All AP Biology courses have a laboratory component that gives students hands-on experience regarding some of the biology topics covered in class. Through these laboratory exercises, you can learn the scientific method, lab techniques, and problem-solving skills. There is not an official set of labs that must be completed, and AP teachers get to choose the ones for their classroom. This means that you will not be tested on memorizing specific protocols or data from the labs. However, all labs teach the same basic skills of critical thinking, developing hypotheses, judging results, making conclusions, adapting experiments, and understanding variables. So, those are the skills that you are expected to fully understand. The exam will likely present you with example experiments and you will need to make decisions and answer questions about them. There are 13 labs that are very popular to do in AP Biology classes, and these are the same labs that often come up on the AP test. We have given you short summaries of those 13 labs. This way, if you encounter a question about one of these labs, you will be one step ahead of students that have never even heard of it before.
This lab explores artificial selection—the process by which humans decide traits to enhance or diminish in other species by crossing individuals with the desired phenotype. You need to understand the basic principles of natural selection and how natural selection drives evolution, listed below:
Variation is present in any population.
Natural selection, or differential reproduction in a population, is a major mechanism in evolution.
Natural selection acts on phenotypic variations in populations. Some organisms will have traits that are more favorable to the environment and will survive to reproduce more than other individuals, causing the genetic makeup of the population to change over time.
This lab specifically deals with Wisconsin Fast Plants. In order to artificially select for certain traits, plants with the desired traits can be crossed, changing the genetic makeup of the population. For example, if you wanted to select for height, you could cross only the tallest plants with one another. The new population will have a higher mean height than the previous generation.
In order to understand everything you need for the AP Biology Exam, you need to be able to use the Hardy-Weinberg principles and equations to determine allele frequencies in a population. One way to study evolution is to study how the frequencies of alleles change from generation to generation:
Know how to calculate the allele and genotype frequencies using the two Hardy-Weinberg equations: p + q = 1 and p2 + 2pq + q2 = 1. Don’t forget: if the population obeys Hardy-Weinberg’s rules, these frequencies remain constant over time.
Review the discussion of the Hardy-Weinberg principle in this book. Know the five conditions of the Hardy-Weinberg equilibrium: (1) large population, (2) no mutations, (3) no immigration or emigration, (4) random mating, and (5) no natural selection.
Review natural selection and how it can lead to changes in the genetic makeup of a population.
This laboratory uses BLAST (Basic Local Alignment Search Tool), a database that allows you to input a DNA sequence for a gene to look for similar or identical sequences present in other species. In order to understand everything you need for the AP Exam you need to be able to do the following:
Look at a phylogenic tree, which is a way to visually represent evolutionary relatedness. Endpoints of each branch correspond to a specific species, and each junction on the tree represents a common ancestor. Species that are closer on a phylogenic tree are more closely related.
Understand BLAST scoring. Most phylogenic trees are constructed by examining nucleotide sequences; the more identical two species’ sequences are for a specific gene, the more closely related they are. BLAST is able to analyze different sequences to tell you how similar they are to one another based on a score. The higher the score, the closer the two sequences align.
This lab investigates the process of diffusion and osmosis in a semipermeable membrane as well as the effects of solute concentration and water potential on these processes.
What are the general concepts you really need to know?
Fortunately, this lab covers the same concepts about diffusion and osmosis that are discussed in this book. Just remember that osmosis is the movement of water across a semipermeable membrane, from a region of high water concentration to one of low water concentration, or from a hypotonic region (low solute concentration) to a hypertonic region (high solute concentration).
Be familiar with the concept of water potential, which is simply the free energy of water. It is a measure of the tendency of water to diffuse across a membrane. Water moves across a selectively permeable membrane from an area of higher water potential to an area of lower water potential.
Be familiar with the effects of water gain in animal and plant cells. In animals, the direction of osmosis depends on the concentration of solutes both inside and outside the cell. In plants, osmosis is also influenced by turgor pressure—the pressure that develops as water presses against a cell wall. If a plant cell loses water, the cell will shrink away from the cell wall and plasmolyze.
Another important concept to understand is the importance of surface area and volume in cells. There are several questions about each of these topics, but the necessary formulas are listed on the AP Biology Equations and Formulas sheet. Cells maintain homeostasis by regulating the movement of solutes across the cell membrane. Small cells have a large surface area-to-volume ratio; however, as cells become larger, this ratio becomes smaller, giving the cell relatively less surface area to exchange solutes. A cell is limited in size by the surface area-to-volume ratio. There are many organisms that have evolved strategies for increasing surface area, like root hairs on plants and villi in the small intestines of animals.
The chemical equation for photosynthesis is:
6CO2 + 6H2O → C6H12O6 + 6O2
Because plants consume some of this energy during photosynthesis, measuring the oxygen produced by a plant can tell us about the net photosynthesis that is occurring. In this laboratory, photosynthesis rates are measured by using leaf discs that begin to float as photosynthesis is carried out, allowing you to see that photosynthesis is occurring.
There are several properties that affect the rates of photosynthesis, including:
light intensity, color, and direction
temperature
leaf color, size, and type
Be able to hypothesize about the effects of these variables: for example, as light intensity increases, so does the rate of photosynthesis. Remember, both plants and animals contain mitochondria and carry out cell respiration!
In this lab, the respiratory rate of germinating and nongerminating seeds and small insects is investigated. The equation for cellular respiration is:
C6H12O6 + O2 → 6CO2 + 6H2O
Germinating seeds respire and need to consume oxygen in order to continue to grow. Non-germinating seeds do not respire actively. In this lab, the amount of oxygen consumed by these types of seeds is measured with a respirometer. The experiment is also conducted at two temperatures, 25°C and 10°C, because seeds consume more oxygen at higher temperatures. You should know the following:
Oxygen is consumed in cellular respiration.
Germinating seeds have a higher respiratory rate than nongerminating seeds, which have a very low respiratory rate.
Know how to design a study to determine the effect of temperature on cell respiration.
Know the significance of a control using glass beads. A control is a condition held constant during an experiment. In this case, glass beads are used as a control because they will not consume any oxygen.
This lab highlights the differences between mitosis and meiosis. In this lab, slides of onion root tips are prepared to study plant mitosis. The important information and skills to review in this lab include the following:
Mitosis produces two genetically identical cells, while meiosis produces haploid gametes.
Cell division is highly regulated by checkpoints that depend, in part, on complexes of proteins called cyclins with other proteins called cyclin-dependent kinases. One such example is the mitosis promoting factor (or MPF) that has its highest concentration during cell division and is thought to usher a cell into mitosis.
Nondisjunction, or the failure of chromosomes to separate correctly, can lead to an incorrect number of chromosomes (too many or too few) in daughter cells.
Know what each phase of the cell cycle looks like under a microscope. Chapter 8 contains diagrams of each phase.
In one section of this lab, the sexual life cycle of the fungus Sordaria fimicola is examined. Sexual reproduction in this fungus involves the fusion of two nuclei—a (+) strain and a (–) strain—to form a diploid zygote. This zygote immediately undergoes meiosis to produce asci, which contain eight haploid spores each.
During meiosis, crossing-over can occur to increase genetic variation. If crossing-over, or recombination, has occurred, different genetic combinations will be observed in the offspring when compared with the parent strain.
These offspring with new genetic combinations are called recombinants. By examining the numbers of recombinants with the total number of offspring, an estimate of the linkage map distance between two genes can be calculated with the following equation.
Map distance (in map units) = [(# recombinants) / (# total offspring)] × 100.
In this lab, the principles of genetic engineering are studied. Biotechnologists are able to insert genes into an organism’s DNA in order to introduce new traits or phenotypes, like inserting genes into a corn genome that help the crops ward off pests. This process is very complicated in higher plants and animals, but relatively simple in bacteria. You are responsible for knowing the ways in which bacteria can accept fragments of foreign DNA:
Conjugation: the transfer of genetic material between bacteria via a pilus, a bridge between the two cells
Transformation: a process in which bacteria take up foreign genetic material from the environment
Transduction: a process in which a bacteriophage (a virus that infects bacteria) transfers genetic material from one bacteria to another
In addition, DNA can also be inserted into bacteria by using plasmids, which are small, circular DNA fragments that can serve as a vector to incorporate genes into the host’s chromosome. Plasmids are key elements in genetic engineering. The concepts you need to know about plasmids include the following:
One way to incorporate specific genes into a plasmid is to use restriction enzymes, which cut foreign DNA at specific sites, producing DNA fragments. A specific fragment can be mixed together with a plasmid, and this recombinant plasmid can then be taken up by E. coli.
Plasmids can give a transformed cell selective advantage. For example, if a plasmid carries genes that confer resistance to an antibiotic like ampicillin, it can transfer these genes to the bacteria. These bacteria are then said to be transformed. That means if ampicillin is in the culture, only transformed cells will grow. This is a clever way scientists can find out which bacteria have taken up a plasmid.
In order to make a bacteria cell take up a plasmid, you must (1) add CaCl2, (2) heat shock the cells, and (3) incubate them in order to allow the plasmid to cross the plasma membrane.
This laboratory introduces you to the technique of gel electrophoresis. This technique is used in genetic engineering to separate and identify DNA fragments. You need to know the steps of this lab technique for the AP exam:
DNA is cut with various restriction enzymes.
The DNA fragments are loaded into wells on an agarose gel.
As electricity runs through the gel, the fragments move according to their molecular weights. DNA is a negatively charged molecule; therefore, it will migrate toward the positive electrode. The longer the DNA fragment, the slower it moves through the gel.
The distance that each fragment has traveled is recorded.
Restriction mapping allows scientists to distinguish between the DNA of different individuals. Since a restriction enzyme will cut only a specific DNA sequence, it will cause each individual to have a unique set of fragments called restriction fragment length polymorphisms, or RFLPs for short. This technology is used at crime scenes to help match DNA samples to suspects.
This lab examines energy storage and transfer in ecosystems. Almost all organisms receive energy from the sun either directly or indirectly:
Producers, or autotrophs, are organisms that can make their own food using energy captured from the sun. They convert this into chemical energy that is stored in high-energy molecules like glucose.
Consumers, or heterotrophs, must obtain their energy from organic molecules in their environment. They can then take this energy to make the organic molecules they need to survive.
Biomass is a measure of the mass of living matter in an environment. It can be used to estimate the energy present in an environment.
This lab investigates the mechanisms of transpiration, the movement of water from a plant to the atmosphere through evaporation. What do you need to take away from this lab?
The special properties of water that allow it to move through a plant from the roots to the leaves include polarity, hydrogen bonding, cohesion, and adhesion.
Know the vascular tissues that are involved in transport in plants. Xylem transports water from roots to leaves, while phloem transports sugars made by photosynthesis in the leaves down to the stem and roots.
Stomata are small pores present in leaves that allow CO2 to enter for photosynthesis and are also a major place where water can exit a plant during transpiration.
In this lab, fruit flies are given the choice between two environments by using a choice chamber, which allows fruit flies to move freely between the two environments. Typically, fruit flies prefer an environment that provides either food or a place to reproduce. They also respond to light and gravity:
Taxis is the innate movement of an organism based on some sort of stimulus. Movement toward a stimulus is called positive taxis, while movement away from a stimulus is negative taxis. In this lab, fruit flies exhibited a negative gravitaxis (or a movement opposite to the force of gravity) and positive phototaxis (a movement toward a light source).
This lab demonstrates how an enzyme catalyzes a reaction and what can influence rates of catalysis. In this lab, the enzyme peroxidase is used to catalyze the conversion of hydrogen peroxide to water and oxygen.
H2O2 + peroxidase → 2H2O + O2 + peroxidase
The following are the major concepts you need to understand for the AP exam:
Enzymes are proteins that increase the rate of biological reactions. They accomplish this by lowering the activation energy of the reaction.
Enzymes have active sites, which are pockets that the substrates (reactants) can enter that are specific to one substrate or set of substrates.
Enzymes have optimal temperature and pH ranges at which they catalyze reactions. Enzyme concentration and substrate concentration can also influence the rates of reaction.
If you’re asked to design an experiment to measure the effect of these four variables on enzyme activity, keep all the conditions constant except for the variable of interest. For example, to measure the effects of pH in an experiment, maintain the temperature, enzyme concentration, and substrate concentration constant as you change pH.
Respond to the following questions:
Which topics from this chapter do you feel you have mastered?
Which content topics from this chapter do you feel you need to study more before you can answer multiple-choice questions correctly?
Which content topics from this chapter do you feel you need to study more before you can effectively compose a free response?
Was there any content that you need to ask your teacher or another person about?