2.0Unit 2: Cells, Development, Biodiversity and Conservation
Overview: Cells, Development, Biodiversity and Conservation — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 7 parts Lesson 1 of 26 1 quiz
Lesson summary
Unit 2 IAL Linear Biology notes: (i) know the properties of gas exchange surfaces in living organisms (large surface area to volume ratio, thickness of surface and difference in concentration) (ii) understand how the rate of diffusion is dependent on these properties and can be c…
- Unit 2 IAL Linear Biology: what to do next
- Unit 2 IAL Linear Biology: revision checklist
- Biodiversity
- Genetic diversity
- Species diversity
- Ecosystem diversity
Part 1 of 6Key ideas
Key ideas
Diverse ecosystems recover faster after disturbance.
Keystone species loss reduces biodiversity.
Part 2 of 6Syllabus points
1
(i) know the properties of gas exchange surfaces in living organisms (large surface area to volume ratio, thickness of surface and difference in concentration) (ii) understand how the rate of diffusion is dependent on these properties and can be calculated using Fick's Law of Diffusion (iii) understand how the structure of the mammalian lung is adapted for rapid gaseous exchange
2
(i) know the structure and properties of cell membranes (ii) understand how models such as the fluid mosaic model of membrane structure are interpretations of data used to develop scientific explanations of the structure and properties of cell membranes
3
understand what is meant by osmosis in terms of the movement of free water molecules through a partially permeable membrane, down a water potential gradient
4
(i) understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis (ii) understand the involvement of carrier and channel proteins in membrane transport
5
- (i) Know the basic structure of an amino acid.
- (ii) Understand the formation of polypeptides and proteins (amino acid monomers linked by condensation reactions to form peptide bonds).
- (iii) Understand the significance of a protein's primary structure in determining its secondary structure, three-dimensional structure and properties (globular and fibrous proteins and the types of bonds involved in its three-dimensional structure).
- (iv) Know the molecular structure of a globular protein and a fibrous protein and understand how their structures relate to their functions (including haemoglobin and collagen).
6
- (i) Understand the mechanism of action and the specificity of enzymes in terms of their three-dimensional structure.
- (ii) Understand that enzymes are biological catalysts that reduce activation energy.
- (iii) Know that there are intracellular enzymes catalysing reactions inside cells and extracellular enzymes catalysing reactions outside cells.
- (iv) Know the basic structure of mononucleotides (deoxyribose or ribose linked to a phosphate and a base,
- including thymine, uracil, adenine, cytosine or guanine) and the structures of DNA and RNA.
- (polynucleotides composed of mononucleotides linked by condensation reactions to form phosphodiester bonds)
- including thymine, uracil, adenine, cytosine or guanine) and the structures of DNA and RNA.
- (v) Know how complementary base pairing and the hydrogen bonding between two complementary strands are involved in the formation of the DNA double helix.
Part 3 of 6Process & sequence
- High biodiversityMore interactionsGreater resilienceStable ecosystem services
Threats (HIPPO)
Habitat lossInvasive speciesPollutionPopulation growthOverharvesting
Part 4 of 6Summary
Summary
Diverse ecosystems are more resilient.
The main threat to biodiversity is habitat loss.
Part 5 of 6Keep going
Unit 2 IAL Linear Biology: what to do next
These Unit 2 IAL Linear Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Unit 2 IAL Linear Biology understanding with the practice questions below, then reread any Unit 2 IAL Linear Biology point you were unsure about before moving on.
Unit 2 IAL Linear Biology: revision checklist
- Revise the main Unit 2 IAL Linear Biology definitions until you can write them from memory.
- Previous lesson: 1.6 SNAB Inheritance — Notes — IAL Biology NotesNext lesson: 2.1 SNAB Cell Structure & Organisation — Notes — IAL Biology NotesCourse: IAL Edexcel Linear — all unitsOfficial syllabus: Pearson Edexcel International A Levels
Part 6 of 6Compare: Compare
| Level | Measures | Importance | Threat | Example | Protection |
|---|---|---|---|---|---|
| Genetic | Allele variety | Adaptation to change | Inbreeding, small populations | Crop varieties | Seed banks |
| Species | Number and evenness of species | Stable food webs | Extinction | Coral reef species | Protected species laws |
| Ecosystem | Variety of habitats | Many services | Habitat loss | Wetlands, forests | Reserves |
Key terms
Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Biodiversity · Genetic diversity · Species diversity · Ecosystem diversity · Resilience · Ecosystem services
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. eukaryotic/prokaryotic, enzyme–substrate complex, active site, complementary).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
Instant feedbackCheck yourself
Q1. Which key term matches this description: "Variation within a species."
- Species diversityGenetic diversityEcosystem diversityBiodiversity
Show answer
Genetic diversity
Q2. Which statement best describes Biodiversity?
1
Variety of species.
2
Variation within a species.
3
Variety of habitats.
4
Variety of genes, species and ecosystems.
Show answer
Variety of genes, species and ecosystems.
Q3. Complete the statement: Diverse ecosystems are more ______.
- Species diversityEcosystem diversityresilientBiodiversity
Show answer
resilient
Q4. Which statement best describes Resilience?
1
Ability to recover from disturbance.
2
Variety of species.
3
Benefits to humans: pollination, clean water.
4
Variety of genes, species and ecosystems.
Show answer
Ability to recover from disturbance.
Last updated:
Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.