Cell Structure And Transport

Question 1

Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue. (3)

Answer 1

• break cells open by homogenising the tissue in an ice cold isotonic, buffer solution and blender
• filter homogenised solution to remove cell debris
• centrifuge at low speed to get pellets of nuclei
• centrifuge the supernatant at a higher speed, for a longer time and the pellet at the bottom is chloroplast ( the second pellet)

Question 2

Describe how you would use the student’s results in table 3 to find the water potential of the potato tissue. (3)

Answer 2

• plot a graph of results
• conc of sucrose on the x-axis and %change in mass of potato on y-axis
• find conc where curve crosses the x-axis
• find water potential of this sucrose solution

Question 3

The scientist concluded that the cells in flask ‘G’ (flask with animal tissue and sodium ions in to investigate the uptake on sodium ions by animal tissue, flask F also has a solution that prevents the formation of ATP by cells. Graph shows the measured conc of sodium ions remaining every every 10 mins; curve of ‘G’ is steadily going down.) took up sodium ions by active transport. Explain how the information given supports this conclusion. (4)

Answer 3

• uptake in flask G is much greater than flask F
• showing use of ATP in flask G
• sodium ion conc in flask G falls to 0
• showing uptake against conc gradient -active transport

Question 4

The curve levelled off after 20 mins. Explain why. (2)

Answer 4

• cells taking up sodium ions by facilitated diffusion
• equilibrium reached so no conc gradient (no ATP so can’t take up by active transport, against conc gradient)

Question 5

Explain why the solution the biologist used was ice-cold, buffered and isotonic. (3)

Answer 5

• Ice cold: prevents action of enzymes within cell that might cause self-digestion of organelles
• Buffered: maintains pH so that proteins aren’t denatured
• Isotonic: prevents osmotic lysis of cell

Question 6

Explain why the biologist used a blender and then filtered the mixture. (2)

Answer 6

• blended moisture to homogenise it, this breaks open the cells
• filter the mixture to remove cell debris that didn’t burst during homogenising

Question 7

A scientist placed plant cells in solutions containing different conc of calcium ions. She measured the rate of uptake of calcium ions by plant cells. A graph shows her results showing conc of calcium ions in solution against rate of uptake of calcium ions; curve Y goes upwards curving round to about 27 and this had oxygen, curve X starts at 0.1 and is a straight line going up to 10 and this had no oxygen.

What can you conclude from the graph about cell processes involved in the uptake of calcium ions by these plant cells? (5)

Answer 7

• between 0.0 and 0.1 calcium ions can’t enter by facilitated diffusion
• between 0.1 and 0.3 ions enter via facilitated diffusion as it doesn’t need oxygen
• between 0.0 and 0.1 ions enter by active transport as its against conc gradient
• oxygen is required for active transport

Question 8

Suggest one way in which the scientist could have ensured the solutions she used for curve X had no oxygen. (1)

Answer 8

• layer of oil on top/ boiled and cooled water

Question 9

(diagram of plant cell producing its cell wall)
Y is a protein. One function of Y is to transport cellulose molecules across the phospholipid bilayer.
Using information from figure 3, describe the other function of Y. (2)

Answer 9

• Y is an enzyme and forms ES complexes
• that attaches substrate to cellulose

Question 10

What is the evidence in figure 3 that the phospholipid bilayer is shown as pat of the cell-surface membrane? (1)

Answer 10

• cell wall forms outside cell-surface membrane
• picture shows cellulose on the outside

Question 11

Give a function of mitochondria. (1)

Answer 11

Site of aerobic respiration yielding ATP

Question 12

Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen molecule. (2)

Answer 12

• cellulose is made of b-glucose and glycogen is made of a-glucose
• cellulose has straight chains and glycogen is branched/ coiled

Question 13

The cells of beetroot contain pigment. A student investigated the effect of temp on the loss of red pigment of beetroot. He put discs cut from beetroot into tubes containing water. He maintained each tube at different temps. After 25 mins, he measured the % of light passing through the water in each tube.

The student put the same volume of water in each tube.
Explain why it was important that he controlled this experimental variable. (2)

Answer 13

• if too much water then the conc of pigment in the solution will be lower
• so results are comparable

Question 14

The cells of beetroot contain pigment. A student investigated the effect of temp on the loss of red pigment of beetroot. He put discs cut from beetroot into tubes containing water. He maintained each tube at different temps. After 25 mins, he measured the % of light passing through the water in each tube.

Describe a method the student could have used to monitor the temp of the water in each tube. (1)

Answer 14

Take reading during the experiment using a thermometer

Question 15

The cells of beetroot contain pigment. A student investigated the effect of temp on the loss of red pigment of beetroot. He put discs cut from beetroot into tubes containing water. He maintained each tube at different temps. After 25 mins, he measured the % of light passing through the water in each tube.

The decrease in the % of light passing through the water between 25’c and 60’c is caused by the release of red pigment from cells of the beetroot.
Suggest how the increase in temp of the water caused the release of the red pigment. (2)

Answer 15

• damage to cell-surface membrane
• membrane proteins denature
• increased fluidity due to damaged phospholipid bilayer

Question 16

Name the process by which prokaryotic cells divide. (1)

Answer 16

Binary fission

Question 17

Match statements to parts of a plant cell: (3)

• has stacked membranes arranged in parallel and contains DNA
• is made of polysaccharide
• is a organelle ad isn’t surrounded by two membranes

Answer 17

• chloroplast
• cell wall
• Golgi apparatus

Question 18

Human breast milk is produced and secreted by gland cells. These gland cells have adaptations that include many mitochondria and many Golgi vesicles. The milk contains a high concentration of protein.

Explain the role of these cell adaptations in the production and secretion of breast milk. (2)

Answer 18

• many mitochondria release ATP for vesicles movement/ synthesis of proteins/ active transport
• many Golgi vesicles transport proteins

Question 19

A scientist measured the rate of uptake of monoglyceride and monosaccharide by epithelial cells of the small intestine of mice, she did this for different concentrations of monoglyceride and monosaccharide. A graph shows the two results plotted, external conc of molecule against rate of uptake by epithelial cells, the monosaccharide shows a increase upwards then a curve to plateau and the monoglyceride shows a straight diagonal line up.

Use your knowledge of transport across membranes to explain the shape of the curve in figure 1 for uptake of monosaccharide between concentrations. (3)

Answer 19

A-B (start of line where its straight upwards): - facilitated diffusion
- rate of uptake proportional to external conc

C-D (where it plateaus): - plateaus as carrier proteins are all saturated

Question 20

A scientist measured the rate of uptake of monoglyceride and monosaccharide by epithelial cells of the small intestine of mice, she did this for different concentrations of monoglyceride and monosaccharide. A graph shows the two results plotted, external conc of molecule against rate of uptake by epithelial cells, the monosaccharide shows a increase upwards then a curve to plateau and the monoglyceride shows a straight diagonal line up.

Figure 1 is evidence for monoglycerides being lipid-soluble molecules. Suggest how. (2)

Answer 20

• rate of uptake is proportional so diffusion is occurring
• lipid-soluble molecules are soluble in phospholipid bilayer so can diffuse through

Question 21

The detail shown in figure 3 wouldn’t be seen with an optical microscope. Explain why. (2)

Answer 21

• light has a longer h than electrons
• so the resolution is lower

Question 22

The movement of substances across cell membrane is affected by membrane structure. Describe how. (5)

Answer 22

• phospholipid bilayer allows movement of non-polar/ lipid-soluble molecules
• phospholipid bilayer prevents diffusion of polar/ lipid- insoluble molecules
• carrier and channel proteins allow active transport and facilitated diffusion
• the shape of the channels determines which substances move
• number of channel/ carrier proteins determines how much movement
• membranes SA determines how much movement/ diffusion
• cholesterol affects rigidity

Question 23

Eukaryotic cells produce and release proteins.
Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. (4)

Do not include details of transcription and translation in your answer.

Answer 23

• DNA is code for protein
• the proteins are made during protein synthesis in the ribosomes which is in the rough E-R
• mitochondria produce ATP for protein synthesis
• Golgi apparatus add carbohydrates to proteins to form glycoproteins
• it packages these in vesicles for secretion (vesicle transport)
• vesicle fuse with cell-surface membrane

Question 24

Give one way the student could ensure the first three beetroot cylinders were kept at 25’c throughout her experiment. (1)

Answer 24

• measure the temp of intervals and use appropriate corrective measure if it changes

Question 25

Using figure 3, what can you conclude about the damage caused to beetroot cells by water, ethanol, hydrochloric acid and different temperatures?

Provide explanations for your conclusions. (4)

Answer 25

• water at 25’c caused no damage to cell-surface membrane as no pigment released
• ethanol caused some damage by dissolving phospholipid bilayer
• acid caused some damage by altering membrane protein
• 70’c cause most damage as denaturing and causing increase permeability of membrane

Question 26

The student want to determine the water potential of chicken eggs. She:
- produced a dilution series of sugar solution
- followed the procedure described: (investigating osmosis in chicken eggs. She dissolved the shells of two eggs, she then -measured the mass of each egg without its shell -covered one egg with vinegar and covered the other egg with a sugar solution -kept both eggs covered at 30’c for 24 hours, a table shows the mass of each egg after this time)

She calculated the final mass to initial mass ratio of the egg covered in each sugar solution.

How would you advise the student to use her calculated ratios to determine the water potential of eggs?
In your answer state the independent variable in the students investigation. (4)

Answer 26

• the indépendant variable is the conc of sugar solutions
• plot a graph with the sugar conc of solutions on x-axis and the range of ratios on y-axis
• plot a calibration curve
• interpolate from ratio of 1:
• change conc into water potential

Question 27

Name two features of HIV particles that aren’t found in bacteria.
Do not include attachment protein in your answer. (2)

Answer 27

• RNA genome
• capsid

Question 28

The student used a sterilised pipette to transfer E. coli into each culture.

Suggest why the number of E. coli cells per mm’3 in each culture after 24 hours might have been lower if the student hadn’t used a sterilised pipette. Explain you answer. (2)

Answer 28

• could have unknown bacteria on it which would affect the culture
• this would grow and take up space on culture

Question 29

Outline the similarities in, and the differences between, the structures of chloroplasts and mitochondria. (4)

Answer 29

• mitochondria and chloroplast have DNA
• both contain ribosomes
• both have outer and inner membrane
• chloroplast have stroma whereas mitochondria have matrix
• mitochondria has cristae whereas chloroplast have granum
• pigment in chloroplast v no pigment in mitochondria

Question 30

Name and describe 5 ways a substance can move across the cell-surface membrane into a cell. (5)

Answer 30

• CO-TRANSPORT: 2 different substances entering the cell via a carrier protein
• DIFFUSION: small, non-polar molecules pass through phospholipid bilayer into cell, down the conc gradient
• FACILITATED DIFFUSION: large polar molecules move through bilayer via carrier/ channel proteins, down conc gradient
• OSMOSIS: movement of water into the cell, down conc gradient
• ACTIVE TRANSPORT: particles move against conc gradient into the cell, via carrier proteins using ATP