Biology 5-6 A-Level Topic 7 of 14

Cells and Organelles

Structure and function of prokaryotic and eukaryotic cells, including the roles of organelles.

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Topic Summary

Cells are the basic structural and functional units of life, with prokaryotic cells lacking a true nucleus and eukaryotic cells having membrane-bound organelles that perform specific functions.

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Key Revision Points

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Prokaryotic cells are typically smaller than eukaryotic cells.
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Eukaryotic cells have a true nucleus and membrane-bound organelles.
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Mitochondria generate energy for the cell through cellular respiration.
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Chloroplasts are responsible for photosynthesis in plant cells.
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Lysosomes contain digestive enzymes that break down waste and foreign substances.
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Ribosomes are found throughout the cytoplasm and are involved in protein synthesis.

💡 Real-World Application

Understanding cell structure and function is crucial in medicine, as it helps doctors diagnose and treat diseases such as cancer and genetic disorders. For example, researchers have developed targeted therapies that exploit the unique features of cancer cells to selectively kill them.

⚠️ Common Exam Misconception

Myth: Cells are just tiny factories with no organization or structure.

Reality: Cells have a highly organized structure with specialized organelles performing specific functions, allowing for efficient energy production and waste management.

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Study Guide & Exam Tips

Simple Explanation

Think of cells like tiny cities. Just as cities have different districts (organelles) that work together to keep the city running, cells have different organelles that work together to keep the cell alive.

Step-by-Step Method

Step 1: Identify the type of cell (prokaryotic or eukaryotic).
Step 2: Determine the function of each organelle based on its structure and location.
Step 3: Understand how the organelles work together to maintain cellular homeostasis.

🎯 Examiner Tips

Focus on understanding the functions of different organelles and how they interact.
Pay attention to the differences between prokaryotic and eukaryotic cells.

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Key Terms & Definitions

Term	Definition
Prokaryote	A cell without a true nucleus or membrane-bound organelles.
Eukaryote	A cell with a true nucleus and membrane-bound organelles.
Organelle	A specialized structure within a eukaryotic cell that performs specific functions.
Mitochondria	The site of cellular respiration, responsible for generating energy.
Nucleus	The control center of the cell where DNA is stored.

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Detailed Subtopics

Prokaryotic cells, such as bacteria, have a single circular chromosome and lack membrane-bound organelles. Eukaryotic cells, including plants and animals, have linear chromosomes and are compartmentalized into different organelles. The cell membrane surrounds the cell and regulates what enters and leaves. The cytoplasm is the jelly-like substance inside the cell where metabolic processes take place.

Metabolic processes such as glycolysis, the citric acid cycle, and oxidative phosphorylation occur in the cytoplasm to generate energy for the cell. Protein synthesis takes place on ribosomes, while DNA replication and repair happen in the nucleus of eukaryotic cells.

Mitochondria are the site of cellular respiration, generating most of the cell's energy through the process of oxidative phosphorylation. Chloroplasts in plant cells perform photosynthesis to produce glucose and oxygen. Lysosomes contain digestive enzymes that break down and recycle cellular waste.

Passive transport, such as diffusion and osmosis, allows molecules to move across the cell membrane without energy input. Active transport, which requires energy, helps maintain proper ion balances and nutrient uptake. The Golgi apparatus packages proteins and lipids for secretion or storage.

Signaling pathways involve the binding of signaling molecules to receptors on the cell surface, triggering a cascade of chemical reactions that affect cellular behavior. This process is crucial for responding to environmental stimuli, regulating growth and development, and maintaining tissue homeostasis.

Mitosis is the process by which eukaryotic cells divide to produce two daughter cells with identical genetic material. Meiosis occurs in reproductive cells to create gametes with unique combinations of chromosomes. Binary fission is the method used by prokaryotic cells to reproduce.

Cells can adapt to changing environments through gene expression, protein modification, and cellular reorganization. This allows them to respond to stressors, such as temperature changes or nutrient availability, and maintain proper function.

Mutations in DNA can lead to genetic disorders, while environmental toxins and radiation can cause DNA damage and mutations. Cancer occurs when normal cellular processes are disrupted, leading to uncontrolled cell growth and division.

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Interactive Practice Questions

Quiz Progress: 0 / 10 answered

What is a characteristic of prokaryotic cells?

What is the function of mitochondria in a cell?

Which type of cells have membrane-bound organelles?

What is the function of lysosomes in a cell?

Which process occurs in the nucleus of eukaryotic cells?

What is the primary function of chloroplasts in plant cells?

Which organelle is responsible for packaging proteins and lipids for secretion or storage?

What is the primary function of ribosomes in a cell?

Which type of cells undergo binary fission for reproduction?

Q10

What is the primary function of the cell membrane?

Question 1 4 Marks

Compare and contrast prokaryotic and eukaryotic cells.

Answer Guide: Discuss the differences in structure and function between prokaryotic and eukaryotic cells.

Question 2 3 Marks

Describe the role of mitochondria in cellular respiration.

Answer Guide: Explain how mitochondria generate energy for the cell through oxidative phosphorylation.

Question 3 4 Marks

Outline the process of protein synthesis on ribosomes.

Answer Guide: Describe the steps involved in protein synthesis, including transcription and translation.

Question 4 5 Marks

Discuss the importance of cellular transport in maintaining proper ion balances and nutrient uptake.

Answer Guide: Explain how passive and active transport mechanisms help maintain cellular homeostasis.

Question 5 3 Marks

Describe the role of lysosomes in cellular waste management.

Answer Guide: Explain how lysosomes contain digestive enzymes that break down and recycle cellular waste.

Essay 1 20 Marks

Discuss the importance of understanding cell structure and function in medicine.

Examiner Marking Scheme Requirements:

Understanding cell structure and function is crucial for diagnosing and treating diseases
Researchers have developed targeted therapies that exploit the unique features of cancer cells

Essay 2 20 Marks

Compare and contrast the processes of mitosis and meiosis.

Examiner Marking Scheme Requirements:

Mitosis occurs in somatic cells to produce two daughter cells with identical genetic material
Meiosis occurs in reproductive cells to create gametes with unique combinations of chromosomes

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