Flashcards in GENERAL BOTANY Deck (22):
Water-Pathways to the Vascular System
(Passive Transport) Movement amongst/within the cell walls and the spaces making up the permeable root apoplast. There is little resistance and is therefore faster. (Stops at the casparian strip). Plant cell walls are connected via the apoplastic pathway.
Movement through the interior of cells, using plasmodesmata tunnels to connect with neighboring cell membranes. There is some resistance and is therefore slower. Such type of movement occurs where living protoplasm is involved (cytoplasm and organelles excluded).
The chemical and physical properties of water molecules allowing them to move directly through cell walls,membranes,and organelles.
Using energy to move a molecule across a membrane, against a concentration gradient.
Directly related to the metabolic rate of neighboring cells.
Movement of molecules without the use of external energy.
Only uses the gradient potential (from areas of high concentration to those of lower), and attraction between charged molecules (facilitative transport) as the driving energy.
Unrelated to the metabolic rate of neighboring cells.
A form of passive transport where the molecule moves across a membrane through the aid of a bound protein, thus changing its' shape (composition) and allowing passage.
Primary Growth (vertical growth)
Is growth that occurs as a result of cell division at the tips of plant stems and roots, causing them to elongate.
Secondary Growth (lateral growth)
Is growth the results from cell division in the cambia/stele(pericycle, vascular cambium) that causes the stems and roots to thicken.
Four Types of Plant Tissue
Areas on the plant where active cell division and source of growth occurs for plants.
1.)shoot apical meristem (primary growth)
2.)root apical meristem (primary growth)
3.) vascular cambium/pericycle (secondary growth)
Cells are closely packed together and undifferentiated, meaning they have the capacity to divide into any kind of cell.
These cells have very large nuclei, small vacuoles with lots of protoplasm, and very thin cell walls.
Do not contain chloroplasts, however contain precursors of plastids, so that the cell may or may not produce them.
Throughout differentiation tremendous amounts of protein, DNA and RNA, ribosomes, PGR's and overall cellular activity is registered.
-Chiefly found in the outer cortex of stems as well as in leaves.
-Are much longer than parenchyma cells.
-Form bundles and strands (example:celery) and help with extra structural support to plants.
-Lack secondary cell walls (lignin) and are flexible.
-In plants with secondary growth, the collenchyma tissue is only temporarily functional and becomes crushed as woody tissue develops (parenchyma-->sclerenchyma).
-The most common of the ground tissues.
-Have primary thin walls, large vacuoles, and retain most of their protoplasts into maturity (the cytoplasm, nucleus, and cell organelles).
-Retain the ability to divide, to regenerate, and fully specialize (adventitious buds/roots).
-These cells may be compact and perform metabolic functions (photosynthesis); such as in the palisade layer of leaves.
-Or may have extensive spaces in between serving gas exchange (respiration); as in the spongy mesophyll.
-Capable of sugar storage (digestion) such as in fruit pulp, carbohydrates in root (tubers)/the inner layer of the stem cortex, or the endosperm of seeds.
-Develop a lignified secondary wall and cannot elongate.
-Serve as support and provide physical protection.
-Dead at maturity leaving lignin shells behind either in the form of sclereids or fibres.
-Sclereids, are a special kind of sclerenchyma that make up the hard coating on seeds, nutshells, beans, hard waxy leaves.
-Fibres seen in the structural support of vascular tissues
Consists of two types of cells that transport water and nutrients through the plant side by side; xylem and phloem cells.
Xylem (passive transport)
Transports water along with dissolved mineral nutrients in a one way direction up the plant.
Starts from absorption at the roots, and through the use of adhesion/cohesion makes its way all the way up to the stems and leaves (where some H20 molecules are then transpired) using passive transport.
Made possible through specialized xylem cells that are efficiently placed end-to-end (.5mm) and are either referred to as tracheids or vessel elements (hardwoods).
The sticking together of particles of the same substance, in this case, that of water molecules.
Adhesion is the tendency of dissimilar particles or surfaces to cling to one another.
In this case the attraction between water molecules and tracheids/vessel elements.
Tracheids and Vessel Elements
Xylem pipes are either tracheids or vessel elements.
Both have re-enforced walls of lignin to prevent the tubes from collapsing in on themselves. Even though they are dead at maturity the lignin retains their shape and functionality.
Tracheids (about the width of a human hair) have pits at their ends thus allowing water to flow through. The cells are tapered and overlap.
Vessel elements have actual perforated holes at the ends of them. In contrast these are actually connected as opposed to overlapping, so that there is even less resistance to the movement of water. Are about 6x wider than a tracheid and can reach up to 10 cm long!
Phloem (active transport)
Function to transport sugars made during photosynthesis from a source (such as chloroplast) to an area of the plant in need of energy; a sink (example: growing bud).
Movement can be upward from the absorbed root nutrients to the leaves
Downward as sugar molecules to be used or saved by some other part of the plant. (sink e.g. tuberous roots).
However movement can not be in both directions at the same time.
Transport of sugars nutrients takes place in the sieve tubes.
Sieve Tubes and Companion Cells
Sieve tubes are specialized elongated cells, that in contrary to the xylem cells, lack lignin and do not die at maturity.
Similar to pits-Sieve tubes contain sieve plates, perforated structures that connect the vertical stack (contain callose).
In maturation sieve tubes loose their nuclei, vacuoles, and ribosomes however retain plastids, an endoplasmic reticulum, and mitochondria.
Without a nucleus the sieve element is forced to merge with a companion cell that carries out the functions of its missing organelles, and essentially keeps it alive.
Energy is required to move sugars through the system and therefore relies on the hydrostatic pressure.
As sieves fill up with sugar, H20 from adjacent Xylem elements follow to lower the concentration, however the sieve can only hold so much pressure and therefore uses this pressure to push the sugars down the line of sieve tubes. Through this same process, eventually the sugar ions reach a sink (area of low and in need of sugar), entering through the plasmodesmata are able to reduce some of the pressure on the system.
Is the movement of substances dissolved (such as sugars) in a fluid from areas of higher concentration to areas of lower concentration (passive transport).
A process by which molecules of H20 tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane (passive transport).