6: Primary Growth & Root Symbiosis Flashcards
What are the 3 distinct organelles of plant cells?
- Chloroplast: absorb sunlight and convert into sugar
- Cell wall: not living, provides structure and strength to cells
- Vacuole: contains 98% water and occupies a large portion of a cell
What happens to the cell membrane when the vacuole has positive pressure (is filled with water)?
The vacuole will push against the membrane which will push against the cell wall and the cell becomes TURGID or sturdy
Describe passive diffusion
the selectively permeable cell membrane will allow some dissolved substances to move through without energy required as they move with the concentration gradient
Describe active transport
energy (ATP) is required for substances to move through the membrane
What is the plasmodesmata?
Allows the flow of water and material between cells
What are the two kinds of cell walls? What are they each made up of?
- Primary Cell Wall: made up of CELLULOSE
2. Secondary Cell Wall: made up of SUBERIN & LIGNIN
What is cellulose?
the composition of the primary cell walls in plant cells that make the cells flexible
What is suberin?
a waterproof compound found in tissues of tree bark and roots
What is lignin?
a very tough compound that makes cells strong
What is lamella?
a glue that holds together the primary and secondary cell walls. Where pectin is found
What are the 3 cell types?
- Parenchyma
- Collenchyma
- Sclerenchyma
What are the 3 key points for parenchyma cells? Where are they found? What is their role?
Key points:
- thin walled cells with soft, flexible cell well - not strong
- Divide easily by mitosis
- Alive at maturity
Location:
in the epidermis and pith
Role:
fill space, store starch, contain chloroplasts
What are the 3 key points for collenchyma cells? Where are they found? What is their role?
Key points:
- Alive at maturity
- Contain thickened primary cell walls for strength
- Cells provide structure for leaf veins
Location:
- young dicot stems and midrib of leaves
Role:
- to provide strong, but flexible/elastic structure to midrib of leaves
What are the 3 key points for sclerenchyma cells? Where are they found? What is their role?
Key points:
- Dead at maturity
- Extra thick secondary cell walls containing lignin
- add strength and toughness
- fibre cells
Location:
- herbaceous and woody stems
Role:
provide strength and structure in woody stems
What are sclereids? Where are they found?
Key points:
- make the pit or endocarp of a stone fruit hard
- the gritty texture of pears
- boxy structure
- dead at maturity
- very thickened secondary cell walls filled with lignin
What are the roles of root systems?
- anchor plants to establish contact with the ground
- ABSORB WATER & NUTRIENTS
- Transport water & nutrients to the shoot
- store carbs in the form of starch
- synthesize hormones
- can be a site for secondary compound production to protect plant tissues from pests/disease
What are the 3 root system types?
- Tap root system
- Fibrous root system
- Storage & Tuberous roots
Describe tap root systems
the primary root starts as a tap root and lateral roots will increase surface area underground
Describe fibrous root systems
the primary root is taken over by lateral roots creating a fibrous system OR
adventitious roots form from the stems or leaves to create a fibrous system
Describe aerial roots
Roots that grow above ground
What are the 5 kinds of roots?
- Fibrous roots
- ex. grass - Adventitious roots
- corn - aerial roots
- tropical plants - Storage tap roots
- carrots - fleshy fibrous roots
- ex. spider plants - tuberous roots
- ex. dahlias
What is primary root growth?
the growth that occurs i the first year
Describe the root cap
- Parenchyma cells cover the apical meristem
- secretes mucigel
- cells live less than 1 week
- site for perception of gravity (downwards growth)
What are the 3 regions of a root tip?
- Region of cell division
- Region of elongation
- Region of maturation
What occurs in the region of cell division in the root tip?
- Mitosis takes place every 12-35 hours
- new cells are shaped like cubes and closely packed
- the new cells subdivide into 3 meristematic groups
What occurs in the region of elongation in the root tip?
- located within 1cm of the tip of the root
1. cells extend several times in length
2. smaller vacuoles within cells merge into one large vacuole (to take up to 90% of space)
What occurs in the region of maturation in the root tip?
- elongation ceases
2. cells mature to their final form
Describe root hairs
tubular extensions of specialized epidermal cells that increase the absorptive surface area of the root system
they only live a few days and are constantly renewed by the growing root tip
What are the 8 tissues with a dicot root?
- Epidermis
- Cortex & Endodermis
- Pericycle
- Phloem
- Xylem
- Cambium
Describe the cortex tissue of a dicot root?
Composed of primarily parenchyma cells that store starch.
The inner layer of the cortex is called the endodermis
Describe the epidermis
The outer layer of cells that cover the outside of the root
Describe the endodermis
The inner layer of the cortex that contains primary xylem and phloem tissue. It also has the Casparian Strip which contains suberin to make portions of the endodermis waterproof. Some of the endodermis is made up of PASSAGE CELLS which do not contain suberin and allow substances to flow through.
Describe Casparian strip
Found in the endodermis layer
A waxy (suberin) deposit in the cell walls of the endodermal cells force water to move through the interior of the cell to filter out unwanted chemicals or spores
Describe pericycle
found in dicot roots
Composed of parenchyma cells which can divide by mitosis if required
the pericycle cells at the end of a xylem “arm” divide by mitosis to produce a root initial that will develop into a lateral root
Describe lateral root development
found in dicot roots
the lateral root will develop its own apical meristem and push outward as more cells are added
eventually it will break through the endodermis, cortex, and epidermis as the root extends
Describe xylem tissue
Big pipes (vessel and tracheid cells) that carry water and nutrients up to the shoot
Describe phloem tissue
Living cells that carry dissolved sugars down the shoots to where they are needed
Describe pro-cambium
found in dicot roots
forms between the xylem and phloem tissue.
the cells divide and produce secondary growth (growth ring)
What tissues do monocot roots have?
- Epidermis
- Endodermis & Casparian Strip & Passage Cells
3: Pericycle - Cortex
- Pith
- Xylem
- Phloem
Describe root nodules. Give an example
Occur when bacteria invade cortical (cortex) cells of certain plants to make a home
ex. It is usually a symbiotic relationship like the one between nitrogen-fixing bacteria and roots
Describe ECTO-Mycorrhizae
Fungi connect to the root tip to find a “home” to IMPROVE the health of the root and share nutrients and sometimes water with the root as part of the exchange for a home
Describe the apical bud and what is its function?
aka the terminal bud
Where new vertical growth occurs
- all new cells are produced i the apical meristem
- cells will expand in size and mature into any type of cell
- they are grouped, depending on location, into meristems which produce more cells that mature into tissues with specific functions
T or F: Monocot stems & roots will develop a pro-cambium between the xylem and phloem
FALSE. A pro-cambium will not develop
