4.15 Chloroplasts convert solar energy to chemical energy ENERGY-CONVERTING ORGANELLES 4.15 Chloroplasts convert solar energy to chemical energy Chloroplasts are found in plants and some protists Chloroplasts convert solar energy to chemical energy in sugars Chloroplast Stroma Inner and outer membranes Granum Intermembrane space Figure 4.15

4.16 Mitochondria harvest chemical energy from food Mitochondria carry out cellular respiration This process uses the chemical energy in food to make ATP for cellular work

MITOCHONDRION Outer membrane Intermembrane space Inner membrane Cristae Matrix Figure 4.16

THE CYTOSKELETON AND RELATED STRUCTURES 4.17 The cell’s internal skeleton helps organize its structure and activities A network of protein fibers makes up the cytoskeleton Figure 4.17A

Microfilaments of actin enable cells to change shape and move Intermediate filaments reinforce the cell and anchor certain organelles Microtubules give the cell rigidity provide anchors for organelles act as tracks for organelle movement

INTERMEDIATE FILAMENT Tubulin subunit Actin subunit Fibrous subunits 25 nm 7 nm 10 nm MICROFILAMENT INTERMEDIATE FILAMENT MICROTUBULE Figure 4.17B

4.18 Cilia and flagella move when microtubules bend Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells A cilia or flagellum is composed of a core of microtubules wrapped in an extension of the plasma membrane

Electron micrograph of sections: FLAGELLUM Electron micrograph of sections: Outer microtubule doublet Plasma membrane Flagellum Central microtubules Outer microtubule doublet Plasma membrane Basal body Basal body (structurally identical to centriole) Figure 4.18A

Clusters of microtubules drive the whipping action of these organelles Microtubule doublet Sliding force Dynein arm Figure 4.18B

4.19 Cell surfaces protect, support, and join cells EUKARYOTIC CELL SURFACES AND JUNCTIONS 4.19 Cell surfaces protect, support, and join cells Cells interact with their environments and each other via their surfaces Plant cells are supported by rigid cell walls made largely of cellulose They connect by plasmodesmata, channels that allow them to share water, food, and chemical messages

Walls of two adjacent plant cells Vacuole PLASMODESMATA Layers of one plant cell wall Cytoplasm Plasma membrane Figure 4.19A

Animal cells are embedded in an extracellular matrix It is a sticky layer of glycoproteins It binds cells together in tissues It can also have protective and supportive functions

Tight junctions can bind cells together into leakproof sheets Anchoring junctions link animal cells Communicating junctions allow substances to flow from cell to cell TIGHT JUNCTION ANCHORING JUNCTION COMMUNICATING JUNCTION Plasma membranes of adjacent cells Extracellular matrix Figure 4.19B

4.20 Eukaryotic organelles comprise four functional categories

Table 4.20 (continued)