The Cell
In this chapter you will learn about cells, their
structure, their types and sizes, how cells communicate with each other, and how
they divide. Cells are the foundation to plants. Like the
bones in the body, the cell wall provides the framework for the plant.
The walls of the cells actually create the structure of the plant. The
understanding of cells will form the foundation of your understanding of Botany.
The microscope provides our window into the world of plant cells. The use
of the Microscope is critical in the study of Botany.
At the end of this chapter the successful student will be able to
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Light Microscopes - Increase magnification as light passes through a series
of transparent lenses made of glass or calcium fluoride crystals. A
Compound Microscope can magnify 1500x times the size. This means that the
scientist can distinguish organelles 2 micrometers or larger in diameter.
This allow a botanist to examine the cells of a plant to study the structure and
function of microscopic components of a plant.
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- Prokaryotic - Cells lacking a nucleus.
- Eukrayotic - Cells containing a nucleus.
- Organelles - Membrane-bound bodies found within eukaryotic cells.
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- Cell Wall surrounds protoplasm (contains all living cell
components).
-
Bound by a plasma membrane.
- Cytoplasm consist of all cellular components between the plasma
membrane and the nucleus.
- Cytosol - Fluid within cytoplasm containing organelles.
- Interact
- with this animation of a cell
until your are comfortable with the plant structures
Look closely at the cell wall:
- Main structural component of cell walls is cellulose.
- Also contain matrix of hemicellulose, pectin, and glycoproteins.
- Middle lamella is first produced when new cell walls are formed.
- Secondary walls are derived from primary walls by thickening and inclusion
of lignin.
Cellular Components
- Plasma Membrane
- Composed of phospholipids arranged in two layers, with proteins
interspersed throughout.
- Some proteins extend across the entire width, while others and embedded
to the outer surface.
- Nucleus
- Nucleus is bound by two membranes, which together constitute the nuclear
envelope.
- Structurally complex pores occupy up to one-third of the total surface
area.
- The Nucleus contains fluid nucleoplasm packed with short fibers, and
contain larger bodies.
- Nucleoi composed primarily of RNA.
- Chromatin Strands - Coil and become chromosomes.
- Endoplasmic Reticulum
- Endoplasmic Reticulum facilitates cellular communication and materials
channeling.
- Enclosed space consisting of a network of flattened sacs and tubes
forming channels throughout the cytoplasm.
- Ribosomes may be distributed on outer surface (Rough ER).
- Associated with protein synthesis.
- Smooth ER is devoid of ribosomes and is associated with lipid
secretion.
- Ribosomes are composed of two subunits composed of RNA and proteins.
- Ribosomal subunits are assembled within the nucleolus, released, and in
association with special RNA molecules, initiate protein synthesis.
- Have no bounding membranes.
- Dictysomes (Golgi Bodies in animals) are often bound by branching tubules
that originate from the ER.
- Involved in the modification of carbohydrates attached to proteins
synthesized and packaged in the ER.
- Polysaccharides are assembled within dictysomes, and collect in small
vesicles.
- Migrate to plasma membrane and secrete contents to the outside.
- Plastids
- Chloroplasts are the most conspicuous plastids.
- Each bound by double membrane.
- Contain stroma - Enzyme-filled matrix.
- Contain grana made up of thylakoids.
- Thylakoid membranes contain chlorophyll.
- Chromoplasts and Leucoplasts are additional plastids found in many
plants.
- Mitochondria release energy produced from cellular respiration.
- Inward membrane forms numerous folds (cristae).
- Increase surface area available to enzymes in the matrix fluid.
- Microbodies are small, spherical bodies with a single membrane,
distributed throughout the cytoplasm which contain specialized enzymes.
- Perixosomes - Serve in photorespiration.
- Glyoxisomes - Aid in converting fat to carbohydrates.
- Vacuoles
- In mature cells, 90% of volume may be taken up by central vacuoles
bounded by vacuolar membranes (tonoplasts).
- Filled with cell sap which helps maintain pressure within the cell.
- Also frequently contains water-soluble pigments.
- Cytoskeleton is an intricate network of microtubules and microfilaments
- Microtubules control the addition of cellulose to the cell wall.
- Microfilaments play a major role in the contraction and movement of
cells in multicellular animals.
- Appear to play a role in cytoplasmic streaming.
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- Cells of higher plants generally vary in length between 10 and 100
micrometers.
- Increase in surface area of a spherical cell is equal to the square of its
increase in diameter, but its increase in volume is equal to the cube of its
increase in diameter.
- Smaller cells have relatively large surface to volume ratios enabling
faster and more efficient cellular communication
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- Fluids and dissolved substances can pass through primary walls of adjacent
cells via plasmodesmota.
- Cytoplasmic strands extending between cells..
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Chloroplasts are the most conspicuous
plastids.
Each bound by double membrane.
Contain
stroma
- Enzyme-filled matrix.
Contain
grana
made
up
of thylakoids.
Thylakoid
membranes
contain
chlorophyll.
Chromoplasts
and
Leucoplasts are
additional
plastids found
in
many
plants.
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- Cytokinesis is the division of a cell, usually following mitosis. The
Cell division process is referred to as the cell cycle. It is divided into
interphase and mitosis.
- Cellular Reproduction
- Cell division process referred to as cell cycle.
- Divided into interphase and mitosis.
- Interphase
- Period when cells are not dividing.
- G1 - Cell increases in size.
- S - DNA replication takes place.
- G2- Mitochondria divide, and microtubules produced
- Mitosis
- Mitosis refers to the process of cellular division that produces two
daughter cells with equal amounts of DNA and other substances duplicated
during interphase.
- Each daughter cell is an exact copy of the parent cell.
- Mitosis occurs in meristems.
- Prophase
- Chromosomes condense.
Strands of chromatin coil and tighten with centromeres holding each
pair of chromatids together.
- Nuclear envelope fragments.
- Kinetochore is located on the outer surface of each centromere.
- Spindle fibers develop and become attached to the kinetochore.
- Metaphase
- Chromosomes align at the cell’s equator.
- Spindle fibers collectively referred to as the spindle.
- At the end of metaphase, the centromeres holding each sister
chromatid separate lengthwise.
- Anaphase
- Sister chromatids separate and are pulled to opposite poles.
- Spindle fibers gradually shorten as material is continuously removed
from the polar ends.
- Telophase
- Each group of daughter chromosomes become surrounded by a nuclear
envelope.
- Daughter chromosomes become indistinguishable.
- Nucleoli reappear
- Spindle fibers disintegrate
- Cell plate forms.
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Last modified:
October 08, 2004 by
Cynthia Herbrandson 
© Copyright 1999, Kellogg Community College.
All rights reserved.
