Objectives 1-3
1. The cell theory is a generalization that all living things are composed of cells. However, viruses are based on a plan simpler than the cell.
The four parts of the cell theory are:
1) All living things are composed of cells and cell products.
2) New cells are formed only by division of preexisting cells.
3) All cells are basically similar in chemical makeup and in metabolic activities.
4) The activity of an organism is due to the collective activities and interactions of all of its cells.

2. Not all of the characteristics of living things apply to every cell. Functions that are essential include metabolism, responsiveness, communication, organization, and homeostasis.

3. Cell size is restricted because small cells can be more efficient. Cells get all of their nutrients and dispose of their wastes across their outer covering, the cell membrane. As you can see, as the volume increases, the surface area does not increase as rapidly.  Thus, as size increases, the surface area eventually becomes insufficient to meet the needs of the contents of the cell.

Cube 1: Surface area: 1 x 1 x 6=6sq.mm.
             Volume:1 x 1 x 1=1cu.mm
             SA/V: 6/1

Cube 2:  Surface Area: 2 x 2 x 6=24sq.mm
               Volume: 2 x 2 x 2=8cu.mm
                SA/V: 24/8 =3/1

Cube 3: Surface Area: 3 x 3 x 6=54sq.mm
            Volume: 3 x 3 x 3=27cu.mm
            SA/V:  54/27 = 2/1

4. Problems of large cells: getting sufficient amounts of oxygen and nutrients for all parts of the cell, getting rid of wastes, control of nucleus over cytoplasm. In small cells, the surface area to volume ration is greater, which means that small cells have a greater surface area in relationship to their interior than do large cells. This means that there is more surface area on small cells for exchange of nutrients and wastes with the cell’s environment.

5. See pages 416-419 in your text for diagrams of various types of animal cells. Cells are often specialized to carry out a particular function and the structure of the cell reflects the function. For example, note the cells that make up the adipose tissue are filled with fat droplets. The cytoplasm (light pink in the drawing) along with the organelles in the cytoplasm(such as the nucleus) are pushed to the periphery of the cell. The function of these cells is to store fat. None of the cells illustrated on these pages are visible without a microscope.

Objective 4
The function of the nucleus is to control the activities of the cell; it contains the chromosomes which carry the hereditary information of an organism.
The cytoplasm contains the cell structures which carry out all of the activities of the cell.
The cellular material within the nucleus is called the nucleoplasm and the material outside the nucleus is called the cytoplasm.

                                            CELL STRUCTURES AND ORGANELLES
The text has an excellent discussion of eukaryotic cells and the organelles of these cells. Study the diagrams of typical plant and animal cells on pages 56 and and 57.
1. P. The cell wall is a thick box-like structure composed mainly of the carbohydrate cellulose and located just outside the cell membrane. Its function is to support, protect, and give a characteristic shape to the cell. It is obviously not a membranous structure.

2. B. The cell membrane is a thin layer, composed of phospholipids and protein, which makes up the outer boundary of all cells. Its function is to regulate the movement of materials into and out of the cell.

3. B. The nucleus is a spherical structure separated from the rest of the cell by a membrane; its function is to control cellular activities.
    a. The chromatin is made up of DNA and protein arranged as long threadlike structures. They contain the information which          controls heredity and the activity of the cell. During cell division the chromatin condenses into chromosomes.
    b.  The nucleolus, composed of both nucleic acid and protein, gives rise to ribosomes.
    c. The nuclear envelope is a double membrane which serves to separate the nucleus from the rest of the cell and to regulate          movement of materials into and out of the nucleus.

4. B. The endoplasmic reticulum is a complex of membranes which runs throughout the entire cell and is involved in transport of materials within the cell. Enzymes associated with it are involved in various metabolic activities.
    a. Smooth ER does not have ribosomes associated with it. Enzymes on its surface are responsible for producing certain          lipids and in some lipid metabolism.
    b. Rough ER looks granular because it has ribosomes associated with it. Rough ER makes protein for export from the cell (for example, digestive enzymes which are made in the pancreas and exported to the small intestine).

5. B. Ribosomes look like granules in the cytoplasm. They are made up of RNA and some protein and are not surrounded by a membrane. They are the site of protein synthesis in the cell.

6. B. The Golgi Apparatus looks like layers of sacs or bags within a cell. Material produced in the ER is passed to the Golgi complex where it may be modified and prepared for export from the cell or for a special purpose within the cell. This sealed packet may then either remain within the cell or move to the edge of the cell and release its contents to the exterior of the cell.

7. B. (probably). Lysosomes are membrane enclosed sacs produced by the Golgi complex which contain hydrolytic enzymes. Their function is to break down unneeded macromolecules. They are sometimes called the cell’s garbage disposal system.

8. P. Plastids are membrane bound organelles which also may have a second membrane folded many times within the structure. Their function is in synthesis or storage of food for the plant cell.
    a. Leukoplasts serve primarily for storage of starch.
    b. Chloroplasts have many folded membranes within them which contain the pigment chlorophyll and the enzymes involved in photosynthesis.

9. B. Mitochondria are double membranous structures, with enzymes embedded in them that are responsible for energy release from glucose in the process of cellular respiration. They are sometimes called the powerhouse of the cell.

10. B. cytoskeleton Supporting structure composed of a network of fibers throughout the cytoplasm that maintain cell shape or change cell shape as well as anchor organelles within the cell or allow organelle movement. The cytoskeleton is composed of three types of protein fibers: microtubules, microfilaments, and microtubules.

11. A. Centrioles, made up of microtubules, are located near the nucleus and are involved in movement of the chromosomes during cell division.

12. B. Cilia and flagella, composed of microtubules in a specific arrangement, project from the outer surface of the cell. They are responsible for motility of the cell or for movement of materials past the cell.

13. B. Vacuoles are fluid filled bags, surrounded by a membrane. A large central vacuole occupies much of the interior of a plant cell and stores wastes and foods as well as playing a major role in maintaining the turgidity of the plant cell. Vacuoles are smaller in animal cells where they may play a role as a mini-digestive area or in storage or removal of excess water from a cell.

1. These membranes separate the structures from the rest of the cell or from the environment and yet allow interaction with the exterior of the structure or the cell and its environment.

2. Its enormous surface area provides an extensive site or "workbench" for enzymes and their activities; the space between the double membrane system provides an area for movement of materials as well as for storage.

3. Cells that manufacture lipids such as the cells of the ovary and testes that make steroid hormones have a large amount of smooth ER.  Muscle cells also have lots of smooth ER since smooth ER is also used for the storage of calcium ions which are needed for muscle contraction. Proteins that will be secreted by the cell are made on the rough ER. For example, cells that secrete digestive enzymes (protein molecules), such as pancreatic cells, contain a lot of rough ER.

4. Certain substances made in the ER are sealed and passed along to the Golgi apparatus where modifications may be made to prepare the substance for export from the cell or for special activity within the cell.

5. The lysosome

6. If the hydrolytic enzymes were free in the cell, they would digest the molecules which make up the cellular organelles. What biochemical process do you think hydrolytic enzymes foster?

7. Mitochondria

8. Chlorophyll. Its function is to capture light energy for photosynthesis.

9. Chloroplasts convert solar energy to chemical energy in the process of photosynthesis. Mitochondria convert energy stored in food to a form which is usable by cells (ATP) through the process of cellular respiration.

10. The hollow microtubules spread extensively throughout the cell are analogous to the skeleton in the body in providing the frame work which maintains the basic shape of the cell.

11. Slender protein threads spread throughout the cell form a web-like arrangement in which the cellular organelles are suspended.

12. Cilia are shorter than are flagella and there are generally many found on a cell while there are generally many found on a cell while there are generally few flagella on a cell.
    a) Cilia are found on many protozoans and in your body on cells which line passages such as the respiratory tract.
    b) Flagella are found on some protozoans and on sperm cells.
    Yes, you would expect to find mitochondria because they provide the energy for the movement of the cilia and flagella.

13. In plant cells, a large central vacuole provides storage for some materials, including wastes because plants lack a system for waste disposal. In animal cells, such as certain white blood cells and some protozoans, vacuoles function as a mini-digestion system or in the collection of excess water for disposal. Lysosomes provide the enzymes for digestion.

14. The cell membrane keeps the cell intact and separate from its environment; the nucleus controls cellular activities by determining the particular type of proteins that the cell makes, ribosomes provide the site for protein synthesis (You can think of proteins as the work horses of the cell. Enzymes, many hormones, carrier molecules, many neurotransmitter chemicals, etc. are protein molecules), and mitochondria provide the needed energy for cells.

15. Plant cells have a cell wall, chloroplasts, and a large central vacuole. None of these are found in animal cells. Animal cells have centrioles which are not found in plant cells.

16.  A cell can not survive long without a nucleus; mature red blood cells do not have nucleus and they survive for only 120 days or so. Ribosomes are needed to make essential protein. Cells can survive without endoplasmic reticulum or mitochondria, as do bacteria. Nevertheless, bacteria do have enzymes of cellular respiration, located on the cell membrane rather than in the mitochondria.

17. It would be unable to perform photosynthesis.

Objective 7
1. Protista, Fungi, Plantae, Animalia

2. There are no membrane-bound organelles found in bacteria. Thus, bacteria do not have ER, mitochondria, chloroplasts, golgi apparatus, or lysosomes.

3. There must be, since all higher, more complex organisms possess a nuclear membrane. it may be that in cells with more chromosomes (bacteria have only one), a membrane provides needed protective and functional separation of the chromosomes from the cytoplasm.

4. Since all higher organisms possess eukaryotic cells, the apparent answer is eukaryotic cell; however, prokaryotic cells are smaller and multiply more rapidly, and can grow almost anywhere, so that there may not be a great difference in total number.

5. Eukaryotic cells are considered to be more advanced.

6. Yes. It seems likely that chloroplasts and mitochondria were prokaryotic cells that became associated with what would become eukaryotic cells in the process of evolution. Both chloroplasts and mitochondria contain some of their own DNA separate from that found in the nucleus of the cell.

Objective 8
1. Bacteriophages are viruses that infect bacteria.

2. Viruses can only reproduce if they are inside a cell; they have no metabolic machinery of their own, and therefore, can not really be classified as living.

3. Review Unit 1, Objective 1, for this answer.

Objective 9
1. To regulate passage of materials into and out of the cell.

2. To receive information about the environment.

3. To recognize, communicate, adhere to and exchange material with other cells.

4. To protect the cell, help in movement of the cell, in secretion, and, in some cells, in transmitting impulses.

Objective 10
1. Lipids (phospholipids, glycolipids, and cholesterol) and proteins(and glycoproteins). The two major components are underlined.

2. The hydrophilic end of the molecule is directed toward the water while the hydrophobic end is directed away from the water.

3. The fluid mosaic model (see a diagram of this on page 80). The lipid bilayer is oriented with the hydrophobic ends of the two layers directed towards each other, while the hydrophilic ends are directed towards the exterior and the interior of the cell. This might be compared to a peanut butter sandwich, with the peanut butter representing the hydrophobic portion of the lipids. The globular proteins are embedded within the lipid layer and can move, like icebergs in a sea of lipids.

4. The hydrophobic and hydrophilic parts of the lipid provide the means to keep the cell contents isolated from, and yet able to interact with, the environment. They are able to interact with the environment because the hydrophilic ends are projecting out and the solvent both inside and outside the cell is water. Thus, materials in solution can make contact with the membrane.  Depending on the size of the particle and the protein carriers of the membrane, the particle may then be able to cross the membrane.

5. The glycoproteins serve the cell by recognizing and communicating with other cells.

6. Microvilli are small outpocketings of the cell membrane and increase the surface area of the membrane, thereby increasing the membrane available for material exchange with the environment.

Objectives 11 and  12
1. A selectively permeable membrane is one which allows some materials to cross it while preventing others from crossing it.

CHART

Iso- means the same as; same; same; no net movement; no effect on cell (this is the normal condition)

Hypo- means less than; less concentrated; more concentrated; net movement of water into cell; causes increase in size of cell and may cause death by bursting of the cell if there is no protective cell wall.

Hyper- means more than; more concentrated; less concentrated; net movement of water is out of cell; causes decrease in size of cell and may cause death by dehydration.

1. Osmosis is the diffusion of water across a selectively permeable membrane. (The movement of water into and out of cells is of such vital importance that it has been given a special name.)

2.  Plant cells have a cell wall whereas animal cells do not have a wall. As water enters an animal cell, eventually the pressure exerted on the cell membrane by the increase in water will cause the fragile membrane to break; the cell lyses.  In plant cells, this does not happen because of the cell wall.

3. As water moves into a cell by osmosis, there is a buildup of pressure in the cell interior on the membrane. The pressure created is known as turgor pressure. The more dissolved particles there are within the cell, the greater is the tendency for water to diffuse into it, and the higher the turgor pressure becomes. At some point, the turgor pressure will equal the tendency of water to move into the cell and there will be no net gain of water after this point.

4. Turgor pressure in all of the cells that compose the plant body maintains the upright position of the plant.

5. It is the pressure against the cell walls in a plant, due to the buildup of water inside the vacuole that maintains the upright position. If you forget to water the plants, the turgor pressure decreases and the upright position isn't maintained.

6. Water has moved, by osmosis, back into the plant cells.

7. The salt creates a hypertonic environment which draws water out of the snail cells and therefore, kills the cells due to  dehydration.

8. To maintain the turgor pressure and keep them nice and plump.

Objective 13
1. Oxygen and other small molecules and some ions.

Simple diffusion: [H] ----> [L], no carrier, no energy, oxygen diffusing into cell.

Facilitated diffusion: [H] ----> [L], carrier, no energy, glucose transport into cell.

Active transport: [L]-----> [H], carrier, energy, movement of K⁺ into cell. Cells have a relatively high concentration of these ions.

2. simple diffusion

3. facilitated diffusion

4. active transport

5. It requires the use of energy.

6. Selective permeability of the membrane keeps many materials outside the cell and active transport can remove them from the cell against a concentration gradient.

7. simple diffusion and facilitated diffusion

8. mitochondria

Objective 14
1. phagocytosis

2. pinocytosis

3. engulf the bacteria by phagocytosis and kill them

4. a) because the concentration of water is greater outside the cell      b) exocytosis

5. Receptor-mediated endocytosis is a type of endocytosis that allows the cell to bring in groups of a specific type of molecule using receptors in the cell membrane. Look at the photomicrograph of this process on page 85 in your text.

6. yes

7. lysosomes

8. Exocytosis removes materials from a cell and endocytosis takes materials into cells.

Objective 15
1. passive transport (diffusion, osmosis), facilitated transport, active transport, and bulk transport (endocytosis/exocytosis)

2. It prevents the passage of large nonlipid soluble (polar) materials.

3. Some act as carrier molecules in facilitated diffusion and some are involved in active transport of materials into the cell.

4. no.  Glycoproteins play various roles related to cell recognition.

5. One which serves as a passive "conveyor" to help move a molecule through the membrane.

6. glucose - facilitated diffusion; potassium ions are concentrated in the cell by active transport; proteins move across the cell by active transport (assuming that they are being moved against a concentration gradient, otherwise the process is facilitated transport); oxygen gas - diffusion.

7. sodium ions - concentrated outside the cell by active transport (note: note that potassium ions are concentrated inside the cell and sodium ions outside the cell - don't worry about this now. When you study the transmission of the nerve impulse, the direction of concentration will be important).; carbon dioxide - diffusion; cellulose - exocytosis; water - osmosis.

Objective 16
1. Efficient division of labor

2. Advantages: division of labor, with certain cells able to perform specific functions; ability to use larger pieces of food; less susceptibility to predators. Disadvantages: one cell is dependent on all the rest to survive, more food is required.

3. Perhaps; the more advanced organisms are all multicellular.

Objective 17
1. Tissues are composed of many cells similar in structure and function; organs are composed of several tissues grouped into one functional unit; systems are groups of organs which cooperate to perform a specific function.

2. Meristematic tissue retains its ability to divide and reproduce, permanent tissue is specialized to perform a specific function.

3. No. Most animal cells lose their ability to reproduce once they have become specialized.