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Key Card for Plant Cell©2002 The Science Source®

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B105

1. Middle Lamella orIntercellular Layer

2. Primary Cell Wall3. Intercellular Space4. Secondary Cell Wall5. Plasma Membrane6. Golgi Body with

Vesicles7. Cytoplasm with

Organelles

8. Rough EndoplasmicReticulum

9. Nucleus10. Nucleolus11. Nuclear Pores12. Chromosome13. Outer Membrane of

Nuclear Envelope14. Inner Membrane of

Nuclear Envelope15. Chloroplast

16. Mitochondrion17. Granum18. Plasmodesmata19. Chloroplast Stroma20. Vacuole21. Lysosome or

Peroxisome22. Vacuolar Membrane23. Smooth Endoplasmic

Reticulum24. Ribosomes

ORGANELLE DESCRIPTIONS

CELL WALL

Mechanically strong extracellular material depositedoutside the plasma membrane of plant cells. Primarycell walls are elastic and found on cells that can growand elongate. Secondary cell walls are more rigid and,when present, are deposited inside the primary cellwalL Cells with secondary walls are common in wood.

A short cylindrical array of nine triplet microtubules.Found in animal cells and cells of most eukaryoticorganisms that produce flagellate cells.

Region close to the nucleus in eukaryotic cells. It is anarea Involved in the development of microtubules(often referred to as a microtubule organizing center)that aa*e necessary for cell movements, e.g. the mitoticspindles. Each pole of the spindle of a dividing nucleuswould have a centrosorne. In animal cells and mostplants and fungi with motile cells, the centrosomecontains a pair of centrioles.

CHLOROPLASTS

Orgaoelles present in photosynthesizing, usually green,eukaryotic plant cells. They share several propertieswith mitochondria, i.e., they are bounded by twomembranes, have circular DNA and bacterial sizeribosQ>mes. The interior of a chloroplast has anelaborate system of membranes that contain thephotosynthetic apparatus. These membranes are calledthylakoids and when they become stacked, they arereferred to as grana.

The interior space in a chloroplast. It contains enzymesthat are involved in the incorporation of C02 intosugars.

CHROMATIN

Complex of the DNA and proteins in the nucleus of aeukaryotic cell.

CHROMOPLAST

A membrane-bounded vacuole in some plant cells.Chroinoplasts contain pigments and the latter are oftenorange-yellow carotenoids

CYTOPLASM

AH the material and organelles inside the plasmamembrane and outside of the nucleus.

CYTOSOL

Everything in the cytoplasm other than the membranebounded organelles.

ENDOPLASMIC RETICULUM

The endoplasmic reticulum (ER) consists of flattenedsheets, sacs and tubes that extend through thecytoplasm. The sheets may be continuous with theouter membrane of the nuclear envelope. If the ER isstudded with ribosomes that are synthesizing proteins,it is called rough ER. In contrast, smooth ER lacksribosomes and is involved in lipid synthesis.

GOLGIBODY

A system of stacked, membrane-bounded sacs. TheGolgi is involved in processing macromolecules forsecretion and delivery to other components of the cell.

GRANUM

Group of stacked membrane-bounded discs inchloroplasts. They contain chlorophylls and are the siteof the light-trapping reactions in photosynthesis

LYSOSOMES

Membrane-bounded vesicles that contain enzymesinvolved in the digestion of foreign elements.Conditions that result in the release of these enzymesinto the cytoplasm may result in cell death.

MIDDLE LAMELLA

A mucilaginous layer between plant cells with primarywalls. The layer is rich in pectin.

MITOCHONDRIA

Organelles present in eukaryotic cells and bounded bytwo membranes. They are often referred to as thepower plants of cells as they are the site of aerobicrespiration that combines oxygen with food moleculesto generate ATP, an important energy containingmolecule. Like chloroplasts, mitochondria usuallycontain circular DNA (similar to the organization ofDNA in bacterial cells) that codes for some of the

mitochondria! proteins. Ribosomes in mitochondria aresmaller than those in the cytosol and of the same size asbacterial ribosomes.

The double membrane structure that surrounds thenucleus and separates it from the rest of the cytoplasm.It has nuclear pores that allow for communicationbetween the nucleus and the cytoplasm.

NUCLEAR PORES

Openings in the nuclear envelope that allow forcommunication between the nucleus and the cytoplasm.

NUCLEOLUS

Site in the nucleus where ribosomes are synthesized.

NUCLEOPLASM

Matrix of the nucleus, not including nucleolus and

chromosomes.

NUCLEUSThis is the most conspicuous organdie in most cells. Itis separated from the cytoplasm by the nuclearenvelope that consists of an inner and outer membranelayer. Nuclear pores in the envelope allow the nucleusto communicate with the cytoplasm. The nucleuscontains most of the cell's genetic material in the DNAthat makes up the chromatin fibers of thechromosomes. The nucleolus is in the nucleus and it isthe site at which ribosomes are assembled.

PEROXISOMES

Membrane-bounded vesicles that contain oxidativeenzymes concerned with the generation and destructionof hydrogen peroxide, a molecule that would causeserious damage if it were released into the cytoplasm

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PLASMA MEMBRANE

The outer boundary of the cell; also called the cellmembrane. A sheet of lipid molecules (bilayer) withproteins embedded in it. The plasma membranecontrols movement of materials into and out of thecytoplasm.

PLASMODESMATA

Cytoplasmic connections between plant cells. Formedduring mitosis at the cell plate as cell wall precursorscondense.

The cell wall produced outside of the plasmamembrane of young and growing plant cells. Thesewalls are elastic and allow for elongation and changesin shape. They contain mostly cellulose andhernicellulose.

RIBOSOMES

Particles composed of RNA and protein that areinvolved with messenger RNA in the synthesis ofproteins.

SECONDARY CELL WALL

Walls formed inside the primary cell wall when cellsdifferentiate for some special function and lose the -ability to grow or elongate. Conductive cells havesecondary wall as do most of the cells in a woody plant.Secondary cell walls have lignins that resistdecomposition and breakdown.

Membrane-bounded structures in the cytoplasm thatmay contain enzymes, crystals and dissolved materials.Animal cells have small vacuoles whereas plant cellscharacteristically have large vacuoles. Plant vacuolesmay store waste materials but also help to maintain theshape of plants. If large amounts of water are removedfrom the vacuoles, wilting occurs.

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