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Cells and Life Processes - Levels of Biological Organization

Grade 7IB

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

🔑Concepts

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The Cell Theory states that all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells come from pre-existing cells.

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Biological organization follows a hierarchical structure: 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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Cells are specialized to perform specific functions. For example, red blood cells are specialized to transport O2O_2 throughout the body.

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Tissues are groups of similar cells working together to perform a specific task, such as muscle tissue or vascular tissue in plants (xylem for H2OH_2O transport).

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Organs consist of different types of tissues working together. The heart, for instance, contains muscle, nervous, and connective tissues.

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Organ systems are groups of organs that coordinate to perform complex functions, such as the Digestive System or the Respiratory System.

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The size of microscopic specimens is often measured in micrometers (μm\mu m), where 1 mm=1000 μm1\text{ mm} = 1000\text{ }\mu m.

📐Formulae

Magnification=Measured Size of ImageActual Size of Object\text{Magnification} = \frac{\text{Measured Size of Image}}{\text{Actual Size of Object}}

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

Total Magnification=Magnification of Eyepiece×Magnification of Objective Lens\text{Total Magnification} = \text{Magnification of Eyepiece} \times \text{Magnification of Objective Lens}

💡Examples

Problem 1:

A student views a plant cell under a microscope. The eyepiece lens has a magnification of 10×10\times and the objective lens has a magnification of 40×40\times. Calculate the total magnification.

Solution:

10×40=400×10 \times 40 = 400\times

Explanation:

To find the total magnification, you multiply the power of the eyepiece lens by the power of the objective lens used.

Problem 2:

If a diagram of a mitochondria has a length of 50 mm50\text{ mm} and the actual length of the mitochondria is 5 μm5\text{ }\mu m, calculate the magnification of the diagram.

Solution:

Magnification=50,000 μm5 μm=10,000×\text{Magnification} = \frac{50,000\text{ }\mu m}{5\text{ }\mu m} = 10,000\times

Explanation:

First, convert all units to the same scale. 50 mm=50,000 μm50\text{ mm} = 50,000\text{ }\mu m. Then, divide the image size by the actual size.

Problem 3:

Identify the level of biological organization for the following: 1. Heart, 2. Nerve Cell, 3. Digestive System, 4. Muscle Tissue.

Solution:

  1. Organ, 2. Cell, 3. Organ System, 4. Tissue

Explanation:

The nerve cell is the basic unit, muscle tissue is a collection of cells, the heart is an organ made of tissues, and the digestive system is a collection of organs.