf and midrib and petiole
Tracheids and vessel elements
Water conducting cells of the xylem
Dead at maturity (when they are functioning, they are dead)
Secondary wall lignified: woodlike polymer, often spiral
Two kinds: tracheids and vessel elements
Function:
Support
Supply of water and minerals
Xylem tissue: tracheids and vessel elements
Differ in their shape
Tracheids
In the xylem of all vascular land plants
Tapered, goes through pit
Vessel Elements
Wider, shorter, not tapered
Thick, stacked on top of each other
Sieve elements
Sieve elements
Sugar conducting cells of the phloem
Alive at maturity
With companion cell: connected to the sieve-tube by plasmodesmata
Function:
Transport sugars (especially sucrose) in liquid form, other organic compounds, some minerals
Meristem
Ultimate source of all parts of mature sporophyte
Undifferentiated
Can divide forever
Two types of meristems
Apical and Lateral
Apical Meristems
- Shoot and Root AM
- Make 3 meristems, those meristems go off to make 3 primary tissues
- primary growth: growth in height
- located at tips of roots and shoots
Describe primary growth
1) Apical meristem produces 3 new meristems: Protoderm that goes on to produce dermal tissue/epidermis. Pro cambium goes on to produce vascular tissue/ xylem to inside, phloem to outside. Ground meristem produces ground tissue: pith and cortex, lies in-between protoderm and pro cambium
Allows plant to grow vertically
Draw a shoot apical meristem
youngest tissues at top
oldest are at the bottom
Shoot structure of Monocot and Eudicot
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Root apical meristem drawing
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root cap is produced by the
protoderm
- protects root as it drives down into the soil
- dead cells
Stele
- protects all vascular tissue in the root
- all vascular tissue
Primary growth in roots
1) Zone of Cell division. Root AM keeps dividing in cells.
2) Zone of Elongation. Root cells get longer and grow
3) Zone of Maturation/Differentiation: cell growth stops, root hairs grow
Root structure in Monocot and Eudicot
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Endodermis
innermost layer of cortex
one cell thick barrier between cortex and vascular tissue
-casparian strip: permits passage
Stele
all vascular tissue in root and stem
everything inside endodermis
pericycle
