Cycling of Matter in Living Systems
Ms. Terkper's Digital Classroom — Nature of Science Emphasis
Focusing Questions
"How did the cell theory replace the concept of 'spontaneous generation' and revolutionize the study of life sciences? How do single-celled organisms carry out life functions? How do plants use specialized cells and processes to accomplish the same functions as a single cell, but on a larger scale? How does imaging technology further our understanding of the structure and function of cells?"
Program Outcomes
Key Concepts
Unit Overview
The fundamental unit of life, the cell, is an efficient open system. Technological advancements in microscopy have enhanced the study of cells. Understanding cellular processes can be applied to multicellular organisms. This unit focuses on structure and function from the molecular level to the whole-plant level.
Cell Theory & Microscopy
The Three Postulates of Cell Theory
Spontaneous Generation vs Cell Theory
Before cell theory, many scientists believed life could arise spontaneously from non-living matter (e.g., maggots from meat). Louis Pasteur's swan-neck flask experiment (1859) disproved this, demonstrating that life only comes from pre-existing life, cementing the third postulate.
| Scientist | Year | Contribution |
|---|---|---|
| Aristotle | ~330 BCE | Proposed spontaneous generation; believed living organisms could arise from non-living matter |
| Robert Hooke | 1665 | First observed and named "cells" (cork slices); used a compound light microscope |
| Antonie van Leeuwenhoek | 1670s | First to observe living single-celled organisms (bacteria, protozoa) |
| Robert Brown | 1831 | Discovered the cell nucleus |
| Schleiden & Schwann | 1838–39 | Proposed that all plants (Schleiden) and animals (Schwann) are made of cells |
| Rudolf Virchow | 1855 | Added the third postulate: "Omnis cellula e cellula" (all cells from cells) |
| Louis Pasteur | 1859 | Swan-neck experiment definitively disproved spontaneous generation |
Microscopy Technology & Advancements
Uses visible light and glass lenses. Can magnify up to ~1000×. Allows viewing of living cells and staining techniques to highlight structures. Limited by the wavelength of light.
Resolution: ~200 nm
Uses a beam of electrons through a thin specimen. Reveals internal ultrastructure of cells — organelles, membranes, ribosomes. Cannot view living cells.
Magnification: up to 1,000,000× | Resolution: ~0.1 nm
Scans cell surface with electrons to produce a 3D image of external structures. Excellent for viewing surface detail of cells and tissues.
Magnification: up to 500,000×
Uses laser light and fluorescent dyes to create 3D images of living cells. Can track molecular movement in real time. Revolutionized cell biology research.
Key application: DNA and gene mapping
Dyes (e.g., iodine for starch, methylene blue for nuclei) bind selectively to cell structures, making them visible under the light microscope. Critical for identifying organelles.
- DNA and gene mapping
- Transport across cell membranes
- HIV drug attachment to cells and liposomes
- Sub-cellular particles (viruses, prions)
Cell Organelles & Interactive Diagram
Click any organelle button on the diagram to learn its structure and function. Toggle between plant and animal cells.
Nucleus
| Organelle | Function | Plant Cell | Animal Cell |
|---|---|---|---|
| Cell Membrane | Controls what enters and exits the cell; semi-permeable; fluid-mosaic model | Yes | Yes |
| Cell Wall | Rigid outer layer (cellulose) providing structural support and protection; freely permeable | Yes | No |
| Nucleus | Control centre; contains DNA; directs all cell activities; surrounded by nuclear membrane | Yes | Yes |
| Mitochondrion | Site of cellular respiration; produces ATP (energy); "powerhouse of the cell" | Yes | Yes |
| Chloroplast | Site of photosynthesis; converts light energy + CO2 + H2O into glucose; contains chlorophyll | Yes | No |
| Ribosome | Site of protein synthesis; translates mRNA into proteins; can be free or on rough ER | Yes | Yes |
| Endoplasmic Reticulum (ER) | Rough ER: protein processing and transport (has ribosomes). Smooth ER: lipid synthesis, detoxification | Yes | Yes |
| Golgi Apparatus | Packages, modifies and ships proteins and lipids; "post office" of the cell; produces lysosomes | Yes | Yes |
| Lysosome | Contains digestive enzymes that break down waste, damaged organelles and foreign material | Rare | Yes |
| Vacuole | Storage of water, nutrients, waste. Central vacuole in plant cells is large; provides turgor pressure | Large (1) | Small (many) |
Transport Across the Cell Membrane
Diffusion
Movement of particles from an area of high concentration to low concentration down the concentration gradient. No energy (ATP) required.
- Follows concentration gradient
- Continues until equilibrium
- Small nonpolar molecules (O2, CO2) can pass directly through the membrane
Osmosis
Diffusion of water specifically, across a semi-permeable membrane from an area of low solute concentration (high water concentration) to high solute concentration (low water concentration).
- No ATP required
- Affected by tonicity (hypotonic, isotonic, hypertonic)
- Creates turgor pressure in plant cells
- Applications: dialysis, desalination, cheese making
Active Transport
Movement of particles from low to high concentration — against the concentration gradient. Requires ATP (energy) and protein carrier molecules.
- Uses carrier proteins (pumps)
- Against the concentration gradient
- Examples: sodium-potassium pump, glucose uptake in intestines
- Also includes endocytosis and exocytosis
Solute concentration lower outside than inside the cell. Water moves INTO the cell by osmosis. Animal cells may lyse (burst). Plant cells become turgid (swollen) — desirable!
Solute concentration equal inside and outside. No net movement of water. Cell maintains its shape. This is the ideal condition for cells (e.g., normal saline = 0.9% NaCl).
Solute concentration higher outside than inside. Water moves OUT of the cell by osmosis. Animal cells crenate (shrink). Plant cells undergo plasmolysis (membrane pulls away from wall).
| Application | Principle | How It Works |
|---|---|---|
| Kidney Dialysis | Osmosis | Blood flows past a semi-permeable membrane; waste diffuses out, nutrients are retained |
| Desalination | Reverse Osmosis | Pressure forces water through a membrane against the osmotic gradient, removing salt |
| Cheese Making | Osmosis | Salt draws water out of curd by osmosis, concentrating proteins and extending shelf life |
| HIV Drug Delivery | Diffusion | Drugs attached to liposomes fuse with cell membranes and diffuse directly into infected cells |
| Traditional Food Preservation (First Nations) | Osmosis | Honey and berries used as preservatives — high sugar concentration draws water out of bacteria |
| Water Purification | Osmosis | Membranes with specific pore sizes separate contaminants from water molecules |
| Cell Staining | Diffusion | Dye molecules diffuse across the cell membrane down their concentration gradient |
Surface Area to Volume Ratio & Cell Size
Why Cell Size Is Limited
As a cell grows larger, its volume increases much faster than its surface area. Since all nutrients, gases and waste must pass through the surface (cell membrane), a low SA:V ratio means the cell cannot sustain itself — it either divides or dies.
The Key Rule
A higher SA:V ratio = more efficient exchange of materials. Small cells are more efficient than large cells. This is why cells divide rather than grow indefinitely.
Examples from Biology
- Red blood cells: biconcave disc shape maximizes SA:V for O2 exchange
- Nerve cells: long, thin axons provide large surface area for signal propagation
- Root hair cells: long projections dramatically increase surface area for water absorption
- Palisade cells: cylindrical and tightly packed to maximize light absorption
- Intestinal villi: finger-like projections increase absorption surface area
Interactive SA:V Calculator
Adjust cell side length to see how SA:V changes as a cube-shaped cell grows.
| Side | SA (mm²) | Vol (mm³) | SA:V |
|---|---|---|---|
| 1 mm | 6 | 1 | 6 : 1 |
| 2 mm | 24 | 8 | 3 : 1 |
| 3 mm | 54 | 27 | 2 : 1 |
| 5 mm | 150 | 125 | 1.2 : 1 |
| 10 mm | 600 | 1000 | 0.6 : 1 |
| 20 mm | 2400 | 8000 | 0.3 : 1 |
Plants as Multicellular Organisms
The Leaf System & Photosynthesis Support
| Cell / Tissue Type | Location | Specialized Function |
|---|---|---|
| Epidermis | Outer surface (upper & lower) | Protection; transparent to allow light through; no chloroplasts in most species |
| Guard Cells | Epidermis (flanking stomata) | Bean-shaped cells that open/close stomata by changing turgor pressure; control gas exchange and water loss |
| Palisade Mesophyll | Upper layer below epidermis | Tightly packed, cylindrical cells; densely packed with chloroplasts; primary site of photosynthesis |
| Spongy Mesophyll | Lower layer above lower epidermis | Loosely arranged; large air spaces for gas diffusion; some photosynthesis |
| Xylem | Vascular bundles (veins) | Transports water and minerals UP from roots; dead, hollow tube cells; thick walls for support |
| Phloem | Vascular bundles (veins) | Transports sugars (glucose) to all parts of the plant; living cells; bidirectional flow |
From Single Cell to Multicellular
When a single-celled organism or colony reaches a certain size, its SA:V ratio becomes too low to sustain all life functions through one cell. This is why multicellular organisms evolved cell specialization — different cells handle different functions, and every cell remains small and efficient.
Photosynthesis Summary
Takes place in chloroplasts; requires light, CO2, and water; produces glucose and oxygen.
Transport Systems in Plants
Moves water and dissolved minerals from roots upward to leaves. Driven by:
- Transpiration pull: evaporation of water from stomata creates negative pressure
- Cohesion: water molecules attract each other (hydrogen bonds) forming a continuous column
- Adhesion: water molecules attracted to xylem walls
- Root pressure: osmotic uptake from soil pushes water upward
Moves dissolved sugars (sucrose) produced by photosynthesis to all parts of the plant. Process called translocation.
- Bidirectional flow (unlike xylem)
- Source-to-sink movement
- Living cells with companion cells
- Requires ATP for active loading
Plants exchange CO2 and O2 by diffusion through:
- Stomata: pores in leaf epidermis; opened/closed by guard cells
- Lenticels: pores in woody stem bark for gas exchange
O2 exits and CO2 enters during photosynthesis (daytime). Reversed during cellular respiration.
Plant Control Systems — Tropisms
The growth of a plant toward (or away from) a light source. Shoot tips grow toward light (positive phototropism); roots may grow away from light.
The growth of a plant in response to gravity. Roots grow downward (positive gravitropism) and shoots grow upward (negative gravitropism).
Mechanism
Specialized cells called statocytes contain starch-filled bodies called statoliths. These settle due to gravity, triggering auxin redistribution. Auxin accumulates on the lower side of roots (inhibiting growth) and shoots (promoting growth).
Practical example: germinating seeds always produce shoots growing up and roots growing down, regardless of seed orientation.
Interactive Practice & Quizzes
Knowledge Check Quiz
Test your understanding of cells, transport and plant systems.
Cycling of Matter — Science 10
Organelle Function Match
Match each organelle on the left with its function on the right.
Vocabulary Flashcards
Click the card to flip. Use arrows to navigate all 20 terms.