7: Secondary Growth & Cell Types Flashcards
What are the two kinds of tissues that make up the vascular tissues?
- Xylem tissue
2. Phloem tissue
What is the function of xylem tissue?
To carry water and nutrients from the roots up through the stems and to the leaves
What is the function of phloem tissue?
To carry sugars and other substances up and down the stems and roots of plants
What are the four types of cells in xylem tissue?
- Vessel elements
- Tracheids
- Sclerenchyma fibers
- Parenchyma cells
Describe tracheids and which vascular tissue do they belong to?
These are found in XYLEM tissue.
- long, narrow tubes with pores along the outside
- dead and hollow at maturity - - have thickened and reinforced cell walls
Describe vessel elements and which vascular tissue do they belong to?
XYLEM tissue
- wide tubes with perforations at the vertical ends to stack like pipes
- dead and hollow at maturity
- cell walls thick and reinforced
What is the purpose of some vascular cells being dead at maturity?
To be hollow so the flow of substances is more efficient
What are the 4 types of cells in phloem tissue?
- Sieve tube elements
- Companion cells
- Sclerenchyma fibers
- Parenchyma cells
Describe sieve tube elements. Which vascular tissue do they belong to?
PHLOEM
- thin walled, not strong tubes
- alive at maturity, but does not contain any organelles
- fitted together end to end for continuous flow
Describe companion cells. Which vascular tissue do they belong to?
PHLOEM
- 1 companion cell is attached to one STE to provide it the necessary nutrients etc that it needs to be alive at maturity
What is the purpose of the sclerenchyma cells in the phloem tissues?
Functions as a shield on the outside of the phloem tissues to protect
Describe apical meristems
areas of intense cell division (mitosis) that add cells that allow the shoot or root tip to lengthen
What are the 6 structures of a woody dicot stem before secondary growth?
From outside to inside:
- Epidermis
- Cortex
- primary phloem
- vascular cambium
- primary xylem
- pith
What is the function of the procambium?
It produces primary xylem and phloem
What occurs to the procambium, primary xylem and phloem of a woody dicot stem during the process of primary –> secondary growth?
the vascular cambium will develop in between the primary xylem and phloem to add secondary xylem and phloem to the vascular bundles
What occurs during the transition of primary to secondary growth in a woody dicot stem?
- the vascular cambium begins to divide within the vascular bundle
- Parenchyma cells in between the vascular bundles start to divide
- the vascular cambium becomes one continuous ring that will produce secondary xylem to the inside and secondary phloem to the outside
T or F: in a woody dicot stem, the vascular cambium develops in the middle of the vascular bundle between the xylem and phloem tissues?
TRUE
What happens as the vascular cambium produces chains of new cells?
As the VC produces secondary tissues, it is moving outwards and the circumference of the stem increases
What strengthens and thickens secondary xylem tissue cells?
Vessel elements and tracheids have thickened and strengthened cell walls because they contain LIGNIN
What is the purpose of sclerenchyma fibres in xylem tissues?
In hardwood stems, they strengthen the wood as they have cell walls that contain lignin
What is the purpose of sclerenchyma fibres in phloem tissues?
Masses of sclerenchyma fibres protect the fragile phloem cells
When does primary growth occur?
In the spring, when the bud expands and the stem becomes longer
When does secondary growth occur?
Each year following the primary growth. The stem becomes thicker as new layers of cells are added through the growing season
T or F: Primary growth refers to the vertical extension of shoots and secondary growth refers to the lateral expansion of shoots?
TRUE
T or F: Secondary growth is responsible for the annual rings of wood?
TRUE
Which tissues are included in bark?
All the tissues outside of the cambium:
- primary phloem (produced by vascular cambium)
- secondary phloem
- cortex tissue (primary)
periderm (aka outer bark): - Phelloderm
- cork cambium
- cork
Describe cork cambium
- Part of the periderm, or outer bark, of a woody dicot stem.
- Cortex cells divide into a ring of cells to produce the cork cambium.
- Cork cambium produces cork tissue to create the bark of a woody stem
What are phloem and xylem rays?
Ribbons of parenchyma cells that transport the respective substances LATERALLY
What does the phelloderm layer of the periderm of bark tissue consist of? Where is the phelloderm located?
Living cork parenchyma cells
Located beneath the cork cambium
Describe spring wood
- vascular cambium becomes active in the spring
- produces large vessel elements of secondary xylem
- as season progresses, vascular cambium will produce vessel elements with progressively smaller diameters in each succession, or there may be fewer VEs produced until tracheids dominate
Describe summer wood
- the xylem that is produced after the spring wood and contains a fewer number of vessel elements and larger numbers of tracheids
What is the product of the alteration of spring and summer wood growth?
A series of rings of alternating dark and light cells
What is an annual ring?
All of the layers of xylem tissues produced in one year’s growth.
T or F: Conifer wood consists mainly of tracheids, yet there are still visible annual rings
TRUE because the vessels and sclerenchyma fibres are mostly absent and the tracheids first produced in the spring are larger and lighter than the ones produced later in the season.
T or F: the vascular cambium produces more secondary phloem tissue than it does xylem. Why/why not?
FALSE. it produces more secondary xylem tissue because xylem tissues are more rigid and strong so they can withhold the weight of a tree trunk.
What can the annual rings of a tree tell us about the tree? Explain
- the age of a tree because generally they only produce one ring per year
- About the climate and the conditions that occurred throughout the tree’s life
- ex. if there was significant rainfall one year, the annual ring for that year will be wider due to more growth
- ex. a burn scar can appear next to a ring if there was a fire one year that didn’t kill the tree
Where does the most recent season’s growth occur?
Next to the vascular cambium
Where would you start counting back the rings to determine an age of a tree?
Count the rings back from the vascular cambium
What device can be used to determine the age of a tree without cutting it down?
An increment borer - removes a plug of wood
Describe heartwood
the older, darker wood at the centre of a stem with clogged xylem tissues that can no longer conduct water or nutrients
- functions in providing strength and support
- darker because the resins, gums, tannins, and pigments clog up the xylem tissues
Describe sapwood
the lighter, still-functioning xylem closest to the vascular cambium
T or F: A tree can continue living after the heartwood has rotted away and the interior is hollow. Why/why not?
TRUE because the heartwood does not conduct water or nutrients and only provides support
Describe softwood and give an example
Trees with xylem that consist mainly of tracheids and lacks sclerenchyma fibres and vessel elements. With no fibres, the wood tends to be softer
ex. Pine and other cone-bearing trees
Describe hardwood and given an example
Woody dicot trees that have xylem with sclerenchyma fibres are much harder
ex. Maple
What are the main differences between softwood and hardwood
SIMILARITIES:
- both have tracheids
- both have parenchyma rays
DIFFERENCES:
- softwood lacks vessels and sclerenchyma fibres, but has resin canals
- hardwood lacks resin canals, but has sclerenchyma fibres and vessels
What are the steps in transition of primary to secondary growth in a woody dicot ROOT?
- the centre of the root is the primary xylem, surrounded by the primary phloem.
- the procambium will form between the primary tissues and produce the vascular cambium to produce secondary tissues
- the pericycle around the vascular tissues will produce the cork cambium
- the cortex and epidermis (outside the cork cambium) will shed off
- a new layer of bark will form
Where does the cork cambium form in a woody root vs. a woody stem?
WOODY ROOT:
- in the pericycle
WOODY STEM:
- in the cortex
What is the order of the structures of a woody dicot root after secondary growth (outside - in)?
- cork
- cork cambium
- phelloderm (living cork)
- primary phloem
- secondary phloem
- vascular cambium
- secondary xylem
- primary xylem
T or F: the centre of a woody dicot root will ALWAYS be primary xylem?
TRUE
