Directional selection occurs when members of a population at one end of a spectrum are selected against, while those at the other end are selected for. Taller giraffes are being selected for; shorter giraffes are being selected against.

Phytochrome is an important pigment to the process of flowering. Of its two forms, the active form, P_fr, is responsible for the production of the hormone florigen, which is thought to assist in the blooming of flowers.

Genetics has no memory . . . it will be 1/2 forever.

Low numbers of stomata help to reduce water loss, helpful in hot and dry regions.

We threw it in here just to remind you that you should not ignore the concepts of this very important chapter. You will be asked about these concepts on the exam.

Neutrophils are phagocytic cells of the immune system. They roam the body looking for rubbish to clear.

The head of the sperm contains the acrosome, which has specialized enzymes that when released, help the sperm to penetrate and fertilize the egg. A plasmid is a small bacterium that can be used in recombinant DNA formation. The capsid is the protein coat that encapsulates a virus’ genetic material. The flagella are important for motility of the sperm but do not contain any enzymes.

Secondary carnivores > primary carnivores > primary consumers = herbivores > primary producers

In allopatric speciation, two species result due to the geographical barrier between the two species. Two birds living in different parts of the tree may result in two separate species over time, if the birds have different mating rituals or mating seasons. This would not be due to a geographical barrier and would be an example of sympatric speciation. Lion prides could still reproduce with one another especially since they inhabit the same area and climate. Insects with the same mating call would interbreed and this would not result in two different species over time. Similarly, two groups of dogs with different fur color should still be able to reproduce. However, two squirrel populations separated by a river may evolve into two different species over time, as the squirrels may be inhabiting different environments and are separated by the body of water.

Follicle stimulating hormone causes the follicle in the ovary to begin to divide to complete meiosis II. The growing follicle that will eventually release the egg during ovulation secretes estrogen. The estrogen then spurs the secretion of luteinizing hormone by the anterior pituitary gland, causing the follicle to rupture and release the egg. It is the estrogen and progesterone that is responsible for readying the endometrium for implantation should fertilization occur.

The descending loop of Henle is only permeable to water. As the urine moves through the loop of Henle, it will become more concentrated as the water is reabsorbed back into the bloodstream. The ascending loop of Henle is permeable to sodium and during this portion of the loop, the urine will be come more diluted, as sodium ions are reabsorbed into the bloodstream.

Only photosystem I is involved in the cyclic reactions. Photosystem II is not.

Heterozygous individuals carry the recessive gene but are themselves healthy.

Calcium ions are essential for muscle contraction to occur. Without the release of calcium, the myosin head would be unable to bind to the actin at the binding sites. It is the calcium that binds and removes troponin from the myosin binding sites on the actin. This is done when the axon terminal nearest a muscle fiber releases acetylcholine, a neurotransmitter, which then causes the sarcoplasmic reticulum to release calcium into the muscle cell to allow for muscle contraction. The endoplasmic reticulum is responsible for protein modification following translation on a ribosome.

When interbreeding ceases because some sort of barrier separates a single population into two (an area with no food, a mountain, etc.), the two populations evolve independently, and if they change enough, then, even if the barrier is removed, they cannot interbreed. This is allopatric speciation.

Since testosterone levels are increased only during the breeding season, we can infer that testosterone has some role in breeding. Since reproductive males express higher testosterone levels only during the breeding season, we hypothesize that testosterone is beneficial, as opposed to detrimental, to breeding.

Genetic drift is a change in allele frequencies that is due to chance events. When drift dramatically reduces population size, it is called a "bottleneck."

Habituation is the loss of responsiveness to unimportant stimuli or stimuli that do not provide appropriate feedback. This is a prime example of habituation.

Posttranscriptional modification actually occurs in the nucleus.

0.04 = q². Therefore, the square root of 0.04 = q = 0.20 and p + q = 1. So p + 0.20 = 1. Therefore, p = 0.80, and 2pq is the frequency of the heterozygote condition: 2(0.20)(0.80) = 0.320 = 32 percent.

DNA polymerase can add dNTPs (deoxynucleoside triphosphates) only to a pre-existing oligonucleotide chain that is annealed to the template DNA. The enzyme adds dNTPs on a free 3′-OH- group. Primers in replication are RNA based. These primers are then cut out via endonuclease activity and replaced with DNA nucleotides. Finally, DNA ligase fuses the gap between the fragments of DNA.

Succession is an ecological process in which landforms evolve over time in response to the environmental conditions. Commensalism is when one organism benefits while the other is unaffected. Mutualism is when both organisms reap benefits from the interaction. Parasitism is when one organism benefits at the other's expense. Competition is the situation in which organisms fight for some limited resource.

Spiral cleavage results in daughter cells after cell division, being located at an angle in relationship to each other. This is common in protostomes. Whereas radial cleavage results in the daughter cells after cell division being stacked on top of each other. Radial cleavage is seen in deuterostomes.

Polygenic traits are traits that require the input of multiple genes to determine the phenotype. Skin color is a classic example of a polygenic trait; three genes combine to provide the various shades of skin tone seen in humans.

If 9 percent of the population is homozygous recessive, this means that q² = 0.09, and that the square root of q² = 0.30 = q. This means that p = 0.70 since p + q = 1. Thus, the percentage of the population that is homozygous dominant: p² = (0.7)² = 0.49 or 49 percent.

Exergonic reactions give off energy, and hydrolysis reactions are reactions that use water to break apart a compound. Redox reactions are reactions that involve the movement of electrons. Dehydration reactions are reactions that bring two molecules together, releasing water as a product.

The experiments are very well represented on the AP Biology exam, and you should read this chapter carefully and learn how to design and interpret experiments.

Veins carry blood to the heart, recollecting it from the body. Conversely, arteries carry blood away from the heart to the body. To prevent backflow and to promote the movement against gravity, veins have valves whereas arteries do not. Arteries also have very thick, muscular walls that enable pumping from the heart to the body. Veins are thinner in comparison and are not considered to have to “pump” blood or be under high pressure.

The endosymbiotic theory proposes that mitochondria and chloroplasts evolved through the symbiotic relationship between prokaryotic organisms.

Meiosis reduces the number of chromosomes in an individual by half: 96 ÷ 2 = 48.

Herbivores tend to be the primary consumers of trophic pyramids, and thus would take up the first level up from the bottom.

Crossover is most likely to occur between two genes that are located far away from each other on the same chromosome.

Prokaryotic and eukaryotic cells do have similar structures, the organelles in eukaryotic cells took care of having a smaller surface area-to-volume ratio, and eukaryotic cells are not able to multiply faster.

A detritivore is an organism that includes the subcategory of decomposers. Fungi are decomposers.

A silent mutation often occurs in the wobble site of the codon on the mRNA strand. For most codons, if the third base pair is changed, the correct amino acid can still be made. A missense mutation results in the addition of an incorrect amino acid, but can still lead to a functional protein. Nonsense mutations result in a polypeptide chain that is shorter and is non-functional. For nonsense mutations, an insertion or deletion of a nucleotide base creates a premature stop codon (UGA, UAG, or UAA), terminating translation before the polypeptide can be completed. Transfer mutation is not an accurate term in biology.