Praxis®️ General Science: Life Science
The Life Science content category has about 27 multiple-choice questions, which account for about 20% of the test.
This part has nine sections:
- Basic Structure and Function of Cells and Their Organelles
- Key Aspects of Cell Reproduction and Division
- Basic Biochemistry of Life
- Basic Genetics
- Theory and Key Mechanisms of Evolution
- Hierarchical Classification Scheme
- Major Structures of Plants and Their Functions
- Basic Anatomy and Physiology of Animals, including the Human Body
- Key Aspects of Ecology
So, let’s start with Basic Structure and Function of Cells and Their Organelles.
Basic Structure and Function of Cells and Their Organelles
This section tests your knowledge of cell biology, structure, and the cell cycle.
Let’s discuss a concept that will more than likely appear on the test.
All organisms are made of one or more cells, and cells carry out specific functions. The main parts of a cell are plasma membrane (also called cell membrane), cytoplasm, and nucleus.
The cell membrane surrounds the entire cell, like a casing. In animal cells, this is a cell membrane; in plant cells, it is the rigid cell wall. The cell membrane is made up of a phospholipid bilayer. Phospholipids are fatty acids arranged in two layers. Each molecule of phospholipids has a “head” and a “tail.” The head is hydrophilic, which means it is attracted to water. The tail is hydrophobic, which means it repels water. This is important to remember it changes how the cell membrane allows things to pass through. Molecules that are hydrophobic can pass through the plasma membrane if they are small enough, and molecules that are hydrophilic cannot easily pass through.
The cell membrane controls what goes in and out of the cell. It does this through either active or passive transport. Both methods use ion channels to move ions across the cell membrane.
Active transport requires energy and work. Active transport moves ions from low concentration to high, using ATP.
Passive transport does not require energy or work. Passive transport moves ions from high concentration to low, using no metabolic energy (no ATP). This is the simplest form of energy transport across the cell membrane.
Key Aspects of Cell Reproduction and Division
This section tests your knowledge on the cell cycle and reproductive processes.
This is a concept that is likely to appear on the test.
Cell Reproduction and Division
The cell cycle refers to the stages that a cell undergoes between its formation (birth) and reproduction.
The cell cycle begins in interphase, the period of cell growth and protein synthesis. Interphase has three stages: G1, S, and G2. In G1 (also known as “gap one,” or “first gap”), the cell is accumulating the building blocks (chromosomal DNA) that it will need for reproduction. Think of this phase as cell growth.
In S phase, the cell begins DNA synthesis (S phase = synthesis phase). Here, DNA replication begins and creates two identical copies of chromosomes, called “sister chromatids.” Later on, these will be important for the division.
Next is the G2 phase, or second gap. Here, the cell replenishes its energy and begins synthesizing proteins that will be necessary for mitosis. In G2, there is more cell growth.
The mitotic phase is next. This process takes the duplicated daughter cells (from G1), and aligns, separates, divides them again. The cell is divided into identical daughter cells in this phase. Mitosis is the process of the cell dividing the nucleus, and cytokinesis (the final portion of mitosis), is where the cytoplasm physically separates into two daughter cells.
Mitosis is divided into five phases: prophase, prometaphase, metaphase, anaphase, and telophase.
- Prophase condenses chromosomes, and spindle fibers emerge. The nuclear envelope begins to break down. Centrosomes move toward opposite poles.
- Prometaphase continues these processes, and the nuclear envelope begins to disappear.
- In metaphase, all of the chromosomes are aligned between the two poles of the cell.
- Anaphase is when the cell becomes visibly elongated.
- Telophase is when the chromosomes reach the opposite poles and begin to unravel. Nuclear envelopes form around the chromosomes.
Cytokinesis is the second part of the mitotic phase, and this is when the cell is physically separated (divided) into two daughter cells.
Meiosis is the fertilization of the daughter cells from mitosis. This produces reproductive cells when the nucleus divides into four nuclei, and chromosomes exchange genetic material (known as “crossing over”).
While mitosis produces two daughter cells that are genetically identical, meiosis creates four cells that are genetically unidentical. Meiosis produces gametes (sperm and egg cells) to form a zygote (a diploid cell with the full number of chromosomes).
Basic Biochemistry of Life
This section tests your knowledge on basic biological functions and building blocks for life.
Let’s talk about a concept that may come up on the test.
Cellular respiration is the process of breaking down sugar so that the cell can use it for energy. Cells of animals, plants, fungi, and protists use oxygen to break down food molecules to create ATP, the chemical compound that cells use for energy.
Cell respiration begins with Step 1. Glucose, the basic energy source for the cell. Then, the cell begins Step 2: Glycolysis (the breakdown of glucose).
Step 3: The Link Reaction, which takes place inside the mitochondria. Link reaction allows the cell to start Step 4: the Krebs Cycle, which converts ADP to ATP by removing oxygen and producing carbon dioxide and water.
Step 5: Most of the ATP is made during the electron transport chain (ETC).
The basic formula for this is:
Glucose (sugar) + oxygen –> carbon dioxide + water + energy (as ATP)
This process is essential for life so that the cell has the energy to function. Cells can’t process just glucose alone but need to convert it to ATP to use it for energy.
This section tests your knowledge on the basic principles of genetics.
Let’s discuss a concept likely to show up on the test.
Gregor Mendel is known as the “father of genetics.” He discovered the 3 essential laws of inheritance:
- Segregation: Every organism contains two alleles for each trait, one from each parent. An allele is a pair of genes on a chromosome that determine a characteristic. For example, an allele can determine eye color.
- Independent assortment: Alleles for separate traits are inherited independently of one another. The inheritance of one trait is not dependent on the inheritance of another.
- Dominance: Genes are either dominant or recessive. The law of dominance states that an organism with alternate forms of a gene (one dominant and one recessive) will always express the form that is dominant.
The hereditary information of a gene is known as its genotype. For example, the genotypes for brown eyes and blue eyes are different codes based on dominant and recessive alleles. The phenotype is the physical (outward) expressed trait of those characteristics. We see brown or blue eyes, and that is the physical expression of the gene. Whether a person has a Widow’s peak is also a phenotype.
Theory and Key Mechanisms of Evolution
This section tests your knowledge on taxonomy and evolution, including how scientists chart organism families, nomenclature, and chart evidence for evolution.
Hierarchical Classification Scheme
This section tests your knowledge of the classification of organisms (taxonomy).
Here’s a concept that is likely to be on the test.
Scientists classify organisms into one of five families or groups: bacteria, animals, plants, fungi, and protists. The classifications are based on the organism’s cellular structure.
Bacteria: Bacteria are prokaryotes, which means that all the DNA is found in the nucleoid and is not surrounded by a cell membrane. Bacteria have no cell nucleus.
Animals: Animal cells do not have a cell wall. Instead, they are encased in a thin cell membrane. Animal cells do not have chloroplasts and cannot undergo photosynthesis.
Plants: All plant cells have a hard cell wall made mostly of cellulose. This helps give plants their structure. Plant cells also have chloroplasts which are used in photosynthesis.
Fungi: Fungi cells have a cell wall, similar to plants. However, they are different from plants because their cell walls are made of chitin, a compound found in the shells of crustaceans. Fungi do not have chloroplasts and do not undergo photosynthesis.
Protists: Protists are unicellular organisms. They are eukaryotes, but they are single-celled. Unlike plant or animal cells, protists can move on their own, usually by using small tails (flagella), tiny hairs (cilia), or arm-like extensions of the cell (pseudocilia). A protist is a complete, single-celled organism.
Major Structures of Plants and Their Functions
This section tests your knowledge on plant biology, structure, and growth.
Basic Anatomy and Physiology of Animals, including the Human Body
This section tests your knowledge on anatomy and physiology of animals.
Let’s discuss a concept that will more than likely appear on the test.
Homeostasis is the process toward a stable equilibrium between elements, especially in physiology. Think of it as maintaining a constant internal environment. In humans, an example of homeostasis is maintaining a constant body temperature by releasing heat or maintaining healthy blood pressure.
Homeostasis controls important functions at the cellular level, and all the way through entire organs and organ systems.
When homeostasis is not achieved, it is imbalanced. Homeostatic imbalance results in disease or toxicity. An example of homeostatic imbalance is the disease of diabetes, where the endocrine system has difficulty maintaining the appropriate blood glucose levels.
This is some information about the Life Science portion of the Praxis®️ General Science exam.