Oogenesis: Make a map diagram of the cat ovary, and
include map outlines of all important components. Be sure to include a caption,
labels, a scale bar, and your scale bar calculations (6 marks). In a separate
text, comment briefly on what is happening at each stage of development of the
gametes (4 marks).
The formation of ova or eggs is
known as oogenesis. Oogonia cells transform into primary oocytes, which go into
meiosis but stop in prophase I. These cells continue to develop during a menstrual
cycle. Next, 10-20 follicles begin to mature, and one becomes dominant and
finishes the first stage of meiotic division. This meiotic division produces a
large secondary oocyte which contains most of the cytoplasm, and a small polar
body. The secondary oocyte also enters meiotic division but stops at metaphase
II and stays there until it is fertilized. If it is fertilized, the second
meiotic division occurs, and the majority of the cytoplasm enters the egg. This
then develops into a mature ovum.
Spermatogenesis: Make a cell detail diagram of part
of a cross section through a mammalian seminiferous tubule to show the
important components. Be sure to include a caption, labels, a scale bar, and
your scale bar calculations (6 marks). In a separate text, comment briefly on
what is happening at each stage of development of the gametes (4 marks).
The production of sperm is
spermatogenesis. Spermatogonia are diploid stem cells that divide by mitosis.
When puberty begins, cells modify into diploid primary spermatocytes. These go
through the first meiotic division which makes secondary spermatocytes.
Secondary spermatocytes undergo the second meiotic division which makes four
haploid spermatids which are originally connected with cytoplasmic bridges but disconnect
shortly after. Spermatids mature into spermatozoa in the testes and motility is
gained in the epididymis.
Examples of mammal sperm: a. Labelled diagrams (3
marks) and comparative table (3 marks). b. State three ways that all the sperm
you observed in the lab (in fact, all sperm everywhere) are similar, or the
same as one another. And state three ways that all sperm are different from one
another? (6 marks).
tail length, description
Medium length tail, very curly
Short tail, slightly wavy
Long tail, fairly straight
head size, description
Medium sized head, thick
Small sized head, thick
Large sized head, thin
There are many ways that the
three sperm are similar, they all consist of both a head and a tail. They all
also exist so that they can fertilize an egg. They all are very small in size
and cannot be seen by the naked eye.
Three differences between the
sperm are that they all consist of different sized and shaped heads. The
abundance of rat sperm on the slide was much smaller than the others, and the
tails are also different sizes and shapes.
Answer the following questions (4 × 4 marks = 16
Why are sperm small and mobile and why are eggs
large and immobile?
Eggs are large and immobile for
many different reasons. The cytoplasm contained within the egg is one of the
reasons that the egg is large, and can be seen by the naked eye (Morris et al. 2016). The egg is immotile to
ensure that the maternally inherited genes remain intact throughout
fertilization (Alberts et al. 2002).
Sperm are small and motile to increase the probability that they will reach the
egg. (Morris et al. 2016).
Why do males produce so many sperm, and females
produce so few eggs?
There is an abundance of sperm produced by the male
body every day for a multitude of reasons. When a female mates with multiple
males in close proximity to one another, each sperm competes to fertilize the
egg. To increase the probability of fertilization, males produce large amounts
of sperm (Pound et al. 2006). Although
males release up to several hundred sperm in one ejaculation, it is quite
common that only several hundred sperm make it to the egg (Morris et al. 2016). Males must produce a
multitude of sperm to increase the likelihood that they will fertilize the egg
What are the functions of the various parts of the
sperm (tail, mitochondria, head, acrosome)?
Each part of the sperm has a different process
which aids its ability to fertilize the egg. The flagellum, also known as the
tail, moves the sperm through the woman’s body towards the egg. The
mitochondria’s job is to power the flagella in order to move the sperm. The
head of the sperm is small in size and contains small amounts of cytoplasm, so
it is agile enough to move (Morris et al.
2016). The acrosome contains the enzyme acrosin which penetrates the outer
walls of the egg in attempt to fertilize it (Schill et al. 1988).
What are the roles of the follicle cells in the
egg, and of the relatively large amount of cytoplasm in the egg?