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Module 2: Foundations in biology
Quick questions on Cell structure and microscopy: organelles, the secretory pathway and magnification - OCR A-Level Biology A
14short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are prokaryotic cells?Show answer
Prokaryotic (bacterial) cells are smaller and simpler. They have no nucleus and no membrane-bound organelles. Their DNA is a single circular loop free in the cytoplasm, not wound around histones, and they may carry plasmids (small DNA rings often bearing antibiotic-resistance genes), a protective capsule, a flagellum for movement, mesosomes, and 70S ribosomes. The cell wall is made of murein (peptidoglycan), not cellulose.
What is nucleus?Show answer
Surrounded by a double membrane (the nuclear envelope) perforated by nuclear pores. Contains chromatin (DNA wound around histone proteins) and a nucleolus that makes ribosomes. Stores genetic information and controls the cell through transcription.
What is rough endoplasmic reticulum?Show answer
A network of membranes studded with ribosomes. Folds and transports proteins destined for secretion or the cell-surface membrane.
What is smooth endoplasmic reticulum?Show answer
Membranes without ribosomes. Synthesises and processes lipids and steroids.
What is golgi apparatus?Show answer
A stack of flattened membrane sacs (cisternae). Modifies, sorts and packages proteins and lipids (for example by glycosylation) into vesicles for secretion or to form lysosomes.
What is mitochondria?Show answer
A double membrane; the inner membrane is folded into cristae surrounding a fluid matrix. The site of aerobic respiration and ATP synthesis. Cells with high energy demand have many.
What are chloroplasts?Show answer
Found in plant and algal cells. A double membrane plus internal thylakoid membranes stacked into grana, surrounded by stroma. The site of photosynthesis; contain their own DNA and 70S ribosomes.
What are ribosomes?Show answer
Made of rRNA and protein, free in the cytoplasm or bound to the RER. The site of translation. Eukaryotic ribosomes are 80S; 70S ribosomes occur in prokaryotes, mitochondria and chloroplasts.
What are lysosomes?Show answer
Golgi-derived vesicles of hydrolytic enzymes that digest worn-out organelles, ingested material and engulfed pathogens.
What are centrioles?Show answer
Two bundles of microtubules at right angles in animal cells; they form the spindle in cell division.
What is cell wall?Show answer
Outside the membrane; cellulose in plants, chitin in fungi. Freely permeable; gives mechanical strength and resists turgor.
What is q1?Show answer
Give three structural features of a prokaryotic cell that a eukaryotic cell does not have. [3 marks]
What is q2?Show answer
Explain why a cell that secretes large amounts of protein has many mitochondria. [2 marks]
What is q3?Show answer
An image of a chloroplast measures 40 mm. The actual chloroplast is 8 micrometres long. Calculate the magnification. [2 marks]