Biology Practice Exam

The reactants in the process of photosynthesis are carbon dioxide and water. Sunlight is needed for the reactions to occur. The products of photosynthesis are oxygen and glucose, a simple carbohydrate. ATP is used in photosynthesis but is neither a reactant nor a product. ATP is produced in a different process called cellular respiration.

A cell membrane is a thin layer of molecules that surrounds the cell. Its function is to allow certain materials to enter the cell, yet, keep harmful materials out. In order to do this, the cell controls which substances can enter the cell through the membrane. The cell membrane is selectively permeable (or semipermeable), which means that certain molecules, such as oxygen and water, are permitted to enter the cell. Molecules that are not recognized as helpful are not able to pass through the membrane.

Enzymes are catalysts, chemicals that speed up chemical reactions. The conditions inside most cells do not allow reactions to proceed quickly enough to support life. For example, temperatures inside organisms are not hot enough for chemical reactions to take place quickly. Enzymes increase the rates of biological chemical reactions.

Inside cells, sequences of chemical reactions take place to support life. These sequences are known as metabolic pathways. Photosynthesis, respiration, and digestion are all examples of metabolic pathways, or sequences. Photosynthesis is the metabolic pathway that produces oxygen and glucose in organisms with chlorophyll. Respiration breaks down molecules called ATP for cells to use as energy. Digestion breaks down food to be used to make energy in the form of ATP. Hydroplasm is not a known metabolic sequence.

Chloroplasts and central vacuole are important organelles in plant cells. Chloroplasts contain chlorophyll and are the site of photosynthesis. Central vacuoles are used to store water in plant cells. All the other organelles listed are important to the function of animal cells and plant cells.

Photosynthesis is the process plant cells use to convert oxygen, water and sunlight into a usable form of energy. The product of photosynthesis is glucose (sugar) molecules. Glucose molecules are a form of potential energy that can be broken down by an organism to produce energy in the form of ATP molecules.

A gene is the basic unit of heredity. Genes are made of DNA sequences and act as instructions for making proteins (although not all genes make proteins). Genes are found on chromosomes. Chromosomes are located in a cell's nucleus.

DNA is made of two strands of nucleotides (basic units of DNA). The DNA molecule looks like a twisted ladder and is referred to as a double helix.  Each nucleotide contains a sugar molecule and a phosphate group, along with a nitrogen base. The sugar molecules and phosphate groups make up the sides of the ladder, and the nitrogen bases make up the “steps” of the ladder.

Genes are sequences of DNA on a chromosome. All DNA is located inside a cell's nucleus.

Messenger RNA (ribonucleic acid) transfers genetic information from the DNA in a cell's nucleus to ribosomes. In the ribosome, the information coded onto messenger RNA is used to make proteins.

During meiosis, gametes (sex cells) are formed by reducing the number of chromosomes found in somatic (body) cells by one half. This occurs so that when two gametes, one from each parent, fuse together, the embryo will contain the correct number of chromosomes. Without meiosis, offspring cells would contain double the number of chromosomes of normal adults and they would not be viable.

Biology uses a system of classification to group organisms together based on their characteristics. The levels of classification, from largest (most inclusive) to smallest (most specific), include domain, kingdom, phylum, class, order, family, genus, species.

Prokaryotic and eukaryotic cells both contain DNA. Prokaryotic cells are found in bacteria and their structure is much more simple than eukaryotic cells. Prokaryotic cells have a few simple cellular structures such as a nucleoid region, ribosomes, and a plasma membrane. Eukaryotic cells have more highly developed cellular structures including organelles that support the function of the cell. Golgi apparatus and mitochondria are found in eukaryotic cells. Chloroplasts are found in eukaryotic cells that contain chlorophyll, such as plants.

Organelles are specialized structures in cells that support the cellular functions. For example, mitochondria are organelles that synthesize energy; ribosomes synthesize protein; chloroplasts convert sunlight, carbon dioxide and water into oxygen and sugar. 

Unicellular organisms are very small compared to most multicellular organisms. If they were as large as a multicellular organism, their surface area to volume ratio would be too low to support life. Staying small gives unicellular organisms a high surface area to volume ratio. Surface area to volume ratio refers to the amount of surface area on the outside of the cell compared to the cell's volume. Larger cells have less surface area compared to their volume. Molecules move into the cell, out of the cell and through the cell slowly through the cell membrane. Having a large surface area provides more space for molecules to diffuse across the cell membrane and less of a distance to travel inside the cell to supply organelles with materials needed for metabolism.

Humans have 46 chromosomes. Each parent contributes 23 chromosomes in a gamete (sex cell). When the gametes combine to form an embryo, the embryo then contains two sets of chromosomes, equal to a total of 46 chromosomes.

Multicellular organisms include organisms with more than one eukaryotic cell. Animals and plants are all multicellular. All prokaryotic organisms are unicellular, meaning the entire organism consists of a single cell. There are some unicellular eukaryotic organisms, such as protists and some fungi (yeast).

Algae bodies that are plantlike, such as the structure of brown algae, are referred to as a thallus. Where plants have roots, stems and leaves, a thallus consists of a holdfast (rootlike part), stipe (stemlike part), and blades (leaflike parts).

Organisms in Kingdom Protista include eukaryotes that do not share all of the characteristics of organisms in the kingdoms Animalia, Fungi or Plantae. Within Kingdom Protista are a group of protists that behave like animals. These single-celled organisms are in the Phylum Protozoa. Protozoa include flagellates, ciliates, amoeba and sporozoans.

The three major body parts of all insects (Class Insecta) are the head, thorax and abdomen. Many animals that are similar in size and appearance are mistaken for insects, such as ticks, mites and spiders. However, these creatures are in the Class Arachnida, not Class Insecta.

Honey bees live in a colony with a division of labor. The worker bees form the largest group of bees in the hive. They serve many different roles, such as removing dead bees, feeding baby drones, packing pollen, building the honeycomb, and taking care of the queen bee. The queen bee is the only fertile female bee in the colony. Worker bees remain infertile as long as the queen bee is alive.

Vertebrates are multicellular organisms in Kingdom Animalia. Vertebrates are animals with a backbone, and include mammals, birds, fish, reptiles and amphibians. Insects, earthworms and sea stars belong to a group of animals without a backbone, invertebrates.
 

Exoskeletons are skeletons located on the outside of an animal's body. They are used for protection and to support the animal. Mollusks and insects are examples of animals with endoskeletons. Birds, turtles and snakes are all animals with endoskeletons. Endoskeletons are internal skeletons. 

Organisms in Kingdom Animalia have muscles and nerves. If an animal can move from one place to another (known as locomotion), it is doing so by contracting its muscles. Not all animals have skin and/or a skeleton.

Gametes are haploid cells, which means they contain half the number of chromosomes that body cells contain. Gametes are used in sexual reproduction to form an offspring. When two gametes fuse together during sexual reproduction, they form a zygote.

In humans, there are two sex chromosomes, referred to as “X” and “Y.” Females have two X chromosomes in each body cell and in each sex cell (gamete). Males have one X chromosome and one Y chromosome. If a person inherits two X chromosomes, one from each parent, that person will develop into a female. If a person inherits an X chromosome from the mother and a Y chromosome from the father, that person will develop into a male.

There are three ways genetic variation may take place: New combinations of chromosomes result from sexual reproduction; chromosome mutation and gene mutation occur during mitosis and/or meiosis.

“Survival of the fittest” is an expression used to describe natural selection. Natural selection takes place when organisms with the characteristics best suited for their environment survive and produce fertile offspring. The “fittest” in the phrase is referring to the organisms that have the characteristics that allow them to survive in their environment. In theory, these organisms will not only survive, but will also reproduce. Their offspring will also have the characteristics that allowed the parent to successfully survive. Over time, these characteristics will continue to be passed on to future generations. Organisms that lack the characteristics to survive will die before reproducing, and therefore, not pass on the less desirable characteristics.

Genetic evidence is the most direct type of evidence used to support the theory of evolution. Since adaptations are passed along genetically, from one generation to another, evidence for evolution can be collected by examining the genome of individuals of the same species and comparing it to genetic information of ancestral species, species of the same phylogenetic groups and/or common ancestors between several species.

Hybridization occurs when individuals of different species mate and form offspring. The offspring are referred to as hybrids. In order for hybridization to occur, the parents must be similar to each other. For example, a horse and a donkey can reproduce to form a mule. However, a fly cannot mate with a bird to create a new organism. When hybridization occurs, the offspring are typically sterile.