Plant cell walls Flashcards
What are the three layers in plant cell wall
Hemicellulose
Cellulose
Pectin/middle lamella
How does a cell wall expand
Cell wall enzymes break connections in wall
New material is deposited
Connections remade
Why is the cell wall of fruits and vegetables softer than other plant cell walls
Reduction of pectin in cell wall due to enzymes causes softening
When is the secondary cell wall made
When expanding stops
Where is the secondary cell wall located
Between the primary and the plasma
What are the functions of the secondary cell wall
Support
Strengthen
Protect
What macromolecules are involved in the secondary thickening of the cell wall
Lignin
Suberin
Cutin
Where is there specific secondary thickening and why is it needed
Endodermis layer in anther
Provide strength for anther to open
When enough pressure in anther bursts open and releases pollen
What occurs in the abscission process
Plant removes organs (leaves and fruit) by digesting middle lamella
Protective layer forms around abscission e.g. suberin, lignin, waterproof
What is the major different between monocots and dicots
Monocots have one cotyledon
Dicots have two cotyledons
What is the difference in leave venation between monocots and dicots
M - veins usually parallel
D - veins usually netlike
What is the difference in stems between monocots and dicots
M - vascular bundles usually complex arrangement
D - vascular bundles usually arranged in ring
What is the difference in roots between monocots and dicots
M - fibrous root system
D - Taproot usually present
What is the difference in flowers between monocots and dicots
M - flowers usually in multiples of three
D - flowers usually in multiples of four or five
What is the difference in epidermis in monocots and dicots
Same
What is the difference in mesophyll layers in monocots and dicots
M - no difference between upper and lower
D - have palisade cells, contain many chloroplasts, bottom have spongy cells less chloroplasts
What is the structure of a dicotyledenous root
Outside layer - epidermis
Multiple layers thick, mid region - cortical cells/cortex
Inside of mid region (thin band) - endodermis
Inside of endodermis - pericycle
Centre - vascular cylinder
What is the structure of a monocotyledonous root
Outside layer - epidermis
Mid region - cortex
Inside of mid region (thin band) - endodermis
Same area in mid - casparian strip
Inside of endodermis - pericycle
Centre - vascular cylinder XYLEM ARRANGED IN BUNDLES IN RING SHAPE
What is the stele made up of
Endodermis
Pericycle
Vascular cylinder
What is the purpose of a casparian strip
Provides a protective layer - thick so is water impermeable
Roots can control what is taken into plant
What are the two routes that nutrients can be taken up from the roots to the casparian strip
Apoplastic pathway
Symplastic pathway
What is the apoplastic pathway
Nutrients travel between cells in the cytoplasm
What is the symplastic pathway
Nutrients enter cells and leave them (travels through cells)
Function of the root cap
Protect
Lubricate so can go through soil and guide root in response to gravity
Know whether going up or down
What are meristem cells
Makes up root
Can be made into anything - waiting to be told
Where does the root hair cell originate from
Epidermis
Where do lateral roots form from
Develop in already formed primary roots
Originate from pericycle cells
What happens when lateral roots begin to form
Outer tissue disformation and cell separation
Signals outside cells to release cell wall modifying enzymes
Allow cells around to stretch move and disengage with each other - can grow through
Lateral root contains all same material as primary
Why must the secondary wall form when lateral root has formed
Prevent pathogens getting in
What do phosphorus deficient plants have to try gain more phosphorus
Increased lateral root and root hair production to try increase phosphorus uptake
What is the xylem and function
Xylem conducts water passively
Elongated cells with secondary cell walls that lack protoplasts at maturity
What is the phloem and function
Actively transport sugars and amino acids
Translocation in both directions
How is the phloem cell wall specialised
Is perforated using sieve plates to allow compounds to travel through
What does the phloem cell wall maintain even when they mature and lose their organelles
ER and mitochondria for energy to move all round
What is special about a companion cell
Extra plasmodesmata to phloem sieve tube
Extra ribosomes and mitochondria
What is the companion cell function
Support sieve tube cell
What is the function of the sclerenchyma, and what is it
Provide structure and support to plant tissue
Their cell walls are thick lignified secondary walls made of cellulose and hemicellulose - often die when mature
What is the collenchyma and its function
Elongated cells with thick cell walls - provide structure and support
Cellulose and pectin irregularly thickened at corners
Where are the collenchyma found
Under epidermis in new growth areas
What is a trichome
Small hair growing from epidermis of plant, algae, lichen
Can be uni/multi-cellular
Can be (un)branched
What are xerophytes
Adapted to prevent water loss through transpiration
Keeps air at higher humidity around stomata
What are hydrophytes
Aerenchyma forms air channels - gas exchange
Important for aquatic plants
Stomata only on top of leaf
Epidermal layer very little strengthening in stems = not rigid
What is the function of a sclereid
Keeps plant together, gives structure and strength without preventing it moving in water
