Cells as the basic units of living organisms
Cambridge A-Level Biology (9700) · Unit 1: Cell structure · 18 flashcards
Cells as the basic units of living organisms is topic 1.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 1 — Cell structure , alongside The microscope in cell studies. In one line: The cell surface membrane is a phospholipid bilayer with embedded proteins. Its main function is to regulate the movement of substances into and out of the cell, providing a selective barrier.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 18 flashcards — 15 definitions and 3 key concepts — covering the precise wording mark schemes reward. Use the 15 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Describe the structure and primary function of the cell surface membrane
The cell surface membrane is a phospholipid bilayer with embedded proteins. Its main function is to regulate the movement of substances into and out of the cell, providing a selective barrier.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Recognise the following organelles and other structures in eukaryotic cells, and outline the structure and function of each. The list is limited to: the cell surface membrane; the nucleus together with its nucleolus and nuclear envelope; smooth and rough endoplasmic reticulum; the Golgi body (also called the Golgi apparatus or Golgi complex); mitochondria, noting that they contain small circular DNA; ribosomes, which are 80S in the cytoplasm but 70S inside mitochondria and chloroplasts; lysosomes; microtubules and centrioles; cilia; microvilli; chloroplasts, noting that they also contain small circular DNA; the cell wall; plasmodesmata; and, in plant cells, the large permanent vacuole with its tonoplast.
- Describe and interpret drawings, photomicrographs and electron micrographs showing typical animal and plant cells.
- Compare how typical animal cells and typical plant cells are structured.
- State that cells obtain the energy for processes that need it from ATP made in respiration.
- Outline the main structural features of a typical bacterium as an example of a prokaryotic cell: single-celled; usually 1 to 5 µm across; cell walls of peptidoglycan; circular DNA; 70S ribosomes; no organelles bounded by a double membrane.
- Compare the structure of a typical bacterial (prokaryotic) cell with that of typical eukaryotic plant and animal cells.
- State that every virus is non-cellular, made of a nucleic acid core (DNA or RNA) inside a protein capsid, and that some viruses also have an outer envelope of phospholipids.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Cells as the basic units of living organisms
- › Use the term 'nuclear envelope' specifically when referring to the double membrane visible in electron micrographs.
- › Associate peptidoglycans exclusively with bacterial cell walls; viruses lack cell walls and are composed primarily of nucleic acids and protein capsids.
- › Always remember that mitochondria and chloroplasts contain 70S ribosomes, which is evidence for their endosymbiotic prokaryotic origin.
- › Recall that a virus contains a single type of nucleic acid; it will have either ribose in its RNA or deoxyribose in its DNA.
- › State clearly that virus particles have a genome of either DNA or RNA and a protective protein coat called a capsid.
Describe the structure and primary function of the cell surface membrane.
The cell surface membrane is a phospholipid bilayer with embedded proteins. Its main function is to regulate the movement of substances into and out of the cell, providing a selective barrier.
What is the role of the nucleolus within the nucleus?
The nucleolus is a structure within the nucleus responsible for ribosome synthesis. It assembles ribosomal RNA (rRNA) and proteins to form ribosomal subunits.
Distinguish between the functions of rough and smooth endoplasmic reticulum (ER).
Rough ER contains ribosomes and is involved in protein synthesis and modification. Smooth ER lacks ribosomes and is involved in lipid synthesis, carbohydrate metabolism, and detoxification.
Outline the structure and function of the Golgi body (Golgi apparatus).
The Golgi body is a stack of flattened membrane-bound sacs called cisternae. It modifies, sorts, and packages proteins and lipids synthesized in the ER for transport to other organelles or secretion.
Describe the structure of a mitochondrion, including the significance of its circular DNA.
Mitochondria have a double membrane; the inner membrane is folded into cristae. They contain their own circular DNA, encoding some mitochondrial proteins, which supports the endosymbiotic theory.
What is the function of ribosomes, and where are 80S and 70S ribosomes found?
Ribosomes are responsible for protein synthesis (translation). 80S ribosomes are found in the cytoplasm of eukaryotic cells, while 70S ribosomes are found in prokaryotes, chloroplasts, and mitochondria.
Describe the role of lysosomes in eukaryotic cells.
Lysosomes contain hydrolytic enzymes. They break down cellular waste, debris, and foreign materials through phagocytosis and autophagy, playing a crucial role in intracellular digestion.
What are the functions of centrioles and microtubules in cell division and structure?
Centrioles organize microtubules, forming the spindle fibers during cell division. Microtubules provide structural support, facilitate intracellular transport, and form cilia and flagella.
Describe the structure and function of chloroplasts, highlighting the role of their circular DNA.
Chloroplasts are organelles in plant cells responsible for photosynthesis, containing chlorophyll. Their circular DNA encodes some of the proteins needed for their function, also supporting the endosymbiotic theory.
What are plasmodesmata and their function in plant cells?
Plasmodesmata are channels that cross plant cell walls, connecting the cytoplasm of adjacent cells. They allow for the transport of water, nutrients, and signaling molecules between cells.
Describe the key structural differences between typical plant and animal cells.
Plant cells possess a cell wall, chloroplasts, and a large central vacuole, which are absent in animal cells. Animal cells have centrioles and lack a cell wall and chloroplasts.
What is the function of ATP in cells?
ATP (adenosine triphosphate) provides energy for cellular processes. It releases energy through hydrolysis, driving energy-requiring reactions such as muscle contraction and active transport.
Outline the key structural features of a prokaryotic cell as found in a bacterium.
Prokaryotic cells are unicellular, generally 1–5 µm in diameter, possess a peptidoglycan cell wall, circular DNA, 70S ribosomes, and lack membrane-bound organelles.
Compare the ribosomes found in prokaryotic and eukaryotic cells.
Prokaryotic cells contain 70S ribosomes, while eukaryotic cells contain larger 80S ribosomes. 'S' refers to Svedberg units, a measure of sedimentation rate during centrifugation.
Describe the structure of a virus.
Viruses are non-cellular structures consisting of a nucleic acid core (DNA or RNA) surrounded by a capsid made of protein. Some viruses also have an outer envelope made of phospholipids.
What type of genetic material is found in viruses?
Viruses contain either DNA or RNA as their genetic material. This nucleic acid is enclosed within a protein capsid.
Identify three structures present in plant cells but absent in animal cells.
Plant cells contain chloroplasts, a cell wall (composed of cellulose), and a large central vacuole, which are not found in animal cells.
Describe the composition of a bacterial cell wall.
Bacterial cell walls are primarily composed of peptidoglycan, a polymer consisting of sugars and amino acids. This provides structural support and protection for the cell.
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Read NotesMore topics in Unit 1 — Cell structure
Cells as the basic units of living organisms sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
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