OCR GCSE Biology B (Twenty First Century)
OCR GCSE Biology B B4.2 How do we know about mitochondria and other cell structures? Exam Questions
Free OCR GCSE Biology B exam questions for B4.2 How do we know about mitochondria and other cell structures?, with a mark scheme for every pack. Covers light and electron microscopes, magnification and resolution, units, cell structures, prokaryotic and eukaryotic cells and the development of cell theory.
B4.2 How do we know about mitochondria and other cell structures? exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR GCSE Biology B B4.2 How do we know about mitochondria and other cell structures?
B4.2 explains how microscopes have revealed the structure of cells and how our ideas developed as technology improved. You need to compare light and electron microscopes, calculate magnification and convert between mm, µm and nm, and describe the structure and function of subcellular structures in animal, plant and bacterial cells. The topic illustrates how scientific explanations change with new evidence, an important idea about science in this course. It supports respiration in B4.1 and mitosis in B4.3. Examiners nearly always include a magnification calculation and often ask why electron microscopes show mitochondria and ribosomes in detail.
What you need to know
- Light microscopes Use light and lenses; can view living cells in colour; maximum useful magnification around x1500 and limited resolution, so mitochondria appear only as dots and ribosomes cannot be seen.
- Electron microscopes Use a beam of electrons; much higher magnification and resolution, revealing internal structure of mitochondria, chloroplasts and ribosomes, but specimens must be dead and prepared in a vacuum.
- Magnification Magnification = image size / actual size. Rearrange to find actual size = image size / magnification. Convert units first: 1 mm = 1000 µm and 1 µm = 1000 nm.
- Resolution Resolution is the ability to distinguish two points that are close together as separate. Higher resolution gives more detail.
- Eukaryotic cells Animal and plant cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cellulose cell wall, chloroplasts and a permanent vacuole.
- Prokaryotic cells Bacteria are much smaller, with no nucleus: DNA is a single loop in the cytoplasm, plus plasmids, ribosomes, a cell wall and sometimes a flagellum.
- Developing cell theory Early microscopists such as Hooke and van Leeuwenhoek first observed cells; improved microscopes later showed all living things are made of cells and revealed organelles.
Common mistakes in B4.2 How do we know about mitochondria and other cell structures?
- Confusing magnification and resolution. Magnification is how much bigger the image is; resolution is how much detail can be seen.
- Not converting units before calculating. Put image size and actual size in the same unit.
- Writing magnification with units. Magnification has no units, for example x400.
- Saying bacterial cells have a nucleus or mitochondria. Prokaryotes have no nucleus and no mitochondria.
- Stating that all plant cells contain chloroplasts. Root cells, for example, have none.
Try three B4.2 How do we know about mitochondria and other cell structures? exam-style questions
1. State one advantage of a light microscope over an electron microscope. (1 mark)
Show the mark scheme answer
Can view living specimens; or shows natural colour; or cheaper and portable.
2. A mitochondrion is 2 µm long. In an electron micrograph its image is 40 mm long. Calculate the magnification. (3 marks)
Show the mark scheme answer
40 mm = 40 000 µm; 40 000 / 2; = x20 000.
3. Explain why scientists could not study the structure of mitochondria until electron microscopes were developed. (3 marks)
Show the mark scheme answer
Mitochondria are very small; light microscopes have low resolution so internal structures cannot be distinguished; electron microscopes have much higher resolution and magnification, revealing the internal membranes.
B4.2 How do we know about mitochondria and other cell structures? FAQs
What does OCR GCSE Biology B B4.2 cover?
It covers light and electron microscopes, magnification and resolution, unit conversions, the structures in animal, plant and bacterial cells, and how cell theory developed.
Which paper is B4.2 examined in?
J257 has two papers at each tier, Breadth in Biology and Depth in Biology, and content from any chapter, including B4, can be assessed on either one. Expect it to be linked to ideas about science and to other chapters.
How do I avoid mistakes in magnification questions?
Write magnification = image size / actual size, convert both measurements to the same unit (usually µm) before dividing, and check your answer is sensible.
