cells Flashcards
Key differences between plant and animal cells
plant cell has a cellulose wall WHEREAS animal cells has no cell wall
plants have chloroplast WHEREAS no chloroplasts
plants have large central vacuole WHEREAS animals don’t
plants have carbohydrates stored as starch WHEREAS in animal cells carbohydrates stored as glycogen
plants have no centrioles WHEREAS animal cell has centrioles
Granum
Stack of thylakoid membranes
Thvlakoid membrane
Contains chlorophyll for photosynthesis &
ATP synthase enzyme to produce ATP.
Stroma
Fluid filled part, some of the
photosynthetic reactions occur here
Starch grains
The energy storage molecule in plants.
DNA and ribosomes
Chloroplasts have their own DNA and 70s
ribosomes to make enzymes needed for
photosynthesis
Describe the function of a chloroplast. (2)
- To absorb photons from the sun for photosynthesis
- Producing sugars
A student viewed impressions of
stomata using an optical
microscope. She then determined
the mean diameter of the stomata.
Describe how the student could
have used an eyepiece graticule to
determine the mean diameter of
stomata (3)
1.
Measure each stomata using an eye piece
graticule
2.
Calibrate the eyepiece graticule against a
stage micrometer
3
Take at least 5 measurements and calculate a
mean (more measurements = more accurate &
more representative)
Describe the principles
and the limitations of using
a transmission electron
microscope to investigate
cell structure. [5]
Principles (how it works)
Limitations (drawbacks /
disadvantages)
Principles:
Electrons pass through / enter (very thin) specimen;
Denser parts absorb more electrons;
(So) denser parts appear darker;
Electrons have short wavelength so give high resolution;
Limitations:
5
Cannot look at living material / Must be in a vacuum;
Specimen must be (very) thin;
Artefacts present;
Complex staining method / complex / long preparation time;
Give one advantage of using a TEM
rather than a SEM.
Higher resolution / higher (maximum) magnification /
higher detail (of image);
OR
Allows internal details / structures within (cells) to be seen /
cross section to be taken;
Give one advantage of using a SEM
rather than a TEM.
Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;
Scientists use optical microscopes and
transmission electron microscopes to
investigate cell structure. Explain the
advantages and limitations of using a
TEM to investigate cell structure.
Advantages:
1. Small objects can be seen;
2. TEM has higher resolution;
3. Wavelength of electrons shorter;
Limitations:
4. Cannot look at living cells;
5. Must be in a vacuum;
6. Must cut section thin specimen;
7. Preparation may create artefacts (false image);
Describe how you could make a
temporary mount of a piece of plant
tissue to observe the position of
starch grains in the cells when using
an optical (light) microscope.
- Add a drop of water to the microscope slide;
- Get a thin section of plant tissue and float on the
drop of water; - Stain with KI solution;
- Lower the cover slip using a mounted needle to
avoid air bubbles;
Describe how you could use cell
fractionation to isolate chloroplasts from
leaf tissue (3)
- Break open the cells in a blender/ homogeniser
and filter to remove cellular debris;
2.
Place in an ice cold, isotonic, buffered solution;
3.
Use differential centrifugation;
4.
Chloroplasts are in the second pellet;
Scientists isolated mitochondria from liver
cells. They broke the cells open in an ice-
cold, buffered isotonic solution. Explain
why the solution was:
a) Isotonic
b) Ice cold
c) buffered
1.
2.
3.
Prevents osmosis
so no osmotic lysis of organelles/named
organelle (e.g. mitochondria);
Reduce/ prevent enzyme activity so organelles
are not digested;
Maintain a constant pH so proteins are not
denatured;
