Human hormone levels were measured over the course of a month. A spike in LH levels was followed by a decline in estrogen levels. This individual is most likely
A.
a female and she is pregnant
B.
a male and the uterine lining is building
C.
a female and this is an example of negative feedback
D.
a male and sperm is being released from the testes
2.
Which of the following correctly describes variation?
A.
Variation is added in mitosis and asexual reproduction.
B.
Variation is added in meiosis and sexual reproduction.
C.
Variation is added by meiosis and asexual reproduction.
D.
Variation is added by mitosis and sexual reproduction.
3.
The reproductive system of the human male produces gametes and
A.
transfers gametes to the female for internal fertilization
B.
produces enzymes that prevent fertilization
C.
releases hormones involved in external fertilization
D.
provides an area for fertilization
4.
Base your answer to the question on the information in the reading passage and on your knowledge of biology.
Stem Cells
If skin is cut, the wound closes within days. If a leg is broken, the fracture will usually mend if the bone is set correctly. Almost all human tissue can repair itself to some extent. Much of this repair is due to the activity of stem cells. These cells resemble those of a developing embryo in their ability to reproduce repeatedly, forming exact copies of themselves. They may also form many other different kinds of cells. Stem cells in bone marrow offer a dramatic example. They can give rise to all of the structures in the blood: red blood cells, platelets, and various types of white blood cells. Other stem cells may produce the various components of the skin, liver, or intestinal lining.
The brain of an adult human can sometimes compensate for damage by making new connections among surviving nerve cells (neurons). For many years, most biologists believed that the brain could not repair itself because it lacked stem cells that would produce new neurons. A recent discovery, however, indicates that a mature human brain does produce neurons routinely at one site, the hippocampus, an area important to memory and learning. This discovery raises the prospect that stem cells that make new neurons in one part of the brain might be found in other areas. If investigators can learn how to cause existing stem cells to produce useful numbers of functional nerve cells, it might be possible to correct a number of disorders involving damage to neurons such as Alzheimer's disease, Parkinson's disease, stroke, and brain injuries.
Stem cells may be similar to the cells of a developing embryo because both cell types can
A.
produce only one type of cell
B.
help the brain to learn and remember things
C.
divide and differentiate
D.
cause Alzheimer's and Parkinson's diseases
5.
All cells in an embryo have the same DNA. However, the embryonic cells form organs such as the brain and the kidneys which have very different structures and functions. These differences are the result of
A.
having two types of cells, one type from each parent
B.
rapid mitosis causing mutations in embryo cells
C.
new combinations of cells resulting from meiosis
D.
certain genes being expressed in some cells and not in others