Barnacles are sessile filter feeders but unlike bivalves they have internal fertilization. How do they solve this problem?
A. The filter sperm from the water column.
B. They get fertilized during free living larval stages.
C. They are only capable of asexual reproduction.
D. They are hemaphrodites with especially long penises.
D. They are hemaphrodites with especially long penises.
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Why haven't humans evolved a resistance to the common cold?
A) Colds are effectively killed by antibiotics, so there's no need. B) Cold viruses haven't been in existence long enough to exert selective pressure. C) Colds are not serious enough to remove nonresistant variants from the population. D) We could evolve resistance if we stopped taking so many over-the-counter medications for colds.
Data were collected from the heterocysts of a nitrogen-fixing cyanobacterium inhabiting equatorial ponds. Study the following graph and choose the most likely explanation for the shape of the curve
A) Enough oxygen (O2 ) enters heterocysts during hours of peak photosynthesis to have a somewhat-inhibitory effect on nitrogen fixation. B) Atmospheric nitrogen (N2 ) levels increase at night because plants are no longer metabolizing this gas, so they are not absorbing this gas through their stomata. C) Heterocyst walls become less permeable to nitrogen (N2 ) influx during darkness. D) The amount of fixed nitrogen that is dissolved in the pond water in which the cyanobacteria are growing peaks at the close of the photosynthetic day (1800 hours).
When does the human embryo implant in the wall of the uterus?
A) within a few hours of fertilization
B) about a day after conception
C) about a week after conception
D) just after gastrulation
Which of the following statements regarding the hepatitis D virus (HDV) is MOST correct?
A) The typical incubation period for HDV infection ranges from 180 to 360 days. B) The most common route of transmission of HDV is through sexual contact. C) Infection with HDV requires the host to be infected with the hepatitis B virus. D) If a documented exposure occurs, testing begins with the person who was exposed.