Hi
Is anybody able to give a clear time of when bipedalism evolved? I was trying to look it up before the SAC a few weeks ago, and couldn't get an exact time period, but I thought I should definitely clarify this before the exam!
There isn't really a clear answer to this. It's very unlikely that you'll have to give a date on the SAC (actually I seem to remember that VCAA said somewhere what source they used for their dates - I'll go see if I can find it). If you get a question on this it'll probably either be multiple choice with only one option being possible, or it'll be a question where you have to identify the correct order that traits evolved in or something like that. I've dumped a bit of info from
here below - really it just shows that we don't know the answer to that though (If I find VCAA's source I'll let you know though!)
In more recent decades, anthropologists have determined that bipedalism has very ancient roots. In 2001, a group of French paleoanthropologists unearthed the seven-million-year-old Sahelanthropus tchadensis in Chad. Known only from a skull and teeth, Sahelanthropus‘ status as an upright walker is based solely on the placement of its foramen magnum, and many anthropologists remain skeptical about the species’ form of locomotion. In 2000, paleoanthropologists working in Kenya found the teeth and two thigh bones of the six-million-year-old Orrorin tugenensis. The shape of the thigh bones confirms Orrorin was bipedal. The earliest hominid with the most extensive evidence for bipedalism is the 4.4-million-year-old Ardipithecus ramidus. In 2009, researchers announced the results of more than 15 years of analysis of the species and introduced the world to a nearly complete skeleton called Ardi.
Although the earliest hominids were capable of upright walking, they probably didn’t get around exactly as we do today. They retained primitive features—such as long, curved fingers and toes as well as longer arms and shorter legs—that indicate they spent time in trees. It’s not until the emergence of H. erectus 1.89 million years ago that hominids grew tall, evolved long legs and became completely terrestrial creatures.
I’ve got a few Qns
1. Are complement proteins not effective against viruses? If so, why
2. Why is the immune response faster in a secondary exposure than a primary exposure?
3. Do autocrine hormones only affect the cell the cell that secretes them or the same type of cell
1.No they're not really effective against virus'.
The three things they do are:
1. Opsonize pathogens: They stick on the surface of pathogens in the extracellular environment and make it easier for leukocytes to recognise them.
2. Attract phagocytes to the area: They are chemoattractants, phagocytes will be drawn to the source of complement proteins.
3. Create pores in bacterial membranes. Form a Membrane Attack Complex (MAC): They create a hole in the bacteria, causing fluid from the extracellular environment to rush in and rupture the bacteria.
So they're only really effective against extracellular pathogens (especially bacteria).
2.This is due to memory cells. During a primary exposure there's one naive immune cell that will recognise the antigen. During a secondary immune response there's lots of memory cells floating around that will recognise the antigen. This means that the antigen will be recognised faster and therefore response will be faster and larger.
3.Only the cell releasing them. It's not only hormones by the way - cytokines can also have autocrine signalling. Also something can be both autocrine and paracrine so it doesn't necessarily just affect it, but only the part where it effects itself is called autocrine.
@sweetcheeks, sorry for answering them anyway but i'd already typed it up before you posted that haha