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Chapter 1. Characteristics of Living Organisms

All living organisms share a set of characteristics that define life. These are often remembered using the acronym MRS GREN:

Movement

Respiration

Sensitivity

Growth

Reproduction

Excretion

Nutrition.

(a) Movement

  • Definition: Movement is an action by an organism or part of an organism that causes a change of position or place.

  • Examples:

    • Animals move from place to place using muscles.

    • Plants show movement, e.g., sunflower heads turning toward light (phototropism).

(b) Respiration

  • Definition: Respiration refers to the chemical reactions that occur in cells to break down nutrient molecules (like glucose) and release energy.

  • Importance: The energy released is used for metabolism (all chemical processes in the body).

  • Types: Aerobic (with oxygen) and anaerobic (without oxygen).

(c) Sensitivity (or Response to Stimuli)

  • Definition: Sensitivity is the ability to detect or sense changes in the environment (stimuli) and make appropriate responses.

  • Examples:

    • Animals reacting to danger (e.g., pulling hand from something hot).

    • Plants responding to gravity or light.

(d) Growth

  • Definition: Growth is a permanent increase in size and dry mass by an increase in cell number or cell size or both.

  • Measured by: Increase in height, weight, or biomass.

(e) Reproduction

  • Definition: Reproduction is the process that makes more of the same kind of organism.

  • Types:

    • Sexual reproduction (involving gametes).

    • Asexual reproduction (without gametes, e.g., budding in yeast).

(f) Excretion

  • Definition: Excretion is the removal of waste products of metabolism and substances in excess of requirements.

  • Examples:

    • Humans excrete carbon dioxide (from respiration) and urea (from the liver).

    • Plants excrete oxygen and carbon dioxide via the stomata.

(g) Nutrition

  • Definition: Nutrition is the taking in of materials for energy, growth, and development.

  • Examples:

    • Plants absorb sunlight, water, and minerals (photosynthesis).

    • Animals eat food to get nutrients.

Concept and Uses of Classification Systems

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Classification helps scientists organize and study the diversity of life.

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State that organisms can be classified into groups by the features that they share

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  • ]Classification is based on similarities in structure, function, and genetics.

 

 Define a species

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  • A species is a group of organisms that can breed together to produce fertile offspring.

1.2.3 Binomial System of Naming Species

  • Binomial nomenclature uses two Latin names: Genus (capitalized) and species (lowercase).

  • Example: Homo sapiens (humans)

  • Developed by Carl Linnaeus; it is universally used by scientists.

1.2.4 Use of Dichotomous Keys

  • A dichotomous key is a series of choices that lead to the identification of an organism.

  • Each step offers two contrasting statements (yes/no, present/absent, etc.)

3. Features of Organisms and Classification into Groups

Core: Classification into Main Kingdoms

  • Plants: Multicellular, cell walls, chlorophyll, photosynthesis.

  • Animals: Multicellular, no cell walls, heterotrophic (consume food).

  • Fungi: Multicellular or unicellular, cell walls (chitin), saprophytic nutrition.

  • Prokaryotes: Unicellular, no nucleus (e.g., bacteria).

  • Protoctists: Mixed group (unicellular or multicellular), some like animals, others like plants.

Supplement Classification

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  • Not living cells.

  • Consist of:

    • Genetic material (DNA or RNA).

    • Protein coat.

  • Reproduce only inside living host cells.

  • Example: HIV virus.

Advanced Classification Concepts (Supplement)

Evolutionary Relationships

  • Modern classification systems show how organisms are related through evolution.

  • Organisms with common ancestors are grouped closely.

 DNA Base Sequences

  • Organisms that are more closely related have similar DNA base sequences.

  • DNA analysis is a modern tool for accurate classification.

 Common Ancestors and DNA Similarity

  • Groups that share a more recent common ancestor have more similar DNA than those with distant ancestors.

  • Example: Humans and chimpanzees share over 98% of DNA.

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Chapter 4: Biological Molecules

Core Content

1. Chemical Elements That Make Up Biological Molecules

 

Molecule Elements Present

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Carbohydrates- Carbon (C), Hydrogen (H), Oxygen (O)

Fats and Oils     (Lipids)Carbon (C), Hydrogen (H), Oxygen (O)

Proteins               Carbon    (C), Hydrogen (H), Oxygen (O), Nitrogen (N) (sometimes Sulfur (S))

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Note: All biological molecules are made primarily of carbon-based compounds.

2. Large Molecules Made from Smaller Molecules

(a) Carbohydrates (e.g., starch, glycogen, cellulose)

  • Made from glucose (a simple sugar, a monosaccharide).

  • Glucose molecules link together to form:

    • Starch – energy storage in plants.

    • Glycogen – energy storage in animals.

    • Cellulose – structural component in plant cell walls.

(b) Proteins

  • Made from amino acids.

  • Amino acids link together in long chains via peptide bonds.

  • The sequence of amino acids determines the protein’s function.

(c) Fats and Oils (Lipids)

  • Made from 3 fatty acids and 1 glycerol.

  • These combine in a condensation reaction to form a triglyceride.

  • Used for energy storage, insulation, and protection.

3. Tests for Biological Molecules

Test  Substance Detected  Procedure   Positive Result

Iodine Test Starch

Add iodine solution to the sampleBlue-black color

Benedict’s TestReducing sugars (e.g. glucose)Add Benedict’s solution and heat in a water bathBrick-red precipitate

Biuret TestProteinsAdd Biuret solution (sodium hydroxide + copper(II) sulfate)Purple/lilac color

Ethanol Emulsion TestFats and oilsMix sample with ethanol, then waterWhite emulsion forms

DCPIP TestVitamin CAdd DCPIP solution to sampleDCPIP changes from blue to colorless

Supplement Content​​​​​​

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4. Structure of DNA Molecule

Deoxyribonucleic acid (DNA) is the molecule that carries genetic information.

Structure Summary:

  • DNA is made of two strands coiled together to form a double helix.

  • Each strand is made up of nucleotides, which contain a sugar, phosphate group, and a base.

  • The strands are held together by bonds between pairs of bases.

Base Pairing Rule:

  • A pairs with T (Adenine with Thymine)

  • C pairs with G (Cytosine with Guanine)

Key Points:

  • The sequence of bases forms the genetic code.

  • The base pairing ensures that DNA can be accurately copied during cell division.

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Chapter: Movement into and out of Cells

3.1 Diffusion

Core Content

1. Definition of Diffusion:

  • Diffusion is the net movement of particles (such as molecules or ions) from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of random movement of the particles.

Key Phrase: Down a concentration gradient.

Example:

  • When perfume is sprayed in one part of a room, its particles gradually spread throughout the air.

  • In living organisms: Oxygen diffuses from the alveoli (lungs) into the blood because the oxygen concentration is higher in the alveoli than in the blood.

2. Source of Energy for Diffusion:

  • The energy for diffusion comes from the kinetic energy of molecules or ions, which causes them to move randomly.

3. Substances Moving by Diffusion Through Cell Membranes:

  • Small, non-polar molecules like oxygen, carbon dioxide, and water can diffuse through the partially permeable cell membrane.

Example:

  • Carbon dioxide diffuses into a leaf through the stomata for photosynthesis.

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4. Importance of Diffusion in Living Organisms:

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Process Substance From to Gas exchange in lungs Oxygen Alveoli Blood

Gas exchange in leaves Carbon dioxide Air Leaf cells

Waste removal Urea Liver cells Blood (to kidneys)

Digestion Glucose Intestines Bloodstream

Diffusion allows cells to obtain essential substances and remove waste products efficiently.

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5. Factors that Influence the Rate of Diffusion:

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Factor                                       Effect

Surface Area                      A larger surface area increases the rate of diffusion. E.g., microvilli in intestines.

Temperature                      Higher temperatures increase kinetic energy, leading to faster diffusion.

Concentration Gradient    A steeper gradient increases the rate.

Distance                 A shorter distance allows faster diffusion. E.g., thin alveolar walls speed up gas exchange.

 

Experiment Idea


Using potassium permanganate crystals in water to observe diffusion rate at different temperatures.

 Osmosis

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Core Content

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1. Role of Water as a Solvent in Organisms:

  • Water dissolves many substances and acts as a medium for transport, digestion, and excretion.

Examples:

  • Digestion: Enzymes dissolve in water to break down food.

  • Excretion: Urea is dissolved in water and excreted in urine.

  • Transport: Blood plasma carries nutrients and hormones dissolved in water.

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 Definition of Osmosis and Movement in Cells

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  • Osmosis is the diffusion of water molecules from a region of higher water potential (more dilute solution) to a region of lower water potential (more concentrated solution) through a partially permeable membrane.

  • Water moves into and out of cells by osmosis through the cell membrane.

4. Investigating Osmosis (Core Experiment):

  • Use dialysis tubing (acts like a cell membrane).

  • Fill with sugar solution and place in water.

  • Water enters tubing by osmosis, causing it to swell.

5. Effects on Plant Tissues (Core):

Solution Type Effect on Plant Cell Observation

Hypotonic (less concentrated than cell sap)Cell becomes turgid Swollen, firm

Isotonic (same concentration)No net movement Normal

Hypertonic (more concentrated than cell sap)Cell becomes flaccid or plasmolyzed Cell membrane pulls away from wall

Experiment: Place potato slices in salt solutions of different concentrations and observe mass change.

6. Support in Plants:

  • Plants are supported by turgor pressure: the pressure of water inside the vacuole pressing against the cell wall, keeping the plant upright.

Supplement Content

7. Full Definition of Osmosis:

  • Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.

8. Plant Cell Terms:

Term    Meaning

Turgid     Full of water; firm due to turgor pressure.

Turgor Pressure   Pressure of cytoplasm and vacuole on cell wall.

Plasmolysis   Cytoplasm shrinks and pulls away from the cell wall in a hypertonic solution.

Flaccid    Loses water and becomes soft or limp.

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9. Importance of Osmosis in Organisms:

  • Osmosis helps in:

    • Uptake of water by root hair cells.

    • Maintaining cell shape.

    • Transport of nutrients and wastes.

    • Support in non-woody plants.

3.3 Active Transport

Core Content

1. Definition:

  • Active transport is the movement of particles across a membrane against a concentration gradient (from lower to higher concentration), using energy from respiration.

Supplement Content

2. Importance of Active Transport:

  • Allows cells to absorb substances even when the concentration is higher inside the cell than outside.

Examples:

  • Root hair cells absorb minerals (like nitrates) from the soil.

  • Intestinal cells absorb glucose from the small intestine even when the concentration in the blood is higher.

3. Role of Carrier Proteins:

  • Carrier proteins in the cell membrane bind to specific molecules and change shape to transport them across the membrane using energy from ATP.

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