Cell Structure, Function, and Energy Transformations: Study Guide for Exam 2

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

Cells are the basic units of life and can be classified as either prokaryotic or eukaryotic based on their structural features.

• Prokaryotic Cells: Lack a true nucleus and membrane-bound organelles. Their DNA is located in a region called the nucleoid. Examples include Bacteria and Archaea.

• Eukaryotic Cells: Possess a true nucleus enclosed by a nuclear envelope and contain membrane-bound organelles. Examples include Animals, Plants, Fungi, and Protists.

Feature	Prokaryotic	Eukaryotic
Nucleus	No	Yes
Membrane-bound organelles	No	Yes
Size	Smaller (1-10 μm)	Larger (10-100 μm)
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Basic Structure of Animal and Plant Cells

Both animal and plant cells are eukaryotic but have some distinct structures.

• Animal Cells: Lack a cell wall and chloroplasts; contain centrioles.

• Plant Cells: Have a cell wall, chloroplasts, and a large central vacuole.

Functions of Major Cell Structures

• Cell Membrane: Semi-permeable barrier that regulates the movement of substances in and out of the cell.

• Cell Wall: Rigid outer layer found in plants, fungi, and some prokaryotes; provides structural support and protection.

• Cytoskeleton: Network of protein filaments that maintain cell shape, enable movement, and organize organelles.

• Nucleus: Contains the cell's genetic material (DNA) and controls cellular activities.

• Ribosomes: Sites of protein synthesis; found free in cytoplasm or attached to rough ER.

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes and processes proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.

• Mitochondria: Site of cellular respiration; produces ATP, the cell's energy currency.

• Chloroplasts: Site of photosynthesis in plant cells; contain chlorophyll.

• Cilia: Short, hair-like structures for movement or moving substances along cell surfaces.

• Flagella: Long, whip-like structures used for cell movement.

Cellular Energy and Enzymes

ATP: The Energy Currency of the Cell

Adenosine triphosphate (ATP) is the primary energy carrier in cells. It stores energy in its high-energy phosphate bonds and releases it to power cellular processes such as muscle contraction, active transport, and biosynthesis.

Enzymes and Their Function

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required.

• Activation Energy: The minimum energy needed to start a chemical reaction.

• Active Site: The region on the enzyme where the substrate binds and the reaction occurs.

• Substrate: The specific reactant that an enzyme acts upon.

• Inhibitors: Molecules that decrease enzyme activity by blocking the active site or altering enzyme shape.

Membrane Transport

Types of Membrane Transport

• Passive Transport: Movement of substances across the membrane without energy input.

  • Diffusion: Movement of molecules from high to low concentration.

  • Osmosis: Diffusion of water across a selectively permeable membrane.

  • Facilitated Diffusion: Movement of molecules via transport proteins.

• Active Transport: Movement of substances against their concentration gradient, requiring energy (usually ATP).

Concentration Gradient: The difference in concentration of a substance across a space or membrane.

Effects of Tonicity on Animal Cells

Solution Type	Effect on Animal Cell
Isotonic	No net water movement; cell remains normal
Hypotonic	Water enters cell; cell may swell and burst (lysis)
Hypertonic	Water leaves cell; cell shrinks (crenation)

Bulk Transport: Endocytosis and Exocytosis

• Endocytosis: Process by which cells take in large molecules or particles by engulfing them in vesicles.

• Exocytosis: Process by which cells expel materials in vesicles that fuse with the plasma membrane.

Energy Flow in Living Systems

Producers vs. Consumers

• Producers (Autotrophs): Organisms that make their own food, usually through photosynthesis (e.g., plants, algae).

• Consumers (Heterotrophs): Organisms that obtain energy by eating other organisms (e.g., animals, fungi).

Relationship Between Cellular Respiration and Photosynthesis

Cellular respiration and photosynthesis are complementary processes. Photosynthesis stores energy in glucose molecules, while cellular respiration releases that energy for cellular use.

Cellular Respiration

Overall Formula

The process of cellular respiration converts glucose and oxygen into carbon dioxide, water, and ATP.

$\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP}$

Three Stages of Cellular Respiration

Stage	Location	Reactants	Products
Glycolysis	Cytoplasm	Glucose	Pyruvate, ATP, NADH
Citric Acid Cycle (Krebs Cycle)	Mitochondrial matrix	Acetyl-CoA	CO2, ATP, NADH, FADH2
Electron Transport Chain	Inner mitochondrial membrane	NADH, FADH2, O2	ATP, H2O

Fermentation

Fermentation is an anaerobic process that allows cells to produce ATP without oxygen, occurring after glycolysis. It regenerates NAD+ so glycolysis can continue.

Photosynthesis

Basic Structure of the Chloroplast

• Outer and Inner Membranes: Enclose the organelle.

• Thylakoids: Flattened sacs where light reactions occur; stacked into grana.

• Stroma: Fluid-filled space where the Calvin cycle takes place.

Overall Formula for Photosynthesis

$\mathrm{6CO_2 + 6H_2O + light\ energy \rightarrow C_6H_{12}O_6 + 6O_2}$

Two Stages of Photosynthesis

Stage	Location	Reactants	Products
Light Reactions	Thylakoid membranes	H2O, light, NADP+, ADP	O2, ATP, NADPH
Calvin Cycle	Stroma	CO2, ATP, NADPH	Glucose, NADP+, ADP

Example: In plants, the light reactions capture solar energy and produce ATP and NADPH, which are then used in the Calvin cycle to synthesize glucose from carbon dioxide.

Additional info: Some explanations and table entries were expanded for clarity and completeness based on standard biology curriculum.