1. Lab Exam: Questions

2. Why choose an embryonic
mass of cells to study the
stages of mitosis
• Unlike most cells in an
adult body, an embryonic
mass of cells is always
dividing. Most cells in the
adult body is quiescent and
will not divide unless
signals have been given to
them to divide, and many
cells such as muscle and
nerve cells have even lost
the ability to divide.

3. What stage of mitosis of
often associated with the
beginning of cytokinesis?
telophase

4. Does the cell cycle have a
beginning and an end?
• cell cycle, the ordered sequence of
events that occur in a cell in
preparation for cell division. The
cell cycle is a four-stage process in
which the cell increases in size (gap
1, or G1, stage), copies its DNA
(synthesis, or S, stage), prepares to
divide (gap 2, or G2, stage), and
divides (mitosis, or M, stage). The
stages G1, S, and G2 make up
interphase, which accounts for the
span between cell divisions. On the
basis of the stimulatory and
inhibitory messages a cell receives,
it “decides” whether or not it
should enter the cell cycle and
divide

5. •
spermatogenesis
•
•
The seminiferous tubules, in which the sperm are produced,
constitute about 90 percent of the testicular mass. In the young
male the tubules are simple and composed of undeveloped spermproducing cells (spermatogonia) and the Sertoli cells. In the older
male the tubules become branched, and spermatogonia are
changed into the fertile sperm cells after a series of transformations
called spermatogenesis. The Sertoli cells found in both young and
adult males mechanically support and protect the spermatogonia.
Each seminiferous tubule of the adult testis has a central lumen, or
cavity, which is connected to the epididymis and spermatic duct
(ductus deferens). Sperm cells originate as spermatogonia along the
walls of the seminiferous tubules. The spermatogonia mature into
spermatocytes, which mature into spermatids that mature into
spermatozoa as they move into the central lumen of the
seminiferous tubule. The spermatozoa migrate, by short
contractions of the tubule, to the mediastinum testis; they are then
transported through a complex network of canals (rete testis and
efferent ductules) to the epididymis for temporary storage. The
spermatozoa move through the epididymis and the spermatic duct
to be stored in the seminal vesicles for eventual ejaculation with
the seminal fluid. Normal men produce about one million
spermatozoa daily.
In animals that breed seasonally, such as sheep and goats, the
testes regress completely during the nonbreeding season and the
spermatogonia return to the state found in the young, sexually
immature males. Frequently in these animals the testes are drawn
back into the body cavity except in the breeding season, when they
again descend and mature; this process is known as recrudescence.

6. Spermatogenesis
• Spermatogenesis: the
process by which stem cells
develop into mature
spermatozoa. There are
three phases: (1)
Spermatocytogenesis
(Mitosis), (2) Meiosis, and
(3) Spermiogenesis

7. Spermatogenesis in the
Sexually Mature Male
• A. The gametogenic function of the
testes is to produce the male gametes
or spermatozoa. This process is termed,
spermatogenesis. The sites of
spermatozoa production are the
seminiferous tubules. The spermatozoa
originate from precursor cells that are
called spermatogonia, and these cells
line the basement membrane of the
seminiferous tubule. Spermatogenesis
can be divided into three portions:
• spermatocytogenesis -- proliferative
phase
• meiosis -- production of the haploid
gamete
• spermiogenesis -- "metamorphosis" of
spermatids into spermatozoa

8. oogenesis
• in the human female
reproductive system,
growth process in which
the primary egg cell (or
ovum) becomes a mature
ovum.

9. oogenesis
• The egg cell remains as a primary
ovum until the time for its release
from the ovary arrives. The egg
then undergoes a cell division. The
nucleus splits so that half of its
chromosomes go to one cell and
half to another. One of these two
new cells is usually larger than the
other and is known as the
secondary ovum; the smaller cell is
known as a polar body. The
secondary ovum grows in the ovary
until it reaches maturation; it then
breaks loose and is carried into the
fallopian tubes. Once in the
fallopian tubes, the secondary egg
cell is suitable for fertilization by
the male sperm cells

10. Oogenesis
Dr. Charlotte Ownby

11. •
Stages of mitosis
•
Prior to the onset of mitosis, the chromosomes
have replicated and the proteins that will form
the mitotic spindle have been synthesized.
Mitosis begins at prophase with the thickening
and coiling of the chromosomes. The nucleolus,
a rounded structure, shrinks and disappears. The
end of prophase is marked by the beginning of
the organization of a group of fibres to form a
spindle and the disintegration of the nuclear
membrane.
The chromosomes, each of which is a double
structure consisting of duplicate chromatids, line
up along the midline of the cell at metaphase. In
anaphase each chromatid pair separates into two
identical chromosomes that are pulled to
opposite ends of the cell by the spindle fibres.
During telophase, the chromosomes begin to
decondense, the spindle breaks down, and the
nuclear membranes and nucleoli re-form. The
cytoplasm of the mother cell divides to form two
daughter cells, each containing the same number
and kind of chromosomes as the mother cell.
The stage, or phase, after the completion of
mitosis is called interphase

12. •
meiosis
•
Prior to meiosis, each of the chromosomes in the diploid
germ cell has replicated and thus consists of a joined pair
of duplicate chromatids. Meiosis begins with the
contraction of the chromosomes in the nucleus of the
diploid cell. Homologous paternal and maternal
chromosomes pair up along the midline of the cell. Each
pair of chromosomes—called a tetrad, or a bivalent—
consists of four chromatids. At this point, the homologous
chromosomes exchange genetic material by the process of
crossing over (see linkage group). The homologous pairs
then separate, each pair being pulled to opposite ends of
the cell, which then pinches in half to form two daughter
cells. Each daughter cell of this first meiotic division
contains a haploid set of chromosomes. The chromosomes
at this point still consist of duplicate chromatids.
In the second meiotic division, each haploid daughter cell
divides. There is no further reduction in chromosome
number during this division, as it involves the separation of
each chromatid pair into two chromosomes, which are
pulled to the opposite ends of the daughter cells. Each
daughter cell then divides in half, thereby producing a total
of four different haploid gametes. When two gametes
unite during fertilization, each contributes its haploid set of
chromosomes to the new individual, restoring the diploid
number

13. Rhizobium and legumes
• Rhizobium organisms in the soil
recognize and invade the root hairs
of their specific plant host, enter
the plant tissues, and form a root
nodule. This process causes the
bacteria to lose many of their freeliving characteristics. They become
dependent upon the carbon
supplied by the plant, and, in
exchange for carbon, they convert
nitrogen gas to ammonia, which is
used by the plant for its protein
synthesis and growth. In addition,
many bacteria can convert nitrate
to amines for purposes of
synthesizing cellular materials or to
ammonia when nitrate is used as
electron acceptor

14. rhizobidium
• Nitrogen Fixation by Legumes
• Legume nitrogen fixation starts with the
formation of a nodule. A common soil
bacterium, Rhizobium, invades the root
and multiplies within the cortex cells.
The plant supplies all the necessary
nutrients and energy for the bacteria.
Within a week after infection, small
nodules are visible with the naked eye.
In the field, small nodules can be seen
2-3 weeks after planting, depending on
legume species and germination
conditions. When nodules are young
and not yet fixing nitrogen, they are
usually white or grey inside. As nodules
grow in size they gradually turn pink or
reddish in color, indicating nitrogen
fixation has started. The pink or red
color is caused by leghemoglobin
(similar to hemoglobin in blood) that
controls oxygen flow to the bacteria.

15. •
•
Steps of Gram stain
•
•
•
Lab 6: Gram Stain
1. The bacteria are first stained with the basic
dye crystal violet. Both Gram-positive and Gramnegative bacteria become directly stained and
appear purple after this step.
2. The bacteria are then treated with Gram's
iodine solution. This allows the stain to be
retained better by forming an insoluble crystal
violet-iodine complex. Both Gram-positive and
Gram-negative bacteria remain purple after this
step.
3. Gram's decolorizer, a mixture of ethyl alcohol
and acetone, is then added. This is the
differential step. Gram-positive bacteria retain
the crystal violet-iodine complex while Gramnegative are decolorized.
4. Finally, the counterstain safranin (also a basic
dye) is applied. Since the Gram-positive bacteria
are already stained purple, they are not affected
by the counterstain. Gram-negative bacteria,
which are now colorless, become directly stained
by th e safranin. Thus, Gram-positive appear
purple, and Gram-negative appear pink.

16. What happens when milk
is pasteurized?
• heat-treatment process that
destroys pathogenic
microorganisms in certain foods
and be
• The times and temperatures are
those determined to be
necessary to destroy the
Mycobacterium tuberculosis and
other more heat-resistant of the
non-spore-forming, diseasecausing microorganisms found in
milk. The treatment also
destroys most of the
microorganisms that cause
spoilage and so prolongs the
storage time of food.verages.

17. • Pasteurization
• Pasteurization is most important
in all dairy processing. It is the
biological safeguard which
ensures that all potential
pathogens are destroyed.
Extensive studies have
determined that heating milk to
63° C (145° F) for 30 minutes or
72° C (161° F) for 15 seconds kills
the most resistant harmful
bacteria. In actual practice these
temperatures and times are
exceeded, thereby not only
ensuring safety but also
extending shelf life.

18. antibiotics
• chemical substance produced by a living
organism, generally a microorganism, that is
detrimental to other microorganisms.
• Antibiotics produce their effects through a
variety of mechanisms of action. A large
number work by inhibiting bacterial cell wall
synthesis; these agents are referred to
generally as β-lactam antibiotics. Production
of the bacterial cell wall involves the partial
assembly of wall components inside the
cell, transport of these structures through
the cell membrane to the growing wall,
assembly into the wall, and finally crosslinking of the strands of wall material.
Antibiotics that inhibit the synthesis of the
cell wall have a specific effect on one or
another phase. The result is an alteration in
the cell wall and shape of the organism and
eventually the death of the bacterium.

19. antibiotics
• Unlike bacteria, viruses
mimic the metabolic
functions of their host cells.
Antibiotics are not effective
against viruses.

21. Fungi

22. How can you tell whether
Rhizopus is reproducing
sexually or asexually?
Fungi - Biology
• Rhizopus stolonifer (bread
mold) is a zygomycete.
• Asexual reproduction in
Rhizopus: Sporangia – note
the root like hyphae
(rhizoids) and horizontallygrowing hyphae (stolons)
at the base
• Sexual reproduction in
Rhizopus: hyphae meeting
(far left) and making a
zygospore (far right).

23. Rhizopus:
Asexual reproduction in Rhizopus:
Sporangia – note the root like hyphae
(rhizoids) and horizontally-growing
hyphae (stolons) at the base

24. Describe the relationship
found in lichen.
Lichens
• lichen is not a single
organism the way most
other living things are, but
rather it is a combination of
two organisms which live
together intimately.

25. Describe the relationship
found in lichen.
Lichens
• Most of the lichen is
composed of fungal
filaments, but living among
the filaments are algal cells,
usually from a green alga or
a cyanobacterium

26. Describe the relationship
found in lichen.
Life History and Ecology of Lichens
• Lichens are formed from a
combination of a fungal
partner (mycobiont) and an
algal partner (phycobiont).
• A lichen may absorb certain
mineral nutrients from any of
these substrates on which it
grows, but is generally selfreliant in feeding itself
through photosynthesis in
the algal cells.

27. Describe the relationship
found in lichen.
Life History and Ecology of Lichens
• Lichens growing in trees
are simply using the tree
as a home. Lichens growing
on rocks, though, may
release chemicals which
speed the degradation of
the rock into soil, and thus
promote production of new
soils.

28. Fungi: Benefits
Symbiotic Fungi
• Lichens are symbioses
involving fungi and
unicellular algae
• Mycorrhizae are symbioses
involving fungi and the
roots of plants
Multiclavula mucida, a lichenized basidiomycete (left) and Parmelia sp., a lichenized ascomycete (right)

29. The only distinction
between a fungi spore and
gamete is function
• Following a period of intensive growth,
fungi enter a reproductive phase by
forming and releasing vast quantities of
spores. Spores are usually single cells
produced by fragmentation of the
mycelium or within specialized
structures (sporangia, gametangia,
sporophores, etc.). Spores may be
produced either directly by asexual
methods or indirectly by sexual
reproduction. Sexual reproduction in
fungi, as in other living organisms,
involves the fusion of two nuclei that
are brought together when two sex
cells (gametes) unite. Asexual
reproduction, which is simpler and
more direct, may be accomplished by
various methods.