Module 2 Flashcards
Cambrian Explosion
Huge diversification of animal life that occurred 540 million years ago
- rise of sea-levels caused erosion of minerals, including calcium and phosphate
- the increased presence of dissolved calcium allowed shell-like forms to develop
- the occurrence of dissolved phosphate created a supply of nutrients
- animals therefore had more raw materials too develop shells and metabolise for energy
- rising sea levels also created more habitats for marine life
Complex food webs
the diversification of animals led to more complex food webs
- this was also facilitated by the development of guts and bilateralism
-bilateral animals with guts were able to prey upon larger animals
Domain etc.
Domain –> Kingdom –> Phylum –> Class –> Order –> Family –> Genus –> Species
Gamete formation
germ cells divide by mitosis and grow in size to create primary oocytes
- primary oocytes are diploid (paired chromosomes)
to create gametes, the reproductive parent cell undergoes meiosis I and II
- meiosis I creates two daughter cells, each with half the amount of chromosomes
- one daughter cell is the larger secondary oocyte containing most of the cell cytoplasm
- the other daughter cell is smaller and forms the polar lobe near the cell membrane
- meiosis II occurs whereby the DNA does not replicate itself
- the secondary oocyte goes on to become the mature haploid oocyte wth a single copy of each chromosome
Germ cells
produce reproductive material
Fertilisation in most marine invertebrates
occurs externally
- animals release a chemotactic factor to attract sperm from the same species
- sperm arrives and attaches themselves to the vitelina envelope outside the egg
- a fertilisation cone develops, allowing the sperm head to be drawn in and blocks other sperms
- once the sperm and egg membranes fuse, the sperm’s tail disintegrates
- the sperm’s nuclear envelope disintegrates, allowing sperm chromatin to expand from a highly condensed state to form a pronucleus
- the sperm pronucleus migrates towards the egg pronucleus
- fusion occurs, forming a diploid zygote
- once fertilised, there is a burst of DNA and protein synthesis
- the process of cleavage begins
Cleavage
the division of the large fertilised zygote to form multiple cells
- beginning of multicellularity
- occurs by mitosis
Cleavage process
prior to beginning, an animal-vegetal axis becomes visible on the embryo
- the yolk collects at one end, known as the vegetal pole
- the distribution of the yolk and cytoplasm in the daughter cells depends on the vegetal-animal axis, which ranges among phyla
- cell division occurs but the mass does not grow in size
- results in a blastula
Gastrulation
early developmental process
an embryo transforms from a one-dimensional layer of epithelial cells and reorganises into a multilayered and multidimensional structure of the gastrula
Diploblastic
two germ layers and radial symmetry
Triploblastic
additional mesoderm between the two germ layers
Differentiation
the way in which cells of the two or three germ layers alter to create specialised tissues
- cytoplasmic specification: partitioning during cleavage
- conditional specification
Bilateria
major grouping of the Animalia which have a symmetrical body plan around the anterior-posterior axis
- tripoblasts
- nephrozoa
Protostomia
Lophotrochozoa
- includes segmented worms and molluscs
- lophophore: horse-shoe shaped wool of tentacles
- contain a trochophore free-swimming larvae which has a band of cilia around the centre wheel and an apical tuft
- contain spiral cleavage and mosaic development
Ecdysozoa
do not have spiral cleavage
shed their cuticle via ecdysis
cleavage can be radial or superficial
