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Biology: Cells, Organization, and Classification - Characteristics of Living Organisms and Spontaneous Generation

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Characteristics of Living Organisms (MRS GREN): All living things exhibit seven vital functions: Movement, Respiration (releasing energy from food), Sensitivity (responding to stimuli), Growth, Reproduction, Excretion (removal of metabolic waste like CO2CO_2 and urea), and Nutrition.

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Respiration: A chemical process in cells to break down glucose (C6H12O6C_6H_{12}O_6) and release energy. The aerobic respiration equation is: C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}.

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Spontaneous Generation: An obsolete theory suggesting that living organisms could arise from non-living matter (e.g., mice from dirty hay or maggots from decaying meat).

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Disproving Spontaneous Generation: Francesco Redi (1668) showed that maggots come from flies, not meat. Louis Pasteur (1859) finally disproved it using swan-neck flasks, showing that microorganisms in the air caused growth, leading to the theory of Biogenesis (life only comes from pre-existing life).

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Levels of Organization: Biological systems are organized hierarchically: Organelles→Cells→Tissues→Organs→Organ Systems→Organism\text{Organelles} \rightarrow \text{Cells} \rightarrow \text{Tissues} \rightarrow \text{Organs} \rightarrow \text{Organ Systems} \rightarrow \text{Organism}.

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Cell Theory: 1. All living organisms are composed of one or more cells. 2. The cell is the basic unit of structure and organization. 3. Cells arise from pre-existing cells.

📐Formulae

C6H12O6+6O2→6CO2+6H2O+Energy (ATP)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}

Magnification=Image SizeActual Size\text{Magnification} = \frac{\text{Image Size}}{\text{Actual Size}}

Actual Size=Image SizeMagnification\text{Actual Size} = \frac{\text{Image Size}}{\text{Magnification}}

💡Examples

Problem 1:

A student views a plant cell under a microscope. The image of the cell measures 50 mm50\text{ mm} in length. If the actual size of the cell is 0.05 mm0.05\text{ mm}, calculate the magnification used.

Solution:

Magnification=50 mm0.05 mm=1000×\text{Magnification} = \frac{50\text{ mm}}{0.05\text{ mm}} = 1000\times

Explanation:

Using the formula M=IAM = \frac{I}{A}, we divide the image size (50 mm50\text{ mm}) by the actual size (0.05 mm0.05\text{ mm}) to find that the microscope magnified the object 10001000 times.

Problem 2:

In Louis Pasteur's experiment, why did the broth in the swan-neck flask remain clear even though it was open to the air?

Solution:

The 'S' shape of the neck trapped dust and microorganisms in the curve, preventing them from reaching the broth.

Explanation:

Because the microorganisms were trapped by gravity in the neck, the broth remained sterile. This proved that life (microbes) did not spontaneously generate from the broth itself, but came from particles in the air.

Problem 3:

Identify the level of organization for the following: Heart, Cardiac Muscle, Human, and Heart Cell.

Solution:

Heart Cell (Cell)→Cardiac Muscle (Tissue)→Heart (Organ)→Human (Organism)\text{Heart Cell (Cell)} \rightarrow \text{Cardiac Muscle (Tissue)} \rightarrow \text{Heart (Organ)} \rightarrow \text{Human (Organism)}

Explanation:

Cells of the same type form tissues; different tissues work together to form an organ; and the whole living entity is the organism.