lecture 1 - plant cells and tissue systems

what are the main organ systems in vascular plants?

• root system

• shoot system

name the primary plant organs.

• roots

• stems

• leaves

list the hierarchical organization levels of vascular plants from largest to smallest

1. systems (root and shoot)

2. organs

3. tissues

4. specialized cells

true or false: all plant structures can be understood by studying just one level of organization

false - plant structures must be studied at multiple levels (systems, organs, tissues, and cells) to understand their complete function and development

explain how the hierarchical organization of vascular plants contributes to their diversity and function

• organization at multiple levels (systems, organs, tissues, cells)

• specialization at each level

• variation in anatomy and chemical composition

what are the primary tissue types in vascular plants?

• meristematic tissue

• ground tissue

• vascular tissue

• dermal tissue

what are the two main categories of plant tissue?

1. permanent tissues

   1. simple tissues

      1. collenchyma

      2. sclerenchyma

      3. parenchyma

   2. complex tissues

      1. vascular tissues: xylem and phloem

      2. epidermis

2. meristemic tissues

   1. apical meristems

   2. lateral meristems

   3. adventitious (?)

   4. intercalary meristems

list the three types of simple tissues that function as ground tissues

• parenchyma

• collenchyma

• sclerenchyma

what are the main functions of ground tissues?

• photosynthesis

• support

• storage

identify the key characteristics of parenchyma cells

• thin primary cell walls (usually lignified)

• contain nucleus, cytoplasm, and vacuoles

• involved in photosynthesis, storage, and local transport

identify the key characteristics of collenchyma cells

• alive at maturity

• thickened cell wall (usually unlignified)

• primary wall stains dark pink-purple with toludine blue )

• provides support and protection

identify the key characteristics of sclerenchyma cells

• contain fibers and sclerieds

• normally dead at maturity

• thickened primary and secondary cell walls (usually lignified)

• cell wall stains blue/blue-green with toludine blue O

• provides support and protection from microorganisms

compare the three different types of simple tissues under a microscope

what is xylem?

• the first of three types of complex tissues

• transports water, minerals, and signaling molecules

• cell types: tracheids, vessels, fibers, and parenchyma

• heavily lignified secondary cell walls, often dead at maturity

what are the different types of cells found in xylem?

• tracheids and vessels

• xylem parenchyma

• tyloses

• fibers

what are the characteristics of tracheids and vessels in their initial and mature states, and how do secondary cell wall thickenings contribute to their function?

• initial state: un-lignified and alive during development

• mature state: highly lignified (rigid and strong) and typically dead, allowing efficient water transport

• secondary cell wall thickenings: vary to reflect the maturity and functional needs of the xylem

  • provide structural support and prevent collapse under the pressure of water transport

what is the function of tracheids and vessels?

essential for water conduction, divided into protoxylem (early xylem) and metaxylem (mature xylem)

what is the function of xylem parenchyma?

storage and lateral transport within the xylem

what is the function of tyloses?

outgrowths of parenchyma cells, involved in blocking damaged vessels during injury or infection

what is the function of fibers?

provide mechanical support

what is phloem?

• the second of three types of complex tissues

  • vascular tissue developed from procambium

• transports sugars (i.e. fixed carbon) and signaling molecules (metabolites)

what are the main cell types found in the phloem of angiosperms?

• sieve elements (or sieve tube members): specialized for nutrient transport, lack nuclei at maturity, rely on companion cells for support

• parenchyma cells: include companion cells, which provide metabolic support to sieve elements

• fiber cells: provide structural support

how do the phloem cell types in gymnosperms differ from those in angiosperms?

gymnosperms lack true sieve tube members and companion cells. instead, they have:

• sieve cells: more primitive than sieve tube members

• albuminous cells: function similarly to companion cells in angiosperms

what is the epidermis?

• the third of three types of complex tissues

• outermost layer; functions include protection, gas exchange regulation, transpiration, secretion and structural roles

• specialized cells: trichomes, guard cells, root hairs

what are trichomes?

specialized epidermal cells that extend from the plant surface, forming hair-like structures for protection, secretion, or other specialized functions

what are guard cells?

specialized epidermal cells that regulate gas exchange and transpiration by controlling the opening and closing of stomata

what are root hairs?

specialized extensions of root epidermal cells (trichoblasts) that increase surface area for water and nutrient absorption

explain the concept of modular development

plants grow through repetitive addition of similar units, aiding repair and reproduction

how can plant growth be classified?

• indeterminate

• determinate

what is indeterminate growth in plants and where is it found?

• found in most stems and roots

• produces parts that can grow for variable periods of time

• size and shape vary depending on local environment

• growth pattern is flexible and responsive to conditions

what is determinate growth in plants and where is it found?

• found in flowers and most dicot leaves

• produces parts with predictable size and form

• results in fixed, predetermined structures

• growth pattern is more strictly controlled

what are the two main processes involved in plant growth and development?

• cell division

• cell expansion/elongation (responsible for most size increase)

how do plant cells differ from animal cells in terms of mobility?

• plant cells are largely immobile

• their position is fixed due to cell walls

• this immobility makes positional signals crucial for development

what role do positional signals play in plant cell development?

• organize cells spatially

• determine cell fate

• guide tissue development

• crucial for proper organ formation

increase in plant size is often more dependent on _____ than on cell division

elongation/expansion

compare and contrast simple and complex permanent tissues in plants

simple tissues

• composed of similar cell types

• primarily function in ground tissue roles (photosynthesis, support, storage)

• include collenchyma, sclerenchyma, and parenchyma

complex tissues:

• composed of multiple cell types working together

• specialized for specific functions like transport (xylem and phloem) or protection (epidermis)

• more structurally and functionally sophisticated than simple tissues

what is the key characteristics of meristematic tissues?

they are undifferentiated (i.e. they continue to divide and contribute to plant growth)

what are apical meristems?

• regions of cell division at the tips of roots and shoots

• consist of SAM (shoot apical meristem) and RAM (root apical meristem)

• specified early in embryo development

• responsible for elaborating adult plant structure

• involved in reproductive transition

what are lateral meristems?

• responsible for secondary growth

• increase plant girth

• include vascular cambium and cork cambium

• form axillary and lateral root meristems

what are adventitious meristems?

• arise ectopically from differentiated tissues

• typically form shoot meristems

• provide alternative growth points

• enable plant regeneration

what are intercalary meristems?

• found in plants without secondary meristems (monocots)

• enable regrowth after cutting

• may be involved in indeterminate leaf growth

• important for grass regeneration

true or false: monocots typically exhibit secondary growth.

false

explain how different types of meristems contribute to plant growth and development

different meristems work together to enable plant growth:

• primary meristems (SAM and RAM) establish basic plant architecture

• lateral meristems enable secondary growth and increase in girth

• adventitious meristems allow for recovery and alternative growth

• intercalary meristems enable continued growth in monocots

this diverse set of meristems allows plants to:

• maintain continuous growth throughout life

• repair damage

• adapt to environmental conditions

• develop complex structures from simple beginnings

what is the primary function of the vacuole in plant cells?

• regulates turgor pressure

• stores resources and isolates waste

• facilitates cell elongation and growth

what is the tonoplast?

a selectively permeable membrane that surrounds the vacuole in plant cells. it controls what enters and exits the vacuole, helping regulate:

• turgor pressure

• cell pH

• storage of nutrients and waste products

• ion concentrations

what are transvacuolar cytoplasmic strands and their key features?

• strands that cross through plant cell vacuoles

• supported by internal actin filaments

• work with microtubules during cell division

• serve as distribution routes for organelles and metabolites

• contain moving golgi and ER for secretion systems

• dynamic structures that can appear and disappear

what structures move through cytoplasmic strands?

• organelles

• metabolites

• golgi apparatus

• endoplasmic reticulum (ER)

• secretory vesicles

what is the role of cytoplasmic strands in cell division?

• work together with microtubules

• help organize cellular components

• assist in formation of phragmosome

• aid in preprophase band formation

• facilitate organelle distribution during division

name the specialized plastids and their functions.

• proplastids: progenitors of other plastids (colourless w/o distinctive morphology)

• chloroplasts: photosynthesis

• chromoplasts: pigment storage

• leucoplasts: synthesis of starch, lipids, and proteins

• amyloplasts: starch storage

what are the three main layers of the plant cell wall? (note: in order of formation)

1. middle lamella: forms first between adjacent cells

2. primary cell wall: thin and flexible, allows for expansion

3. secondary cell wall: forms inside primary wall after full expansion

what is the middle lamella?

• first layer to form between adjacent cells

• connects neighboring cells together

• contains mostly pectin

• important for cell adhesion

what are the characteristics of the primary cell wall?

• relatively thin and flexible

• allows for cell expansion

• contains cellulose microfibrils

• includes hemicellulose

• contains pectin and proteins

what is the secondary cell wall?

• forms inside the primary wall

• develops only after cell has finished expanding

• typically thicker than primary wall

• often contains additional layers

• provides additional strength and support

what are the main components visible in plant cell wall structure?

• cellulose: strong fibers that provide structural support and tensile strength

• hemicellulose: cross-links cellulose fibers and adds flexibility

• pectin: enables cell adhesion and wall flexibility

• proteins: provide enzymatic activity and structural support

• plasma membrane: selective barrier between cell wall and cytoplasm

why are plasmodesmata essential for plants?

• mosaic of symplastically (via cytoplasm through plasmodesmata) connected cells

• enable cell-to-cell communication

• allows regulated movement of molecules between cells

• creates continuity in plant tissues

what is the cytoplasmic sleeve and its function?

• channel within plasmodesmata

• allows regulated movement of larger molecules

• provides pathway for symplastic connection

• controls molecular transport between cells

what types of molecules can pass through plasmodesmata?

• smaller molecules (ions, sugars, amino acids) pass freely

• some small proteins like GFP can pass through

• larger proteins (>10kDa) are regulated or prevented

• nucleic acids have limited movement

what are the two types of plasmodesmata and how do they form?

• primary plasmodesmata: formed during cell division when ER gets trapped across middle lamella

• secondary plasmodesmata: form between mature cells after cell wall formation

how do plasmodesmata compare to animal cell gap junctions?

• have limited functional similarity

• both transport small molecules

• plasmodesmata are more complex structurally

• plasmodesmata have more diverse transport capabilities

• gap junctions are simpler channels

explain how plasmodesmata contribute to plant cell communication

establish a symplastic continuum throughout plant tissues while enabling selective transport of different sized molecules between cells

• structures are crucial for regulating cell-to-cell communication and maintaining proper tissue organization

• enable plants to coordinate their responses to various signals

their formation both during cell division and between mature cells ensures continuous cellular connectivity throughout plant development