Unit 1 Notes – Organization in Life (MYP 4, 2024-25)

Key Concept, Related Concepts and Global Context

This unit is framed by the key concept of Systems, with related concepts Pattern and Function guiding analysis. In the Global Context Identities and Relationships, students explore how cellular patterns and functions underpin personal biological identity. In other words, the way countless cells cooperate as a system literally constitutes “who we are”.

Statement of Inquiry (SOI)

Our identity is determined by the relationship between different patterns and functioning of the cells that work together to create a larger, functioning system.

Purpose of the Notes

These notes condense all essential ideas, facts, examples and implications from the lesson so you can:

1. Review rapidly before assessments.

2. Visualise how discrete facts connect into a coherent model of life.

3. Personalise learning by adding margin annotations or highlighting difficult sections.

Learning Outcomes

By mastering these notes you should be able to:
• Distinguish living from non-living things using the \text{MRS H. GREN} framework.
• Describe and evaluate Cell Theory.
• Contrast prokaryotic and eukaryotic cells.
• Identify all major organelles in plant and animal cells and explain their functions.

What Makes Something Alive? – \text{MRS H. GREN}

Living organisms share eight universal characteristics that separate them from inanimate matter:

1. Movement – voluntary or growth-related displacement. Animals migrate, plants turn towards light.

2. Respiration – intracellular chemical reactions that release usable energy (e.g.
   C6​H12​O6​+6O2​→6CO2​+6H2​O+Energy (ATP)

3. Reproduction – the process by which living organisms produce new individuals of the same species, ensuring the continuation of genetic material.

   Sensitivity – the ability of organisms to respond to stimuli in their environment, which is crucial for their survival and adaptation.

4. Sensitivity (Response to Stimuli) – detection of and reaction to light, gravity, temperature, pH, chemicals.

5. Homeostasis – self-regulating mechanisms (temperature, \text{pH}, water potential) that stabilise the internal environment.

6. Growth – permanent increase in dry mass via cell size increase and/or cell division.

7. Reproduction – production of offspring genetically related to parents (asexual or sexual).

8. Excretion – removal of toxic metabolic waste (e.g. \text{NH}3, \text{CO}2, urea).

9. Nutrition – acquisition of materials and energy (autotrophic photosynthesis or heterotrophic feeding).

Historical Milestones in Cytology

• 1665 – Robert Hooke: coined the word “cell” after viewing cork honey-combs with a homemade compound microscope.
• 1674 – Anton van Leeuwenhoek: first to visualise live bacteria and protozoa with his superior single-lens microscopes.
• 1831 – Robert Brown: discovered the ubiquitous nucleus in plant cells.
• 1840 – Jan Purkinje: introduced the term “protoplasm” for cell’s living substance.
• 1838 – Matthias Schleiden: declared all plant tissues are cellular and perform metabolism.
• 1839 – Theodor Schwann: applied the same idea to animals—cells as functional life units.
• 1855 – Rudolf Virchow: added "\text{Omnis cellula e cellula}"—all cells arise from pre-existing cells.

Cell Theory – Three Corner‐stones

1. All living organisms are composed of one or more cells (unicellular or multicellular).

2. The cell is the fundamental structural and functional unit of life.

3. New cells originate only from the division of existing cells.

Philosophical implication: life is continuous; there is no spontaneous generation at the scale of modern biology.

Levels of Biological Organisation

Atoms \rightarrow Molecules \rightarrow Cells \rightarrow Tissues \rightarrow Organs \rightarrow Organ Systems \rightarrow Organism.
• Cell – smallest autonomous life unit.
• Tissue – cohesive group of similar cells (e.g. muscle, xylem).
• Organ – structure of several tissues performing a task (e.g. heart, leaf).
• Organ System – organs cooperating (e.g. circulatory system, plant vascular bundle).
The hierarchy illustrates Systems thinking: properties emerge at each level not predictable from lower levels alone.

Unicellular vs. Multicellular Life

Unicellular organisms (bacteria, Amoeba) handle every MRS H. GREN function within one cell. Multicellular organisms specialise; division of labour  higher efficiency but interdependence.

Prokaryotic and Eukaryotic Cells – Comparative Overview

Evolutionary context: prokaryotes appeared ~3.5 billion y ago; eukaryotes later via endosymbiosis (mitochondria, chloroplasts once free bacteria).

Plant vs. Animal Cells – Key Differences

Plant cells: cellulose cell wall, large central vacuole, plastids (chloroplasts), generally larger, starch storage, limited lysosomes, no centrosome.
Animal cells: no cell wall, small or absent vacuoles, no plastids, glycogen storage, abundant lysosomes, have centrosome containing centrioles.

The Protoplasm

Everything inside the plasma membrane – cytoplasm + nucleus – constitutes the protoplasm, poetically “the physical basis of life”.

Detailed Tour of Eukaryotic Organelles

Plasma (Cell) Membrane

Bi-layer of phospholipids studded with proteins and carbohydrates produces a selectively permeable barrier. Regulates ion traffic, cell signalling, and maintains homeostasis.

Cell Wall (plants, fungi, bacteria)

Rigid exoskeleton of cellulose (plants) or peptidoglycan (bacteria). Provides shape, prevents osmotic lysis, enables turgor-driven growth.

Cytoplasm

70–90 % water gel with ions, enzymes, and cytoskeletal filaments. Exhibits cytoplasmic streaming for nutrient distribution and organelle repositioning.

Endoplasmic Reticulum (ER)

• Rough ER – ribosome-studded; synthesises secretory and membrane proteins.
• Smooth ER – lipid, steroid and hormone synthesis; detoxification; Ca^{2+} reservoir in muscle cells.
The ER’s labyrinth increases surface area \Rightarrow more metabolic sites.

Golgi Apparatus

Stack of cisternae that further modify proteins (glycosylation), package them into vesicles, and build lysosomes. Think of it as the cell’s “post-office”.

Lysosomes

Vesicles loaded with hydrolytic enzymes ((pH \approx 5)). Digest worn organelles (autophagy) or engulfed pathogens (phagocytosis). Nicknamed “suicide bags” because membrane rupture releases enzymes causing cell death (apoptosis).

Vacuoles

Large central vacuole in plants maintains turgor pressure \Rightarrow structural support and drives growth. Contractile vacuoles in protists expel excess water. Food vacuoles aid intracellular digestion (e.g. Amoeba).

Mitochondria

Double membrane; inner membrane folded into cristae. Site of aerobic respiration and ATP production via oxidative phosphorylation. Contains its own circular DNA and 70 S ribosomes—evidence for endosymbiotic origin.

Plastids (Plants)

• Leucoplasts – colourless; store starch, oil, proteins.
• Chromoplasts – red/orange/yellow pigments (carotenoids).
• Chloroplasts – green; perform photosynthesis.

Chloroplast Ultrastructure

Outer + inner membranes enclose stroma. Flattened sacs thylakoids form stacks (grana). Chlorophyll embedded in thylakoid membranes captures light; light reactions occur here, Calvin cycle in stroma. Each granum ≈ 10–20 thylakoids.

Centrosome (Animal Cells)

Pair of perpendicular centrioles surrounded by pericentriolar material. Organises microtubules and forms spindle fibres in mitosis/meiosis.

Nucleus

Encased by double nuclear envelope perforated with pores. Contains:
• Nucleoplasm – matrix.
• Nucleolus – ribosome factory (rRNA + protein).
• Chromatin – DNA-protein complex; condenses into chromosomes during cell division. Governs gene expression and heredity.

Guiding Questions for Self-Assessment

1. Which eight features constitute the \text{MRS H. GREN} mnemonic, and why does each matter?

2. Trace how a zygote grows into a multicellular organism through mitosis, differentiation and organogenesis.

3. Starting from a single cell, map the hierarchy up to an organism and explain emergent properties at each level.

4. Match each scientist (Hooke, Leeuwenhoek, Brown, Schleiden, Schwann, Virchow, Purkinje) with their cell discovery.

5. For every organelle listed above, describe structure ↔ function relationships and predict the consequence of its failure.

Ethical, Philosophical and Real-World Connections

• Understanding cell theory underpins modern medicine—antibiotics target prokaryotic ribosomes without harming human 80 S ribosomes.
• Organelle pathology explains diseases: mitochondrial disorders, lysosomal storage diseases, ER stress in diabetes.
• Biotechnology leverages cellular systems (e.g. chloroplast genetic engineering for sustainable bio-factories).
• Discussions of identity: If cellular patterns change (mutations, stem-cell therapies), how might that affect “who we are”?

Numerical / Statistical Nuggets

• Typical prokaryote diameter: 1–10\,\mu\text{m}; eukaryote: 5–100\,\mu\text{m}.
• One human cell hosts \approx 10^{13} ATP molecules at any instant, recycling entire body mass of ATP daily.

Formulae & Equations Highlight

• Aerobic respiration: C6​H12​O6​+6O2​→6CO2​+6H2​O+36ATP
• Photosynthesis (overall): 6CO2​+6H2​Olight​C6​H12​O6​+6O2​

Recommended Resources for Extended Study

Books: Mindorff & Allott – MYP Biology 4/5; Davis & Patricia – MYP by Concepts 4 & 5; Mackean & Hayward – Cambridge IGCSE Biology; Anita Prasad – ICSE Biology.
Articles/Websites: AAP (2022) on cell structure–function; SEER Training (NCI); CK-12 Foundation; Meritnation online tutorials.