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PSPM BiologySB015/SB025

2 papers200 marks4 h

What we predict comes up

From the syllabus weighting and how the papers are usually set. The papers below follow it.

  1. Biomolecules, cells and membranes18%Biomolecules, organelles and membrane transport open SB015 and together usually take the first three questions.
  2. Animal form and function18%The largest SB025 chapter: transport, nervous coordination and homeostasis are each likely to get a question.
  3. Cellular respiration and photosynthesis13%The energy chapters are long in the syllabus and are tested in two questions, with ATP accounting and respiratory quotient common.
  4. Plant form and function12%Transport in plants and plant growth and response usually take two questions.
SB015

Semester 1: Biology 1

2 h · 100 marks · Calculator allowed

120:00
  • This question paper consists of 8 structured questions.
  • Answer all questions.
  • Write your answers in the answer booklet provided. Show all working for calculations.
  • Non-programmable scientific calculators may be used.

Answer or mark a question and your score adds up here.

Answer all questions100 marks

112 marks
(a)Two molecules of α-glucose join to form maltose. Name the reaction and the bond formed, state which carbon atoms are linked, and state how maltose can be broken down again.[3]
(b)Explain how the structure of cellulose makes it suitable as the main component of plant cell walls.[3]
(c)A polypeptide contains 150 amino acids in a single unbranched chain. State the number of water molecules released when it is formed.[1]
(d)Describe the tertiary structure of a protein and name the bonds that maintain it.[3]
(e)Explain how the structure of a phospholipid molecule allows it to form a bilayer in water.[2]
212 marks
The table shows the features of three cells, X, Y and Z, seen with an electron microscope.
FeatureCell XCell YCell Z
Nuclear envelopeAbsentPresentPresent
Cell wallPresent (peptidoglycan)Present (cellulose)Absent
MitochondriaAbsentPresentPresent
ChloroplastsAbsentPresentAbsent
Ribosomes70S only80S in cytoplasm80S in cytoplasm
CentriolesAbsentAbsentPresent
(a)Identify the type of cell X, Y and Z, giving one feature from the table that supports each identification.[3]
(b)On an electron micrograph of cell Z with a magnification of ×12 000, a mitochondrion measures 30 mm long. Calculate its actual length in µm.[2]
(c)Cell Z secretes a digestive enzyme. Describe the roles of the rough endoplasmic reticulum, the Golgi apparatus and vesicles in producing and secreting this enzyme.[4]
(d)Cell Y comes from a leaf. Explain how two of its organelles are adapted to their functions.[3]
312 marks
(a)Explain why the plasma membrane is described by the fluid mosaic model.[3]
(b)A plant cell has a solute potential of -800 kPa and a pressure potential of +300 kPa. Calculate its water potential in kPa, and state the direction of water movement when it is placed in a solution with a water potential of -700 kPa.[3]
(c)Potato strips were placed in sucrose solutions for 2 hours and their percentage change in mass was recorded. Estimate, by linear interpolation, the sucrose concentration that is isotonic with the potato cells, in mol dm⁻³.[3]
Sucrose concentration (mol dm⁻³)0.10.20.30.4
Change in mass (%)+8.0+3.2-1.6-6.0
(d)Describe how the sodium-potassium pump moves ions across the plasma membrane.[3]

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Not included: The laboratory practical assessment, which is marked as coursework and not in the PSPM written paper, is not included.