Study guide
7.1 Cell Biology, Transport, and Cellular Energetics
Adamson University College Entrance Test AdUCET
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1 Introduction & Exam Overview
1.1 AdUCET Overview, Format, and Admission Process 1.2 Test-Taking and Time-Management Strategies
2 Chapter 2: Mathematics I — Numbers, Algebra, and Functions
2.1 Number Sense, Operations, and Fraction–Decimal–Percent Conversions 2.2 Algebra, Polynomials, and Linear/Quadratic Equations 2.3 Inequalities, Absolute Value, and Systems of Equations 2.4 Radicals, Rational Expressions, and Scientific Notation 2.5 Coordinate Geometry, Lines, and Functions
3 Chapter 3: Mathematics II — Geometry, Measurement, and Trigonometry
3.1 Plane Geometry: Angles, Triangles, Polygons, and Circles 3.2 Solid Mensuration, Measurement, and Unit Conversion 3.3 Right-Triangle Trigonometry and Applications
4 Chapter 4: Mathematics III — Sequences, Proportion, and Data
4.1 Arithmetic and Geometric Sequences and Series 4.2 Ratio, Proportion, Percentage, Work, and Mixture Problems 4.3 Descriptive Statistics and Data Interpretation 4.4 Probability: Rules, Compound Events, and Conditional Probability 4.5 Counting Principles: Permutations and Combinations
5 Chapter 5: English I — Reading Comprehension and Vocabulary
5.1 Reading Comprehension: Main Idea, Purpose, and Passage Structure 5.2 Inference, Supporting Detail, and Author's Tone 5.3 Word Roots, Prefixes, and Suffixes 5.4 Vocabulary in Context, Synonyms, Antonyms, and Confusables
6 Chapter 6: English II — Grammar, Usage, and Written Expression
6.1 Subject-Verb Agreement and Verb Tenses 6.2 Pronouns, Modifiers, and Parallel Structure 6.3 Sentence Boundaries, Clauses, and Punctuation 6.4 Sentence Correction, Redundancy, and Idiomatic Usage 6.5 Verbal Analogies and Relationship Bridges 6.6 Paragraph Organization, Coherence, and Transitions
7 Chapter 7: General Science I — Biology and Chemistry
7.1 Cell Biology, Transport, and Cellular Energetics 7.2 Genetics, Heredity, and Molecular Biology 7.3 Human Body Systems, Ecology, and Evolution 7.4 Matter, Phase Changes, and Atomic Structure 7.5 Periodic Trends, Chemical Bonding, Reactions, Acids and Bases
8 Chapter 8: General Science II — Physics and Earth Science
8.1 Mechanics: Motion, Newton's Laws, Work, and Energy 8.2 Waves, Sound, Light, Heat, Electricity, and Magnetism 8.3 Earth's Structure, Plate Tectonics, and the Rock Cycle 8.4 The Atmosphere, Weather, the Water Cycle, and Astronomy
9 Chapter 9: Aptitude and Abstract Reasoning
9.1 Figure Series and Pattern Progression 9.2 Matrix Reasoning and Figural Analogies 9.3 Spatial Reasoning: Rotation, Reflection, and Chirality 9.4 Paper Folding, Cube Nets, and Orthographic Views 9.5 Deductive Reasoning, Syllogisms, and Venn Diagrams 9.6 Number, Letter, and Alphanumeric Series 9.7 Odd-One-Out, Classification, and Logic Puzzles
7.1 Cell Biology, Transport, and Cellular Energetics
Key Takeaways Explain This Topic AI
The sodium-potassium pump spends one ATP to expel 3 sodium ions and admit 2 potassium ions, both against their gradients, leaving the cell interior slightly negative.
One glucose molecule yields about 36 to 38 ATP through aerobic respiration but only 2 ATP net through lactic acid or alcoholic fermentation.
In a hypertonic solution an animal cell crenates and a plant cell plasmolyses; in a hypotonic solution the animal cell bursts by lysis while the plant cell becomes firmly turgid.
The oxygen released by photosynthesis comes from the splitting of water in the thylakoid membranes, not from carbon dioxide; carbon dioxide is fixed in the stroma by the Calvin cycle.
Mitosis produces 2 genetically identical diploid daughter cells for growth and repair, while meiosis produces 4 genetically varied haploid gametes.
Last updated: August 2026
7.1 Cell Biology, Transport, and Cellular Energetics
Adamson University publishes no content outline for the AdUCET, so the sensible preparation target for the science items is the Grades 11 to 12 K-12 core — and no part of that core is denser than the cell. What follows is standard senior-high material that rewards precise vocabulary and a few exact numbers far more than it rewards memorised paragraphs.
1. Cell theory and the two great cell types
Cell theory is the organising idea of biology and rests on three statements:
Every living thing is built from one or more cells .
The cell is the smallest unit that is both structural and functional in a living thing.
New cells arise only from the division of existing cells; they do not appear spontaneously.
Cells come in two architectures. A prokaryote (Greek for “before the nucleus”) keeps its DNA loose in a region called the nucleoid . A eukaryote (“true nucleus”) seals its DNA inside a membrane.
- Feature Prokaryotic cell Eukaryotic cell
- Nuclear membrane Absent — DNA lies free in the nucleoid Present — DNA enclosed by a nuclear envelope
- Form of the DNA One circular chromosome, plus plasmids Several linear chromosomes wound on protein
- Membrane-bound organelles None Mitochondria, ER, Golgi, lysosomes and more
- Ribosomes Smaller, 70S Larger, 80S (70S inside mitochondria and chloroplasts)
- Typical size 0.1 to 5 micrometres 10 to 100 micrometres
- Examples Bacteria, Archaea Protists, fungi, plants, animals
- Plant cell versus animal cell
Both are eukaryotic, so both carry a nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi and a cell membrane. Four differences separate them:
A cell wall of cellulose sits outside the membrane of a plant cell, giving it a fixed boxy outline and preventing it from bursting.
Chloroplasts allow the plant cell to manufacture its own food; animal cells have none.
One large central vacuole fills most of a mature plant cell and supplies internal pressure, whereas animal cells carry only small scattered vacuoles.
Animal cells contain centrioles that organise the spindle during division, and their lysosomes are far more prominent than a plant's.
2. The organelle roll call
Organelle Structure Function
Nucleus Double membrane pierced by pores Stores DNA and directs all cell activity; the nucleolus inside it builds ribosomes
Mitochondrion Double membrane, the inner one folded into cristae around a matrix Site of aerobic respiration; carries its own circular DNA
Chloroplast Double membrane enclosing stacked thylakoid discs (grana) bathed in stroma Traps light using chlorophyll and runs photosynthesis
Ribosome Ribosomal RNA plus protein; no membrane at all Assembles polypeptides (the mechanism of translation belongs to 7.2)
Rough ER Flattened sacs studded with ribosomes Folds and modifies proteins bound for export or for membranes
Smooth ER Tubules with no ribosomes Synthesises lipids and steroids, stores calcium, detoxifies drugs in liver cells
Golgi apparatus Stack of flattened cisternae Modifies, sorts, labels and ships products in vesicles
Lysosome Single-membrane sac of digestive enzymes Breaks down worn-out organelles and engulfed material; the “suicide sac”
Vacuole Membrane-bound sac (the tonoplast in plants) Stores water, salts, pigments and waste; supplies turgor pressure
Cytoskeleton Microfilaments, intermediate filaments, microtubules Maintains shape, anchors organelles, moves chromosomes and vesicles
Cell wall Cellulose in plants, chitin in fungi, peptidoglycan in bacteria Rigid support and protection; freely permeable
Cell membrane Phospholipid bilayer with embedded proteins Selectively permeable boundary controlling entry and exit
3. The fluid mosaic membrane
The fluid mosaic model describes the membrane as a double sheet of phospholipids whose water-loving phosphate heads face the watery fluid on either side and whose water-fearing fatty-acid tails point inward at each other. It is fluid because the phospholipids drift sideways like boats on a pond, and a mosaic because proteins are scattered irregularly through it: channel proteins form pores, carrier proteins change shape to ferry one specific solute, receptor proteins bind hormones, and cholesterol in animal cells stops the sheet becoming too runny when hot or too rigid when cold. OUTSIDE THE CELL
- ooooooooo ooooo ===== oooooooooo o = phosphate head (water-loving)
- ||||||||| ||||| ===== |||||||||| | = fatty-acid tail (water-fearing)
- ||||||||| ||||| ===== |||||||||| === = transport protein spanning
- ooooooooo ooooo ===== oooooooooo the whole bilayer
- INSIDE (CYTOPLASM)
Only small uncharged molecules — oxygen, carbon dioxide, and to a limited extent water — slip straight between the tails. Glucose, amino acids and every ion need a protein.
4. Passive transport and tonicity
Passive transport costs no ATP; particles move down their concentration gradient until evenly spread.
Simple diffusion — small non-polar molecules such as O₂ and CO₂ pass directly through the bilayer.
Facilitated diffusion — polar or charged particles such as glucose and Na⁺ still move down their gradient, but through a channel or carrier protein.
Osmosis — the diffusion of water across a selectively permeable membrane, from the side with more water (fewer dissolved particles) to the side with less.
Tonicity always describes the outside solution relative to the inside of the cell.
Outside solution Net water movement Animal cell Plant cell
Hypertonic (more solute outside) Out of the cell Shrivels — crenation Protoplast peels away from the wall — plasmolysis ; the plant wilts
Hypotonic (less solute outside) Into the cell Swells and bursts — lysis (haemolysis in red blood cells) Becomes firm — turgid ; the wall prevents bursting
Isotonic (equal) None Normal shape; hospital saline is 0.9% NaCl for exactly this reason Limp and flaccid , which is poor for a plant
Worked example 1 — settle tonicity by counting particles
A cell whose cytoplasm behaves like 0.30 osmol/L is dropped into 0.20 M sodium chloride . Does it swell or shrink?
Sodium chloride is ionic and dissociates completely: each formula unit yields one Na⁺ and one Cl⁻.
Particle concentration outside = 0.20 × 2 = 0.40 osmol/L .
Compare: 0.40 outside is greater than 0.30 inside, so the solution is hypertonic .
Water therefore leaves by osmosis. An animal cell crenates; a plant cell plasmolyses.
The trap is comparing “0.20 M” with “0.30 osmol/L” and calling the solution dilute. Convert to particles first. Had the solute been 0.20 M glucose, which does not dissociate, the solution would have been hypotonic and the cell would have swollen instead.
5. Active transport, endocytosis and exocytosis
Active transport spends ATP to drive a solute against its gradient, from low concentration to high. The standard case is the sodium-potassium pump (Na⁺/K⁺-ATPase) present in every animal cell membrane: for each ATP hydrolysed it ejects 3 Na⁺ and imports 2 K⁺ . Since three positive charges leave for every two that enter, the interior is left slightly negative — the resting condition a nerve cell needs before it can fire.
Cargo too large for any protein forces the membrane itself to move:
Endocytosis folds the membrane inward and pinches off a vesicle into the cell. Phagocytosis (“cell eating”) takes in solids, as when a white blood cell swallows a bacterium; pinocytosis (“cell drinking”) takes in droplets of fluid.
Exocytosis fuses a vesicle with the membrane and empties it out of the cell: insulin from pancreatic cells, neurotransmitter at a synapse, mucus from goblet cells.
6. Photosynthesis — banking the energy 6 CO 2 + 6 H 2 O + light energy → C 6 H 12 O 6 + 6 O 2 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2 6 CO 2 + 6 H 2 O + light energy → C 6 H 12 O 6 + 6 O 2
It runs in two stages inside the chloroplast:
Light-dependent reactions , in the thylakoid membranes : chlorophyll absorbs light, water is split by photolysis , oxygen escapes as waste, and the captured energy is parked in ATP and NADPH .
Calvin cycle , or light-independent reactions, in the stroma : carbon dioxide is fixed by the enzyme RuBisCO and reduced to sugar using the ATP and NADPH made in stage one. It needs no light directly, yet it halts within minutes of darkness because its supply of ATP and NADPH dries up.
Remember that the oxygen you breathe was pulled out of water , not out of carbon dioxide.
7. Aerobic respiration — spending it C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O + energy \text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2 \rightarrow 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} + \text{energy} C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O + energy
- Stage Location Main output per glucose
- Glycolysis Cytoplasm; no oxygen required 2 pyruvate, net 2 ATP , 2 NADH
- Link reaction Mitochondrial matrix 2 acetyl-CoA, 2 CO₂, 2 NADH
- Krebs (citric acid) cycle Mitochondrial matrix 4 CO₂, 2 ATP , 6 NADH, 2 FADH₂
Electron transport chain Inner mitochondrial membrane (cristae) Water, plus about 32 to 34 ATP through ATP synthase
Worked example 2 — the ATP ledger and the price of losing oxygen
Using the senior-high convention that one NADH is worth 3 ATP and one FADH₂ is worth 2 ATP:
Direct (substrate-level) ATP: 2 from glycolysis + 2 from the Krebs cycle = 4 ATP .
Total NADH: 2 + 2 + 6 = 10 , so 10 × 3 = 30 ATP .
Total FADH₂: 2 , so 2 × 2 = 4 ATP .
Grand total = 4 + 30 + 4 = 38 ATP per glucose. Where the two glycolytic NADH must be shuttled into the mitochondrion at a cost, the figure falls to 36; careful modern measurements put the real yield closer to 30 to 32.
Now price the loss of oxygen. A sprinter's thigh fibre burns 5 glucose molecules . Aerobically that is 5 × 38 = 190 ATP . If the oxygen supply fails and the fibre switches entirely to fermentation, it collects 5 × 2 = 10 ATP — a shortfall of 180 ATP , which is why all-out anaerobic effort lasts seconds rather than minutes.
8. Anaerobic respiration and the two fermentations
Both pathways begin with the same glycolysis and both net only 2 ATP . Their real job is to regenerate NAD⁺ so that glycolysis can keep turning without oxygen.
Lactic acid fermentation : pyruvate becomes lactic acid. It runs in overworked human muscle and in the bacteria that sour milk into yoghurt or ferment rice for burong isda .
Alcoholic fermentation : pyruvate becomes ethanol plus CO₂. Yeast does this; the carbon dioxide raises pandesal dough while the ethanol produces tuba and lambanog .
9. ATP, and mitosis against meiosis
ATP (adenosine triphosphate) is adenine plus ribose plus three phosphate groups. Snapping off the terminal phosphate releases usable energy: ATP + H 2 O → ADP + P i + energy \text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy} ATP + H 2 O → ADP + P i + energy
ATP is a rechargeable battery rather than a fuel tank: a cell holds only seconds' worth at a time and rebuilds it continuously.
- Mitosis Meiosis
- Purpose Growth, repair, asexual reproduction Production of gametes
- Number of divisions One Two, meiosis I and meiosis II
- Daughter cells 2 4
- Ploidy Diploid (2n) to diploid (2n) Diploid (2n) to haploid (n)
- Genetic outcome Identical to the parent cell Genetically varied
- Where in humans Body (somatic) cells Testes and ovaries only
- Common traps
Calling the cell hypertonic when the item asks about the solution . Tonicity describes the outside relative to the inside.
Believing osmosis moves the solute. Osmosis moves water ; the solute is usually the thing that cannot cross.
Assuming active transport always means inward. The sodium pump drives Na⁺ out .
Claiming plants only photosynthesise. Plants respire day and night, and at night they are net consumers of oxygen.
Placing the Calvin cycle in the thylakoid, or glycolysis in the mitochondrion. Calvin cycle equals stroma; glycolysis equals cytoplasm.
Writing that fermentation yields no ATP. It yields 2 — merely far fewer than 38.
Forgetting that the cell wall is freely permeable. Selection is the job of the membrane .