CSET Practice Test Subtest II Science

The Reproductive System

The reproduction system uses the process of producing
 a new generation to continue the existence of the 
species by the fusion of two cells from different 
individuals; this is achieved in humans by the fusion of 
one sperm and one ovum (egg). This fusion is called 
"fertilization" and is achieved by sexual intercourse 
between a male and female or by artificial insemination. 
The male body is designed to allow the manufacture, 
storage and transfer of male sex cells (or sperm). The 
female body is designed to manufacture, store and 
release eggs (ova). The creation of human life is a 
miracle to behold as two tiny cells - the sperm and the 
ovum - fuse to form a new cell which, after fertilization, 
resides in the female womb. Nine months later, a 
fully-formed, breathing, living human being in tiny replica 
is born. 

Animals' reproductive systems can be divided into the 
internal reproductive organs and the external genitalia. 
The gonads are the actual organs that produce the 
gametes. In the male, testes (singular = testis) produce 
sperm, and in the female, ovaries make eggs.

In most animals, individuals are either definite males or 
definite females. However, in some species, individual 
organisms are both male and female. Hermaphroditism 
is when one organism has both sexes. Earthworms 
and garden snails always have both male and female 
organs, and when, for example, two earthworms mate, 
they fertilize each other. A special variation on the 
theme is sequential hermaphroditism, in which an 
organism changes sex during its life. If an organism is 
female first and later changes to male, that organism 
is protogynous, and if the organism is male first and 
changes to female, it is said to be protandrous. In 
different species, sequential hermaphroditism can be 
influenced by the organism's age or size or by various 
environmental/climatic factors.

While most higher animals reproduce sexually, there are 
some species in which the females can, under certain 
conditions, produce offspring without mating. 
Parthenogenesis is the ability of an unfertilized egg to 
develop and hatch. This seems to be especially 
prevalent among insects. Some of the giant walkingsticks 
at the Zoo are females who, without mating, lay eggs 
that hatch into more females generation after generation. 
Other insects, like some aphids, have complicated life 
cycles that involve sexually-reproducing generations 
alternating with parthenogenically produced generations. 
In honeybees, fertilized eggs turn into females (workers 
and queens), while unfertilized eggs, which are only 
produced in the spring, turn into males.

In sexual reproduction, there must be some way of 
getting the sperm to the egg. Since sperm and eggs 
are designed to be in a watery environment, aquatic 
animals can make use of the water in which they live, 
but terrestrial animals must, in some way, provide the 
wet environment neeeded for the sperm to swim to 
the egg. There are, thus, two major mechanisms of 
fertilization. In external fertilization, used by many 
aquatic invertebrates, eggs and sperm are 
simultaneously shed into the water, and the sperm 
swim through the water to fertilze the egg. In internal 
fertilization, the eggs are fertilized within the 
reproductive tract of the female, and then are covered 
with eggshells and/or remain within the body of the 
female during their development.

In species with external fertilization, at an appropriate 
developmental stage, the eggs hatch, and the new 
young simply swim away. However, females of species 
with internal fertilization must, at some point, expel 
the growing young. There are three general ways of 
doing this:

Oviparous organisms, like chickens and turtles, lay eggs 
that continue to develop after being laid, and hatch later. 
Viviparous organisms, like humans and kangaroos, are 
live-bearing. The developing young spend proportionately 
more time within the female's reproductive tract, portions 
of which are specially-modified for this purpose. Young 
are later released to survive on their own. 

Ovoviviparous organisms, like guppies, garter snakes, and 
Madagascar hissing roaches, have eggs (with shells) that 
hatch as they are laid, making it look like "live birth." 

Male Reproductive System
The male reproductive system is illustrated to the right. 
Sperm are produced in the testes located in the scrotum. 
Normal body temperature is too hot thus is lethal to 
sperm so the testes are outside of the abdominal cavity 
where the temperature is about 2° C (3.6° F) lower. 
Note also that a woman's body temperature is lowest 
around the time of ovulation to help insure sperm live 
longer to reach the egg. If a man takes too many long, 
very hot baths, this can reduce his sperm count. 
Undescended testes (testes are supposed to descend 
before birth) will cause sterility because their 
environment is too warm for sperm viability unless the 
problem can be surgically corrected.

From there, sperm are transferred to the epididymis, 
coiled tubules also found within the scrotum, that store 
sperm and are the site of their final maturation.

In ejaculation, sperm are forced up into the vas 
deferens (plural = vasa deferentia). From the epididymis, 
the vas deferens goes up, around the front of, over the 
top of, and behind the bladder. A vasectomy is a fairly 
simple, outpatient operation that involves making a small 
slit in each scrotum, cutting the vasa deferentia near 
where they begin, and tying off the cut ends to prevent 
sperm from leaving the scrotum. Because this is a 
relatively non-invasive procedure (as compared to doing 
the same to a woman's oviducts), this is a popular method 
of permanent birth control once a couple has had all the 
children they desire. Couples should carefully weigh their 
options, because this (and the corresponding female 
procedure) is not designed to be a reversible operation.

The ends of the vasa deferentia, behind and slightly 
under the bladder, are called the ejaculatory ducts. 
The seminal vesicles are also located behind the bladder. 
Their secretions are about 60% of the total volume of 
the semen (= sperm and associated fluid) and contain 
mucus, amino acids, fructose as the main energy source 
for the sperm, and prostaglandins to stimulate female 
uterine contractions to move the semen up into the 
uterus. The seminal vesicles empty into the ejaculatory 
ducts. The ejaculatory ducts then empty into the 
urethra (which, in males, also empties the urinary 
bladder).

The initial segment of the urethra is surrounded by the 
prostate gland (note spelling!). The prostate is the 
largest of the accessory glands and puts its secretions 
directly into the urethra. These secretions are alkaline 
to buffer any residual urine, which tends to be acidic, 
and the acidity of the woman's vagina. The prostate 
needs a lot of zinc to function properly, and insufficient 
dietary zinc (as well as other causes) can lead to 
enlargement which potentially can constrict the urethra 
to the point of interferring with urination. Mild cases of 
prostate hypertrophy can often be treated by adding 
supplemental zinc to the man's diet, but severe cases 
require surgical removal of portions of the prostate. This 
surgery, if not done very carefully can lead to problems 
with urination or sexual performance.

The bulbourethral glands or Cowper's glands are the 
third of the accessory structures. These are a small 
pair of glands along the urethra below the prostate. 
Their fluid is secreted just before emission of the 
semen, thus it is thought that this fluid may serve as 
a lubricant for inserting the penis into the vagina, but 
because the volume of these secretions is very small, 
people are not totally sure of this function.

The urethra goes through the penis. In humans, the 
penis contains three cylinders of spongy, erectile tissue. 
During arousal, these become filled with blood from the 
arteries that supply them and the pressure seals off the 
veins that drain these areas causing an erection, which 
is necessary for insertion of the penis into the woman's 
vagina. In a number of other animals, the penis also has 
a bone, the baculum, which helps to stiffen it. The 
head of the penis, the glans penis, is very sensitive to 
stimulation. In humans, as in other mammals, the glans 
is covered by the foreskin or prepuce, which may have 
been removed by circumcision. Medically, circumcision 
is not a necessity, but rather a cultural "tradition". Males 
who have not been circumcised need to keep the area 
between the glans and the prepuce clean so bacteria 
and/or yeasts don't start to grow on accumulated 
secretions, etc. there. There is some evidence that 
uncircumcised males who do not keep the glans/prepuce 
area clean are slightly more prone to penile cancer.

Source:
Special thanks to the University of Cincinnati Clermont 
College Biology Department

Photosynthesis

Today we obtain almost all of our food from plants, or 
from animals which have eaten plants, and so we ought 
to know a bit about how photosynthesis works. It is a 
fascinating story of molecular changes. First a molecule 
called chlorophyll is able to absorb the energy of light 
and some of its electrons become excited, that is, they 
move faster than before. Eventually one of these 
electrons leaves the chlorophyll and passes to an 
electron acceptor (or oxidizing agent). 

Meanwhile the chlorophyll is able to get an electron 
back by taking one from a water molecule. There is 
good evidence that two or more manganese atoms in 
association with protein can take four electrons from 
two water molecules. This releases four protons.

The by-product of this is that two oxygen atoms, 
which originally formed part of the water molecules, 
are left without their hydrogen. These can be joined 
together, by enzymes, to form a molecule of oxygen
O2.

Some of these freed protons are captured, by the 
electrons, and tied to a molecule called NADPH. The 
rest of the electrons are carried by floating molecules 
across an oily membrane to the other side, so 
forming an electrical field across the membrane. 
Embedded within the membrane are molecules shaped 
like tunnels. The electrical field makes protons flow 
down this tunnel, attracted by the electrons on the 
other side, and as they pass the protons generate 
molecules of ATP, the main energy carrying molecule 
in life.

In a series of reactions known as the Calvin cycle, 
the energy of these ATP molecules is used to join 
carbon dioxide molecules together into sugars. This 
requires the addition of protons, which are carried by 
the NADPH molecules which we saw formed earlier in 
the photosynthesis process.