Plant cell walls Flashcards by Yasmin Yau

What are the three layers in plant cell wall

Hemicellulose
Cellulose
Pectin/middle lamella

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How does a cell wall expand

Cell wall enzymes break connections in wall
New material is deposited
Connections remade

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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

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When is the secondary cell wall made

When expanding stops

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Where is the secondary cell wall located

Between the primary and the plasma

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What are the functions of the secondary cell wall

Support
Strengthen
Protect

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What macromolecules are involved in the secondary thickening of the cell wall

Lignin
Suberin
Cutin

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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

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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

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What is the major different between monocots and dicots

Monocots have one cotyledon

Dicots have two cotyledons

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What is the difference in leave venation between monocots and dicots

M - veins usually parallel

D - veins usually netlike

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What is the difference in stems between monocots and dicots

M - vascular bundles usually complex arrangement

D - vascular bundles usually arranged in ring

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What is the difference in roots between monocots and dicots

M - fibrous root system

D - Taproot usually present

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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

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What is the difference in epidermis in monocots and dicots

Same

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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

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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

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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