Oxygen gas is essential to life as we know it. Earth's atmosphere contains approximately $21 \%$ oxygen gas. Would a higher concentration of atmospheric oxygen gas be desirable? Explain.

Which best explains why a description of weather can affect the tone of a piece of writing?

What is the major source of free oxygen in Earth's atmosphere?

What is the major source of free oxygen in Earth's atmosphere?

In a eukaryotic cell, DNA is found in the _______.

Which of the following statements describes the nucleic acid in a eukaryotic cell?

A. Multiple, linear chromosomes

B. Wrapped around histones

C. Referred to as chromatin

D. Found in the nucleus, chloroplast, mitochondria

E. All of the above

What substances can and cannot diffuse through the lipid bilayer?

You are looking at a sample of epithelial tissue under a microscope. What would you look for to determine the type of epithelium you are viewing?

You observe a protist under a microscope. It moves by forming temporary bulges of the cytoplasm. What type of protist is it? Explain your answer.

With which cellular structure does the extracellular matrix interact:

A. cytoskeleton

B. nucleus

C. smooth endoplasmic reticulum

If the nucleolus were not able to carry out its function, what other cellular organelles would be affected?

The atmosphere has the highest concentration of which greenhouse gas? A. carbon dioxide B. carbon monoxide C. methane D. water vapor

What is a nucleolus, and what is its function?

Which statement best explains how atmospheric dust particles influence the water cycle?

(1) Dust particles are the main source of dissolved salts in the sea.

(2) Dust particles increase the capacity of the atmosphere to hold water vapor.

(3) Dust particles increase the amount of evaporation that takes place.

(4) Dust particles provide surfaces oon which water vapor can condense.