Chapter summary
Cells and microscopy, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Cells are the units of life
Why does a cell count as living when an isolated ribosome does not?
Key idea and reminders
A cell is the smallest unit able to carry out the coordinated processes of life; new cells arise from existing cells.
- Living organisms are cellular.
- Cells are the smallest living units.
- Present-day cells come from pre-existing cells.
Keep in mind: Chemical activity is necessary for life but does not make an isolated molecule or organelle a living cell.
02
Follow a protein through a cell
Why does a protein-secreting cell have extensive rough ER and Golgi?
Key idea and reminders
Ribosomes make polypeptides; the ER and Golgi process and route suitable products in membrane vesicles.
- Ribosomes: translation.
- ER and Golgi: processing and transport.
- Lysosomes: compartmentalised hydrolysis.
Keep in mind: Ribosomes synthesise the chain. Golgi enzymes modify and sort products already made.
03
Match organelles to their jobs
Which visible features justify an organelle identification?
Key idea and reminders
Identify a structure using its boundary and internal pattern, then connect those features to its function.
- Nucleolus: rRNA and ribosomal subunits.
- Cristae: inner mitochondrial membrane folds.
- Grana: stacks of thylakoids, surrounded by stroma.
Keep in mind: Photosynthetic plant cells normally have both. They convert energy through different pathways.
04
Recognise a bacterial cell
How can a cell function without a nucleus?
Key idea and reminders
A bacterium has a membrane, cytoplasm, DNA and ribosomes, but no membrane-bound nucleus or other membrane-bound organelles.
- Typical wall: peptidoglycan.
- DNA: usually a circular chromosome, without a nuclear envelope.
- 70S ribosomes; no membrane-bound organelles.
Keep in mind: Respiratory reactions can occur in the cytoplasm and at the bacterial cell membrane.
05
Calibrate a microscope measurement
What does one eyepiece division represent at this objective?
Key idea and reminders
Calibrate the eyepiece scale at each objective before converting a specimen measurement to a real length.
- Calibration = known length / graticule divisions.
- Recalibrate after changing objective.
- Resolution means separating two close points.
Keep in mind: Eyepiece divisions have no fixed specimen length until calibrated at the selected objective.