HortBotany
Lesson Plan 3
Plant Cells
In class worksheet: Read pages 16-22, through the section entitled
“Growth Processes”, of your text and answer the following questions:
1) Define the following terms. Leave a little room to revise your
definitions as we will go over this lesson plan later:
Organelle:
Cell structures, suspended in the cell cytoplasm, each
having a special or unique function.
Protoplasm:
The living part (substance) of a cell consisting of the
nucleus, cytoplasm and cell membrane, but not
including the cell wall
Nucleus:
The structure within a cell that is the center of
inheritance and cellular control.
Cytoplasm:
Soft, jelly-like material where most cell metabolism
takes place. Cellular organelles are “suspended” in
the cytoplasm.
Cytoplasmic Membrane:
Cell Membrane
The sac or membrane enclosing
(surrounding) the cytoplasm.
Chloroplasts:
Cellular organelles where photosynthesis takes place.
Chloroplasts are unique to plants.
Mitochondria:
Cellular organelles where respiration takes place.
Both plant and animal cells have mitochondria.
Ribosomes:
Cellular organelles that are the sites of protein
synthesis (production).
Vacuole:
A membrane-bound sac within a cell.
Plasmodesmata: Interconnecting strands of cytoplasm. Plasmodesmata
connect the cytoplasms of all the living cells in a plant.
Cell Wall:
The rigid, outer covering of a plant cell. The cell wall
surrounds the cell protoplasm.
Middle Lamella: A layer of pectin binding (gluing together) two
adjacent cell walls.
Since the following 2 terms are not in your text, I will provide the
definitions for them.
Golgi Apparatus: cell organelle that is the “packaging” and “shipping”
center of the cell. Small packages called “vesicles” are pinched-off and
can move to various locations within the cell.
Inter-cellular Spaces: The spaces between plant cells. Plant cells are not
shaped like shoe boxes. They are irregularly shaped and small spaces
are created where they touch one another. The inter-cellular spaces
contain water.
2) What kinds of things are stored in the vacuoles of plant cells?
WATER
WASTE MATERIAL
SOMETIMES FOOD
3) Refer to the diagram at the top of page 19 to answer the questions
that follow:

What is the primary cell wall made out of?
THIN STRANDS OF CELLULOSE CALLED CELLULOSE
MICROFIBRILS.

Describe what happens to the cell wall as the cell gets older:
THE FIRST LAYER OF CELLULOSE MICROFIBRILS LAID
DOWN IS CALLED THE PRIMARY CELL WALL. AS THE
CELL GETS OLDER, ADDITIONAL LAYERS OF
CELLULOSE MICROFIBRILS ARE LAID DOWN INSIDE OF
THE PRIMARY CELL WALL.

What is the role of lignin in secondary cell wall development?
LIGNIN IS A “HARDENING” SUBSTANCE THAT HELPS
STIFFEN THE CELL WALL.

As the cell continues to age, what eventually happens to the living
protoplasm?
EVENTUALLY, THE PROTOPLASM DIES AND ALL THAT
IS LEFT IS THE CELL WALL.
4) Approximately what percentage of a tree is composed of dead cells
(cells lacking a protoplast):
ABOUT 98%
5) See the section entitled Wall Structure and Cell Growth on page 20 of
your text. Pay close attention to the diagram at the bottom of the page.
One explanation why stems and roots grow longer is because cells, at
the stem and root tips, elongate or lengthen.
o What moves into these cells that causes them to elongate:
WATER
o What is it about the arrangement of the cellulose microfibrils in the
side-walls that allows cells to elongate:
THE CELLULOSE MICROFIBRILS IN THE SIDE WALLS
ARE ARRANGED IN A PARALLEL FASHION.
o How are the cellulose microfibrils arranged in the end-walls of the
cells and explain how this affects cell elongation:
THE CELLULAR MICROFIBRILS IN THE END WALLS ARE
ARRANGED IN A CRISS-CROSSED PATTERN.
o Explain why a plant cell cannot continue to elongate indefinitely:
SECONDARY WALL THICKENING PREVENTS
ADDITIONAL CELL ELONGATION.
WATER
VACUOLE
6) Why, do you think, most plant growth occurs in the spring of the
year:
IN THE SPRING, WATER IS USUALLY AVAILABLE TO
PLANTS IN ABUNDANCE. AS WATER MOVES INTO PLANT
CELLS IT “STRETCHES” THE PRIMARY CELL WALL
CAUSING GROWTH. AFTER THE SECONDARY CELL
WALL FORMS NO FURTHER GROWTH (ELONGATION)
CAN OCCUR.
The Virtual Plant Cell Websites:
http://www.life.uiuc.edu/cgi-bin/plantbio/cell/cell.cgi
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