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Plant Biology - Cells

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    Study Guide Plant Biology – Cells 1. Cell Theory 1.1 What Is Cell Theory? Cell theory is a basic idea in biology that explains what cells are and why they are important. The modern cell theory says: • All living organisms are made of one or more cells . • New cells come from pre - existing cells . This means life has continued without a break from the first cells that appeared on Earth more than 3.5 billion years ago . • Hereditary information (DNA) is passed from a parent cell to its daughter cells. • All the basic chemical reactions of life happen inside cells. In simple words: cells are the building blocks of life , and everything living depends on them. 1.2 Methods of Studying Cells Microscopes The study of cells is called cytology . Our knowledge of cells has grown because microscopes have improved over time. Light Microscopes • Invented in the 1500s . • Can magnify objects 100× to 1000× . • Their maximum resolving power is about 0.2 μ m (micrometer) . • Resolution depends on the wavelength of visible light , which limits how clear the image can be. Resolution means the ability to see two close objects as separate.

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    Study Guide 1.3 Electron Microscopes • Use beams of electrons , which have much shorter wavelengths than light. • Can magnify over 100,000× . • Have a resolution of 2 – 0.4 nm (nanometer) . There are two main types: • Transmission Electron Microscope (TEM): • Electrons pass through thin sections of a specimen to show internal details. • Scanning Electron Microscope (SEM): • Electrons bounce off the surface to create a 3D - like image. 1.4 Laboratory Techniques • In light microscopy , special dyes (stains) are used to color different cell parts. • For electron microscopy , specimens must be: o Cut into very thin sections o Observed in a vacuum • Living cells cannot be seen with electron microscopes. This creates a challenge: scientists must ask whether the image truly represents the living cell or if preparation changed its appearance. Today, cell knowledge comes from: 1. Biochemical studies , and 2. High - magnification microscopy 1.5 Cell Size • Plant cells range from about 7 μ m (dividing cells at root and shoot tips) to very long fiber cells . • Most plant and animal cells are 10 – 100 μ m in size.

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    Study Guide • The human eye can only resolve objects larger than 100 μ m , so cells cannot be seen without a microscope . Magnification makes objects look bigger, but resolution makes them clearer. 1.6 Limits to Cell Growth Cells are surrounded by: • A cell wall (in plants) • A plasma membrane that encloses the cytoplasm and nucleus As a cell grows: • Volume increases faster than surface area • Materials must move in and out through the cell surface Eventually, the surface area cannot support the cell’s needs. This limits how large a cell can grow. The solution? Many small cells instead of one large cell This led to multicellular organisms , which have advantages: • Cells can specialize for different functions • Complex structures can form • The nucleus controls fewer activities per cell , making regulation more efficient 1.7 Two Kinds of Cells: Prokaryotes and Eukaryotes All cells contain: • A plasma membrane made of a lipid bilayer with proteins • DNA , which stores genetic information 1.8 The Fundamental Difference Living organisms are divided into two major groups based on cell structure: • Prokaryotes (bacteria):

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    Study Guide o No nucleus o No membrane - bound organelles • Eukaryotes (plants, animals, fungi, protists): o Have a true nucleus o Have membrane - bound organelles 1.9 Origin of Eukaryotic Cells Scientists believe that the earliest life forms were prokaryotes . Over billions of years, these organisms adapted to Earth’s changing conditions. Modern organisms still carry genetic evidence of these ancient adaptations.

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