Structure and Function of Animals: Introduction (01:39)
All animals require oxygen and nutrients to live, and they need to move and eliminate waste. The first animals lived in the oceans; some gradually evolved to live on land. Land animals retain some qualities of marine animals.
Form Follows Function: Land to Water (02:17)
Animal structure is related to function. To adapt to land, the structures of marine animals evolved to serve new functions. Plants and insects were the first life forms on land, then amphibians adapted to live on land and water.
Size Limitations in Animals (01:27)
Reptiles grew large due to an abundance of food. When the atmosphere changed, and Earth became cooler, large reptiles eventually went extinct.
Thermoregulation and Homeostasis (01:28)
Animals keep their body temperature within a safe range close to their ideal level. Animals regulate blood, sleep, and digestion, among other things.
Animal Reproduction (02:43)
Sexual reproduction involves fusion of two gametes through fertilization, either internal or external. Asexual reproduction involves one parent and requires no fertilization. Most animals reproduce sexually, but some reproduce in both ways.
Animal Development (01:30)
The fertilized egg divides to produce multiple cells, which become blastocysts. After moving into the uterus, this becomes an embryo made of three cell layers. During organogenesis, the organs develop.
Viral Structure and Replication (01:56)
Viruses require a host cell to survive, infecting and destroying cells to reproduce. Classified by nucleic acids, viruses have double or single-stranded DNA or double or single-stranded RNA.
Double-Stranded DNA Virus (02:22)
Herpesvirus contains double-stranded DNA enclosed by a protein capsid, and surrounded by tegument, which holds viral protein. A herpesvirus binds with the plasma membrane of a cell, injecting tegument and capsid. Viral proteins force the cell to replicate the viral DNA and transcribe it onto mRnA, which travels to ribosomes to be translated; new virus capsids rupture the cell.
Single-Stranded DNA Virus (01:23)
Parvovirus B19 contains a single-strand of chromosome in a capsid, which it injects into a cell. After replication and transcription, ribosomes translate mRNA into proteins, which become new capsids. Single-stranded viruses make far fewer proteins than double-stranded viruses.
RNA Viruses (01:29)
Single-stranded RNA viruses are positive or negative sense. Ribosomes can directly translate positive sense viruses into proteins, while negative sense viruses require a polymerase. Double-stranded RNA does not involve the nucleus in the replication and translation process.
The retrovirus HIV codes for reverse transcriptase, which makes a DNA copy from an RNA template. The virus transports the DNA copy to the cell nucleus where the viral DNA mixes with the cell chromosomes.
Prions contain no nucleic acids, only protein. The protein is folded in an unusual shape, and it passes this shape to other proteins it encounters.
Credits: Organisms and Populations (00:16)
Credits: Organisms and Populations
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