Download Chapter 6: Cells 2

C. Eukaryotic Plant Cell- Plant cells vary, in a few organelles,
from animal cells.
a. Chloroplasts- found in plants and eukaryotic algae, are the site
of photosynthesis. They convert solar energy to chemical energy
and synthesize new organic compounds from CO2 and H2O.
•Like mitochondria, chloroplasts have small quantities of DNA that
direct the synthesis of the polypeptides produced by internal
ribosomes. Both Mitochondria and chloroplasts grow and reproduce
as semiautonomous organelles.
•Chloroplasts gain their color from high levels of the green pigment
chlorophyll, which captures sunlight energy and converts it into
chemical energy stored in the bonds of sugars, such as glucose.
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•The processes in the chloroplast are separated from the cytosol
by two membranes. The innermost membrane is a fluid-filled
space, the stroma, in which float membranous sacs, the
thylakoids.
•The stroma contains DNA, ribosomes, and enzymes for part of
photosynthesis.
•The thylakoids, flattened sacs, are stacked into grana and are
critical for converting light to chemical energy.
•Like mitochondria, chloroplasts are dynamic structures. Their shape
is plastic and they can reproduce themselves by pinching in two.
•Mitochondria and chloroplasts are mobile and move around the cell
along tracks in the cytoskeleton.
b. Peroxisomes- contain enzymes that transfer hydrogen from
various substrates to oxygen. An intermediate product of this process
is hydrogen peroxide (H2O2), a poison, but the peroxisome has
another enzyme that converts H2O2 to water.
•Some peroxisomes break fatty acids down to smaller molecules that
are transported to mitochondria for fuel. Others detoxify alcohol and
other harmful compounds.
•Specialized peroxisomes, glyoxysomes, convert the fatty acids in
seeds to sugars, an easier energy and carbon source to transport.
C. Central vacuoles are found in mature plant cells.
•The membrane surrounding the central vacuole, the tonoplast, is
selective in its transport of solutes into the central vacuole.
•The functions of the central vacuole include stockpiling proteins or
inorganic ions, depositing metabolic byproducts, storing pigments,
and storing defensive compounds against herbivores.
• It also increases surface to volume ratio for the whole cell.
d. Cell Wall- In plants, the cell wall protects the cell, maintains its
shape, supports the plant against the force of gravity, and prevents
excessive uptake of water.
•The basic design consists of microfibrils of cellulose embedded in a
matrix of proteins and other polysaccharides.
•Plant cells are perforated with plasmodesmata, channels allowing
cysotol to pass between cells.
D. Eukaryotic Fungal Cells- Fungal hyphae have cell walls.
These are built mainly of chitin, a strong but flexible nitrogencontaining polysaccharide, identical to that found in arthropods.
The vegetative bodies of most fungi are constructed of tiny filaments
called hyphae that form an interwoven mat called a mycelium.
•Ecosystems would be in trouble without fungi to decompose dead
organisms, fallen leaves, feces, and other organic materials.
This decomposition recycles vital chemical elements back to the
environment in forms other organisms can assimilate.
D. Eukaryotic Cells- Protists- Protists are so diverse that few
general characteristics can be cited without exceptions.
Most of the 60,000 known protists are unicellular, but some are
colonial and others multicellular.
•Euglena, a single celled mixotrophic protist, can use chloroplasts to
undergo photosynthesis if light is available or live as a heterotroph by
absorbing organic nutrients from the environment.
Paramecium use cilia to move and feed.
In a Paramecium, cilia along the oral groove draw in food that are
engulfed by phagocytosis. Like other freshwater protists, the
hyperosmotic Paramecium expels accumulated water from the
contractile vacuole.