Question: Does penicillin prevent infection? Hypothesis: If the medicine prevents infection, then the medicine will prevent the growth of bacteria that cause infection.
Experiment: Leo placed two circles of paper in a Petri dish (something used for growing bacteria). One circle of paper was soaked in penicillin. The other had nothing on it. He poured a liquid filled with bacteria into the Petri dish. Both circles of paper were placed in the Petri dish about 3cm apart.
At the end of the experiment, a circle with a radius of 2cm formed around the circle of paper soaked in penicillin. There were no bacteria growing in the 2cm circle. No change had occurred around the other circle of paper. The bacteria were growing well.
A. What was the independent variable?
B. What was the dependent variable?
C. What were the controlled variables?

a community that experiences major changes undergoes progress

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.

the answer is a) cell division.

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