Plant Cells and Tissues

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Chapter 4

• Plant Cells and Tissues

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Plant Cells

• Cells and products of cells combine into tissue
  systems, organs and organism which is a plant
• Organelles are internal compartments of cells
  with specific function
• division of labor

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Important Terms

• Cytoplasm all material inside the cell membrane
  but outside of the nucleus
• Cytosol semi-fluid matrix that baths the
  organelles, includes ctyoskeleton and ribosomes
• Protoplast cell membrane inward (plant cell)
• Cell wall cellulose and other polymers,
  considered extracellular, outside the protoplast

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Plant Cell
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Cell or Plasma Membrane

• Surrounds the cell and regulates movement into
  and out of the cell
• Receives chemical and environmental signals from
  outside to change cellular activities such as
  hormones
• Take raw materials and help to assemble into cells

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Other Membranes

• Also surround and form the exterior of organelles
• leads to organelles having different enzymes and
  chemicals inside to do a specific function
• compartmentalization causes an increase in
  efficiency and prevents interference from other
  enzymes
• allows different reactions to take place
  simultaneously even if they are opposites

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Nucleus

• Contained in a double membrane called the nuclear
  envelop
• Contains DNA that controls cell activities
• chromatin DNA protein
• DNA template for mRNA and then leaves the nucleus
  to direct protein synthesis in cytoplasm
• Nuclear pores in the envelop allow for
  communication between nucleoplasm and cytoplasm
• Nucleolus center where ribosomal genes are
  transcribed and subunits built

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Internal Membranes

• Continuum of organelles either directly connected
  or indirectly linked by the movement of transfer
  or transport vesicles
• Membrane system cell membrane, ER, dictyosome
  (Golgi apparatus), nucleus and vacuoles
• Biochemical processes occur in or on membranes

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Endoplasmic Reticulum

• Much of the cells membrane surface area
• flattened tubes and sacs that are continuous with
  the plasma membrane and outer membrane of the
  nucleus
• Contains many enzymes (concentrated) and the site
  for polymer biosynthesis
• 2 types
• rough ER processes proteins made by ribosomes
  on the surface, adds sugars and disulfide bonds,
  proteins destined for surface of the plasma
  membrane or outside the cell
• smooth ER no ribosomes, makes phospholipids and
  other lipids for the cells use and new membranes
• Small membrane bound vesicles to fuse with other
  structures

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Dictyosomes or Golgi Apparatus

• Receive proteins, lipids and other material from
  ER by vesicles
• Does chemical modification of these molecules,
  sorts and exports biomolecules by vesicles and
  move to plasma membrane
• Can secrete other substances by way of the Golgi
  to the surface such as cellulose

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Plasmodesmata

• Membrane lined channels thru the cell walls of
  adjacent cells, also contain ER
• Form a continuous internal membrane between cells
• Can move small substances from cell to cell

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Vacuoles

• Regulate H2O content and contains numerous
  enzymes or pigments
• digest storage molecules to recycle
• red/blue anthocyanins make flowers, fruit and
  other parts colorful
• may contain toxic compounds
• Made from fusion of ER and dictyosome - 95 of
  cell
• Membrane is called the tonoplast
• cell enlarges because of H2O absorption

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Turgor Pressure

• H2O in the vacuole causes pressure on the cell
  wall and creates outward pressure
• accounts for the rigidness of the cells
• Plants low on H2O are limp and wilted
• see in carrots older carrots are limp and
  rubbery but if you trim off the end and place
  in water, it will again become crisp
• snap when you bite a carrot is the release in the
  turgor pressure

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Ribosomes

• Equal parts protein and RNA (rRNA)
• May be part of ER or free in cytosol
• Cluster around mRNA and directs protein synthesis
• No membrane on this structure
• All organisms have ribosomes, even mitochondria
  and chloroplasts
• important in evolution

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Mitochondria and Chloroplasts

• Both convert energy needed for cellular
  metabolism
• Both contain own DNA, RNA and ribosomes, can grow
  and divide in a cell on their own
• Chloroplast photosynthesis
• CO2 H2O light energy ? sugars O2
• green pigment chlorophyll traps light energy to
  fix CO2 into sugars, then sucrose and starch,
  eventually amino acids and fatty acids
• Mitochondria cellular respiration
• convert sugar into ATP eneergy
• sugar O2 ? CO2 H2O ATP

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Endosymbiont Hypothesis

• Believe mitochondria and chloroplasts were
  independent organisms, probably bacteria, that
  set up a symbiotic relationship with a eukaryotic
  cell
• Reasons circular DNA, smaller ribosomes, gene
  structure different than nuclear genes, proteins
  synthesis in them is halted by antibiotics

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Cytoskeleton

• Forms a network within the cell
• 3 small protein filaments in order of size
• actin or microfilament
• intermediate filament
• microtubule
• Have many roles in the cell
• organize organelles
• movement of chromosomes during cell division
• form channels to move large molecule
• No membrane so some do not consider an organelle

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Cell Wall

• Surround and shape cells
• Most easily observed part of cell
• Sometimes there is no protoplast cork cells
• SEM of water-conducting vessel element (no
  protoplast)

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Primary Cell Wall

• See in new plant growth
• Usually very thin and flexible
• lt25 cellulose with rest being hemicellulose,
  pectins and glycoproteins, occasional lignin
• Changes shape, divides or differentiate into
  other cells, when reach maturity it stops growing
  and cell develops a secondary cell wall inside
  the primary cell wall

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Secondary Cell Wall

• Much more rigid strong support structure
• Cellulose is one of the main components with as
  much as 25 lignin which hardens and resists
  decay
• Cells dont expand and grow and many will die
  when reach functional maturity

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Other Extracellular Molecules

• Some cells have a suberin (wax) coat to protect
  from H2O loss
• Adjacent cells are help together with pectin
  (outside the 1 cell wall) and is called the
  middle lamella
• apples have a lot of pectin and it is extracted
  and used to thicken jams and jellies

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Membranes

• Active and changeable participants in cell
  metabolism are directly or indirectly associated
  with membranes
• Composed mainly of proteins and phopsholipids in
  the Fluid Mosaic Model
• double layer of phospholipids that move around
  and spin
• proteins that pass thru or are associated with
  the membrane serve many functions
• contains other lipids that influence fluidity

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Membrane Proteins

• Control most membrane function
• 50 or more different proteins in plasma membrane
  and as many in other organelle membranes
• on the surface or penetrating thru the membrane
• Activities
• unrestricted movement of water, certain small
  dissolved molecules in and out of the cell
  maintain turgor pressure and important in
  metabolism
• block/control passage of some molecules
  selectively permeable
• usually ions are moved by proteins that require
  ATP energy
• enzymes that work in a multi-step process are
  localized together
• cell signaling take messages from outside cell
  to change activity in the cell

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Phospholipids

• Forms the thin bilayer of membranes
• 2 sheets of phospholipids sandwiched together
  making a permeability barrier
• Fluidity is the movement of the molecules in the
  membrane both phospholipids and proteins
• Carbohydrates may be added to the lipids and
  proteins on the OUTER surface to facilitate in
  cell signaling
• glycolipid and glycoprotein, respectively

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Movement of Molecules

• Diffusion, convection and bulk flow account for
  most of the movement
• All molecules have random thermal motion
• allows for dissolved molecules to diffuse from
  high to low concentration
• Diffusion net movement of molecules from an
  area of greater concentration to an area of lower
  concentration

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Rates of Diffusion

• Dependent on
• size of the molecules larger are slower
• temperature of solution higher faster
• solubility of molecules in solvent no
  dissolution means no movement
• Overall diffusion is really slow

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Convection

• Involves pressure or temperature
• Put a drop of dye in water and eventually the dye
  would