Clasification and Characteristic of Living Things, Cell Structure, and Enzymes in IGCSE

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Clasification and Characteristic of Living Things, Cell Structure, and Enzymes in IGCSE

IGCSE Biology Module: Characteristics of Life to Enzymes

Prepared by: Aghry Wiranata Anugrah, S.Pd., Gr. | @dna_edukasi

Welcome to your interactive IGCSE Biology module! This guide covers SLO 1 through 10, structured to build your mastery step-by-step. Click on each section to expand and study the materials.

Section 1: Characteristics of Living Organisms & Classification (SLO 1 & 2) ▼

Characteristics of Living Organisms (SLO 1)

Biologists use seven key characteristics to distinguish living organisms from non-living things[cite: 3]. You can remember them using the acronym MRS GREN:

• Movement: An action by an organism or part of an organism causing a change of position or place[cite: 3, 53].
• Respiration: The chemical reactions in cells that break down nutrient molecules and release energy for metabolism[cite: 3, 48].
• Sensitivity: The ability to detect and respond to changes in the internal or external environment[cite: 3, 52].
• Growth: A permanent increase in size and dry mass[cite: 3, 59].
• Reproduction: The processes that make more of the same kind of organism[cite: 3, 61].
• Excretion: The removal of the waste products of metabolism and substances in excess of requirements[cite: 3, 60].
• Nutrition: The taking in of materials for energy, growth, and development[cite: 3, 54].

Dichotomous Keys (SLO 2)

To classify and identify organisms, we construct and use dichotomous keys based on identifiable features[cite: 3]. A dichotomous key is a series of questions, each with only two answers (e.g., YES or NO), leading you step-by-step to the organism's identity[cite: 87, 94].

Section 2: Cell Structure & Functions (SLO 3, 4 & 5) ▼

Comparing Plant, Animal, and Bacterial Cells (SLO 3 & 4)

Cells are the basic units of life, but their structures vary depending on the kingdom they belong to[cite: 3, 550].

• Animal Cells: Contain a cell membrane, nucleus, cytoplasm, ribosomes, mitochondria, and small temporary vacuoles[cite: 3, 552]. They lack a cell wall and chloroplasts[cite: 602, 603].
• Plant Cells: Contain all animal cell structures, plus a cellulose cell wall, large permanent vacuole, and chloroplasts[cite: 3, 554, 615, 616].
• Bacterial Cells: Simpler structures containing a cell wall, cell membrane, cytoplasm, and ribosomes[cite: 3]. They lack a nucleus; instead, they have circular DNA and small DNA rings called plasmids[cite: 3].

Functions of Cell Structures (SLO 5)

Structure	Function
Cell Wall	Provides structural support and protects against osmotic damage[cite: 624, 625].
Cell Membrane	Controls the entry and exit of dissolved substances and separates cell contents from surroundings[cite: 605].
Nucleus	Contains genetic material (DNA) and carries instructions for controlling the activities of the cell[cite: 609, 610].
Cytoplasm	Contains water and dissolved substances where chemical reactions take place[cite: 606, 607].
Chloroplasts	Contain chlorophyll to absorb light and enzymes necessary for glucose production by photosynthesis[cite: 619].
Ribosomes	Organelles in the cytoplasm where proteins are made[cite: 607].
Mitochondria	Organelles where energy is released by aerobic respiration[cite: 607].
Vacuoles	Large and permanent in plants to provide turgor pressure; small and temporary in animals for digestion or excretion[cite: 597, 620].
Circular DNA & Plasmids	Carry the genetic information in bacterial cells[cite: 3].

Section 3: Specialised Cells (SLO 6) ▼

Structure Follows Function (SLO 6)

In multicellular organisms, cells differentiate to perform highly specific tasks. State that specialised cells have specific functions, limited to[cite: 3, 636]:

• Ciliated cells: Movement of mucus in the trachea and bronchi using tiny hairs[cite: 3, 633].
• Root hair cells: Absorption of minerals and water; they feature a long extension to increase surface area[cite: 3, 633].
• Palisade mesophyll cells: Photosynthesis; packed with chloroplasts to maximize light absorption[cite: 3, 638].
• Neurones: Conduction of electrical impulses; feature a long axon and many-branched endings[cite: 3, 633].
• Red blood cells: Transport of oxygen; they lack a nucleus to leave more space for the pigment haemoglobin[cite: 3, 633].
• Sperm and egg cells (Gametes): Reproduction; highly specialized to carry genetic material and facilitate fertilization[cite: 3, 633].

Section 4: Enzymes as Biological Catalysts (SLO 7, 8, 9 & 10) ▼

Catalysts and Enzymes (SLO 7 & 8)

A catalyst is described as a substance that increases the rate of a chemical reaction and is not changed by the reaction[cite: 3, 1016]. Enzymes are defined as specialized proteins that function as biological catalysts involved in all metabolic reactions within an organism[cite: 3, 1016].

The Necessity of Enzymes (SLO 9)

Why are enzymes essential? They are necessary in living organisms because they maintain a reaction rate fast enough to sustain life at normal body temperatures[cite: 3]. Without them, metabolic processes (like respiration and digestion) would be too slow to keep the organism alive.

How Enzymes Work (SLO 10)

Enzyme action is highly specific, often described by the "lock and key hypothesis"[cite: 1025]:

1. An enzyme is folded into a complex 3D shape, featuring a specific pocket called the active site[cite: 1025, 1026].
2. Substrate molecules fit exactly into the active site because they have a complementary shape to the active site[cite: 3, 1034].
3. This forms an enzyme-substrate complex, lowering the energy needed for the reaction[cite: 1034, 1041].
4. The substrates react and the subsequent formation of products occurs[cite: 3, 1036].
5. The products leave the active site, leaving the enzyme unchanged and ready to catalyze the next reaction[cite: 1028, 1036].

Mastery Check: SLO 1-10

1. Which characteristic of life refers to "the removal of the waste products of metabolism and substances in excess of requirements"?

a) Nutrition b) Respiration c) Excretion d) Sensitivity

2. Which cell structures are present in a bacterial cell?

a) Cell wall, cell membrane, nucleus, plasmids b) Cell wall, cell membrane, cytoplasm, circular DNA, plasmids, ribosomes c) Cell wall, mitochondria, cytoplasm, circular DNA d) Cell membrane, chloroplasts, plasmids, ribosomes

3. What is the specific function of a ciliated cell?

a) Absorption of water b) Movement of mucus in the trachea and bronchi c) Conduction of electrical impulses d) Transport of oxygen

4. Why are enzymes necessary in living organisms?

a) They provide energy directly to the cell. b) They act as the primary source of nutrition. c) They maintain a reaction rate fast enough to sustain life at normal body temperatures. d) They permanently change their shape to form new products.

5. According to the mechanics of enzyme action, why does a specific enzyme only act on a specific substrate?

a) Because the active site has a complementary shape to the substrate. b) Because enzymes are changed by the reaction. c) Because the substrate is a catalyst. d) Because enzymes only work at high temperatures.

© 2026 Fitrah Islamic World Academy (FIWA) | Crafted for educational mastery by @dna_edukasi

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