Cells and Microscopy | OCR A-Level Biology B (Advancing Biology) (H422)

Cells and Microscopy

170 questions
11 subtopics
Biology content, examined on all three papers
Component 01, Component 02 and Component 03

Cells and Microscopy is examined in all three written papers — the specification states that Components 01, 02 and 03 can each assess content from any of the five modules, so nothing is confined to one paper.

It covers microscopy and the cell theory, blood smears, staining and microscope drawings, blood cells and their structure, magnification and measuring cells, haemocytometer cell counts and dilutions, flow cytometry in blood analysis, ultrastructure of the animal cell, plant and prokaryotic cells, membrane lipids and the fluid mosaic model, movement of molecules across membranes and the roles of membranes and the secretion of proteins.

Sample questions from Cells and Microscopy

Answer each one closed book first, then open the answer.

Microscopy and the cell theory

What sets the limit of resolution of a light microscope at roughly 200 nm?

Show the answer
The wavelength of visible light, since two points closer together than about half a wavelength of the light used cannot be resolved.
Blood smears, staining and microscope drawings

What is meant by differential staining?

Show the answer
It is the use of a stain, or a mixture of stains, that colours different cell types or different cell components differently so that they can be told apart.
Blood cells and their structure

What are platelets and where do they come from?

Show the answer
Platelets are small membrane-bound cell fragments with no nucleus, formed by the breaking up of large cells called megakaryocytes in the bone marrow.
Magnification and measuring cells

A mitochondrion measures 25 mm long on an electron micrograph taken at ×25 000. Calculate its actual length in micrometres.

Show the answer
Actual length is 25 mm ÷ 25 000 = 0.001 mm, which is 1.0 μm.
Haemocytometer cell counts and dilutions

Describe how a haemocytometer is loaded with a cell suspension.

Show the answer
The coverslip is moistened and pressed firmly onto the supports until Newton's rings appear, then a small drop of well-mixed suspension is touched to the edge of the coverslip and drawn under the chamber by capillary action, with no bubbles and no overflow into the moat.
Flow cytometry in blood analysis

How can a neutrophil and a lymphocyte be distinguished by scattered light alone?

Show the answer
The neutrophil is larger, so it gives greater forward scatter, and it is far more granular with a lobed nucleus, so it gives much greater side scatter than the small, agranular lymphocyte.
Ultrastructure of the animal cell

How does smooth endoplasmic reticulum differ from rough endoplasmic reticulum in structure and role?

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Smooth endoplasmic reticulum is a network of tubules with no ribosomes attached, and it synthesises lipids and steroids and stores calcium ions rather than processing proteins.
Plant and prokaryotic cells

What is the tonoplast and what does it do?

Show the answer
The tonoplast is the partially permeable membrane surrounding the vacuole, and it controls which substances pass between the cell sap and the cytoplasm.

The 11 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Microscopy and the cell theory	Recall questions on the cell theory, resolution and magnification, the resolution limit of the light microscope, transmission and scanning electron microscopes, artefacts, the confocal scanning laser microscope, and why light microscopy is still used in clinical blood work.	14
Blood smears, staining and microscope drawings	Recall questions on preparing and drying a blood smear safely, differential staining with Leishman's stain, recognising erythrocytes, neutrophils, lymphocytes, monocytes and platelets in a stained smear, and the conventions for biological drawings, plan drawings and high-power drawings.	14
Blood cells and their structure	Recall questions on the biconcave shape of erythrocytes and their lack of a nucleus and mitochondria, platelets and megakaryocytes, the functions of neutrophils, lymphocytes and monocytes, and what a differential white cell count shows.	14
Magnification and measuring cells	Recall questions on the magnification formula and unit conversions, calculating magnification and actual size from micrographs, typical cell sizes, calibrating an eyepiece graticule with a stage micrometer, field of view calculations and sources of measurement error.	17
Haemocytometer cell counts and dilutions	Recall questions on the ruling and 0.1 mm depth of the haemocytometer, volumes over its squares, loading it until Newton's rings appear, diluting blood and the boundary-line rule, calculating dilution factors and erythrocyte and leucocyte counts, recognising anaemia, and sources of counting error.	17
Flow cytometry in blood analysis	Recall questions on how cells are made to pass a laser singly, what forward- and side-scattered light reveal, fluorescent antibody labelling, reading a scatter plot, and the technique's limitations.	13
Ultrastructure of the animal cell	Recall questions on the ultrastructure of the nucleus, nuclear pores and nucleolus, rough and smooth endoplasmic reticulum, ribosomes, the Golgi apparatus, lysosomes and vesicles, mitochondria and their cristae, the cytoskeleton and centrioles.	16
Plant and prokaryotic cells	Recall questions on the structure and function of chloroplasts, palisade mesophyll cells, the vacuole, cell sap and tonoplast, the cellulose cell wall, and prokaryotic cells with their nucleoid, plasmids, mesosomes, pili and flagella, and how they differ from eukaryotic cells.	16
Membrane lipids and the fluid mosaic model	Recall questions on triglycerides and ester bonds, saturated and unsaturated fatty acids, phospholipids and the bilayer, the fluid mosaic model with intrinsic and extrinsic proteins, cholesterol, glycolipids and glycoproteins, and why membranes leak above about 40 °C.	16
Movement of molecules across membranes	Recall questions on simple and facilitated diffusion, channel and carrier proteins, active transport and respiratory inhibitors, endocytosis, phagocytosis, pinocytosis and exocytosis, surface area to volume ratio in agar cubes, and investigating membrane permeability with beetroot and a colorimeter.	18
The roles of membranes and the secretion of proteins	Recall questions on the roles of the plasma membrane, compartmentalisation, membranes that hold enzymes and store energy as ion gradients, cell signalling, and the secretory pathway from nucleus and rough endoplasmic reticulum through the Golgi apparatus, transport vesicles and motor proteins to exocytosis.	15

Cells and Microscopy is 170 of the 2,895 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.