ACT SSC Biology · Unit 2
ACT SSC Biology Unit 2: Cells and Organisms — Flashcards & Quiz
ACT SSC Biology Unit 2 focuses on cells and organisms within the BSSS framework. This unit covers cell theory, prokaryotic and eukaryotic cell structure, the fluid mosaic model, membrane transport mechanisms and the relationship between cellular processes and organism function. These flashcards and quiz questions help you revise the key concepts tested in ACT assessments.
Key Terms
- Cell Theory
- The foundational biological principle that all living things are composed of cells, cells are the basic unit of life, and all cells arise from pre-existing cells; a starting point for BSSS Biology Unit 2 school-based assessments.
- Selectively Permeable Membrane
- A membrane that allows certain molecules to pass while blocking others based on size, charge or solubility; central to BSSS questions on transport mechanisms across the cell membrane.
- Fluid Mosaic Model
- The accepted model of cell membrane structure describing a phospholipid bilayer with embedded proteins that move laterally, giving the membrane both fluidity and a mosaic-like composition as assessed in ACT SSC unit tasks.
- Active Transport
- The movement of substances across a membrane against the concentration gradient, requiring cellular energy in the form of ATP; a frequently examined concept in ACT Board of Senior Secondary Studies assessments.
- Organelle
- A specialised membrane-bound or non-membrane-bound structure within a eukaryotic cell that performs a specific function, such as mitochondria for respiration or ribosomes for protein synthesis.
- Prokaryote
- A single-celled organism lacking a membrane-bound nucleus and membrane-bound organelles, with DNA located in a nucleoid region; distinguished from eukaryotes in BSSS comparative cell biology tasks.
- Concentration Gradient
- The difference in concentration of a substance between two regions, which drives the direction of passive transport processes such as diffusion and osmosis in ACT SSC Biology.
Sample Flashcards
Q1: Describe the structure of DNA.
DNA is a double helix made of two antiparallel polynucleotide strands. Each nucleotide has a deoxyribose sugar, phosphate group, and nitrogenous base (A, T, G, C). Bases pair by hydrogen bonds: A–T (2 bonds), G–C (3 bonds).
Q2: Outline the process of DNA replication.
Helicase unwinds and separates strands. DNA polymerase adds complementary nucleotides to each template strand (5' to 3'). Leading strand is continuous; lagging strand is made in Okazaki fragments joined by ligase.
Q3: What is transcription?
Transcription is the synthesis of mRNA from a DNA template. RNA polymerase binds to the promoter, separates DNA strands, and assembles a complementary mRNA strand using RNA nucleotides (A, U, G, C).
Q4: Describe translation.
Translation is protein synthesis at the ribosome. mRNA codons are read by tRNA anticodons carrying specific amino acids. Amino acids are joined by peptide bonds to form a polypeptide chain.
Q5: State Mendel's Law of Segregation.
During gamete formation, the two alleles for each gene segregate so that each gamete carries only one allele for each trait.
Q6: What is the difference between genotype and phenotype?
Genotype is the genetic makeup of an organism (e.g. Tt). Phenotype is the observable characteristics (e.g. tall plant) resulting from genotype and environment.
Q7: Distinguish between homozygous and heterozygous.
Homozygous: both alleles are the same (TT or tt). Heterozygous: alleles are different (Tt). Homozygous dominant (TT) and heterozygous (Tt) may show the same phenotype.
Q8: What is codominance?
Codominance occurs when both alleles in a heterozygote are fully expressed, producing a phenotype showing both traits simultaneously rather than a blend.
Sample Quiz Questions
Q1: DNA is a single-stranded molecule.
Answer: FALSE
DNA is double-stranded, forming a double helix with two antiparallel polynucleotide strands.
Q2: Adenine pairs with thymine in DNA via two hydrogen bonds.
Answer: TRUE
A–T pairs have 2 hydrogen bonds; G–C pairs have 3 hydrogen bonds.
Q3: DNA polymerase synthesises new DNA strands in the 3' to 5' direction.
Answer: FALSE
DNA polymerase adds nucleotides in the 5' to 3' direction.
Q4: RNA uses uracil instead of thymine.
Answer: TRUE
RNA has uracil (U) instead of thymine (T). A pairs with U in RNA.
Q5: Translation occurs in the nucleus.
Answer: FALSE
Translation occurs at ribosomes in the cytoplasm. Transcription occurs in the nucleus.
Why It Matters
Cells and Organisms in ACT SSC Biology Unit 2 builds the foundational understanding of how living things function at the cellular level. BSSS assessments expect you to explain cell structure through microscopy, describe membrane transport mechanisms, and connect cellular processes such as photosynthesis and respiration to organism function. This unit develops both theoretical knowledge and practical laboratory skills, as microscopy techniques and experimental design are frequently assessed. Students who master cellular concepts thoroughly find that heredity, internal environments and organism physiology in later units make significantly more sense. Membrane transport concepts connect directly to the homeostasis unit, where understanding how cells regulate their internal environment depends on active and passive transport mechanisms. BSSS exam questions on cells commonly require you to compare prokaryotic and eukaryotic structures using diagrams, so practise labelling organelles and explaining each structure's function from memory.
Key Concepts
Cell Structure and Function
Prokaryotic and eukaryotic cells differ in their level of structural complexity. Understanding the function of each organelle and how they work together as a system prepares you for BSSS questions that ask you to relate structure to function at the cellular level.
Membrane Structure and Transport
The fluid mosaic model explains how the cell membrane selectively controls the movement of substances. Mastering passive transport, active transport, endocytosis and exocytosis allows you to explain how cells maintain homeostasis in varying environments.
Microscopy and Cell Imaging
Light and electron microscopes reveal different levels of cellular detail. Understanding magnification, resolution and specimen preparation develops the practical skills that BSSS assessments evaluate through both practical reports and theoretical questions.
Cellular Energy Processes
Photosynthesis and cellular respiration are complementary processes that convert energy for cellular use. Understanding the inputs, outputs and locations of these metabolic pathways is essential for explaining how organisms obtain and use energy.
Common Mistakes to Avoid
- Stating that osmosis is the movement of solute rather than solvent — BSSS marking guides specifically penalise this reversal; osmosis is the net movement of water molecules across a selectively permeable membrane.
- Confusing facilitated diffusion with active transport in ACT SSC assessments — both use proteins, but facilitated diffusion is passive and moves substances down their concentration gradient without ATP.
- Omitting the double membrane when describing mitochondria or chloroplasts — BSSS examiners expect structural detail including inner membrane folds (cristae or thylakoids) and their functional significance.
- Labelling ribosomes as membrane-bound organelles — this is a common ACT SSC exam trap; ribosomes lack a surrounding membrane and are found free in the cytoplasm or attached to rough ER.
Study Tips
- Practise drawing and labelling cell diagrams from memory, then use your textbook to identify any structures you missed or mislabelled.
- Create flashcards pairing each organelle with its function and appearance under electron microscopy, reviewing with spaced repetition for long-term retention.
- Work through membrane transport problems by always identifying the concentration gradient direction before determining the transport type.
- Use past BSSS practical reports as models for structuring your own laboratory write-ups with clear methods and error analysis.
- Compare prokaryotic and eukaryotic cells using a detailed table to reinforce the key structural differences for short-answer questions.
- Before your exam, work through the practice questions in this set at least twice using spaced repetition. Testing yourself repeatedly is the most effective revision strategy for long-term retention.
Related Topics
Frequently Asked Questions
What does ACT SSC Biology Unit 2 cover?
Unit 2 covers cell theory, prokaryotic and eukaryotic cell structure, organelle function, the fluid mosaic model, membrane transport, photosynthesis and cellular respiration.
How many flashcards are in this set?
This free set contains 20 flashcards and 20 true/false quiz questions covering all key concepts in Unit 2, aligned to the BSSS Biology framework.
Are these flashcards aligned to the ACT curriculum?
Yes — every flashcard and quiz question is mapped to the BSSS Science Framework for ACT SSC Biology Unit 2.
Last updated: March 2026 · 20 flashcards · 20 quiz questions · Content aligned to the BSSS Framework