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Cells and Life Processes - Organelles and Functions

Grade 7IB

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

🔑Concepts

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The Cell Theory states three major principles: all living things are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

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The Nucleus acts as the control center of the cell, containing genetic material in the form of DNADNA (Deoxyribonucleic acid).

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Mitochondria are the sites of aerobic cellular respiration, where glucose C6H12O6C_{6}H_{12}O_{6} is broken down to release energy in the form of ATPATP (Adenosine Triphosphate).

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Chloroplasts are organelles found in plant cells that contain chlorophyll to capture light energy for photosynthesis, producing C6H12O6C_{6}H_{12}O_{6} and O2O_{2}.

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The Cell Membrane is a semi-permeable barrier that regulates the transport of molecules such as H2OH_{2}O, CO2CO_{2}, and nutrients into and out of the cell.

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Ribosomes are the sites of protein synthesis, translating genetic code into polypeptide chains.

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Plant cells differ from animal cells by having a rigid Cell Wall made of cellulose, large central vacuoles, and chloroplasts.

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The levels of biological organization are: Cells →\rightarrow Tissues →\rightarrow Organs →\rightarrow Organ Systems →\rightarrow Organism.

📐Formulae

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

6CO2+6H2O+light energy→C6H12O6+6O26CO_{2} + 6H_{2}O + \text{light energy} \rightarrow C_{6}H_{12}O_{6} + 6O_{2}

C6H12O6+6O2→6CO2+6H2O+ATP (Energy)C_{6}H_{12}O_{6} + 6O_{2} \rightarrow 6CO_{2} + 6H_{2}O + \text{ATP (Energy)}

1 mm=1000 μm1 \text{ mm} = 1000 \text{ } \mu m

💡Examples

Problem 1:

A student views a plant cell under a microscope. The image of the cell measures 40 mm40 \text{ mm} in length. If the microscope magnification is set to 400×400\times, calculate the actual size of the cell in micrometers (μm\mu m).

Solution:

Actual Size =Image SizeMagnification=40 mm400=0.1 mm= \frac{\text{Image Size}}{\text{Magnification}} = \frac{40 \text{ mm}}{400} = 0.1 \text{ mm}. To convert to micrometers: 0.1 mm×1000=100 μm0.1 \text{ mm} \times 1000 = 100 \text{ } \mu m.

Explanation:

We use the magnification formula A=IMA = \frac{I}{M} and then apply the metric conversion factor where 1 mm=103 μm1 \text{ mm} = 10^{3} \text{ } \mu m.

Problem 2:

Identify which organelle would be most abundant in a muscle cell that requires a high amount of ATPATP for contraction.

Solution:

Mitochondria.

Explanation:

Mitochondria are responsible for cellular respiration, which converts C6H12O6C_{6}H_{12}O_{6} and O2O_{2} into ATPATP. Cells with high energy demands, like muscle cells, contain more mitochondria to sustain activity.

Problem 3:

Explain what happens to a plant cell if its large central vacuole loses too much H2OH_{2}O.

Solution:

The turgor pressure decreases, causing the cell membrane to pull away from the cell wall (plasmolysis), leading the plant to wilt.

Explanation:

The vacuole stores water and maintains internal pressure against the cell wall. Without sufficient H2OH_{2}O, the structural integrity provided by turgidity is lost.