Plants Lesson 4 Flashcards
What are plant cell walls made of?
Cellulose
Cell walls
Outside the cell membrane and has a set of functions to stabilize the plant.
Cellulose
Polysaccharide of glucose units. Made by the membrane. Most common organic polymer.
Cell wall increasing in size
Cellulose microfibril (made of parallel cellulose molecules, connected by a hydrogen bond), then 36 chains of these can make a microfibril, then cellulose fibril, then they are laid down in sheets in all different directions to make a cell wall.
Plant cell walls
Extracellular—outside of membrane.
2 kinds:
Primary wall—thin, in all cells
Secondary wall—thicker, in some cells (strength) and only in some plants.
Functions of plant cell wall
- determines & maintains cell shape.
- provides support and mechanical strength (allows plants to get tall, hold out thin leaves to obtain light).
- prevents the cell membrane from bursting and calapsing (i.e., resists water pressure).
- controls the rate and direction of cell growth and regulates cell volume.
- ultimately responsible for the plant architectural design (shape).
- 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.
- carbohydrate storage — the components of the wall can be reused in other metabolic processes (especially in seeds).
Two many functions of waxy cells in the cell wall?
Allow fluids to flow through the plant. Prevent fluid from flowing through the walls.
3 Kinds of polysaccharides (plant cell wall compositions)?
- Cellulose: Polymer (chain) of up to 25,000 glucose molecules and ~36 chains bond to make microfibril. Gives the cell its strength.
- Cross-linking glycans (hemicellulose)—bond with
cellulose. - Pectin—jellylike; glue. A polysaccharide.
The two things that hold the cellulose together?
Pectin and hemicellulose
Middle Lamella
Material between cells. Made of pectic substances. Holds the cells together.
Plasmodesmata
Connection between cells that cytoplasm flows through.
Which cell wall is made first?
The primary then the secondary because both is made by the cell membrane.
The 3 tissue systems in vascular plants
Dermal, Vascular, Ground
Dermal tissue
Single layer; secretes cuticle (waxy). On the outside. The epidermis.
Vascular tissue
Xylem & phloem; support & supply. Moves fluids around. Moves fluid around.
Types: Tracheids & vessel elements, and Sieve elements
Ground Tissue
Tissue other than dermal or vascular; bulk of young plant; fills space between dermal & vascular tissues;
mostly parenchyma; storage, photosynthesis, support.
Types: Parenchyma, Collenchyma, Sclerenchyma
How many cell types in plants?
6
Epidermal cells
Outermost cells. Single layer (single sheet) covering leaves, stems & roots of non-woody plants or plant
parts. If woody this gets replaced. All plants have them. Forms the epidermis of shoots.
Epidermal cells functions
Waterproofing. Protection from pathogens: viruses, bacteria, fungi. Other specialized roles: Hairs (trichomes), make nectary, Guard cells: gas exchange (open and close).
Cuticle
Formed by the epidermal cells, outermost part is wax. Cuticle protects against: Water loss, Pathogens,
Ultraviolet (UV) radiation, because of the wax.
Wax on chamomile petal does what?
Makes it white because of how it reflects the light.
Pitcher plant
Eats insects. They get trapped in there because they fall down it because the way the wax is arranged because the insects can’t climb back up. When it falls down it gets digested because of acidic fluid.
Secretory trichomes
Means hair. They have smells from the oils in the Epidermal cells. Or has fluid to make you sting.
Cannibis
Secretory trichomes that have Epidermal cells filled with THC.
Marjoram
3 kinds of trichomes on 1 leaf. 2 that secrete oils and 1 that hinders crawling insects. Both used for defence.
Parenchyma cells
Most general. A type of ground tissue (when in stems & roots)(make up most of the young plant). Usually lack secondary wall. Can often divide & differentiate at maturity. They have different shapes and look a lot different.
Parenchyma cells functions
Many; often specialized. Most metabolic processes (photosynthesis, storage, secretion, food storage).
Parenchyma cells examples
Fruit flesh, Endosperm, Pith & cortex of stems & roots, Chloroplast-laden cells inside leaves (photosynthesis).
Collenchyma cells
A type of ground tissue. Thick, uneven primary wall (why it’s easy to recognize). No secondary wall. Always occur just below epidermis. Often occur in strands. Alive at maturity: can elongate. Support, esp. of young & growing organs. ie. Celery leaf midrib & petiole.
Sclerenchyma cells
Hard cells. Support, protection (of tissues no longer
elongating). A type of ground tissue. Thick secondary wall with lignin (a rigid polymer). Cannot elongate at maturity (may be dead). They don’t divide at maturity. 2 forms: fibers & sclereids.
Sclerenchyma (fibers)
Burlap and hemp. Fibers are in a bundle.
Sclerenchyma (sclereids)
Makes pear gritty. Have thick wall. Makes nuts hard, like acorn. 2 sclereids make lilies unpleasant to taste.
Water-conducting cells of the xylem: tracheids & vessel elements
Support & supply of water and minerals. Dead at maturity, the plants kills them so they can be functional. Secondary wall lignified, often spiral. Two kinds: Tracheids & vessel elements (different shapes). A type of vascular tissue.
Xylem
Moves water and materials from the soil up through the plant.
Vessels
Wider and thicker.
Tracheids
Pits with water that goes through them. Very narrow.
Pites
Holes in secondary wall where only primary wall remains.
Lignin
Gives wood its woodiness. Class of complex organic polymers (NOT a polysaccharide). 2nd -most abundant natural polymer, after cellulose. Deposited in cell walls; fills spaces and binds cellulose, hemicellulose & pectin. Gives strength to wood & bark. Can occur in cell walls of non-woody plants (palm trees, bamboo, wheat straw, …)
Lignin Human uses
- Wood: 20–33% lignin by dry weight
- Rope, clothing, rugs, … (sclerenchyma fibers)
- Paper—lignin removed to leave cellulose
- Artificial vanillin (real vanillin is from vanilla
orchid)
Sugar-conducting cells of the phloem: sieve-tube elements?
Transport sugars (esp. sucrose), other organic compounds, some minerals. A type of vascular tissue. Alive at maturity. With companion cell (parenchyma).
Meristems
They are stem cells. Ultimate source of all parts of the mature sporophyte. Undifferentiated. Retain “forever” the ability to divide. They maintain themselves. Meristems divides into daughter cells and only the daughter cell come become other types of cells.
How do plants grow?
Meristems
The youngest part of the plant?
The top and as you go down it gets older and older. Can look at different stages of development.
Types & location of meristems
Apical meristems (AM): Root AM and shoot AM and Primary growth. All plants have them.
Lateral meristems: Vascular cambium & cork
cambium and Secondary growth. Only woody ones have them. In the many part of it.
These tissue systems (dermal, vascular, and ground) arise from what?
3 new meristems (aka intermediates) that later become specialized, they are made by the apical meristems.
The intermediate meristem that makes dermal tissue?
Protoderm. The youngest type.
The intermediate meristem that makes vascular tissue?
Procambium
The intermediate meristem that makes ground tissue?
Ground meristem
Leaf primordia
Part of the shoot that will develop into mature leaves.
3 Different stages all in one plant
Apical Meristems to Primary meristems to Primary tissues.
What’s in the vascular bundle?
Xylem (near middle) and phylum (near the outside).
Vascular bundles in eudcots vs. monocots?
Eudcots: in a circular line.
Monocots: Smaller in random spots.
Root cap is what?
Made of dead cells. It protects.
3 zones of root growth?
Zone of cell division, zone of elongation, and zone of maturation. Pushes downwards.
Zone of maturation
Once it stops elongating it makes root hair, this prevents root hair damage.
Root hair
Each is one epidermal cell. They branch from the vascular tissue (from inside) because it needs a constant flow of water. They increase surface area.
4-month-old rye plant
14 billion root hairs. Surface area 400 sq. meters. Placed end to end >10,000km.
Steele
Everything in the endodermis, arise from prcambium. (aka vascular cylinder). Center of roots. Contains vascular tissue and gound tissues.
Endodermis
The innermost layer of cortex. Only roots have them. Surrounds the vascular cylinder
Xylem and Phloem shapes in roots: Eudicot vs. Monocots
Eudicot: In a + shape
Monocots: Smaller, circular line.
Lateral Root
Originates in pericycle (outermost layer of vascular cylinder. Grows out through cortex & epidermis.
Roots absorb what?
Water and minerals
Pericycle
Between vascular cylinder and endodermis. Origin of lateral roots.
