Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 3
3.1
1. A cell is the smallest unit of life.
2. Hooke was the first to see and name cells. Leeuwenhoek improved microscopes and
described a wide range of previously invisible organisms.
3. The main components of cell theory are that all life is made of cells, that cells are the
fundamental unit of life, and that all cells come from preexisting cells
4. A conventional light microscope focuses visible light on an object. A confocal microscope uses
laser light. Transmission and scanning electron microscope use beams of electrons to visualize
slices of objects or their surfaces. A scanning probe microscope uses a moving probe to reveal
the surface of an object.
5. All cells have DNA, proteins, RNA, ribosomes, a watery cytoplasm, and a cell membrane.
6. Adaptations that increase the surface area to volume ratio include elongated or flattened cell
shapes. An efficient transportation system, a water-filled vacuole, and improved efficiency help
cells sidestep surface area limitations.
3.2
1. The hydrophilic heads naturally make contact with water while the hydrophobic tails naturally
avoid water. When many phospholipids join, the hydrophilic heads and hydrophobic tails align,
forming a bilayer.
2. The main components of the cell membrane are phospholipids and proteins. Sterols are
important components and carbohydrates attached to membrane proteins are important as “name
tags” that help the body recognize its own cells.
3. Membrane proteins have the following functions:
- transport proteins move substances into and out of cells;
- enzymes facilitate chemical reactions;
- recognition proteins on cell surfaces allow the body to recognize its own cells;
- adhesion proteins allow cells to stick together;
- receptor proteins bind molecules to the outside of the cell and trigger chemical reactions
inside the cell
4. Cells detect external signals through the reactions of receptor proteins. In signal transduction,
the signal molecule does not enter the cell, but instead begins a chemical reaction within the cell
that causes a change of function.
3.3
1. Prokaryotic cells lack a nucleus and other membrane-bounded organelles, have cell walls
made of peptidoglycan, and are typically much smaller than eukaryotic cells.
2. Bacteria and archaea are small cells that lack nuclei and membrane-bounded organelles. The
two groups differ in the composition of the cell wall and the lipids in the cell membrane.
3. Organelles contribute to efficiency in eukaryotic cells because they concentrate the
biochemicals needed for chemical reactions so that the reactions proceed more rapidly, leading
to efficiency. Also, because of organelles, a eukaryotic cell can get along with high concentrations
of biochemical only in certain areas. The biochemicals do not have to be in high concentrations
throughout the cell.
3.4
1. The nucleus, ribosomes, smooth ER, Golgi apparatus, and vesicles are organelles involved in
the production of milk.
2. The nucleus contains DNA (the molecule that contains the instructions for making proteins)
and the nucleolus (where ribosomes are assembled). mRNA molecules also are present in the
nucleus, where they gather information and exit to the cytoplasm through nuclear pores.
3. Lysosomes, vacuoles, and peroxisomes are the cell’s recycling centers.
4. Chloroplasts are plastids that carry out photosynthesis. Other plastids store pigments or food,
or they help a plant to detect gravity.
5. Mitochondria house the reactions that extract chemical energy from nutrient molecules.
6. DNA occurs in the nucleus, chloroplasts, and mitochondria.
3.5
1. The cytoskeleton provides a structural framework for the cell, is a transportation system within
the cell, allows the cell to move, and connects cells together.
2. The major components of the cytoskeleton are microtubules, microfilaments, and intermediate
filaments.
3. In eukaryotes, cilia and flagella are similar in their internal structure (the 9+2 arrangement of
microtubules). Both structures move, but they differ in their length and in how they move. Cilia
are short and move in wave-like motions. Flagella are much longer and move with a whiplike
motion.
3.6
1. Cell walls provide rigidity, prevent a cell from bursting if it takes on too much water, and allow
interactions with other cells to determine how a cell of a complex plant becomes specialized.
2. Plant cell walls are made mostly of cellulose but also contain hemicellulose and pectin.
3. Plasmodesmata are tunnels that connect adjacent cell walls.
4. Tight junctions, gap junctions, and anchoring junctions link cells in animals.