I got a 29 in the bio section
the harder questions are derived from the following areas
Biochemistry
Cell Biology
Research techniques (Read up on things like PCR, Western Blots, FRAP, etc) these are all pretty standard lab techniques.
Development
Check the notes I made up for development they may help you a bit 👍
The harder bio questions expect you to not know everything but using what you do know and a bit of intelligence to make an educated guess.
Secondary oocyte released from developed Graafian follicle at ovulation.
Oocyte surrounded by same layer of granulose cells as it was within the follical
-beween the granulose cells and the eggs plasma membrane is the glycoprotein layer called the zona pellucida.
Sperm is capped by an organelle called the acrosome, which contains glycoprotein digesting enzymes.
Effects of sperm upon entering egg
1)stimulates the egg nucleus to complete second meiotic division, producing two egg nuclei, one is extruded from the egg as a second polar body. This leaves a single haploid egg nucleus.
2)Sperm penetration triggers movement in egg cytoplasm which establish the bilateral symmetry of developed animals.
3)Activation is characterized by a sharp increase in protein synthesis and an increase of metabolic activity.
Cell Cleavage-rapid divisions with no significant increase in cell size so nucleus to cytoplasma ratio increase.
When zygote reaches ~32 cells becomes a solid ball of cells know as a morula. Each individual cell of the morula is known as a blastomere.
Bastomeres continue to divide and secrete a fluid into the center of the morula, when a hollow ball of 500-2000 cells exist its known as a blastula with a fluid filled center known as a blastocoel.
The pattern of cleavage division is influenced by the presence and location of yolk.
-when egg contains little or no yoke cleave occurs throughout the whole egg as holoblastic cleavage. This pattern is still seen in ancenstors of the vertebrates such as echinoderms, tunicates, lancelets, and mammals. This holoblastic cleavage results in formation of a symmetrical blastula.
Even tho cleavage is not impeded by yolk in mammalian eggs, the inner cell mass is concentrated at one pole. Opposite this inner cell mass (across the blastula) on the outside is what is called the trophoblast.
-part of the trophoblast enters the maternal endometrium and contributes to the placenta.
-part of placenta is composed from the trophoblast and another part is composed of modified endometrial tissue called the deciduas basalis of the mothers uterus.
In mammals blastula is called a blastocyst.
-blastocyst cells are pluripotient which means they can turn into ANY cell in the body (aka stem cells), they CANNOT develop into a complete organism. The cells from the morula are totipotient, which means 1 cell can develop into a new organism.
GASTRULATION
Actin filament contractions that change the shape of the migrating cells cause an invagination of the blasula tissue. Pattern of gastrulation amoung vertebrate groups depend on the shape of the blastulas produced during cleavage.
The invagination produced is called the archenteron. This will later become the digestive gut (these cells that make up the archenteron will become endoderm dervived. The open pore to the archenteron is called the blastopore. In deuterosomes (thats us and our friends echinodermata, hemichordate, and xenoturbellida) the blastopore becomes the anus. In protosomes however, the blastopore becomes the mouth. (I always think dodo since deudo sounds like dodo and it becomes the anus you get it, ok ok Ill get back to work jeez).
So anyway gastrulation officially begins as the surface of the blastula invaginates into the blastocoel.
Two layer gastrula
-composed of the ectoderm (cells outside) and the endoderm (cells that formed the archenteron.
Three layer gastrula
-third layer (mesoderm) forms between the ectoderm cells and endoderm cells. Remember you build your muscle last!!! In mammals gastrulation requires the involution of surface cells into a blastopore or primitive streak, and the mesoderm is dervived from some of these involuted cells.
In mammalian gastrulation, the amniotic cavity forms within the inner cell mass and its base. Layers of ectoderm and endoderm differentiate, a primitive streak develops through which cells destined to become mesoderm migrate into the interior. The trophoblast moves away from the embryo and begins to play a role in forming the placenta.
NEURULATION
Two morphological features found only in chordates, the notochord and the hollow dorsal nerve cord, the development of the dorsal nerve cord is called neurulation.
The notochord is first visible soon after gastrulation is complete. It is a flexible rod located along the dorsal midline in the embryos of all chordates although in us its function is later replaced by the vertebral column when it developes from mesoderm.
After the notochord is in place a layer of ectodermal cells above the notochord invaginates forming a long crease called the neural groove, down the long axis of the embryo.
Once the edges of the neural groove fuse together it becomes a long hollow cylinder called the neural tube.
-so notochord comes first then the neural groove then neural tube.
-the neural tube later differentiates into the spinal cord and brain
In vertebrates just before the neural tube closes its edges pinch off to form a small strip of cells called the neural crest which becomes incorporated into the roof of the neural tube. Its a key point of evolution between veterbrates and lesser chordates.
Ectodermal cells associated with the neural crest cells thicken into placodes, which develop into parts of the sense organs in the head.
Neural crest cells migrate toward notochord and become sensory neurons in the dorsal root ganglia, others become specialized as Schwann cells which insulate nerve fibers, others form the autonomic ganglia and the adrenal medulla, this is why cells that secrete adrenaline from the adrenal glands is so similar to the neurotransmitter nor-adrenaline from the sympathetic neurons, both these nerves and glands arise from the neural crest cells.
