CSET Practice Test Subtest II Science

Modeling Earth Systems

Radiation from the Sun 
The amount of energy coming up from the earth's interior 
is minuscule compared to the energy that comes down 
from the sun in the form of radiation. Most of the power 
that drives biological, geophysical and geochemical 
surface processes comes from the sun, at the rate of 
1367 watt/m2, which arrive directly at the top of the 
earth's atmosphere.
The hotter a radiating body is the shorter the 
wavelength of radiation that it emits. The sun's surface 
is at about 5780 K so it radiates strongest in the visible 
part of the spectrum, with a peak at about 500 nm, 
which corresponds roughly to the color green. Light 
from the sun is yellowish because other colors are also 
radiated with strong intensity.

Living cells are divided into two types - prokaryotic 
and eukaryotic (or procaryotic and eucaryotic). This 
division is based on internal complexity. 
Eukaryotic: The cells of protozoa, higher plants and 
animals are highly structured. These cells tend to be 
larger than the cells of bacteria, and have developed 
specialized packaging and transport mechanisms that 
may be necessary to support their larger size. 
Prokaryotic: These cells are simple in structure, with 
no recognizable organelles. They have an outer cell 
wall that gives them shape. Just under the rigid cell 
wall is the more fluid cell membrane. The cytoplasm 
enclosed within the cell membrane does not exhibit 
much structure when viewed by electron microscopy.

The Plant Cell (Eukaryotic)

Nucleus
The nucleus is the most obvious organelle in any 
eucaryotic cell. It is a membrane-bound organelle 
and is surrounded by a double membrane. It 
communicates with the surrounding cytosol via 
numerous nuclear pores.

Within the nucleus is the DNA responsible for 
providing the cell with its unique characteristics. 
The DNA is similar in every cell of the body, but 
depending on the specific cell type, some genes 
may be turned on or off - that's why a liver cell is 
different from a muscle cell, and a muscle cell is 
different from a fat cell. When a cell is dividing, the 
DNA and surrounding protein condense into 
chromosomes that are visible by microscopy.

The prominent structure in the nucleus is the 
nucleolus. The nucleolus produces ribosomes, which 
move out of the nucleus to positions on the rough 
endoplasmic reticulum where they are critical in 
protein synthesis.

Endoplasmic Reticulum 

Throughout the eucaryotic cell, especially those 
responsible for the production of hormones and 
other secretory products, is a vast amount of 
membrane called the endoplasmic reticulum, or ER 
for short. The ER membrane is a continuation of the 
outer nuclear membrane and its function suggests 
just how complex and organized the eucayotic cell 
really is.

When viewed by electron microscopy, some areas of 
the endoplasmic reticulum look "smooth" (smooth ER) 
and some appear "rough" (rough ER). The rough ER 
appears rough due to the presence of ribosomes on 
the membrane surface. Smooth and Rough ER also 
have different functions. Smooth ER is important in 
the synthesis of lipids and membrane proteins. Rough 
ER is important in the synthesis of other proteins.

Information coded in DNA sequences in the nucleus is 
transcribed as messenger RNA. Messenger RNA exits 
the nucleus through small pores to enter the cytoplasm. 
At the ribosomes on the rough ER, the messenger 
RNA is translated into proteins. These proteins are 
then transferred to the Golgi in "transport vesicles" 
where they are further processed and packaged into 
lysosomes, peroxisomes, or secretory vesicles.

Centrosome

PLANT CELL CENTROSOME: Plant cells have centrosomes 
that function much like animal cell centrosomes. 
However, unlike centrosomes in animal cells, they do not 
have centrioles.

ANIMAL CELL CENTROSOME: The centrosome, also called 
the "microtubule organizing center", is an area in the cell 
where microtubles are produced. Within an animal cell 
centrosome there is a pair of small organelles, the 
centrioles, each made up of a ring of nine groups of 
microtubules. There are three fused microtubules in each 
group. The two centrioles are arranged such that one is 
perpendicular to the other.

During animal cell division, the centrosome divides and 
the centrioles replicate (make new copies). The result 
is two centrosomes, each with its own pair of centrioles. 
The two centrosomes move to opposite ends of the 
nucleus, and from each centrosome, microtubules grow 
into a "spindle" which is responsible for separating 
replicated chromosomes into the two daughter cells.

Cytoskeleton

As its name implies, the cytoskeleton helps to maintain 
cell shape. But the primary importance of the 
cytoskeleton is in cell motility. The internal movement of 
cell organelles, as well as cell locomotion and muscle 
fiber contraction could not take place without the 
cytoskeleton.

The cytoskeleton is an organized network of three primary 
protein filaments: microtubules, actin filaments, and 
intermediate fibers. The complexity of the cytoskeleton 
can be seen in the abundant F-actin stress fibers 
(green) in the endothelial cell shown above.

Golgi Apparatus 

The Golgi apparatus is a membrane-bound structure 
with a single membrane. It is actually a stack of 
membrane-bound vesicles that are important in 
packaging macromolecules for transport elsewhere 
in the cell. The stack of larger vesicles is surrounded 
by numerous smaller vesicles containing those 
packaged macromolecules. The enzymatic or hormonal 
contents of lysosomes, peroxisomes and secretory 
vesicles are packaged in membrane-bound vesicles at 
the periphery of the Golgi apparatus.

Mitochondria 

Mitochondria provide the energy a cell needs to move, 
divide, produce secretory products, contract - in short, 
they are the power centers of the cell. They are about 
the size of bacteria but may have different shapes 
depending on the cell type.

Mitochondria are membrane-bound organelles, and like 
the nucleus have a double membrane. The outer 
membrane is fairly smooth. But the inner membrane is 
highly convoluted, forming folds called cristae. The 
cristae greatly increase the inner membrane's surface 
area. It is on these cristae that food (sugar) is combined 
with oxygen to produce ATP - the primary energy source 
for the cell.

Lysosomes

Lysosomes (common in animal cells but rare in plant cells) 
contain hydrolytic enzymes necessary for intracellular 
digestion. In white blood cells that eat bacteria, lysosome 
contents are carefully released into the vacuole around 
the bacteria and serve to kill and digest those bacteria. 
Uncontrolled release of lysosome contents into the 
cytoplasm can also cause cell death (necrosis).

Peroxisomes

This organelle is responsible for protecting the cell 
from its own production of toxic hydrogen peroxide. 
As an example, white blood cells produce hydrogen 
peroxide to kill bacteria. The oxidative enzymes in 
peroxisomes break down the hydrogen peroxide into 
water and oxygen.

Vacuole

A vacuole is a membrane-bound sac that plays roles 
in intracellular digestion and the release of cellular 
waste products. In animal cells, vacuoles are 
generally small.

Vacuoles tend to be large in plant cells and play a 
role in turgor pressure. When a plant is well-watered, 
water collects in cell vacuoles producing rigidity in 
the plant. Without sufficient water, pressure in the 
vacuole is reduced and the plant wilts.

Cell Membrane

Every cell is enclosed in a membrane. The membrane 
is a double layer of lipids (lipid bilayer) but is made 
quite complex by the presence of numerous proteins 
that are important to cell activity. These proteins 
include receptors, pores, and enzymes. The membrane 
is responsible for the controlled entry and exit of ions 
like sodium (Na) potassium (K), calcium (Ca++). 

Cytosol

The cytosol (cytoplasm) is the "soup" within which all 
the other cell organelles reside and where most of the 
cellular metabolism occurs. Though mostly water, the 
cytosol is full of proteins that control cell metabolism 
including signal transduction pathways, glycolysis, 
intracellular receptors, and transcription factors.

Cell Wall 

Prokaryotic cells and plant cells both have a rigid cell 
wall made up of polysaccharides. The cell wall provides 
and maintains the shape of these cells and serves as a
protective barrier.

Chloroplast 

Chloroplasts are specialized organelles found in all 
higher plant cells. These organelles contain the plant 
cell's chlorophyll, hence provide the green color. 
They have a double outer membrane. Within the 
stroma are other membrane structures - the 
thylakoids and grana (singular = granum) where 
photosynthesis takes place.