SUMMARY QUESTIONS - Cell structure Flashcards
Distinguish between magnification and resolution
- Magnification is how many times bigger the image is compared to the real object
- Resolution is the minimum distance apart that 2 objects can be in order for them to appear as separate items
An organelle that is 5 micrometers in diameter appears under a microscope to have a diameter of 1mm. Calculate how many times an organelle has been magnified
200 times
A cell organelle called a ribosome is typically 25 nm in diameter. Calculate its diameter when viewed under an electron microscope that magnifies it 400 000 times
10 mm
At a magnification of x12 000 a structure appears to be 6mm long. Determine its actual length
500nm (0.5 micrometers)
Chloroplasts have a greater mass than mitochondria but a smaller mass than nuclei. Starting with a sample of plant cells, describe briefly how you would obtain a sample rich in chloroplasts
- Keep the plants in a cold, buffered solution with the same water potential as the cells
- Break up the cell using a mortar and pestle/homogeniser
- Filter the homogenise to remove cell debris
- Centrifuge the homogenate at 1000 times gravity and remove supernatant liquid (leaving nuclei behind in the sediment)
- Then centrifuge the supernatant liquid at 2000-3000 times gravity
- The sediment produced will be rich in chloroplasts
Explain how the electron microscope is able to resolve objects better than a light microscope
- EM uses beam of electrons that has a much smaller wavelength than light
Explain why specimens have to be kept in a near-vacuum in order to be viewed effectively using an electron microscope
Electrons are absorbed by the molecules in air and, if present, this would prevent the electrons reaching the specimen
In practice, the theoretical resolving power of an electron microscope can’t always be achieved. Why not?
- The preparation of the specimens may not be good enough
- A higher energy electron beam is required and this may destroy the specimen
In a photomicrograph, an organelle measures 25mm when its actual size is 5 micrometers. Calc the magnification of this photmicrograph
The organelle measures 25mm (=25 000 micrometers) long and represents 5 micrometers.
Magnification is therefore 25 000 divided by 5
Magnification = 5000 times
Finnish the Gap:
To measure the size of the object under a ____ microscope you can use an ___ graticule and a _____ micrometer
Light
Eyepiece
Stage
Finish the Gap:
Before you can use the graticule to measure the size of objects it must first be ____.
Calibrated
Finish the sentence:
A photograph of a cell under an electron microscope is magnified 5000 x. On the photograph the nucleus measures 100mm in diameter. The actual size of the nucleus is therefore ___ micrometers
20
State in which process ribosomes are important
Protein synthesis
List 3 carbohydrates that are absorbed by an epithelial cell of the small intestine
Glucose, fructose, galactose
State the organelle that is being referred to in each of the following descriptions:
A: possesses structures called cristae
B: contains chromatin
C: It synthesises glycoproteins
D: It digests worn out organelles
A: mitochondrion
B: nucleus
C: Golgi apparatus
D: lysosome
The following list gives a type of cell and a brief description of its role. Suggest 2 organelles that might be numerous and/or well developed in each of the cells
A: A sperm cell swims a considerable distance carrying the male chromosome
B: One type of white blood cell engulfs and digests foreign material
C: Liver cells manufacture proteins and lipids at a rapid rate
A: Mitochondria, nucleus
B: Golgi apparatus, lysosomes
C: Rough ER, ribosomes, mitochondria, smooth ER
Explain what is meant by a tissue
Collection of similar cells working together to perform a specific function
Explain why an artery is described as an organ whereas a blood capillary isn’t
- Artery is made up of more than one tissue (epithelial, muscular, connective)
- whereas a blood capillary is made up of only 1 (epithelial)
State whether each of the following is a tissue or an organ
A: Heart
B: xylem
C: lungs
D: epithelium
A: O
B: T
C: O
D: T
This table lists some of the features of cells. For each letter in the box, write down if it is present, absent, or sometimes (occurs in some cells and not others)
A = absent
B = present
C = present
D = sometimes
E = sometimes
F = sometimes
G = present
H = present
I = sometimes
J = absent
K = present
L = present
M = absent
N = absent
If a bacterium is 6 micrometers long and a virus is 150 nano meters long, calculate how many times larger the bacterium is than the virus
- 6 micrometers = 6000 nanometers
- 6000nm divided by 150nm = 40 times
Suggest an advantage and a disadvantage of having offspring that are genetically identical to thrift parents
- ADV: genetic make-up of parent has enabled it to survive and reproduce, if offspring has same make-up, they’re also likely to survive and reproduce
-DADV: genetic variety is limited, if environmental conditions change —> species may not have individuals with necessary genes to survive in new conditions —> fails to adapt and becomes extinct
Fill in the gaps:
The period when a cell isn’t dividing is called (A). The stage of mitosis when the chromosomes are first visible as distinct structures is called (B). During this stage thin threads develop that span the cell from end to end and together form a structure called the (C). Towards the end of this stage, the (D) breaks down and the (E) disappears. The stage when the chromosomes arrange themselves across the centre of the cell is called (F). During the stage called (G) the chromatids move to opposite ends of the cell.
A = interphase
B = prophase
C = spindle
D = nuclear envelope
E = nucleolus
F = metaphase
G = anaphase
State the names of the 5 stages represented by the letters A-E in the following picture. In each case give a reason for choosing your answer
A = telophase: chromosomes in two sets, one at each pole
B = prophase: chromosomes visible but randomly arranged
C = interphase: no chromosomes visible
D = metaphase: chromosomes lined up at the equator
E = anaphase: chromatids in two sets, each drawn towards pole
