What is the simplest collection of matter that can live?
A cell.
From what do all cells descend?
Earlier cells.
What is the ratio of an image’s size to an object’s real size called?
Magnification.
What does resolution describe in microscopy?
Image clarity or the minimum distance at which two points remain distinguishable.
What kind of light do light microscopes use?
Visible light.
How do scanning electron microscopes depict specimen surfaces?
With a three-dimensional appearance.
Which domains contain organisms with prokaryotic cells?
Bacteria and Archaea.
Which groups have eukaryotic cells?
Protists, fungi, animals, and plants.
What four structures are present in all cells?
A plasma membrane, cytosol, chromosomes, and ribosomes.
Where is DNA located in a prokaryotic cell?
In a nucleoid.
What distinguishes eukaryotic cells from prokaryotic cells in DNA enclosure and organelles?
Eukaryotic cells enclose DNA in a nuclear envelope and contain membrane-bound organelles.
What regulates molecular entry into and exit from the nucleus?
Nuclear envelope pores.
What do DNA and proteins form in the nucleus?
Chromatin.
What does chromatin condense to form?
Discrete chromosomes.
What are ribosomes made of?
Ribosomal RNA and protein.
What do ribosomes synthesize?
Proteins.
Where do free ribosomes synthesize proteins?
In the cytosol.
Which structures comprise the endomembrane system?
The nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and plasma membrane.
What is the endoplasmic reticulum?
An extensive membrane network of tubules and sacs called cisternae.
How does smooth ER differ from rough ER?
Smooth ER lacks ribosomes, while rough ER bears ribosomes.
Where does the Golgi apparatus receive ER products?
At its cis face.
What is a lysosome?
A membranous sac of hydrolytic enzymes.
What cellular process occurs in mitochondria and generates ATP?
Cellular respiration generates ATP.
Which process occurs in chloroplasts of plants and algae?
Photosynthesis.
What three features do mitochondria and chloroplasts share?
They have double membranes, their own DNA, and proteins made by free ribosomes.
Which membrane system excludes mitochondria and chloroplasts?
The endomembrane system.
Which prokaryotes does endosymbiont theory propose gave rise to mitochondria?
Oxygen-using, non-photosynthetic prokaryotes.
What folds in a mitochondrion’s inner membrane increase its surface area?
Cristae.
What is the fluid-filled compartment inside a chloroplast’s inner membrane called?
The stroma.
What is the cytoskeleton?
A network of fibers throughout the cytoplasm that organizes cell structures and activities and anchors many organelles.
How does the cytoskeleton contribute to cell movement and shape changes?
It interacts with motor proteins and can be rapidly dismantled and reassembled.
How do microtubule, intermediate filament, and microfilament diameters compare?
Microtubules are thickest, intermediate filaments are intermediate, and microfilaments are thinnest.
What are microtubules made of, and how are they assembled?
They are hollow tubulin rods assembled from 13 protofilaments.
How do cilia and flagella differ in length and movement?
Cilia are short and beat with power and recovery strokes; flagella are longer and propel cells with undulating waves.
What constrains microtubule sliding to bend eukaryotic cilia and flagella?
Protein cross-links constrain dynein-driven sliding.
What three functions do plant cell walls perform?
They protect cells, maintain their shape, and prevent excessive water uptake.
What materials make up plant cell walls?
Cellulose fibers are embedded in polysaccharides and proteins such as pectin and lignin.
What is the extracellular matrix?
A network of proteoglycans containing glycoproteins such as collagen and fibronectin that bind integrins and support, adhere, enable movement, and regulate cells.
What distinguishes tight junctions, desmosomes, and gap junctions?
Tight junctions prevent extracellular-fluid leakage, desmosomes fasten cells into strong sheets, and gap junctions form cytoplasmic channels.
What is the typical diameter range of most cells?
1 to 100 μm.
Why can electron microscopes not examine live cells?
Specimen preparation kills the cells.
What barrier controls exchange between a cell and its surroundings?
The plasma membrane selectively permits exchange of oxygen, nutrients, and waste.
What constrains cell size?
The need to contain enough DNA and organelles while maintaining effective transport and exchange with extracellular fluid.
How does surface area change when cell dimensions increase by a factor of ?
It increases by a factor of .
What does the nuclear lamina help maintain?
The shape of the nucleus.
Where is ribosomal RNA synthesized?
In the nucleolus.
How do secretory proteins leave the rough ER?
Packaged inside transport vesicles.
What happens to engulfed material during phagocytosis?
The food vacuole fuses with a lysosome for digestion.
What do contractile vacuoles do in many freshwater protists?
They pump excess water out of cells.
What do peroxisomal enzymes produce when transferring hydrogen to oxygen?
Hydrogen peroxide.
What is the microtubule-organizing center in animal cells?
The centrosome near the nucleus, which contains a pair of centrioles.
What is the composition and diameter of microfilaments?
They are solid actin rods about 7 nm in diameter.
How does the plant primary cell wall differ from the secondary wall?
The primary wall is relatively thin and flexible; the secondary wall lies between it and the plasma membrane.
What attaches adjacent plant cells at their primary walls?
The pectin-rich middle lamella.
What passes between adjacent plant cells through plasmodesmata?
Water, small solutes, and sometimes proteins and RNA.
Which cellular structures coordinate a macrophage's destruction of bacteria?
The cytoskeleton, lysosomes, and plasma membrane.
Answer 26 questions on A Tour of the Cell.
1. An image is enlarged, but two nearby points still appear as one. Which interpretation best distinguishes magnification from resolution?
2. What happens to chromatin as a cell forms discrete chromosomes?
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