Plant structure Flashcards
What are the 4 features unique to plant cells?
Chloroplasts
Cell wall
Central vacuole
Plasmodesmata
What are the 6 plastids?
Chloroplast Chromoplast (coloured compounds) Amyloplast (starch) Elaioplast (fat) Proteinoplast (protein) Gerontoplast (senescence)
What is the purpose of the cell wall?
Maintains cell shape
Provides structural support that permits plant to withstand gravity
What does the cell wall consist of?
Cellulose microfibrils embedded in a matrix of polysaccharides & proteins
What do developing plant cells secrete?
A primary cell wall = thin, flexible cell wall which thickens & strengthens w/ development
What is between the primary cell walls of adjacent cells?
The middle lamella
- made of pectins
( = polysaccharides that hold cells together & strength them)
What do some cells secrete in addition to a primary cell wall?
A secondary cell wall
- between plasma membrane & primary cell wall for further strengthening
What are plasmodesmata?
Perforations of the cell wall that provide channels for inter-cellular communication
What are the 5 major plant cell types?
Parenchyma Collenchyma Sclerenchyma Water-conducting cells of xylem Sugar-conducting cells of phloem
What are the features of Parenchyma cells?
> thin & flexible primary cell walls > NO secondary cell walls > least specialised > retain ability to divide & differentiate > alive at maturity
What are the features of Collenchyma cells?
> thicker & more uneven cell walls than parenchyma
NO secondary cell walls
grouped in strands
alive at maturity
What are the features of Sclerenchyma cells?
> rigid due to this secondary walls strengthened by lignin
impermeable to water
dead at functional maturity
Why do Sclerenchyma cells die at maturity?
Cell walls are so thick that the cell is completely cut off from extracellular environment & dies
What are the 2 types of Sclerenchyma cells?
Sclereids:
= short & irregular in shape & have thick lignified secondary walls
Fibres:
= long, slender & arranged in threads
What are the functions of Sclerenchyma cells?
Support
Non-conducting
What are the functions of Collenchyma cells?
Support young parts of shoot
Provide flexible support w/out restricting growth
What are the functions of Parenchyma cells?
> perform most metabolic functions:
- photosynthetic leaf cells
- storage cells
What are the 2 types of water-conducting cells?
Tracheids
- found in xylem of ALL vascular plants
Vessel elements
- common to most angiosperms & a few gymnosperms
- align to form long micro pipes = vessels
What are the features of water conducting cells?
> Dead at maturity
- through programmed cell death
Type of conducting sclerenchyma
Lignin makes it impermeable to water
What is the main function of water-conducting cells?
Transport water & mineral ions
What is between vessel elements?
Perforation plates
What are pits and what is their function?
Thinner primary cell walls
Enable lateral transport of water between adjacent xylem cells
What are the 3 sugar-conducting cells of the phloem?
> Sieve-tube elements
Sieve plates
Companion cell
What are the features of sieve-tube elements?
Alive at maturity
Lack organelles
Chains of these make up phloem
What are sieve plates?
Porous end walls that allow fluid to flow between cells along sieve tube
What are companion cells?
Each sieve-tube element has 1
Their nucleus & ribosomes serve both themselves & the sieve-tube element
What is the function of the sugar-conducting cells?
Conduct soluble organic material made during photosynthesis to all parts of plant
What are the 3 tissues each plant organ has?
Dermal
Vascular
Ground
How does vascular tissue differ in roots and stems?
Central in roots
Peripheral in stems
How can dermal tissue differ?
Epidermis = single cell layer in leaves protected y waxy cuticle Periderm = thick layer in woody plants
What is the function of dermal tissue?
1st line of defence against pathogen attack or physical damage
What are the 2 types of ground tissue?
Pith = internal Cortex = external to vascular tissue
Where are the apical meristems on a plant?
Apical bud
Axillary bud
What can the axillary buds grow into?
Lateral vegetative or reproductive shoots
What are the functions of roots?
> Anchoring the plant
Absorbing minerals & water
Storage
What is the structure of roots?
>No chlorophyll, leaves or buds >Grow apically >Lateral roots grow from pericycle (stem branches arise superficially) >Taproot system w/ lateral roots or fibrous root system
What does the root cap do?
> Protects the apical meristem
>Produces a polysaccharide slime that lubricates root movement
What are the 3 zones of root growth?
Zone of cell division
Zone of elongation
Zone of differentiation
What is the zone of cell division made up of?
Root apical meristem & its derivatives
Stem cells
What happens in the zone of cell division?
New root cells are produced
- including cells of the root cap
What happens in the zone of elongation?
Most of the growth occurs as the cells elongate
–> pushes the root tip further into the soil
What happens in the zone of differentiation?
Cells at the older end start to mature & differentiate even while they’re still undergoing elongation
What’s the difference between monocots & dicots?
Mono = embryo w/ 1 cotyledon Di = embryo w/ 2 cotyledons
What is the steele?
The central vascular cylinder of xylem & phloem
How are the xylem vessels arranged in dicots?
What about monocots?
In a star
Ring of xylem & ring of phloem
Which cell type fill the cortex in roots?
Parenchyma cells
From what do lateral roots arise?
The pericycle that surrounds the vascular cylinder
What do storage roots store?
Photosynthate (mostly starch) for use in later growth
Modified root
How do pneumatophores in mangroves at like snorkels?
Get oxygen to roots growing in mud w/ little O2
Modified root
What are the functions of stems?
> Support structure for leaves & flowers
Contains vascular tissue for transport
Stores sugar & other nutrients in winter
What is the structure of stems?
Alternating system of nodes (points where leaves attach) & internodes (stem segments between nodes)
What are the 2 types of growth?
Primary & secondary
What is primary growth?
When apical meristems in the apical & axillary buds divide
- -> produces more cells
- -> plant elongates
What is secondary growth?
When lateral meristems located in the vascular & cork cambium produce layers of vascular tissues & tougher periderm
–> increases girth
How are vascular bundles arranged in dicot stems?
In a ring w/ xylem adjacent to pith & phloem adjacent to cortex
How are vascular bundles arranged in monocot stems?
Distributed throughout ground tissue rather than forming a ring
What is a bulb?
A short stem w/ fleshy leaves
Modified stem
What is a cladophyll?
A flattened photosynthetic branch assuming the form of an ordinary leaf
Modified stem
What is a pseudobulb?
A storage organ derived from the part of a stem between 2 leaf nodes
Modified stem
What is a corm?
Swollen underground plant stem that serves as a storage organ to survive adverse conditions
Modified stem
What is a rhizome?
A creeping stem that can produce roots
e.g. ginger
Modified stem
What is a tuber?
An underground stem that thickens to produce a storage organ
e.g. potato
Modified stem
What is the vascular cambium?
A continuous cylinder of meristematic cells located outside the pith & primary xylem, but inside the cortex & phloem
How does the vascular cambium cause stems to thicken?
Cell division in this area adds secondary xylem internally & secondary phloem externally
What happens as the vascular cambium’s diameter increases?
- The secondary phloem & other external tissues no longer divide
- -> so rupture - A secondary lateral meristem (cork cambium) develops from parenchyma cells in the cortex
- Cork cambium produces cork cells
- -> replace epidermis
What does bark consist of?
All tissues exterior to vascular cambium
When are the rings in tree trunks wider?
What can the widths enable?
In good summers w/ warm weather
The climate during a year can be estimated
