The Fundamental Unit of Life

This chapter introduces the cell as the basic structural and functional unit of life. You will learn how Robert Hooke observed tiny compartments in a thin slice of cork in 1665 and called them cells, how Leeuwenhoek first saw free-living cells, how Robert Brown discovered the nucleus in 1831, and how Schleiden, Schwann and later Virchow developed the cell theory, which states that all living things are made of cells and new cells arise from pre-existing cells. You will compare unicellular and multicellular organisms, and prokaryotic cells, which lack a nuclear membrane, with eukaryotic cells. You will study the plasma membrane as a selectively permeable barrier, the movement of substances by diffusion and osmosis, and how cells behave in hypotonic, isotonic and hypertonic solutions, including plasmolysis. You will learn the structure and functions of the cell wall, nucleus, cytoplasm and cell organelles: endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, plastids and vacuoles, compare plant and animal cells, and study cell division by mitosis and meiosis.

Detailed Worksheet: The Fundamental Unit of Life Section A - Definitions (10 marks) 1. Who discovered the cell and how? What is the cell theory? (2 marks) 2. Distinguish between prokaryotic and eukaryotic cells on two points. (2 marks) 3. What is osmosis? How is it different from diffusion? (2 marks) 4. What is plasmolysis? When does it occur? (2 marks) 5. Why are mitochondria called the powerhouse of the cell and lysosomes the suicide bags of the cell? (2 marks) Section B - Calculations and Applications (15 marks) 6. A compound microscope has an eyepiece of magnification 10x and an objective of 40x. What is the total magnification? An onion peel cell appears 8 mm long in the image. What is its actual length in micrometres? (3 marks) 7. A bacterial cell divides by binary fission every 20 minutes. Starting with one cell, how many cells will there be after 2 hours? (3 marks) 8. In an osmosis experiment, a potato cube of mass 20 g was placed in each of three solutions for an hour. Its mass became 22 g in distilled water, 20 g in solution X and 17 g in solution Y. Find the percentage change in mass in each case and identify each solution as hypotonic, isotonic or hypertonic. (3 marks) 9. A cell at the start of mitosis has 46 chromosomes. How many chromosomes will each daughter cell have after mitosis? How many will each cell have after meiosis? Why is this difference important? (3 marks) 10. A cube-shaped cell has a side of 2 micrometres and another has a side of 4 micrometres. Find the surface area to volume ratio of each. Which cell exchanges materials more efficiently? (3 marks) Section C - Diagrams (10 marks) 11. Draw a neat labelled diagram of a plant cell showing the cell wall, plasma membrane, nucleus, chloroplast, mitochondria, vacuole, endoplasmic reticulum and Golgi apparatus. (4 marks) 12. Draw a labelled diagram of an animal cell and mark lysosomes, centrosome and mitochondria. (3 marks) 13. Draw diagrams to show what happens to an animal cell (red blood cell) placed in hypotonic, isotonic and hypertonic solutions. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Compare plant and animal cells on five points. Explain why plant cells can withstand greater changes in the surrounding medium than animal cells. (5 marks) 15. Describe the structure and functions of the endoplasmic reticulum and the Golgi apparatus. How do they work together in the formation and transport of proteins? (5 marks) 16. What would happen if (i) the plasma membrane ruptures (ii) there were no Golgi apparatus (iii) a plant cell had no plastids (iv) lysosomes burst inside a cell (v) a cell had no nucleus? Explain each. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw diagrams neatly in pencil and label all parts.