Somatic cancer cells often are unstable and divide inappropriately (divide when they should not be dividing). In addition such cells often contain losses of some chromosomes and extra copies of other chromosomes. Defects in which of the following may be partially responsible for the aberrant behavior of cancer cells? (Select all that apply.)
A)spindle-assembly checkpoint
B)G1/S checkpoint
C)homologous chromosome pairing
D)crossing over

G1/S checkpoint

Explanation:

G1/S checkpoint is one of the points in the cell cycle, between growth phase 1 and DNA synthesis phase, where a cell that has been damaged is sensed by DNA repair enzymes and further degraded by apoptosis. In cancer cells, there is mutation in these DNA repair enzymes and thus nothing to correct the cells from dividing even when damaged and thus there is no arrest of division and cells continue dividing

A ( spindle assembly checkpoint)

B ( G1/S Checkpoint)

Explanation:

Transitions between phases of the cell cycle are controlled by checkpoints.

This process is regulated by cyclins, cyclin-dependent kinases and tumor suppressors.

A defect at any of these internal checkpoints would result in mutation that would lead to the formation of abnormal cells.

question#1

ans:

cell is the basic unit of organization of all living things. cells are often called the building block of life and it is the smallest unit of life. the study of cell is called cell biology. cell consists of cytoplasm enclosed within membrane, which contain bio-molecules such as proteins and nucleic acid.

two third of cell is water, which means that two-third of your whole body is water. the rest is the mixture of molecules, mainly proteins, lipids and carbohydrates.

question#2

ans:

organ:

an organ is a group of tissues specialized to form a functional unit. an example is the heart in animals.

organ system:

an organ system is a group of several organs whose functions are synchronized to release an effective action in a living organism. an example is digestive system.

question#3

different systems perform different function at tissue level. for example, the respiratory system facilitates breathing. in the alveoli tissue of the lungs, the exchange of oxygen and carbon dioxide molecules between the air and the bloodstream occurs by passive transport, so that oxygen is taken in and carbon dioxide and water are removed. different systems of the body carry out different functions. for example, your digestive system is responsible for taking in and processing food, while your respiratory system working with your circulatory system is responsible for taking up oxygen and getting rid of carbon dioxide.

question#4

different systems perform different function at tissue level. for example, the respiratory system facilitates breathing. in the alveoli tissue of the lungs, the exchange of oxygen and carbon dioxide molecules between the air and the bloodstream occurs by passive transport, so that oxygen is taken in and carbon dioxide and water are removed. different systems of the body carry out different functions. for example, your digestive system is responsible for taking in and processing food, while your respiratory system—working with your circulatory system is responsible for taking up oxygen and getting rid of carbon dioxide.

question#5

our body works because of the interactions that happen between organs and organ systems.  

for example:  

the heart to regulate blood flow throughout the body. the blood carries oxygen and nutrients to the cells and carries carbon dioxide and waste away from the cells. body systems work together in maintaining a constant internal environment. when this balance is disrupted, the body systems may not function properly, and human health can suffer.   you start to feel bad.