UPCAT Biology — Basic Life Functions & The CellStudy Notes
Thorough study notes for Basic Life Functions & The Cell — the fastest path from zero to ready for UPCAT Biology. Structured for self-study reviewers who cannot attend a review centre, these notes cover the full concept library plus the UPCAT-specific twists University of the Philippines adds to its questions.
Exam context
On the UPCAT 2026, the Biology subtest carries a "Core" weight in University of the Philippines's pattern. Basic Life Functions & The Cell lands at position 1st out of 7 in the standard review order. Target score is UPG ≤ 2.2 typical, and roughly 20 items come from Biology on a typical UPCAT paper.
Basic Life Functions & The Cell - Study notes
Biology is the study of life and living organisms. All living things share certain characteristics that distinguish them from non-living matter. These basic life functions, summarized by the acronym MRS GREN (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition), are essential for survival. At the foundation of all life is the cell - the basic structural and functional unit of all living organisms. Understanding cells and their functions is crucial for understanding how life works at its most fundamental level.
Summary
Living organisms are distinguished from non-living matter by seven basic life functions (MRS GREN): Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. All life is based on cells, which are the structural and functional units of life according to Cell Theory. There are two main cell types: simple prokaryotic cells (bacteria, archaea) and complex eukaryotic cells (plants, animals, fungi, protists) with membrane-bound organelles. Plant cells perform photosynthesis in chloroplasts, converting light energy and CO₂ into glucose and oxygen through light-dependent reactions and the Calvin cycle. All cells perform cellular respiration to break down glucose and produce ATP energy through glycolysis, Krebs cycle, and oxidative phosphorylation. Cell division occurs through mitosis (producing identical diploid cells for growth/repair) or meiosis (producing diverse haploid gametes for reproduction). Understanding these fundamental processes is essential for comprehending how life functions at the cellular level.
Sections
All living organisms exhibit seven basic life processes that distinguish them from non-living things. These can be remembered using the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. Movement includes all forms of motion, from muscle contraction in animals to the flow of water and nutrients in plants. Respiration involves breaking down nutrients to release energy through cellular respiration. Sensitivity refers to an organism's ability to detect and respond to changes in their environment. Growth occurs when organisms increase in size through cell division or cell enlargement. Reproduction ensures species survival through sexual or asexual means. Excretion removes toxic waste products from metabolism. Nutrition involves obtaining and using food for energy and building materials.
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Basic Life Functions (MRS GREN)
Examples
- Movement: Blood circulation, muscle contraction, plant growth toward light
- Respiration: Cellular respiration in mitochondria, breathing in humans
- Sensitivity: Plants growing toward sunlight, animals fleeing from predators
- Growth: A child growing taller, a plant increasing in size
- Reproduction: Birds laying eggs, bacteria dividing
- Excretion: Kidneys filtering blood, plants releasing oxygen
- Nutrition: Animals eating food, plants making glucose through photosynthesis
Key Points
- MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition
- All seven functions must be present for something to be considered alive
- Movement includes molecular movement within cells and transport of materials
- Respiration releases energy from nutrients through cellular processes
- Sensitivity allows organisms to respond to internal and external stimuli
- Growth results from anabolic reactions exceeding catabolic reactions
- Reproduction can be sexual or asexual
- Excretion eliminates metabolic wastes, different from egestion of undigested food
The Cell Theory, developed by scientists like Robert Hooke, Matthias Schleiden, Thomas Schwann, and Rudolf Virchow, consists of six fundamental principles: (1) All living things are made of cells, (2) Cells are the structural and functional units of life, (3) Cells arise from pre-existing cells, (4) Cells contain hereditary information passed from cell to cell, (5) All cells have the same basic chemical composition, and (6) Energy flow occurs within cells. There are two main types of cells: prokaryotic cells (bacteria and archaea) that lack a membrane-bound nucleus and organelles, and eukaryotic cells (plants, animals, fungi, protists) that have a true nucleus and specialized organelles enclosed by membranes.
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Cell Theory and Types of Cells
Examples
- Prokaryotes: E. coli bacteria, cyanobacteria, methane-producing archaea
- Eukaryotes: Human skin cells, leaf cells, yeast cells, amoeba
- Cell Theory applications: Understanding cancer as uncontrolled cell division
- Size comparison: Bacterial cells vs. human cells vs. plant cells
Key Points
- Cell Theory has six main principles established by multiple scientists
- Robert Hooke first observed cork cells and coined the term 'cell'
- Prokaryotic cells are simpler, lack nucleus and membrane-bound organelles
- Eukaryotic cells are complex with nucleus and specialized organelles
- Prokaryotes include bacteria and archaea
- Eukaryotes include plants, animals, fungi, and protists
- Cell size: prokaryotes usually <2 micrometers, eukaryotes 2-100+ micrometers
Cells contain various structures and organelles that perform specific functions. Common to both prokaryotes and eukaryotes are the cell membrane (controls entry/exit of substances), cytoplasm (gel-like matrix containing organelles), and ribosomes (protein synthesis sites). Eukaryotes additionally have a nucleus (contains genetic material), mitochondria (powerhouse generating ATP), endoplasmic reticulum (rough ER for protein transport, smooth ER for lipid synthesis), Golgi apparatus (protein processing and packaging), and lysosomes (digestive enzymes). Plant cells uniquely have cell walls (structural support), chloroplasts (photosynthesis), and large central vacuoles (storage and support). Animal cells have centrioles (cell division) and small vesicles instead of large vacuoles.
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Cell Structure and Organelles
Examples
- Cell membrane: Like a security checkpoint controlling entry to a building
- Nucleus: Like the control center or headquarters of a cell
- Mitochondria: Like power plants generating electricity (ATP) for the city (cell)
- Ribosomes: Like factories manufacturing products (proteins)
- Chloroplasts: Solar panels converting light energy to chemical energy
- Vacuoles in plants: Like water storage tanks maintaining plant structure
Key Points
- Cell membrane is selectively permeable, controlling molecular traffic
- Nucleus contains DNA and controls cellular activities
- Mitochondria produce ATP through cellular respiration
- Ribosomes synthesize proteins using mRNA instructions
- ER system transports materials throughout the cell
- Golgi apparatus modifies and packages proteins
- Plant cells have cell walls, chloroplasts, and large vacuoles
- Animal cells have centrioles and small vesicles
Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. The overall equation is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. This process occurs in chloroplasts and has two main stages: light-dependent reactions (in thylakoid membranes) and light-independent reactions or Calvin cycle (in stroma). Light-dependent reactions use photosystems I and II to capture light energy, split water molecules, and produce ATP and NADPH. The Calvin cycle uses CO₂, ATP, and NADPH to synthesize glucose through three steps: carbon fixation, reduction to form G3P, and regeneration of RuBP. The enzyme RuBisCO catalyzes carbon fixation, making it one of the most important enzymes on Earth.
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Photosynthesis
Examples
- Photosystem II: P680 chlorophyll absorbs 680nm light wavelength
- Photolysis: Water splitting produces 2H⁺ + 2e⁻ + ½O₂
- Chemiosmosis: Proton gradient drives ATP synthesis
- Calvin cycle: 3CO₂ + 9ATP + 6NADPH → 1 G3P (glucose precursor)
- Real-world: Plants in sunlight making food and releasing oxygen we breathe
Key Points
- Photosynthesis converts light energy to chemical energy (glucose)
- Occurs in chloroplasts of plant cells
- Two stages: light-dependent reactions and Calvin cycle
- Light reactions produce ATP, NADPH, and oxygen
- Calvin cycle fixes CO₂ into glucose using ATP and NADPH
- RuBisCO enzyme fixes carbon dioxide to RuBP
- Six CO₂ molecules needed to make one glucose molecule
- Oxygen is released as a byproduct from water splitting
Cellular respiration is the process that breaks down glucose to produce ATP energy for cellular activities. The overall equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. This process has four stages: glycolysis (in cytoplasm), pyruvate oxidation (mitochondrial matrix), Krebs cycle (mitochondrial matrix), and oxidative phosphorylation (inner mitochondrial membrane). Glycolysis breaks glucose into two pyruvate molecules, producing 2 ATP and 2 NADH. Pyruvate oxidation converts pyruvate to acetyl-CoA, producing NADH and CO₂. The Krebs cycle oxidizes acetyl-CoA, producing ATP, NADH, FADH₂, and CO₂. Oxidative phosphorylation uses the electron transport chain and chemiosmosis to produce most ATP (about 32-34 molecules). In the absence of oxygen, fermentation occurs, producing lactic acid or ethanol.
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Cellular Respiration
Examples
- Glycolysis: Glucose → 2 Pyruvate + 2 ATP + 2 NADH
- Krebs cycle: 2 Acetyl-CoA → 4CO₂ + 6NADH + 2FADH₂ + 2ATP
- Lactic acid fermentation: Muscle fatigue during intense exercise
- Alcoholic fermentation: Yeast in bread making and brewing
- ATP usage: Muscle contraction, active transport, protein synthesis
Key Points
- Cellular respiration extracts energy from glucose to make ATP
- Four stages: glycolysis, pyruvate oxidation, Krebs cycle, oxidative phosphorylation
- Glycolysis occurs in cytoplasm, others in mitochondria
- Complete breakdown of one glucose yields about 36-38 ATP molecules
- NADH produces about 3 ATP, FADH₂ produces about 2 ATP
- Electron transport chain creates proton gradient for ATP synthesis
- Fermentation occurs without oxygen, producing less ATP
- Oxygen is the final electron acceptor in aerobic respiration
Cell division is essential for growth, repair, and reproduction. The cell cycle consists of interphase (G1, S, G2 phases) where cells grow and replicate DNA, and M phase where division occurs. Mitosis produces two identical diploid cells for growth and repair, involving four stages: prophase (chromosome condensation, nuclear envelope breakdown), metaphase (chromosome alignment at cell center), anaphase (sister chromatid separation), and telophase (nuclear envelope reformation, chromosome decondensation). Meiosis produces four genetically different haploid gametes for sexual reproduction, involving two divisions (meiosis I and II) with crossing over during prophase I creating genetic diversity. Binary fission is the simpler division process in prokaryotes where DNA replicates and the cell splits into two identical cells.
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Cell Division: Mitosis and Meiosis
Examples
- Mitosis: Skin cell repair, plant root growth, wound healing
- Meiosis: Sperm and egg cell formation in animals
- Binary fission: Bacterial reproduction, amoeba division
- Crossing over: Genetic recombination creating diversity in offspring
- Cell cycle checkpoints: Preventing damaged DNA from being passed on
Key Points
- Cell cycle: Interphase (G1-S-G2) and M phase (mitosis/meiosis)
- Mitosis produces 2 identical diploid cells
- Meiosis produces 4 genetically different haploid cells
- Mitosis stages: prophase, metaphase, anaphase, telophase
- Meiosis has two divisions with crossing over in prophase I
- Binary fission occurs in prokaryotes
- Cytokinesis divides the cytoplasm after nuclear division
- Chromosomes condense during division for proper segregation
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