B2 exam qs Flashcards
Explain why the solution the biologist used was ice-cold, buffered and the same water
potential as the liver tissue (step 1).
Ice-cold
Buffered
Same water potential
- Ice-cold –stops enzyme activity to prevent digestion of organelles
- Buffered – Maintains pH so that enzymes are not denatured;
- Same water potential – Prevents osmosis so no lysis
contrast the structure of a bacterial cell and human cell
- bacterial is smaller
- bacterial cell has cell wall, human doesnt
- bacterial cell lack a nucleus, human cell has nucleus
- bacterial cell lacks membrane bound organelles, human cell has
- bacterial ribosomes smaller than human cell ribosomes
- bacterial DNA is circular. human DNA is linear
- bacterial DNA is naked, human DNA bound to proteins/histones
contast how an optical microscope and a TEM work
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- So with TEM smaller organelles can be seen and in greater detail
- TEM view only dead specimens and optical can view live specimens;
- TEM does not show colour and optical can;
- TEM requires thinner specimens;
- TEM requires a more complex and time consuming preparation;
- TEM focuses using magnets and optical uses (glass) lenses;
describe and explain how cell fractionation and ultracentrifugation can be used ti isolate mitochondria from a suspension if animal cells
- Cell homogenisation to break open cells;
- Filter to remove large debris;
- Use isotonic solution to prevent damage to organelles;
- Keep cold to reduce damage by enzymes /
- Use buffer to prevent protein / enzyme denaturation;
- Centrifuge at lower speed to separate heavy organelles;
- Re-spin supernatant at higher speed to get organelle at bottom.
describe the behaviour of chromosomes during mitosis and explain how this results in the production of how genetically identical cells
- chromosomes shorten / thicken / supercoiling;
- chromosomes (each) two identical chromatids / strands / copies (due to replication);
- chromosomes / chromatids move to equator / middle of the spinde / cell;
- attach to individual spindle fibres;
- spindle fibres contract / centromeres divide / repel;
- (sister) chromatids / chromosomes (separate)
move to opposite poles / ends of the spindle; - each pole / end receives all genetic information / identical copies of each chromosome;
- nuclear envelope forms around each group of chromosomes / chromatids / at each pole;
Some substances can cross the cell-surface membrane of a cell by simple diffusion through the phospholipid bilayer. Describe other ways by which substances cross this membrane.
By osmosis
1. From a high water potential to a low water potential / down a water potential gradient;
By facilitated diffusion
3. Channel / carrier protein;
4. Down concentration gradient;
By active transport
5. Carrier protein / protein pumps;
6. Against concentration gradient;
7. Using ATP / energy (from respiration);
By phagocytosis / endocytosis
8. Engulfing by cell surface membrane to form vesicle / vacuole;
By exocytosis / role of Golgi vesicles
9. Fusion of vesicle with cell surface membrane;
Many different substances enter and leave a cell by crossing its cell surface membrane. Describe how substances can cross a cell surface membrane.
- Simple and facilitated diffusion from high to low concentration, down concentration gradient;
- Small, non-polar, lipid-soluble molecules pass via phospholipid bilayer;
- Large / polar / water-soluble molecules go through proteins;
- Water moves by osmosis from high water potential to low water potential
- Active transport is movement from low to high concentration, against concentration gradient;
- Active transport / facilitated diffusion involves proteins / carriers;
- Active transport requires energy from ATP;
the movement of substances across cell membranes is affected by membrane structure
describe how
- Phospholipid bilayer allows diffusion of non-polar, lipid-soluble substances;
- Phospholipid bilayer prevents diffusion of charged, lipid-insoluble substances
- Carrier proteins allow active transport;
- Channel and carrier proteins allow facilitated diffusion and co-transport;
- Shape or charge of channel or carrier determines which substances move;
- Number of channels or carriers determines how much movement;
7.Membrane surface area determines how much diffusion; - Cholesterol affects fluidity/rigidity/permeability;
Eukaryotic cells produce and release proteins.
Outline the role of organelles in the production, transport and release of proteins from
eukaryotic cells
- DNA in nucleus is code (for protein);
- Ribosomes produce (protein);
- Mitochondria produce ATP (for protein synthesis);
- Golgi apparatus modifies proteins
- Vesicles transport
OR
RER transports; - (Vesicles) fuse with cell(-surface) membrane;
Give one advantage of viewing a biological specimen using a transmission electron
microscope compared with using a scanning electron microscope.
higher resolution
view internal structure of organelles due to short wavelength
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 drop of water to (glass) slide;
- Obtain thin section (of plant tissue) and place on slide / float on drop of water;
- Stain with / add iodine in potassium iodide.
Explain the function of this ATP hydrolase.
Releases energy;
allows ions to be moved against a concentration gradien
The movement of Na+ out of the cell allows the absorption of glucose into the cell lining
the ileum.
Explain how.
Maintains concentration gradient for Na+
OR lower concentration of Na+
inside
the cell compared with outside the cell’.
- Na+
moving (in) by facilitated diffusion, brings glucose with it
Describe and explain two features you would expect to find in a cell specialised for
absorption.
- Folded membrane/microvilli so large surface area
- Large number of carrier/channel proteins so fast rate
Describe how amino acids join to form a polypeptide so there is always NH2 at one end and
COOH at the other end.
- One amine/NH2 group joins to a carboxyl/COOH group to form a peptide bond;
- there is a free amine/NH2 group at one end and a free
carboxyl/COOH group at the other
Give two similarities in the movement of substances by diffusion and by osmosis.
- (Movement) down a gradient from high concentration to low concentration
- Passive / not active processes; (doesnt require energy)
Explain the advantages of lipid droplet and micelle formation.
- Droplets increase surface areas (for lipase / enzyme action);
- (So) faster hydrolysis / digestion (of triglycerides / lipids);
- Micelles carry fatty acids and glycerol / monoglycerides to /
through membrane / to (intestinal epithelial) cell;
how is the golgi apparatus involved in the absorption of
lipids.
- Modifies / processes triglycerides;
- Combines triglycerides with proteins;
- Packaged for release / exocytosis
describe co-transport in the absorption of glucose/amino acids
Na+ actively transported out of epithelial cells into blood by sodium potassium pump
Creates a Na+ conc gradient between lumen and epithelial cell
Na+ diffuse down conc gradient through carrier protein into epithelial cell ,taking glucose/amino acids with it
glucose/amino acids move by facilitated diffusion from epithelial cell to blood
co transport
- Uses (hydrolysis of) ATP;
- Sodium ion and proton bind to the protein;
- Protein changes shape (to move sodium ion and / or proton across the
membrane);
(a) Suggest one improvement to the design of the table above and one improvement to the
way she presented the data contained in the table
- Name of solution/independent variable in first column;
- Same number of decimal places in final/column on right
(b) Suggest and explain an advantage of carrying out this investigation at 30 °C rather than at
20 °C.
- warmer = more KE
- quicker osmosis
The student concluded from the information in the table above that the water potential of
the solution inside the egg is higher than the water potential of the vinegar.
Is the student’s conclusion correct? Justify your answer
(No)
1. Egg mass increased;
2. Water moves in by osmosis;
3. (So) egg water potential lower
How would you advise the student to use her calculated ratios to determine the water
potential of the eggs?
Independent variable
1. Concentration of (sugar) solution
2. Plot calibration curve
4. Change concentration into water potential
Describe the method the student would have used to obtain the results in the graph. Start
after all of the cubes of potato have been cut. Also consider variables he should have
controlled.
- Method to ensure all cut surfaces of the eight cubes are exposed to the sucrose
solution; - Method of controlling temperature;
‘at room temperature’ - Method of drying cubes before measuring;
- Measure mass of cubes at stated time intervals;
In this investigation, the scientists cut the strawberries into slices (step 1).
Explain the advantage of this.
increases SA/ internal cells exposed
producing water loss
The scientists blotted the strawberry slices dry before weighing them (step 3).
Explain why.
liquid (on the slices) would add to the mass
would vary
Give three properties of water that are important in biology
- metabolite
- solvent
- high heat capacity
*large latent heat of vaporisation - cohesion
Name the three phases of mitosis shown by C, D and E on the figure above.
Describe the role of the spindle fibres and the behaviour of the chromosomes during each
of these phases.
C = prophase and
D = metaphase and
E = anaphase;
- prophase: chromosomes condense;centromeres attach to spindle fibres;
-metaphase: chromosomes line up at equator of cell;
- anaphase: centromeres divide;
, chromatids pulled to (opposite) poles/ends (of cell);
- prophase/metaphase/anaphase, spindle fibres shorten;
Name the fixed position occupied by a gene on a DNA molecule.
loci
Describe how a gene is a code for the production of a polypeptide.
- base/nucleotide sequence;
- (In) triplet(s);
- (Determines) order/sequence of amino acid sequence/primary structure
Use the information provided to suggest how Trexall slows cell division
1. (Trexall acts as a) competitive inhibitor
2. less ES complexes formed
3. not enough nucleotides available for DNA repliation
Mitosis is important in the life of an organism. Give two reasons why.
- Replace cells
- Asexual reproduction
Describe the role of the spindle during mitosis.
; Separation of centromeres /
chromatids / chromosomes
) Meiosis also occurs during the life cycle of organisms. What is the importance of meiosis?
Halves chromosome number / haploid;
Diploid / full number restored at fertilisation
Suggest why the student soaked the root tips in hydrochloric acid in step 2.
- To break down links between/separate cell walls;
- Allowing the stain to pass/diffuse into the cells
Pressing the coverslip downwards enabled the student to observe the stages of mitosis
clearly.
Explain why.
- To create a single/thin layer of cells
- so light can pass through
active transport process
- Na+ ions transported out of epithelial cells in ileum into blood by sodium-potassium pump (Na+-K+)
[creates concentration gradient - more Na ions in ileum than epithelial cell] - conc gradient causes Na+ ions to diffuse into epithelial cell down conc gradient
[do this through Na+ - glucose cotransporter protein]
- glucose enters cell with sodium - higher conc of glucose in epithelial cell than blood, glucose diffuses into blood down conc gradient by facilitated diffusion
factors affecting active transport
- speed of carrier proteins
- no. of carrier proteins
- rate of respiration (ATP)
simple diffusion
movement of small and non-polar molecules from area of high to low conc
factors affecting simple diffusion
- conc gradient
- membrane thickness
- SA
- temp
facilitated diffusion
movement of large, polar and charged molecules through specialised carrier and channel proteins
carrier protein
- move large molecules across membrane
- different proteins facilitate diffusion of diff molecules
- large molecules attach and protein changes shape releasing molecule on other side of membrane
channel protein
- form pores for charged particles to diffuse through
- different protein channels facilitate diffusion of different charged particles
- no changing shape - tunnel
factors affecting facilitated diffusion
- conc gradient
- no. of channel proteins
