Edexcel IAL Biology unit 4, June-8-2015 !

What are the roles of T-Killer cells. B effector cells and B memory cells in Immune response??

T-killer cells
kills any cell with foreign antigens, including infected body cells

B-effector cells
produce and secrete large amounts of antibodies which assist in the destruction of microbes by binding to them and making them easier targets for phagocytes

B-memory cells
differentiate from activated B cells
These cells are able to live for a long time, and can respond quickly following a second exposure to the same antigen
involved in the secondary immune response

(reply to this if you want more details)

Can someone help me in learning the SPECIATION section please?

Can someone please tell me the role of Memory cells in details?

When a pathogen enters the body for the fist time the antigens on its surface activate the immune system. This is called the primary response. The primary response is slow because there aren't many B cells that can make the antibody needed to bind to the antigen. Eventually, the body will produce enough of the right antibody to overcome the infection. Meanwhile, the infected person will show symptoms of the disease.

Now, the interesting part comes .....

After being exposed to an antigen, both T and B cells produce memory cells. These memory cells remain in the body for a long time. Memory T cells remember the specific antigen and will recognise it a second time round. Memory B cells record the specific antibodies needed to bind to the antigen. The person is now immune - their immune system has the ability to respond quickly to a second infection.

If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response. This is called the secondary immune response. Memory B cells divide into plasma cells that produce the right antibody to the antigen. Memory T cells divide into the correct type of T cells to kill the cells carrying the antigen. The secondary response often gets rid of the pathogen before you begin to show any symptoms.

Speciation

Speciation is the development of new species. It occurs when populations of the same species become reproductively isolated, where changes in allele frequency cause changes in phenotype that mean they can no longer breed together to produce fertile offspring.

Reproductive Isolation could occur in many ways

Here are some of the ways changes in phenotype prevent two populations from successfully breeding together:
1. Seasonal changes- individuals from the same population develop different flowering or mating seasons, or become sexually active at different times of the year.
2. Mechanical changes- changes in genitalia prevents successful mating.
3. Behavioural changes- a group of individuals develop courtship rituals that aren't attractive to the main population.

A population could become reproductively isolated due to geographical isolation or random mutations.

Random mutations

Random mutations could occur with in a population, resulting in the changes mentioned above, preventing members of that population breeding with other members of the species.

Geographical isolation

Geographical isolation happens when a physical barrier ( floods, volcanic eruptions and earthquakes ) divides a population of a species. Conditions on either side of the barrier will be slightly different e.g. Different climate. Because the environment is different on each side, different characteristics will become more common due to natural selection.

Different characteristics will be advantageous on each side, therefore the allele frequencies will change in each population e.g. if one allele is more advantageous on one side of the barrier, the frequency of the allele on that side will increase. Mutations will take place independently in each population, also changing the allele frequencies. The changes in allele frequencies will lead to changes in phenotype frequencies, where the advantageous characteristics will become more common on that side.

Eventually, individuals from different populations will have changed so much that they wont be able to breed with one another to produce fertile offspring- they'll have become reproductively isolated. The two groups will have become separate species.

Thank you sooo much!!!

Guys please can someone give me a good answer for succession on a dead body? Like I don't know how to write it properly, please help me Thank you so much!

guys! how was it??
what did everyone write for the first question how light is used?

I wrote about photophosphorylation and photolysis

Yeah likewise thankyou