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Tutor profile: Angela K.

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Angela K.
Passion for Biology, Fan of R, Coach and Cheerleader for Writing
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Questions

Subject: R Programming

TutorMe
Question:

What is wrong with this ggplot2 code? I want to make a bar graph but I can't. ggplot(data=mpg)+ geom_bar(aes(x=displ,y=hwy))

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Angela K.
Answer:

When this code runs, it will produce the error: "Error: stat_count() can only have an x or y aesthetic." This is because geom_bar automatically uses the count statistic to determine the height of the bar. To fix this, we would do this instead: ggplot(data=mpg)+ geom_bar(aes(x=displ,y=hwy),stat="identity") The statement : stat="identity" tells R that we want the height of our bar to be the variable assigned to y.

Subject: Environmental Science

TutorMe
Question:

You would like to quantify the abundance of each of 3 grass species in a field at the end of the summer. Which sampling or estimation methods should you use? What factors should you take into consideration?

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Angela K.
Answer:

The harvest method will help you estimate biomass per meter squared. To do this, you will create a quadrat (frame of a predetermined area), randomly placed throughout the field. Harvest separate samples of each species, then dry them in an oven to get the plant's dry mass per meter squared. This method gives raw aboveground biomass per meter squared, but it is very disruptive to the ecosystem and time-consuming for the researchers. If you want to sample plants with a non-destructive method, density and frequency would be better; density is the count of individual plants of each species in a quadrat, and frequency is the percentage of quadrats that have the species of interest. Percent cover is an estimation of the percentage of each quadrat's canopy (leaves, stems) that is a particular species. This method is nondestructive and allows for an estimation of each species' relative importance in the area, but estimation of cover can be subjective.

Subject: Biology

TutorMe
Question:

Compare and contrast lysosomes and peroxisomes. How does their abundance and function differ between animals and plants? In what organs or tissue types would you expect to find them?

Inactive
Angela K.
Answer:

Lysosomes and peroxisomes are both single membrane-bound organelles that contain enzymes, and often break down materials inside the cell. Lysosomes are more common in animals than in plants, while peroxisomes are predominant in plants. Lysosomes contain hydrolytic enzymes, peroxisomes contain oxidative enzymes. Hydrolytic enzymes catalyze hydrolysis, the breakdown of a larger molecule with water. With hydrolytic enzymes, lysosomes perform functions like digestion of food taken in by the cell, recycling of old organelles, catalyzing apoptosis, or destroying pathogens. White blood cells have many active lysosomes as they fight disease. Peroxisomes contain oxidative enzymes (catalyze oxidation reactions; the loss of electrons), and they perform functions like catalyzing the conversion of harmful hydrogen peroxide to water in animals. They also break down fatty acids. In mammals, peroxisomes are common in liver cells because fats are made, recycled, and stored there. In plants, peroxisomes help chloroplasts with photorespiration. Therefore, plants would be expected to have lots of peroxisomes in leaf cells.

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