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Biology > Topic 2. Cells > Flashcards

Topic 2. Cells Flashcards

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1
Q

List 3 ways eukaryotic cells differ from prokaryotic cells

A

-membrane bound organelles
-DNA enclosed in a nucleus
Have larger ribosomes (80s) than prokaryotic cells

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2
Q

Prokaryotic cells include bacterial cells. List the differences b/t prokaryotic and eukaryotic cells

A
  • No membrane bound organelles e.g. mitochondria, endoplasmic reticulum, Golgi)
  • No nucleus- instead hey have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins
  • Smaller ribosomes
  • has a murein cell wall, a capsule and plasmids
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3
Q

Describe the replication process of bacterial cells (6 marks)

A
  • Binary fission
  • circular DNA and plasmids replicate
  • circular DNA attaches to opposite ends of cell membrane
  • Bacterial cell grows
  • The cell membrane pinches inwards in the middle of the cell, so the cytoplasm divides
  • A cell wall is formed around each daughter cell
  • Two daughter cells produced (each has a variable number of plasmids)
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4
Q

How does a virus replicate?

A
  1. Virus attaches to a host cell
  2. Virus injects its genetic material into the host cell
  3. The host cell transcribes and translates the viral genes
  4. These proteins form new virus particles
  5. The virus particles burst out of the host cell, so the host cell is destroyed.
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5
Q

Define magnification

A

how much bigger he image is than the specimen

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6
Q

Define resolution

A

the minimum distance apart the 2 objects can be in order for them to appear as separate items

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7
Q

Describe the procedure to prepare a slide

A
  1. Add a drop of water to the slide
  2. Remove a thin section of tissue and place it onto the slide (as flat as possible)
  3. (ONLY IF IT IS A PLANT TISSUE) Add 1 drop of iodine dissolved in potassium iodide to stain the sample
  4. Lower a coverslip on top using a mounting needle
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8
Q

Explain why it is important that the sections of tissue prepared on a slide are thin

A
  • A thin section allows more light through;

- Allows a single layer of cells to be viewed

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9
Q

Explain why you should push down hard on the cover slip, but you should not push the coverslip sideways

A
  • Push hard to squash the tissue to create a single layer of cells
  • Do not push sideways as this will cause the cell to roll together
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10
Q

A plant cell was observed with an optical microscope. Describe how the length of the cell could be estimated

A
  • Use a stage micrometer to help you calibrate the size of the eyepiece graticule
  • Measure the length of the plant cell with an eyepiece graticule
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11
Q

How would you calibrate a stage micrometer?

A

1) Find out the length of the stage micrometer (change from mm to micrometres)
[e.g. 10mm=10,000 micrometres]
2) find out how many divisions there are [100]
3) Work out how many micrometres are in each division [10000/100= 100 micrometres in 1 division]
4) place the stage micrometer on the stage
5) Line up the divisions on the eyepiece graticule with those of the stage micrometer
[lets say 100 units on the eyepiece graticule fit 30 units of the stage micrometer]
6) Work out the length of 1 eyepiece graticule unit in micrometres
eye piece graticule : stage micrometer
100 divisions:30 divisions
[As shown in 3) 100 micrometres = 1 division in the stage micrometer]
[30 divisions= 30(100)= 3,000 micrometres
100 divisions: 3,000 micrometres
1 division: 30 micrometres
7) Place your slide on the stage
8) Measure the length of the cell using eyepiece graticule units

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12
Q

Why are electron microscopes used to view cells?

A
  • They have a high resolution
  • because electrons have a shorter wavelength than light
  • This allows you to view internal structures/ organelles of cells
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13
Q

Name 2 structures in a Eukaryotic cell that cannot be identified using an optical microscope

A
  • Mitochondria
  • Ribosome
  • Endoplasmic Reticulum
  • Lysosome
  • Cell-surface membrane
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14
Q

Describe the principles and the limitations of using a transmissiom electron microscope to investigate cell structure

A
  1. Electrons pass through/ enter (thin) specimen
  2. Denser parts absorb more electrons
  3. (So) denser parts appear darker
  4. Electrons have short wavelengths so they give a high resolution
    LIMITATIONS
  5. Cannot look at living material/ Must be in a vacuum
  6. Specimen must be (very) thin
  7. Artefacts present
  8. Complex staining method/ long preparation time
  9. Image not in 3-D/ only 2-D images produced
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15
Q

What is the advantage of TEM (transmission) compared to SEM (scanning)

A

TEM :

  • Has a higher resolution
  • Allows internal structures within a cell to be seen
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16
Q

What is the advantage of SEM (scanning) compared to TEM (transmission)

A

SEM :

  • Do not require thin sections of tissue
  • shows surface of specimen
  • can have 3-D images
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17
Q

Write an equation for magnification

A

magnification = [size of image] / [size of object]
OR
magnification = [Image length] / [Actual length]
(lengths in micrometres)

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18
Q 
What are the conversions b/t 
nanometres
micrometres
mm
cm
m
A

nano to micro [divide by 1000]
micro to mm [divide by 1000]
mm to cm [divide by 10]
cm to m [divide by 100]

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19
Q

If a scale bar is provided this represents the size of what? How do we use it?

A
  1. Measure the scale bar, using a rule in mm
  2. Convert to micrometres - Use value as image size
  3. The value written underneath the scale bar is actual size
  4. Use these values to calculate the magnification
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20
Q

What is meant by cell fractionation and why would scientists want to do it?

A
  • Separating out the contents of a cell into the different “fractions”
  • ; sepearting out the different organelles
  • This is useful as it allows scientists to study individual organelles
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21
Q

What is homogenisation? What is the point of it?

A

Using a blender (homogeniser) to break open the cell membrane to release all of the organelles inside

22
Q

why is the solution in cell fractionation filtered?

A

to remove any whole cells or cell debris before carrying out centrifugation

23
Q

What conditions must the cells used in cell fractionation be kept in? and why?

A

1) cold; to slow down enzyme activity to prevent digestion of organelles
2) Isotonic; to prevent osmosis, so that the organelles do not shrivel or burst
3) Buffered; so that the pH is kept constant, so that proteins are not denatured

24
Q

Describe what happens in Ultracentrifugation

A
  1. The sample is put into a test tube
  2. It is spun at a low speed (low revolutions per minute RPM)
  3. The most dense organelle forms a sediment/ pellet at the bottom of the test tube
  4. The other organelles remain suspended in the supernatant
  5. The supernatant is removed and put into a clean test tube and spun at higher RPM
  6. The second most dense organelle forms a sediment at the bottom, etc
25
Q

Why is the plasma membrane referred to as being fluid- mosaic?

A

FLUID- molecules within the membrane able to move

MOSAIC- mixture of phospholipids and proteins

26
Q

How does the bilayer formed by phospholipids affect entry and exit of substances into and out of a cell?

A
  • Allows movement of small, lipid soluble, non-polar molecules such as gases through the membrane
  • prevents large, water soluble, polar molecules such as ions and amino acids
  • The membrane is selective and partially permeable
27
Q

Define diffusion

A

It is the movement of substances from an area of high concentration to an area of low concentration down a concentration gradient
(passive process)

28
Q

Which substances can simply diffuse across the phospholipid bilayer?

A
  • small
  • non-polar
  • non-charged
  • lipid soluble molecules
29
Q

Why can molecules of oxygen and carbon dioxide diffuse across the membrane?

A
  • The hydrophobic fatty acid part of the membrane is non-polar
  • Oxygen and carbon dioxide are small, non-polar molecules;
  • Oxygen/ carbon dioxide can diffuse through the fatty acid layer
  • Down a concentration gradient
30
Q

What is the equation for Fick’s law?

A

Rate of diffusion is directly proportional to

[conc gradient x SA] / [diffusion pathway]

31
Q

Define facilitated diffusion

A

The movement of substances from a high concentration to a low concentration, down a concentration gradient, through a channel or carrier protein.

32
Q

What sorts of substances are transported via facilitated diffusion? why?

A

-Large
-Polar
-Charged
-water soluble molecules
BECAUSE: the fatty acid layer of the plasma membrane is hydrophobic and non-polar; it will not allow polar substances to diffuse through (e.g. ions or amino acids)

33
Q

Describe how a channel protein works

A

The protein forms a pore which does not change shape when a substance travels through it

34
Q

Describe how a carrier protein works

A

The substance to be transported binds to one side of the protein, this causes it to change shape so the substrate is released on the other side of membrane

35
Q

Define active transport

A

It is the movement of a substance from a low concentration t a high concentration, against the concentration gradient
(active; it requires energy (ATP) which binds to a carrier protein and enables it to change shape

36
Q

How does active transport move substances against their concentration gradient?

A
  • Substance binds to a carrier protein
  • ATP binds to a carrier protein
  • ATP is converted to ADP and releases energy
  • This causes the carrier protein to change shape
  • The substance is released on the other side of the membrane
37
Q

Define osmosis

A

The net movement of water from an area of high water potential to an area of lower water potential through a partially permeable membrane

38
Q

What is the water potential of pure water?

A

0

39
Q

What happens to the water potential of a solution when more solute is added?

A

It decreases (becomes more negative)

40
Q

What does it mean if 2 solutions are isotonic

A

They have the same water potential

41
Q

When investigating osmosis/ diffusion, where would you take a cutting from a vegetable that is made up of many different types of tissue?

A
  • You must ensure it’s through 1 tissue only
  • in order for it to be a fair test
  • because, different tissues may affect water potential differently
42
Q

Why would you calculate ratio’s or percentage change in mass from a set of results

A

To allow a valid comparison when the initial length/ mass is not the same

43
Q

why would you take additional readings/ repeat experiments?

A

To identify any anomalies and calculate a mean

44
Q

A graph can be improved if you take additional readings. Why?

A

because

  • your line of best fit will be more reliable
  • where the point crosses the x-axis is sometimes more precise
45
Q

Join graphs dot-to-dot when…

A

…you cannot predict intermediate values

46
Q

Summarise how the products of carbohydrate digestion are absorbed

A
  1. Sodium/ potassium pump moves 3 sodium ions out of the cell (into the blood) and 2 potassium ions into the cell by active transport. This uses ATP
  2. This creates a lower concentration of sodium ions in the epithelial cell than in he lumen of the intestine
  3. Sodium ions move into the epithelial cell by facilitated diffusion. They travel through a symport protein and bring glucose with them. This is called co- transport
  4. The glucose is moving into the cell against its concentration gradient
  5. The glucose concentration in the epithelial cell increases
  6. Glucose moves into the blood from the epithelial cell through a carrier protein by facilitated diffusion.
47
Q

Summarise how the products of protein digestion are absorbed

A
  1. Sodium/ potassium pump moves 3 sodium ions out of the cell (into the blood) and 2 potassium ions into the cell by active transport. This uses ATP
  2. This creates a lower concentration of sodium ions in the epithelial cell than in he lumen of the intestine
  3. Sodium ions move into the epithelial cell by facilitated diffusion. They travel through a symport protein and bring amino acids with them. This is called co- transport
  4. The amino acids move into the cell against the concentration gradient
  5. The amino acid concentration in the epithelial cell increases
  6. The amino acids move into the blood from the epithelial cell through a carrier protein by facilitated diffusion.
48
Q

Adaptations of the epithelial cell

A
  • Lots of mitochondria; release energy in the form of ATP. ATP is needed for active transport
  • Lots of enzymes attached to their membrane; breaks down maltose into glucose
  • Microvilli; provide a large surface area for maximum absorption
  • Carrier proteins for active transport
  • Channel/ carrier proteins for facilitated diffusion
  • Co-transport (or symport) protein, for the transport of sodium ions and glucose/ amino acids
49
Q

What is co-transport?

A

When a transport protein transports more than 1 substamce at the same time

50
Q

What is a symport protein?

A

A type of co transport protein

- It transports 2 substances through the membrane in the same direction together

51
Q

What is an anti-port protein?

A

A type of co transport protein

-It transports 2 substances through the membrane in the opposite direction.

Biology (7 decks)

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