Most animals use more than one species as food. Therefore, the term “food web” is a better description of food relationships than “food chain”. A food web is a complex feeding system that contains several food chains. For example, mice, rabbits, and deer eat plants. owls eat mice and rabbits. Mountain lions eat rabbits and deer. These five species are parts of food chains that together form a food web.
The first link in a food chain is always a green plant. Only organisms with chlorophyll, such as green plants can make food. for example, the first link aquatic food chains is algae. Most algae are microscopic green plants that produce food by photosynthesis. In photosynthesis, energy from sunlight converts carbon dioxide and water to sugar. Tiny fish in lakes, streams and oceans eat algae. In turn, these tiny fish are eaten by larger fish. The larger fish are eaten by still larger fish. The food supply for fish is made by algae. This food is then passed through the food chains as one animal eats another.
Organisms may be divided into three groups based on how they obtain food. These groups are producers, decomposer and consumer. Organisms containing chlorophyll are producers. thus, green plants are producers. Animals that eat other animals and plants as consumers. Microbes, one-celled organisms that cause the decay of dead plants and animals are decomposers. Since decomposers cannot make their own food, they are also consumers.
1. The main purpose of the passage is to
A. determine which food chain is the most efficient
B. describe the food network among plants and animals
C. explain the process of photosynthesis in green plants
D. appeal to conservationists to protect endangered plant species
2. According to the author, what is a “food web”?
A. A complicated system of several food chains
B. A society that distributes food
C. The relationship of one green plants to another
D. The device that spiders use to catch food
3. Which of the following would most likely be the first link in a food chain?
A. Termites B. Fish C. Lions D. Grass
4. The author divides organisms according to
A. how they use up energy
B. how they obtain food
C. how much energy they require in order to move
D. whether they live on the land or in the sea
5.Which of the following organism could not be a consumer as described in the passage?
A. a microbe B. a rabbit C. a tree D. a fish
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Enzymes are often used as nonrecoverable chemical reagents, in which case they are added to the substrate incubated at the required temperature and pH for a period and subsequently destroyed. Amylase, proteases and other inexpensive bulk enzymes are used in this way. Alternatively, enzymes may be attached to an inert support (immobilized). This offers the advantages of (1) recovery and re-use of the enzymes, in batch reactors; or (2) the development of continuously operated enzyme reactions similar to continuous fermentation systems used for microorganisms; (3) the possibility of multi-enzyme systems; and (4) the enzyme does not remain in the processed solution. However, there are some disadvantages, the enzyme may be stabilized by immobilization but it may also lose activity, and the process becomes technically more complex.
There are many ways to immobilize enzymes, the common procedures involve (1)absorption to an insoluble support of either organic or inorganic origin. Cellulose, dextran, nylon and bentonite are some of the many carriers that have been used. Attachment may be by physical adsorption, ionic binding or covalent bonding. (2) Entrapment methods in which the enzyme is localized within a polymer matrix are popular and include gel or fiber entrapment and microencapsulation in which the enzyme is enclosed within sperical semipermeable polymer membranes. (3) A simple but effective procedure is to immobilize the enzyme within the host cell by heat treatment or covalent cross-linking following by pelleting the cells.
Are the following statements true or false?
（1）Amylase, proteases and other inexpensive bulk enzymes are destroyed after the enzyme-catalyzed reaction is completed
（2）The advantages of immobilization of the enzymes include the stability of the enzymes and the increase of the enzyme activity
（3）By immobilization of the enzymes, it is possible to operate the enzyme reactions continuously
（4）In the last paragraph, the word “insoluble support” has the same meaning as the word “carrier”
