UPCAT Biology — Basic Life Functions & The CellFlash Cards

What does the acronym MRS GREN represent in biology?

MRS GREN represents the seven basic life functions: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. These are essential activities needed for survival and the maintenance of life in all living organisms.

Cell Theory

The Cell Theory consists of three main principles: 1) All living things are made up of cells (Robert Hooke), 2) Cells are the structural and functional unit of all living organisms (Schwann and Schleiden), and 3) Cells arise from pre-existing cells through cell division (Rudolf Virchow). Additional principles include that all cells contain hereditary information, have the same basic chemical composition, and energy flow occurs within cells.

What is the difference between prokaryotic and eukaryotic cells?

Prokaryotic cells are simple, unicellular organisms that lack a nucleus and membrane-bound organelles (examples: bacteria, archaea). Eukaryotic cells are complex organisms that have a membrane-bound nucleus and specialized organelles (examples: plants, animals, fungi, protists). Prokaryotes have DNA as a single circular molecule, while eukaryotes have linear DNA in chromosomes.

Mitochondria

Mitochondria are double-membraned organelles found in eukaryotic cells, known as the 'powerhouse of the cell.' They generate ATP energy through cellular respiration by breaking down glucose and other nutrients. They contain their own DNA and ribosomes (70S), suggesting they evolved from symbiotic bacteria.

What are the main differences between plant and animal cells?

Plant cells have: cell wall (present), chloroplasts (present), centrioles (absent), lysosomes (rare), and one large central vacuole. Animal cells have: cell wall (absent), chloroplasts (absent), centrioles (present), lysosomes (common), and many small vesicles instead of vacuoles.

Write the overall equation for photosynthesis.

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. This equation shows that carbon dioxide and water combine using light energy to produce glucose and oxygen. Photosynthesis occurs in chloroplasts and consists of light-dependent reactions (in thylakoids) and light-independent reactions or Calvin Cycle (in stroma).

What happens during the light-dependent reactions of photosynthesis?

Light-dependent reactions occur in thylakoid membranes and include: 1) Photosystem II absorbs light at 680nm, splitting water (photolysis) to release electrons, H⁺, and O₂; 2) Photosystem I absorbs light at 700nm, transferring electrons to NADP⁺ to form NADPH; 3) Chemiosmosis uses H⁺ gradient to produce ATP through ATP synthase. Products: ATP, NADPH, and O₂.

Calvin Cycle (Light-Independent Reactions)

The Calvin Cycle occurs in the stroma and has three phases: 1) Carbon Fixation - RUBISCO adds CO₂ to RuBP forming 3-PGA; 2) Formation of G3P - 3-PGA is reduced using ATP and NADPH to form glyceraldehyde 3-phosphate; 3) Regeneration of RuBP - five G3P molecules reform three RuBP using ATP. For every 6 cycles, one glucose molecule is formed.

Write the overall equation for cellular respiration.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. This shows glucose and oxygen react to form carbon dioxide, water, and energy (ATP). Cellular respiration is the opposite of photosynthesis and occurs in mitochondria through glycolysis, pyruvate oxidation, Krebs cycle, and oxidative phosphorylation.

What happens during glycolysis?

Glycolysis occurs in the cytoplasm and breaks down glucose into two pyruvate molecules. It has two phases: Energy-investing phase (uses 2 ATP) and Energy-harvesting phase (produces 4 ATP and 2 NADH). Net yield: 2 ATP, 2 NADH, and 2 pyruvate. This process is anaerobic and consists of 10 enzyme-catalyzed reactions.

What is the total ATP yield from one glucose molecule during cellular respiration?

Approximately 32-38 ATP molecules per glucose: Glycolysis (2 ATP), Pyruvate oxidation (0 ATP), Krebs cycle (2 ATP), and Oxidative phosphorylation (32-34 ATP from 10 NADH and 2 FADH₂). NADH yields about 2.5-3 ATP each, while FADH₂ yields about 1.5-2 ATP each through the electron transport chain.

Compare lactic acid fermentation and alcoholic fermentation.

Both are anaerobic processes that regenerate NAD⁺ for glycolysis. Lactic acid fermentation: pyruvate → lactate (occurs in muscle cells during intense exercise). Alcoholic fermentation: pyruvate → ethanol + CO₂ (occurs in yeast and bacteria, used in brewing and baking). Both produce only 2 ATP per glucose compared to 32-38 in aerobic respiration.

What are the phases of the cell cycle?

The cell cycle has two major phases: Interphase (G₁, S, G₂ phases where cell grows and DNA replicates) and M phase (mitosis and cytokinesis where cell divides). G₀ is a resting phase where cells stop dividing. The cycle is regulated by checkpoints to ensure proper cell division and prevent errors.

What happens during each phase of mitosis?

Prophase: chromosomes condense, nuclear membrane disappears, spindle fibers form. Metaphase: chromosomes align at cell center. Anaphase: sister chromatids separate to opposite poles. Telophase: nuclear membranes reform, chromosomes decondense, spindle disappears. Cytokinesis: cytoplasm divides, forming two identical diploid daughter cells.

How does meiosis differ from mitosis?

Meiosis produces four genetically different haploid gametes through two divisions (meiosis I and II), while mitosis produces two identical diploid somatic cells through one division. Meiosis includes synapsis of homologous chromosomes, crossing over for genetic recombination, and independent assortment. It's essential for sexual reproduction and genetic diversity.

What is crossing over and when does it occur?

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes. It occurs during prophase I of meiosis, specifically in the pachytene stage, when chromosomes form chiasmata (crossover points). This process increases genetic diversity by creating new combinations of genes in gametes.

Binomial Nomenclature

A two-term naming system established by Carolus Linnaeus for standardizing organism names. Format: Genus species (e.g., Homo sapiens). Rules: first letter of genus capitalized, species lowercase, italicized when printed, underlined when handwritten. Each scientific name is unique and universally accepted, governed by the International Code of Biological Nomenclature.

List the taxonomic hierarchy from most general to most specific.

Kingdom → Phylum → Class → Order → Family → Genus → Species. Memory device: 'King Philip Cried Over For Good Spaghetti.' Each level becomes more specific, with species being the most precise classification where organisms can interbreed and produce fertile offspring.

A student observes a cell under a microscope and sees a cell wall, chloroplasts, and a large central vacuole. What type of cell is this and what organism could it be from?

This is a plant cell. The presence of a cell wall (rigid structure for support), chloroplasts (for photosynthesis), and a large central vacuole (for water storage and structural support) are characteristic features of plant cells. This could be from any plant tissue, such as leaf mesophyll cells or root cortex cells.

Why do muscle cells have many mitochondria?

Muscle cells require large amounts of ATP for contraction, especially during intense physical activity. Since mitochondria are the 'powerhouses' that produce ATP through cellular respiration, having many mitochondria ensures sufficient energy production. This is an example of structure-function relationship - cells with high energy demands have more energy-producing organelles.

Explain why oxygen is released as a byproduct of photosynthesis.

Oxygen is released during the light-dependent reactions when water molecules undergo photolysis (splitting). The equation 2H₂O → 4H⁺ + 4e⁻ + O₂ shows that when water provides electrons to replace those lost by chlorophyll in Photosystem II, oxygen atoms combine to form O₂ gas. This oxygen is not used by the plant and is released as a 'waste' product that is essential for aerobic life.

What is the relationship between photosynthesis and cellular respiration in ecosystems?

Photosynthesis and cellular respiration are complementary processes that cycle carbon and oxygen through ecosystems. Photosynthesis converts CO₂ and H₂O into glucose and O₂ using solar energy, while cellular respiration breaks down glucose using O₂ to release CO₂, H₂O, and ATP. Plants perform both processes, but produce more O₂ than they consume, supporting other organisms that only perform cellular respiration.