A-Level Biology – Cell Structure & Microscopy

30 Question-and-Answer style flashcards covering cell theory, microscopy techniques, prokaryotic and eukaryotic cell structures, life processes, and practical microscopy skills, drawn from the provided lecture notes.

What is the basic structural unit of all living organisms?

The cell.

What reasoning predicts that a newly discovered organism will be cellular based on cell theory?

Deductive reasoning.

State the three pillars of the modern cell theory.

(1) All living things are composed of cells; (2) The cell is the smallest unit of life; (3) Cells arise only from pre-existing cells by division.

List the key practical skills needed to calculate magnification with a light microscope.

Preparing temporary mounts, staining specimens, using an eyepiece graticule for measurement, focusing with coarse and fine adjustments, calculating actual size and magnification, drawing a scale bar, and photographing the image.

Give two advantages of electron microscopy over light microscopy.

Much higher resolution and magnification, revealing ultrastructure of organelles.

Which microscopy techniques use fluorescent tags to locate specific molecules?

Fluorescent staining and immunofluorescence.

Name three recent developments that have advanced microscopy.

Electron microscopy, freeze-fracture preparation, and cryogenic electron microscopy (cryo-EM).

Identify three structures found in every known cell.

DNA genetic material, a cytoplasm mostly of water, and a plasma (cell) membrane composed of lipids.

Why is a lipid bilayer plasma membrane essential for life?

It encloses the cytoplasm, creates a distinct internal environment, controls transport, and maintains homeostasis.

What size ribosomes are characteristic of prokaryotes?

70S ribosomes.

List five components of a typical Gram-positive bacterium such as Bacillus.

Cell wall, plasma membrane, cytoplasm, naked DNA loop (nucleoid), and 70S ribosomes.

Which type of ribosomes are found in the cytoplasm of eukaryotic cells?

80S ribosomes.

Name four membrane-bound organelles common to all eukaryotes.

Mitochondria, endoplasmic reticulum, Golgi apparatus, and various vesicles/vacuoles (e.g., lysosomes).

What is the role of nuclear pores?

They regulate the movement of RNA, proteins, and other molecules between the nucleus and cytoplasm.

Which cytoskeletal filaments are mentioned as universal in eukaryotes?

Microtubules and microfilaments.

List the eight essential life processes performed by unicellular organisms.

Homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli, and reproduction.

Give two structural differences between typical plant and animal cells.

Plant cells have a cellulose cell wall and a large permanent vacuole, whereas animal cells lack these and usually possess centrioles.

Which organelle enables photosynthesis in plant cells?

The chloroplast.

How do fungal cell walls differ chemically from plant cell walls?

Fungal walls are made of chitin; plant walls are primarily cellulose.

Give one example of a multinucleate (syncytial) eukaryotic cell.

Skeletal muscle fibre, aseptate fungal hypha, or phloem sieve tube element.

What makes mature mammalian red blood cells atypical among eukaryotes?

They have no nucleus.

How can you recognise a prokaryotic cell in an electron micrograph?

Presence of a nucleoid with naked DNA, 70S ribosomes, a cell wall, and absence of membrane-bound organelles like mitochondria.

Which organelle appears as stacked, flattened membrane sacs associated with vesicles?

The Golgi apparatus.

When drawing from an electron micrograph, what must annotations include?

Labels of structures (e.g., nucleus, mitochondria, ER, Golgi, plasma membrane) plus their functions.

A cell measures 50 mm on a micrograph; its actual size is 100 µm. What is the magnification?

500× (50 mm = 50 000 µm; 50 000 µm ÷ 100 µm = 500).

Why can isolated organelles not survive on their own?

They depend on the integrated cellular environment for materials, energy, and control; the cell is the smallest unit capable of life.

Which process ensures cells arise only from pre-existing cells?

Cell division (mitosis, meiosis, or binary fission).

State one key advantage of cryogenic electron microscopy.

It images hydrated biological samples in a near-native state at high resolution without staining.

What is the function of microvilli on certain animal cells?

To increase surface area for absorption or secretion.

Name two structures typically present in animal cells but absent in most plant cells.

Centrioles and motile cilia/flagella.