Progression kRQ

Question 1

What is digestion?

Answer 1

The hydrolysis of large biological molecules into smaller molecules that can be absorbed across the cell membrane of epithelial cells in the lumen (small intestine)

Question 2

Describe and explain how carbohydrate digestion occurs in mammals?

Answer 2

Starch digestion begins in the mouth when salivary amylase from salvia mixes with food in the mouth. Salivary amylase hydrolyses glycosidic bonds turning some starch into maltose.Food is swallowed and enters the stomach where salivary amylase is denatured due to low pH. Pancreatic amylase is released into the small intestine along with alkaline bile slats from the liver to neutralise the acid. Pancreatic amylase hydrolyses the remaining starch into maltose. In the cell membranes of the epithelial cells lining the lime are membrane bound disaccharides, maltose, lactase,sucrase. These hydrolyse disaccharides into monosaccharides for absorption

Question 3

What is the advantage of membrane bound enzymes?

Answer 3

They do not need to be constantly replenished as they are not removed with waste from the small intestine because they are bound to the cell surface membrane of the epithelial cell membrane,so have a very short diffusion distance into the cell

Question 4

What are the membrane bound enzymes and what are their substates and products

Answer 4

Sucrase-hydrolyses sucrose into fructose and glucose
Maltose-hydrolyses maltose into glucose
Lactase-hydrolyses lactose into galactose and glucose
Dipeptidase-hydrolyses dipeptides into amino acids

Question 5

Describe how proteins are digested into the human gut endorses produced by the stomach.

Answer 5

Endopeptidases produced by the stomach. Endopeptidases are also made by the pancreas and are released into the small intestine. Endopeptidases hydrolyse internal peptide bonds which breaks polypeptides into smaller polypeptide chains.
Exopeptidases are made by the pancreas and released into the small intestine. They hydrolyse peptide bonds at the ends of the polypeptide chain releasing amino acids or dipeptides.
Dipeptidases hydrolyse dipeptides into amino acids.

Question 6

6. What are the advantages of using endopeptidases and exopeptidases

Answer 6

Endopeptidases hydrolyse internal peptide bonds therefore there are more ends or increase in surface area for exopeptidases which hydrolyse bonds at ends of chains.

Question 7

7. Describe how glucose/amino acids are absorbed by cotransport.

Answer 7

Sodium ions actively transported from ileum/epithelial cell to blood; This forms a concentration gradient for sodium to enter cells from gut lumen and with it, glucose/amino acids enters by facilitated diffusion with sodium ions against the glucose/amino acid concentration gradient; Glucose/amino acid diffuses into the blood, down the concentration gradient, through another protein channel.

Question 8

8. Explain why cotransport of glucose and amino acids is called indirect active transport.

Answer 8

Energy is used to actively transport the sodium ions out of the epithelial cell into the blood, glucose/amino acids are transported passively at the other end of the cell.

Question 9

9. Describe and explain how lipids are digested in the human gut.

Answer 9

Bile salts emulsify lipids from large droplets to small droplets, small lipid droplets have a large surface area for lipase to hydrolyse ester bonds forming monoglycerides and fatty acids. The monoglycerides and fatty acids remain bound to the bile salts in small droplets called micelles.

Question 10

10. Explain why the pH decreases when lipids are hydrolysed.

Answer 10

Fatty acids are produced, which are acidic and so lower the pH.

Question 11

11. Describe and explain how lipids are absorbed.

Answer 11

Micelles interact with the phospholipid bilayer of the epithelial cells and the fatty acids/monoglycerides enter by simple diffusion as they are lipid soluble. Once in the cell triglycerides are reformed by the smooth endoplasmic reticulum, then the golgi modifies the triglyceride but forming structures called chylomicrons (triglycerides, cholesterol, protein and phospholipids) the golgi packages chylomicrons into vesicles. Vesicles perform exocytosis releasing chylomicrons into lacteals (lymph system). The lymph system then carries the chylomicrons to the cardiovascular system.

Question 12

11. What are the benefits of small droplet and micelle formation?

Answer 12

Droplets increase surface areas for lipase action; So faster hydrolysis of lipids; Micelles make the fatty acids and monoglycerides more soluble in water and carry fatty acids and monoglycerides to the cell membrane of intestinal epithelial cell wo they can be absorbed.

Question 13

12. State two functions of bile salts

Answer 13

Emulsification of lipids into small droplets. Neutralisation of hydrochloric acid.

Question 14

1. Describe the cohesion-tension theory of water transport in the xylem.

Answer 14

Water evaporates from leaves, lowers water potential of leaf cells; Water pulled up xylem creating tension; Water molecules are cohesive due to hydrogen bonds between water molecules; forming a continuous water column. Adhesion of water molecules to walls of xylem also occurs; reducing the trunk diameter.

Question 15

2. Describe the mass flow hypothesis for the mechanism of translocation in plants.

Answer 15

At source sucrose is actively transported into the phloem;
By companion cells; this lowers water potential in phloem and water enters by osmosis; This produces high hydrostatic pressure; Causing the mass flow towards sink tissue; At sink sucrose is removed; and used in respiration or stored as starch, water moves out by osmosis so the hydrostatic pressure is lower. Mass flow is down a hydrostatic pressure gradient.

Question 16

3. Explain how sieve cells are adapted for mass transport.

Answer 16

They have few organelles and very little cytoplasm; So easier flow. End walls have perforations to allow movement of substances between cells.

Question 17

4. Explain how companion cells are adapted for mass transport.

Answer 17

Mitochondria release energy / ATP; For active transport.
Ribosomes produce proteins; for carrier proteins for active loading of sucrose into sieve tube elements.

Question 18

5. Explain how xylem is adapted for mass transport.

Answer 18

Xylem vessels have no end walls so form a series of unbroken tubes from root to leaf. Cells are dead so no cytoplasm or organelle which would restrict flow. Spirals of lignin withstand changes in pressure and prevent collapsing of the tube. Pits in the lignin allow lateral movement of water around blocked vessels.

Question 19

6. Describe and explain the precautions you should take when using a photometer, to obtain reliable results.

Answer 19

1. Seal joints to ensure watertight; 2. Cut shoot under water to prevent air entering the xylem;
2. Cut shoot at a slant; 4. Dry off leaves to increase the diffusion gradient; 5. Insert into apparatus under water to prevent air getting into the xylem; 6. Ensure no air bubbles are present;
3. Shut tap; 8. Note where bubble is at start to find the distance it moves;

Question 20

7. A potometer measures the rate of water uptake rather than the rate of transpiration. Give two reasons why the potometer does not truly measure the rate of transpiration.

Answer 20

Water used for support of plant; Water used in photosynthesis; Water produced in respiration;

Question 21

8. Explain why transpiration rate is highest around midday.

Answer 21

There is more photosynthesis at midday as there is more sunshine, so rate of water uptake will be higher. It is usually warmer, so more evaporation will take place, increase transpiration rate.

Question 22

9. What does a ringing experiment show about translocation?

Answer 22

The phloem is involved in translocation, (bulge at top of ring) shows mass flow down the stem.

Question 23

10. Why can radioactively labelled CO2 be used to investigate translocation.

Answer 23

The CO2 is made into glucose/sucrose in the leaf via photosynthesis, then transported round the plant in translocation. It can be seen using an x-ray of the plant.

Question 24

1. Sketch and describe an oxygen dissociation curve.

Answer 24

Partial pressure of oxygen on the x-axis, percentage saturation of haemoglobin on the y-axis up to 100%. A S-shaped curve, reaching plateau just below 100%

Question 25

2. Use an oxygen dissociation curve to describe how haemoglobin loads and unloads oxygen in the body.

Answer 25

Haemoglobin Loading takes place at high pp.O2 (in the lungs); In lungs haemoglobin is almost fully saturated as it has a high affinity for oxygen; Haemoglobin Unloads or dissociates oxygen at low pp.O2 (at the respiring cells). The higher carbon dioxide concentration at cells further decreases the affinity of haemoglobin for oxygen (Bohr affect).

Question 26

3. Why is haemoglobin considered a quaternary structure?

Answer 26

Due to the presence of 4 polypeptide chains. It also has four prosthetic groups (Fe2+).

Question 27

4. Explain why the binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind./ Explain changes in the shape of haemoglobin lead to the S-shaped curve.

Answer 27

Binding of first oxygen changes tertiary and quaternary structure of haemoglobin; this leads to another binding site as it uncovers another haem group for oxygen to bind to; So it allows more oxygen to bind; After the third oxygen binds, the tertiary structure changes again making it more difficult for oxygen to bind to the 4th binding site causing a plateau on the curve.

Question 28

5. Animals that are more active/have larger surface are to volume ratios have different haemoglobin which shows a dissociation curves shifted to the right. Explain why.

Answer 28

Larger SA:V means more heat loss so an increased metabolic rate is needed to regenerate heat. More active organisms require more aerobic respiration to make more ATP. The curve is shifted to the right so lower affinity of haemoglobin for oxygen; Haemoglobin dissociates from oxygen more readily; More oxygen to cells/tissues / muscles; for more respiration; to provide energy for muscle contraction OR to release heat energy to maintain body temperature.

Question 29

6. Animals that live in low oxygen situations such as: Foetus, high altitudes, stagnant water, etc. have different haemoglobin which shows a curve shifted to the left. Explain why.

Answer 29

Curve to the left so the haemoglobin has a higher affinity for oxygen; There is a low partial pressure of oxygen available; So haemoglobin is able to load more oxygen, as it becomes saturated at low pressure of oxygen; Collecting more oxygen for aerobic respiration to occur.

Question 30

7. After birth fetal haemoglobin is replaced with adult haemoglobin. Explain why this is an advantage to the baby.

Answer 30

Adult haemoglobin has a lower affinity for oxygen, so it dissociates more readily; Therefore more oxygen dissociates at respiring tissues / muscles / cells;

Question 31

8. Explain how high levels of aerobic respiration lead to a change in pH of the blood, and why is this an advantage for respiring organisms.

Answer 31

CO2 is produced in respiration; forms carbonic acid; this lowers pH; H-bonds/ionic bonds in haemoglobin affected by pH level; change in tertiary structure of haemoglobin; Curve shifts to the right so haemoglobin has a lower affinity to oxygen; more O2 is released faster at cells; as active cells need more O2; (for muscle contraction, etc.)

Question 32

1. Draw, label, describe and give the function of the cell surface membrane.

Answer 32

A Phospholipid bilayer, in a fluid mosaic model. Controls what enters and leaves the cell. It is a single membrane.

Question 33

2. Draw, label, describe and give the function of the nucleus.

Answer 33

The nucleus has a double membrane to control what enters and leaves. It has pores in the membrane to allow larger molecules such as mRNA to pass out. The nucleus contains genetic information in the form of chromosomes. It produces mRNA, tRNA and ribosomes, along with DNA during replication.

Question 34

2. Draw, label, describe and give the function of the nucleus.

Answer 34

The nucleus has a double membrane to control what enters and leaves. It has pores in the membrane to allow larger molecules such as mRNA to pass out. The nucleus contains genetic information in the form of chromosomes. It produces mRNA, tRNA and ribosomes, along with DNA during replication.

Question 35

3. Describe chromosomes found in the nucleus.

Answer 35

Protein-bound linear DNA.

Question 36

4. Draw, label, describe and give the function of mitochondria.

Answer 36

The site of aerobic respiration. The mitochondria has a double membrane. The inner membrane (cristae) is folded, to increase the surface area for reactions in aerobic respiration. The matrix contains enzymes for aerobic respiration, ribosomes and small circular DNA to allow the mitochondria to produce proteins.

Question 37

5. Draw, label, describe and give the function of a chloroplast in plants and algae.

Answer 37

The site of photosynthesis. The chloroplast has a double membrane. They contain membrane bound discs called thylakoids, which are stacked into grana. This increases the surface area for reactions involved in photosynthesis. The stroma contains enzymes for photosynthesis, ribosomes and small circular DNA to allow chloroplasts to produce proteins. Starch grains can store products of photosynthesis.

Question 38

6. Draw, label, describe and give the function of Golgi apparatus and Golgi vesicles.

Answer 38

A series of flattened sacs called cisternae. It modifies proteins and lipids, attaching carbohydrates to them to make glycoproteins/glycolipids. It also labels molecules so they can be transported to the right destination. Proteins and other molecules can be packaged in to vesicles or lysosomes to transport substances around the cell. They have a single membrane.

Question 39

7. Draw, label, describe and give the function of lysosomes.

Answer 39

Larger vesicles produced by the Golgi apparatus which contain enzymes called lysozyme. They are used to hydrolyse materials ingested by white blood cells, or digest worn out organelles and cells. They have a single membrane.

Question 40

8. Describe how lysosomes are different from vesicles.

Answer 40

Lysosomes are different from vesicles because they have lysozymes (enzymes) in them, whereas vesicles contain other molecules. They are both made by the Golgi apparatus.

Question 41

9. Draw, label, describe and give the function of ribosomes.

Answer 41

Ribosomes are the site of protein synthesis. They are made of protein and rRNA. They have 2 subunits that lock together. They can be found on membranes or free floating in the cytoplasm. In eukaryotes they are 80s.

Question 42

10. Draw, label, describe and give the function of the rough endoplasmic reticulum.

Answer 42

A system of ribosome covered, sheet like membranes. It provides a large surface area for protein synthesis and transports proteins and other molecules throughout the cell.

Question 43

11. Draw, label, describe and give the function of the smooth endoplasmic reticulum.

Answer 43

A system of smooth, sheet like membranes. It provides a large surface area for the synthesis and transport of lipids (and some carbohydrates throughout the cell.

Question 44

12. Draw, label, describe and give the function of a cell wall.

Answer 44

The cell wall provides mechanical strength to stop cells bursting. It is made of microfibrils of cellulose (plants) arranged as a lattice, and has a thin layer of pectin between cells called the middle lamellae.

Question 45

13. Give the molecules cell walls are made from in plants, algae and fungi.

Answer 45

Plant and algae cell walls are made of cellulose, fungi cell wells are made of chitin

Question 46

14. Draw, label, describe and give the function of the vacuole (in plants).

Answer 46

A large, fluid filled sac surrounded by a single membrane called the tonoplast. It is a temporary store of sugars and amino acids, and helps to support plants by making cells turgid.

Question 47

15. Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. Do not include details of transcription and translation in your answer

Answer 47

1. DNA in nucleus is code (for protein); 2. Ribosomes/rough endoplasmic reticulum produce (protein); 3. Mitochondria produce ATP (for protein synthesis); 4 Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus; 5 Vesicles transport OR Rough endoplasmic reticulum transports proteins around the cell; 6. Vesicles fuse with cell(-surface) membrane to release the proteins by exocytosis;

Question 48

1. Describe how translation leads to the production of a polypeptide.

Answer 48

• mRNA attaches to a ribosome
• Ribosome reads the first codon (start codon)
• tRNA with complementary anticodon attaches to the codon on mRNA.
• The tRNA carries a specific amino acid
• A second tRNA and amino acid arrives at the ribosome and binds to the next codon.
• The two amino acids form a peptide bonds via a condensation reaction. The formation of peptide bonds require ATP.
• This process continues until stop codon is reached.

Question 49

2. Describe how mRNA is produced (transcription)

Answer 49

• DNA helicase attaches to a specific DNA sequence at the start of the gene (promoter region)
• DNA helicase breaks hydrogen bonds and the DNA “unwinds” exposing the bases
• RNA polymerase attaches to specific section of DNA called a start sequence.
• Free floating RNA nucleotides attach to the template strand DNA. A-U and G-C
• RNA polymerase joins adjacent nucleotides together creating phosphodiester bonds
• The RNA polymerase moves down the DNA molecule until it reaches a stop sequence.
• As RNA polymerase moves down the DNA strand, hydrogen bonds reform between complementary bases and strands coil back together.
• The pre-mRNA strand is spliced to remove introns and non-coding repeats. Exons are joined together forming mature mRNA.
• Mature mRNA leaves via a nuclear pore.

Question 50

3. Describe the structure of mRNA

Answer 50

• Single stranded RNA
• Helix

Question 51

4. Describe the structure of tRNA

Answer 51

•Short (around 80 nucleotides)
•Single stranded chain
•Hydrogen bonds form between nucleotides forming a clover leaf shape
•Has an amino acid binding site at one end
•Anticodon at one end which complementary base pairs with a specific codon on mRNA
•There are many types of tRNA each with a different anticodon (as many as there are amino acids codons) each binding to a specific amino acid

Question 52

5. Compare and contrast mRNA and tRNA.

Answer 52

Both are made of RNA and have nucleotides have a phosphate group, ribose sugar and the bases A, U, C and G; mRNA does not have hydrogen bonds, whereas tRNA does; mRNA does not have an amino acid binding site, whereas tRNA does; mRNA is usually longer (has more nucleotides) than tRNA; mRNAs can be different lengths, whereas tRNA are all a similar length;
mRNA has codons, whereas tRNA has anticodons;

Question 53

6. A polypeptide is this many amino acids long, what is the minimum number of bases needed to code for this polypeptide?

Answer 53

This x 3 = answer

Question 54

7. A gene is this many nucleotides long, what is the maximum number of amino acids it could code for?

Answer 54

This ÷ 3 = answer

Question 55

8. What is a ribosome made of?

Answer 55

A molecule of ribosomal RNA and a protein.

Question 56

9. Explain the term non-overlapping.

Answer 56

Each base is part of only one triplet code.

Question 57

10. Explain the term degenerate.

Answer 57

More than one triplet code (or codon) codes for each amino acid.

Question 58

11. Explain how the genetic code is universal.

Answer 58

All organisms DNA triplet code in every organism codes for the same amino acid.

Question 59

12. Explain the difference between transcription in prokaryotes and eukaryotes.

Answer 59

Eukaryotic DNA contains introns with genes whereas prokaryotes don’t; These regions are removed from the pre-mRNA in eukaryotes whereas this isn’t necessary in prokaryotes;

Question 60

13. Describe the genome.

Answer 60

The complete set of genes in a cell/organism;

Question 61

14. Describe the proteome.

Answer 61

The full range of proteins a cell is able to produce;

Question 62

15. Describe the role of RNA polymerase in producing mRNA

Answer 62

RNA polymerase joins adjacent RNA nucleotides in a condensation reaction to form a phosphodiester bond. Repeating this process produces mRNA.

Question 63

16. Describe the role of ribosomes in translation.

Answer 63

mRNA binds to ribosome; there are two codons binding sites; Allows tRNA with anticodons to bind; Catalyses formation of peptide bond between amino acids held by tRNA molecules; Moves along mRNA to the next codon;

Question 64

17. Describe the role of tRNA in translation.

Answer 64

The anticodon is complementary to codon on mRNA; each tRNA has a specific amino acid; carried to ribosome; this gives the correct sequence of amino acids along polypeptide;

Question 65

18. Describe the role of ATP in translation.

Answer 65

ATP is hydrolysed to release the energy needed for the two amino acids on tRNA to be joined by a peptide bond. This is catalysed by an enzyme.

Question 66

19. Describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer.

Answer 66

The base sequence is organised into triplets, each triplet codes for an amino acid so the sequence of triplets determines the sequence of amino acids in the polypeptide.