Biology Flashcards

Farm runoff washes fertilizer into a pond, causing increased algal growth, decreased oxygen, and eventually the death of the fish. Which of the following processes best describes this sequence of events?

Answer: Eutrophication

Eutrophication is the process where a body of water becomes overly enriched with nutrients, typically from agricultural runoff containing fertilizers. This excess nutrient load stimulates an explosive growth of algae (algal bloom). When these algae die and decompose, bacteria consume large amounts of dissolved oxygen, leading to hypoxia or anoxia, which ultimately causes the death of aquatic life like fish.

Dogs, bats, whales, and humans all have a long bone in their front limbs that is attached to two parallel bones at a joint. Anatomical structures such as these are referred to as

Answer: Homologous

Homologous structures are anatomical similarities between different species that indicate a shared ancestry, even if the structures now serve different functions. The forelimbs of dogs, bats, whales, and humans, despite their varied uses (walking, flying, swimming, grasping), share a fundamental underlying bone structure (humerus, radius, ulna), which is a classic example of homology and evidence for common descent.

Why is it likely that a single nucleotide substitution of uracil for thymine in a DNA strand's coding region will have little effect on the organism? I. Uracil and thymine nucleotides will both bind to adenosine II. The genetic code is duplicative III. Single nucleotide substitutions rarely have a significant impact IV. Because uracil is not normally found in DNA, the substitution is likely to be detected and repaired.

Answer: I and IV

A single nucleotide substitution of uracil for thymine in DNA is unlikely to have a significant effect for two main reasons. First, both uracil and thymine nucleotides bind to adenosine, meaning the base pairing rules are maintained during replication and transcription, thus preserving the original genetic information and resulting in the same mRNA codon. Second, uracil is not a normal component of DNA, and specialized DNA repair enzymes are present in cells to detect and remove uracil, replacing it with thymine, thereby preventing the persistence of this unusual base.

In humans, what is the end result of anaerobic respiration?

Answer: Lactic acid

In humans, when oxygen is scarce, such as during intense exercise, cells switch from aerobic respiration to anaerobic respiration to produce ATP. This process, known as lactic acid fermentation, breaks down glucose without oxygen, yielding a small amount of ATP and producing lactic acid as a byproduct. The accumulation of lactic acid contributes to muscle fatigue and soreness.

Chyme is a semi-fluid mass of partially digested food. Chyme formation takes place in

Answer: Stomach

Chyme is the semi-fluid, acidic mass of partially digested food that is formed in the stomach. After food is chewed and swallowed, it enters the stomach where it is mixed with gastric juices (containing hydrochloric acid and enzymes like pepsin) and churned by muscular contractions, transforming it into chyme before it passes into the small intestine.

During the metabolization of glucose molecules in an aerobic cell, the energy is used to produce ATP through a series of biochemical steps. Put these events in the correct order. I. Acetyl Coenzyme A is synthesized from pyruvate. II. Electron carriers in the mitochondrion donate electrons to the electron transport chain, resulting in a proton gradient. III. A molecule enters the citric acid cycle, also known as the Krebs cycle, producing 3 NADH, 1 FADH2, and 1 ATP. IV. During glycolysis, a molecule is cleaved into two parts, giving NADH molecules and two ATP molecules. V. ATP synthase allows protons into the mitochondrion's interior matrix, producing up to 34 ATP.

Answer: IV, I, III, II, V

The metabolization of glucose begins with glycolysis (IV), where glucose is cleaved into pyruvate, producing NADH and ATP. Next, pyruvate is converted into Acetyl Coenzyme A (I), which then enters the Citric Acid Cycle (III) to generate more NADH, FADH2, and ATP. Finally, the electron carriers (NADH, FADH2) donate electrons to the electron transport chain (II), creating a proton gradient that ATP synthase (V) uses to produce a large amount of ATP.

Which of the following bacteria is an example of denitrifying bacteria?

Answer: Pseodomonas sp

Denitrifying bacteria are microorganisms that convert nitrates (NO3-) back into nitrogen gas (N2), completing the nitrogen cycle. *Pseudomonas* species are well-known examples of such bacteria, playing a crucial role in returning nitrogen to the atmosphere. In contrast, *Rhizobium* fixes atmospheric nitrogen, and *Nitrobacter* and *Nitrosomonas* are involved in nitrification, converting ammonia to nitrates.

What is Engrailed proteins?

Answer: Transcription factors

Engrailed proteins are a class of homeodomain proteins, which are characterized by a specific DNA-binding motif called the homeodomain. These proteins function as transcription factors, meaning they regulate gene expression by binding to specific DNA sequences and controlling the transcription of target genes. They are critical for pattern formation and segment identity during embryonic development in many organisms.

Which of the following cellular organelles are more likely to be present in a cell that produces steroid hormones?

Answer: Smooth endoplasmic reticulum

Cells that produce steroid hormones, such as those in the adrenal cortex or gonads, require extensive machinery for lipid synthesis. The smooth endoplasmic reticulum (SER) is the primary site for lipid synthesis, including steroid hormones, as well as detoxification and calcium storage. Therefore, a cell specializing in steroid hormone production would have an abundance of smooth endoplasmic reticulum.

What is the process by which the endosperm of a flowering plant's seeds is produced?

Answer: Two sperm enter the pollen tube and travel to the embryo sa. The one fertilizes the egg, while the other fertilizes the two polar nuclei, resulting in triploid endosperm.

The endosperm of a flowering plant is produced through a unique process called double fertilization. One sperm cell fertilizes the egg to form the diploid zygote, while the other sperm cell fuses with the two polar nuclei in the embryo sac. This fusion results in a triploid (3n) cell that develops into the endosperm, which serves as a nutrient-rich tissue for the developing embryo.

Human babies with low birth weights and high birth weights have a lower chance of survival than those with average birth weights. Which of the following is an example of a process?

Answer: Stabilizing selection

Stabilizing selection is a type of natural selection that favors intermediate phenotypes over extreme variations. In this scenario, human babies with average birth weights have the highest survival rate, while those with very low or very high birth weights have lower survival chances. This pattern indicates that the population is being selected for the intermediate trait, stabilizing the average birth weight.

Foreign proteins that bind to an antibody are referred to as

Answer: Antigens

Antigens are molecules, often foreign proteins or polysaccharides, that can elicit an immune response in an organism. When an antigen enters the body, it is recognized by the immune system, which then produces specific antibodies that bind to it. This binding is a key step in neutralizing the foreign substance and initiating an immune response.

The molecule used by animals as a quick energy source is

Answer: Glycogen

Glycogen is the primary storage form of glucose in animals, predominantly found in the liver and muscle cells. It is a highly branched polysaccharide that can be rapidly broken down into glucose molecules when the body needs a quick source of energy. Starch is the energy storage in plants, while triglycerides are for long-term energy storage in animals.

When a neuron reaches the action potential threshold:

Answer: The sodium channels are open.

When a neuron reaches the action potential threshold, voltage-gated sodium channels rapidly open. This influx of positively charged sodium ions into the cell causes a rapid depolarization of the membrane, leading to the rising phase of the action potential. Subsequently, potassium channels open to repolarize the membrane.

Catabolic reactions necessarily require:

Answer: None of the above

Catabolic reactions are metabolic processes that break down complex molecules into simpler ones, typically releasing energy in the process. These reactions are exergonic, meaning they do not necessarily require an input of energy; instead, they often generate energy (e.g., ATP) that can be used for other cellular activities. Anabolic reactions, conversely, require energy input.

Approximately 99% of blood cells are involved in what process?

Answer: Transporting oxygen

Red blood cells, also known as erythrocytes, constitute approximately 99% of all blood cells in the human body. Their primary and most critical function is to transport oxygen from the lungs to the body's tissues and to carry carbon dioxide back to the lungs. This vital process is facilitated by the hemoglobin protein contained within them.

What is an example of a cofactor?

Answer: Zinc

Cofactors are non-protein chemical components that are essential for the catalytic activity of many enzymes. They can be inorganic ions or complex organic molecules (coenzymes). Zinc is a common example of an inorganic metallic ion that serves as a cofactor for a wide range of enzymes, assisting in their proper functioning and catalytic reactions.

Enzymes catalyze biochemical reactions by what process?

Answer: Reducing the reaction's activation energy

Enzymes are biological catalysts that accelerate the rate of biochemical reactions without being consumed in the process. They achieve this by lowering the activation energy, which is the minimum energy required for a reaction to occur. By reducing this energy barrier, enzymes allow reactions to proceed much faster under physiological conditions.

Which of the following is most likely to perform CAM photosynthesis?

Answer: Cacti

CAM (Crassulacean Acid Metabolism) photosynthesis is an adaptation found in plants that live in arid environments, such as cacti. These plants open their stomata at night to take in CO2, minimizing water loss during the hot day. They then store the CO2 as organic acids and release it during the day for photosynthesis, making them well-suited for desert conditions.

The combination of DNA and histones is known as

Answer: Chromatin

Chromatin is the complex material consisting of DNA and proteins, primarily histones, found within the nucleus of eukaryotic cells. Histones act as spools around which DNA winds, compacting the long DNA molecules into a more manageable structure. This packaging is crucial for fitting the genome into the cell nucleus and for regulating gene expression.