1. What is a "eukaryotic cell" ?
Answer
A cell that contains a nucleus.
2. Are plant cells eukaryotic or prokaryotic ? And bacterial cells ?
Answer
Plant cells are eukaryotic. Bacterial cells are prokaryotic.
3. Cells differentiate as an organism develops. What does differentiate mean ?
Answer
Different types of cells are formed, cells become specialised.
4. Two cells labelled A and B are shown in the figure below. Describe how cell A is different from cell B. Calculate the length of cell B.
Answer
Cell A is smaller and has flagella. Cell B has a nucleus, a mitochondria, a vacuole and chloroplasts. The length of cell B is 200 μm.
5. Mitochondrion, ribosome and nucleus are cell structures. Write these structures in order of size from smallest to largest.
Answer
Ribosome, mitochondrion, nucleus.
6. Which cell structures are present in both eukaryotic and prokaryotic cells ?
Answer
Cell membrane, cell wall and cytoplasm.
7. Explain shortly the function of chloroplasts, mitochondria, cell wall, permanent vacuole and ribosome.
Answer
Chloroplasts is the site of photosynthesis.
Mitochondria is the site of aerobic respiration.
Cell wall gives structure and support to the cell.
Vacuole supports the cell, filled with cell sap.
Ribosome is the site of protein synthesis.
9. Cells may differentiate to become specialised cells. Explain what happens when a cell differentiates. Describe the main difference between differentiation in animal cells and plant cells.
Answer
During differentiation, the cell acquires various sub-cellular structures, allowing it to carry out a specific function. Most types of animal cells differentiate at an early stage, whereas many plant cells are able to differentiate throughout life.
10. Describe at least three of the structures and functions of specialised plant cells.
Answer
Root hair cell function is to absorb water from the soil by osmosis and minerals by active transport so it has a large surface area for rapid diffusion and many mitochondria to provide energy.
Xylem cell function is to transport water and mineral ions from roots to other parts of the plant so it has dead cells so water does not move into cells and continuous tubes so uninterrupted flow of water and lignin in walls for strength.
Phloem cell function is to transport sugar made during
photosynthesis from leaf to other parts of the plant so it has few cell organelles so solution can flow more easily and elongated cells can form tubes.
11. Describe how cheek cells can be prepared and viewed under high power using a light microscope.
Answer
Gently rub a cotton bud inside your cheek to collect some cells then rub the cotton bud on the surface of a glass slide. Add one drop of (methylene blue) stain and lower a glass coverslip onto the slide. Put the slide on the stage and select the low power (smallest) objective lens. Look at the specimen through the eyepiece lens and adjust the coarse focus until the image is clear. Change the objective lens to the high power (larger) lens, then use the fine focus to produce a clear image.
12. A student is given a pure culture of bacteria in liquid nutrient broth. Describe how this student can prepare an uncontaminated culture of bacteria on solid agar jelly using aseptic technique. Explain why each of the steps is necessary.
Answer
The Petri dish and agar jelly need to be sterilised before using them so there are no unwanted bacteria. The student needs to sterilise an inoculating loop by passing it through a flame to kill any bacteria on the loop. The sterile loop can be used to collect bacteria from the liquid broth and then spread the liquid on the solid agar jelly. The lid of the Petri dish should be lifted up as little as possible so that bacteria from the air do not enter and contaminate the culture. The student should secure the lid of the Petri dish with four pieces of tape so that the lid cannot fall off and let bacteria enter. Finally, the Petri dish should be incubated upside down (so that condensation does not drip onto the colonies) and at 25°C so the bacteria can grow (but not potential pathogens).