Cells Flashcards
(30 cards)
Explain why it is not possible to see sub-cellular structures using an optical microscope.
-Resoloution too low
-Because the wavelength of light is too long.
Describe the role of one named organelle is digesting bacteria (phagocytosis)
-Lysosomes
-Fuse with vesicle
-Release hydrolytic enzymes/ lysozyme.
Suggest why plasmid replication would be faster in a culture with higher amino acid concentration.
-Amino acids used in protein synthesis
-So more enzymes/ DNA polymerase formed for plasmid replication
or
- Amino acids used in respiration
-So more ATP for DNA replication.
Describe how a sample of chloroplasts can be separated from leaves.
-Grind to break open cell walls AND filter. (accept homogenise and filter)
-In cold, isotonic, and ph controlled solution
-Centrifuge to remove nuclei
-Centrifuge again at higher speed to remove chloroplasts
Give one feature of the chloroplast that allows proteins to be synthesised in it. Explain one difference between this feature present in the chloroplasts and present in the rest of the cell.
-Ribosomes
-Smaller 70s ribosomes in chloroplast, larger 0s ribosomes in rest of cell.
or
-DNA
-Not associated with histones or proteins in chloroplast, in rest of cell it is.
-Is circular whereas nuclear DNA is linear
-Is shorter than nuclear DNA.
Outline the roles of organelles in the production, transportation, and release of proteins. do not include details of transcription or translation.
- Dna in nucleus provides code for proteins
- Ribosomes produce/ synthesise proteins.
- Golgi body modifies and packages the proteins
- Golgi body adds carbohydrates to form glycoproteins.
-Golgi vesicles transport proteins/ rough endoplasmic reticulum transports proteins.
-Mitchondria provides energy through atp hydrolysis
-Vesicles fuse with cell surface membrane to release- accept cell surface membrane site of exocytosis
Why might an organelle not be visible in a picture of a cell. (light microscope)
- Part of a different section/ slide
- Not stained.
Give one advantage of using a TEM instead of an SEM
-Higher resolution
Why can’t sub cellular structures be seen using an optical microscope?
- Resolution too low
-Because the wavelength of light is too long
Name an organelle found in a chloroplast and a prokaryotic cell
70s ribosome.
When preparing a solution for cells to stay in, what three conditions must be met, and why?
- PH buffered- to stop enzymes from denaturing
- Cold - to slow/ stop/ reduce enzyme activity
- Isotonic- to reduce/ stop osmotic activity and ensure cells aren’t plasmolyse or made turgid.
Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.
-TEM uses electrons and optical uses light
-TEM allows a greater resolution
-Smaller organelles can be observed with greater detail using TEM
-TEM can only view dead specimens whereas optical can view live swell (because TEM must be done in a vacuum, and optical does not.)
-TEM does not show colour, but optical does
-TEM requires thinner specimens
-TEM requires a more complex/time consuming preparation
-TEM focuses using magnets whereas optical focuses using lenses.
Give two ways in which the nucleotides in DNA are different from the nucleotides in RNA.
-DNA contains thymine whereas RNA contains uracil
-DNA contains deoxyribose sugar whereas RNA contains ribose
Before a cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface membrane to appear as two dark lines.
Suggest an explanation for the appearance of the cell-surface membrane as two dark lines.
-Membrane has a phospholipid bilayer
-Stain binds to phosphate/glycerol
-On inside and outside of membrane
No organelles are visible in the cytoplasm of a red blood cell. Suggest why
Cytoplasm of red blood cell filled with haemoglobin
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 a glass slide
-Obtain a thin section of plant tissue and place on slide
-Stain with/ add iodine in potassium iodide
-Lower cover slip using mounted needle.
Describe binary fission in bacteria
-Replication of circular DNA
-Replication of plasmids
-Division of cytoplasm
Describe the role of the spindle fibres and the behaviour of the chromosomes during mitosis
-In prophase chromosomes condense
-In prophase OR metaphase, centromeres attach to spindle fibres
-In metaphase, chromosomes/pairs of chromatids move to centre of cell
-In anaphase centrometeres divide
-In anaphase, chromatids from each pair are pulled to opposite poles/ ends of the cell
-In prophase, metaphase, and anaphase spindle fibres shorten/contract.
A student prepared a stained squash of cells from the tip of an onion root and observed it using an optical microscope.Explain why the student:
1. used only the first 5 mm from the tip of an onion root
2. pressed down firmly on the cover slip.
1-Where dividing cells are found / mitosis occurs or it is a length that will fit under the cover slip
2-Single / thin layer of cells / spread out cells so light passes through
What are three pieces of evidence that may be ovserved if a cell is undergoing mitosis?
-The individual chromosomes are visible because they have condensed
-Each chromosome is made up of two chromatids because DNA has replicated
-It is definitely mitosis, as the chromosomes are not arranged in homologous pairs, which they would be if it was meiosis
When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.
Suggest how this procedure moved the chromosomes apart
-Water moves into the cells cytoplasm through osmosis
-Cell/cytoplasm gets bigger/swells
The dark stain used on the chromosomes binds more to some areas of the
chromosomes than others, giving the chromosomes a striped appearance.
Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas
-Difference in base sequences
-Differences in condensation
-Differences in histones/interactions with histones
What is a homologous pair of chromosomes?
Two chromosomes that carry the same genes
Describe the appearance and behaviour of chromosomes during mitosis.
During prophase
-Chromosomes coil / condense / shorten / thicken / become visible
- Chromosomes appear as two sister chromatids joined at the centromere
During metaphase
-Chromosomes line up on the equator / centre of the cell
-Chromosomes attached to spindle fibres
- By their centromere
During anaphase
-The centromere splits / divides
-Sister chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate
During telophase
- Chromatids / chromosomes
uncoil / unwind / become longer / thinner.
