Concept 4.3 Eukaryotic Cells Have A Nucleus and Other Membrane Bound
Plant and algae cells contain plastids that can differentiate into organelles—some are used for
A chloroplast contains chlorophyll and is the site of photosynthesis.
Photosynthesis converts light energy into chemical energy.
A chloroplast is enclosed within two membranes, with a series of internal membranes called
A granum is a stack of thylakoids.
Light energy is converted to chemical energy on the thylakoid membranes.
Carbohydrate synthesis occurs in the stroma—the aqueous fluid surrounding the thylakoids.
Other organelles perform specialized functions.
Peroxisomes collect and break down toxic by-products of metabolism, such as H2O2, using
Glyoxysomes, found only in plants, are where lipids are converted to carbohydrates for growth.
Vacuoles occur in some eukaryotes, but mainly in plants and fungi. Functions of vacuoles
o Storage of waste products and toxic compounds; some may deter herbivores
o Structure for plant cells—water enters the vacuole by osmosis, creating turgor pressure
o Reproduction—vacuoles in flowers and fruits contain pigments whose colors attract
pollinators and aid seed dispersal
o Catabolism—digestive enzymes in seeds’ vacuoles hydrolyze stored food for early
Contractile vacuoles in freshwater protists get rid of excess water entering the cell due to solute
The contractile vacuole enlarges as water enters, then quickly contracts to force water out
through special pores.
Concept 4.4 The Cytoskeleton Provides Strength and Movement
o Supports and maintains cell shape
o Holds organelles in position
o Moves organelles
o Is involved in cytoplasmic streaming
o Interacts with extracellular structures to anchor the cell in place
The cytoskeleton has three components with very different functions:
o Intermediate filaments o Microtubules:
o Help a cell or parts of a cell to move
o Determine cell shape
o Microfilaments are polymers made from the protein (monomer) actin
o Microfilaments are dynamic and often change organization and length in a cell.
o Actin polymer (filament) ⇌ Actin monomers
o Dynamic instability allows quick assembly or breakdown ofthe cytoskeleton.
o In muscle cells, actin filaments are associated with the “motor protein” myosin; their