Skip to content
Marlbridge
Free trial

Flashcards · 9700 · AS Topic 1

Cell structure (AS Level) flashcards

17 cards on AS Topic 1, subtopics 1.1 to 1.2. Pick a subtopic or study them all.

Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.

All 17 cards

For a quick read-through or printing. Cover the right-hand side to test yourself.

1.1 The microscope in cell studies

Magnification
How many times larger the image is than the actual size of the object. Magnification = image size ÷ actual size. It has no unit (write ×8000).
Resolution
The ability to distinguish two points that are close together as separate. It is not "how clear the image is".
Unit conversions for cell measurements
1 mm = 1000 µm 1 µm = 1000 nm 1 mm = 1 000 000 nm Convert both measurements to the same unit before dividing.
A nucleus on a TEM micrograph at ×14 000 measures 84 mm. What is its actual size?
84 mm = 84 000 µm. Actual size = image size ÷ magnification = 84 000 ÷ 14 000 = 6 µm.
How do you calibrate an eyepiece graticule?
Put a stage micrometer (a scale of known length) on the stage and line up the two scales. Find where lines coincide exactly, far along. One eyepiece unit = micrometer length ÷ number of eyepiece units. Recalibrate after changing the objective.
Why do electron microscopes have a much better resolution than light microscopes?
Resolution is limited by wavelength. An electron beam has a much shorter wavelength than light, so points much closer together can be distinguished. Light microscope limit: about 200 nm.
TEM vs SEM
TEM: the beam passes through an ultra-thin section; 2-D image of internal structure; highest resolution. SEM: the beam scans the surface; 3-D image of the surface. Both: dead specimens in a vacuum, black-and-white images.
Rules for a plan diagram compared with a high-power drawing
Plan diagram (low power): outlines of tissue layers in correct proportions, no individual cells. High-power drawing: individual cells, only visible contents, two lines for each cell wall, no shading, ruled label lines.

1.2 Cells as the basic units of living organisms

Organelles surrounded by two membranes (an envelope)
Nucleus (nuclear envelope with pores), mitochondria and chloroplasts.
Cell structures with a single membrane
Cell surface membrane, RER, SER, Golgi body, lysosomes, vesicles and the tonoplast.
Cell structures with no membrane
Ribosomes, nucleolus, centrioles, microtubules and the cell wall.
Functions of the RER, SER and Golgi body
RER: transports proteins made on its ribosomes. SER: makes lipids, including steroids. Golgi body: modifies and packages proteins; makes lysosomes.
Cilia vs microvilli
Cilia: long, with a 9 + 2 arrangement of microtubules and a basal body; they beat to move fluid or mucus. Microvilli: short folds of the cell surface membrane with no microtubule core; they increase surface area for absorption.
Ribosomes in prokaryotic and eukaryotic cells
Prokaryotes: 70S only. Eukaryotes: 80S in the cytoplasm and on the RER; 70S inside mitochondria and chloroplasts.
Structural features of a typical bacterium
Unicellular, generally 1–5 µm across, peptidoglycan cell wall, circular DNA free in the cytoplasm, 70S ribosomes, no double-membrane organelles.
Structure of a virus
Non-cellular. A nucleic acid core (DNA or RNA) inside a protein capsid. Some have an outer envelope of phospholipids.
Why is "a bacterium has no organelles" wrong?
A bacterium has ribosomes. It lacks a nucleus and double-membrane organelles such as mitochondria.

Revise Cell structure further