8 Key Concepts for AP Biology AP Exams Spring 2021
The Princeton Review
Hi, there!
I’m Rob Franek, Editor-in-Chief at The Princeton Review, and today we’re sharing the top
8 AP Biology concepts you’ll need to master before exam day.
#1 – The Chemistry of Life: This will constitute between 8 and 11% of the exam.
As you might expect, the AP Biology exam will test your understanding of the chemical basis
of life.
This includes understanding essential elements and their subatomic particles – protons,
neutrons, and electrons – and the ways in which they combine to form chemical compounds
and create chemical reactions.
You should also know about hydrogen bonding and the versatile properties of water, such
as cohesion and adhesion, surface tension, and water’s high heat capacity.
You’re very likely to see a question on pH.
So, be sure to understand the relationship between hydronium ion concentration and the
pH scale, as well as how reactions are influenced by whether the solution they occur in is acidic,
basic, or neutral.
It’s also essential to understand the 4 important organic macromolecules in biology
– carbohydrates, proteins, lipids, and nucleic acids.
All of these macromolecules are polymers, which are chains of building blocks called
monomers, so it’s also crucial that you understand in detail how monomers bond together
to form polymers.
Next up:
#2 – Cell Structure and Function: This will account for somewhere between 10 and 13% of
the exam.
As you may already know, all living things are composed of cells.
Cells are the smallest unit of living organisms that can carry out the activities necessary
for life.
In preparation for the exam, you should understand the 2 distinct types of cells – prokaryotic
cells and eukaryotic cells.
Prokaryotes, like bacteria, do not have a nucleus or membrane-bound organelles, while
eukaryotes do have a nucleus and membrane-bound organelles.
Be sure to study the function and structure of both cell types.
It’s also important to understand the vital role the membrane plays in controlling the
exchange of material with the cell’s external environment, so review the concepts of membrane
permeability and membrane transport.
And while you’re at it, be sure to review the different types of cellular transport,
including simple diffusion, facilitated transport, active transport, bulk flow, endocytosis,
dialysis, and exocytosis!
Moving on...
#3 – Cellular Energetics: This will account for somewhere between 12 and 16% of the exam.
In order to carry out the processes necessary for life, cells are able to release energy
when they need it and store it away when they don’t.
This is accomplished through bioenergetics, which is the study of how energy from the
sun is transformed into energy in living things.
So, you’ll need to master the concept of how cells capture and use energy, which includes
understanding how chemical reactions are catalyzed by enzymes and the ways in which the environment
plays a role in how enzymes perform their function.
You should also gain a deep understanding of photosynthesis, the process by which plants
use energy from sunlight to make sugar.
The College Board will also test you on cellular respiration, the process by which glucose
is oxidized to produce ATP.
There are five processes involved in cellular respiration: glycolysis, the formation of
acetyl coenzyme A via the PDC, fermentation, the Krebs cycle, and oxidative phosphorylation.
You should be well acquainted with each stage by test day!
And last but not least, you should know which processes are aerobic (require oxygen) or
anaerobic (do not require oxygen).
Glycolysis and fermentation are anaerobic, while the rest are aerobic.
Next up:
#4 – Cell Communication and Cell Cycle: This will account for somewhere between 10
and 15% of the exam.
Sometimes cells do not pass molecules through the membrane, but instead, they just pass
a message.
This is known as signal transduction, wherein a ligand binds to a receptor on the outside
of the cell and causes changes to the inside of the cell.
Common examples of this are ligand-gated ion channels, catalytic receptors, and G-Protein-coupled
receptors.
The exam will test your knowledge of how cells communicate with one another, so you’ll
need to fundamentally understand how cells generate and receive signals, coordinate mechanisms
for growth, and respond to environmental cues.
You also need to study the various phases of the cell cycle, which is divided into two
periods: interphase and mitosis.
This includes understanding the 3 stages of interphase: G1, G2, and S phase.
This also includes knowing the 4 stages of mitosis (or cellular division): prophase,
metaphase, anaphase, and telophase.
During prophase, the nuclear envelope disappears and chromosomes condense.
In metaphase, chromosomes align at the metaphase plate and mitotic spindles attach to kinetochores.
Next, in anaphase, chromosomes are pulled away from the center.
And finally, telophase terminates mitosis as the two new nuclei form.
You should know both periods of the cell cycle (interphase and mitosis) in detail by test
day!
Moving on to...
#5 – Heredity: This covers between 8 and 11% of the exam.
In its simplest form, genetics is the study of heredity.
It explains how certain characteristics are passed on from parents to children by genes,
which are found on chromosomes.
Every organism has a certain number of unique chromosomes.
For example, fruit flies have 4 chromosomes, dogs have 39 chromosomes, and humans have
23 chromosomes.
Much of what we know about genetics was discovered by the monk Gregor Mendel in the 19th century,
so expect to be tested on his findings and the fundamentals of genetics.
This means understanding the definition of traits, genes, diploid vs haploid cells, alleles,
and homozygous vs. heterozygous organisms – to name just a few!
There are also three important laws in Mendelian genetics: the Law of Dominance, the Law of
Segregation, and the Law of Independent Assortment.
You should know all three!
You should also review non-Mendelian genetics, which refers to a situation in which traits
do not follow (or violate) Mendel’s laws.
Examples include incomplete dominance, codominance, and polygenic inheritance.
Lastly, you should understand how chromosomes transmit genetic information from one generation
to the next through meiosis.
Meiosis involves two rounds of cell division – meiosis I and meiosis II.
You should know what takes place during meiosis I and meiosis II in detail and how the two
processes are different by exam day.
Pedigrees are a visual representation of a family’s ancestry and are commonly used
to depict the heredity of a specific trait or disease.
It will also be pertinent for the AP Biology exam to know how to read pedigrees and how
to solve pedigree-related FRQs.
Next up is...
#6 – Gene Expression and Regulation: This will constitute between 12 and 16% of the
AP Biology exam.
From the simplest single-celled organism to the largest mammal, all living things possess
an astonishing degree of organization as a result of their DNA.
DNA is the genetic material of the cell and as you prepare for the exam, it’s essential
that you understand its molecular structure.
This includes understanding the subunits of DNA called nucleotides and how each nucleotide
has a five-carbon sugar, a phosphate, and one of 4 different nitrogenous bases – adenine,
guanine, cytosine, or thymine.
Nucleotides can link up in a long chain to form a single strand of DNA and each DNA molecule
consists of two strands that wrap around each other to form a long, twisted double helix.
Next, it’s important to understand genome structure.
All the DNA in a cell is the genome.
It is divided up into chromosomes, which are divided up into genes that each encode a particular
genetic recipe.
Chromosomes contain the recipe for all the processes necessary for life and have the
ability to pass themselves and their information on to future generations, as seen in the process
of DNA replication.
Speaking of which, you should have an in-depth understanding of the steps involved in DNA
replication!
You should also understand transcription and translation.
Transcription occurs in the nucleus and involves making an RNA copy of a bit of DNA code and
it is completed in three phases: initiation, elongation, and termination.
Translation occurs in the cytoplasm and is the process by which the mRNA is translated
into a protein.
You may also come across questions related to the regulation of gene expression.
So, be sure to review the various times at which gene regulation can occur, as it can
occur pre-transcriptionally as well as post-transcriptionally or post-translationally.
Gene regulation is dynamic and can either increase or decrease gene expression, RNA
levels, and protein levels according to the needs of the cell.
You’ll also need to understand mutations and how they are formed as a result of changes
in the DNA or the mRNA.
Mutations can be small as seen in single nucleotide swaps or they can be large as seen when big
chunks or entire chromosomes are swapped, duplicated, or deleted.
And finally, you should be familiar with biotechnology, including recombinant DNA, polymerase chain
reaction (PCR), transformation of bacteria, and gel electrophoresis.
Next:
#7 – Natural Selection: This accounts for between 13 and 20% of the exam.
Evolution can be described as a change in a population over time.
Changes in the population occur through what is known as natural selection.
Much of what we now know about natural selection is through the work of 19th century British
naturalist, Charles Darwin, who sailed the world aiming to understand why similar animals
in different areas had different traits.
He placed his theory of natural selection in a book entitled On the Origin of Species.
And folks, you can bet that the AP exam will most certainly test your knowledge of his
observations and findings.
So, in nutshell, this is what you must know: (1) Each species produces more offspring than
can survive (2) Offspring compete with each other for limited resources (3) Organisms
in every population vary and (4) The offspring with the most favorable traits are most likely
to survive and reproduce.
You should also review the evidence for evolution, including fossils, biogeography, embryology,
comparative anatomy, molecular biology, and continuing evolution.
This evidence provides scientists with a good handle on how the evolution of certain species
occurred, which by the way, all comes down to common ancestry!
As such, you also should aim to understand how scientists use charts called phylogenetic
trees, or cladograms, to study relationships between organisms and track common ancestry.
You should also study the causes of evolution.
Evolution requires genetic variation and an environmental pressure that gives some individuals
an advantage, which permits survival and reproduction in a varied population.
There are also key causes of natural selection you should be familiar with including random
mutation, adaptation, sexual selection, and genetic drift.
And, finally, you need to understand the Hardy-Weinberg law, which says that a population will be
in genetic equilibrium and can be described by the equations p2 + 2pq + q2 = 1 and p +
q = 1 only if it meets these five conditions: (1) a large population, (2) no mutations,
(3) no immigration or emigration, (4) random mating, and (5) no natural selection.
And last but not least...
#8 – Ecology: This will be somewhere between 10 and 15% of the exam.
This last concept deals with how organisms interact with their environments.
For the AP Biology Exam, you’ll have to know a bit about different types of behavior,
including instinctual behavior, learned behavior, and social behaviors.
There are also plant-specific behaviors you should be familiar with known as tropisms,
of which there are 3 basic types – phototropism, gravitropism, and thigmotropism.
You’ll also need to understand the principles of ecology.
While biology spends a lot of time on individual organisms, ecology studies the interactions
between living things.
There is a hierarchy within the world of ecology, and each level – the biosphere, ecosystem,
community, and population – represents a different level of ecological interaction.
Let’s review them!
First, you should know that the largest unit is the biosphere.
It can be divided into large regions called biomes, which include tundra, taiga, temperate
deciduous forests, grasslands, deserts, and tropical rainforests.
Each biome can then be broken down into ecosystems, which are self-contained regions that include
both living and nonliving factors.
Ecosystems are made up of communities.
A community refers to a group of interacting plants and animals that show some degree of
interdependence.
Within a community, you should understand the levels of the food chain, which consists
of 3 main roles: (1) producers or autotrophs (2) consumers or heterotrophs and (3) decomposers.
Then there’s the smallest unit of ecology – the population.
Population ecology is the study of how populations change.
You should understand related concepts such population growth and carrying capacity, along
with knowing the exponential growth and logistic growth equations.
You should also have a general understanding of ecological succession, which refers to
the predictable procession of plant communities over decades or centuries.
And lastly, you should understand the ways in which humans have unfortunately disturbed
the existing ecological balance.The human impact on the planet includes, the greenhouse
effect, ozone depletion, acid rain, deforestation, and pollution, to name few.
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