While you may have been told you need zero science knowledge to answer any ACT Science questions, this is NOT true. There are typically around four questions per test that you cannot answer without previous background knowledge. That's the difference between a 31 and a 36 on the Science section!
In this article, I will give an overview of the 18 topics that will NOT be explained in the ACT Science passages that the ACT expects you to know. The ACT assumes you know these topics from school and science class. To gather this info, I dissected dozens of previous ACT Science test sections to find the concepts you have to know. As far as we can tell, we're the only ones who have taken the time to research this.
If you've gotten bad grades in science classes in school, this article will give you a refresher on the only concepts you need to know.
Reminder: If you haven't already, check out our Ultimate Study Guide for ACT Science. It contains dozens of ACT Science guides going into every question type tested, strategies to tackle the questions, and how you should be organizing your prep to raise your score.
In order to best answer this question of what science you actually need to know for the ACT Science section, I am going to start with what topics the ACT says the Science section covers. According to the ACT makers, "The content of the Science Test includes biology, chemistry, physics, and the Earth/space sciences (for example, geology, astronomy, and meteorology)."
So much information.
No, and even the ACT makers admit that "Advanced knowledge in these subjects is not required, but background knowledge acquired in general, introductory science courses is needed to answer some of the questions. The test emphasizes scientific reasoning skills over recall of scientific content, skill in mathematics, or reading ability."
In other words, it's more important that you understand the principles behind scientific thought and logical reasoning than the science itself!
In the ACT Science passages, they give you the majority of the information you need to answer the questions. They explain most of the terms within the passage. See for yourself in this example passage, from a free ACT online practice test:
You can see in this passage they give you definitions for most of the terms: refracted, seismograph, focus, shadowzone, the types of seismic waves, the difference between p and s waves. Because of that, you won't have to know tons about geology to answer this question.
Very little. Most of the questions can be answered using your knowledge of reading graphs and charts. Check out our article on the types of ACT Science Passages for more information about this strategy. For the questions that you can't answer with the visuals, you can usually figure them out by reading the passage.
However, there will be times you can't find the answer in the passage—and that's what we're discussing in this article.
As I mentioned earlier, there are typically around four questions per test that you cannot answer without previous knowledge. In my study of old ACT Science sections, I have found a total of 18 topics spanning biology, chemistry, physics, and math (yes, math) that you need to know. Here is the overview. I'll go into more depth on each topic below.
The basic overviews that I present below should be all you need to know for the test, but I provide links to more in-depth explanations if you would like to do more reading.
In our first topic, Cell Biology, you'll also see the first example of a question that you wouldn't be able to answer without prior knowledge, even after reading the passage.
You need to know certain cell organelles (parts of cells), their functions, and whether they are found in animal or plant cells.
Animal Cell Structure
Lysosomes hold enzymes. Lysosomes digest food or break down the cell when it dies.
Mitochondria are organelles that act like a digestive system, which takes in nutrients, breaks them down, and creates energy-rich molecules (ATP) for the cell.
The cell nucleus acts as the brain of the cell. It contains the cell's DNA, or the genetic information, from which proteins are made (see Topic 2, coming up next). It also helps control eating, movement, and reproduction.
Chloroplasts only exist in plant cells and assist in the process of photosynthesis, converting light into energy (which only plants do, not animals).
The cell membrane holds all of the pieces of the cell and serves as the barrier between the cell and other cells.
Below is a sample question where you need an understanding of these organelles to select the correct answer. The chemical reaction mentioned in the passage was photosynthesis.
Knowing that photosynthesis happens in chloroplasts, I can correctly choose answer F.
But nowhere in the passage was it said that chloroplasts are where photosynthesis happens! This is a fact you had to know before the test.
While there are many other organelles, the ones listed above and ribosomes (which I will cover in the next topic) should be the only organelles you need to know for the test. Also, you should not need to know any other information about these organelles. If you would like to do more reading on cell biology, click here.
DNA contains the genetic information needed for making proteins (protein synthesis). Protein synthesis involves DNA, RNA, ribosomes, and proteins. DNA acts as the blueprint for protein production.
The Process of Protein Synthesis
Messenger RNA (known as mRNA) makes a copy of the sequence of DNA of a specific gene. This process is known as transcription and happens in the nucleus.
Once the mRNA is made, it leaves the nucleus and enters the cytosol of the cell. Ribosomes use mRNA as a guide to make protein of the same amino acid sequence as the original DNA. The process of producing protein from the mRNA is referred to as translation. So, the process of protein synthesis consists of two steps: DNA to mRNA transcription and mRNA to protein translation.
Natural selection is also known as 'survival of the fittest.' In a specific environment, traits that allow organisms to reproduce more effectively will become more common, and traits that reduce reproductive success will become less common. A classic example of this is the change in peppered moth color during the industrial revolution.
In England, the burning of coal during the industrial changed tree bark from light brown to dark brown in color. The peppered moth blended in perfectly and was hidden from predators. However, once clean air acts were passed, the trees quickly returned to a lighter color, making the dark moths easily visible to predators. Meanwhile, lighter colored moths were still hidden from view and survived to lay eggs. Thus, because of natural selection, over the course of years, the moths turned from dark to light in color! Click here for more information on evolution by natural selection.
The Strong Survive, the Weak Hang On
Greenhouse gases are gases that trap heat in the atmosphere. Sunlight can pass through them as it goes towards the earth, but greenhouse gases prevent the heat sunlight produces at Earth's surface from leaving the atmosphere. This mean the heat stays close to Earth, increasing the planet's temperature. Human activity has caused the amount of greenhouse gases in the atmosphere to increase in recent decades, and they are a major contributor to climate change.
There are six main greenhouse gases:
Look at this sample question:
The correct answer is is J because methane (CH4), as a greenhouse gas, absorbs heat not when it enters the earth from space, but when it comes up from the earth. This causes warming.
Photosynthesis is the process where plants capture sunlight to make food for themselves. During photosynthesis, the plant takes in carbon dioxide, water, and energy, and it produces glucose (which it consumes to live) and oxygen (which humans and other animals breathe). You don't need to memorize the formula for photosynthesis, but you may see it on the ACT, and it's useful to understand it ahead of time. This is what it looks like:
Respiration is basically the inverse of photosynthesis. Respiration is when cells break down molecules into a type of energy they can use. While only plants go through photosynthesis, both plants and animals go through respiration. In respiration, glucose and oxygen are converted into carbon dioxide, water, and ATP (a chemical that provides energy to cells). Here's the formula:
Taxonomy is the science of naming and classifying all organisms. It allows scientists to see how closely different organisms are related and what characteristics they share. Taxonomic rank is the seven levels organisms are classified in. Know the seven taxonomic levels which are (from broadest to most specific):
