Paper 1 EQs

Question 1

(2022) Describe the structure and function of the nucleus
(4)

Answer 1

Structure
1. Double membrane and pores/nuclear envelope and pores
2. Chromosomes/chromatin
3. Nucleolus

Function
4. Stores genetic material for polypeptides
5. DNA replication occurs
6. Transcription occurs
7. Production of ribosomes

Question 2

(2022) Name the main polymer that forms the following cell walls
Plant
Fungi
(1)

Answer 2

Plant - Cellulose
Fungi - Chitin

Question 3

(2022) Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria
becoming a common cause of infection acquired when in hospital. (3)

Answer 3

1. Some bacteria have resistant alleles
2. Non resistant bacteria die
3. More antibiotics used in hospital compared with elsewhere so high frequency of resistance allele

Question 4

(2022) Describe how the scientists could use aseptic techniques to transfer 0.3 cm3 of C. difficile in liquid culture from a bottle onto an agar plate. (3)

Answer 4

1. Wash hands with soap/disinfect surfaces
2. Flame neck of bottle
3. Lift agar plate lid slightly
4. Work close to upward air movement
5. Use sterile spreader

Question 5

(2022) Give two features of all prokaryotic cells that are not features of eukaryotic cells (1)

Answer 5

1. No membrane-bound organelles#
2. Single circular/loop DNA
3. DNA free in cytoplasm
4. DNA not associated with proteins/histones
5. Murein/peptidoglycan in cell wall
6. Prokaryotes have smaller ribosomes (70s)

Question 6

(2022) Describe viral replication (3)

Answer 6

1. Attachment proteins attach to receptor
2. Viral nucleic acid enters cell
3. Nucleic acid replicated in cell/reverse transcriptase makes DNA from RNA
4. Cell produces viral protein/capsid/enzymes
5. Virus assembled and released from cell

Question 7

(2022) Define the quaternary structure of a protein (1)

Answer 7

More than one polypeptide chain

Question 8

(2022) Explain how two enzymes with different amino acid sequences can catalyse the same reaction. (2)

Answer 8

1. Both active sites have similar/identical tertiary
   structures
2. So form enzyme-substrate complexes with the
   same substrate

Question 9

(2022) Give three differences between DNA molecules and
tRNA molecules (3)

Answer 9

1. Deoxyribose v ribose
2. Double-stranded v single-stranded
3. Many nucleotides v few
4. Thymine v uracil
5. Linear v clover leaf structure/double helix v clover leaf structure
6. Does not bind to amino acid v does bind to
   amino acid;
7. No exposed bases v anticodon

Question 10

(2022) Describe how the scientists would remove large organelles from a suspension of cell contents (2)

Answer 10

1. Use centrifuge/centrifugation at
   slow/low/increasing sequence of speeds
2. Large/dense organelles removed in first/early pellet

Question 11

(2022) To observe the fish gills with the optical microscope, the scientists used two different stains. The first stain binds to DNA; the second stain binds to the red blood cells.

Explain why a second stain would be needed to stain the red blood cells. Suggest which molecule the stain could bind to in the red blood cells. (2)

Answer 11

1. Red blood cells do not have a nucleus/DNA
2. Haemoglobin

Question 12

(2022) Describe the transport of carbohydrate in plants. (5)

Answer 12

1. Sucrose actively transported into phloem cell/sucrose is co-transported/moved with H+ into
   phloem cell
2. By companion/transfer cells
3. Lowers water potential (in phloem) and water
   enters (from xylem) by osmosis
4. Produces higher hydrostatic pressure/produces hydrostatic pressure gradient
5. Mass flow to respiring cells/mass flow to storage tissue/organ
6. Unloaded/removed from phloem by active
   transport

Question 13

(2022) Compare and contrast the structure of starch and the structure of cellulose. (6)

Answer 13

1. Both polysaccharides/both are glucose polymers/both are made of glucose monomers
2. Both contain glycosidic bonds between monomers
3. Both contain carbon, hydrogen and oxygen/C, H and O
4. Starch has α-glucose and cellulose has β glucose
5. Starch molecule is helical/coiled and cellulose molecule is straight
6. Starch molecule is branched and cellulose is not/unbranched
7. Cellulose has micro/macro fibrils and starch does not

Question 14

(2022) Describe the complete digestion of starch by a mammal. (4)

Answer 14

1. Hydrolysis
2. Of glycosidic bonds
3. Starch to maltose by amylase
4. Maltose to glucose by disaccharidase/maltase
5. Membrane-bound disaccharidase/maltase

Question 15

(2017) Give the two types of molecule from which a ribosome is made (1)

Answer 15

• rRNA
• Protein

Question 16

(2017) Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer. (3)

Answer 16

1. mRNA binds to ribosome;
2. Idea of two codons/binding sites
3. Allows tRNA with anticodons to bind/associate
4. Catalyses formation of peptide bond between amino acids held by tRNA molecules
5. Moves along mRNA to the next
   codon)/translocation described

Question 17

(2017) In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA.

Explain why. (2)

Answer 17

1. Introns in pre-mRNA
2. Removal of sections of pre-mRNA)/splicing

Question 18

(2017) Describe the structure of glycogen. (2)

Answer 18

1. Polysaccharide of α-glucose/polymer of α-glucose
2. Joined by glycosidic bonds/branched structure

Question 19

(2017) Suggest how glycogen acts as a source of energy.

Do not include transport across membranes in your answer. (2)

Answer 19

1. Hydrolysed to glucose
2. Glucose used in respiration

Question 20

(2017) Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients. (2)

Answer 20

1. Membrane folded so increased/large surface area
   /Membrane has increased/large surface area for fast diffusion/facilitated diffusion/active transport/co-transport
2. Large number of protein channels/carriers in membrane for facilitated diffusion
3. Large number of protein carriers in membrane for active transport
4. Large number of protein channels/carriers in membrane for co-transport;

Question 21

(2017) Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3.

NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell.

Use your knowledge of transport across cell membranes to suggest how NHE3 does this. (3)

Answer 21

1. Co-transport;
2. Uses hydrolysis of ATP
3. Sodium ion and proton bind to the protein;
4. Protein changes shape to move sodium ion
   and/or proton across the membrane

Question 22

(2017) High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid.

Explain how. (3)